Thread by @radiologistpage

It is a bit ambitious to try and sum up the magic of MRI physics in one post but here goes! (Thread 1/11) #foamrad #meded #radiology #mri #foamed

Hydrogen atoms are abundant in all of us and are all made up of a single positively charged proton

Each proton has its own magnetic field

When placed inside a magnet (such as within an MRI scanner) the magnetic fields of the protons line up with the main magnetic field (2/11)

Whilst lined up the protons aren’t completely still but rotate 🌀(or ‘precess’) along the axis of the magnetic field

(3/11)

A RADIOFREQUENCY (RF) PULSE 〰️is then applied - instead of precessing in the direction of the main magnetic field (called the z axis) the protons gradually change their axis of precession so they now precess in the x-y plane

(4/11)

It is the precession in the x-y axis that generates the MR signal (5/11)

After delivery of the RF pulse the protons want to return to their original state (‘relaxation’) - this can be considered in two planes:
1️⃣LONGITUDINAL - return to the z axis known as T1 relaxation
2️⃣TRANSVERSE - reduction of magnitude along the xy axis (6/11)

T1 relaxation time is the time taken for the longitudinal signal to return to 63% of its original value

T2 relaxation time is the time taken for the transverse component to decay to 37% of its original value (7/11)

The RF pulses can be delivered in different ways to produce an effective signal (spin echo v gradient echo)

The ‘echo time (TE)’ is the time taken from the RF pulse to the maximum amplitude of the echo in the x-y plane
(8/11)

Further magnetic fields are applied (gradients) to help localise the signal in a 3D space - these are repeated at a set ‘repetition time (TR)’

All the data is collated in a matrix known as ‘k space’ before mathematical functions are performed to produce the image
(9/11)

Substances have predefined T1 and T2 relaxation times, and we can alter the parameters of the scan such as the TR or TE to highlight contrast differences between the two (T1 and T2 weighting)
(10/11)

This is a very simplified account of a very complex subject but hopefully sheds some light on what is an amazing part of medicine (11/11)