Evaluation of trabecular bone orientation in wrists of young volunteers using MR relaxometry and high resolution MRI.

Abstract

Dual energy X-ray absorptiometry (DXA) is the most commonly used method to evaluate skeletal status in clinical practice. The method has a great limitation, however, as it cannot distinguish between trabecular and cortical bone. As osteoporosis is a surface process, the trabecular bone is more vulnerable to a negative bone balance than the cortical bone, due to the greater surface area of trabecular bone. Because only about 10% to 15% of the bone mineral is trabecular bone, small changes in the trabecular bone are concealed by the cortical bone when evaluated by DXA. By using quantitative computed tomography (QCT) the amount of trabecular bone can be evaluated1but no information of the structure is obtained. To enable evaluation of the trabecular bone structure, two principally different techniques using magnetic resonance (MR) have been developed. One method is direct imaging of the trabecular bone, using high resolution2-4and the other is based on indirect measurements.5-9Using these indirect measurements, the magnetic field inhomogeneity occurring at the interface between trabecular bone and bone marrow is quantified and used as a measurable characteristic of trabecular bone density and structure. Several studies have shown that both methods can evaluate trabecular bone structure in vitro.10-13To prove that the methods also are able to evaluate trabecular bone structure in vivo is, however, a difficult task, as there are no non-invasive methods to evaluate trabecular bone structure at resolutions comparable to those obtained in vitro.