Myocardial Perfusion Scan

Myocardial perfusion scintigraphy, MIBI stress test, exercise radioisotope scan, thallium imaging, thallium scan, thallium, mIBI or tetrofosmin scintigraphy, and perfusion imaging.

• To assess the amount of blood reaching the heart muscle.
• To identify areas of heart muscle lacking an adequate blood supply as a result of a heart attack.
• To identify blocked coronary arteries and evaluate the effectiveness of coronary bypass grafts or angioplasty.

• Following an exercise stress test, you are injected with radioisotopes, such as thallium, MIBI (Cardiolite), or tetrofosmin (Myoview), that concentrate in heart muscle and can be tracked by a gamma scintillation (or detection) camera.
• The radioisotope circulates through the body and collects in the heart, revealing heart areas receiving insufficient amounts of blood.
• The gamma scintillation camera photographs your heart shortly after the injection and again several hours later, allowing doctors to compare thallium uptake immediately after exercise and again after rest.
• If MIBI or tetrofosmin is used, a second injection at rest is necessary.
• Because the test has two sections (four hours apart), evaluation may be performed on the same day or on consecutive days.

• You should not consume or use alcohol, caffeine, or tobacco (or any other source of nicotine) for 24 hours before the test.
• Do not eat anything for at least three hours before the test.
• You may be instructed to stop certain medications before the test.
• At the test site, blood pressure is measured, and ECG leads are attached to your chest, arm, and leg.
• An IV line is started in your arm.

• You exercise at increasing levels (as for an exercise stress test).
• Near the end of the test's exercise portion, the radioisotope is injected into the IV line, and you resume exercising for another minute. This allows the substance to travel through your body and concentrate in the heart muscle.
• If you are unable to exercise, a drug such as dipyridamole (Persantine), adenosine (Adenoscan), or dobutamine can be used to increase blood flow before the radioisotope is injected.
• After you stop exercising, you are positioned on a narrow examination table directly under the gamma scintillation camera. One or both arms are placed on a rest over your head, and the camera takes multiple pictures. In many instances, it rotates slowly around you, thereby producing three-dimensional images (SPECT or single-photon emission computed tomography).

• After the initial pictures are taken, you return for a second set of scans. Between sessions, you should remain relatively quiet, even though you may be permitted to leave the testing center. You can drink water or other plain, noncaloric beverages, but you should not eat.
• In some instances, another set of scans is made 24 hours later. In these cases, your doctor will give specific instructions regarding food consumption and other activities.

• The consumption or use of caffeine, alcohol, nicotine, and certain other drugs.
• Inadequate exercise before or after injection of the radioisotope.

The ECG taken during the exercise test and the scans are examined for abnormalities by a physician trained in nuclear cardiology. "Cold" spots on the scan (areas of decreased radioisotope uptake) indicate heart muscle areas receiving inadequate oxygen due to blocked or narrowed coronary arteries or a previous heart attack.

• It provides more information about the heart muscle and its blood supply than a conventional exercise stress test.
• It's more accurate than exercise testing.

• Some people are disturbed by the closeness of the camera; lying still for 30 to 45 minutes may also be uncomfortable.
• It's more expensive than routine exercise testing and requires an intravenous injection of a radioactive isotope.

Results indicating diseased coronary arteries may be confirmed by cardiac catheterization and angiography.