Biomedical subjects

K Engelke

Publications and source records attributed to K Engelke.

At least 19 recordsLinked to original sources

PubMed2006

Quality and performance measures in bone densitometry. Part 2: fracture risk.

INTRODUCTION: This is part 2 of a core chapter of the forthcoming Report on Bone Densitometry commissioned by the International Commission on Radiation Units (ICRU). It is written with the aim to review definitions of quantities and units used in bone densitometry research and to describe parameters and methods that can be used to compare and standardize densitometric equipment and measurements. Part 2 of this chapter contains the section on fracture risk. PERFORMANCE MEASURES IN THE ASSESSMENT OF FRACTURE RISK: Building on concepts of risk assessment, including risk ratios and odds ratios, we review statistical concepts commonly used in cross-sectional and prospective fracture studies. Performance measures are defined that allow a comparison of the ability of densitometry techniques to assess fracture risk. DISCUSSION: The methods of discriminant analysis, logistic regression, Poisson regression models, and the Cox proportional hazard model are presented and compared. In addition, statistical concepts to characterize risk for the individual patient are reviewed.

Aged↗

PubMed2006

Quality and performance measures in bone densitometry: part 1: errors and diagnosis.

INTRODUCTION: Bone densitometry is one of the main pillars in the assessment of osteoporosis. The most important modalities are dual x-ray absorptiometry (DXA), quantitative computed tomography (QCT), and quantitative ultrasound (QUS). MATERIALS AND METHODS: For each modality a variety of technical solutions and numerous commercial devices are available and widely used for patient measurements. While the field of bone densitometry may be considered mature, new modalities and devices are being introduced. Consequently, there is a constant need to assess and compare the quality of bone densitometry approaches and devices in a rigorous way. RESULTS: The International Commission on Radiation Units has commissioned a report on bone densitometry to address some of these issues, in particular to provide clear definitions of quantities and units used and to describe parameters and methods that can be used to compare and standardize densitometric equipment and measurements. One of the core chapters of the report summarizes quality and performance measures in bone densitometry. It is divided into four sections: physical performance measures, diagnosis, fracture risk, and monitoring. Here we publish part 1 of this chapter containing the first two sections: physical performance measures and issues in diagnosing osteoporosis. CONCLUSION: Following the international standard (ISO 5725-1), trueness, bias, repeatability, and reproducibility are defined along with terms common to osteoporosis research, such as accuracy and precision. Building on the conceptual definition of osteoporosis, diagnostic criteria are defined and discussed including criteria for reference data. Based on this, clinical performance measures commonly used for the diagnosis of osteoporosis are reviewed and discussed.

Absorptiometry, Photon↗

PubMed2006

Volumetric quantitative computed tomography of the proximal femur: relationships linking geometric and densitometric variables to bone strength. Role for compact bone.

INTRODUCTION: In assessing cervical fractures of the proximal femur, this in vitro quantitative computed tomography (QCT) study had three objectives: to compare QCT to dual-energy X-ray absorptiometry (DXA) for predicting the failure load of the proximal femur, to compare the contributions of density and geometry to bone failure load, and to compare the contributions of cortical and trabecular bone to bone failure load. A novel three-dimensional (3D) analysis tool [medical image analysis framework (MIAF-Femur)] was used to analyze QCT scans. METHODS: The proximal ends of 28 excised femurs were studied (1) using QCT to separately measure bone mineral density (BMD) and geometric variables of trabecular and cortical bone, (2) using mechanical tests to failure in a stance configuration, and (3) using DXA to measure BMD. The variables were described with mean, standard deviation, and range. Correlation matrix and multivariate linear models were computed. RESULTS: Among correlations, cortical thicknesses of the femoral neck were significantly correlated with femoral failure load, especially of the inferoanterior quadrant (r2=0.41; p<0.001), as was cortical volume at the "extended neck" (r2=0.41; p<0.001). Femoral failure load variance was best explained by a combination of QCT variables. Combining densitometric and geometric variables measured by QCT explained 76% of femoral failure load variance compared with 69% with the DXA model. Geometric variables (measured by QCT) explained 43% of femoral failure load variance compared with 72% for densitometric variables (measured by QCT). A model including only trabecular variables explained 52% of femoral failure load variance compared with 59% for a model including only cortical variables. CONCLUSION: The QCT-MIAF reported here provides analysis of both geometric and densitometric variables characterizing cortical and trabecular bone. Confirmation of our results in an independent sample would suggest that QCT may better explain failure load variance for cervical fracture than the gold standard DXA-provided BMD.

Absorptiometry, Photon↗

PubMed2006

Effect of exercise, body composition, and nutritional intake on bone parameters in male elite rock climbers.

A low body mass index is considered essential for high performance in rock climbing; however its effect on bone may be negative. In this study we compared the BMD of competitive male rock climbers (n = 20) and age- and BMI-matched non-training controls (n = 11). Subjects with any medication or illness affecting bone metabolism or a family history of osteoporosis were not included in the analysis. Total body BMD was measured by dual-energy X-ray absorptiometry. Quantitative computed tomographic scans were made from the femoral neck and the lumbar spine. Dietary intake was assessed by a 5-day protocol. BMD of the TB-scan was significantly higher in the climbers group for all sub-regions except the skull (p = 0.191) and the lower extremities (p = 0.079). Trabecular and cortical BMD of the LS were significantly higher (p = 0.036 and p = 0.004) in the climbers. The same was true for total (p = 0.005) and cortical (p = 0.002) BMD of the FN. Trabecular BMD (p = 0.054), CSA (p < 0.343) and cortical thickness (p = 0.065) of the FN was non-significantly higher for the climbers. Our study indicates that the effect of climbing on bone parameters PER SE is not detrimental in elite male athletes. Contrarily climbers demonstrated significantly higher BMD values at all loaded regions without "steal effects" at skeletal sites with low mechanical impact. Although we determined a moderately negative effect of low BMI on BMD we could not decide whether a low BMI value should be used as an exclusion criterion in high level climbing competitions as practized by the Austrian Sportclimbing Organization.

Absorptiometry, Photon↗

PubMed2005

Exercise maintains bone density at spine and hip EFOPS: a 3-year longitudinal study in early postmenopausal women.

It is an important aim in the prevention of osteoporosis to stop or decelerate bone loss during the early postmenopausal years. Here we report on results of the 3-year EFOPS exercise trial in osteopenic women. The exercise strategy emphasized low-volume high-resistance strength training and high-impact aerobics. Forty-eight fully compliant women (55.1+/-3.3 years) with no medication or illness affecting bone metabolism participated in the exercise group (EG); 30 women (55.5+/-3.0 years) served as non-training controls (CG). At baseline there were no significant between-group differences with respect to physical fitness, bone mineral density, pain and nutritional status. The training consisted of two group training and two home training sessions per week. The study participants of both groups were individually supplemented with calcium and vitamin D (cholecalciferol). Bone mineral density (BMD) was measured by DXA at the lumbar spine, proximal femur and distal forearm and by QCT at the lumbar spine. Speed of sound and broadband ultrasound attenuation were determined at the calcaneus by quantitative ultrasound (QUS). Pain frequency and intensity at different skeletal sites were assessed via questionnaire. After 38 months, the following within-group changes were measured: DXA lumbar spine, EG: 0.8% n.s.; CG: -3.3% P<0.001; QCT trabecular ROI, EG: 1.1% n.s; CG: -7.7% P<0.001; QCT cortical ROI, EG: 5.3% P<0.001; CG: -2.6% P<0.001; DXA total hip: EG: -0.2% n.s; CG -1.9%, P<0.001; DXA distal forearm, EG: -2.8% P<0.001; CG: -3.8% P<0.001; BUA, EG: -0.3% n.s; CG -5.4% P<0.001; SOS, EG: 0.3% n.s; CG -1.0% P<0.001. At year 3 between-group differences relative to the exercise group were: DXA lumbar spine: 4.1% P<0.001; QCT trabecular ROI: 8.8% P<0.001; QCT cortical ROI: 7.9% P<0.001; DXA total hip: 2.1%, P<0.001; DXA distal forearm: 1.0% n.s.; BUA: 5.8% P<0.05; SOS: 1.3% P<0.001. Pain frequency and intensity in the spine significantly decreased in the exercise group and increased in the control group, while no between-group differences were detected in the main joints. In summary, over a period of 3 years our low-volume/high-intensity exercise program was successful to maintain bone mineral density at the spine, hip and calcaneus, but not at the forearm.

Aging↗

PubMed2005

Power training is more effective than strength training for maintaining bone mineral density in postmenopausal women.

Physical exercise has a favorable impact on bones, but optimum training strategies are still under discussion. In this study, we compared the effect of slow and fast resistance exercises on various osteodensitometric parameters. Fifty-three postmenopausal women were randomly assigned to a strength training (ST) or a power training group (PT). Both groups carried out a progressive resistance training, a gymnastics session, and a home training over a period of 12 mo. During the resistance training, the ST group used slow and the PT group fast movements; otherwise there were no training differences. All subjects were supplemented with Ca and vitamin D. At baseline and after 12 mo, bone mineral density (BMD) was measured at the lumbar spine, proximal femur, and distal forearm by dual-energy X-ray absorptiometry. We also measured anthropometric data and maximum static strength. Frequency and grade of pain were assessed by questionnaire. After 12 mo, significant between-group differences were observed for BMD at the lumbar spine (P < 0.05) and the total hip (P < 0.05). Whereas the PT group maintained BMD at the spine (+0.7 +/- 2.1%, not significant) and the total hip (0.0 +/- 1.7%, not significant), the ST group lost significantly at both sites (spine: -0.9 +/- 1.9%; P < 0.05; total hip: -1.2 +/- 1.5%; P < 0.01). No significant between-group differences were observed for anthropometric data, maximum strength, BMD of the forearm, or frequency and grade of pain. These findings suggest that power training is more effective than strength training in reducing bone loss in postmenopausal women.

Aged↗

PubMed2004

The effect of habitual physical activity, non-athletic exercise, muscle strength, and VO2max on bone mineral density is rather low in early postmenopausal osteopenic women.

CONTEXT: Although the positive effect of well-designed exercise regimes on bone mineral density (BMD) is established the osteo-anabolic relevance of habitual physical activity and non-athletic exercise is still under discussion. OBJECTIVE: To determine the effects of habitual physical activity, non-athletic exercise muscle strength, VO2max and anthropometric parameters on BMD in early post-menopausal women. DESIGN: Cross-sectional study. METHODS: 150 early postmenopausal women (55.5+/-3.4 years), which were free of diseases or medication affecting bone metabolism and had no athletic history were investigated. The influence of weight, body composition, physical activity, isometric strength, VO2max, and nutritional intake on BMD was measured at multiple sites using different techniques. Further bone markers (Osteocalcin, CTX) were determined. Activity and weight-bearing activity were assessed by questionnaire. Maximum strength was measured isometrically. Aerobic capacity was measured with an spirometric system in a stepwise treadmill test and dietary intake was monitored over 5 days. RESULTS: Slight relationships between physical activity, exercise, muscle strength and VO2max with bone parameters were determined by univariate analysis. After adjusting for confounding variables in a stepwise regression analysis, significant relationships with BMD measured at the hip or the spine could no longer be detected for physical activity, exercise, and physical fitness (strength indices, VO2max). The same was true for osteocalcin and CTX. Arm strength explained 4.5% of the variation of forearm BMD (DXA). At the calcaneal site, osteogenic exercise was significantly related to the quantitative ultrasound index (r2 = 0.27). CONCLUSION: The isolated effect of habitual physical activity, unspecific exercise participation, and muscle strength on bone parameters is rather low in (early-) postmenopausal women. CLINICAL RELEVANCE: Women at risk should take specific exercise programs into consideration rather than to increasing the amount of habitual physical activity.

Biomarkers↗

PubMed2003

Acute hormonal responses of a high impact physical exercise session in early postmenopausal women.

The effect of a single bout of exercise on hormones affecting bone metabolism was studied in 25 early postmenopausal women with osteopenia. The complex training session was performed between 8:00 a.m. and 9:05 a.m. Serum concentrations of dehydroepiandrosterone-sulfate (DHEA-S), total testosterone, free testosterone, 17beta-estradiol, cortisol, human growth hormone (hGH), insulin-like growth factor-I (IGF-I), and insulin-like growth factor binding protein-3 (IGFBP-3) were determined. Blood samples were obtained immediately before (baseline) and after exercise, as well as 2 h and 22 h post-exercise. DHEA-S increased by 10% immediately after exercise and remained increased 2 h later. Testosterone showed no increase immediately after exercise but fell by 21% 2 h post-exercise. Free testosterone was increased by almost 20% immediately after exercise and returned to baseline levels after 2 h. Two hours post-exercise a 20% increase in the estradiol level was measured. Cortisol decreased by 36% during exercise and a further 14% during the next 2 h, a loss higher than the normal diurnal decrease. hGH increased by 80% during exercise and fell 30% under baseline values after 2 h. Even though the assessment period was prolonged to 22 h no significant change could be demonstrated for IGF-I. Serum IGFBP-3 showed a biphasic increase. During the exercise session IGFBP-3 increased by 35%, returned to baseline values 2 h post-exercise and increased again by 40% 22 h post-exercise. In summary, this study showed that a single bout of exercise typically used in osteoporosis prevention programs could have an influence on hormones affecting bone metabolism.

Adaptation, Physiological↗

PubMed2002

Accuracy and precision of bone mineral density and bone mineral content in excised rat humeri using fan beam dual-energy X-ray absorptiometry.

The aim of this study was the evaluation of fan beam dual-energy X-ray absorptiometry (DXA) for measuring bone mineral density (BMD) and bone mineral content (BMC) of isolated rat humeri. Defleshed rat humeri from male Lewis rats were examined with a Hologic QDR 4500 A (Hologic, Inc., Bedford, MA) high-resolution densitometer both in water and 0.9% saline solution. The small animal scan protocol with the regional high-resolution mode was used. BMC measured by DXA was compared with bone dry weight, ash weight, and bone calcium content. Furthermore, DXA BMD and BMC precision were determined. We also evaluated the effect of salinity of the water bath in which the bones were measured. Correlations (r(2)) of BMC, as determined by DXA with dry weight, ash weight, and bone calcium content, were 0.978, 0.988, and 0.890, respectively. DXA overestimated ash weight by 5%-9%. Precision errors for BMC (BMD) were 0.90% (0.76%) without and 1.3 (0.86) with repositioning. Changes in the salinity of the water bath had a significant influence on the DXA results: At the 0.9% physiological level, BMC (-4.4%) and area (-4.1%), but not BMD, values were significantly lower (p < 0.005) compared with measurements in tap water. Fan beam DXA is a highly accurate and precise technique for measuring BMC and BMD in excised small animal bones. A physiological saline concentration in the water bath had a significant impact on BMC and area, but not on BMD, and should therefore be strictly controlled to avoid an underestimation of BMC.

Absorptiometry, Photon↗

PubMed2002

Diagnostic agreement of two calcaneal ultrasound devices: the Sahara bone sonometer and the Achilles+.

Quantitative ultrasound for the assessment of skeletal status is an evolving method in the diagnosis of osteoporosis. In this cross-sectional study we investigated the diagnostic agreement between the Sahara bone sonometer and the Achilles+ with respect to broadband ultrasound attenuation (BUA), speed of sound (SOS) and stiffness/quantitative ultrasound index (QUI). 309 healthy females without diseases or medications known to influence bone metabolism (with the exception of oestrogen) were recruited at two participating centers (Erlangen and Berlin). 33% of subjects were taking oestrogens. There was no significant difference in BUA, SOS, and stiffness/QUI between oestrogen and non-oestrogen takers. In vivo precision (expressed as root mean square coefficient of variation) was calculated from two repeat measurements and analyzed in both centres. Mean values were 1.57% (BUA Achilles+), 3.64% (BUA Sahara), 0.35% (SOS Achilles+), 0.39% (SOS Sahara), 2.22% (stiffness Achilles+) and 3.04% (QUI Sahara). Between the two devices we observed a strong correlation for SOS (r=0.89, p<0.01) and stiffness/QUI (r=0.83, p<0.01), and a moderate correlation for BUA (r=0.68, p<0.01). All parameters were moderately negatively associated with age (r=-0.38 to -0.48; p<0.01 for all correlations). Kappa (kappa) scores used to report diagnostic agreement were calculated for tertiles and "equivalent T-scores". The tertiles divide the cohort on both scanners into the same number of subjects above and below a given T-score. Diagnostic agreement using tertiles was poor to moderate (kappa< or =0.51). Diagnostic agreement using equivalent T-score agreement, again, was poor to moderate for BUA but fair to good for SOS and stiffness/QUI (0.59< or =kappa< or =0.73). We conclude that diagnostic agreement between the two devices is at best comparable to the agreement of a dual X-ray absorptiometry measurement using the same densitometer at two different skeletal sites. It is therefore insufficient to compare directly two measurements of an individual patient on both ultrasound devices. Standardization of quantitative ultrasound is very much needed.

Adult↗

PubMed2001

Structural analysis of high resolution in vitro MR images compared to stained grindings.

The recent advancement of high resolution magnetic resonance imaging has opened up new avenues for the determination of structural characteristics of the trabecular network, which may significantly improve the diagnosis of osteoporosis. An analysis of the calcaneus in healthy women has shown similar age-related changes when comparing structural parameters in high resolution MR images and BMD as measured by DXA [1]. Here we undertook an in vitro study to further compare structural measurements in MR images with those from stained grindings. A 3D gradient echo sequence on a 1.5 T scanner was used to obtain four contiguous sagittal MR images with a slice thickness of 1 mm and an in plane pixel size of 195 microns. Twenty-one stained grindings with a slice thickness of 1 micron each were obtained from a 3 mm thick slab of the same volume investigated by MR. The stack of stained grindings was also used to simulate the influence of variations in slice thickness and in plane resolution. Results for structural parameters derived from the high resolution MR images differed considerably from those derived from the stained grindings because the MR images are heavily influenced by partial volume artifacts. This finding was supported by simulations which also revealed that even at a slice thickness of 500 microns and an in plane pixel size of 13 microns, accurate results could not be obtained when a histomorphometric type analysis was applied. Results also depended strongly on the segmentation method. However, contrary to the stained grindings, images averaged over several slices reveal the three-dimensional network character of the trabecular structure. New efforts should be undertaken to develop analysis strategies that are more adequate for in vivo high resolution images instead of using analysis techniques applied in classical histomorphometry.

Cadaver↗

PubMed2001

Stereolithographic models simulating trabecular bone and their characterization by thin-slice- and micro-CT.

The analysis of bone structure in vivo is an important goal in osteoporosis, because the determination of bone mineral density alone is insufficient to predict whether an individual patient will eventually suffer an osteoporotic fracture or not. An additional structural analysis may significantly improve the statistical assessment of fracture risk. In this study we present a method to generate realistic although enlarged 3D phantoms of trabecular bone. These phantoms are useful in characterizing the potential of in vivo imaging procedures for the analysis of bone structure and to verify textural or structural analysis methods applied to these images. Our phantoms are based on a real trabecular bone specimen that was converted to a plastic model using the technique of stereolithography. The trabecular network is modeled by hydroxyapatite. Limitations of the stereolithographic process prevent the generation of exact 1:1 replicas of the real bone. A histomorphometric analysis of microCT scans of the phantoms showed that an excellent replication of the bone structure could be achieved in phantoms enlarged by a factor of 2.5 with "trabecular" hydroxyapatite concentrations up to 400 mg/cm3. In order to demonstrate the usefulness of our phantoms, we investigated one of them with various thin-slice CT protocols using clinical single- and multi-slice spiral CT scanners. The enlargement of the phantoms limits their use on high spatial resolution CT scanners (resolution >20 lp/cm). The limited hydroxyapatite concentration requires enhanced exposure rates for the phantoms scans to offset the larger impact of noise due to the lower contrast in the phantoms.

Bone and Bones↗

PubMed2001

Implementation of a cone-beam reconstruction algorithm for the single-circle source orbit with embedded misalignment correction using homogeneous coordinates.

We present an efficient implementation of an approximate cone-beam image reconstruction algorithm for application in tomography, which accounts for scanner mechanical misalignment. The implementation is based on the algorithm proposed by Feldkamp et al. and is directed at circular scan paths. The algorithm has been developed for the purpose of reconstructing volume data from projections acquired in an experimental x-ray micro-tomography (microCT) scanner. To mathematically model misalignment we use matrix notation with homogeneous coordinates to describe the scanner geometry, its misalignment, and the acquisition process. For convenience analysis is carried out for x-ray CT scanners, but it is applicable to any tomographic modality, where two-dimensional projection acquisition in cone beam geometry takes place, e.g., single photon emission computerized tomography. We derive an algorithm assuming misalignment errors to be small enough to weight and filter original projections and to embed compensation for misalignment in the backprojection. We verify the algorithm on simulations of virtual phantoms and scans of a physical multidisk (Defrise) phantom.

Algorithms↗

PubMed1999

[Micro-CT. Technology and application for assessing bone structure].

The strength and fracture resistance of bone is determined by the structure of the trabecular network and the cortical shell. While standard 2D techniques like histomorphometry are inadequate to assess the 3D nature of the trabecular network, isotropic 3D datasets of this network can be acquired with the new imaging modality of microCT. However, so far the quantitative analysis of the generated datasets, in particular the extraction of appropriate parameters describing the bone structure, has not been finally solved. In this article we describe the technology and applications of microCT systems relevant in the field of osteology. The most important technical features of current microCT systems in this context are: 1. A spatial resolution down to 5-10 microns can be achieved. 2. The maximum sample size is related to the desired resolution by a factor of approximately 1000, that is, a resolution of 10 microns limits the maximum sample size to approximately 1 cm. 3. Scan times for microCT systems vary between minutes and hours. Currently five areas for the application of microCT systems in osteology can be identified: 1. The search of parameters characterizing the 3D trabecular structure. 2. The application of finite element models to determine the biochemical competence of the structural parameters. 3. The use of microCT in preclinical trials to study drug effects in small animals. 4. The validation of analysis methods used in high-resolution in-vivo imaging systems. 5. The 3D quantification of modeling and remodeling processes.

Adult↗

PubMed1999

Accuracy limits for the determination of cortical width and density: the influence of object size and CT imaging parameters.

In this study we analysed the accuracy of computed tomography (CT) measurements in assessing cortical bone. We determined the dependency of thickness and density measurements on the true width and density of the cortex and on the spatial resolution in the CT images using two optimized segmentation methods. As a secondary goal, we assessed the ability of CT to reflect small changes in cortical thickness. Two different bone-mimicking phantoms with varying cortical thickness were scanned with single-slice CT on a Somatom Plus 4 scanner. Images were reconstructed with both a standard and a high-resolution convolution kernel. Two special operator-independent segmentation methods were used to automatically detect the edges of the cortical shell. We measured cortical thickness and density and compared the phantom measurements with theoretical computations by simulating a cross-sectional shape of the cortical shell. Based on the simulations, we calculated CT's power to detect small changes in cortical thickness. Simulations and phantom measurements were in very good agreement. Cortical thickness could be measured with an error of less than 10% if the true thickness was larger than 0.9 (0.7) mm for the standard (high-resolution) kernel which is close to the full width at half maximum (FWHM) of the point spread functions for these kernels and our scanner. Density measurements yielded errors of less than 10% for true cortical thickness values above two to three times the FWHM corresponding to 2.5 (2) mm in our case. The simulations showed that a 10% change in cortical width would not be detected with satisfying probability in bones with a cortical shell thinner than 1.2 mm. An accurate determination of the cortical thickness is limited to bones with a thickness higher than the FWHM of the scanner's point spread function. Therefore, the use of a high-resolution reconstruction kernel is crucial. Cortical bone mineral density can only be measured accurately in bones two to three times thicker than this number. In thinner bones, the measured density becomes dependent on the thickness. Changes in cortical thickness can only be assessed if the change is rather large or if the measured bone has sufficient thickness. Therefore, assessing density or thickness of the vertebral shell by CT should be treated with caution.

Bone Density↗

PubMed1998

Accuracy and diagnostic sensitivity of radiographic absorptiometry of the second metacarpal.

The accuracy of a radiographic absorptiometry (RA) technique called digital image processing (DIP), discriminative ability of RA for osteoporotic fracture, and the relationship between RA and dual X-ray absorptiometry (DXA) of the spine and forearm were evaluated. We measured 16 cadaver hands, 32 healthy non-black premenopausal women, 39 healthy non-black postmenopausal women, and 35 non-black osteoporotic postmenopausal females. The overall correlation between the ash weights of the entire metacarpal and the DIP values was excellent (r = 0.954, P < 0.001, SEE = 0.14, CV = 6.4%). Short-term precision error of DIP was 3.5%. Age-related bone loss determined by DIP is comparable to that of spinal and forearm DXA: annual BMD decreases were 0.46% for DIP, 0.45% for forearm, and 0.32% for the spine. DIP of the 2nd metacarpal shows a gradient of risk for spinal fracture only slightly below that of forearm DXA, but substantially below that of spinal DXA. Age-adjusted odds ratios were 1.81 for RA, 2.45 for spinal DXA, and 1.94 for forearm DXA.

Absorptiometry, Photon↗

PubMed1997

High resolution magnetic resonance imaging of the calcaneus: age-related changes in trabecular structure and comparison with dual X-ray absorptiometry measurements.

A high-resolution magnetic resonance imaging (MRI) protocol, together with specialized image processing techniques, was applied to the quantitative measurement of age-related changes in calcaneal trabecular structure. The reproducibility of the technique was assessed and the annual rates of change for several trabecular structure parameters were measured. The MR-derived trabecular parameters were compared with calcaneal bone mineral density (BMD), measured by dual X-ray absorptiometry (DXA) in the same subjects. Sagittal MR images were acquired at 1.5 T in 23 healthy women (mean age: 49.3 +/- 16.6 [SD]), using a three-dimensional gradient echo sequence. Image analysis procedures included internal gray-scale calibration, bone and marrow segmentation, and run-length methods. Three trabecular structure parameters, apparent bone volume (ABV/TV), intercept thickness (I.Th), and intercept separation (I.Sp) were calculated from the MR images. The short- and long-term precision errors (mean %CV) of these measured parameters were in the ranges 1-2% and 3-6%, respectively. Linear regression of the trabecular structure parameters vs. age showed significant correlation: ABV/TV (r2 = 33.7%, P < 0.0037), I.Th (r2 = 26.6%, P < 0.0118), I.Sp (r2 = 28.9%, P < 0.0081). These trends with age were also expressed as annual rates of change: ABV/TV (-0.52%/year), I.Th (-0.33%/year), and I.Sp (0.59%/year). Linear regression analysis also showed significant correlation between the MR-derived trabecular structure parameters and calcaneal BMD values. Although a larger group of subjects is needed to better define the age-related changes in trabecular structure parameters and their relation to BMD, these preliminary results demonstrate that high-resolution MRI may potentially be useful for the quantitative assessment of trabecular structure.

Absorptiometry, Photon↗

PubMed1997

Assessment of osteoporosis: comparison of radiographic absorptiometry of the phalanges and dual X-ray absorptiometry of the radius and lumbar spine.

PURPOSE: To evaluate radiographic absorptiometry (RA) of the phalanges in healthy women and in women with osteoporosis and to compare the results of RA with those of dual x-ray absorptiometry (DXA) of the radius and spine. MATERIALS AND METHODS: Thirty-two healthy premenopausal women, 39 healthy postmenopausal women, and 35 postmenopausal women with osteoporosis underwent RA of the phalanges and DXA of the radius and lumbar spine. Pairwise comparisons, age-related bone losses, and percentage decrements and Student t values for intergroup discrimination were calculated. The ability to identify patients with osteoporotic fractures was evaluated by using receiver operating characteristic and age-adjusted logistic regression analyses. The diagnostic agreement for osteoporosis was assessed with kappa statistics. RESULTS: Findings from RA were correlated with those from spinal DXA (r = .56). The annual bone losses in healthy women, as measured with RA, radial DXA, and spinal DXA, were 0.47%, 0.47%, and 0.32%, respectively. Intergroup percentage decrements and t values obtained with RA were comparable to those obtained with radial and with spinal DXA. Receiver operating characteristic analysis showed no statistically significant differences. The odds ratios for RA, radial DXA, and spinal DXA were 2.1, 1.9, and 2.4, respectively. The kappa scores were 0.44 for both RA versus radial DXA and RA versus spinal DXA, and the score was 0.22 for radial DXA versus spinal DXA. CONCLUSION: RA appears to be a useful technique for assessing age- and menopause-related bone loss and for identifying women with osteoporosis.

Absorptiometry, Photon↗