Rationale and Objectives
Improvements in imaging technology have led to the increased use of computed tomography (CT). For example, micro-CT and quantitative CT (QCT) are now often used in osteoporosis research, in which micro-CT is able to analyze small bones or bone samples with high spatial resolution. In contrast, QCT is able to investigate large samples with low spatial resolution. The aim of this study was to test the usefulness of flat-panel volumetric CT (fpVCT) in a rat model of osteopenia.
Material and Methods
Twenty-two 3-month-old rats underwent ovariectomy and were either left untreated or supplemented with estradiol for 15 weeks. After sacrificing, the rats’ second lumbar vertebral body bone mineral density (BMD) was analyzed using fpVCT and ashing. The results were compared to those of a microstructural analysis of the first lumbar vertebrae and a biomechanical evaluation of the fourth lumbar vertebrae.
Results
BMD measurements using both fpVCT (0.39 vs 0.35 mg/cm 3 ) and ashing (0.52 vs 0.48 mg/cm 3 ) demonstrated a significant improvement after estradiol supplementation. The correlation coefficient of the two methods was 0.858. After estradiol supplementation, the bone microstructural and bone biomechanical parameters were improved, compared to no treatment. The correlations of both the microstructural and the biomechanical evaluations were closer for BMD measured using fpVCT (r = 0.482–0.769) than on the basis of ashing (r = 0.345–0.573). FpVCT was not able to display the trabecular microstructure of the rat lumbar vertebrae.
Conclusion
The use of fpVCT demonstrated a close relationship between morphologic and biomechanical evaluations in a rat model of osteopenia. Because of its different proportions, fpVCT might be able to bridge the gap between micro-CT and QCT in analyzing larger animals.
The introduction of multidetector-row computed tomography (CT) has opened avenues for the examination of large body sections within short examination times, while maintaining high spatial resolution . A novel approach in hardware development, however, uses flat-panel detectors. Flat-panel detectors allow for greater spatial resolution, isotropic voxel imaging, and volumetric coverage than conventional CT . The flat-panel detectors used were initially developed for conventional radiographic applications and are known for offering excellent image quality in high-contrast structures . The main difference between flat-panel volumetric CT (fpVCT) and conventional multidetector-row CT is that the rows of detector elements (usually four, 16, or 64) are replaced by an area detector . Currently, only a few prototypes for fpVCT exist, and data on the diagnostic benefit of these devices are scarce. Therefore, the aim of this study was to evaluate the possibilities of fpVCT for use in osteoporosis research.
Osteoporosis in postmenopausal women mainly affects the trabecular bones of the body (eg, vertebral body, femoral neck, distal radius, or proximal humerus). Because of their high clinical relevance, lumbar vertebral bodies were chosen for this study. Vertebral fractures are an important clinical indicator of the progression of osteoporosis and the ongoing fracture risk for new osteoporotic fractures, independent of bone mineral density (BMD) ( ).
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Materials and methods
Animals and Substances
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fpVCT
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Ashing
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Biomechanical Testing
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Preparation for Microscopy and Microradiography
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Statistical Analysis
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Results
Body Weight
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Table 1
Results of the Animal Trial
Variable Controls Estradiol-treated Rats Body weight After 15 weeks (g) 317.9 ± 26.1 246.5 ± 24.7 ∗ Vertebral body Volume (cm 3 ) 0.192 ± 0.014 0.165 ± 0.012 ∗ BMD (g/cm 3 ) fpVCT 0.357 ± 0.022 0.394 ± 0.020 ∗ Ashing 0.484 ± 0.034 0.517 ± 0.016 ∗ Biomechanical properties Maximum load (N/cm 3 ) 1020 ± 154 1217 ± 184 ∗ Yield load (N/cm 3 ) 856 ± 239 1090 ± 150 ∗ Young’s modulus (N/mm/cm 3 ) 841 ± 180 1274 ± 301 ∗ Microradiography Cortical percentage (%) 56.1 ± 3.7 59.7± 5.4 ∗ Cortical width (mm) 0.135 ± 0.019 0.146 ± 0.021 ∗ Cancellous area (mm 2 ) 1.56 ± 0.40 1.33 ± 0.18 ∗ Trabecular area (mm 2 ) 0.53 ± 0.12 0.62 ± 0.13 ∗ Number of nodes ( n /mm 2 ) 24.8 ± 6.1 34.1 ± 10.2 ∗ Trabecular width (μm) 5.88 ± 0.64 5.74 ± 0.65
BMD, bone mineral density; fpVCT, flat-panel volumetric computed tomography.
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fpVCT
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Ashing
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Biomechanical Testing
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Microradiographic Evaluation
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Table 2
Pearson’s r and R 2 Values of the Different Correlations Between the BMD Measurements and the Biomechanical and Structural Evaluations
fpVCT Ashing Variable_r__R_ 2 r__R 2 Biomechanical properties Maximum load (N/cm 3 ) 0.769 0.591 0.573 0.328 Yield load (N/cm 3 ) 0.523 0.274 0.473 0.227 Young’s modulus (N/mm/cm 3 ) 0.482 0.232 0.516 0.266 Microradiography Cortical percentage (%) 0.515 0.265 0.426 0.181 Cancellous area (mm 2 ) 0.353 0.125 0.272 0.074 Trabecular area (mm 2 ) 0.445 0.198 0.345 0.119 Number of nodes ( n /mm 2 ) 0.511 0.261 0.419 0.175 Trabecular width (μm) 0.486 0.236 0.436 0.190
BMD, bone mineral density; fpVCT, flat-panel volumetric computed tomography.
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Discussion
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Conclusion
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Acknowledgments
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