Proton Density in Multiple Sclerosis
It is well known that Proton Density sequence is valuable in evaluation of Multiple Sclerosis (MS) plaques located under tentorium cerebelli. Proton Density (PD) - also known as second echo from T2 sequence, is something we get "for free" with normal T2. However compared to "pure T2" the "double echo T2" is somehow degraded in quality. But the price is worth to pay. Note this plaque laterally on the left side in the pons. It is much better depicted on this scan from 3T MRI compared to T2 and FLAIR. I like FLAIR (third image) as the most "sensitive" sequence for detection of plaques. However PD is "the king" under tentorium.
Also, do not forget the Sagittal T2 showing characteristic "Dawson Fingers" in the other MS patient. We use 3mm slice sequence covering corpus callosum and adjacent structures. I prefer it to volume (3D) sagittal FLAIR.