04/14/2022
Dual-energy x-ray absorptiometry (DXA) has long been the gold standard for osteoporosis screening. But now, thousands of patients may be inappropriately undergoing bone mineral density studies via quantitative computed tomography (QCT) -- which may be less accurate and more expensive, with far higher radiation exposure.
QCT focuses on density changes in the inner, trabecular bone in the spine. It does not include the cortical shell on the outside of the vertebrae. The DXA includes both, and is a better way to measure bone density, he continued, because cortical bone plays an important role in bone density measurement.
Many doctors agree “that the QCT exaggerates bone mineral density loss in the spine if the T-score is used. If it is, more patients will be diagnosed incorrectly with osteoporosis with a QCT than with a DXA”
For example, if a T-score given by a DXA of the spine says -2.0, then there is a likelihood that the QCT T-score on the same patient would be -2.7, showing more bone density loss than actually exists.
WHEN IS QCT BENEFICIAL?
Naveen Subhas, MD, who chairs the American College of Radiology's practice parameters committee for imaging, said that while the QCT gives different values for bone mineral density for the spine than DXA, the QCT is not inaccurate nor does it lead to a false diagnosis if appropriately interpreted using specific established ranges for QCT.
As for the differences between the two, he continued, QCT's ability to measure bone loss in the trabecular region of the spine is important because that's where bone loss first appears, so the QCT may be more sensitive to detecting early change.
But for clinical purposes, he said, "DXA should be the first line." "We just feel that the higher costs and higher radiation is usually not needed,"
QCT delivers far more radiation and exaggerates spinal bone loss, so why is it on the rise?
