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What is SPECT imaging and how does it work?

Posted on: 03.07.19

SPECT stands for single-photon emission computerized tomography. In layman’s terms, it’s a type of non-invasive nuclear imaging test that allows your doctor to see how well your internal organs are functioning. It uses a radioactive substance and a special gamma camera to create 3-D pictures of your organs at different angles.

Gamma cameras like the Digirad Cardius® 3 XPO and the X-ACT+ employ advanced solid-state technology that uses a silicon-based photodiode, coupled with cesium iodide (CsI). The technology not only offers better sensitivity and high energy resolution, but it also makes the camera smaller in size than a traditional MRI machine. And, with their open and upright design, they’re much more ergonomic and patient-friendly.

While an x-ray takes a picture of what your organs look like at a given point in time, a SPECT image shows blood flowing to and from the heart or blood flow restrictions due to narrow or blocked arteries. It can also be used to evaluate brain and neurological conditions and bone disorders.

In what cases is SPECT imaging ordered?

Not only can SPECT imaging capture how well your heart is performing, but it can also help diagnose disease processes that may be underway, including narrowing of the arteries, clogged arteries, identifying scar tissue due to heart attacks, or evaluating the success of surgeries like bypass surgery.

How does SPECT imaging work?

SPECT scans use a radioactive material called a tracer. The tracer is injected intravenously and mixes with your blood. As your blood moves through your body, it’s “taken up” or absorbed by your living heart muscle.

The Digirad Cardius® 3 XPO and the X-ACT+ allow for patients to be imaged in a comfortable seated position but other gamma cameras require you to lie down on a table. During the scan, the SPECT camera rotates around you. It picks up signals from the radioactive tracer, which are then converted to 3-D images by a computer.

When you undergo a nuclear stress test, a SPECT scan will be taken while you’re exercising and again when you’re at rest. The comparison of the images will allow your physician to evaluate blood flow under different levels of exertion.

Your images may show different shades of color that will indicate which areas of your heart absorbed more of the radioactive tracer and which areas absorbed less. A normal test result indicates there is sufficient and unrestricted blood flow to your heart, while an abnormal result means your heart’s blood flow is insufficient. Once your physician reviews your images, you’ll meet to discuss the results and any necessary treatment plan.

Example of SPECT imaging heart scan

What are the risks of SPECT imaging?

SPECT imaging is generally safe and most patients can go back to their normal activity right away. The amount of radioactive material injected into your bloodstream is small and your body will expel it through your kidneys in 24 to 72 hours. Be sure to drink plenty of water for a few days following the procedure.

If you are pregnant, think you may be pregnant, or are a nursing mother, be sure to notify your doctor prior to the scan. The test uses a low-dose of radiation, which is contraindicated for pregnant women. Nursing mothers may be advised to wait additional time before nursing again so that your body can excrete the tracer.

Patients may also have an allergic reaction to the radioactive tracer, although it’s uncommon.

SPECT imaging is a popular, cost-effective, and safe method of evaluating your heart and diagnosing disease. While you may be a little anxious, be assured that the scan is painless and it provides important clinical value to your physician.



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