Images courtesy of Kim Allan Williams, MD.
What is SPECT?
You may have heard SPECT MPI referred to as several different terms, such as:
- Nuclear stress test
- Noninvasive cardiac imaging
- Cardiac nuclear scan
What does SPECT show?
SPECT scans show clinical information about a patient's heart health and can detect perfusion defects. Multiple perfusion defects in different coronary territories may indicate severe CAD.1
SPECT works by using a gamma camera to capture images of photons emitted by radiotracers as they are taken up by viable myocytes proportional to the amount of blood flow to the heart.6 The SPECT radiotracers are technetium-99m (Tc-99m) and thallium-201 (Tl-201).8 A series of images captures different sections of the heart, which are digitally reassembled to produce a 3D image of the heart.6
Scans are performed at stress and rest. The color indicates areas of perfusion where the radiotracer has entered the myocardium. Lighter color signifies higher uptake of the radiotracer, whereas darker color means lower uptake. If the color is light on a rest scan and dark on a stress scan, it may be due to stress-induced ischemia or an obstruction of blood flow to the region.6,9
What is SPECT used for?
SPECT is used for the detection of CAD, risk stratification of patients with known or suspected CAD, and guidance in clinical management decisions. It helps measure the functional capacity of the heart and has independent prognostic value. It provides information about the extent, severity, and location of perfusion defects.6
The extent and severity of stress-induced perfusion abnormalities are directly related to the degree of risk for ischemic events, namely, cardiovascular death and myocardial infarction (MI).1
- Normal exercise stress SPECT test results are associated with a very low annual risk of cardiovascular death or MI (<1%)
- Moderate to severe abnormalities are associated with an increased annual risk of cardiovascular death or MI (≥5%)
This test is considered an applicable imaging service under the Medicare AUC program.10
2. Radiotracer Injection
When choosing an appropriate test, it's important to consider whether the benefit of information from SPECT imaging results would outweigh the risk of exposing a patient to any amount of radiation.3
Also, image quality and diagnostic accuracy of SPECT may be affected by attenuation artifacts, which can be seen in obese patients or those with a large amount of breast tissue. Artifacts can be reduced with several techniques.1
- Using Tc-99m radiotracers
- Imaging patients in the prone position
- Applying attenuation correction algorithms in image-processing software