Single Photon Emission Computed Tomography (SPECT Scan)
SPECT Scanning, or single photon emission computed tomography, is a medical nuclear imaging test, which means it uses a radioactive substance and a special camera to create 3-D images of the inside of the body. While imaging tests like X-rays can show what the structures inside your body look like, a SPECT scan produces images that show how your organs work.
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.
A SPECT scan integrates two technologies to view your body: computed tomography (CT) and a radioactive material (tracer). The tracer is what allows doctors to see how blood flows to tissues and organs.
SPECT scans are effective for getting information about blood flow to tissues and chemical reactions in the body, and are often used for diagnosing and monitoring treatment for brain tumours and cancers affecting bones.
Why a SPECT Scan is Done
SPECT imaging is generally added when doctors need information they can’t get through routine Nuclear Medicine images such as a CT or MRI.
The most common uses of SPECT are to help diagnose or monitor brain disorders, heart problems and bone disorders:
Brain Disorders: SPECT can be helpful in determining which parts of the brain are being affected by dementia, clogged blood vessels, seizures, epilepsy, or head injuries.
Heart Problems: Because the radioactive tracer highlights areas of blood flow, SPECT can check for clogged coronary arteries. If the arteries that feed the heart muscle become narrowed or clogged, the portions of the heart muscle served by these arteries can become damaged or even die. SPECT can also show reduced pumping efficiency; how completely your heart chambers empty during contractions.
Bone Disorders: Areas of bone healing or cancer progression usually light up on SPECT scans, so this type of test is being used more frequently to help diagnose hidden bone fractures. SPECT scans can also diagnose and track the progression of cancer that has spread to the bones.
Performing the Procedure
SPECT scans involve two steps: receiving a radioactive dye (called a tracer) and using a SPECT machine to scan a specific area of the body:
Receiving a Radioactive Substance
Your child will be injected with a radioactive substance through an intravenous (IV) infusion into a vein in the arm. The tracer dose is very small, only a few drops, and they may feel a cold sensation as it enters their body.
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 safely through your body and be detected by the scanner. Various drugs and other chemicals can be labelled 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 tumour, he or she might use radio-labelled glucose (FDG) and watch how it is metabolized by the tumour.
Your child may be asked to lie quietly in a room for 15 minutes or more before the scan while their body absorbs the radioactive tracer. In some cases they may need to wait several hours between the injection and the SPECT scan.
The tracer travels to places in the body where there is tumour activity. The body’s more active tissues will absorb more of the radioactive substance. For instance, during a seizure, the area of the brain causing the seizure may retain more of the radioactive tracer, which allows doctors to pinpoint the area of the brain causing your child’s seizures.
Undergoing the SPECT Scan
The SPECT machine is a large circular device containing a camera that detects the radioactive tracer your child’s body absorbs. During your scan, your child will lie on a table while the SPECT machine rotates around them.
The SPECT machine takes pictures of the internal organs and other structures. The pictures are sent to a computer that uses the information to create 3-D images of the body.
How long your child’s scan takes depends on the reason for their procedure.
Most of the radioactive tracer leaves the body through your urine within a few hours after a SPECT scan.
Your doctor may instruct you to give your child more fluids to drink such as juice or water, after their SPECT scan to help flush the tracer from their body. Their body breaks down the remaining tracer over the next day or two.
Potential Side Effects
SPECT scans are safe for most people. Your health care team uses the lowest amount of radiation possible in order to perform the scan. The amount of radiation exposure is less than during a chest X-ray or CT scans.
If your child receives an injection or infusion of radioactive tracer, they may experience bleeding, pain or swelling where the needle was inserted; rarely, an allergic reaction to the radioactive tracer.
Special Considerations for Children
If the Nuclear Medicine study that your child is having requires SPECT imaging, it will be incorporated into your child’s exam.
Your child will remain on the exam table and the camera will rotate around the table while it takes pictures. SPECT imaging will add 30 to 60 minutes to your child’s Nuclear Medicine procedure. Sedation may be required due to the added time
Be sure to ask about what instructions are needed to prepare for the SPECT Scan.
There may be special dietary instructions, and there may also be additional instructions if your child needs sedation.