Brain Imaging Alphabetical Soup: Making Sense of CAT, PET, MRI, fMRI, SPECT: MRI

I started this mini-series with the articles on how imaging got started, and on CT scans. Now we’ll move on to MRI scans.

MRI, or magnetic resonance imaging, is used to create images of the body’s tissues, specifically of the soft tissues, like organs. X-rays pass through soft tissues undistorted and relatively easily. Now, most human tissue is water-based (which makes sense considering we’re 70% water).  The amount of water in tissues differ. So different tissues will behave differently. These differences can then be used to construct a 3D image.

MRI scans are constructed by applying a strong magnetic field around the body. In water, you can find single protons (Hydrogen atoms, like H20). In MRI scans, it is the H nuclei that create the signal.

So, initially, the fields are randomly oriented. When a strong external magnetic field is applied, a fraction will organize themselves, and align themselves with the external field. This external field is applied in a constant manner throughout the scanning session.

Now, when the protons are aligned, a brief radio frequency is applied. This radio frequency then knocks the protons out of alignment by 90 degrees to their original orientation. So now the protons are spinning in this new state, and as they do this, they produce a detectable change in the magnetic field. This then is what forms the MRI signal.

Eventually, the protons are pulled back into their original alignment (they “relax”). The MRI scanner then repeats the process by sending the radio frequency to excite the protons in different slices of the brain that is being scanned.

Now there are different types of MRI scans, including the T1 and T2 scans.

T1-weighted images are used for structural imaging of the brain. In a T1-weighted image, gray matter looks gray, and white matter looks white. Pretty simple to distinguish.

When the protons are misaligned at 90 degrees to the magnetic field, the MRI signal decays because of interactions with other nearby molecules. This is the T2 image.




5 thoughts on “Brain Imaging Alphabetical Soup: Making Sense of CAT, PET, MRI, fMRI, SPECT: MRI

  1. Pingback: Brain Imaging Alphabetical Soup: Making Sense of CAT, PET, MRI, fMRI, SPECT: fMRI | neuravinci

  2. It’s hard to find your blog in google. I found it on 16 spot, you should build quality backlinks , it
    will help you to increase traffic. I know how to help you, just type in google – k2 seo tips and tricks

  3. I almost never leave remarks, but i did some searching and wound up here
    Brain Imaging Alphabetical Soup: Making Sense of CAT, PET, MRI, fMRI, SPECT: MRI | neuravinci.

    And I actually do have a few questions for you if you tend
    not to mind. Could it be just me or does it give the impression like some of these comments look like they are coming from
    brain dead individuals? 😛 And, if you are writing at other places, I would like to keep up
    with everything new you have to post. Could you
    make a list of all of all your public pages like your twitter
    feed, Facebook page or linkedin profile?

    • Hi 🙂

      I am not sure what you mean about wanting a list of all my public pages? What is your intention with them?

      Thanks 🙂

  4. I read a lot of interesting articles here. Probably you spend a lot of time writing,
    i know how to save you a lot of work, there is an online tool that creates high quality, SEO friendly articles in seconds, just search in google –
    laranitas free content source

Leave a Reply: A few words won't kill ya (plus, it's good for your brain)

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s