Heart & Vascular system
The applications of Nuclear Medicine to heart and vascular diseases – innovative techniques include imaging during exercise for accurate diagnosis and appropriate treatment.
by Partha Ghosh, Siemens AG
The major application of Nuclear Medicine imaging
in diseases of the heart is to evaluate myocardial perfusion
What it is used for?
Myocardial perfusion imaging is used to measure the blood flow to the heart muscle during exercise and sometimes at rest in order to assess if there is decreased flow due to coronary artery disease.
How is it performed?
The patient is exercised to the near maximum capacity or infused with drugs which increase the heart workload and then a radioactive substance is injected which goes into the heart muscle directly proportional to the blood flow. The patient is then imaged using a gamma camera to visualize the uptake of the radioactive isotope in the heart muscle. Any area of lower uptake than normal is regarded as ischemia secondary to coronary artery disease.
What does myocardial perfusion show?
During exercise, the heart work load is high and blood flow abnormalities become pronounced and can be visualized as region of low uptake in the nuclear medicine study. Nuclear Medicine studies have shown high accuracy for identification of functionally significant myocardial ischemia and coronary artery disease.
How does heart work?
Heart muscle with decreased blood flow due to coronary artery disease may have functioning intact cells which would regain back complete function if blood flow is increased by treatment like angioplasty. This kind of heart muscle is called viable myocardium. Decreased blood flow measured by nuclear medicine study during exercise but with normalization of flow at rest suggests the heart muscle is ischemic but viable and likely to benefit from treatment. Non-viable or infracted heart muscle on the other hand is too damaged for recovery and shows very low blood flow both at exercise and rest. Nuclear Medicine studies thus makes it possible to separate which heart muscle with benefit from angioplasty or bypass surgery and thus help guide the proper procedure.
Although most of nuclear medicine studies for the heart are performed on gamma camera, there is progressive use of PET/CT studies for the heart which also evaluates perfusion and viability but with different isotopes.