MRI of bone marrow in the distal radius: in vivo precision of effective transverse relaxation times

Abstract

The effective transverse relaxation time T2^* is influenced by the presence of trabecular bone, and can potentially provide a measure of bone density as well as bone structure. We determined the in vivo precision of T2^* in repeated bone marrow measurements. The T2^* measurements of the bone marrow of the distal radius were performed twice within 2 weeks in six healthy young volunteers using a modified water-presaturated 3D Gradient-Recalled Acquisition at Steady State (GRASS) sequence with TE 7, 10, 12, 20, and 30; TR 67; flip angle (FA) 90 °. An axial volume covering a length of 5.6 cm in the distal radius was measured. Regions of interest (ROIs) were determined manually and consisted of the entire trabecular bone cross-section extending proximally from the radial subchondral endplate. Reproducibility of T2^* and area measurements was expressed as the absolute precision error (standard deviation [SD] in ms or mm²) or as the relative precision error (SD/mean × 100, or coefficient of variation [CV] in %) between the two-point measurements. Short-term precision of T2^* and area measurements varied depending on section thickness and location of the ROI in the distal radius. Absolute precision errors for T2^* times were between 1.3 and 2.9 ms (relative precision errors 3.8–9.5 %) and for area measurements between 20 and 55 mm² (relative precision errors 5.1–16.4 %). This MR technique for quantitative assessment of trabecular bone density showed reasonable reproducibility in vivo and is a promising future tool for the assessment of osteoporosis.