A Myocardial Perfusion Scan (MPS) is a non-invasive nuclear imaging procedure designed to assess blood flow to the heart muscle, known as the myocardium. This test helps determine if there are areas of poor blood supply, which can indicate coronary artery disease. Patients should plan for a significant time commitment, as the entire process typically takes about three to five hours, although some protocols may split the test over two separate days. The total time is largely composed of necessary waiting periods between the injection of a radioactive tracer and the image acquisition.
Required Preparation Before the Appointment
Several preparatory steps are necessary before a myocardial perfusion scan to ensure image accuracy. Patients are typically instructed to fast for at least four hours before the test, consuming only water. This fasting requirement helps to reduce background activity from the digestive tract, which can interfere with the clarity of the heart images.
A crucial preparation involves avoiding all caffeine and methylxanthine-containing products for at least 12 to 24 hours prior to the appointment. This includes coffee, tea (even decaffeinated), chocolate, certain soft drinks, and over-the-counter medications, as these substances can counteract the effect of the pharmacological stress agents used in the test. Patients may also be instructed to temporarily stop certain cardiac medications, such as beta-blockers or calcium channel blockers, 24 to 48 hours beforehand.
Upon arrival, the initial intake process includes completing necessary paperwork and having an intravenous (IV) line placed, which will be used for administering the radioactive tracer and, if needed, the pharmacological stress agent. Patients are advised to wear comfortable, two-piece clothing and athletic shoes if scheduled for an exercise stress test. Removing radiopaque objects, such as jewelry or metal near the chest, is also required before imaging to prevent artifacts.
The Initial Rest Phase and Imaging Session
The first major segment of the MPS focuses on establishing a baseline of blood flow to the heart while the patient is at rest. This phase begins with the injection of a small dose of a radioactive tracer directly into the patient’s IV line. This tracer is taken up by the heart muscle in proportion to the existing blood flow in the coronary arteries.
A mandatory waiting period follows the injection to allow the tracer to circulate and be absorbed by the myocardial cells. This distribution time typically ranges from 30 to 60 minutes. During this time, the patient may be asked to remain still or consume a fatty meal to help clear the tracer from the liver and gallbladder, which improves the image quality by reducing background activity.
Once the waiting period is complete, the patient is positioned on a table for the imaging acquisition. A specialized camera, called a gamma camera, will rotate around the patient’s chest to capture images of the heart, a process known as Single-Photon Emission Computed Tomography (SPECT). This image acquisition typically takes about 15 to 30 minutes, resulting in a total time for the initial rest phase of approximately one to one and a half hours.
The Stress Induction and Second Imaging Session
The second major phase of the procedure introduces a controlled stress on the heart to reveal any blood flow limitations not apparent at rest. Stress is induced either through physical exercise, such as walking on a treadmill, or by administering a pharmacological agent. If the patient is physically able, the exercise method is preferred, with the intensity gradually increasing while the patient is continuously monitored with an electrocardiogram (ECG) and blood pressure cuff.
For patients unable to exercise, a medication is administered through the IV line to chemically dilate the coronary arteries, effectively mimicking the effect of physical exertion. At the point of peak stress, whether from exercise or medication, a second, larger dose of the radioactive tracer is injected. The patient continues the stressor for a brief period to ensure the tracer is fully distributed to the heart muscle under maximum blood flow conditions.
Following the second injection, another waiting period is necessary before the final stress images can be acquired. This waiting time allows for the optimal concentration of the second tracer dose and for the background activity to diminish, ranging from 15 minutes to over an hour. The final image acquisition takes another 15 to 30 minutes.
Post-Procedure Timeline and Receiving Results
After the final imaging session is complete, the IV line is removed, and the patient is free to leave the facility immediately. There are no restrictions on resuming normal daily activities, including driving and eating. Patients are generally advised to drink plenty of fluids for the next 24 to 48 hours and empty their bladder frequently to help naturally flush the remaining radioactive material from their body.
The images acquired during both the rest and stress phases must be processed, reconstructed, and analyzed by a nuclear cardiologist or radiologist. The physician compares the two sets of images to identify any areas of reduced blood flow, which may indicate blockages or scarring. The complexity of this analysis means the final report is typically not available immediately. Patients can generally expect their referring doctor to receive the official results and discuss the findings with them within 24 to 72 hours following the completion of the scan.