Journal
QUANTITATIVE IMAGING IN MEDICINE AND SURGERY
Volume 11, Issue 8, Pages 3715-3725Publisher
AME PUBL CO
DOI: 10.21037/qims-20-1373
Keywords
Osteoporosis; magnetic resonance imaging (MRI); spine; bone density; T2* mapping; chemical shift encoding-based water-fat separation
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Chemical shift encoding-based water-fat separation techniques can be used for fat quantification and bone marrow T2* assessment. This study found significant correlations between T2*, bone mineral density, trabecular number, and trabecular spacing. T2* mapping allows for differentiation between low-energy osteoporotic and high-energy traumatic vertebral fractures, suggesting its potential as a biomarker for bone fragility.
Background: Chemical shift encoding-based water-fat separation techniques have been used for fat quantification [proton density fat fraction (PDFF)], but they also enable the assessment of bone marrow T2*, which has previously been reported to be a potential biomarker for osteoporosis and may give insight into the cause of vertebral fractures (i.e., osteoporotic vs. traumatic) and the microstructure of the bone when applied to vertebral bone marrow. Methods: The 32 patients (78.1% with low-energy osteopenic/osteoporotic fractures, mean age 72.3 +/- 9.8 years, 76% women; 21.9% with high-energy traumatic fractures, 47.3 +/- 12.8 years, no women) were frequency-matched for age and sex to subjects without vertebral fractures (n=20). All study patients underwent 3T-MRI of the lumbar spine including sagittally acquired spoiled gradient echo sequences for chemical shift encoding-based water-fat separation, from which T2* values were obtained. Volumetric trabecular bone mineral density (BMD) and trabecular bone parameters describing the three-dimensional structural integrity of trabecular bone were derived from quantitative CT. Associations between T2* measurements, fracture status and trabecular bone parameters were assessed using multivariable linear regression models. Results: Mean T2* values of non fractured vertebrae in all patients showed a significant correlation with BMD (r=-0.65, P<0.001), trabecular number (TbN) (r=-0.56, P<0.001) and trabecular spacing (TbSp) (r=0.61, P<0.001); patients with low-energy osteoporotic vertebral fractures showed significantly higher mean T2* values than those with traumatic fractures (13.6 +/- 4.3 vs. 8.4 +/- 2.2 ms, P=0.01) as well as a significantly lower TbN (0.69 +/- 0.08 vs. 0.93 +/- 0.03 mm(-1), P<0.01) and a significantly larger trabecular spacing (1.06 +/- 0.16 vs. 0.56 +/- 0.08 mm, P<0.01). Mean T2* values of osteoporotic patients with and without vertebral fracture showed no significant difference (13.5 +/- 3.4 vs. 15.6 +/- 3.5 ms, P=0.40). When comparing the mean T2* of the fractured vertebrae, no significant difference could be detected between low-energy osteoporotic fractures and high-energy traumatic fractures (12.6 +/- 5.4 vs. 8.1 +/- 2.4 ms, P=0.10). Conclusions: T2* mapping of vertebral bone marrow using using chemical shift encoding-based water-fat separation allows for assessing osteoporosis as well as the trabecular microstructure and enables a radiation free differentiation between patients with low-energy osteoporotic and high-energy traumatic vertebral fractures, suggesting its potential as a biomarker for bone fragility.
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