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

Abstract

BackgroundOsteoporosis (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.PurposeTo demonstrate water + fat suppressed 1H MRI to compute bone matrix density in ex vivo rat femurs in the preclinical model.Study TypeProspective.Animal ModelFifteen 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/Sequence7T, zero echo time sequence with water + fat (VAPOR) suppression capability, μCT imaging, and gravimetric measurements.AssessmentCortical 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 TestsANOVA and linear regression were used for data analysis, with P‐values <0.05 statistically significant.ResultsThe 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 ConclusionRat femur images were obtained using a modified pulse sequence and a custom‐designed double‐tuned (1H/31P) 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 Evidence2Technical EfficacyStage 2