SPECT (Single Photon Emission Computed Tomography) Scan
What is Nuclear Medicine Imaging?
Nuclear Medicine Imaging often enable physicians to accurately diagnose and stage complex diseases — including cancer, and cardiovascular and neurological disorders in their early stages — as well as monitor disease progression or response to treatment.
Also referred to as molecular imaging or functional imaging, these diagnostic procedures provide detailed pictures of what is happening inside the body at the molecular and cellular level. Where other diagnostic imaging procedures (such as x-rays and computed tomography (CT)) offer pictures of physical structure, nuclear medicine imaging allows physicians to see how the body is functioning and to evaluate its chemical and biological processes.
In nuclear medicine imaging procedures, patients are injected with a radiopharmaceutical agent and imaged with PET (Positron Emission Tomography) or SPECT (Single Photon Emission Computed Tomography) cameras that read the emissions given off by the radiopharmaceutical agent.
How does a SPECT scan work?
SPECT is a nuclear imaging scan that integrates computed tomography (CT) and a radioactive tracer. The tracer is what allows doctors to see how blood flows to tissues and organs.
Before the SPECT scan, a tracer is injected into your bloodstream. The tracer is radiolabeled, meaning it emits gamma rays that can be detected by the CT scanner. The computer collects the information emitted by the gamma rays and displays it on the CT cross-sections. These cross-sections can be added back together to form a 3D image of your brain.
The radioisotopes typically used in SPECT to label tracers are iodine-123, technetium-99m, xenon-133, thallium-201, and fluorine-18. These radioactive forms of natural elements will pass through your body and be detected by the scanner. Various drugs and other chemicals can be labeled with these isotopes.
The type of tracer used depends on what your doctor wants to measure. For example, if your doctor is looking at a tumor, he or she might use radiolabled glucose (FDG) and watch how it is metabolized by the tumor.
The test differs from a PET scan in that the tracer stays in your blood stream rather than being absorbed by surrounding tissues, thereby limiting the images to areas where blood flows. SPECT scans are cheaper and more readily available than higher resolution PET scans.
What does a SPECT scan show?
A SPECT scan is primarily used to view how blood flows through arteries and veins in the brain. Tests have shown that it might be more sensitive to brain injury than either MRI or CT scanning because it can detect reduced blood flow to injured sites.
SPECT scanning is also useful for presurgical evaluation of medically uncontrolled seizures (Fig. 2). The test can be performed between seizures (interictal) or during a seizure (ictal) to determine blood flow to areas where the seizures originate.
This type of scanning is also useful in diagnosing stress fractures in the spine (spondylolysis), blood deprived (ischemic) areas of brain following a stroke, and tumors.
What happens during the test?
First, you will receive an injection of a small amount of radioactive tracer. You’ll be asked to rest for about 10–20 minutes until the tracer reaches your brain. Next, you’ll lie comfortably on a scanner table while a special camera rotates around your head. Be sure to remain as still as possible so that the machine can take accurate pictures.
Once the scan is complete, you can leave. Be sure to drink plenty of fluids to flush the tracer from your body.
What is the use of SPECT?
Evaluating patients with suspected dementia.
Diagnosing encephalitis.
Monitoring and assessing vascular spasm following subarachnoid hemorrhage.
Mapping of brain perfusion during surgical interventions.
Detecting and evaluating cerebrovascular disease.
Predicting the prognosis of patients with cerebrovascular accidents.
Corroborating the clinical impression of brain death.
Evaluating patients for coronary artery disease.
What are the risks?
The tracer is radioactive, which means your body is exposed to radiation. This exposure is limited, however, because the radioactive chemicals have short half-lives. They breakdown quickly and are removed from the body through the kidneys.
The long-term risk of radiation exposure is usually worth the benefits of diagnosing serious medical conditions. Your exposure risk could vary, however, depending on how many CT or other scans you have had. If you have concerns about your cumulative radiation exposure, talk to your doctor.
Women who are pregnant or nursing should not undergo a SPECT scan. Some people may have an allergic reaction to the tracer or the contrast agent.
Thank you for reading !