origin of signal from bone in musculoskeleton imaging protocols

[AndrewBworth]

I have been passively interested in T2 relaxation of long carbon chains (fats) in MRI for a short time, but I have been somewhat unsure how to program the simulation. Unfortunately, research wise it is a low priority for me currently.

It is my strong suspicion that the short T2 relaxation in fats in some sequences is a "false impression" as it appears in voxels. Long chains in fats, 16 to 18 carbons, have on the order of 30 protons each, with small but disparate J couplings along the chain. This causes the protons along the chain to oscillate at slightly varying frequencies along the chain and they become out of phase with one another. When the proton signals are added cumulatively into a voxel/pixel, they cancel and the fat appears hypointense. A spin echo however should reverse the J-dephasing, and the fat will again appear bright. So, the T2 of fats appears to be much longer in turbo spin echo sequences, due to the rephasing caused by spin echoes. In MRI images, where the bone appears bright, it is generally fat on a T1/T2 TSE image, or a standard T1 image.

There are researchers working to image the water in bone as well. To my knowledge - this is a field known as short-T2 imaging - useful for slowly moving water.

(07-23-2016 05:50 AM)gautam Wrote:  Since most of my work has been in neuroimaging, I have long held the view that bone (i.e skull) appears dark because of very short T2 for highly structured biomaterials like bone. Recently, I have been looking at Imaging for other body parts, specifically MSK protocols, where one can also see the bone as bright / moderately hyperintense structure in the image. I am wondering, how does the bone appear with such sufficient signal in these protocols? What parameters (and how) are used to make the bony structures appear visible (and bright) ?
If there is a section on this site that already covers this, please direct me to it.
Thanks,
Sid.