Correlations of cortical bone microstructural and mechanical properties with water proton fractions obtained from ultrashort echo time (UTE) MRI tricomponent T2* model

Abstract

Mechanical and microstructural evaluations of cortical bone using ultrashort echo time magnetic resonance imaging (UTE-MRI) have been performed increasingly in recent years. UTE-MRI acquires considerable signal from cortical bone and enables quantitative bone evaluations. Fitting bone apparent transverse magnetization (T2*) decay using a bicomponent model has been regularly performed to estimate bound water (BW) and pore water (PW) in the quantification of bone matrix and porosity, respectively. Human cortical bone possesses a considerable amount of fat, which appears as MRI T2* signal oscillation and can subsequently lead to BW overestimation when using a bicomponent model. Tricomponent T2* fitting model has been developed to improve BW and PW estimations by accounting for fat contribution in the MRI signal. This study aimed to investigate the correlations of microstructural and mechanical properties of human cortical bone with water pool fractions obtained from a tricomponent T2* model. 135 cortical bone strips (~4 × 2 × 40 mm 3 ) from tibial and femoral midshafts of 37 donors (61 ± 24 years old) were scanned using ten sets of dual-echo 3D-UTE-Cones sequences (TE = 0.032-24.0 ms) on a 3 T MRI scanner for T2* fitting analyses. Average bone porosity and pore size were measured using microcomputed tomography (μCT) at 9 μm voxel size. Bone mechanical properties were measured using 4-point bending tests. Using a tricomponent model, bound water fraction (Frac BW ) showed significant strong (R = 0.70, P < 0.01) and moderate (R = 0.58-0.62, P < 0.01) correlations with porosity and mechanical properties, respectively. Correlations of bone microstructural and mechanical properties with water pool fractions were higher for tricomponent model results compared with the bicomponent model. The tricomponent T2* fitting model is suggested as a useful technique for cortical bone evaluation where the MRI contribution of bone fat is accounted for. K E Y W O R D S bone mechanics, cortical bone, fat, MRI, T2* fitting model, ultrashort echo time Abbreviations: 3D, three-dimensional; 3D-UTE, three-dimensional ultrashort echo time imaging; BMD, bone mineral density; CT, computed tomography; DEXA, dual-energy X-ray absorptiometry; FA, flip angle; FOV, field of view; HR-pQCT, peripheral quantitative computed

Quantitative Magnetic Resonance Imaging of Cortical and Trabecular Bone

“…Estimated water fractions by tricomponent T2 Ã fitting demonstrated improved correlations with micro-CT-based porosity compared with bicomponent analysis. 83,89 Tricomponent analysis also showed higher correlations with bone mechanical properties as investigated in 136 human cortical bone strips. 89 Tricomponent T2 Ã fitting 83,89 improves bicomponent analysis by estimating the fat proton fraction in addition to the BW and PW proton fractions and by avoiding the common BW overestimation in the endosteal side of the cortex that commonly occurs in bicomponent analysis in the endosteal side of the cortex.…”

“…3b and 3c show the micro-CT images of two representative specimens (samples I and II with 15% and 33% average porosities, respectively). 89 Bicomponent and tricomponent fitting analysis are demonstrated in ►Fig. S3d-g for both specimens.…”

“…89 Tricomponent T2 Ã fitting 83,89 improves bicomponent analysis by estimating the fat proton fraction in addition to the BW and PW proton fractions and by avoiding the common BW overestimation in the endosteal side of the cortex that commonly occurs in bicomponent analysis in the endosteal side of the cortex. 83,89 ►Fig. S3 shows a UTE-MRI image covering a set of bone specimens with 4 Â 2-mm cross sections placed in a 1-inch birdcage coil.…”

Quantitative Ultrashort Echo Time (UTE) Magnetic Resonance Imaging of Bone: An Update

“…The oscillating signal decay in cortical bone specimens is better fitted by including the signal contribution of fat using the tri-component model (higher fitting R2 values). This figure was previously presented by Jerban et al (53). Reprinting permission is granted through Rightslink system.…”

“…Tricomponent analysis has also shown higher correlation with the mechanical properties of bone (53). The tricomponent model avoids BW overestimation in the endosteal side of the cortex, a common error in bicomponent analysis (53,54). However, the tricomponent model needs more data points which in turn requires a longer scan time, posing a challenge for translation to clinical applications.…”