Assessing cortical bone mechanical properties using collagen proton fraction from ultrashort echo time magnetization transfer (UTE-MT) MRI modeling

Abstract

Cortical bone shows as a signal void when using conventional clinical magnetic resonance imaging (MRI). Ultrashort echo time MRI (UTE-MRI) can acquire high signal from cortical bone, thus enabling quantitative assessments. Magnetization transfer (MT) imaging combined with UTE-MRI can indirectly assess protons in the organic matrix of bone. This study aimed to examine UTE-MT MRI techniques to estimate the mechanical properties of cortical bone. A total of 156 rectangular human cortical bone strips were harvested from the tibial and femoral midshafts of 43 donors (62 ± 22 years old, 62 specimens from females, 94 specimens from males). Bone specimens were scanned using UTE-MT sequences on a clinical 3 T MRI scanner and on a micro-computed tomography (μCT) scanner. A series of MT pulse saturation powers (400°, 600°, 800°) and frequency offsets (2, 5, 10, 20, 50 kHz) was used to measure the macromolecular fraction (MMF) utilizing a two-pool MT model. Failure mechanical properties of the bone specimens were measured using 4-point bending tests. MMF from MRI results showed significant strong correlations with cortical bone porosity (R = -0.72, P < 0.01) and bone mineral density (BMD) (R = +0.71, P < 0.01). MMF demonstrated significant moderate correlations with Young modulus, yield stress, and ultimate stress ( R = 0.60–0.61, P < 0.01). These results suggest that the two-pool UTE-MT model focusing on the organic matrix of bone can potentially serve as a novel tool to detect the variations of bone mechanical properties and intracortical porosity.

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

“…Recently, we employed a UTEbased two-pool MT modeling to measure collagen proton fraction at 3 T and observed significant correlations with bone strips' mechanical properties (n = 156, R = 0.60-0.61). 52 In spite of an increasing number of MRI-based bone evaluation techniques, the effect of intracortical bone fat on different MRI-based bone evaluation techniques is not well understood. As highlighted in this study, the intracortical bone fat content needs to be considered when analyzing the bone water fractions, which in turn may lead to better prediction of mechanical properties using any of reported UTE-MRI based techniques.…”

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

“…shown strong correlation with both human bone microstructure measured via µCT and histomorphometry (51,61) and with mechanical properties (44,51,58,61). Although UTE-MT modeling requires a relatively longer MRI scan time compared with basic UTE and IR-UTE methods for TW and BW content estimations, respectively, it provides a unique quantification of the collagenous matrix of bone.…”

“…MMF, as well as macromolecular proton relaxation time (T2 mm ) and exchange rates, can be obtained using two-pool modeling performed on UTE-MT data acquired with a series of RF pulse powers and frequency offsets ( 60 ). MMF from UTE-MT modeling has shown strong correlation with both human bone microstructure measured via μCT and histomorphometry ( 51 , 61 ) and with mechanical properties ( 44 , 51 , 58 , 61 ). Although UTE-MT modeling requires a relatively longer MRI scan time compared with basic UTE and IR-UTE methods for TW and BW content estimations, respectively, it provides a unique quantification of the collagenous matrix of bone.…”

“…T2 * of PW is roughly ten times the T2 * of PW, and can be distinguished from one another using UTE MRI acquisition techniques combined with multi-component T2 * analysis (16,58,74). Such techniques, however, do not estimate absolute water proton contents, which makes them more appropriate for longitudinal studies.…”

Quantitative Magnetic Resonance Imaging of Cortical and Trabecular Bone

“…77,98 Biomarkers from UTE-MT modeling demonstrated significant correlations with mechanical properties. 58,77,98,100 Moreover, UTE-MT modeling technique was utilized to detect ex vivo fibular bone stress injury induced by cyclic loading where BMD was unchanged. 97 ►Fig.…”