Single-Photon Emission Computed Tomography–Computed Tomography, commonly called SPECT-CT, is a hybrid imaging test that combines functional information from a nuclear medicine scan with detailed anatomical images from CT.
The SPECT component uses a small amount of a radioactive substance called a radiotracer. The tracer is selected according to the organ, tissue or biological process being examined. A gamma camera detects energy released by the tracer and produces three-dimensional images showing where it has accumulated in the body.
The CT component provides detailed structural information. Combining the two scans allows doctors to match areas of tracer uptake with their precise anatomical location. In cancer care, SPECT-CT may be used for selected purposes such as evaluating the bones, localising sentinel lymph nodes, imaging certain tumour types and planning or assessing some radionuclide treatments.
SPECT-CT is not routinely required for every cancer. Its usefulness depends on the cancer type, radiotracer available and specific clinical question.
Role in Cancer Care
What to Expect
Before the Scan
Preparation varies considerably according to the radiotracer and examination. The nuclear medicine team will provide instructions specific to your scan.
Before the examination, inform the team if you:
Are pregnant or may be pregnant
Are breastfeeding
Have kidney disease or reduced kidney function
Have allergies or have previously reacted to CT contrast material
Have recently undergone another nuclear medicine test or treatment
Have recently had surgery, chemotherapy, immunotherapy or radiation therapy
Take prescription medicines, non-prescription medicines or supplements
Have difficulty lying still or experience anxiety in enclosed spaces
Some examinations may require fasting, dietary changes, temporary adjustment of certain medicines, blood tests or other preparation. Do not stop or alter any medicine unless instructed.
If contrast-enhanced CT is planned, kidney-function testing or additional preparation may be required. Jewellery and other metal objects may need to be removed. Previous imaging and reports should be provided whenever possible.
During the Scan
The radiotracer is usually administered through a cannula placed in the hand or arm. Depending on the examination, imaging may begin soon afterwards or after an uptake period lasting several hours. Some scans may require delayed images later the same day or on another day.
When imaging begins, you will lie on a table while the gamma-camera heads rotate slowly around you. The detectors may come close to the body but should not touch you. It is important to remain still to prevent blurring.
The CT component is usually performed during the same session without changing position. This allows the SPECT and CT images to be accurately combined.
Imaging time varies according to the examination and body area. The scan may take approximately 30 to 60 minutes, although some studies require longer or involve more than one set of images. The technologist can see, hear and communicate with you throughout the scan.
The examination is generally painless apart from the radiotracer injection. Remaining in one position may cause temporary discomfort.
After the Scan
You may need to wait briefly while the images are checked to ensure that no additional views are required. The cannula will usually be removed before you leave unless it is needed for another procedure.
Most patients can resume normal activities after the scan. Drinking water may be recommended to help the radiotracer pass out of the body through urine. Follow any hygiene and radiation-safety instructions provided by the nuclear medicine team.
Depending on the radiotracer, you may be advised to limit prolonged close contact with pregnant people and young children for a specified period. Breastfeeding instructions are tracer-specific and must be followed carefully.
A nuclear medicine physician or appropriately trained radiologist will interpret the SPECT, CT and fused images and issue a report. The findings will be considered alongside previous scans, pathology results and other clinical information.
Potential Benefits
- Functional imaging: SPECT shows how a radiotracer is distributed and provides information about tissue or organ activity.
- Precise localisation: CT helps identify the exact structure responsible for abnormal tracer uptake.
- Improved characterisation: Combined images may help distinguish suspicious findings from some non-cancerous causes of tracer uptake.
- Bone assessment: SPECT-CT can help clarify indeterminate areas identified during bone imaging.
- Sentinel-node mapping: It can help locate sentinel lymph nodes before selected cancer operations.
- Tumour-specific imaging: Different radiotracers can target particular organs, cell types or molecular characteristics.
- Treatment planning: SPECT-CT can support selected radionuclide therapies and interventional oncology procedures.
- Post-treatment assessment: Imaging can help confirm where a therapeutic radiopharmaceutical has accumulated.
