Associations between Bone Mineral Density and Longitudinal Changes of Vertebral Bone Marrow and Paraspinal Muscle Composition Assessed Using MR-Based Proton Density Fat Fraction and T2* Maps in Patients with and without Osteoporosis

Abstract

Background: Proton-density fat fraction (PDFF) and T2* of the vertebrae, as well as the cross-sectional area (CSA) of the paraspinal musculature (PSM), have been suggested as biomarkers for bone fragility. The aim of this study was to longitudinally assess changes in PDFF, T2* and CSA of the PSM over 6 months in patients with and without osteoporosis. Methods: Opportunistic bone mineral density (BMD) measurements (BMD < 120 mg/cm3) were obtained from a CT acquired during the clinical routine work up in osteoporotic/osteopenic patients (n = 29, mean age 72.37 ± 10.12 years, 16 women). These patients were frequency-matched for age and sex to subjects with normal BMD values (n = 29). All study patients underwent 3T MR imaging at baseline and 6-month follow up, including spoiled gradient echo sequences for chemical shift encoding-based water-fat separation, from which T2* and PDFF values of the lumbar spine and the PSM were obtained. Moreover, the CSA of the PSM was assessed longitudinally. Changes in T2*, PDFF and CSA over 6 months were calculated for the vertebrae and PSM and associations with baseline BMD values were assessed. Results: The change in CSA of the PSM over 6 months was significantly lower in the osteoporotic/osteopenic group (−91.5 ± 311.7 mm2), compared to the non-osteoporotic group, in which the CSA increased (29.9 ± 164.0 mm2, p = 0.03). In a further analysis, patients with higher vertebral PDFF at baseline showed a significantly stronger increase in vertebral T2*, compared to those patients with lower vertebral PDFF at baseline (0.9 ± 1.6 ms vs. 0.0 ± 1.8 ms, p = 0.04). Moreover, patients with higher PSM PDFF at baseline showed a significantly stronger increase in vertebral T2*, compared to those patients with lower PSM PDFF at baseline (0.9 ± 2.0 ms vs. 0.0 ± 1.3 ms, p = 0.03). Conclusion: The PSM CSA decreased significantly longitudinally in patients with osteoporosis/osteopenia, compared to those without. Additionally, higher vertebral and PSM PDFF at baseline were associated with stronger changes in vertebral bone marrow T2*. Therefore, longitudinal PDFF and T2* mapping may be useful quantitative radiation-free tools for the assessment and prediction of muscle and bone health in patients with suspected osteoporosis/osteopenia.

Keywords: bone marrow; magnetic resonance imaging; osteoporosis; spine.

Figure 1

Example PDFF map showing the segmentations of the PSM.

Figure 2

Longitudinal changes over 6 months in non-osteoporotic/osteopenic patients (≥120 mg/cm³) and in osteoporotic/osteopenic patients (BMD < 120 mg/cm³). Changes in vertebral PDFF (A, diff_PDFF_spine), changes in PSM PDFF (B, diff_PDFF_PSM), changes in vertebral T2* values (C, diff_T2*_spine) and changes in CSA of the PSM (D, diff_CSA_PSM) between baseline and 6-month follow-up (asterisks indicate significant difference). Boxplots: ° = outlier; * = extreme outlier.

Figure 3

Example color-coded PDFF maps of a 84-year old osteopenic (BMD = 107 mg/cm³) female patient (A,C) and a 69-year old male patient with normal BMD values (123 mg/cm³) (B,D) at baseline (A,B) and 6 months follow-up (C,D). Although the maps of the osteopenic patient (A,C) show a strong increase in PDFF in vertebral bone and in the PSM, the increase in the maps of the non-osteopenic/osteoporotic patient (B,D) show only a very subtle increase in PDFF.