Calibration of trabecular bone structure measurements of in vivo three-dimensional peripheral quantitative computed tomography with 28-mu m-resolution microcomputed tomography

It has recently been shown that high-resolution computed tomography and mag netic resonance imaging have the potential to assess information about the microarchitecture of hone in a noninvasive way. However, due to the limited spatial resolution of the in vivo measurements, the individual trabeculae are not depicted with their true thickness. Nevertheless, the spacing of th e structural elements allows the assessment of trabecular number. In a prev ious publication, the ridge number density (RND) was introduced as a measur e for this structural index. It can be extracted front high-resolution thre e-dimensional (3D) images of patients and shows a reproducibility of 1.6%. In this work; the Ridge extraction procedure is compared to and calibrated with microcomputed tomography (mu CT) measurements. Three-dimensional measu rements of 15 bone biopsies are made cr with a 28-mu m-resolution mu CT sca nner as well as with a 165-mu m-resolution peripheral quantitative computed tomography (pQCT) scanner. For the latter, the same settings are used as f or patient examinations. The 15 pairs of measurements are analyzed and the resulting structural indices are compared. The results show that structural indices such as trabecular number, mean thickness, and mean separation can he determined from the 3D pQCT data with an r(2) of between 0.81 and 0.96 if the mu CT data are taken as the gold standard. The calibration equation found for the hone volume fraction has an intercept of 0.04 slid a slope of 0.86 (r(2) = 0.98), and trabecular number as the main additional structura l index shows a nonsignificant intercept and 21 calibration slope of 0.31 w ith the mu CT. The calibration procedure carl he used directly for patient examinations. Applied to time-series measurements it may be of value for mo nitoring and quantifying microarchitectural changes due to therapy or aging . (C) 1999 by Elsevier Science Inc. All rights reserved.