Purpose
To evaluate the agreement of bone mineral density (BMD) between lumbar (L) and individual thoracic (T) vertebrae and identify a standard thoracic spine level for BMD assessment in cardiac computed tomography (CT) images.
Materials and Methods
Three hundred subjects who underwent simultaneous chest and abdomen CT scans for clinical indications were included. A calibration phantom that extended from the first thoracic spine (T 1 ) to the fifth lumbar (L 5 ) was employed. Vertebral BMD were measured by QCT 5000 and NVivo systems. The association between three consecutive lumbar (L1–L3) and thoracic BMD (3T, initiation site equivalent to left main coronary caudally) was evaluated.
Results
There was a gradual decrease in BMD values from T 1 to L 3, subsequently increasing in L 4 and L 5 in both genders. When stratified by gender, 3T BMD was significantly higher versus L 1-3 BMD (156.9 versus 141.9vmg/cm 3 , P < .001) for women as well as for men (164.8 versus 151.0 mg/cm 3 , P < .001). There is good correlation between 3T and L 1-3 BMD, the Pearson’s correlation coefficients are 0.91 and 0.93 for women and men, respectively. We further analyzed the associations between L 1-3 and any individual spine of T 1 –L 5 and similar relationships were observed ( r value, 0.62–0.98). The intraobserver, interobserver, and interscan variation measurement of thoracic quantitative CT was 2.5 (1.0, 95% CI 0.099–1.004); 2.6 (1.0, 95CI% 0.992–1.007), and 2.8% (1.0,95% 0.0994–1.008), respectively.
Conclusion
The 3T BMD was highly correlated with L 1-3 BMD. Thoracic BMD can be measured during cardiac and lung CT imaging without need for additional participant burden or radiation dose. This highly reproducible methodology is actively being applied to large cohort studies to evaluate the prevalence of osteoporosis and track BMD over time.
Osteoporosis and coronary atherosclerosis are increasingly being recognized as coexisting conditions in an aging population. Computed tomography (CT), as a powerful tool for atherosclerosis diagnosis, obstructive coronary artery disease (CAD) evaluation, and cardiac events detection has seen significant increased utilization over the past 20 years . Quantitative computed tomography (QCT) measured lumbar bone mineral density (BMD) is increasingly used for osteoporosis because of its ability to provide three-dimensional information compared to traditional dual x-ray absorptiometry two-dimensional images . Bone density evaluations have been performed with both phantoms and phantomless studies, and can be obtained whether contrast or noncontrast CT studies are obtained, by use of conversion factors .
Current 64-slice multidetector CT has been shown to be a feasible modality for providing improved cardiac imaging quality with decreased radiation doses (≤1 mSv) while simultaneously providing images of the thoracic spine. These studies provide the opportunity to study BMD during thoracic or cardiac imaging without additional radiation. If high correlation can be found in BMD measures between L 1-3 and thoracic spinal imaging, it will allow thoracic BMD to be a potential screening tool for osteoporosis during acquisitions of other scans at no additional burden (except measurement time) .
Materials and methods
Study Subjects
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Table 1
Demographic Data Profile of 300 Subjects with Whole Body Scan
Women ( n = 147) Men ( n = 153) Age, y 53 ± 8 57 ± 10 Height (cm) 162.9 ± 8.8 175.7 ± 9.1 Weight (kg) 66.4 ± 13.7 84.8 ± 16.4 Body mass index (kg/m 2 ) 25.0 ± 4.9 27.5 ± 4.9 Ethnicity Caucasian (%) 73 (49.7) 80 (52.3) Hispanic (%) 34 (23.1) 29 (19.0) African American (%) 11 (7.5) 13 (8.5) Asia (%) 24 (16.3) 19 (12.4) Other (%) 5 (3.4) 12 (7.8)
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Scan Technique
Thoracic and abdominal scanning
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CAC scanning
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Measurement and Analysis
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Table 2
BMD Value, R Value, and Difference between L 1∼3 and Individual Vertebrae
Sites T1 T4 T7 T10 T12 L3 L5 Women BMD (mg/cm 3 ) 198.1 184.8 168.4 162.8 157.3 145.0 157.1R value 0.81 0.85 0.91 0.92 0.96 0.98 0.90 Difference (%) 32.1 23.3 12.3 8.6 4.9 −3.3 4.8 Men BMD (mg/cm 3 ) 190.0 182.4 161.6 152.1 145.9 137.6 153.6R value 0.62 0.77 0.85 0.89 0.94 0.97 0.86 Difference (%) 34.3 28.9 14.2 7.5 3.1 −2.7 8.6
BMD, bone mineral density.
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Table 3
Mean BMD Value of 3T and L 1∼3 in Women Stratified by Age Group
Age_n_ 3T L 1∼3 Difference_R_ 35–45 19 185.8 ± 38.8 177.4 ± 32.5 11.8 ± 11.1 0.94 45–55 64 172.9 ± 39.1 159.8 ± 37.8 15.0 ± 11.4 0.92 55–65 40 155.0 ± 25.5 140.5 ± 22.8 15.9 ± 13.3 0.87 65–75 21 139.9 ± 30.6 120.0 ± 32.4 20.1 ± 11.8 0.90 Sum 144 156.9 ± 32.9 141.9 ± 33.7 17.1 ± 12.1 0.91
BMD, bone mineral density.
Table 4
Mean BMD Value of 3T and L 1∼3 in Men Stratified by Age Group
Age_n_ 3T L 1∼3 Difference_R_ 35–45 23 169.5 ± 32.0 164.1 ± 34.9 10.1 ± 7.7 0.94 45–55 45 163.9 ± 36.7 149.5 ± 33.7 16.7 ± 11.6 0.94 55–65 47 152.5 ± 26.0 131.8 ± 26.2 21.0 ± 13.1 0.82 65–75 27 144.5 ± 32.5 129.5 ± 33.0 17.1 ± 12.2 0.93 Sum 142 164.8 ± 37.1 151.0 ± 36.7 15.6 ± 12.1 0.93
BMD, bone mineral density.
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Assessment of Variability
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Results
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Discussion
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Acknowledgment
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