Nuclear cardiology is the study of the heart using small amounts of radioactive tracers. It allows us to study the function of the heart non-invasively (without inserting any instruments into the heart itself).
The most commonly used test in nuclear cardiology is called myocardial perfusion imaging. This is a form of stress test which makes use of myocardial perfusion tracers and gamma camera imaging methods to assess the adequacy of blood flow to the heart, as well as to find out if how much of the heart muscle is viable (alive) and how much is scarred and damaged beyond repair. It is a diagnostic tool that is often used for the detection of coronary artery disease (narrowing of the heart arteries) and for the assessment of the severity and extent of its effects on blood flow to the heart and myocardial viability.
How it works:
During the stress nuclear test, a small amount of a radioactive perfusion tracer (such as thallium, sestamibi or tetrofosmin) is injected into a hand vein while the patient is undergoing stress testing (Figure 1). These tracers are taken up by heart muscle in proportion to blood flow. Areas of myocardium with impaired blood flow or viability will have reduced tracer uptake. The uptake of tracer in the heart is then assessed by imaging the patient with a gamma camera, which is capable of detecting the small amounts of radiation emitted by the tracer. By rotating the camera around the patient to take multiple views from different angles (Figure 2), a 3-dimensional image of the distribution of tracer in the heart can be reconstructed using computerised methods (Single photon emission computed tomography, or SPECT Figure 3). The uptake of tracer in the heart can then be assessed in a tomographic (3-dimensional) way, which avoids overlap between different parts of the heart and allows us to localise the area and extent of any abnormalities with greater accuracy (Figure 4).
This technique is more accurate for detecting abnormal blood flow and heart disease than the standard ECG stress test.