Cross-calibration of dual-energy X-ray densitometers for a large, multi-center genetic study of osteoporosis

Osteoporosis is a common disease with a strong genetic component characterized by reduced bone mass and an increased risk of fragility fractures. Bone mineral density (BMD) is the most important determinant of osteoporotic fracture risk, but the genes responsible for BMD regulation and fracture are incompletely defined. To enable multi-center studies to examine the genetic influences on BMD there is a requirement to standardize measurements across different manufacturers of bone densitometers, different versions of machines and different normative ranges. This paper describes a method developed to allow near-identical subjects with low age-adjusted BMD (based on Z-scores) to be recruited in 17 centers using 27 different densitometers. Cross-calibration was based on measurements using a European spine phantom circulated to all centers and measured ten times on each individual machine. From theses values an individual exponential curve, based on nominal versus observed BMD, was derived for each machine. As expected, there were large and significant variations in nominal BMD values, not only between scanners from different manufacturers but also between different versions of scanners from the same manufacturer. Hologic scanners tended to underestimate the nominal BMD, while Lunar scanners overestimated the value. Norland scanners gave mixed values over estimating BMD at the lower nominal value (0.5 g/cm²) while underestimating the value at the higher value (1.5 g/cm²). The validity of the exponential equations was tested using hip and spine measurements on 991 non-proband women from a familial osteoporosis study (FAMOS). After cross-calibration there was a considerable reduction in variation between machines. This observation, coupled with the absence of a similar reduction in variation attributable to a linear regression on age, demonstrated the validity of the cross-calibration approach. Use of the cross-calibration curves along with a standard normative range (in the case of this study, the Hologic normative range) allowed age-specific Z-scores to be used as an inclusion criterion in this genetic study, a method that will be useful for other trials where age-specific BMD inclusion criteria are required.     

双能X线吸收法及定量CT法诊断骨质疏松症的比较研究

本研究比较了双能Ｘ线吸法（ＤＸＡ）与定量ＣＴ（ＱＣＴ）在骨质疏松症诊断中的应用。对５６例健康妇女（Ｈ组）及４８例骨折后骨质疏松妇女（ＯＰ组）进行了ＤＸＡ及ＱＣＴ测量。ＤＸＡ与ＱＣＴ在Ｈ、ＯＰ组均显著相关（ｒ＝０．７５，Ｐ＜０．０００１，ｒ＝０．５８，Ｐ＜０．０００１）。Ｈ组及ＯＰ组，随年龄增长的骨减少率，ＱＣＴ较ＤＸＡ法为高。而两组中骨密度的差别，ＱＣＴ较ＤＸＡ法更大（Ｐ＜０．０５）。结论；由于ＱＣＴ可以选择性测量椎体松质骨，故可较ＤＸＡ更能很好地区分健康人与骨质疏松病人。     

Spinal Trabecular Bone Loss and Fracture in American and Japanese Women

This study examined trabecular bone mineral density (BMD) in Japanese women with and without spinal fracture, and compared the results to American women with and without fracture. The quantitative computed tomography (QCT) systems used at the University of California, San Francisco (UCSF) and at Nagasaki University were cross-calibrated. Normative BMD was assessed with the K₂HPO₄ liquid phantom in 538 Americans aged 20–85 years, and with the B-MAS200 phantom in 577 Japanese aged 20–83 years. These BMD were adjusted for use with the Image Analysis solid phantom using the result of cross-calibration. The trabecular BMD in 111 postmenopausal American women (55 with fracture), and in 185 postmenopausal Japanese women (67 with fracture) were compared for investigation of the difference in BMD values relative to fracture status. The absolute BMD values in Japanese were lower than those in Americans, and the differences were greater with advancing age. The magnitude of the BMD difference was 8.6, 20.5, 38.1 mg/cm³ in women aged 20–24 years, 40–44 years, 60–64 years, respectively. In premenopausal women, BMD began to decrease at the age of 20 in Japanese, whereas the peak bone mass was maintained until the age of 35 in the American women. In immediate postmenopausal women, BMD significantly decreased in both populations. In later postmenopausal women, BMD significantly decreased with age in the Japanese women but decreased less rapidly in the American women. The aging decrease of BMD was 1.4% and 2.2% per year in the later postmenopausal American and Japanese women, respectively. The fracture threshold is considered to be lower in Japanese women. However, the BMD difference between American and Japanese women with fracture was similar to that without fracture. The Z-scores of fracture subjects versus controls were 2.9 in American and 1.8 in Japanese women. In conclusion, Japanese women were found to have a lower BMD and lower fracture threshold than American women. The significant decrease of spinal trabecular BMD in late postmenopause is potentially responsible for the higher prevalence of spinal fracture in Japanese women. Received: 18 December 1995 / Accepted: 23 September 1996     

Accuracy,Linearity and Precision of Spine QCT vBMD Phantom Measurements for Different Brands of CT Scanner: A Multicentre Study

We describe a multicenter study using the European Spine Phantom (ESP) to compare the accuracy, linearity and precision of QCT measurements of spine vBMD between different brands of scanner, different models of the same brand and identical units of the same model. Ten scans of the same ESP with repositioning were performed on forty CT scanners from five manufacturers in different hospitals across China, all calibrated with the Mindways QCT system. The three ESP vertebral bodies simulating low (L1), medium (L2) and high (L3) vBMD and their average (L1-3 vBMD) were compared with phantom values. Linearity was assessed using the standard error of the estimate derived from linear regression. Precision errors were expressed as the standard deviation of the ten measurements on each scanner. Median (IQR) vBMD over all forty CT scanners compared with phantom values were: L1: 52.2 (49.9?56.4) vs 51.0; L2: 104.4 (101.2?108.6) vs 102.2; L3: 201.4 (195.0?204.9) vs 200.4; L1-3: 119.3 (116.6?123.2) vs 117.9 mg/cm³. Statistically significant differences in L1-3 vBMD were found between different brands (p= 0.005) and between different models of the same brand and identical units of the same model (both p< 0.001). Cross-calibration using linear regression gave a good fit for all forty systems with a median standard error of the estimate of 1.7 mg/cm³. The median precision error for L1-3 vBMD was 0.61 mg/cm³. Statistically significant differences in spine vBMD measurements between different scanners reinforce the importance of cross-calibration in multi-center studies. Cross-calibration can be reliably performed using linear regression equations.     

A Comparison of Phantoms for Cross-Calibration of Lumbar Spine DXA

The aim of this project was to compare three phantoms used for cross-calibration of dual-energy X-ray absorptiometers with an in vivo cross-calibration. The phantoms used were the Bona Fide Phantom (BFP), the European Spine Phantom (ESP) and the GE Lunar Aluminum Spine Phantom (ASP). The cross calibration was for L2–L4 lumbar spine bone mineral density (BMD) on a GE Lunar DPX-L and Hologic QDR 2000. The in vivo cross-calibration was obtained using 72 subjects (61 female, 11 male; mean age 49 years, range 14–84 years). The phantoms were measured 10 times without repositioning on both instruments. A further, long-term cross-calibration was obtained with the BFP over a 9 month period. The true linear relationship between the two instruments was calculated used a standardized principal components method. The mean residuals were calculated between each phantom cross-calibration line and the in vivo data to obtain a measure of the goodness of fit between the phantom cross-calibration and the in vivo data. There was no significant difference between the in vitro and in vivo cross-calibrations. The long-term BFP cross-calibration gave an in vitro cross-calibration that is closest to the in vivo cross-calibration in this group of subjects. When calculating Hologic QDR BMD from results on the GE Lunar DPX-L, the ASP underestimates Hologic QDR 2000 BMD by 4% at high BMD and overestimates by 4% at low BMD. The ESP cross-calibration overestimates Hologic QDR2000 BMD by 1% at high BMD and 4% at low BMD. The BFP performs best, overestimating Hologic QDR2000 BMD by between 1.2% and 1.8%, whilst the difference between the long-term BFP cross-calibration and the in vivo data is less than 1% over the range of BMD covered. Received: 19 October 2001 / Accepted: 9 July 2002     

快速千伏切换能谱CT与QCT测定羊椎体骨密度的相关性及一致性研究

目的利用羊椎体标本评价快速千伏切换能谱CT物质分离技术测定的骨松质骨密度与QCT测定的骨密度的一致性。方法新鲜羊椎体骨3副(共23个椎体),在快速千伏切换的能谱CT机上进行能谱模式扫描,利用物质分离技术获得椎体骨松质的羟基磷灰石含量(骨密度),并在同一台CT机上对每副羊骨进行标准QCT扫描,用QCT骨密度分析软件获得对应感兴趣区内的椎体骨密度。采用Pearson相关性分析、配对样本t检验、组内相关系数及Bland-Altman法进行两种方法测量结果的相关性及一致性分析。结果能谱CT物质分离技术测得的羊椎体骨密度值为(286.7±103.8) mg/cm~3,显著低于QCT测量的骨密度值(321.3±123.6) mg/cm~3,但二者高度线性相关(r=0.989,P0.001)。两种方法测量的骨密度值组内相关系数为0.974(P0.001)。对原始数据进行对数转换后应用Bland-Altman分析,差值大部分位于差值平均值±1.96标准差范围内,提示两种测量一致性好。结论能谱CT物质分离技术测定的羊椎体骨密度与QCT测定的骨密度的一致性及相关性好,有望用于临床患者骨密度的评价及随访。     

Cross-calibration of a GE iDXA and Prodigy for Total and Regional Body Bone Parameters: The Importance of Using Cross-calibration Equations for Longitudinal Monitoring After a System Upgrade

We aimed to determine if cross-calibration equations could be applied to convert GE Lunar Prodigy total and regional bone measurements to the GE iDXA model to support longitudinal monitoring of subjects. The cross-calibration group comprised 63 adults (age 45.1 [12.8] yr; body mass index: 25.6 [3.7] kg/m²) and the validation group comprised 25 adults (age 40.5 [11.5] yr; body mass index: 25.7 [3.5] kg/m²). The parameters reported were total and regional bone mineral density (BMD), bone mineral content, and bone area. There were significant differences between densitometers for all anatomical regions and reported bone parameters (p < 0.0001); iDXA reported lower BMD than the Prodigy apart from the ribs. Linear regression indicated good agreement for all measurements. Bland-Altman analyses indicated significant bias for all measurements and that cross-calibration equations were required. The derived cross-calibration equations were effective in reducing differences between predicted and measured results for each parameter and at each region apart from leg BMD, where the difference remained significant (0.013 g/cm²; p < 0.05). Our results indicate that cross-calibration is important to maintain comparability of total body-derived regional bone measurements between the Lunar Prodigy and iDXA.     

Trabecular Bone Score (TBS) Cross-Calibration for GE Prodigy and IDXA Scanners

Dual-energy X-ray absorptiometry (DXA) is used for osteoporosis diagnosis, fracture prediction and to monitor changes in bone mineral density (BMD). Change in DXA instrumentation requires formal cross-calibration and procedures have been described by the International Society for Clinical Densitometry. Whether procedures used for BMD cross-calibration are sufficient to ensure lumbar spine trabecular bone score (TBS) cross-calibration is currently uncertain. The Manitoba Bone Density Program underwent a program-wide upgrade in DXA instrumentation from GE Prodigy to iDXA in 2012, and a representative a sample of 108 clinic patients were scanned on both instruments. Lumbar spine TBS (L1-L4) measurements were retrospectively derived in 2013. TBS calibration phantoms were not available at our site when this was performed. We found excellent agreement for lumbar spine BMD, without deviation from the line of perfect agreement, and low random error (standard error of the estimate [SEE] 2.54% of the mean). In contrast, spine TBS (L1-L4) showed significant deviation from the line of identity: TBS(iDXA) = 0.730 x TBS(Prodigy) + 0.372 (p<0.001 for slope and intercept); SEE 5.12% of the mean with negative bias (r=-0.550). Results were worse for scans acquired in thick versus standard mode, but similar when the population was stratified as BMI < or > 35 kg/m². In summary, it cannot be assumed that just because BMD cross-calibration is good that this applies to TBS. This supports the need for using TBS phantom calibration to accommodate between-scanner differences as part of the manufacturer's TBS software installation.     

Rapid small-animal dual-energy X-ray absorptiometry using digital radiography.

Although dual-energy X-ray absorptiometry (DEXA) is an established technique for clinical assessment of areal bone mineral density (BMD), the spatial resolution, signal-to-noise ratio, scan time, and availability of clinical DEXA systems may be limiting factors for small-animal investigations using a large number of specimens. To avoid these limitations, we have implemented a clinical digital radiography system to perform rapid area DEXA analysis on in vitro rat bone specimens. A crossed step-wedge (comprised of epoxy-based materials that mimic the radiographic properties of tissue and bone) was used to calibrate the system. Digital radiographs of bone specimens (pelvis, spine, femur, and tibia from sham-ovariectomized [SHAM] and ovariectomized [OVX] rats) were obtained at 40 kilovolt peak (kVp) and 125 kVp, and the resulting areal BMD values were compared with those obtained with a clinical fan-beam DEXA system (Hologics QDR 4500). Our investigation indicates that the cross-wedge calibrated (CWC) DEXA technique provides high-precision measurements of bone mineral content (BMC; CV = 0.6%) and BMD (CV = 0.8%) within a short acquisition time (<30 s). Areal BMD measurements reported by the CWC-DEXA system are within 8.5% of those reported by a clinical fan-beam scanner, and BMC values are within 5% of the known value of test specimens. In an in vivo application, the CWC-DEXA system is capable of reporting significant differences between study groups (SHAM and OVX) that are not reported by a clinical fan-beam DEXA system, because of the reduced variance and improved object segmentation provided by the CWC-DEXA system.     

Cross-Calibration of Prodigy and Horizon A Densitometers and Precision of the Horizon A Densitometer

We performed this study to enable a reliable transition for clinical study participants and patients from a GE Lunar Prodigy to a Hologic Horizon A dual-energy X-ray absorptiometry (DXA) scanner and to assess the reproducibility of measurements made on the new DXA scanner. Forty-five older adults had one spine, hip, and total body scan on a Prodigy dual-energy X-ray absorptiometry (DXA) scanner and 2 spine, hip, and total body scans, with repositioning, on a new Hologic Horizon A DXA scanner. Linear regression models were used to derive cross calibration equations for each measure on the 2 scanners. Precision (group root-mean-square average coefficient of variation) of bone mineral density (BMD) of the total hip, femoral neck, and lumbar spine (L1-L4), and total body fat, bone, and lean mass, appendicular lean mass, and trabecular bone score (TBS) was assessed using the International Society of Clinical Densitometry's (ISCD's) Advanced Precision Calculation Tool. Correlation coefficients for the BMD and body composition measures on the 2 scanners ranged from 0.94 to 0.99 (p<0.001). When compared with values on the Prodigy, mean BMD on the Horizon A was lower at each skeletal site (0.136 g/cm² lower at the femoral neck and 0.169 g/cm² lower at the lumbar spine (L1-4)), fat mass was 0.47 kg lower, and lean mass was 4.50 kg higher. Precision of the Horizon A scans was 1.60% for total hip, 1.94% for femoral neck, and 1.25% for spine (L1-4) BMD. Precision of TBS was 1.67%. Precision of total body fat mass was 2.16%, total body lean mass was 1.26%, appendicular lean mass was 1.97%, and total body bone mass was 1.12%. The differences in BMD and body composition values on the 2 scanners illustrate the importance of cross-calibration to account for these differences when transitioning clinical study participants and patients from one scanner to another.     

Liquid Calibration Phantoms in Ultra-Low-Dose QCT for the Assessment of Bone Mineral Density

Introduction: Cortical bone is affected by metabolic diseases. Some studies have shown that lower cortical bone mineral density (BMD) is related to increases in fracture risk which could be diagnosed by quantitative computed tomography (QCT). Nowadays, hybrid iterative reconstruction-based (HIR) computed tomography (CT) could be helpful to quantify the peripheral bone tissue. A key focus of this paper is to evaluate liquid calibration phantoms for BMD quantification in the tibia and under hybrid iterative reconstruction-based-CT with the different hydrogen dipotassium phosphate (K₂HPO₄) concentrations phantoms. Methodology: Four ranges of concentrations of K₂HPO₄ were made and tested with 2 exposure settings. Accuracy of the phantoms with ash gravimetry and intermediate K₂HPO₄ concentration as hypothetical patients were evaluated. The correlations and mean differences between measured equivalent QCT BMD and ash density as a gold standard were calculated. Relative percentage error (RPE) in CT numbers of each concentration over a 6-mo period was reported. Results: The correlation values (R² was close to 1.0), suggested that the precision of QCT-BMD measurements using standard and ultra-low dose settings were similar for all phantoms. The mean differences between QCT-BMD and the ash density for low concentrations (about 93 mg/cm³) were lower than high concentration phantoms with 135 and 234 mg/cm³ biases. In regard to accuracy test for hypothetical patient, RPE was up to 16.1% for the low concentration (LC) phantom for the case of high mineral content. However, the lowest RPE (0.4 to 1.8%) was obtained for the high concentration (HC) phantom, particularly for the high mineral content case. In addition, over 6 months, the K₂HPO₄ concentrations increased 25% for 50 mg/cm³ solution and 0.7 % for 1300 mg/cm³ solution in phantoms. Conclusion: The excellent linear correlations between the QCT equivalent density and the ash density gold standard indicate that QCT can be used with submilisivert radiation dose. We conclude that using liquid calibration phantoms with a range of mineral content similar to that being measured will minimize bias. Finally, we suggest performing BMD measurements with ultra-low dose scan concurrent with iterative-based reconstruction to reduce radiation exposure.     

Quantitative computed tomography of spine: comparison of three-dimensional and two-dimensional imaging approaches in clinical practice.

Quantitative computed tomography (QCT), a widely utilized technique for determining bone mineral density (BMD) at various skeletal sites, may yield less precise measurements if there are operator measurement errors and other technical variables. Two-dimensional (2D)and three-dimensional (3D)QCT scans of the lumbar spine of 21 women were compared in order to investigate the effects of potential operator variability on the precision of BMD measurements and to examine resulting differences of these imaging approaches in clinical practice. No significant difference was found (p > 0.05) in precision between the 2D and 3D QCT BMD measurements owing to operator measurement errors on the CT scans. The variability in BMD values within numerous small regions of interest (ROIs)( approximately 75 mm (2) ) of cancellous bone within a single vertebra was 10.1%, larger than the 2D or 3D BMD variability measured in typical regions ( approximately 250 mm (2)) by an order of magnitude. 3D BMD values in this population, which represented a wide range of clinical values, were found to be significantly greater than 2D BMD values by an average of 5.6% (p = 0.00024) relative to the 2D QCT values. Our findings suggest technical measurement error does not have a significant effect on precision of BMD measurements obtained with either QCT method. Several factors, however, including the incorporation of focal regions of higher density bone mass within the 3D QCT ROI may account for the higher BMD values compared with those for 2D QCT.     

Quantitative computed tomography precision and accuracy for long-term follow-up of bone mineral density measurements: a five year in vitro assessment.

The purpose of this work was to test the long-term precision of quantitative computed tomography (QCT) on a CT scanner partly used for the measurement of bone mineral density (BMD). A spine phantom (ESP), which simulates three lumbar vertebrae (Li, i = 2-4) with given mineral densities of 50, 100, and 200 mg hydroxyapatite equivalents (HAP)/cm(3), respectively, was measured periodically over more than 5 yr on a Elscint-Marconi CT-Twin scanner. A total of 80 measurements were taken. The measured BMDi values were 48.4 +/- 1.2, 101.3 +/- 1.1, and 212.6 +/- 1.7 mg HAP/cm3, respectively (coefficient of variation [CV%] = 2.4, 1.1, and 0.8), and they were linearly correlated with the given density values (r > 0.99). The mean BMD value of the three simulated vertebrae was 120.8 +/- 1.1 mg HAP/cms(3) (CV% = 0.9), a value that corresponds to the mean lumbar BMD value in normal 65-yr-old women. We concluded that QCT is a precise and accurate method for long-term follow-up of BMD assessment in the population affected by osteoporosis.     

Comparison of DXA Hip Structural Analysis with Volumetric QCT

Hip structural analysis (HSA) estimates geometrical and mechanical properties from hip dual-energy X-ray absorptiometry (DXA) images and is widely used in osteoporosis trials. This study compares HSA to volumetric quantitative computed tomography (QCT) measurements in the same population. A total of 121 women (mean age 58 yr, mean body mass index 27 kg/m²) participated. Each woman received a volumetric QCT scan and DXA scan of the left hip. QCT scans were analyzed with in-house software that directly computed geometric and mechanical parameters at the neck and trochanteric regions. DXA HSA was performed with an implementation by GE/Lunar. Pair-wise linear regression of HSA variables was conducted by method to site matched QCT variables for bone density, cross-sectional area, and cross-sectional moment of inertia (CSMI) of the femur neck. HSA correlated well with QCT (r² = 0.67 for neck bone mineral density [BMD] and 0.5 for CSMI) and standard DXA at the neck (r² = 0.82 for BMD). HSA and volumetric QCT compared favorably, which supports the validity of a projective technique such as DXA to derive geometrical properties of the proximal hip.     

A low-radiation exposure protocol for 3D QCT of the spine

Summary

Cadaver and phantom measurements and simulations confirmed that radiation exposure in 3D QCT of the spine can be reduced if 80 kV instead of 120 kV protocols are used; 120 mAs and slice thicknesses of 1–1.3 mm should be usable but obese patient will require higher milliampere-second settings.

Purpose

To develop a low-radiation exposure CT acquisition protocol for 3D QCT of the thoracolumbar spine.

Methods

Twenty-six cadavers were scanned with a standard protocol of 120 kV, 100 mAs and with a low-dose protocol using 90 kV, 150 mAs. The scan range included the vertebrae T6 to L4. Each vertebra was segmented and the integral volume and BMD of the total vertebral body were determined. Effective dose values were estimated. The impact of milliampere-second reduction on image quality was simulated by adding noise.

Results

One hundred ninety-six vertebrae were analyzed. Integral volume as well as integral BMD correlated significantly (p?<?0.001) between standard and low-dose protocols (volume, r ²?=?0.991, residual root mean square (RMS) error, 0.77 cm³; BMD, r ²?=?0.985, RMS error, 4.21 mg/cm³). The slope significantly differed from 1 for integral BMD but not for volume hinting at residual field inhomogeneity differences between the two voltage settings that could be corrected by cross-calibration. Compared to the standard protocol, effective dose was reduced by over 50 % in the low-dose protocol. Adding noise in the 90 kV images to simulate a reduction from 150 to 100 mAs did not affect the results for integral volume or BMD.

Conclusions

For 3D QCT of the spine, depending on scanner type, 80 or 90 kV instead of 120 kV protocols may be considered as an important option to reduce radiation exposure; 120 mAs and slice thicknesses of 1–1.5 mm are usable if segmentation is robust to noise. In obese patients, higher milliampere-second settings will be required.     

Cross-Calibration and Comparison of Variability in 2 Bone Densitometers in a Research Setting: The Framingham Experience

New technology introduced over time results in changes in densitometers during longitudinal studies of bone mineral density (BMD). This requires that a cross-calibration process be completed to translate measurements from the old densitometer to the new one. Previously described cross-calibration methods for research settings have collected single measures on each densitometer and used linear regression to estimate cross-calibration corrections. Thus, these methods may produce corrections that have limited precision and underestimate the variability in converted BMD values. Furthermore, most of the previous studies have included small samples recruited from specialized populations. Increasing the sample size, obtaining multiple measures on each machine, and using linear mixed models to account for between- and within-subject variability may improve cross-calibration estimates. The purpose of this study was to conduct an in vivo cross-calibration of a Lunar DPX-L (Lunar Corporation, Madison, WI) with a Lunar Prodigy densitometer (GE Medical Systems Lunar, Madison, WI) using a sample of 249 healthy volunteers who were scanned twice on each densitometer, without repositioning, at both the femur and spine. Scans were analyzed using both automated and manual placement of regions of interest. Wilcoxon rank-sum tests and Bland-Altman plots were used to examine possible differences between repeat scans within and across densitometers. We used linear mixed models to determine the cross-calibration equations for the femoral neck, trochanter, total hip, and lumbar spine (L2–L4) regions. Results using automated and manual placement of the regions of interest did not differ significantly. The DPX-L densitometer exhibited larger median absolute differences in the BMD values by repeat scans of femoral neck (0.016 vs 0.012, p = 0.1) and trochanter (0.011 vs. 0.009, p = 0.06) compared with the Prodigy densitometer. The Bland-Altman plots revealed no statistically significant linear relationship between the differences in paired measures between machines and mean BMD. In our large sample of healthy volunteers, we did detect systematic differences between the DPX-L and Prodigy densitometers. Our proposed cross-calibration method, which includes acquiring multiple measures and using linear mixed models, provides researchers with a more realistic estimate of the variance of cross-calibrated BMD measures, potentially reducing the chance of making a type I error in longitudinal studies of changes in BMD.     

Converted Lumbar BMD Values Derived from Sagittal Reformations of Contrast-Enhanced MDCT Predict Incidental Osteoporotic Vertebral Fractures

We obtained baseline and follow-up bone mineral density (BMD) values of the lumbar spine from sagittal reformations of routine abdominal contrast-enhanced multidetector computed tomography (MDCT) using a reference phantom and assessed their performance in differentiating patients with no, existing, and incidental osteoporotic fractures of the spine. A MDCT-to-QCT (quantitative computed tomography) conversion equation for lumbar BMD measurements was developed by using 15 postmenopausal women (63 ± 12 years), who underwent standard lumbar QCT (L1-L3) and afterward routine abdominal contrast-enhanced MDCT. Sagittal reformations were used for corresponding lumbar BMD measurements. The MDCT-to-QCT conversion equation was applied to baseline and follow-up routine abdominal contrast-enhanced MDCT scans of 149 postmenopausal women (63 ± 10 years). Their vertebral fracture status (no, existing, or incidental osteoporotic fracture) was assessed in the sagittal reformations. A correlation coefficient of r = 0.914 (p < 0.001) was calculated for the BMD values of MDCT and standard QCT with the conversion equation BMD(QCT) = 0.695 × BMD(MDCT) - 7.9 mg/mL. Mean follow-up time of the 149 patients was 20 ± 12 months. Fifteen patients (10.1 %) had an existing osteoporotic vertebral fracture at baseline. Incidental osteoporotic vertebral fractures were diagnosed in 13 patients (8.7 %). Patients with existing and incidental fractures showed significantly (p < 0.05) lower converted BMD values (averaged over L1-L3) than patients without fracture at baseline and at follow-up. In this longitudinal study, BMD values of the lumbar spine derived from sagittal reformations of routine abdominal contrast-enhanced MDCT predicted incidental osteoporotic vertebral fractures.     

腹部脂肪含量对低毫安定量CT测量腰椎体模骨密度的影响

目的 评估不同含量腹部脂肪对低毫安定量CT(quantitative computed tomography, QCT)测量腰椎体模骨密度(bone mineral density, BMD)准确性的影响。方法 选取不同面积的新鲜猪离体皮下脂肪包裹于欧洲腰椎体模(European spine phantom, ESP)周围,模拟人体腹部不同含量总脂肪组织(total adipose tissue, TAT),根据TAT面积分为四组：TAT=0、200、320、420 cm²。利用常规QCT及低毫安QCT对每组体模重复扫描10次,测定L_1～3椎体BMD值。采用单样本t检验分析低毫安QCT测量值与体模真实值之间的差异。利用单因素方差分析Tukey检验,比较不同TAT条件下低毫安QCT测量值组内差异。以配对样本t检验比较常规QCT与低毫安QCT之间各椎体BMD测量值的差异。计算并比较BMD测量值的均方根误差(RMSE);以Pearson相关分析观察RMSE与TAT的相关性。结果 TAT=0、200、320 cm²时,常规QCT...     

Normal Changes in Spinal Bone Mineral Density in a Chinese Population: Assessment by Quantitative Computed Tomography and Dual-Energy X-ray Absorptiometry

This study was designed to determine age- and gender-based normative values for spinal bone mineral density (BMD) in a Chinese population. In addition, we compared our data with those of other countries and populations. Four hundred and forty-three healthy Chinese subjects, aged 10–79 years (189 males, mean age 46.9 years; 254 females, mean age 45.7 years) were recruited for BMD assessment. BMD was measured by quantitative computed tomography (QCT) and dual-energy X-ray absorptiometry (DXA), including postero-anterior DXA (PA-DXA), lateral DXA (L-DXA) and midlateral DXA (mL-DXA). For both genders, BMD values peaked in the 10–19 year age group when measured by QCT, and in the 30–39 year age group when measured by PA-DXA. BMD values decreased with age after reaching peak bone density in males and females for all measurements, except for PA-DXA in males. Male BMD values by DXA tended to increase beginning with the 60–69 age group through the 70–79 age group whether by PA-DXA, or L-DXA and mL-DXA. However, male QCT data showed stable BMD values among these two older groups. Comparative results showed female QCT data were higher in the 20–39 age group and lower after the 40–49 age group compared with American females. The peak BMD value by PA-DXA in Chinese females was reached in the same age group as American and European females and was similar in magnitude (p > 0.05). However, the peak BMD value for Chinese females was reached earlier and was significantly higher than that observed in Japanese females (p < 0.001). We conclude that the age group in which the peak BMD values are reached is different depending on the technique used, as is the calculated age-related rate of bone loss. It can be speculated that such differences reflect different timing for bone maturation in cancellous and cortical bone. Received: 21 February 1998 / Accepted: 28 May 1998