MRI Techniques for the Examination of Trabecular Bone Structure

It is well known that bone mineral density measurement is a widely available means of identifying individuals with osteoporosis. However, bone strength depends not only on the amount of material but also on properties related to bone quality. Significant progress has been made in the development of magnetic resonance imaging (MRI) techniques for assessing bone status during the past years. This review discusses the technical principles, clinical applications, recent advances, limitations, and future trends of MRI techniques available for the diagnosis of osteoporosis. Using MRI, bone status can be evaluated either by T2* measurements, which are sensitive to field inhomogeneities caused by susceptibility differences at the marrowbone interfaces, or by high-resolution imaging. In T2* relaxometry, the decrease in marrow T2* measurements and its decay characteristics provide useful information about the structure and quality of the trabecular bone. T2* measurements have been performed at several locations of the axial and peripheral skeleton such as spine, proximal femur and calcaneus. It has also been shown that osteoporotic and normal subjects may be distinguished using T2* decay characteristics. In addition to T2* relaxometry, high-resolution MR imaging may be used to quantify trabecular bone architecture. Gradient echo and spin echo sequences have been used to obtain images in vitro and in vivo mainly at peripheral sites of the skeleton. Several image-processing methods have been applied to measure bone structure. Technological advances in MRI scanners offer exciting new possibilities in bone analysis and may contribute to our understanding of osteoporosis.