Bone density scanning, also called dual x-ray absorptiometry (DXA) or bone densitometry, is an enhanced form of x-ray technology that is used to measure bone mineral density (BMD) or bone loss. DXA is most often performed on the lower spine and hips although the whole body is sometimes scanned. DXA is commonly used to diagnose osteoporosis, a condition that involves loss of calcium along with structural changes that cause the bones to become brittle and more likely to break. The DXA 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 then be subtracted from the total so that the remainder is the patient’s bone density. Special software is used that can compute and display the bone density measurements on a computer monitor.
There are two types of DXA equipment — a large central imaging device and a peripheral device. The central device measures bone density in the hip and spine and is usually located in a hospital imaging department. The peripheral device (pDXA) measures bone density in the wrist, heel, or finger and is often used for screening in clinics, mobile vans, or various locations in the community. The pDXA is a small, portable box-like structure with space for the foot or forearm to be placed for imaging.
The DXA test is usually completed within 10 to 30 minutes depending on the equipment used and the parts of the body being examined. An additional procedure called lateral vertebral assessment (LVA) is also performed on the DXA machine. LVA is a low-dose x-ray examination of the spine to screen for vertebral fractures and adds only a few minutes to the DXA procedure. The pDXA device obtains a bone density reading within a few minutes.
A computed tomography machine with special software (QCT) can also be used to diagnose low bone mass and a specially-designed portable ultrasound machine is sometimes used for screening.
This article is an update of a previous post.