The SPECT scan uses a combination of a CT scan (computed tomography) and a radioactive tracer that flows through the blood and looks at how blood flows through tissues and organs. It is often used in brain scans to see what the blood flow to the brain looks like following trauma.
Prior to the SPECT scan, the patient is injected with a radioactive chemical that emits the gamma rays necessary to be picked up by the scanner. The computer on the CT scanner picks up the information from the radioactive tracer and translates the images into two-dimensional cross-sections of the body.
The cross sections can then be put together to create a three dimensional image of the brain. The most common radioisotopes used in SPECT scanning that label the tracer chemicals are iodine 123, xenon 133, fluorine 18 and thallium 201.
These belong to elements that are quickly and safely passed through the body once the detection phase has passed. In some cases, various chemicals and drugs can be labeled with these elemental isotopes.
The type of tracer used depends on what the doctor is looking to measure. If, for example, the doctor is examining a tumor, he or she might radio-label glucose to see how glucose is metabolized by the tumor. The SPECT scan is similar but different from a PET scan because in a SPECT scan, the tracer remains in your blood stream and is not absorbed by the tissues. This limits the area where the SPECT scanner can detect but it is far cheaper and more available than a higher resolution PET scan.
The SPECT scan is usually used on the brain-usually used to detect blood flow through the different arteries and veins inside the brain. Some doctors feel that a SPECT scan is more sensitive in detecting brain injury than either the CT scan or MRI scan of the brain because it can detect reduced blood flow to areas of the brain that are injured.
It is also used as a presurgical test for people who have uncontrolled seizures with medicines. The tests can be done during the time between seizures and the time during a seizure to see what happens to the blood flow in the brain at the point where the seizure begins.
SPECT scanning can also be used in the detection of stress fractures of the spine, also called spondylolysis.
It can be used to see which areas of the brain are involved in a stroke and in identifying tumors. The test is performed by a specially trained technologist, skilled in nuclear medicine.
The test is performed at a hospital or outpatient imaging center in the nuclear medicine department.
In preparing for the examination, you need only to wear comfortable clothes and to expect your time there to last 1-2 hours.
During the test, the technologist will give you an IV and place in it a small amount of radioactive tracer.
After a ten to twenty minute wait, the tracer will be in the brain and you will be scanned in the CT scanner.
You will be asked to lie still while the CT scanner takes the necessary pictures. Drink plenty of water afterward so you can flush the radioactive tracer out of your system.