QCT

QCT uses a standard CT scanner along with a special calibration tool called a phantom to measure bone density. Unlike DEXA, which gives an average density over a flat area, QCT can measure the true volumetric density of bone, separating the outer dense shell (cortical bone) from the spongy inner bone (trabecular bone). This gives a more detailed look at bone structure, especially in the spine and hip.

Doctors sometimes use QCT when DEXA results are hard to interpret, such as in people with significant spinal arthritis, scoliosis, or prior spine surgery, since these conditions can falsely raise DEXA numbers. QCT isn't affected by these issues in the same way. It's also used in some research settings to study bone quality in greater detail.

QCT does involve more radiation exposure than a standard DEXA scan, and it tends to be more expensive and less widely available. For these reasons, it isn't used as a routine first-line test for most people. If your doctor is considering QCT, it's worth asking why it's being recommended over a standard DEXA scan, and any decisions about testing or treatment should be made together with your healthcare provider.