So there’s loads of different neuroimaging methods out there that are used depending on what it is you’re looking for! I’ve had the privilege of actually studying it and there’s so so many different types more than just functional MRI that people don’t really know about so here are a few and what they’re used for an how they work.
MRI - Magnetic Resonance Imaging
The most commonly used form of neuroimaging and for good reason. MRI uses the body’s tissue density and magnetic properties of water to visualise structures within the body. It has really incredible spatial and temporal quality and is predominantly used in neuroscience/neurology for looking for any structural abnormalities such as tumours, tissue degeneration etc. It’s fantastic a fantastic form of imaging and is used in numerous amounts of research.
These images are captured the same way as MRI but the quality is a little bit lower because the aim is to capture function (those blobs you can see) as quickly and accurately as possible so the quality is compromised a little bit. Nonetheless, fMRI usually uses the BOLD response to measure function. It measures the amount of activity in different areas of the brain when doing certain things, so during a memory test for example, and it does that by measuring the amount oxygen that a certain area requires. The increased oxygen is believed to be sent to an area where there is more neuronal activity, so it’s not a direct measurement but rather we’re looking at a byproduct. There are numerous studies trying to find the direct link between the haemodynamic response and neuronal activity, particularly at TUoS (where I’m doing my masters!) but for the moment this is all we have. This sort of imaging is used a lot for research and checking the general function of the brain, so if you were to have had surgery on your brain, they may run one of these just to see which areas might be affected from it and how, or in research we’ve used this a lot to research cognition - which areas are affected during certain cognitive tasks (ie my MSc thesis - Cognition in schizophrenia and consanguinity).
Diffusion Tensor Imaging (DTI)
This is my current favourite type of NI right now! DTI is beautiful, unique and revolutionary in this day and age, it’s almost like sci-fi stuff! DTI measures the rate of water diffusion along white matter tracts and with that calculates the directions and structural integrity of them to create these gorgeous white matter brain maps. They are FANTASTIC for finding structural damage in white matter - something that is making breakthroughs in research lately ie. schizophrenia, genetics and epilepsy. It measures the rate of diffusion which tells you about possible myelin/axonal damage and anisotropy, so the directions and if they are “tightly wound” or loosely put together - think of it like rope, good FA is a good strong rope, poor FA is when it starts to fray and go off in different directions - like your white matter tracts. My current research used DTI and it was honestly surreal to work with, the images are also acquired through an MRI scanner so you can actually get these images the same time you’re getting MRI’s done, functional or otherwise!
Positron Emission Tomography (PET)
One of the “controversies” (if you could call it that) is the use of radioactive substances in PET scanning. It requires the injection of a nuclear medicine to have the metabolic processes in your brain light up like Christmas! It uses a similar functional hypothesis to BOLD fMRI, in that it is based on the assumption that higher functional areas would have higher radioactivity and that’s why it lights up in a certain way. It depends on glucose or oxygen metabolism, so high amounts of glucose/oxygen metabolism would show up red and less active areas would show up blue, perfect for showing any functional abnormalities in the overall brain. However it has incredibly poor temporal resolution and due to it’s invasive nature, MRI is chosen more often. (The pictures are gorgeous though!)
Electroencephalography/Magnetoencephalography (EEG & MEG)
These are not “imaging” types in the stereotypical sense. They create a series of waves that you can physically see (think of the lines you get on a lie detector!). Electrodes/Tiny magnets are placed on the scalp/head in specific areas corresponding to certain brain structures. EEG picks up on electrical activity which is the basis of neuronal function, whereas MEG picks up on magnetic fields - the same property that is utilised by MRI. One of the biggest issues with EEG is that deeper structures passing through tissues get distorted, whereas MEG doesn’t because it only measures the magnetic properties. I’ve not had a lot of experience with either of these but I do know EEG is used in a lot of medical procedures to measure brain activity, from measuring seizures and sleep disorders to measuring brain activity in a coma. It’s fantastic and if you can actually figure out how to conduct and interpret results it’s an invaluable tool into looking at electrical activity.
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