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PubMed2004

Fundamentals and pitfalls of bone densitometry using dual-energy X-ray absorptiometry (DXA).

Measurement of bone mineral density (BMD) with central dual-energy X-ray absorptiometry (DXA) is the current "gold standard" for diagnosing osteoporosis and for monitoring patients. Errors in demographic information, improper patient positioning, incorrect scan analysis, and mistakes in interpretation can all lead to a wrong clinical decision or action. This paper reviews the fundamentals of positioning, scan analysis, and interpretation for central DXA and highlights some of the common pitfalls that may lead to erroneous results.

Absorptiometry, Photon↗
PubMed2004

Comparison between the Klemetti index and heel DXA BMD measurements in the diagnosis of reduced skeletal bone mineral density in the elderly.

Osteopenia/osteoporosis affect many elderly people and might not be detected until symptoms of fractures occur. Early detection of osteopenia/osteoporosis is important and would allow preventive measures and treatment. Access to screening for osteopenia/osteoporosis is often limited, whereas panoramic radiography is commonly used in dentistry. The aim of this study was to determine the validity of the Klemetti index (KI), measured on panoramic radiographs, in the diagnosis of osteopenia/osteoporosis as defined by a bone mineral density (BMD) measurement below -1.5 standard deviations (SDs) of a community based sample. In total, 211 consecutive participants (102 men and 109 women) 60-96 years in the SNAC-Blekinge study (Swedish National Study on Ageing and Care) underwent bone densitometry [by dual-energy X-ray absorptiometry (DXA)] of both heels. A panoramic radiograph was taken of each participant, and mandibular cortex on a panoramic radiograph was classified as '0' or normal (even and sharp endosteal margin), '1', moderately eroded (evidence of lacunar resorption or endosteal cortical residues), or '2', severely eroded (unequivocal porosity). From logistic regression, the odds ratio of having a BMD measurement below -1.5 SD was 8.04 (95% CI 2.39 to 27.12, P<0.001) in the 'osteopenic' (KI category 2), compared with the 'normal' group (KI categories 0 and 1). Receiver operating characteristic (ROC) curve analysis was used to measure the validity of the KI indicating osteopenia (KI category 2) in predicting reduced BMD. This point provided a sensitivity of 50% and a specificity of 89%. Positive and negative predictive values were 21% and 97%, respectively. There were 87% correctly classified subjects. The area under the ROC curve was 0.64. The present study demonstrated that a negative finding (KI category <2) is highly predictive of the absence of osteopenia/osteoporosis as defined by the DXA measurements.

Absorptiometry, Photon↗
PubMed2000

Long-term precision of DXA scanning assessed over seven years in forty postmenopausal women.

The reproducibility of dual-energy X-ray absorptiometry (DXA) measurements of bone mineral density (BMD) is an important factor for longitudinal studies. We assessed the long-term precision of posteroanterior lumbar spine, femoral neck and total hip BMD in 40 postmenopausal women who formed the control arm of a clinical trial of tibolone. BMD was measured at 0, 6 and 12 months and thereafter every 12 months up to 7 years. For each subject the trend of BMD with time was analyzed using linear regression. Each residual was expressed as the percentage difference from predicted BMD and the validity of assuming linear change with time was checked using the mean residuals for each visit number. For spine BMD a chi-squared test showed that the mean residuals were not statistically significantly different from zero. Although statistically significant deviations from linearity were found for the femoral neck and total hip sites the weighted root mean square residuals were small compared with the precision errors. When residuals were binned into histograms a statistical test for skewness was not significant for all three sites. However, a test for kurtosis yielded a statistically significant result for each histogram due to outlying residuals. To determine the standard deviation (SD) of the core gaussian distribution, outliers were trimmed using the method of Melton et al. For lumbar spine BMD outliers with residuals exceeding +/- 3 SD arose mainly from subjects with a body mass index (BMI) >28 kg/m(2) or from subjects who had undergone a large change in BMI during the study. For femoral neck BMD and total hip BMD the outliers were frequently due to inconsistent rotation of the hip. Results for long-term precision calculated from the standard deviation of residuals using the trimmed (untrimmed) data were: lumbar spine BMD, 1.12% (1.65%); femoral neck BMD, 2.21% (2.48%); and total hip BMD, 1.32% (1.57%). These errors were only slightly worse than short-term errors despite changes of DXA scanner during the course of the study. However, obesity may have an adverse effect on precision errors in individual patients and particular care is necessary to ensure reproducible patient positioning for femur scans.

Absorptiometry, Photon↗
PubMed1998

Correlation of femoral and lumbar DXA and calcaneal ultrasound, measured in situ with intact soft tissues, with the in vitro failure loads of the proximal femur.

The objective of this study was to determine experimentally the sex-specific correlation of femoral and lumbar DXA and calcaneal ultrasound, measured in situ, with the in vitro failure loads of the proximal femur. Fifty-eight cadavers with intact skin and soft tissues (34 male, aged 81.2 +/- 8.7 years; 24 female, aged 83.7 +/- 10.6 years) were examined. The bone mass of the proximal femur and the lumbar spine were determined using dual-energy X-ray absorptiometry and the ultrasonic properties of the calcaneus with quantitative ultrasound. Afterwards, the right femora were excised 18 cm distal to the minor trochanter, and their load to failure determined with a material testing machine. Femoral fracture loads were significantly higher in males than in females, both before and after correcting for body height and weight. Femoral neck bone mineral density (BMD) was significantly correlated with femoral failure loads (r = 0.65 all specimens, 0.57 males (0.64 after excluding trochanteric fractures) and 0.77 females; p < 0.001). The correlations with the ultrasonic Stiffness Index of the calcaneus were in a similar range (r = 0.67 all specimens, 0.48 males (0.64 after excluding trochanteric fractures) and 0.65 females; p < 0.001). The correlations between femoral failure loads and the spinal BMD were lower (r = 0.40, p < 0.01), particularly in males (r = 0.30, not significant). In contrast to previous experimental investigations on excised bones, our results are consistent with clinical studies that have reported that ultrasound and femoral DXA have a similar ability to predict the risk of hip fracture.

Absorptiometry, Photon↗
PubMed1999

In vivo MRI measurements of bone quality in the calcaneus: a comparison with DXA and ultrasound.

Magnetic resonance imaging (MRI) has shown promise in the assessment of bone architecture. The precision and feasibility of MRI measurements in osteoporosis in vivo have been assessed in this study. T2' was calculated from measurements of T2 and T2* in the calcaneus of 32 postmenopausal women using a gradient-echo sequence PRIME (Partially Refocused Interleaved Multiple Echo). This sequence allows the measurement of T2 and T2* in one acquisition. In vivo measurements of bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA) were made in the calcaneus, spine and femoral neck. The ultrasound parameters broadband ultrasound attenuation (BUA) and speed of sound (SOS) were also measured in the calcaneus. These three techniques have not previously been compared in the same study population. The precision of the MRI technique was poor relative to the DXA and ultrasound techniques, with a CV of 6.9% +/- 4.4% for T2' and 5.5% +/- 3.6% for T2*. Approximately 4% of this is due to system error as determined by phantom measurements. The postmenopausal women were classified as having low BMD if they had a lumbar spine (L2-4) BMD of less than 0.96 g/cm2 (more than 2 standard deviations below normal peak bone mass). Calcaneal T2' was significantly correlated with calcaneal BMD (r = -0.79, p < 0.0001), BUA (r = -0.59, p = 0.0004) and SOS (r = -0.58, p = 0.0006). T2' was significantly different in postmenopausal women with normal BMD and those with low BMD (p < 0.01). However, the difference was of only borderline significance (p < 0.06) after adjustment for age and years since menopause.

Absorptiometry, Photon↗
PubMed2001

Reproducibility of DXA: potential impact on serial measurements and misclassification of osteoporosis.

The reproducibility of bone mineral density (BMD) measurements by dual-energy X-ray absorptiometry (DXA), based on 12 successive monthly determinations, was assessed in a group of 24 subjects (23 postmenopausal women, 1 man) using six trained operators. The variability (S2A) was calculated from both duplicate operator measurements and the standard error of estimate from nonparametric regression of the individual subject series. Robust estimates of SA from the 90th percentile of the sampling distribution of variances were calculated for the spine (25 mg/cm2), femur neck (20 mg/cm2) and total femur (15.5 mg/cm2) using the bootstrap technique. The critical difference for a significant decrease (p = 0.05) at the spine, femoral neck and total femur was estimated at 57, 46 and 36 mg/cm2 respectively. Estimation of S2A allowed calculation of the probability that the true BMD, for an observed BMD near the osteoporosis diagnostic threshold (T-score < -2.5), is not misclassified. Analysis of covariance established a significant operator-subject interaction at all sites, but only the total femur was associated with a significant difference between operators. The percentage of body fat was a significant covariate for the spine and total femur regions. ANOVA showed that the greater proportion of variance was instrument-related. The limitations of DXA as an analytical method are discussed.

Absorptiometry, Photon↗
PubMed2001

Ability of peripheral DXA measurements of the forearm to predict low axial bone mineral density at menopause.

The aim of this study was to evaluate the ability of peripheral dual-energy X-ray absorptiometry (pDXA) measurement of the forearm to predict low axial bone mineral density (BMD) as defined according to the WHO classification. Two hundred and thirty-four healthy women aged 45-60 years were investigated. BMD was measured at the proximal and distal radius + ulna by pDXA and at the lumbar spine and femoral neck by DXA. There was a significant but moderate correlation between peripheral and axial BMD measurements, with r values ranging from 0.4 to 0.6 (SEE: 13.5-17%). The cutoff values for the proximal and distal radius BMD that allow the identification with 95% sensitivity of postmenopausal women with either a lumbar spine or femoral neck T-score < -1, corresponded to a T-score of +0.5 (proximal radius) and +1 (distal radius). More than 90% of the whole population had a peripheral T-score below these thresholds. Using an axial T-score < or = -2.5 as the definition of abnormality reduced to 48% (proximal radius) to 66% (distal radius) the number of women who would have required DXA axial measurements (i.e., with a pDXA T-score below the cutoff value of -0.7). Of the 33 women (14%) with a proximal radius T-score < or = -2.5 (osteoporosis), only 1 had a lumbar spine and femoral neck T-score > or = -1 (normal). Conversely, of the 50% (proximal radius) to 65% (distal radius) of the women with normal forearm measurement, 5% (proximal radius) to 9% (distal radius) were found to be osteoporotic and an additional 57% (proximal radius) to 59% (distal radius) could be classified as osteopenic (T-score between -1 and -2.5) at either the lumbar spine or femoral neck. In conclusion, use of pDXA forearm measurement as a prescreening tool in early postmenopausal women should allow the direct identification of about 50% of the women with no axial osteoporosis. However, this study highlights the difficulties in using a unique T-score that could be applied to different sites to diagnose osteoporosis.

Absorptiometry, Photon↗
PubMed2002

Hip fracture risk and proximal femur geometry from DXA scans.

In this retrospective study of hip fracture risk evaluation from hip dual-energy X-ray absorptiometry (DXA) scans, our objectives were to determine which part of the femoral neck length contributes most to the fracture risk and to define a geometric parameter better than hip axis length (HAL) for discriminating hip fracture patients. Forty-nine Caucasian women with a nontraumatic femoral neck fracture were matched on age to 49 normal women and on both age and femoral neck bone mineral density (BMD) to 49 unfractured women. In addition to BMD, geometric parameters including neck-shaft angle, neck width and several HAL segments were evaluated by discriminant analysis to determine which was the best hip fracture discriminator. Neck-shaft angle had a limited influence on the hip fracture risk. Age-related bone loss was associated with a neck width increase in unfractured and fractured patients. HAL was significantly longer in fractured patients and was a significant discriminator between fractured patients and normal controls. HAL was not significant as a discriminator between fractured and low-BMD unfractured patients. The intertrochanter-head center distance (from the intertrochanteric line to the femoral head center) coincides with the femoral lever arm and includes no segments that adapt to BMD changes, such as the greater trochanter-intertrochanter distance. Among all tested lengths, this segment was the part of HAL that discriminated best between fractured and low-BMD unfractured patients. A longer intertrochanter-head center distance increased the risk of femoral neck fracture among low-BMD patients. Including automatic measurement of this segment in standard DXA protocols may prove useful in identifying patients at high risk for hip fracture. At present, HAL remains the easier neck length to measure, but automatic evaluation of the intertrochanter-head center distance must be a goal for future image analysis development.

Absorptiometry, Photon↗
PubMed2003

Pattern of periprosthetic bone remodeling around stable uncemented tapered hip stems: a prospective 84-month follow-up study and a median 156-month cross-sectional study with DXA.

Bone resorption in the proximal femur is commonly seen after total hip arthroplasty (THA). With dual energy X-ray absorptiometry (DXA), the amount of bone mass (BMD) after implantation of a total hip stem can be precisely determined. However, prospective evaluation of the change of bone mass around the stem is only available for selected stems and short-term follow-up (up to 36 months). We analyzed BMD in patients who had undergone uncemented THA by DXA. Only patients with good clinical outcome (Merle d' Aubigné score > 12) were included to obtain normative data for regular bone response. Two separate studies were performed: a prospective longitudinal study over 84 months with baseline values acquired within the first postoperative week (group A) (n = 26 patients) and a separate cross-sectional study, median follow-up 156 (124-178) months (group B) (n = 35 patients). Regions of interest were defined according to Gruen (ROI 1-7) and as net average ROI (net avg) for the periprosthetic femoral bone. After the initial remodeling process (12 months), BMD was compared to the 84-month (longitudinal) and the 156-month (cross-sectional) follow-up values to determine long-term periprosthetic changes of bone mineral density. The longitudinal study (group A), after the initial bone remodeling, showed no relevant further bone loss for women and men with BMD values 1.19 +/- 0.15 and 1.40 +/- 0.19, respectively, 12 months (women 89.8%, men 93.6%), and 1.19 +/- 0.13 and 1.36 +/- 0.18, respectively, after 84 months (women 90.0%, men 91.3%) (P = 0.98, P = 0.08,) respectively. The distribution of the BMD around the stem changed during the first 12 months. The ROIs around the proximal stem (ROI 1 and 7) showed the lowest absolute values at the 12-month follow-up and BMD in ROI 7 decreased most during the further follow-up until 84 months. The cross-sectional study (group B) showed no significant difference in BMD (net avg) values at a median of 156 months follow-up compared to the 12-month values (group A) (women: P = 0.77, men: P = 0.44). Initial BMD, implant diameter, and body mass index did not influence BMD loss (net avg) in this study, whereas age showed a weak correlation with BMD loss. The results show that after the initial remodeling process, no relevant further bone loss (net avg) occurs up to 84 months postsurgery, and values after a median of 156 months are similar. Normative long-term changes in the periprosthetic bone can be demonstrated in defined ROIs after implantation of a tapered corundum-blasted titanium stem with a good clinical result.

Absorptiometry, Photon↗
PubMed2001

Effect of fixation, soft-tissues, and scan projection on bone mineral measurements with dual energy X-ray absorptiometry (DXA).

The objective of this study was to determine the effect of fixation, soft tissues, and scan projection on bone mineral measurements with dual energy X-ray absorptiometry (DXA). In seven fresh cadavers, DXA scans were obtained within 48 hours of death and after 10 months of fixation with 5% formalin/95% ethanol. The measurements showed a high linear relationship (r2 > 0.97; SEE% < 10%), with no significant deviation after fixation (except for total body BMD: -3.1%). In 14 specimens, the precision of femoral and spinal analyses was determined under in situ and ex situ conditions. There was no significant difference between ex situ and in situ reproducibility, the coefficient of variation being < 3% for the BMC and < 2% for the BMD (except at the greater trochanter). The effect of the soft tissues and scan projection was assessed in 83 cadavers aged 80.4 +/- 10.3 years. The soft tissues had only a small effect on analyses of the total femur (r2 > 0.90; SEE% < 9%), but led to more substantial deviations in regional femoral analyses and in the spine (r2 = 0.78-0.90; SEE% = 8-22%). Comparing lateral with anterior-posterior (AP) spinal scans, the vertebral bodies were found to occupy 40.2 +/- 7.2% of the BMC, and 62.0 +/- 11.2% of the BMD, the ranges being 26-58%, and 38-91%, respectively. There were large deviations from linearity between in situ AP and ex situ lateral spinal scans with r2 values of 0.63 and 0.73 for BMD and BMC (SEE% = 52% and 27% relative to the vertebral body), respectively.

Absorptiometry, Photon↗
PubMed1996

Replacing DXA scanners: cross-calibration with phantoms may be misleading.

The high precision and stable calibration of dual X-ray absorptiometry (DXA) has led to its widespread use in clinical trials of new therapies for osteoporosis. Daily scanning of phantoms provides a check on the continuity of the bone mineral density (BMD) calibration and allows for correction of minor changes. However, because clinical trials may last up to 5 years, it is likely that the scanner will need replacing during the course of a study. We report the upgrade of a Hologic QDR-2000 to a QDR-2000plus. The new scanner was cross-calibrated with the old according to the manufacturer's instructions using the Hologic spine phantom. The accuracy of cross-calibration was checked by in vivo scans of patients in clinical trials and also using the European spine phantom (ESP). Daily QC scans with the Hologic phantom over the 6-week period of the in vivo study showed that the new scanner agreed within 0.2% with the old. However, in vivo scans at 10 sites in the spine, hip, total body, and forearm showed significant mismatch between the two systems with five sites differing by more than 2%. Results for the ESP phantom lay closer to the in vivo spine data than the Hologic phantom. The mismatch revealed was larger than anticipated and emphasized the importance of performing adequate in vivo cross-calibration studies whenever DXA systems are replaced. Typically, scans of 20-30 subjects are required at each scan site to achieve an accuracy of 1%. Such studies require careful planning and make significant demands on space, patient cooperation, scanning time, scientific resources, and, not least, the implementation of the findings.

Absorptiometry, Photon↗
PubMed2004

A DXA study of muscle-bone relationships in the whole body and limbs of 2512 normal men and pre- and post-menopausal women.

A whole-body DXA study of 1450 healthy Caucasian individuals [Bone 22 (1998) 683] found that mineral mass, either crude (BMC) or statistically adjusted to fat mass (FM-adjusted BMC), correlated linearly with lean mass (LM, proportional to muscle mass). The results showed similar slopes but decreasing intercepts (ordinate values) in the order: pre-MP women > men > post-MP women > children. This supports the hypothesis that sex hormones influence the control of bone status by muscle strength in all species. Now we further study those relationships in 2512 healthy Hispanic adults (307 men, 753 pre-MP women, 1452 post-MP women), including separate determinations in their upper and lower limbs. The slopes of the BMC or FM-adjusted BMC vs. LM relationships were parallel in all the studied regions. However, region-related differences were found between the ordinates of the curves. In the whole body, the crude-BMC/LM relationships showed the same ordinate differences as previously observed. In the lower limbs, those differences were smaller in magnitude but highly significant, showing the order: pre-MP women > men = post-MP women. In the upper limbs, the decreasing ordinate order was: men > pre-MP women > post-MP women. After fat adjustment of the BMC, order in both limbs was: men > pre-MP women > post-MP women. Parallelism of the curves was maintained in all cases. LM had a larger independent influence on these results than FM, body weight, or age. The parallelism of the curves supports the idea that a common biomechanical control of bones by muscles occurs in humans. Results suggest that sex-hormone-associated differences in DXA-assessed muscle-bone proportionality in humans could vary according to the region studied. This could be related to the different weight-bearing nature of the musculoskeletal structures studied. Besides the obvious anthropometric associations, FM would exert a mechanical effect as a component of body weight, evident in the lower limbs, while muscle contractions would induce a more significant, dynamical effect in both lower and upper limbs. Muscles seem to exert a larger influence than FM, body weight, and age on BMC in the whole body and lower limbs, regardless of the gender and reproductive status of the individual. The muscle-bone relationships studied may provide a rationale for a future differential diagnosis between disuse-related and other types of osteopenia.

Absorptiometry, Photon↗
PubMed2004

Does follow-up duration influence the ultrasound and DXA prediction of hip fracture? The EPIDOS prospective study.

While the potential of quantitative ultrasound (QUS) in the management of osteoporosis has been accepted, its interaction with follow-up time has never been investigated. The aim of our study is to prospectively evaluate the influence of follow-up time on the prediction of hip fracture by ultrasound parameters in the elderly as compared to bone mineral density (BMD) and to establish a long-term fracture prediction model. In the multicenter prospective study EPIDOS, 5898 Caucasian healthy women, aged 75 and over, had femoral dual-energy X-ray absorptiometry (DXA) and heel ultrasound measurements at baseline. A survey of fracture occurrence was conducted every 4 months. Statistical analyses were performed for three different average lengths of follow-up, namely, 1.5, 2.5 and 3.5 years. Relative risks per standard deviation decrease (RR) and the area under the receiver operating characteristic (AUC) curves were given. Estimates of the long-term hip fracture prediction by DXA and QUS were extrapolated. During an average of 3.5 years follow-up, 227 women sustained their first non-traumatic hip fracture. For the three categories of follow-up, low values of both calcaneal ultrasound and hip BMD were associated with a significant increased risk of hip fracture [e.g. ultrasound Stiffness index RR = 2.8 (2.1-3.8), 2.1 (1.7-2.6) and 1.9 (1.7-2.3) for 1.5, 2.5 and 3.5 years of follow-up, respectively]. The combination of femoral neck BMD with the Stiffness showed an improvement of the hip fracture prediction model. Using extrapolation, the prediction of hip fracture by the Stiffness remained significant up to 7.5 years [RR = 1.2 (1.03-1.41)], whereas the limit of significance was reached at 10 years for the femoral neck BMD [RR = 1.25 (1.04-1.52)]. Our results indicate that the Stiffness tends to be the best short- and long-term predictor of hip fracture among ultrasound parameters. This paper provides additional information on the long-term prediction of hip fracture, which has always been an important issue in routine clinical practice as it influences the management of the disease. Our model should give a relatively good estimation of the fracture risk prediction at 5 years with the ultrasound and 10 years for the femoral neck BMD.

Absorptiometry, Photon↗
PubMed2005

Dual X-ray absorptiometry (DXA) of the lumbar spine in a clinical paediatric setting: does the method of size-adjustment matter?

UNLABELLED: Dual X-ray absorptiometry (DXA) is increasingly used in a clinical setting to evaluate bone mass in children. Areal Bone Mineral Density (aBMD) measurements are known to be influenced by body size, but there is no consensus on the optimal way to deal with this for individual patients. AIM: To compare parameters of bone mass with varying degrees of size correction and to determine the effect on the categorisation of patients as normal or abnormal. SUBJECTS AND METHODS: Healthy children (n = 78) and 4 groups of patients (n = 194) underwent DXA scans of the lumbar spine (L2-4, GE Lunar Prodigy). Five measures of bone mass were derived, all adjusted for age and sex: aBMD, BMAD (BMC/BA (1.5)), BMCh (BMC/height3), BMCa (BMC adjusted for BA), BMCt (BMC adjusted for BA and height). SD scores were calculated for each parameter for patients using data from healthy controls. RESULTS: Compared to healthy children, all patient groups had significantly reduced BMD SD scores (P < 0.001). Mean BMAD, BMCa and BMCt SD scores were significantly lower in only 2/4 patient groups, whilst BMCh SD scores were low only in one group. BMCt showed no advantage over BMCa. The proportion of patients with SD scores <-2 was 27% for aBMD but between 10-13% for BMAD, BMCh and BMCa. CONCLUSIONS: All size-corrected parameters of bone mass performed similarly and classified significantly fewer patients as abnormal than did aBMD. The use of one of these parameters should reduce the number of patients diagnosed inappropriately with 'low bone mass'. However, without validation against an outcome measure or 'gold standard' of bone density or structure, it is not possible to determine which parameter is most correct.

Absorptiometry, Photon↗
PubMed2005

The use of micro-CT to evaluate cortical bone geometry and strength in nude rats: correlation with mechanical testing, pQCT and DXA.

In both clinical and experimental settings, access to quantitative methods enabling the objective evaluation of cortical bone mass, structure, geometry and strength are essential for the assessment of efficacy and safety of different treatments aimed to improve bone strength. The ability of non-invasive methodologies (DXA, pQCT and micro-CT) to assess and quantify cortical bone mass and geometry was tested in a nude rat model in which bone loss was induced by surgical castration. Treatment with a bone antiresorptive (alendronate) or a bone forming (PTH) drug was used to: (A) validate the nude rat model in terms of bone metabolism, (B) test the ability of each technology to detect change in cortical bone geometry and (C) correlate cortical bone geometry with bone strength data obtained by 3-point bending method. Our observations regarding effect of castration and treatment with PTH and alendronate on cortical bone parameters in nude rats is in general agreement with previously published data obtained in immunocompetent male rats under similar experimental conditions. Data presented here support the hypothesis that nude rats have similar bone physiology and response to known bone therapies to that observed in normal rats and therefore could be effectively used to predict skeletal response in humans. All three technologies deployed in this study (DXA, pQCT and micro-CT) proved useful in describing cancellous and/or cortical bone parameters and positive correlations were demonstrated between data obtained by different methods. The cross-sectional area of a bone structure is crucial for resisting loads in bending or torsion and is described as "areal moment of inertia" for bending, and as "polar moment of inertia" in torsion. Novel, three-dimensional micro-CT methodology used in this study to assess geometry of cortical bone provides data that accurately describes cortical bone geometry and parallels cortical bone strength results obtained by the 3-point bending method. Our micro-CT data meet the criteria of providing quick, reproducible and accurate answers regarding cortical bone geometry as a predictor of cortical bone strength.

Absorptiometry, Photon↗
PubMed2006

Between-centre variability versus variability over time in DXA whole body measurements evaluated using a whole body phantom.

This study aimed to compare the variability of whole body measurements, using dual energy X-ray absorptiometry (DXA), among geographically distinct centres versus that over time in a given centre. A Hologic-designed 28 kg modular whole body phantom was used, including high density polyethylene, gray polyvinylchloride and aluminium. It was scanned on seven Hologic QDR 4500 DXA devices, located in seven centres and was also repeatedly (n=18) scanned in the reference centre, over a time span of 5 months. The mean between-centre coefficient of variation (CV) ranged from 2.0 (lean mass) to 5.6% (fat mass) while the mean within-centre CV ranged from 0.3 (total mass) to 4.7% (total area). Between-centre variability compared well with within-centre variability for total area, bone mineral content and bone mineral density, but was significantly higher for fat (p<0.001), lean (p<0.005) and total mass (p<0.001). Our results suggest that, even when using the same device, the between-centre variability remains a matter of concern, particularly where body composition is concerned.

Absorptiometry, Photon↗
PubMed2006

Antecedent 99mTc-MDP and 99mTc-sestamibi administration corrupts bone mineral density measured by DXA.

Previous reports of the effect of antecedent administration of radionuclide on bone mineral density (BMD) measurements have yielded inconsistent results. Ten subjects scheduled for (99m)Tc-methylene diphosphonate ((99m)Tc-MDP) bone scanning and 10 scheduled for (99m)Tc-sestamibi cardiac scanning had BMD measured by dual X-ray absorptiometry (DXA) (GE/Lunar) before and within 5 hours of diagnostic radionuclide injection. Paired t test and Wilcoxon-signed rank tests were used to compare the measured differences in BMD at multiple skeletal sites. Differences were subjected to multivariate analysis of demographic factors. Mean change in measured BMD following (99m)Tc-sestamibi administration (DeltaBMD-(99m)Tc-sestamibi) was -0.216+/-0.113 g/cm(2) at the total body and -0.348+/-0.300 g/cm(2) at the lumbar spine (p<0.005). Mean change in measured BMD following (99m)Tc-MDP administration (DeltaBMD-(99m)Tc-MDP) was -0.058+/-0.037 g/cm(2) at the total body and -0.053+/-0.049 g/cm(2) at the lumbar spine (p<0.05). Mean DeltaBMD-(99m)Tc-sestamibi exceeded least significant change (LSC) in all skeletal sites except the femoral trochanter. Mean DeltaBMD-(99m)Tc-MDP exceeded LSC only at the lumbar spine. The effect was correlated with (99m)Tc dose but not with gender, age, body mass index, baseline BMD, or time interval from injection to scan acquisition. In conclusion, BMD measured by the GE/Lunar Prodigy densitometer is corrupted by antecedent (99m)Tc-sestamibi and to a lesser extent by (99m)Tc-MDP. This effect is greater at the total body and lumbar spine than at the hip. Caution is warranted in scheduling and interpreting DXA studies when (99m)Tc has been recently administered.

Absorptiometry, Photon↗
PubMed2006

Comparison of body composition measurements obtained by two fan-beam DXA instruments.

Although dual-energy X-ray absorptiometry (DXA) has been widely used for measuring body composition, discrepancies have been reported to exist among results obtained from different instruments. In the course of longitudinal studies lasting for many years, old instruments may be required to be replaced with new ones, necessitating comparison and validation between the values obtained by the old and new instruments. We compared the data obtained by the two fan-beam DXA instruments, QDR-2000 (Hologic, Waltham, MA) and Delphi (Hologic). Body composition was first measured by the Hologic QDR-2000 and next by the Delphi W within 30 days in 99 healthy subjects. Whole-body fat mass (FM), percentage of FM, arm FM, and leg FM measured by the Hologic QDR-2000 were significantly larger than those measured by the Delphi W. Lean tissue mass (LTM), bone mineral content, and bone mineral density of the whole body, trunk FM, arm LTM, and leg LTM measured by the QDR-2000 were significantly smaller than those measured by the Delphi W. After converting the QDR-2000 values by equations developed by multiple regression analysis, they were not significantly different from the corresponding Delphi values. Measurements by the QDR-2000 and the Delphi W were not interchangeable and the conversion equations reduced the discrepancy to a level that enabled direct comparison of the data obtained by the two instruments. However, cautious interpretation is necessary when the conversion equations are applied to other instruments even of the same type or when evaluating data of individual subjects.

Absorptiometry, Photon↗