SI Joint SPECT-CT

SI joint SPECT-CT is a bone-activity scan fused with CT, focused on the sacroiliac joints — the two joints where the base of the spine meets the pelvis. These joints can be a genuine but easily overlooked source of low back and buttock pain, partly because they often look normal on ordinary scans, including MRI. By showing where there is active bone and ligament reaction around the joint, this scan can reveal a problem that other tests miss.

The scan uses a tracer that concentrates in areas of active bone turnover. Long-standing strain or dysfunction of a sacroiliac joint tends to produce subtle, ongoing bone and ligament reaction, which shows up as increased activity on the scan even when the joint looks unremarkable on structural imaging. The fused CT then locates that activity precisely to the joint and its surrounds. This is why the combined scan can succeed where MRI, which relies on a different kind of signal, sometimes appears normal.

As with any bone SPECT-CT, you receive the tracer through a small injection into a vein and then wait a couple of hours while it settles, before lying still for the scan while the camera rotates around the pelvis; the CT is taken at the same visit. The scan is painless, involves a small amount of radiation, and requires a longer overall appointment because of the waiting period. Staying well hydrated during the wait helps produce clearer images.

Sacroiliac joint problems are notoriously hard to confirm, and many affected people have normal-looking standard scans. SI joint SPECT-CT can identify a characteristic pattern of activity that points to genuine joint dysfunction, helping distinguish it from other causes of low back pain. Confirming the joint as a source can open the way to focused treatment such as a targeted injection. The result is interpreted alongside symptoms, examination and, often, a confirming diagnostic injection.

• —Royal College of Radiologists — iRefer: Making the Best Use of Clinical Radiology
• —Royal College of Radiologists / British Nuclear Medicine Society — Guidance
• —British Association of Spine Surgeons (BASS)

This information is for general patient education and is not a substitute for an individual consultation. Always seek personalised advice from a qualified spinal specialist.