Week 2: Perfusion

This week, I decided to focus my Immersion experience by learning about perfusion imaging on multiple modalities.

I got this idea when I started looking at perfusion in echo, which in the textbook was described as a promising contrast-enhanced ultrasound application, but the clinicians today almost never associate echo with perfusion whatsoever.

Before I go any further, let me explain what perfusion is. Perfusion refers to the delivery of oxygenated blood through the vessels and capillaries to the tissue, and perfusion imaging allows us to get functional information about specific anatomies that we are interested in.

For example, abnormal myocardial perfusion is dangerous to the patient, as it can indicate a higher risk of cardiac death, or myocardial infarction (MI). The abnormality suggests insufficient blood supply due to coronary artery stenosis or some other phenomena, and if detected, the patient can be treated appropriately to reduce or eliminate future heart attacks.

After a meeting with Jonathan yesterday (Thursday) in which we discussed a potential project for the immersion, he helped me make an arrangement to spend a few days in the Nuclear Cardiology department.

I started today at the Nuclear Cardiology department, and learned about SPECT imaging and the different kinds of stress tests that were done. In exchange for the opportunity for me to stay for a few days, they jokingly asked me to make them a new camera; the photomultiplier tube system in the SPECT scanner.

I also got to briefly see a CT and a PET scan for the perfusion-type of tests, and was also able to sit through each of the three stress tests done in the lab; on the treadmill, injection of adenosine, and the infusion of dobutamine. Each of these stress tests also needs two SPECT images of the heart; one before and one after the test. We then get the following kind of image profile:

Source: http://www.bocaradiology.com

For each axial slice image of the left ventricle, we observe the heart at rest, and the heart under stress. The idea is to look for discrepancies that can indicate perfusion abnormalities. If healthy, the injected radioactive thallium can be observed throughout the entire myocardium. If diseased, we will observe gaps in the SPECT images taken after the stress test.

There's apparently a number of way for misdetection of abnormal perfusion to happen; most notably due to large breasts, implants or anything else that can shield the signal from the thallium; thus it requires great practice in order to quickly and accurately read these images. I thought that was cool.

I'm very thankful to Sandy and Sunil, who took me around for the entire day today. I'm looking forward to visiting the nuclear cardiology lab again next week.