Week 6 - Jiahao

This week most time was spent in the lab with effort to get my project moving towards. Besides lab working on my immersion project involving MRI contrast enhancement based post processing, I also attended the daily radiology residency noon meeting.

The noon meeting this week focused on musculoskeletal imaging. MSK cores actively engage X-ray, CT, MRI and ultrasound, for diagnostic and interventional radiology, with focused on arthroplasty, shoulder, knee, etc. CT is usually very sensitive for MSK imaging considering calcification which makes it popular for related examination. As for clinical practice, CT often plays as the gold standard. Of course, as MR researchers always try to compete with CT with priority for non-ionizing radiation, lots of MRI techniques and novel sequences have been developed to handle with issues like fat-water separation and motion correction, hoping to make it substitute or even replace for CT. So it is very interesting to know about how radiologists think about CT and MRI for MSK, which makes sense that MRI people are doing hard to improve and "sell" their techniques for competing with CT. After all, all those methods will hopefully eventually be implemented in hospital MR machines and produce images with quality and make themselves convincible in the view of radiologists.

The lab work I am doing recently is on contrast optimization based on multiple gradient echo sequences to improve the visualization of central vein signs in white matter lesions in multiple sclerosis. Central vein is a significant sign in MS lesion involving its formation by pathology and is prevalently found in lesions located in periventricular or deep white matter areas in MS patients both ex vivo and in vivo. In radiological findings, central vein usually is depicted on a T2* weighted image as a hypointense thin line or a hypointense small dot inside of the lesion, which is positioned centrally as well as runs partially or entirely through the lesion. It has been long hypothesized that those central veins introduce blood-brain-barrier leakage which leads to autoimmune attack by immune cells targeting at myelin-like antigen, causing demyelination of the axon and cascading inflammation, eventually resulting in axonal loss. Longitudinal lesion development remains as another interesting topic by focusing on focal relapse-remitting patterns. Due to its distinct pathology, central vein signs can greatly provide for multiple sclerosis differential diagnosis. However, since central veins are usually tiny and need to be demonstrated by high or even ultra-high magnetic field which utilize the susceptibility difference or so-called T2* weighted information, T2* based techniques such as multiecho GRE sequence are preferred for central vein visualization. During sequent echo times, vein signal decays faster than surrounding lesion tissue due to a higher R2*, making the contrast become better. The best contrast is acquired at the echo time which equals to the vein T2*.  On the other hand, R2* map can also be extracted by multiecho GRE. Using information from R2* map, the contrast can be further improved by designed filter suppressing vein signal according to the R2* map.




Sati, Pascal, et al. "The central vein sign and its clinical evaluation for the diagnosis of multiple sclerosis: a consensus statement from the North American Imaging in Multiple Sclerosis Cooperative." Nature Reviews Neurology 12.12 (2016): 714.

Filippi, Massimo, et al. "Association between pathological and MRI findings in multiple sclerosis." The Lancet Neurology 18.2 (2019): 198-210.