A Combined 1H and 31P Magnetic Resonance Imaging Technique to Assess Bone Matrix and Mineral Densities in Rats with Osteoporosis and Osteomalacia.

Abstract

Purpose: This work evaluated a combined multinuclear solid-state magnetic resonance imaging (ssMRI) technique using ¹H and ³¹P acquisitions for quantitative, non-ionizing assessment of bone matrix and mineral densities, and to determine whether this approach can differentiate normal bone from osteoporosis and renal osteodystrophy (ROD) in rat models.

Methods: Fifteen rats were assigned to control (CON), ovariectomized (OVX), and vitamin-D-deficient/5-6 nephrectomy (VIT-D) groups. Femurs were imaged ex vivo using a custom double-tuned ¹H/³¹P RF coil on a 7T system. Water- and fat-suppressed ¹H ssMRI quantified organic matrix density, while ³¹P ssMRI quantified bone mineral density. The Extent of Bone Mineralization (EBM) was calculated as the mineral-to-matrix ratio. Validation was performed using μCT and gravimetric analyses. MANOVA and multinomial logistic regression were used to assess group differences and classification accuracy.

Results: MRI-derived matrix and mineral densities showed strong correlations with gravimetric and μCT measures (r = 0.85-0.89, p < 0.001). Cortical vMAT_MRI and vBMD_MRI decreased progressively from CON to OVX to VIT-D, while trabecular values reflected greater microarchitectural heterogeneity. EBM remained near normal in OVX but was markedly altered in VIT-D, consistent with impaired mineralization. MANOVA confirmed significant effects of group and bone region (p < 0.001). Combined cortical-trabecular ssMRI predictors achieved 86.7% cross-validated accuracy in classifying the three bone conditions.

Conclusion: Multinuclear ¹H/³¹P ssMRI provided quantitative, non-ionizing estimates of bone matrix and mineral density and, in this ex-vivo proof-of-concept, distinguished the osteoporotic from the osteomalacic phenotype by jointly evaluating matrix, mineral, and EBM. Because acquisition currently requires several hours per specimen, these findings establish analytical feasibility rather than clinical readiness; substantial acceleration and in-vivo validation are required, and EBM is best regarded as a promising candidate compositional marker pending validation in larger cohorts.