Quantitative 1 H Magnetic Resonance Imaging on Normal and Pathologic Rat Bones by Solid-State 1 H 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 1 H 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, ∼15 weeks old.

FIELD STRENGTH/SEQUENCE: 7T, zero echo time sequence with water + fat (VAPOR) suppression capability, μCT 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 (r2  = 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 (1 H/31 P) 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.