Short for Single Photon Emission Computed Tomography, the SPECT scan is a type of nuclear imaging test that helps determine if a patient suffers from coronary artery disease, or if they had a heart attack. In many ways, the SPECT test looks like a PET scan, but they are different for a specialist who knows exactly how the test is performed.
PET vs SPECT
At first glance, it might seem that these tests are identical. While it may be so in terms of patient experience, the difference between them lies in the type of radioactive tracers used. PET scans use particles called positrons, while SPECT scans measure gamma rays.
The positrons characteristic to the PET scan counteract the electrons in the human body because they are differently charged. When these two particles meet, they annihilate each other, sparking a small amount of energy that’s picked up by the PET scanner, in order to recreate digital images of the heart.
Even if the SPECT scan involves injecting a radioactive substance in the bloodstream, the radiation to which the patient is exposed is rather safe. It takes between 24 and 72 hours for the body to completely eliminate the substance.
Before the SPECT scan
It’s best for pregnant or nursing mothers to avoid a SPECT scan, as it can harm the baby. Because of that, it’s important to let your doctor know if you are pregnant or breastfeeding.
Doctors will always prepare you for the test beforehand, telling you to:
- Avoid drinks that contain caffeine or alcohol the day before the test.
- Avoid eating any kind of food six hours before the test (water is allowed).
- Avoid taking certain types of medication that could interfere with the results of the test (always let your doctor know about every prescription or over-the-counter pills, medication, herbs, or supplements you might be taking).
- Dress comfortably, because the test can last a few hours.
During the SPECT scan
This type of test requires specialized equipment, which means it’s performed in either a hospital or a clinic. You will have electrodes attached to your arms, legs, and chest, electrodes that are connected to an EKG machine. The doctor or technician will place the cuff around your arm to constantly keep track of your blood pressure. You will be connected to an IV that injects tracer in your bloodstream. Here is where the SPECT scan starts to differentiate from a PET scan.
The radioactive tracer that is now in your bloodstream will produce gamma rays. A special gamma camera that rotates around your chest area will pick up the tracer’s signals, sending images to the computer or how blood flows through the heart. The thin-slice images can be converted to 3D images by the computer.
When your coronary arteries are narrow or blocked, they will show up dark on the images. More advanced SPECT scanners now create colored images, with codes to identify the amount of tracer uptake.
The SPECT scan can be performed while you are resting, or when you’re exercising. If you are taking the test while at rest, you will be required to lie on a table and have the gamma camera rotates around your chest, taking images.
The exercise stress test is performed in order for your doctor to understand how your heart performs when it has to pump extra oxygen, basically determining how much you can take before you reach a safety limit. If you are physically unable to exercise, the doctors will give you special medication that increases the blood flow to the heart.
Understanding the results
Your doctor will be the one to assess your current heart conditions, as well as provide a suitable solution and treatment for your problem. There are multiple results that could arise from a SPECT scan:
- People who show normal results when resting and exercising have healthy coronary artery and won’t require any medical treatment.
- Some patients can have good results when resting, but problematic ones when they’re exercising. This can be caused by coronary artery blockage, which is a blood clot that prevents normal blood flow. If this occurs, the tracer will not be visible past the blockage point in that coronary artery.
- If the results of the test are abnormal when resting and when exercising, there will be areas where the tracer is not visible.
- If a patient has previously experienced a heart attack, the lack of tracer will indicate dead cells.
Conclusion
The SPECT scan is a non-invasive nuclear imaging test that involves injecting a radioactive tracer into the bloodstream. The tracer sends signals to a gamma camera that rotates around your chest, which helps create thin-sliced images of your heart on a computer.
The pictures will give your doctor plenty of information related to your heart’s status, as well as point out if your coronary arteries are healthy. The SPECT scan is performed when you are resting, but also when you’re exercising, because it lets doctors know what are your heart’s healthy stress limits.