MRI Evaluation of Osteoporosis

Abstract

Trabecular architecture is usually studied extremely well by computed tomography (CT) and micro-CT. The limitation of clinical CT is radiation dose. High-resolution clinical magnetic resonance (MR) imaging is also used to study trabecular architecture in the peripheral skeleton, particularly the distal radius and calcaneum. The MR imaging of trabecular micro-architecture has quite good precision and has demonstrated expected changes on longitudinal in vivo study. While clinical MR imaging may currently be limited to examination of fine bone structure only in the peripheral appendicular skeleton, it also has the capacity to study other aspects of bone physiology not readily measurable by other techniques, namely marrow fat content, perfusion and molecular diffusion. Magnetic-resonance-based studies have shown that as spinal bone mineral density decreases, vertebral marrow fat content increases while vertebral marrow perfusion decreases. This reduction in marrow perfusion is an intraosseous phenomenon and is not related to a more generalized circulatory impairment. Females across all groups (normal, osteopaenia and osteoporosis) tend to have slightly higher vertebral fat content than males. Pre-menopausal women have on average lower MR diffusion coefficient than post-menopausal women. In postmenopausal women, the change in fat content or perfusion indices seen with change in bone mineral density does not have any appreciable effect on MR diffusion parameters.