Water proton density in human cortical bone obtained from ultrashort echo time (UTE) MRI predicts bone microstructural properties

Abstract

Purpose: To investigate the correlations between cortical bone microstructural properties and total water proton density (TWPD) obtained from three-dimensional ultrashort echo time Cones (3D-UTE-Cones) magnetic resonance imaging techniques.Materials and Methods: 135 cortical bone samples were harvested from human tibial and femoral midshafts of 37 donors (61±24 years old). Samples were scanned using 3D-UTE-Cones sequences on a clinical 3T MRI and on a high-resolution micro-computed tomography (μCT) scanner. TWPD was measured using 3D-UTE-Cones MR images. Average bone porosity, pore size, and bone mineral density (BMD) were measured from μCT images at 9 μm voxel size. Pearson's correlation coefficients between TWPD and μCT-based measures were calculated.Results: TWPD showed significant moderate correlation with both average bone porosity (R=0.66, p<0.01) and pore size (R=0.58, p<0.01). TWPD also showed significant strong correction with BMD (R=0.71, p<0.01). Conclusions:The presented 3D-UTE-Cones imaging technique allows assessment of TWPD in human cortical bone. This quick UTE-MRI-based technique was capable of predicting bone microstructure differences with significant correlations. Such correlations highlight the potential of UTE-MRI-based measurement of bone water proton density to assess bone microstructure.

Quantitative Magnetic Resonance Imaging of Cortical and Trabecular Bone

“…58 A mixture of distilled water and deuterated water (e.g., 20% H 2 O and 80% D 2 O, 22 mol/L 1 H) doped with manganese chloride and titrated to match the effective T2 Ã of cortical bone (e.g., T2 Ã $ 0.4 ms) has been used as the external reference by several research groups, 50,53,55,57,58 Although it should be noted that any material with known apparent PD and with a range of MRI properties similar to bone, such as a rubber eraser, can be used as the external phantom. 59 The estimated TW content in cortical bone showed significant correlations with bone microstructural properties. 58,59 ►Fig.…”

“…59 The estimated TW content in cortical bone showed significant correlations with bone microstructural properties. 58,59 ►Fig. 3 shows conventional GRE, 2D UTE, and 2D adiabatic inversion recovery UTE (IR-UTE) imaging of the tibial midshaft of a volunteer.…”

“…50,60 Due to the short T1 in cortical bone, the T1 effect on the TW content calculation can be neglected if one uses a relatively low FA combined with a relatively high repetition time (TR) in a PDweighted UTE sequence. 59…”

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

“…Several research groups have used a mixture of distilled water and deuterated water (e.g., 20% H 2 O and 80% D2O, 22 mol/L 1 H) doped with MnCl2 and titrated to match the effective T2 * of cortical bone (e.g., T2 * ≈ 0.4 ms) as the external reference for this estimation technique (38,39,41,43,44), but, notably, any phantom with known apparent proton density and with a range of MRI properties similar to bone, such as a rubber eraser, can be used (45). Significant correlations have been reported between the estimated TW content in human cortical bone and its microstructural properties (44,45). For accurate estimation of TW content, we should consider, first, the difference between relaxation times of cortical bone and the external phantom, second, the spatial variation of coil sensitivity in scanned field of view (FOV), and third, the duration of radiofrequency (RF) pulse and its inhomogeneity [or actual flip angle (FA)] (38,70).…”

“…For accurate estimation of TW content, we should consider, first, the difference between relaxation times of cortical bone and the external phantom, second, the spatial variation of coil sensitivity in scanned field of view (FOV), and third, the duration of radiofrequency (RF) pulse and its inhomogeneity [or actual flip angle (FA)] (38,70). Due to the short T1 in cortical bone, the T1 effect on the TW content calculation can be neglected if one uses a relatively low FA combined with a relatively high repetition time (TR) in a proton density (PD)-weighted UTE sequence (45).…”