Wednesday, June 20, 2007


My clinical mentor for the summer immersion program is Dr. Jonathan Weinsaft. He is a cardiologist who specializes in diagnosis of ischemic heart disease using noninvasive imaging techniques such as MRI. This week I learned a lot about the procedure used in diagnosis of ischemic heart disease. For ischemic heart disease, the accurate distinction between viable and infarcted myocardium is important for prognosis and treatment planning. Currently, the “gold standard” is to use delayed enhancement magnetic resonance imaging (DE-MRI). The technique basically is injecting a contrast agent (typically gadolinium) into the body. When the contrast agent perfuse through the myocardium, we take an MRI image of the heart. Typical DE-MRI images are shown below:

As shown in the left figure above, if the myocardium is viable, then it shows up dark in an MRI image. If infarcted myocardium is presented, it will show up as bright region (termed hyperenhancement) as shown in the upper part of the myocardium in the image on the right. The mechanism at the cellular level responsible for hyperenhancement is still not fully understood.

This week I also visit the nuclear medicine laboratory. For cardiovascular disease, the main procedure using SPECT is myocardial perfusion study. This is a form of functional imaging, in which the functional state of the tissue is accessed rather then the anatomical structure of the body. The procedure usually goes as follows: nuclear medicine (usually Tc-tetrofosmin or Tc-sestamibi) is injected into the patient. After the administered of radiopharmaceutical, a stress test is performed to increase the heart rate (either by doing exercise or administered with another drug such as adenosine). Then SPECT images are taken after the test to see the blood perfusion of the myocardium. The underlying principle is that under conditions of stress, diseased myocardium receives less blood flow than normal myocardium.

I found out all these from the technicians in the lab, which is kind of surprising that they know a lot of the theory behind the procedure. During my stay in the lab, it appears to me that the lab with only two SPECT scanners is run by at least 4 or 5 technicians. However, after I talked to them, I found out that it is pretty easy to operate the scanner. They usually assist the patient to get on the bench of the scanner, then adjust several parameters on the computer and let the SPECT scanner runs. The parameters are basically how long the scanner should run depending on the person body size and how many slices of images to take etc. I wonder, shouldn’t these settings be easily calculated by the computer automatically rather then entering manually?

I also found out that my project for this summer is related to another MRI imaging technique called t1 mapping. However, I have no idea what that is. Oh well, this means more reading besides the 20 or so clinical papers Dr. Weinsaft give me on cardiovascular disease diagnosis. Will let u guys know when I find the time to read about it …

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