QUANTITATIVE-ANALYSIS OF TRABECULAR MICROSTRUCTURE BY 400-MHZ NUCLEAR-MAGNETIC-RESONANCE IMAGING

A new approach for the quantitative analysis of trabecular microstruct ure, based on high-field proton nuclear magnetic resonance (NMR) imagi ng, is presented. NMR is ideal because it provides high contrast betwe en the marrow proton signal and the bone, which appears with backgroun d intensity. Images from 1 cm(3) defatted specimens of trabecular bone , suspended in water doped with 1 mM Gd(DTPA) to shorten T-1 to about 300 ms, can be obtained at a resolution on the order of 30-50 mu m and slice thickness of 150 mu m, in 10 minutes at 400 MHz proton frequenc y. Digital image processing algorithms were designed and evaluated for the measurement of bone area fraction, perimeter length, mean trabecu lar thickness, and separation. Bone area fraction derived from the NMR images was found to be in excellent agreement with bone volume fi act ion measured independently (slope 0.96, r(2) = 0.924, p < 0.0001). Err ors in the mean trabecular thickness and separation were < 6%. The eff ects of finite imaging slice thickness and signal-to-noise ratio (SNR) were also evaluated. The data suggest a resolution of 50 x 50 x 200 m u m(3) and an SNR on the order of 10 to provide safe margins for preci se and accurate structural analysis by means of the algorithms present ed in this paper. The method allows simultaneous measurement at multip le locations within the specimen volume without the need for physical sectioning.