Myocardial perfusion scan or imaging is an imaging technique used to evaluate the blood flow to the myocardium (muscle of the heart) using a small amount of radioactive chemical. It is used to diagnose the coronary heart diseases, myocardial abnormalities, and also used as a diagnostic tool for many heart conditions. It can also image scar tissue resulting from the heart attack. Myocardial perfusion imaging (MPI) provides accurate diagnostic and prognostic information than other standard techniques with better sensitivity.
Radioactive substances either radio pharmaceutical chemical or radioactive tracers is intravenously administered to the patient. Radioactive tracer is absorbed by the healthy heart tissue indicating that the blood flow is abundant. In areas where blood flow is less due to damage of the tissue or blockage of the vessel, absorption is not noticed. Images obtained show differently revealing the absorption levels of radioactive tracer. Pictures are captured using a single photon emission computed tomography (SPECT) imaging with gamma cameras, which rotate around the patient while taking images. Images are taken from 10 to 60 minutes after the administration of the radionuclide.
MPI is performed in resting condition and in stress. Stress radionuclide MPI examines the blood flow during exercise. If the patients cannot exercise, medicine to increase blood flow is injected for the evaluation. Food and drug administration (FDA) approved radiopharmaceuticals for MPI include Technetium 99m, Thallium 201, and Sestamibi or Tetrofosmin.
MPI is safe; the risk of heart disease is far greater compared to the radiation exposure for the patients. Wheezing is noticed in some patients with the medication administered to stress the heart. Pregnant and lactating women need to inform their doctor before exposure to any kind of radiations.