Comparison of semi-quantitative and quantitative dynamic contrast-enhanced MRI evaluations of vertebral marrow perfusion in a rat osteoporosis model

BACKGROUND This study aims to investigate the technical feasibility of semi-quantitative and quantitative dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in the assessment of longitudinal changes of marrow perfusion in a rat osteoporosis model, using bone mineral density (BMD) measured by micro-computed tomography (micro-CT) and histopathology as the gold standards. METHODS Fifty rats were randomly assigned to the control group (n=25) and ovariectomy (OVX) group whose bilateral ovaries were excised (n=25). Semi-quantitative and quantitative DCE-MRI, micro-CT, and histopathological examinations were performed on lumbar vertebrae at baseline and 3, 6, 9, and 12 weeks after operation. The differences between the two groups in terms of semi-quantitative DCE-MRI parameter (maximum enhancement, Emax), quantitative DCE-MRI parameters (volume transfer constant, Ktrans; interstitial volume, Ve; and efflux rate constant, Kep), micro-CT parameter (BMD), and histopathological parameter (microvessel density, MVD) were compared at each of the time points using an independent-sample t test. The differences in these parameters between baseline and other time points in each group were assessed via Bonferroni's multiple comparison test. A Pearson correlation analysis was applied to assess the relationships between DCE-MRI, micro-CT, and histopathological parameters. RESULTS In the OVX group, the Emax values decreased significantly compared with those of the control group at weeks 6 and 9 (p=0.003 and 0.004, respectively). The Ktrans values decreased significantly compared with those of the control group from week 3 (p<0.05). However, the Ve values decreased significantly only at week 9 (p=0.032), and no difference in the Kep was found between two groups. The BMD values of the OVX group decreased significantly compared with those of the control group from week 3 (p<0.05). Transmission electron microscopy showed tighter gaps between vascular endothelial cells with swollen mitochondria in the OVX group from week 3. The MVD values of the OVX group decreased significantly compared with those of the control group only at week 12 (p=0.023). A weak positive correlation of Emax and a strong positive correlation of Ktrans with MVD were found. CONCLUSIONS Compared with semi-quantitative DCE-MRI, the quantitative DCE-MRI parameter Ktrans is a more sensitive and accurate index for detecting early reduced perfusion in osteoporotic bone.