MRI

Jessica Wallach, Reston, Virginia, March 25, 2020

These cartoons show the reaction of the magnetism in some hydrogen protons in our body when they are in an MRI machine…or how I imagine they react.

Here is an oversimplification of how MRI’s work just in case you don’t know: MRIs run on magnetic fields, there are two main fields: B0 and B1…When you enter the MRI, some hydrogen protons line up parallel with the B0 magnetic field. I like to think of this as the protons’ happy place. Then the MRI tech puts on B1 which knocks the protons by applying a resonance frequency. This tips the protons 90-degree angle and causes them to get out of step with each other (they naturally percess or turn in time with one another), but B1 causes them to be “out of phase” with each other. Once B1 is turned off, the protons eventually stand back up and they start precessing in time with one another. These two processes are called T1 and T2 relaxation. These cartoons show a number of T1 relaxations where protons going from being knocked down to getting back to their happy place and the last frame shows T2 relaxation where the protons are trying to recover from being out of precession with each other…