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SPECT-CT imaging involves the acquisition of a low dose, non-contrast CT (computed tomography) scan immediately before SPECT (single-photon emission computed tomography) imaging, which uses a rotating gamma camera. It is usually performed in nuclear medicine as an adjunct to standard single plane, gamma camera imaging.
CT images are superimposed or fused with the SPECT images, enabling precise anatomical localisation of radiopharmaceutical uptake. The CT also enables correction for potential artefact that results from attenuation of emitted gamma rays by the patient’s body tissues before being detected on the rotating gamma camera.
The low-dose CT is usually sufficient to detect gross structural abnormalities, such as degenerative arthropathy of the joints or spine, large soft tissue masses and viscera. Given the lower radiation dose and absence of IV contrast, the contrast resolution may not be adequate to detect subtle disease, such as small metastases, non-displaced fractures or intra-abdominal lymph nodes.
For bone scans, common indications include pain, arthritis or joint replacement assessment and assessing for skeletal metastases. For cardiac scans, the most common indication is to assess myocardial perfusion; and for lung scans, suspected pulmonary embolism.
Referral for a SPECT-CT scan is usually given after consultation between the nuclear medicine specialist and the referrer. The nuclear medicine specialist may consider the SPECT-CT to be helpful in delineating pathology when standard planar gamma camera imaging is difficult to interpret.
To enable accurate image fusion, patients must be able to stay still for the duration of the imaging (usually 30–40 minutes).
There are no absolute contraindications. Pregnant women should discuss the benefit versus risk with their referring clinician and the nuclear medicine specialist.
See InsideRadiology: Nuclear Medicine for further information about the precautions to take with nuclear medicine studies for breast-feeding patients and those in close contact with children.
Relative contraindications include patients who exceed the weight limit for the SPECT or CT scanner table (this varies depending on the machine, but usually at least 150 kg). It is best to check with the technologist staff at your nuclear medicine department first. Patients must be capable of voluntarily staying still, usually between 20 and 40 minutes.
There are no adverse effects of a SPECT-CT scan.
Risks from the additional radiation required from the low-dose CT scan are very minimal, notably the dosage using the standard low-dose CT technique is approximately 20–25% that of a comparable standard radiology diagnostic CT scan.
Women who are breast-feeding, or the primary or sole carer for young children may need to make special preparations before and after the test to stop breast-feeding and to avoid close contact with young children (usually 24 hours) due to the small amount of radioactivity released after the test.
Sometimes, the low-dose CT part of the SPECT-CT scan does not provide enough diagnostic information about the abnormality identified on the scan. This may have to be supplemented by a full-dose CT or MRI examination for further diagnostic anatomical information.
Page last modified on 19/12/2019.
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