Single-photon emission computed tomography (SPECT CT) is a non-invasive nuclear medicine test that enables doctors to evaluate disease based on functional and metabolic information. SPECT CT uses a gamma camera just like conventional nuclear medicine (2D images), but creates cross-sectional slices that can be reconstructed into 3D information. The gamma camera is rotated around the patient through a full 360° while projections are acquired typically every 3–6°. A small dose of radioactive tracer is injected through a vein, usually in the arm. The type of trace depends on the application or problem. For example for functional cardiac imaging a cardiac-specific radiopharmaceutical is administered.
Nuclear medicine uses a gamma camera to measure gamma rays emitted by the tracer. These gamma rays are attenuated by the deeper body tissues, which could lead to a significant underestimation of activity from areas deeper in the body. SPECT CT uses the x-ray attenuation information from computed tomography to correct for SPECT attenuation, which is important for accurate 3D signal measurement.
In addition, SPECT CT provides more anatomical images that precisely localise disease, which improves sensitivity and specificity. SPECT CT has proven to be valuable in oncology for identifying metastatic cancer. Improved treatment is possible because the 3D images allow radiation dose and target volume estimates for external beam radiation therapy.
The combined image SPECT CT provides enables the radiologist who analyses the scan to pinpoint the site of any abnormality more accurately. In complex bony areas such as the spine or feet, determining exactly which bone is affected on 2D nuclear medicine scans is challenging. Combining SPECT and CT provides essential anatomical mapping to allow precise localisation in 3D.
If the patient is pregnant or suspect that she might be pregnant, you should add this information to the request form and ask the patient to advise staff when the booking is made. If the patient is breastfeeding, this is important information for our staff to know. See our patient safety page for further information about pregnancy and radiation.
If you are having a SPECT CT scan at the same time as another type of scan you will need to follow the preparation instructions for that particular scan. If you are unsure of the preparation advice you were given when you made your appointment, simply call the staff at the location you are attending.
SPECT scans are generally painless, relatively fast and straightforward, although the injection might sting a little. The examination time varies, but averages around 30-40 minutes. The patient should expect to be in the department for at least two (2) hours. The actual scan time varies depending on the acquisition protocol for the area of interest.
All South Coast Radiology nuclear medicine technologists are accredited with the Australian and New Zealand Society of Nuclear Medicine (ANZSNM) and registered with the Medical Radiation Technologists Board of Queensland.
Ionising radiation and pregnancy
Pregnant women should advise their referring doctor, as well as the nuclear medicine technologist, before their scan. In most cases exposure to ionising radiation should be avoided during pregnancy, but their doctor will weigh-up the risks and benefits. See our patient safety page for further information about pregnancy and radiation.
Will there be an injection?
For SPECT CT, a small dose of short-lived radioactive tracer is injected into a vein, usually an arm vein. The radioactive tracer is incorporated into a compounds used by the body, such as glucose, water or ammonia, or into binding molecule. The gamma camera measures the concentrations of the radioactive tracer in the region of interest.
After SPECT CT
The patient may resume normal activities after the scan. If there are any special instructions the patient needs to follow after the scan, he or she will be told before they leave the department.
The radioactive tracer will decay over time and the body will eliminate any residue through the kidneys and bowel. The patient should drink plenty of water after the scan to help the elimination process.
Processing and reporting of the SPECT CT scan could take up to two hours. The patient will be advised to return to the referring doctor to discuss the results.
If you are a registered a referrer you can access your patient’s SPECT CT images and report through our secure online archival system, or view the films we provide. For more information about registering to access patient images visit the Access Medinexus Portal section.