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Subscribe to this feed ScienceDirect Publication: Magnetic Resonance Imaging Segmented diffusion-weighted imaging of the prostate: Application to transperineal in-bore 3T MR image-guided targeted biopsy Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: October 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 8 Author(s): Andriy Fedorov, Kemal Tuncali, Lawrence P. Panych, Janice Fairhurst, Elmira Hassanzadeh, Ravi T. Seethamraju, Clare M. Tempany, Stephan E. Maier Objective This study aims to evaluate the applicability of using single-shot and multi-shot segmented diffusion-weighted imaging (DWI) techniques to support biopsy target localization in a cohort of targeted MRI-guided prostate biopsy patients. Materials and methods Single-shot echo-planar diffusion-weighted imaging (SS-DWI) and multi-shot segmented (MS-DWI) were performed intra-procedurally on a 3Tesla system in a total of 35 men, who underwent in-bore prostate biopsy inside the scanner bore. Comparisons between SS-DWI and MS-DWI were performed with (in 16 men) and without (in 19 men) parallel coil acceleration (iPAT) for SS-DWI. Overall image quality and artifacts were scored by a radiologist and scores were compared with the Wilcoxon-Mann-Whitney rank test. Correlation between the presence of air and image quality scores was evaluated with Spearman statistics. To quantify distortion, the anteroposterior prostate dimension was measured in SS and MS b =0 diffusion- and T2-weighted images. Signal-to-noise ratio was estimated in a phantom experiment. Agreement and accuracy of targeting based on retrospective localization of restricted diffusion areas in DWI was evaluated with respect to the targets identified using multi-parametric MRI (mpMRI). Results Compared to SS-DWI without iPAT, the average image quality score in MS-DWI improved from 2.0 to 3.3 (p<0.005) and the artifact score improved from 2.3 to 1.4 (p<0.005). When iPAT was used in SS-DWI, the average image quality score in MS-DWI improved from 2.6 to 3.3 (p<0.05) and the artifact score improved from 2.1 to 1.4 (p<0.01). Image quality (ρ=−0.74, p<0.0005) and artifact scores (ρ=0.77, p<0.0005) both showed strong correlation with the presence of air in the rectum for the SS-DWI sequence without iPAT. These correlations remained significant when iPAT was enabled (ρ=−0.52, p<0.05 and ρ=0.64, p<0.01). For the comparison MS-DWI vs SS-DWI without iPAT, median differences between diffusion- and T2-weighted image gland measurements were 1.1(0.03–10.4)mm and 4.4(0.5–22.7)mm, respectively. In the SS-DWI-iPAT cohort, median gland dimension differences were 2.7(0.4–5.9)mm and 4.2(0.7–8.9)mm, respectively. Out of the total of 89 targets identified in mpMRI, 20 had corresponding restricted diffusion areas in SS-DWI and 28 in MS-DWI. No statistically significant difference was observed between the distances for the targets in the target-concordant SS- and MS-DWI restricted diffusion areas (5.5mm in SS-DWI vs 4.5mm in MS-DWI, p>0.05). Conclusions MS-DWI applied to prostate imaging leads to a significant reduction of image distortion in comparison with SS-DWI. There is no sufficient evidence however to suggest that intra-procedural DWI can serve as a replacement for tracking of the targets identified in mpMRI for the purposes of targeted MRI-guided prostate biopsy. Noninvasive evaluation of radiation-enhanced glioma cells invasiveness by ultra-high-field 1H-MRS in vitro Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: October 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 8 Author(s): Yan-Jie Xu, Yi Cui, Hong-Xia Li, Wen-Qi Shi, Fu-Yan Li, Jian-Zheng Wang, Qing-Shi Zeng Introduction Glioma is the most common type of the primary CNS tumor. Radiotherapy is an important treatment measure after surgery. However, its highly invasive character is the main reason of postoperative recurrence. The aim of the study was to probe the correlation between the invasion ability and the metabolite characteristics of glioma cells at the cellular level after irradiation by using 14.7T high-resolution nuclear proton magnetic resonance spectroscopy (1H-MRS). Methods To determine the matrix metalloproteinase-2 (MMP-2) activity and metabolite ratios of glioma cells after irradiation with different doses of X-rays, U87 and C6 glioma cells were exposed to X-ray irradiation of 0, 1, 5, 10, and 15Gy. After 20h, the perchloric acid (PCA) extraction method was used to evaluate water-soluble metabolites [choline (Cho), creatine (Cr), and N-acetylaspartate (NAA)], and 1H-MRS patterns and changes in metabolite ratios were observed in vitro by 14.7T high resolution 1H-MRS. Matrigel invasion assays and gelatin zymography were performed to test the invasion ability of U87 and C6 glioma cells. Results Good MR spectra were obtained from PCA method extracts of U87 and C6 glioma cells. Both radiation-induced MMP-2 activity and the Cho/Cr and Cho/NAA ratios increased after irradiation, and their increase occurred in a dose-dependent manner. The MMP-2 activity and the Cho/Cr and Cho/NAA ratios of glioma cells increased after irradiation up to 10Gy and decreased thereafter. In particular, the Cho/NAA ratio of U87 cells increased from 3.55±0.06 (0Gy) to 9.13±0.30 (10Gy) and then declined to 5.94±0.15 (15Gy). Furthermore, the invasion ability of glioma cells had a strong positive correlation with the Cho/Cr and Cho/NAA ratios. Both the Cho/Cr ratio and the Cho/NAA ratio of U87 glioma cells were highly positively correlated with the number of invading cells in the Matrigel invasion assay. The Pearson's correlation coefficient (r) values of U87 cells were 0.89 (Cho/Cr ratio versus invasion ability) and 0.91 (Cho/NAA ratio versus invasion ability) (P <0.01). C6 cells exhibited similar changes to those of U87 cells. Conclusions In vitro high-resolution 1H-MRS is useful for detecting glioma invasiveness at the cellular level. Wavelet-domain TI Wiener-like filtering for complex MR data denoising Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: October 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 8 Author(s): Kai Hu, Qiaocui Cheng, Xieping Gao Magnetic resonance (MR) images are affected by random noises, which degrade many image processing and analysis tasks. It has been shown that the noise in magnitude MR images follows a Rician distribution. Unlike additive Gaussian noise, the noise is signal-dependent, and consequently difficult to reduce, especially in low signal-to-noise ratio (SNR) images. Wirestam et al. in [20] proposed a Wiener-like filtering technique in wavelet-domain to reduce noise before construction of the magnitude MR image. Based on Wirestam's study, we propose a wavelet-domain translation-invariant (TI) Wiener-like filtering algorithm for noise reduction in complex MR data. The proposed denoising algorithm shows the following improvements compared with Wirestam's method: (1) we introduce TI property into the Wiener-like filtering in wavelet-domain to suppress artifacts caused by translations of the signal; (2) we integrate one Stein's Unbiased Risk Estimator (SURE) thresholding with two Wiener-like filters to make the hard-thresholding scale adaptive; and (3) the first Wiener-like filtering is used to filter the original noisy image in which the noise obeys Gaussian distribution and it provides more reasonable results. The proposed algorithm is applied to denoise the real and imaginary parts of complex MR images. To evaluate our proposed algorithm, we conduct extensive denoising experiments using T1-weighted simulated MR images, diffusion-weighted (DW) phantom and in vivo data. We compare our algorithm with other popular denoising methods. The results demonstrate that our algorithm outperforms others in term of both efficiency and robustness. Superiority of the extracellular volume fraction over the myocardial T1 value for the assessment of myocardial fibrosis in patients with non-ischemic cardiomyopathy Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: October 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 8 Author(s): Keisuke Inui, Masaki Tachi, Tsunenori Saito, Yoshiaki Kubota, Koji Murai, Koji Kato, Hitoshi Takano, Yasuo Amano, Kuniya Asai, Wataru Shimizu Purpose This study aimed to assess the efficacies of the myocardial T1 value and the extracellular volume fraction (ECV) for determining the severity of myocardial fibrosis in patients with non-ischemic cardiomyopathy. Materials and methods Myocardial fibrosis is considered the most important indicator of cardiac damage associated with non-ischemic cardiomyopathy. Recently, modified Look-Locker inversion recovery imaging (MOLLI) has been used for T1 mapping and measurement of the ECV for the assessment of myocardial fibrosis. The present study included 22 patients (mean age, 61.5±12.7; 21 male) with non-ischemic heart failure. Motion corrected myocardial T1 mapping was automatically performed using a MOLLI sequence, and the ECV was estimated from the pre- and post-contrast blood and myocardial T1 values corrected for the hematocrit level. All endomyocardial biopsy specimens were obtained from the inferoposterior left ventricular wall. The percentage of myocardial fibrosis (%F) was determined after Elastica Masson-Goldner staining as follows: (fibrosis area/[fibrosis area+myocardial area])×100. Results No correlation was noted between the %F and the pre- (r=0.290, p=0.191) or post-contrast T1 values (r=−0.190, p=0.398); however, a significant correlation was noted between the %F and ECV (r=0.750, p<0.001). Conclusions In this study, the ECV reflected the extent of myocardial fibrosis, but the pre- and post-contrast T1 values did not. The ECV may be used to estimate the severity of myocardial fibrosis in patients with non-ischemic cardiomyopathy. Comprehensive cortical thickness and surface area comparison between young Uyghur and Han Chinese cohorts Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: October 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 8 Author(s): Jun Lu, Chunhui Jiang, Jian Wang, Wenxiao Jia We hypothesized that the brain structural differences as discovered previously between Westerners and East Asians could also be revealed between Han Chinese and Uyghur, which were genetically related ethnic groups with distinct languages. We conducted a brain MRI structural comparison in terms of cortical thickness and surface area between 15 healthy young Uyghurs and 15 age-matched Han Chinese. Widespread regions with significantly greater cortical thickness were found in the Uyghurs, and their distribution showed strong resemblance to previous “Westerners vs. Asians” findings. While surface area analysis displayed less widespread brain differences. Notably, our detected regions with structural differences contained a large part of language-specific or at least closely language-related brain areas, which may partly be attributable to the brain plasticity respectively driven by Uyghur and Mandarin. Our findings will help to better understand the neurobiological basis of interethnic differences along with the language processing mechanisms of Han Chinese and Uyghur. Intravoxel incoherent motion diffusion weighted MRI of cervical cancer — Correlated with tumor differentiation and perfusion Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: October 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 8 Author(s): Yan Zhou, Jianyu Liu, Congrong Liu, Jing Jia, Nan Li, Lizhi Xie, Zhenyu Zhou, Ziheng Zhang, Dandan Zheng, Wei He, Yang Shen, Weidan Lu, Huici Zhu Objectives To investigate the value of parameters derived from IVIM model in grading of uterine cervical cancer and the relationship between perfusion parameters derived from IVIM and that from DCE-MRI. Methods Parameters of DWI (ADC, D, f, D*) and semi-quantitative parameters of DCE-MRI (Slop, Maxslop, CER, Washout, AUC90) were assessed in 24 female with cervical cancers. Except for ROIs encompassed all of the area of tumors in axial plane (A_all), ROIs on tumor edge (A_peri) and tumor center (A_central) were drawn. All of the parameters were compared among three pathology grades. Perfusion parameters derived from IVIM were correlated with that from DCE-MRI. Results For G1, G2 and G3 tumors, on tumor edge ADC=(1.03±0.11), (1.05±0.10), (0.90±0.05)×10−3 mm2/s, D=(0.80±0.11), (0.78±0.07), (0.69±0.06)×10−3 mm2/s, and f=(0.19±0.03), (0.22±0.02), (0.24±0.03). The differences among groups were significant (P <0.05). On tumor center, ADC=(0.90±0.10), (0.85±0.03), (0.80±0.07)×10−3 mm2/s with significant differences (P =0.027). The other parameter, D and f of tumor center, as well as D* of all tumor areas, were of no statistic significance. Most of the DCE-MRI parameters negatively correlated with tumor volume. Although the correlation between f and slop was statistic significant, R =0.277 meant a negligible correlation. f had week correlation with Maxslop, CER and AUC90 (R =0.361, 0.400 and 0.405; P <0.001). D* showed no statistic significant correlation with all of the DCE parameters. Conclusion IVIM model could possibly be used to evaluate tumor differentiation and perfusion, providing an alternative for DCE-MRI. A target field design of open multi-purpose RF coil for musculoskeletal MR imaging at 3T Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: October 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 8 Author(s): Fei Gao, Rui Zhang, Diange Zhou, Xiaoying Wang, Kefu Huang, Jue Zhang Musculoskeletal MR imaging under multi-angle situations plays an increasingly important role in assessing joint and muscle tissues system. However, there are still limitations due to the closed structures of most conventional RF coils. In this study, a time-harmonic target-field method was employed to design open multi-purpose coil (OMC) for multi-angle musculoskeletal MR imaging. The phantom imaging results suggested that the proposed OMC could achieve homogeneously distributed magnetic field and high signal-to-noise ratio (SNR) of 239.04±0.83 in the region of interest (ROI). The maximum temperature in the heating hazard test was 16°C lower than the standard regulation, which indicated the security of the designed OMC. Furthermore, to demonstrate the effectiveness of the proposed OMC for musculoskeletal MR imaging, especially for multi-angle imaging, a healthy volunteer was examined for MR imaging of elbow, ankle and knee using OMC. The in vivo imaging results showed that the proposed OMC is effective for MR imaging of musculoskeletal tissues at different body parts, with satisfied B1 field homogeneity and SNR. Moreover, the open structure of the OMC could provide a large joint movement region. The proposed open multi-purpose coil is feasible for musculoskeletal MR imaging, and potentially, it is more suitable for the evaluation of musculoskeletal tissues under multi-angle conditions. Comparison of actual with default hematocrit value in dynamic contrast enhanced MR perfusion quantification in grading of human glioma Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: October 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 8 Author(s): Prativa Sahoo, Pradeep K. Gupta, Ashish Awasthi, Chandra M. Pandey, Rana Patir, Sandeep Vaishya, Indrajit Saha, Rakesh K. Gupta Purpose Dynamic contrast enhanced (DCE) MRI is used to grade and to monitor the progression of glioma while on treatment. Usually, a fixed hematocrit (Hct) value for adults is assumed to be & known for individual variations. Purpose of this study was to investigate the effect of measured Hct values in glioma grading using DCE-MRI. Materials and methods Fifty glioma patients were included in this study. Kinetic and hemodynamic parameters were estimated for each patient using assumed as well as measured Hct values. To look the changes in Hct value over time, Hct was measured multiple times from 10 of these glioma patients who were on treatment. Simulation was done to look for the effect of extreme variations of Hct values on perfusion metrics. The data was compared to look for significant differences in the perfusion metrics derived from assumed and measured Hct values. Results The measured Hct value in patients was found to be (40.4±4.28)%. The sensitivity and specificity of DCE-MRI parameters in glioma grading were not significantly influenced by using measured vis-a-vis assumed Hct values. The serial Hct values from 10 patients who were on treatment showed a fluctuation of 15–20% over time. The simulated data showed linear influence of Hct values on kinetic parameters. The tumor grading was altered on altering the Hct values in borderline cases. Conclusion Hct values influence the hemodynamic and kinetic metrics linearly and may affect glioma grading. However, perfusion metrics values might change significantly with large change in Hct values, especially in patients who are on chemotherapy necessitating its use in the DCE model. Self-reported gadolinium toxicity: A survey of patients with chronic symptoms Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: October 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 8 Author(s): Lauren M.B. Burke, Miguel Ramalho, Mamdoh AlObaidy, Emily Chang, Michael Jay, Richard C. Semelka Purpose This study aims to describe the self-reporting symptoms experienced by individuals with self-reported normal renal function after gadolinium based contrast agent (GBCA) administration. Materials and methods This HIPAA-compliant, IRB-approved study consisted of an anonymous online survey of patients who believe that they suffer from gadolinium toxicity. 50 respondents completed the nine-question survey. Results Fifty (100%) of the subjects ascribed their complaints to gadolinium exposure. Thirty-three (66%) described the onset immediately following GBCA administration and 16 (32%) within 6weeks. The most common symptoms included bone/joint pain and head/neck symptoms including headache, vision change, and hearing change (77.6% each). Other symptoms occurred with lesser incidence. Conclusions This survey represents an initial description of patients with normal renal function who self-described toxicity related to GBCA administration. Bone and joint complaints and skin changes are two of the most common complaints. Multiparametric MR can identify high grade prostatic intraepithelial neoplasia (HGPIN) lesions and predict future detection of prostate cancer in men with a negative initial prostate biopsy Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: October 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 8 Author(s): Durgesh Kumar Dwivedi, Rajeev Kumar, Girdhar Singh Bora, Sanjay Sharma, Sanjay Thulkar, Siddhartha Datta Gupta, Naranamangalam R. Jagannathan Purpose This study aims to determine the pre-biopsy diffusion-weighted imaging (DWI) and magnetic resonance spectroscopic imaging (MRSI) characteristics of patients with high-grade prostatic intraepithelial neoplasia (HGPIN) and perform follow-up studies in these patients to assess the clinical implications. Materials and methods One hundred sixteen men with prostate specific antigen between 4 and 10ng/ml underwent pre-biopsy MR examinations. Nine of them had HGPIN lesions without concomitant prostate cancer (PCa) on biopsy. Apparent diffusion coefficient (ADC) and metabolite ratio [Citrate/(Choline+Creatine)] were calculated and these 9 patients were followed to determine the clinical outcomes. Results Mean ADC for HGPIN foci was 1.01±0.16×10−3 mm2/s while for the normal peripheral zone it was 1.69±0.25×10−3 mm2/s (p<0.005). Mean metabolite ratio for voxels in the HGPIN region of initial biopsy was 0.24±0.16 while for the normal peripheral zone the value was 2.66±1.57 (p<0.005). Four of 5 patients who were available for follow-up were detected to have prostate cancer on repeat biopsy. No significant change in metabolite ratio and PSA was observed while ADC showed further reduction on follow-up. Conclusion HGPIN foci have ADC and metabolite ratio values similar to adenocarcinoma prostate, indicating that such patients have a high likelihood of developing cancer. DWI may help identify such men who may be candidates for close follow-up. Shape and diffusion tensor imaging based integrative analysis of the hippocampus and the amygdala in Alzheimer's disease Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: October 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 8 Author(s): Xiaoying Tang, Yuanyuan Qin, Jiong Wu, Min Zhang, Wenzhen Zhu, Michael I. Miller We analyzed, in an integrative fashion, the morphometry and structural integrity of the bilateral hippocampi and amygdalas in Alzheimer's disease (AD) using T1-weighted images and diffusion tensor images (DTIs). We detected significant hippocampal and amygdalar volumetric atrophies in AD relative to healthy controls (HCs). Shape analysis revealed significant region-specific atrophies with the hippocampal atrophy mainly being concentrated on the CA1 and CA2 while the amygdalar atrophy was concentrated on the basolateral and basomedial. In all structures, the structural integrity displayed a significantly decreased mean fractional anisotropy (FA) value and an increased mean trace value in AD. In addition to the inter-group comparisons, we systematically evaluated the discriminative power of our three types of features (volume, shape, and DTI), both individually and in their possible combinations, when differentiating between AD and HCs. We found the volume features to be redundant when the more sophisticated shape features were available. A combination of the shape and DTI features of the right hippocampus, with classification automatically performed by support vector machine, yielded the strongest classification result (overall accuracy, 94.6%; sensitivity, 95.5%; specificity, 93.3%). A new NOE-mediated MT signal at around −1.6ppm for detecting ischemic stroke in rat brain Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: October 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 8 Author(s): Xiao-Yong Zhang, Feng Wang, Aqeela Afzal, Junzhong Xu, John C. Gore, Daniel F. Gochberg, Zhongliang Zu In the present work, we reported a new nuclear Overhauser enhancement (NOE)-mediated magnetization transfer (MT) signal at around −1.6ppm (NOE(−1.6)) in rat brain and investigated its application in the detection of acute ischemic stroke in rodent model. Using continuous wave (CW) MT sequence, the NOE(−1.6) is reliably detected in rat brain. The amplitude of this new NOE signal in rat brain was quantified using a 5-pool Lorentzian Z-spectral fitting method. Amplitudes of amide, amine, NOE at −3.5ppm (NOE(−3.5)), as well as NOE(−1.6) were mapped using this fitting method in rat brain. Several other conventional imaging parameters (R1, R2, apparent diffusion coefficient (ADC), and semi-solid pool size ratio (PSR)) were also measured. Our results show that NOE(−1.6), R1, R2, ADC, and APT signals from stroke lesion have significant changes at 0.5–1h after stroke. Compared with several other imaging parameters, NOE(−1.6) shows the strongest contrast differences between stroke and contralateral normal tissues and stays consistent over time until 2h after onset of stroke. Our results demonstrate that this new NOE(−1.6) signal in rat brain is a new potential contrast for assessment of acute stroke in vivo and might provide broad applications in the detection of other abnormal tissues. Relationship between morphological features and kinetic patterns of enhancement of the dynamic breast magnetic resonance imaging and tumor expression of metalloproteases and their inhibitors in invasive breast cancer Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: October 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 8 Author(s): Estela Fernández Cuadriello, Óscar Fernández-Guinea, Noemí Eiró, Luis O. González, Sara Junquera, Francisco J. Vizoso Aim Matrix metalloproteases (MMPs) expression and their inhibitors (TIMPs) play an important role in tumor physiopathology, so we investigated the relationship between the magnetic resonance (MR) and MMPs/TIMPs expression by breast carcinomas. Materials and methods MRI parameters of 64 breast carcinomas were investigated. An immunohistochemical study was also performed in these cases using tissue microarrays and specific antibodies against MMP-1, MMP-2, MMP-7, MMP-9, MMP-11, MMP-13, MMP-14, TIMP-1, TIMP-2 and TIMP-3. Results Tumors with spiculated margins had a high global (score) values of MMP-1 or MMP-7, and high expression of TIMP-3 by tumor cells. Heterogeneous tumors had a higher score values of MMP-1, MMP-13, TIMP-2 or TIMP-3, and frequent expression of TIMP-3 by tumor cells. Tumors showing fast enhancement, had higher score values of MMP-1 or MMP-11. Associations between washout curve (type III) and MMP-1, MMP-11, MMP-13 and TIMP-1 expression by tumor cells, were found. Conclusions MRI features may predict in some grade the expressions of MMPs/TIMPs in breast tumors, which might to contribute to a better biological characterization of breast cancer. Fat fraction estimation of morphologically normal lumbar vertebrae using the two-point mDixon turbo spin-echo MRI with flexible echo times and multipeak spectral model of fat: Comparison between cancer and non-cancer patients Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: October 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 8 Author(s): Seung Hyun Lee, Young Han Lee, Seok Hahn, Jin-Suck Suh Purpose This study aims to compare fat fraction of lumbar vertebrae between cancer and non-cancer patients, using the two-point modified Dixon (mDixon) turbo spin-echo (TSE) MRI with flexible echo times and multipeak fat spectral model. Materials and methods Fat fraction was calculated from fat and water images reconstructed by the mDixon TSE technique. Fat fraction of fat–water phantoms measured with the mDixon TSE method was compared with actual fat percentages. Patients who had undergone mDixon spine MRI and dual-energy X-ray absorptiometry within one year and had no bone metastasis were divided into cancer (n=7) and non-cancer (n=23) groups. Fat fraction and bone mineral density (BMD) were compared between the two groups. Results Fat fraction of phantoms measured with mDixon MRI was highly correlated with their actual fat percentages (P<0.01, R2 =0.93). Fat fraction of lumbar vertebrae was significantly lower in cancer patients (58.27±3.16%) than in non-cancer patients (70.48±1.83%) (P<0.01). BMD was not different between cancer (0.912±0.057g/cm2) and non-cancer patients (0.876±0.032g/cm2) (P=0.58). Fat fraction and BMD showed no significant correlation (P=0.95, R=0.006). Conclusions A two-point mDixon TSE method for assessing fat fraction was reliable. Fat fraction of morphologically normal lumbar vertebrae was significantly lower in cancer patients compared to non-cancer patients, using the two-point mDixon TSE technique. Use of quantitative brain water imaging as concentration reference for J-edited MR spectroscopy of GABA Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: October 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 8 Author(s): Georg Oeltzschner, Alfons Schnitzler, Frithjof Wickrath, Helge Jörn Zöllner, Hans-Jörg Wittsack Purpose To compare two different methods of obtaining the water reference for determination of quantitative water-scaled in vivo concentration estimates of γ-aminobutyric acid (GABA). Methods Water-scaled GABA estimates from localized J-difference edited MR spectroscopy experiments can be computed using standard values for tissue-specific water content and relaxation times. Water content and relaxation may, however, be altered in pathology. This work re-analyzed data from a recent study in healthy controls and patients with minimal (mHE) or grade I (HE 1) hepatic encephalopathy, a disease associated with slight elevation of brain water content. J-difference edited MR spectroscopy data were combined with quantitative brain water measures, which provided individual water density references and T 1 relaxation times. Resulting GABA estimates were compared to concentration values obtained using standard tissue-specific water content and relaxation values. Results Occipital GABA concentration values obtained from individual water and T 1 maps were 1.64±0.35mM in controls, and significantly higher (P <0.01) than in mHE (1.15±0.28mM) and HE 1 patients (1.18±0.09mM). Results from the tissue-dependent approach (1.58±0.30mM (controls), 1.10±0.27mM (mHE) and 1.12±0.12mM (HE 1)) were slightly lower (P <0.05 in each group). Conclusion Water-scaled in vivo GABA estimates can be obtained with individual water density and T 1 relaxation mapping. This approach may be useful for studying GABA levels in pathologies with substantial brain water content or relaxation changes. Multiparametric MRI for prostate cancer detection: Preliminary results on quantitative analysis of dynamic contrast enhanced imaging, diffusion-weighted imaging and spectroscopy imaging Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: September 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 7 Author(s): Roberta Fusco, Mario Sansone, Mario Petrillo, Sergio Venanzio Setola, Vincenza Granata, Gerardo Botti, Sisto Perdonà, Valentina Borzillo, Paolo Muto, Antonella Petrillo Introduction Early promising data suggest that combined use of both morphological and functional MRI (multi-parametric MR, mpMRI) including MRSI, DWI and DCE may be of additional value for prostate cancer localization and its local staging. The objective of this paper is to evaluate the diagnostic performance of mpMRI in the detection of prostate cancer. Methods Thirty-one consecutive male patients were screened to be enrolled in a single center prospective observational study. All eligible patients underwent multi-parametric MRI and TRUS (Trans Rectal Ultra Sound) guided prostate biopsies. A register, approved by the Institutional Ethics Committee, included patients enrolled in this study. All patients who decided to undergo the MRI examination signed an explicit informed consensus. MRI data were aligned on a common spatial grid and several functional parameters (perfusion, diffusion and metabolic parameters) were computed. Statistical analysis was conducted in order to compare mpMRI with biopsy-based analysis. Results Statistically significant differences between median values in high Gleason score (≥5) and low Gleason score (<5) to Wilcox on rank sum test were obtained for MRSI parameters and for plasma fraction (Tofts model) of DCE-MRI. The area under curve obtained with ROC analysis showed that the best-performing single-parameter was vp (plasma fraction of Tofts model), while the best parameters combination to discriminate the area with high Gleason score were (Cho+Cr)/Cit and Cho+Cr. Linear Discrimination Analysis showed that the best results were obtained considering the linear combination of all MRSI parameters and the linear combination of all features (perfusion, diffusion and metabolic parameters). Conclusions In conclusion, our findings showed that by combining morphological MRI, DWI, DCE-MRI and MRSI, an increase in sensitivity and specificity correlated to biopsy Gleason grade could be obtained. Furthermore, morphological and functional MRI could have a diagnostic role in patients with prostate cancer, identifying those patients who will have a negative work-up and those patients at high risk for a high Gleason score cancer of the prostate. Compressed sensing for rapid late gadolinium enhanced imaging of the left atrium: A preliminary study Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: September 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 7 Author(s): Srikant Kamesh Iyer, Tolga Tasdizen, Nathan Burgon, Eugene Kholmovski, Nassir Marrouche, Ganesh Adluru, Edward DiBella Current late gadolinium enhancement (LGE) imaging of left atrial (LA) scar or fibrosis is relatively slow and requires 5–15min to acquire an undersampled (R=1.7) 3D navigated dataset. The GeneRalized Autocalibrating Partially Parallel Acquisitions (GRAPPA) based parallel imaging method is the current clinical standard for accelerating 3D LGE imaging of the LA and permits an acceleration factor &g (CS) methods have been developed to achieve higher acceleration factors: a patch based collaborative filtering technique tested with acceleration factor R& a 3D radial stack-of-stars acquisition pattern (R&on constraint. The long reconstruction time of these CS methods makes them unwieldy to use, especially the patch based collaborative filtering technique. In addition, the effect of CS techniques on the quantification of percentage of scar/fibrosis is not known. We sought to develop a practical compressed sensing method for imaging the LA at high acceleration factors. In order to develop a clinically viable method with short reconstruction time, a Split Bregman (SB) reconstruction method with 3D total variation (TV) constraints was developed and implemented. The method was tested on 8 atrial fibrillation patients (4 pre-ablation and 4 post-ablation datasets). Blur metric, normalized mean squared error and peak signal to noise ratio were used as metrics to analyze the quality of the reconstructed images, Quantification of the extent of LGE was performed on the undersampled images and compared with the fully sampled images. Quantification of scar from post-ablation datasets and quantification of fibrosis from pre-ablation datasets showed that acceleration factors up to R&of the LA wall, using a 3D TV constraint and constrained SB methods. This corresponds to reducing the scan time by half, compared to currently used GRAPPA methods. Reconstruction of 3D LGE images using the SB method was over 20 times faster than standard gradient descent methods. A visualization study on two-phase gravity drainage in porous media by using magnetic resonance imaging Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: September 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 7 Author(s): Ying Teng, Yu Liu, Lanlan Jiang, Yongchen Song, Jiafei Zhao, Yi Zhang, Dayong Wang Gravity drainage characteristics are important to improve our understanding of gas–liquid or liquid–liquid two-phase flow in porous media. Stable or unstable displacement fronts that controlled by the capillary force, viscous force, gravitational force, etc., are relevant features of immiscible two-phase flow. In this paper, three dimensionless parameters, namely, the gravity number, the capillary number and the Bond number, were used to describe the effect of the above mentioned forces on two-phase drainage features, including the displacement front and final displacing-phase saturation. A series of experiments on the downward displacement of a viscous fluid by a less viscous fluid in a vertical vessel that is filled with quartz beads are performed by using magnetic resonance imaging (MRI). The experimental results indicate that the wetting properties at both high and low capillary numbers exert remarkable control on the fluid displacement. When the contact angle is lower than 90°, i.e., the displaced phase is the wetting phase, the average velocity V f of the interface of the two phases (displacement front velocity) is observably lower than when the displaced phase is the non-wetting phase (contact angle higher than 90°). The results show that a fingering phenomenon occurs when the gravity number G is less than the critical gravity number G’= Δμ/μg. Moreover, the higher Bond number results in higher final displacing-phase saturation, whereas the capillary number has an opposite effect. Multi-contrast T2⁎-relaxometry upon visual stimulation at 3T and 7T Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: September 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 7 Author(s): Moritz C. Berger, Peter Bachert, Jens Gröbner, Armin M. Nagel This study aims to quantify the mean change of the effective transverse relaxation time T 2 ⁎ in active brain regions of human volunteers at field strengths of B 0 =3 T and 7 T. Besides the mono-exponential signal decay model an extended model is tested that considers mesoscopic field gradients across imaging voxels. Both models are checked for cross-talk and correlations between the parameters. A visual checkerboard-stimulation experiment with pause and stimulation periods of 50s and six repetitions was performed on healthy volunteers. Eleven contrasts were acquired in about 1.47s/1.43s at 3T/7T using a segmented multi-contrast echo-planar imaging (EPI) sequence. Average BOLD-signal time courses were calculated in a multi-step (non-)linear least-squares process. Baseline T 2 ⁎ values of 37.72ms/24.99ms (47.34ms/33.71ms) with stimulus-correlated changes ∆ T 2 ⁎ of 1.32ms/0.74ms (1.99ms/1.43ms) resulted from the mono-exponential (extended) model for 3T/7T. A dependence of those values on the initial intensity S 0 was observed. Stimulus-correlated changes of S 0 in the order of 1% were measured at both field strengths. The mono-exponential model was found to be less prone to instabilities in the regression of both parameters. Signal alterations due to inflow were observed. Measured relaxation times agree with values from literature using repetitive stimulation. A strong dependence of the measured relaxation times on the inflow-related model parameter was found for both models. The extended model is applicable to dynamic neurofunctional measurements, but is currently limited due to the low number of contrasts acquired. CPMG relaxation rate dispersion in dipole fields around capillaries Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: September 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 7 Author(s): F.T. Kurz, T. Kampf, L.R. Buschle, S. Heiland, H.-P. Schlemmer, M. Bendszus, C.H. Ziener Transverse relaxation rates for Carr-Purcell-Meiboom-Gill (CPMG) sequences increase with inter-echo time in presence of microscopic magnetic field inhomogeneities due to nuclear spin diffusion. For a weak field approximation that includes diffusion effects, the CPMG relaxation rate shift for proton diffusion around capillaries in muscle tissue can be expressed in terms of a frequency correlation function and the inter-echo time. The present work provides an analytical expression for the local relaxation rate shift that is dependent on local blood volume fraction, diffusion coefficient, capillary radius, susceptibility difference and inter-echo time. Asymptotic regions of the model are in agreement with previous modeling results of Brooks et al., Luz et al. and Ziener et al. In comparison with simulation data, the model shows an equal or better accuracy than established approximations. Also, model behavior coincides with experimental data for rat heart and skeletal muscle. The present work provides analytical tools to extract sub-voxel information about uniform capillary networks that can be used to study capillary organization or micro-circulatory remodeling. The temporal evolution of diffusional kurtosis imaging in an experimental middle cerebral artery occlusion (MCAO) model Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: September 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 7 Author(s): Shun Zhang, Yihao Yao, Jingjing Shi, Xiangyu Tang, Lingyun Zhao, Wenzhen Zhu Purpose Diffusional kurtosis imaging (DKI), as a non-Gaussian diffusion model, has been applied in human and animal studies of ischemic stroke. This study aimed to intensively characterize the temporal evolution of DKI-derived variables in an experimental middle cerebral artery occlusion (MCAO) model, and to explore its potential application in ischemic stroke. Materials and methods Eleven MCAO rats and ten control rats underwent DKI and diffusion weighted imaging (DWI) scans, at different time points of 0.5, 2, 6, 12, 24 and 72h after operation respectively. The infarct area in DKI- and DWI-derived variables was compared among different time points, and between different groups [INFARCTION, MIRROR, CONTROL-R (right side of the control group, the same side as in the infarction group), CONTROL-L (left side of the control group)] using repeated measures analysis of variance (ANOVA). The percent changes from normal to that in ischemic tissues and histology were also evaluated. Results In the infarct region, from 0.5 to 72h, MK, K∥, K⊥ demonstrated irregular high signal, whereas relative homogeneous low signals were revealed by MD, D∥, D⊥ and ADC. Compared with the MIRROR and CONTROL-R group, MK, K∥, K⊥ in the infarcted area increased aggressively which peaked at 12h and gradually decreased; MD, D∥, D⊥ and ADC decreased gradually until 12h and then began to increase gradually; FA decreased rapidly from 0.5 to 72h. MD, D∥ and ADC were significantly different between Mirror and CONTROL-L group (P <0.05). Conclusion DKI can provide more detailed information to describe ischemic lesion, and has great potential application in ischemic stroke. Application of histogram analysis for the evaluation of vascular permeability in glioma by the K2 parameter obtained with the dynamic susceptibility contrast method: Comparisons with Ktrans obtained with the dynamic contrast enhance method and cerebral blood volume Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: September 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 7 Author(s): Toshiaki Taoka, Hisashi Kawai, Toshiki Nakane, Saeka Hori, Tomoko Ochi, Toshiteru Miyasaka, Masahiko Sakamoto, Kimihiko Kichikawa, Shinji Naganawa Purpose The “K2” value is a factor that represents the vascular permeability of tumors and can be calculated from datasets obtained with the dynamic susceptibility contrast (DSC) method. The purpose of the current study was to correlate K2 with Ktrans, which is a well-established permeability parameter obtained with the dynamic contrast enhance (DCE) method, and determine the usefulness of K2 for glioma grading with histogram analysis. Methods The subjects were 22 glioma patients (Grade II: 5, III: 6, IV: 11) who underwent DSC studies, including eight patients in which both DSC and DCE studies were performed on separate days within 10days. We performed histogram analysis of regions of interest of the tumors and acquired 20th percentile values for leakage-corrected cerebral blood volume (rCBV20%ile), K2 (K220%ile), and for patients who underwent a DCE study, Ktrans (Ktrans20%ile). We evaluated the correlation between K220%ile and Ktrans20%ile and the statistical difference between rCBV20%ile and K220%ile. Results We found a statistically significant correlation between K220%ile and Ktrans20%ile (r =0.717, p <0.05). rCBV20%ile showed a significant difference between Grades II and III and between Grades II and IV, whereas K220%ile showed a statistically significant (p <0.05) difference between Grades II and IV and between Grades III and IV. Conclusions The K2 value calculated from the DSC dataset, which can be obtained with a short acquisition time, showed a correlation with Ktrans obtained with the DCE method and may be useful for glioma grading when analyzed with histogram analysis. Evaluation of renal allografts function early after transplantation using intravoxel incoherent motion and arterial spin labeling MRI Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: September 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 7 Author(s): Tao Ren, Cheng-Long Wen, Li-Hua Chen, Shuang-Shuang Xie, Yue Cheng, Ying-Xin Fu, Niels Oesingmann, Andre de Oliveira, Pan-Li Zuo, Jian-Zhong Yin, Shuang Xia, Wen Shen Purpose To evaluate renal allografts function early after transplantation using intravoxel incoherent motion (IVIM) and arterial spin labeling (ASL) MRI. Methods This prospective study was approved by the local ethics committee, and written informed consent was obtained from all participants. A total of 82 participants with 62 renal allograft recipients (2–4weeks after kidney transplantation) and 20 volunteers were enrolled to be scanned using IVIM and ASL MRI on a 3.0T MR scanner. Recipients were divided into two groups with either normal or impaired function according to the estimated glomerular filtration rate (eGFR) with a threshold of 60ml/min/1.73m2. The apparent diffusion coefficient (ADC) of pure diffusion (ADCslow), the ADC of pseudodiffusion (ADCfast), perfusion fraction (PF), and renal blood flow (RBF) of cortex were compared among three groups. The correlation of ADCslow, ADCfast, PF and RBF with eGFR was evaluated. The receiver operating characteristic (ROC) curve and binary logistic regression analyses were performed to assess the diagnostic efficiency of using IVIM and ASL parameters to discriminate allografts with impaired function from normal function. P <0.05 was considered statistically significant. Results In allografts with normal function, no significant difference of mean cortical ADCslow, ADCfast, and PF was found compared with healthy controls (P >0.05). Cortical RBF in allografts with normal function was statistically lower than that of healthy controls (P <0.001). Mean cortical ADCslow, ADCfast, PF and RBF were lower for allografts with impaired function than that with normal function (P <0.05). Mean cortical ADCslow, ADCfast, PF and RBF showed a positive correlation with eGFR (all P <0.01) for recipients. The combination of IVIM and ASL MRI showed a higher area under the ROC curve (AUC) (0.865) than that of ASL MRI alone (P =0.02). Conclusion Combined IVIM and ASL MRI can better evaluate the diffusion and perfusion properties for allografts early after kidney transplantation. Comparison of diffusion-weighted imaging and T2-weighted single shot fast spin-echo: Implications for LI-RADS characterization of hepatocellular carcinoma Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: September 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 7 Author(s): Robert M. Hicks, Judy Yee, Michael A. Ohliger, Stefanie Weinstein, Jeffrey Kao, Nabia S. Ikram, Thomas A. Hope Purpose To evaluate the performance of diffusion-weighted imaging (DWI) and T2-weighted single shot fast spin-echo (SSFSE) imaging of the liver in the detection of hepatocellular carcinoma (HCC) in reference to the LI-RADS classification system. Methods MR images of 40 patients with 68 LI-RADS grade 3–5 lesions were analyzed. Two readers independently reviewed sequences and characterized lesion signal intensity, followed by consensus evaluation. CE-MRI served as reference standard. Sensitivities were compared across sequences. Lesion-to-liver contrast-to-noise ratios (CNRs) and apparent diffusion coefficients (ADCs) were measured and compared using the Wilcoxon signed-rank test across sequences and the Mann–Whitney U or Kruskal–Wallis test between LI-RADS categories. Inter-reader variability was assessed using Cohen's kappa statistic. Results Consensus sensitivities of LI-RADS 3–5 lesions using SSFSE images versus DWI were similar (0.53–0.63, p=0.089), however, the sensitivity with DWI b=700 was higher (0.63) than DWI b=0 (0.53, p=0.039). Lesion-to-liver CNRs were larger for all DWI sequences compared to SSFSE images (p<0.001 for all). ADCs of large (>2cm) LIRADS 3–5 lesions were lower than those of small lesions (1.09±0.33 vs. 1.31±0.26, p=0.02), however lesion ADCs were not different from those of adjacent hepatic parenchyma for any LI-RADS lesion. Conclusions DWI has a similar sensitivity compared to SSFSE, but intensity on DWI likely represents intrinsic T2 signal hyper-intensity rather than restricted diffusion as the ADC values were not lower than adjacent parenchyma. Therefore it may not be appropriate to consider hyper-intensity on high b-value as a separate ancillary criteria to T2 hyper-intensity in LI-RADS. Pitfalls in whole body MRI with diffusion weighted imaging performed on patients with lymphoma: What radiologists should know Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: September 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 7 Author(s): Domenico Albano, Ludovico La Grutta, Emanuele Grassedonio, Caterina Patti, Roberto Lagalla, Massimo Midiri, Massimo Galia The technological advances in radiological imaging and the relevance of a diagnostic tool that may reduce radiation-induced long-term effects have led to a widespread use of whole body magnetic resonance imaging (WB-MRI) with diffusion weighted imaging for oncologic patients. A lot of studies demonstrated the feasibility and reliability of WB-MRI as an alternative technique for lymphoma staging and response assessment during and after treatment. In this paper, taking advantage of our 2years of experience using WB-MRI for lymphoma, we discuss the main pitfalls and artifacts radiologists should know examining a WB-MRI performed on this typology of patients in order to avoid images misinterpretation. T1rho and T2 mapping of lumbar intervertebral disc: Correlation with degeneration and morphologic changes in different disc regions Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: September 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 7 Author(s): Min A Yoon, Suk-Joo Hong, Chang Ho Kang, Kyung-Sik Ahn, Baek Hyun Kim Purpose To assess regional variations of T1rho (T1ρ) and T2 rates within lumbar intervertebral discs and to evaluate the correlation of T1ρ and T2 rates in different disc regions with Pfirrmann grades of degeneration and morphologic changes. Materials and methods We retrospectively evaluated 105 lumbar discs in 22 subjects who were examined at 3.0-T MRI. T1ρ and T2 relaxation rates (1/T1ρ and 1/T2) were measured in five segmented regions of discs: anterior annulus fibrosus (AF), anterior junction, nucleus pulposus (NP), posterior junction, and posterior AF. Disc degeneration was graded using 5-level Pfirrmann grading system and morphologic change was categorized into five groups (normal, bulging, annular fissure, protrusion, and extrusion). Regional differences of T1ρ and T2 rates and correlation with degeneration and morphologic changes were statistically analyzed. Results Most of the five segmented regions showed statistically different T1ρ and T2 rates from each other. T1ρ and T2 relaxation rates were positively associated with Pfirrmann grades of degeneration and morphologic changes, with different strength of relation in each region. T2 rates in the posterior junction showed the strongest correlation with degeneration (r=0.810) and T2 rates in the anterior junction showed the highest association with morphologic changes (r=0.621). Conclusions Regional variations of T1ρ and T2 rates within discs and different strength of relation with degeneration and morphologic changes should be taken into account when evaluating lumbar discs. GOCART: GOlden-angle CArtesian randomized time-resolved 3D MRI Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: September 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 7 Author(s): Yinghua Zhu, Yi Guo, Sajan Goud Lingala, R. Marc Lebel, Meng Law, Krishna S. Nayak Purpose To develop and evaluate a novel 3D Cartesian sampling scheme which is well suited for time-resolved 3D MRI using parallel imaging and compressed sensing. Methods The proposed sampling scheme, termed GOlden-angle CArtesian Randomized Time-resolved (GOCART) 3D MRI, is based on golden angle (GA) Cartesian sampling, with random sampling of the ky-kz phase encode locations along each Cartesian radial spoke. This method was evaluated in conjunction with constrained reconstruction of retrospectively and prospectively undersampled in-vivo dynamic contrast enhanced (DCE) MRI data and simulated phantom data. Results In in-vivo retrospective studies and phantom simulations, images reconstructed from phase encodes defined by GOCART were equal to or superior to those with Poisson disc or GA sampling schemes. Typical GOCART sampling tables were generated in <100ms. GOCART has also been successfully utilized prospectively to produce clinically valuable whole-brain DCE-MRI images. Conclusion GOCART is a practical and efficient sampling scheme for time-resolved 3D MRI. It shows great potential for highly accelerated DCE-MRI and is well suited to modern reconstruction methods such as parallel imaging and compressed sensing. Multiscale coherence regularization reconstruction using a nonlocal operator for fast variable-density spiral imaging Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: September 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 7 Author(s): Sheng Fang, Lyu Li, Wenchuan Wu, Juan Wei, Bida Zhang, Dong-Hyun Kim, Chun Yuan, Hua Guo Purpose Nonlinear reconstruction can suppress pseudo-incoherent aliasing artifacts from variable-density spiral (VDS) trajectories when interleaves are undersampled for acquisition acceleration during MR imaging. However, large-scale aliasing artifact suppression often conflicts with fine-scale structure preservation and may cause deterioration of image quality in the reconstructed images. To address this issue, a sequential, multiscale coherence regularization algorithm using a nonlocal operator (mCORNOL) is proposed. Methods mCORNOL is formed by exploiting the scale-control capacity of nonlocal operators in image structure measurement. By changing the scale of the structure measurement, the smoothing constraint scales can be adjusted. Starting with a large value, mCORNOL gradually reduces the smoothing constraint scale until it reaches the same level as the noise. Therefore, the large-scale smoothing constraint dominates the first few iterations of the reconstruction and removes aliasing artifacts as well as fine structures. In the following iterations, the smoothing constraint is restricted to a smaller and smaller scale, so the fidelity term progressively dominates and restores lost structures. Thus, aliasing artifact removal and structure preservation can be decoupled and achieved sequentially, which alleviates the conflicts between them. Results Numerical simulation and in vivo experiment results demonstrate the superiority of mCORNOL for aliasing artifact suppression and image structure preservation at high reduction factors, compared to SENSE, Total Variation and the original CORNOL reconstruction. Conclusions mCORNOL reconstruction provides an effective way to improve image quality for undersampled VDS acquisitions. Joint correction of Nyquist artifact and minuscule motion-induced aliasing artifact in interleaved diffusion weighted EPI data using a composite two-dimensional phase correction procedure Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: September 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 7 Author(s): Hing-Chiu Chang, Nan-kuei Chen Diffusion-weighted imaging (DWI) obtained with interleaved echo-planar imaging (EPI) pulse sequence has great potential of characterizing brain tissue properties at high spatial-resolution. However, interleaved EPI based DWI data may be corrupted by various types of aliasing artifacts. First, inconsistencies in k-space data obtained with opposite readout gradient polarities result in Nyquist artifact, which is usually reduced with 1D phase correction in post-processing. When there exist eddy current cross terms (e.g., in oblique-plane EPI), 2D phase correction is needed to effectively reduce Nyquist artifact. Second, minuscule motion induced phase inconsistencies in interleaved DWI scans result in image-domain aliasing artifact, which can be removed with reconstruction procedures that take shot-to-shot phase variations into consideration. In existing interleaved DWI reconstruction procedures, Nyquist artifact and minuscule motion-induced aliasing artifact are typically removed subsequently in two stages. Although the two-stage phase correction generally performs well for non-oblique plane EPI data obtained from well-calibrated system, the residual artifacts may still be pronounced in oblique-plane EPI data or when there exist eddy current cross terms. To address this challenge, here we report a new composite 2D phase correction procedure, which effective removes Nyquist artifact and minuscule motion induced aliasing artifact jointly in a single step. Our experimental results demonstrate that the new 2D phase correction method can much more effectively reduce artifacts in interleaved EPI based DWI data as compared with the existing two-stage artifact correction procedures. The new method robustly enables high-resolution DWI, and should prove highly valuable for clinical uses and research studies of DWI. Morphological asymmetries of mouse brain assessed by geometric morphometric analysis of MRI data Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: September 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 7 Author(s): Jimena Barbeito-Andrés, Valeria Bernal, Paula N. Gonzalez Mammalian brain has repeated structures at both sides of the median plane, although some asymmetries have been described even under normal conditions. Characterizing normal patterns of asymmetry in mouse brain is important to recognize features that depart from expected ranges in the most widely used mammalian model. Analyses on brain morphology based on magnetic resonance image (MRI) have largely focused on volumes while less is known about shape asymmetry. We introduce a flexible protocol based on geometric morphometrics to assess patterns of asymmetry in shape and size of mouse brain from microMRI scans. After systematic digitization of landmarks and semilandmarks, we combine multivariate methods for statistical analyses with visualization tools to display the results. No preliminary treatment of the images (e.g. space normalization) is needed to collect data on MRI slices and visual representations improve the interpretation of the results. Results indicated that the protocol is highly repeatable. Asymmetry was more evident for shape than for size. Particularly, fluctuating asymmetry accounted for more variation than directional asymmetry in all brain regions. Since this approach can detect subtle shape variation between sides, it is a promising methodology to explore morphological changes in the brain of model organisms and can be applied in future studies addressing the effect of genetic and environmental factors on brain morphology. Non-local MRI denoising using random sampling Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: September 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 7 Author(s): Jinrong Hu, Jiliu Zhou, Xi Wu In this paper, we propose a random sampling non-local mean (SNLM) algorithm to eliminate noise in 3D MRI datasets. Non-local means (NLM) algorithms have been implemented efficiently for MRI denoising, but are always limited by high computational complexity. Compared to conventional methods, which raster through the entire search window when computing similarity weights, the proposed SNLM algorithm randomly selects a small subset of voxels which dramatically decreases the computational burden, together with competitive denoising result. Moreover, structure tensor which encapsulates high-order information was introduced as an optimal sampling pattern for further improvement. Numerical experiments demonstrated that the proposed SNLM method can get a good balance between denoising quality and computation efficiency. At a relative sampling ratio (i.e. ξ =0.05), SNLM can remove noise as effectively as full NLM, meanwhile the running time can be reduced to 1/20 of NLM's. Early prediction of functional outcome using dynamic contrast enhanced magnetic resonance imaging in experimental stroke Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: September 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 7 Author(s): Wei-Yuan Huang, Gang Wu, Jian-Jun Li, Dao-Ying Geng, Wen-Li Tan, Xiang-Rong Yu Background and purpose Early prediction of functional outcome in cerebral ischemia stroke using MRI remains a challenge. The aim of this study was to evaluate the predictive value of dynamic contrast-enhanced (DCE) MRI in terms of functional outcome of ischemia stroke. Methods Right middle cerebral artery occlusion (MCAO) was performed in male SD rats (n=50), followed by withdrawal of the occluding filament after 3 (n = 10), 4 (n = 10), 5 (n = 10), 6 (n = 10) or 7 (n = 10) h to establish ischemia and reperfusion stroke. DCE and conventional MRI were performed in each animal 60 ± 15 min before and after reperfusion. The outcome was assessed by the modified Neurological Severity Scores (mNSS) (before reperfusion and at 72 h after reperfusion) and the infarct volume. Comparisons of functional prognosis and DCE parameters (Ktrans, Ve and Kep) were performed using binary logistic regression and operating characteristic (ROC) analysis. Results DCE parameters results indicated that blood brain barrier (BBB) permeability increased with prolonged reperfusion timing. Using binary logistic regression analysis on stroke characteristics (reperfusion timing, infarct volume) and BBB permeability parameters (drKtrans subcortex, drKtrans cortex, drVesubcortex, drVecortex, drKepsubcortex and drKepcortex) as covariates , the results demonstrated that reperfusion timing, infarct volume, drKtrans subcortex and drKepsubcortex were independent factors that were associated with prognosis (OR=0.01, OR=0.23, OR=245.23, OR=1.29). ROC analysis indicated that a drKtrans subcortex threshold of 0.88 with a sensitivity of 95.7% and a specificity of 85.2% and a drKepsubcortex threshold of -0.25 with a sensitivity of 69.6% and a specificity of 70.4% for differentiation between favourable and unfavourable prognosis. Conclusions Quantitative DCE-MRI can be used to predict the functional outcomes of cerebral ischemia injury. Effects of donepezil on brain morphometric and metabolic changes in patients with Alzheimer's disease: A DARTEL-based VBM and 1H-MRS Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: September 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 7 Author(s): Chung-Man Moon, Byeong-Chae Kim, Gwang-Woo Jeong A few studies have performed on the brain morphometric changes over the whole brain structure following donepezil treatment in patients with Alzheimer's disease (AD). We evaluated the gray matter (GM) and white matter (WM) volume alterations and cellular metabolic changes in patients with AD before and after donepezil treatment, and further to reveal the correlations of the scores of various neuropsychological scales with the volumetric and metabolic changes. Twenty-one subjects comprising of 11 patients with AD and 10 age-matched healthy controls participated in this study. All of the patients participated in the follow-up study 24weeks following donepezil treatment. In this study, a combination of voxel-based morphometry (VBM) and proton magnetic resonance spectroscopy (1H-MRS) was used to assess the brain morphometric and metabolic alterations in AD. In the GM volumetric analysis, both of the untreated and treated patients with donepezil showed significantly reduced volumes in the hippocampus (Hip), parahippocampal gyrus (PHG), precuneus (PCu) and middle frontal gyrus compared with healthy controls. However, donepezil-treated patients showed significantly increased volumes in the Hip, PCu, fusiform gyrus and caudate nucleus compared to untreated patients. In the WM volumetric analysis, untreated and treated patients showed significant volume reductions in the posterior limb of internal capsule (PLIC), cerebral peduncle of the midbrain and PHG compared to healthy controls. However, there was no significant WM morphological change after donepezil treatment in patients with AD. In MRS study, untreated patients with AD showed decreased N-acetylaspartate/creatine (NAA/Cr) and increased myo-inositol (mI)/Cr compared to healthy controls, while treated patients showed only decreased NAA/Cr in the same comparison. However, the treated patients showed simultaneously increased NAA/Cr and decreased mI/Cr and choline (Cho)/Cr ratios compared to untreated patients. This study shows the regional GM and WM volume changes in combination with metabolic changes following donepezil treatment in AD. These findings would be helpful to aid our understanding of the neuroanatomical mechanisms associated with effects of donepezil on the cognitive function in AD. Accelerating dual cardiac phase images using undersampled radial phase encoding trajectories Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: September 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 7 Author(s): Karis Letelier, Jesus Urbina, Marcelo Andía, Cristián Tejos, Pablo Irarrazaval, Claudia Prieto, Sergio Uribe A three-dimensional dual-cardiac-phase (3D-DCP) scan has been proposed to acquire two data sets of the whole heart and great vessels during the end-diastolic and end-systolic cardiac phases in a single free-breathing scan. This method has shown accurate assessment of cardiac anatomy and function but is limited by long acquisition times. This work proposes to accelerate the acquisition and reconstruction of 3D-DCP scans by exploiting redundant information of the outer k-space regions of both cardiac phases. This is achieved using a modified radial-phase-encoding trajectory and gridding reconstruction with uniform coil combination. The end-diastolic acquisition trajectory was angularly shifted with respect to the end-systolic phase. Initially, a fully-sampled 3D-DCP scan was acquired to determine the optimal percentage of the outer k-space data that can be combined between cardiac phases. Thereafter, prospectively undersampled data were reconstructed based on this percentage. As gold standard images, the undersampled data were also reconstructed using iterative SENSE. To validate the method, image quality assessments and a cardiac volume analysis were performed. The proposed method was tested in thirteen healthy volunteers (mean age, 30years). Prospectively undersampled data (R =4) reconstructed with 50% combination led high quality images. There were no significant differences in the image quality and in the cardiac volume analysis between our method and iterative SENSE. In addition, the proposed approach reduced the reconstruction time from 40min to 1min. In conclusion, the proposed method obtains 3D-DCP scans with an image quality comparable to those reconstructed with iterative SENSE, and within a clinically acceptable reconstruction time. Background field removal technique using regularization enabled sophisticated harmonic artifact reduction for phase data with varying kernel sizes Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: September 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 7 Author(s): Hirohito Kan, Harumasa Kasai, Nobuyuki Arai, Hiroshi Kunitomo, Yasujiro Hirose, Yuta Shibamoto An effective background field removal technique is desired for more accurate quantitative susceptibility mapping (QSM) prior to dipole inversion. The aim of this study was to evaluate the accuracy of regularization enabled sophisticated harmonic artifact reduction for phase data with varying spherical kernel sizes (REV-SHARP) method using a three-dimensional head phantom and human brain data. The proposed REV-SHARP method used the spherical mean value operation and Tikhonov regularization in the deconvolution process, with varying 2–14mm kernel sizes. The kernel sizes were gradually reduced, similar to the SHARP with varying spherical kernel (VSHARP) method. We determined the relative errors and relationships between the true local field and estimated local field in REV-SHARP, VSHARP, projection onto dipole fields (PDF), and regularization enabled SHARP (RESHARP). Human experiment was also conducted using REV-SHARP, VSHARP, PDF, and RESHARP. The relative errors in the numerical phantom study were 0.386, 0.448, 0.838, and 0.452 for REV-SHARP, VSHARP, PDF, and RESHARP. REV-SHARP result exhibited the highest correlation between the true local field and estimated local field. The linear regression slopes were 1.005, 1.124, 0.988, and 0.536 for REV-SHARP, VSHARP, PDF, and RESHARP in regions of interest on the three-dimensional head phantom. In human experiments, no obvious errors due to artifacts were present in REV-SHARP. The proposed REV-SHARP is a new method combined with variable spherical kernel size and Tikhonov regularization. This technique might make it possible to be more accurate backgroud field removal and help to achive better accuracy of QSM. Analysis of pharmacokinetics of Gd-DTPA for dynamic contrast-enhanced magnetic resonance imaging Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: September 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 7 Author(s): Saeid Taheri, N. Jon Shah, Gary A. Rosenberg The pharmacokinetics (PK) of the contrast agent Gd-DTPA administered intravenously (i.v.) for contrast-enhanced MR imaging (DCE-MRI) is an important factor for quantitative data acquisition. We studied the effect of various initial bolus doses on the PK of Gd-DTPA and analyzed population PK of a lower dose for intra-subject variations in DCE-MRI. First, fifteen subjects (23–85years, M/F) were randomly divided into four groups for DCE-MRI with different Gd-DTPA dose: group-I, 0.1mmol/kg, n=4; group-II, 0.05mmol/kg, n=4; group-III, 0.025mmol/kg, n=4; and group-IV, 0.0125mmol/kg, n=3. Sequential fast T1 mapping sequence, after a bolus i.v. Gd-DTPA administered, and a linear T1-[Gd-DTPA] relationship were used to estimate the PK of Gd-DTPA. Secondly, MR-acquired PKs of Gd-DTPA from 58 subjects (28–80years, M/F) were collected retrospectively, from an ongoing study of the brain using DCE-MRI with Gd-DTPA at 0.025mmol/kg, to statistically analyze population PK of Gd-DTPA. We found that the PK of Gd-DTPA (i.v. 0.025mmol/kg) had a half-life of 37.3±6.6min, and was a better fit into a linear T1-[Gd-DTPA] relationship than higher doses (up to 0.1mmol/kg). The area under the curve (AUC) for 0.025mmol/kg was 3.37±0.46, which was a quarter of AUC of 0.1mmol/kg. In population analysis, a dose of 0.025mmol/kg of Gd-DTPA provided less than 5% subject-dependent variation in the PK of Gd-DTPA. Administration of 0.025mmol/kg Gd-DTPA enabled us to estimate [Gd-DTPA] from T1 by using a linear relationship that has a lower estimation error compared to a non-linear relationship. DCE-MRI with a quarter dose of Gd-DTPA is more sensitive to detect changes in [Gd-DTPA]. Least squares reconstruction of non-linear RF phase encoded MR data Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: September 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 7 Author(s): Somaie Salajeghe, Paul Babyn, Jonathan C. Sharp, Gordon E. Sarty Purpose The numerical feasibility of reconstructing MRI signals generated by RF coils that produce B 1 fields with a non-linearly varying spatial phase is explored. Theory A global linear spatial phase variation of B 1 is difficult to produce from current confined to RF coils. Here we use regularized least squares inversion, in place of the usual Fourier transform, to reconstruct signals generated in B 1 fields with non-linear phase variation. Methods RF encoded signals were simulated for three RF coil configurations: ideal linear, parallel conductors and, circular coil pairs. The simulated signals were reconstructed by Fourier transform and by regularized least squares. Results The Fourier reconstruction of simulated RF encoded signals from the parallel conductor coil set showed minor distortions over the reconstruction of signals from the ideal linear coil set but the Fourier reconstruction of signals from the circular coil set produced severe geometric distortion. Least squares inversion in all cases produced reconstruction errors comparable to the Fourier reconstruction of the simulated signal from the ideal linear coil set. Conclusion MRI signals encoded in B 1 fields with non-linearly varying spatial phase may be accurately reconstructed using regularized least squares thus pointing the way to the use of simple RF coil designs for RF encoded MRI. Usefulness of cervical magnetic resonance imaging for detecting type A acute aortic dissection with acute stroke symptoms Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: September 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 7 Author(s): Hiroaki Matsumoto, Yasuhisa Yoshida, Yutaka Hirata Type A acute aortic dissection (TAAAD) sometimes presents with acute stroke-like symptoms. When intravenous tissue plasminogen activator (IV-tPA) therapy is considered for acute ischemic stroke, TAAAD must be excluded. Painless TAAAD presenting with acute stroke may be easily missed. Two cases of painless TAAAD presenting with acute stroke in which IV-tPA therapy was considered are reported. In these cases, cervical magnetic resonance angiography (MRA) was useful for detecting TAAAD, and IV-tPA therapy was canceled. The mottled high signal (“snowstorm”) in the common carotid artery on cervical MRA is specific for TAAAD. We have thus named this phenomenon the “snowstorm sign” and believe it can help diagnose TAAAD. Editorial Board Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: July 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 6 Table of Contents Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: July 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 6 Estimation of turbulent kinetic energy using 4D phase-contrast MRI: Effect of scan parameters and target vessel size Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: July 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 6 Author(s): Hojin Ha, Dongha Hwang, Guk Bae Kim, Jihoon Kweon, Sang Joon Lee, Jehyun Baek, Young-Hak Kim, Namkug Kim, Dong Hyun Yang Quantifying turbulence velocity fluctuation is important because it indicates the fluid energy dissipation of the blood flow, which is closely related to the pressure drop along the blood vessel. This study aims to evaluate the effects of scan parameters and the target vessel size of 4D phase-contrast (PC)-MRI on quantification of turbulent kinetic energy (TKE). Comprehensive 4D PC-MRI measurements with various velocity-encoding (VENC), echo time (TE), and voxel size values were carried out to estimate TKE distribution in stenotic flow. The total TKE (TKEsum), maximum TKE (TKEmax), and background noise level (TKEnoise) were compared for each scan parameter. The feasibility of TKE estimation in small vessels was also investigated. Results show that the optimum VENC for stenotic flow with a peak velocity of 125cm/s was 70cm/s. Higher VENC values overestimated the TKEsum by up to six-fold due to increased TKEnoise, whereas lower VENC values (30cm/s) underestimated it by 57.1%. TE and voxel size did not significantly influence the TKEsum and TKEnoise, although the TKEmax significantly increased as the voxel size increased. TKE quantification in small-sized vessels (3–5-mm diameter) was feasible unless high-velocity turbulence caused severe phase dispersion in the reference image. Gd-EOB-DTPA-enhanced-MR imaging in the inflammation stage of nonalcoholic steatohepatitis (NASH) in mice Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: July 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 6 Author(s): Tomomi Yamada, Atsushi Obata, Yuto Kashiwagi, Takemi Rokugawa, Shuuichi Matsushima, Tadateru Hamada, Hiroshi Watabe, Kohji Abe Objective The purpose of this study is to investigate the correlation between the liver kinetics of gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) and liver histopathology in a mouse model of NASH by using dynamic contrast-enhanced MRI. Materials and methods Twenty male C57/BL6 mice aged 8weeks were fed a methionine–choline-deficient (MCD) diet for 2, 4 and 6weeks (MCD groups: MCD 2w, 4w, or 6w). Gd-EOB-DTPA-enhanced MR imaging of the liver was performed at 2, 4 and 6weeks after the MCD feeding. The signal intensity of the liver was obtained from dynamic MR images and relative enhancement (RE), and the time to maximum RE (Tmax) and half-life of elimination RE (T1/2) were calculated. After MRI scan, histopathological scores of hepatic steatosis and inflammation and blood biochemistry data, such as aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels, were obtained. Results Plasma AST and ALT levels were significantly increased in mice fed MCD. Histopathological scores indicated that steatohepatitis progressed with the MCD feeding period from 2 to 6weeks, but significant fibrosis was observed only in mice fed MCD for 6weeks. Gd-EOB-DTPA-enhanced MRI showed that Tmax was significantly prolonged in the livers of the 6-week group compared to the control group (control, 4.0±0.7min; MCD 6w, 12.1±1.6min), although there was no alteration in the 2- and 4-week groups. T1/2 was significantly prolonged in mice fed MCD for 4 and 6weeks compared to the control group (control, 19.9±2.0min; MCD 4w, 46.7±8.7min; MCD 6w, 65.4±8.8min). The parameters of Gd-EOB-DTPA kinetics (Tmax and T1/2) in the liver were positively correlated with the liver histopathological score (steatosis vs Tmax, rho=0.69, P =0.0007; inflammation vs Tmax, rho=0.66, P =0.00155; steatosis vs T1/2, rho=0.77, P <0.0001; inflammation vs T1/2, rho=0.73, P =0.0003). Conclusions The liver kinetics of Gd-EOB-DTPA correlated well with the inflammation score in the mouse model of NASH, suggesting the possibility of detecting the steatohepatitis stage without fibrosis by Gd-EOB-DTPA-enhanced MR imaging. Simultaneous optimization of power and duration of radio-frequency pulse in PARACEST MRI Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: July 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 6 Author(s): Mohammad-Reza Rezaeian, Gholam-Ali Hossein-Zadeh, Hamid Soltanian-Zadeh Chemical exchange saturation transfer (CEST) MRI is increasingly used to probe mobile proteins and microenvironment properties, and shows great promise for tumor and stroke diagnosis. The CEST effect is complex and depends not only on the CEST agent concentration, exchange rates, the characteristic of the magnetization transfer (MT), and the relaxation properties of the tissue, but also varies with the experimental conditions such as radio-frequency (RF) pulse power and duration. The RF pulse is one of the most important factors that promote the CEST effect for biological properties such as pH, temperature and protein content, especially for contrast agents with intermediate to fast exchange rates. The CEST effect is susceptible to the RF duration and power. The present study aims at determining the optimal power and the corresponding optimal duration (that maximize the CEST effect) using an off-resonance scheme through a new definition of the CEST effect. This definition is formulated by solving the Bloch-McConnell equation through the R 1ρ method (based on the eigenspace solution) for both of the MT and CEST effects as well as their interactions. The proposed formulations of the optimal RF pulse power and duration are the first formulations in which the MT effect is considered. The extracted optimal RF pulse duration and power are compared with those of the MTR asymmetry model in two- and three-pool systems, using synthetic data that are similar to the muscle tissue. To validate them further, the formulations are compared with the empirical formulation of the CEST effect and other findings of the previous researches. By extending our formulations, the optimal power and the corresponding optimal duration (in the biological systems with many chemical exchange sites) can be determined. Mapping blood flow directionality in the human brain Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: July 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 6 Author(s): Sung-Hong Park, Won-Joon Do, Seung Hong Choi, Tiejun Zhao, Kyongtae Ty Bae Diffusion properties of tissue are often expressed on the basis of directional variance, i.e., diffusion tensor imaging. In comparison, common perfusion-weighted imaging such as arterial spin labeling yields perfusion in a scalar quantity. The purpose of this study was to test the feasibility of mapping cerebral blood flow directionality using alternate ascending/descending directional navigation (ALADDIN), a recently-developed arterial spin labeling technique with sensitivity to blood flow directions. ALADDIN was applied along 3 orthogonal directions to assess directional blood flow in a vector form and also along 6 equally-spaced directions to extract blood flow tensor matrix (P) based on a blood flow ellipsoid model. Tensor elements (eigenvalues, eigenvectors, etc) were calculated to investigate characteristics of the blood flow tensor, in comparison with time-of-flight MR angiogram. While the directions of the main eigenvectors were heterogeneous throughout the brain, regional clusters of blood flow directionality were reproducible across subjects. The technique could show heterogeneous blood flow directionality within and around brain tumor, which was different from that of the contralateral normal side. The proposed method is deemed to provide information of blood flow directionality, which has not been demonstrated before. The results warrant further studies to assess changes in the directionality map as a function of scan parameters, to understand the signal sources, to investigate the possibility of mapping local blood perfusion directionality, and to evaluate its usefulness for clinical diagnosis. Complex-valued time-series correlation increases sensitivity in FMRI analysis Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: July 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 6 Author(s): Mary C. Kociuba, Daniel B. Rowe Purpose To develop a linear matrix representation of correlation between complex-valued (CV) time-series in the temporal Fourier frequency domain, and demonstrate its increased sensitivity over correlation between magnitude-only (MO) time-series in functional MRI (fMRI) analysis. Materials and methods The standard in fMRI is to discard the phase before the statistical analysis of the data, despite evidence of task related change in the phase time-series. With a real-valued isomorphism representation of Fourier reconstruction, correlation is computed in the temporal frequency domain with CV time-series data, rather than with the standard of MO data. A MATLAB simulation compares the Fisher-z transform of MO and CV correlations for varying degrees of task related magnitude and phase amplitude change in the time-series. The increased sensitivity of the complex-valued Fourier representation of correlation is also demonstrated with experimental human data. Since the correlation description in the temporal frequency domain is represented as a summation of second order temporal frequencies, the correlation is easily divided into experimentally relevant frequency bands for each voxel's temporal frequency spectrum. The MO and CV correlations for the experimental human data are analyzed for four voxels of interest (VOIs) to show the framework with high and low contrast-to-noise ratios in the motor cortex and the supplementary motor cortex. Results The simulation demonstrates the increased strength of CV correlations over MO correlations for low magnitude contrast-to-noise time-series. In the experimental human data, the MO correlation maps are noisier than the CV maps, and it is more difficult to distinguish the motor cortex in the MO correlation maps after spatial processing. Conclusions Including both magnitude and phase in the spatial correlation computations more accurately defines the correlated left and right motor cortices. Sensitivity in correlation analysis is important to preserve the signal of interest in fMRI data sets with high noise variance, and avoid excessive processing induced correlation. Improvement of water saturation shift referencing by sequence and analysis optimization to enhance chemical exchange saturation transfer imaging Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: July 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 6 Author(s): Anja Müller-Lutz, Felix Matuschke, Christoph Schleich, Frithjof Wickrath, Johannes Boos, Benjamin Schmitt, Hans-Jörg Wittsack Purpose To optimize B0-field inhomogeneity correction for chemical exchange saturation transfer (CEST) imaging by investigating different water saturation shift referencing (WASSR) Z-spectrum shapes and different frequency correction techniques. Methods WASSR Z-spectra were simulated for different B1-fields and pulse durations (PD). Two parameter settings were used for further simulations and experiments (WASSR1: B1 =0.1 μT, PD=50ms; WASSR2: B1 =0.3 μT, PD=40ms). Four frequency correction techniques were investigated: 1) MinW: Minimum of the spline-interpolated WASSR-spectrum; 2) MSCF: maximum symmetry center frequency algorithm; 3) PMSCF: further development of MSCF algorithm; 4) BFit: fit with Bloch equations. Performance of frequency correction was assessed with Monte-Carlo simulations and in-vivo MR examinations in the brain and intervertebral disks. Results Different shapes of WASSR-Z-spectra were obtained by changing B1 and PD including spectra with one (1-Peak) or two (2-Peak) minima. WASSR1 resulted in 1-Peak WASSR-spectrum, whereas WASSR2 resulted in 2-Peak WASSR-spectrum. Both Monte-Carlo simulations and in-vivo MR examinations revealed highest accuracy of field-inhomogeneity correction with WASSR1 combined with PMSCF or BFit. Conclusion Using a WASSR sequence, which results in a Z-spectrum with a single absorption peak, in combination with advanced postprocessing algorithms enables improved B0-field inhomogeneity correction for CEST imaging. Targeted brain activation using an MR-compatible wrist torque measurement device and isometric motor tasks during functional magnetic resonance imaging Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: July 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 6 Author(s): Martijn P. Vlaar, Winfred Mugge, Paul F.C. Groot, Sarvi Sharifi, Lo J. Bour, Frans C.T. van der Helm, Anne-Fleur van Rootselaar, Alfred C. Schouten Dedicated pairs of isometric wrist flexion tasks, with and without visual feedback of the exerted torque, were designed to target activation of the CBL and BG in healthy subjects during functional magnetic resonance imaging (fMRI). Selective activation of the cerebellum (CBL) and basal ganglia (BG), often implicated in movement disorders such as tremor and dystonia, may help identify pathological changes and expedite diagnosis. A prototyped MR-compatible wrist torque measurement device, free of magnetic and conductive materials, allowed safe execution of tasks during fMRI without causing artifacts. A significant increase of activity in CBL and BG was found in healthy volunteers during a constant torque task with visual feedback compared to a constant torque task without visual feedback. This study shows that specific pairs of motor tasks using MR-compatible equipment at the wrist allow for targeted activation of CBL and BG, paving a new way for research into the pathophysiology of movement disorders. Altered intraoperative cerebrovascular reactivity in brain areas of high-grade glioma recurrence Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: July 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 6 Author(s): Jorn Fierstra, Bas van Niftrik, Marco Piccirelli, Jan Karl Burkhardt, Athina Pangalu, Roman Kocian, Antonios Valavanis, Michael Weller, Luca Regli, Oliver Bozinov Introduction Current MRI sequences are limited in identifying brain areas at risk for high grade glioma recurrence. We employed intraoperative 3-Tesla functional MRI to assess cerebrovascular reactivity (CVR) after high-grade glioma resection and analyzed regional CVR responses in areas of tumor recurrence on clinical follow-up imaging. Methods Five subjects with high-grade glioma that underwent an intraoperative Blood Oxygen-Level Dependent (BOLD) MRI CVR examination and had a clinical follow-up of at least 18months were selected from a prospective database. For this study, location of tumor recurrence was spatially matched to the intraoperative imaging to assess CVR response in that particular area. CVR is defined as the percent BOLD signal change during repeated cycles of apnea. Results Of the 5 subjects (mean age 44, 2 females), 4 were diagnosed with a WHO grade III and 1 subject with a WHO grade IV glioma. Three subjects exhibited a tumor recurrence on clinical follow-up MRI (mean: 15months). BOLD CVR measured in the spatially matched area of tumor recurrence was on average 94% increased (range−32% to 183%) as compared to contralateral hemisphere CVR response, 1.50±0.81 versus 1.03±0.46 respectively (p=0.31). Conclusion For this first analysis in a small cohort, we found altered intraoperative CVR in brain areas exhibiting high grade glioma recurrence on clinical follow-up imaging. Quantification of breast tumor heterogeneity for ER status, HER2 status, and TN molecular subtype evaluation on DCE-MRI Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: July 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 6 Author(s): Ruey-Feng Chang, Hong-Hao Chen, Yeun-Chung Chang, Chiun-Sheng Huang, Jeon-Hor Chen, Chung-Ming Lo Purpose Recognizing molecular markers is helpful for guiding treatment plans for breast cancer. This study correlated estrogen receptor (ER), human epidermal growth factor receptor 2 (HER2), and triple-negative breast cancer (TNBC) statuses to the degree of heterogeneity on breast dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). Materials and methods A total of 102 biopsy-proven cancers from 102 patients between October 2010 and December 2012 were used in this study, including ER (59 positive, 43 negative), HER2 (47 positive, 55 negative), and TNBC (22 TNBC, 80 non-TNBC). At first, the tumor region was segmented by using a region growing method. Then, the region-based features were extracted by the proposed regionalization method to quantify intra-tumoral heterogeneity on breast DCE-MRI. The three-dimensional morphological features (texture features and shape feature) and the pharmacokinetic model were also extracted from the segmented tumor region. After feature extraction, a logistic regression was used to classify ER, HER2, and TNBC statuses respectively. The performances were evaluated by using receiver operating characteristic (ROC) curve analysis. Results The proposed region-based features achieved the accuracy of 73.53%, 82.35%, and 77.45% for ER, HER2, and TNBC classifications. The corresponding area under the ROC curves (Az) achieves 0.7320, 0.8458, and 0.8328 that were better than those of texture features, shape features, and Tofts pharmacokinetic model. Conclusion The intra-tumoral heterogeneity quantified by the region-based features can be used to reflect the vasculature complexity of different molecular markers and to provide prediction information of cell surface receptors on clinical examination. Correlation between subjective and objective assessment of magnetic resonance (MR) images Σάββατο, 18 Ιουνίου 2016, 9:12:23 μμ Publication date: July 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 6 Author(s): Li Sze Chow, Heshalini Rajagopal, Raveendran Paramesran Medical Image Quality Assessment (IQA) plays an important role in assisting and evaluating the development of any new hardware, imaging sequences, pre-processing or post-processing algorithms. We have performed a quantitative analysis of the correlation between subjective and objective Full Reference - IQA (FR-IQA) on Magnetic Resonance (MR) images of the human brain, spine, knee and abdomen. We have created a MR image database that consists of 25 original reference images and 750 distorted images. The reference images were distorted with six types of distortions: Rician Noise, Gaussian White Noise, Gaussian Blur, DCT compression, JPEG compression and JPEG2000 compression, at various levels of distortion. Twenty eight subjects were chosen to evaluate the images resulting in a total of 21,700 human evaluations. The raw scores were then converted to Difference Mean Opinion Score (DMOS). Thirteen objective FR-IQA metrics were used to determine the validity of the subjective DMOS. The results indicate a high correlation between the subjective and objective assessment of the MR images. The Noise Quality Measurement (NQM) has the highest correlation with DMOS, where the mean Pearson Linear Correlation Coefficient (PLCC) and Spearman Rank Order Correlation Coefficient (SROCC) are 0.936 and 0.938 respectively. The Universal Quality Index (UQI) has the lowest correlation with DMOS, where the mean PLCC and SROCC are 0.807 and 0.815 respectively. Student's T-test was used to find the difference in performance of FR-IQA across different types of distortion. The superior IQAs tested statistically are UQI for Rician noise images, Visual Information Fidelity (VIF) for Gaussian blur images, NQM for both DCT and JPEG compressed images, Peak Signal-to-Noise Ratio (PSNR) for JPEG2000 compressed images. Motion and distortion correction of skeletal muscle echo planar images Πέμπτη, 9 Ιουνίου 2016, 12:23:39 πμ Publication date: July 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 6 Author(s): Andrew D. Davis, Michael D. Noseworthy This paper examines two artifacts facing researchers who use gradient echo (GRE) echo planar imaging (EPI) for time series studies of skeletal muscles in limbs. The first is through-plane blood flow during the acquisition, causing a vessel motion artifact that inhibits proper motion correction of the data. The second is distortion of EPI images caused by B 0 field inhomogeneities. Though software tools are available for correcting these artifacts in brain EPI images, the tools do not perform well on muscle images. The severity of the two artifacts was described using image similarity measures, and the data was processed with both a conventional motion correction program and custom written tools. The conventional program did not perform well on the limb images, in fact significantly degrading image quality in some trials. Data is presented which proves that arterial pulsatile signal caused the impairment in motion correction. The new tools were shown to perform much better, achieving substantial motion correction and distortion correction of the muscle EPI images. Magnetic resonance spectroscopy and imaging for the study of fossils Τρίτη, 7 Ιουνίου 2016, 12:16:42 πμ Publication date: July 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 6 Author(s): Giulio Giovannetti, Andrea Guerrini, Piero A. Salvadori Computed tomography (CT) has long been used for investigating palaeontological specimens, as it is a nondestructive technique which avoids the need to dissolve or ionize the fossil sample. However, magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) have recently gained ground as analytical tools for examination of palaeontological samples, by nondestructively providing information about the structure and composition of fossils. While MRI techniques are able to reveal the three-dimensional geometry of the trace fossil, MRS can provide information on the chemical composition of the samples. The multidimensional nature of MR (magnetic resonance) signals has potential to provide rich three-dimensional data on the palaeontological specimens and also to help in elucidating paleopathological and paleoecological questions. In this work the verified applications and the emerging uses of MRI and MRS in paleontology are reviewed, with particular attention to fossil spores, fossil plants, ambers, fossil invertebrates, and fossil vertebrate studies. Magnetic resonance imaging for the study of mummies Τρίτη, 7 Ιουνίου 2016, 12:16:42 πμ Publication date: July 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 6 Author(s): Giulio Giovannetti, Andrea Guerrini, Emiliano Carnieri, Piero A. Salvadori Nondestructive diagnostic imaging for mummies study has a long tradition and high-resolution images of the samples morphology have been extensively acquired by using computed tomography (CT). However, although in early reports no signal or image was obtained because of the low water content, mummy magnetic resonance imaging (MRI) was demonstrated able to generate images of such ancient specimens by using fast imaging techniques. Literature demonstrated the general feasibility of nonclinical MRI for visualizing historic human tissues, which is particularly interesting for archeology. More recently, multinuclear magnetic resonance spectroscopy (MRS) was demonstrated able to detect numerous organic biochemicals from such remains. Although the quality of these images is not yet comparable to that of clinical magnetic resonance (MR) images, and further research will be needed for determining the full capacity of MR in this topic, the information obtained with MR can be viewed as complementary to the one provided by CT and useful for paleoradiological studies of mummies. This work contains an overview of the state of art of the emerging uses of MRI in paleoradiology. Accelerated cardiac cine MRI using locally low rank and finite difference constraints Τρίτη, 7 Ιουνίου 2016, 12:16:42 πμ Publication date: July 2016Source:Magnetic Resonance Imaging, Volume 34, Issue 6 Author(s): Xin Miao, Sajan Goud Lingala, Yi Guo, Terrence Jao, Muhammad Usman, Claudia Prieto, Krishna S. Nayak Purpose To evaluate the potential value of combining multiple constraints for highly accelerated cardiac cine MRI. Methods A locally low rank (LLR) constraint and a temporal finite difference (FD) constraint were combined to reconstruct cardiac cine data from highly undersampled measurements. Retrospectively undersampled 2D Cartesian reconstructions were quantitatively evaluated against fully-sampled data using normalized root mean square error, structural similarity index (SSIM) and high frequency error norm (HFEN). This method was also applied to 2D golden-angle radial real-time imaging to facilitate single breath-hold whole-heart cine (12 short-axis slices, 9–13s single breath hold). Reconstruction was compared against state-of-the-art constrained reconstruction methods: LLR, FD, and k-t SLR. Results At 10 to 60 spokes/frame, LLR+FD better preserved fine structures and depicted myocardial motion with reduced spatio-temporal blurring in comparison to existing methods. LLR yielded higher SSIM ranking than FD; FD had higher HFEN ranking than LLR. LLR+FD combined the complimentary advantages of the two, and ranked the highest in all metrics for all retrospective undersampled cases. Single breath-hold multi-slice cardiac cine with prospective undersampling was enabled with in-plane spatio-temporal resolutions of 2×2mm2 and 40ms. Conclusion Highly accelerated cardiac cine is enabled by the combination of 2D undersampling and the synergistic use of LLR and FD constraints. 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