Cortical Bone Mechanical Assessment via Free Water Relaxometry at 3 T

Abstract

Background: Investigation of cortical bone using magnetic resonance imaging is a developing field, which uses short/ultrashort echo time (TE) pulse sequences to quantify bone water content and to obtain indirect information about bone microstructure.

Purpose: To improve the accuracy of the previously proposed technique of free water T₁ quantification and to seek the relationship between cortical bone free water T₁ and its mechanical competence.

Study type: Prospective.

Subjects: Twenty samples of bovine tibia bone.

Field strength/sequences: 3.0 T; ultra-fast two-dimensional gradient echo, Radio frequency-spoiled three-dimensional gradient echo.

Assessment: Cortical bone free water T₁ was quantified via three different methods: inversion recovery (IR), variable flip angle (VFA), and variable repetition time (VTR). Signal-to-noise ratio was measured by dividing the signal of each segmented sample to background noise. Segmentation was done manually. The effect of noise on T₁ quantification was evaluated. Then, the samples were subjected to mechanical compression test to measure the toughness, yield stress, ultimate stress, and Young modulus.

Statistical tests: All the statistical analysis (Shapiro-Wilk, way analysis of variance, paired t test, Pearson correlation, and Bland-Altman plot) were done using SPSS.

Results: Significant difference was found between T₁ quantification groups (P < 0.05). Average T₁ of each quantification method differed significantly after adding noise (P < 0.05). VFA-T₁ values significantly correlated with toughness (r = -0.68, P < 0.05), ultimate stress (r = -0.71, P < 0.05), and yield stress (r = -0.62, P < 0.05). No significant correlation was found between VTR-T₁ values and toughness (P = 0.07), ultimate stress (P = 0.47), yield stress (P = 0.30), and Young modulus (P = 0.39).

Data conclusion: Pore water T₁ value is associated with bone mechanical competence, and VFA method employing short-TE pulse sequence seems a superior technique to VTR method for this quantification.

Level of evidence: 2 TECHNICAL EFFICACY: 1.

Keywords: T1 quantification; cortical bone water; short-TE magnetic resonance imaging; variable flip angle; variable repetition time.