MRI vs. NMR

[bdj]

Does anybody remember the term NMR? I seem to remember that it stands for Nuclear Magnetic Resonance. I ask because I was reading an article in Popular Science about MRIs and it never said anything about NMR. I thought that NMR was change to MRI because of the stigma from the word nuclear. Any comments.


bdj

[ben-the-slacker]

Yep, NMR stands for N uclear Magnetic Resonance.

[osprey4]

Yes, true story. NMR is the instrumental method, still widely used in many college and industry labs. But when the technique was introduced to a hospital setting, the term "nuclear" (sometimes pronounced "nookular") scared people and the term was changed to magnetic resonance imaging. Of course, the same thing is happening, atomic nuclei are still resonating.

NMR is based on the measurement of absorption of electromagnetic radiation in the radio frequency region. The radio waves are absorbed by nuclei subjected to intense magnetic fields. The magnets are strong enough to cause some serious havok when not respected. Just a couple weeks ago, a lab tech at a university was killed by an improperly secured gas cylinder that flew across the room when the MRI was switched on.

Jn

[krusty the klown]

Bang on the nail! It was changed because of the word 'nuclear'.

The only thing 'nuclear' about NMR/MRI is the effects of the very large magnetic field on the atomic nuclei in the body.

It's all to do with elecrons and their associated spins. Medical MRI units use superconducting magnets (always on). Electromagnets can be used, but over the relatively long time of the image acquisition, the magnet would heat up and the field pattern would change.

The idea is that the powerful magnet causes the electrons' spins to align in the same direction. The loud banging that you hear during a scan are radio frequency (RF) pulses being sent to secondary coils within the scanner. These pulses knock the electrons' spin orientation back down. The spins recover (as they are still in the main field) and in doing so, generate a signal which is recorded by yet more coils of wire.

The signals are computationally back-projected to form an image.

MRI units image hydrogen atoms in the body (i.e. they image water), so fat, muscle and bone gives different signal intensities and therefore appear as different brightness levels on the image.

Sometimes, a contrast agent is injected to enhance the detail of the image. Examples are for MR angiography (looking at blood vessels and flow) or to assess the effectiveness of cancer treatment. A pre-treatment scan is done with contrast agent, a region of interest is drawn. Graphs are plotted of the uptake and washout of contrast agent. The process is repeated after treatment to quantify tumour reduction.

Don't go neat the MR scanner with yer credit cards & don't go near them if you have a pacemaker