Methods and Clinical Issues in Bone Densitometry and Quantitative Ultrasonometry

Abstract

This chapter describes the various methods used to measure bone mineral density (BMD), which has become an essential element in the evaluation of patients at risk for osteoporosis. The methods currently available for the noninvasive assessment of the skeleton for the diagnosis of osteoporosis and/or the evaluation of an increased risk of fracture include dual X-ray absorptiometry (DXA), spinal quantitative computed tomography (QCT), peripheral DXA (pDXA), peripheral QCT (pQCT), radiographic absorptiometry (RA), and quantitative ultrasonometry (QUS). DXA has established itself as the most widely used method of measuring BMD because of its advantages of high precision, short scan times, low radiation dose, and stable calibration. QCT is usually applied to measure the trabecular bone in the vertebral bodies and they can be performed on any clinical CT scanner, if the patient is scanned with an external reference phantom to calibrate the CT numbers to bone equivalent values. Radiographic absorptiometry (RA) has the advantage of using conventional X-ray equipment with the addition of a small aluminum wedge in the image field for calibration. The radiographic image is captured on a PC and then processed automatically using a specially developed software application to measure BMD in the phalanges. QUS for measuring the peripheral skeleton has raised considerable interest in recent years and they include a wide variety of equipment, with most devices using the heel as the measurement site. The calcaneus is the most popular one as it encompasses a large volume of trabecular bone between relatively flat faces and is readily accessible for transmission measurements.