Week 2 J. Zhang

This week I spent my time among the reading room, MRI scanning room, and my laboratory. In the reading room, I came across several interesting cases.

• A patient came in, claiming back ache. CT shows a hyper-intensity spot in the intervertebral disc between T7 and T8. The intensity of the spot is much higher than the spine itself, which make us wonder what exactly in that spot. There is no sign of cancer or abnormality in the surrounding tissue. One possibility is trauma.
• CT is also used to follow up surgical implants, mainly bone fixation. I personally think CT is superior in this area compared to MRI because of the imaging speed, the compatibility issue, and the strong contract between the fixation sites (hyper-intensity) and the surrounding soft tissue (hypo-intensity). The cases I saw were mostly spine fixation.
• A stroke patient came in. First CT images showed obvious perfusions in the left brain. 90 minutes later, MRI was performed. Interestingly no obvious perfusion was shown on T2 FLAIR. Typically, T2FLAIR is sensitive to perfusion. Doctors believed it might be due to the fact that the local tissues were hyper-acute. Second CT, 18 hours after the first CT, showed further progression of the perfusion.  
• On a patient’s MR images, a black hole was observed in the right ICA. Similar situation happened to another patient’s MR images a few weeks ago. It was suspected that the black hole was an artifact from the 3T MRI scanner. Patients were told to be re-scanned in the 1.5T scanner.  

In the MRI scanning room, I observed a cardiac MRI using cine imaging. It is a MRI technique used to take ‘real time’ sequential images for patient’s beating heart for functional evaluation. With the assistance of contracting agent, blood flow, heart valve movement, and muscle contractions can be seem in ‘real time’. During imaging, patients are told to hold their breath to avoid motion artifacts. Each cycle takes about 12 seconds. 12 imaging cycles are performed.

It is worth noticing that cine is not really ‘real time’. The scanner samples partial K-space during each heartbeat. The imaging cycle repeats until K-space is fully sampled. Then the entire sampling process restarts at a slightly different time point of the heartbeat in order to acquire next frame. Therefore, assumption has been made that heartbeats are almost identical through the time of sampling.