MRI Quantification of Cortical Bone Porosity, Mineralization, and Morphologic Structure in Postmenopausal Osteoporosis

Abstract

Background Preclinical studies have suggested that solid-state MRI markers of cortical bone porosity, morphologic structure, mineralization, and osteoid density are useful measures of bone health. Purpose To explore whether MRI markers of cortical bone porosity, morphologic structure, mineralization, and osteoid density are affected in postmenopausal osteoporosis (OP) and to examine associations between MRI markers and bone mineral density (BMD) in postmenopausal women. Materials and Methods In this single-center study, postmenopausal women were prospectively recruited from January 2019 to October 2020 into two groups: participants with OP who had not undergone treatment, defined as having any dual-energy x-ray absorptiometry (DXA) T-score of -2.5 or less, and age-matched control participants without OP (hereafter, non-OP). Participants underwent MRI in the midtibia, along with DXA in the hip and spine, and peripheral quantitative CT in the midtibia. Specifically, MRI measures of cortical bone porosity (pore water and total water), osteoid density (bound water [BW]), morphologic structure (cortical bone thickness), and mineralization (phosphorous [P] density [³¹P] and ³¹P-to-BW concentration ratio) were quantified at 3.0 T. MRI measures were compared between OP and non-OP groups and correlations with BMD were assessed. Results Fifteen participants with OP (mean age, 63 years ± 5 [SD]) and 19 participants without OP (mean age, 65 years ± 6) were evaluated. The OP group had elevated pore water (11.6 mol/L vs 9.5 mol/L; P = .007) and total water densities (21.2 mol/L vs 19.7 mol/L; P = .03), and had lower cortical bone thickness (4.8 mm vs 5.6 mm; P < .001) and ³¹P density (6.4 mol/L vs 7.5 mol/L; P = .01) than the non-OP group, respectively, although there was no evidence of a difference in BW or ³¹P-to-BW concentration ratio. Pore and total water densities were inversely associated with DXA and peripheral quantitative CT BMD (P < .001), whereas cortical bone thickness and ³¹P density were positively associated with DXA and peripheral quantitative CT BMD (P = .01). BW, ³¹P density, and ³¹P-to-BW concentration ratio were positively associated with DXA (P < .05), but not with peripheral quantitative CT. Conclusion Solid-state MRI of cortical bone was able to help detect potential impairments in parameters reflecting porosity, morphologic structure, and mineralization in postmenopausal osteoporosis. © RSNA, 2023 Supplemental material is available for this article. See also the editorial by Bae in this issue.

Graphical abstract

Figure 1:

STROBE flow chart diagram for the study. BMI = body mass index, DXA = dual-energy x-ray absorptiometry, pQCT = peripheral quantitative CT.

Figure 2:

Representative MRI axial magnitude scans for each noncontrast sequence compared between a 70-year-old woman with osteoporosis (OP; osteoporotic participant) and a 62-year-old woman without OP (non-osteoporotic participant). The circular structure above the tibia is the calibration reference sample that converts signal intensities to absolute concentrations. The sample concentrations and relaxation times are approximately matched to those of the bone water properties and are therefore not visible on the ultrashort echo time (UTE) echo 2 image. The UTE images in the participant with OP exhibit the characteristic cortical thinning from periosteal expansion and endosteal resorption. The phosphorous 31 (³¹P) zero–echo time (ZTE) image indicates a general reduction in the phosphorus signal in the OP subject. IR = inversion recovery, r-UTE = rapid UTE.

Figure 3:

Representative cortical segmentation and quantitative parametric color maps overlaid on ultrashort echo time (UTE) images for the same women pertaining to Figure 2. (A) Yellow boundaries depict manually drawn contours of cortical bone overlaid on a UTE echo 2 image, which has strong bone-tissue contrast. Color maps for each MRI parameter, (B) total water, (C) pore water, (D) bound water, and (E) phosphorous, are overlaid on UTE echo 1 images. ROI = region of interest.

Figure 4:

Box and whisker plots show comparison of means between the groups with osteoporosis (OP) and without OP (non-OP). OP was diagnosed with a dual-energy x-ray absorptiometry (DXA) T-score of –2.5 or less at the measurement location. Boxes represent median and IQR. Outliers (ie, individual data >1.5 IQRs outside of the first or third quartile) are represented by dots. Whiskers extend to the maximum and minimum data points unless there are outliers; in that case, the whiskers extend 1.5 IQRs beyond the boxes. * P value less than .05.

Figure 5:

Associations between MRI markers and dual-energy x-ray absorptiometry (DXA)-derived total hip areal bone mineral density (aBMD). The solid line is the best fit and the dotted lines are the 95% CIs for the regression line. Total and pore water are negatively correlated with density values. The red dots indicate each participant's data.

Figure 6:

Correlations of MRI biomarkers versus tibia peripheral quantitative CT volumetric bone mineral density (vBMD). The solid bold black line is best fit and dotted lines are 95% CIs for the line of best fit. Red dots are each participant's data. Total and pore water are negatively correlated with density values.