Bone Density Scan (DXA)

bone density A dual-energy X-ray absorptiometry (DXA) bone density scan is an examination that uses an enhanced form of X-ray technology to measure bone mineral density most commonly in the lower spine and hips.  It is the most accurate method available for the diagnosis of osteoporosis and is also considered an accurate estimator of fracture risk.

The exam, which usually takes between 10 minutes and a half hour, is completely painless.  During the exam, a machine sends a thin, invisible beam of low-dose X-rays with two distinct energy peaks through the bones being examined. One peak is absorbed mainly by soft tissue and the other by bone. The soft tissue amount can be subtracted from the total, and the difference is the patient's bone mineral density.

A vertebral fracture assessment can be performed during the same exam.  That assessment is used to screen for bone problems in the lower spine that are common among patients who have lost more than an inch of height or have unexplained back pain.

bone density The results give the information necessary to determine the best treatment plan to help protect against an osteoporosis-related fracture.

Routine evaluations every two years may be needed to see a significant change in bone mineral density.

The physicians and staff at UCSF are specialists in the diagnosis of osteoporosis, utilizing the latest technology in bone density measurement.  DXA machines feature special software that computes and displays the bone density measurements on a computer monitor.

UCSF also offers an advanced technique, Quantitative Computed Tomography (QCT), to measure bone density. 

Quantitative Computed Tomography (QCT)

Quantitative Computed Tomography (QCT), which was invented at UCSF, has advantages over dual-energy X-ray absorptiometry (DXA) to measure bone density in patients who are very small or large, patients with degenerative disease of the back, and patients with prostate cancer who are being treated with Androgen deprivation therapy.  QCT is used for a number of other applications as well.

Unlike DXA, which provides measurements in terms of area, QCT provides measurements in terms of volume.  A standard CT scanner equipped with special hardware and software, QCT uses cross-sectional CT images of the spine and hip to measure bone density.  The low-dose scan takes approximately 10 minutes.