Quantitative 1H Magnetic Resonance Imaging on Normal and Pathologic Rat Bones by Solid-State 1H ZTE Sequence with Water and Fat Suppression

Background: Osteoporosis (OP) and osteomalacia (OM) are metabolic bone diseases characterized by mineral and matrix density changes. Quantitative bone matrix density differentiates OM from OP. MRI is a noninvasive and nonionizing imaging technique that can measure bone matrix density quantitatively in ex vivo and in vivo. Purpose: To demonstrate water + fat suppressed 1H MRI to compute bone matrix density in ex vivo rat femurs in the preclinical model. Study Type: Prospective. Animal Model: Fifteen skeletally mature female Sprague-Dawley rats, five per group (normal, ovariectomized (OVX), partially nephrectomized/vitamin D (Vit-D) deficient), 250-275 g, similar to 15 weeks old. Field Strength/Sequence: 7T, zero echo time sequence with water + fat (VAPOR) suppression capability, mu CT imaging, and gravimetric measurements. Assessment: Cortical and trabecular bone segments from normal and disease models were scanned in the same coil along with a dual calibration phantom for quantitative assessment of bone matrix density. Statistical Tests: ANOVA and linear regression were used for data analysis, with P-values <0.05 statistically significant. Results: The MRI-derived three-density PEG pellet densities have a strong linear relationship with physical density measures (r(2) = 0.99). The Vit-D group had the lowest bone matrix density for cortical bone (0.47 +/- 0.16 g cm(-3)), whereas the OVX had the lowest bone matrix density for trabecular bone (0.26 +/- 0.04 g cm(-3)). Gravimetry results confirmed these MRI-based observations for Vit-D cortical (0.51 +/- 0.07 g cm(-3)) and OVX trabecular (0.26 +/- 0.03 g cm(-3)) bone groups. Data Conclusion: Rat femur images were obtained using a modified pulse sequence and a custom-designed double-tuned (H-1/P-31) transmit-receive solenoid-coil on a 7T preclinical MRI scanner. Phantom experiments confirmed a strong linear relation between MRI-derived and physical density measures and quantitative bone matrix densities in rat femurs from normal, OVX, and Vit-D deficient/partially nephrectomized animals were computed. Level of Evidence: 2 Technical Efficacy: Stage 2