Dual-energy x-ray absorptiometry scanner mismatch in follow-up bone mineral density testing.

Scanner mismatch occurs frequently with follow-up dual-energy x-ray absorptiometry (DXA) scans. Nearly one-in-five follow-up DXA scans were conducted on non-cross-calibrated scanners (scanner mismatch) and more than a quarter of patients who had a follow-up DXA scan had experienced scanner mismatch. INTRODUCTION: Detecting significant changes in bone mineral density (BMD) with dual-energy x-ray absorptiometry (DXA) scanners relies on the least significant change (LSC). Results from two different DXA scanners can only be compared, albeit with decreased sensitivity for change, if the LSC between the two scanners has been directly determined through cross-calibration. Performing follow-up DXA scans on non-cross-calibrated scanners (scanner mismatch) has safety and economic implications. This study aims to determine the proportion of scanner mismatch occurring at a population level. METHODS: All patients who completed at least two DXA scans between 1 April 2009 and 31 December 2018 in the province of Alberta, Canada, were identified using population-based health services databases. Scanner mismatch was defined as a follow-up DXA scan completed on a DXA scanner that differed from and was not cross-calibrated to the previous DXA scanner. Multivariate logistic regression models were used to assess predictive factors that may contribute to scanner mismatch. RESULTS: A total of 264,866 patients with 470,641 follow-up DXA scans were identified. Scanner mismatch occurred in 18.9% of follow-up DXA scans; 28.7% of patients experienced at least one scanner mismatch. Longer duration between scans (OR 1.25, 95% CI 1.24-1.26) and major osteoporotic fracture history before index scan (OR 1.06, 95% CI 1.03-1.08) increased risk of scanner mismatch. Osteoporosis medication use before index scan (OR 0.89; 95% CI 0.88-0.91), recency of follow-up scans (OR 0.98, 95% CI 0.73-0.98), female sex (OR 0.97, 95% CI 0.94-1.00), and age at last scan (OR 0.99, 95% CI 0.99-1.00) were associated with lower risk of scanner mismatch. CONCLUSION: Scanner mismatch is a common problem, occurring in one-in-five follow-up DXA scans and affecting more than a quarter of patients. Interventions to reduce this large proportion of scanner mismatch are necessary.

Short-Term Precision Error of Bone Strain Index, a New DXA-Based Finite Element Analysis Software for Assessing Hip Strength.

Bone Strain Index (BSI) is a new finite element analysis tool applied to hip dual energy X-ray absorptiometry scans. The aim of this study was to assess the short-term precision error of BSI on the proximal femur, both on a phantom and patients. The International Society for Clinical Densitometry guidelines were followed for short-term precision error assessment. Dual energy X-ray absorptiometry measurements were performed on an anthropomorphic femur phantom that was scanned twice for 30 times, for a total of 60 scans. For the in vivo part, 30 subjects were scanned twice. BSI precision error was compared to that of bone mineral density (BMD). Both for the phantom and the in vivo study BSI reproducibility was lower compared to that of BMD, as the precision error of BSI resulted 3 times higher compared to that BMD. For phantom measurements, the highest precision value was that of total femur (TF) BMD (coefficient of variation [CoV] = 0.63%, reproducibility = 98.24%), while the lowest precision was the femoral neck (FN) BSI (CoV = 3.08%, reproducibility = 91.48%). Similarly, for the in vivo study, the highest precision was found at TF BMD (CoV = 1.36%, reproducibility = 96.22%), while the lowest value of precision was found for FN BSI (CoV = 4.17%, reproducibility = 88.46%). Reproducibility at TF was always better compared to that of the FN. BSI precision error was about 3 times higher compared to BMD, confirming previous results of lumbar spine BSI. The main source of variability of this new software is related to patient positioning.

Added values of DXA-derived visceral adipose tissue to discriminate cardiometabolic risks in pre-pubertal children.

BACKGROUND: The new generation of dual energy X-ray absorptiometry (DXA) scanners provide visceral adipose tissue (VAT) estimates by applying different algorithms to the conventional DXA-derived fat parameters such as total fat, trunk fat and android fat for the same image data. OBJECTIVE: This cross-sectional study aimed to investigate whether VAT estimates from Hologic scanners are better predictors of VAT than conventional DXA parameters in pre-pubertal children, and to explore the discrimination ability of these VAT methods for cardiometabolic risks. METHODS: Healthy pre-pubertal children aged 7-10 years were recruited for basic anthropometric, DXA and magnetic resonance imaging (MRI) measurements. Laboratory tests included lipid profile, glycaemic tests and blood pressure. RESULTS: All VAT methods had acceptable to excellent performance for the diagnosis of dyslipidaemia (area under the curve [AUC] = 0.753-0.837) and hypertensive risk (AUC = 0.710-0.821) in boys, but suboptimal performance for these risks in girls, except for VAT by MRI in the diagnosis of dyslipidaemia. In both sexes, all VAT methods had no or poor discrimination ability for diabetes risk. CONCLUSIONS: DXA-derived VAT estimates are very highly correlated with standard methods but has equivalent discrimination abilities compared to the existing DXA-derived fat estimates.

Deriving pQCT-Type Spatial Density from DXA Images.

INTRODUCTION: Musculoskeletal overuse injuries are a serious problem in the military, particularly in basic combat training, resulting in hundreds of millions of dollars lost because of limited duty days, medical treatment, and high rates of reinjury. Injury risk models have been developed using peripheral computed tomography (pQCT)-based injury correlates. However, pQCT image capture on large number of recruits is not practical for military settings. Thus, this article presents a method to derive spatial density pQCT images from much lower resolution but more accessible dual-energy X-ray absorptiometry (DXA). MATERIALS AND METHODS: Whole-body DXA images and lower leg pQCT images for 51 male military recruits were collected before a 40-day School of Infantry. An artificial neural network model was constructed to relate the DXA density profiles to spatial pQCT density at the 38% and 66% tibial locations. RESULTS: Strong correlation, R2 = 0.993 and R2 = 0.990 for the 38% and 66% pQCT slices, respectively, was shown between spatial density predicted by the artificial neural network model and raw data. CONCLUSIONS: High potential exists to create a practical protocol using DXA in place of pQCT to assess stress fracture risk and aid in mitigating musculoskeletal injuries seen in military recruits.

Cross-calibration, Least Significant Change and Quality Assurance in Multiple Dual-Energy X-ray Absorptiometry Scanner Environments: 2019 ISCD Official Position.

In preparation for the International Society for Clinical Densitometry Position Development Conference (PDC) 2019 in Kuala Lumpur, Malaysia, a cross-calibration and precision task force was assembled and tasked to review the literature, summarize the findings, and generate positions to answer 4 related questions provided by the PDC Steering Committee, which expand upon the current ISCD official positions on these subjects. (1) How should a provider with multiple dual-energy X-ray absorptiometry (DXA) scanners of the same make and model calculate least significant change (LSC)? (2) How should a provider with multiple DXA systems with the same manufacturer but different models calculate LSC? (3) How should a provider with multiple DXA systems from different manufacturers and models calculate LSC? (4) Are there specific phantom procedures that one can use to provide trustworthy in vitro cross calibration for same models, different models, and different makes? Based on task force deliberations and the resulting systematic literature reviews, 3 new positions were developed to address these more complex scenarios not addressed by current official positions on single scanner cross calibration and LSC. These new positions provide appropriate guidance to large multiple DXA scanner providers wishing to offer patients flexibility and convenience, and clearly define good clinical practice requirements to that end.

Technological Advances in Diagnostic Imaging in Exotic Pet Medicine.

Diagnostic imaging relies on interpretation of interactions between the body tissue and various energies, such as x-rays, ultrasound, and magnetic or nuclear energies, to differentiate normal from abnormal tissues. Major technological improvements regarding emission and detection of the energetic waves, as well as reconstruction and interpretation of the images, have occurred. These advances made possible visualization of smaller structures, quantitative evaluation of functional processes, and development of unique imaging-guided procedures. This article reviews the technological advances that allowed development of cone beam computed tomography, dual-energy x-ray absorptiometry, and contrast-enhanced ultrasonography, which all could have applications in exotic pet medicine.

Usefulness of Reflection Scanning in Determining Whole-Body Composition in Broadly Built Individuals Using Dual-Energy X-ray Absorptiometry.

Whole-body composition analysis by dual-energy X-ray absorptiometry (DXA) requires subjects to fit within the width limits of the DXA bed. To overcome this limitation, the aim of this study was to validate a partial scanning technique at which the upper left limb is deliberately left unscanned and measurements are "reflected" from the right-side upper limb. A Hologic Explorer-W densitometer was used in a sample of 189 participants, including athletes and nonathletes, ranging from underweight to obese (body mass index: 17.0-40.1 kg/m2). A whole-body scan was analyzed as the reference procedure to determine bone mineral content (BMC), lean soft tissue (LST), and fat mass (FM), and reanalyzed using a partial reflection scanning (RS) technique. RS estimates of BMC were associated with athletic status and differed significantly from reference estimates (p < 0.05). Also, the RS estimates of LST and FM were different (p < 0.05) from those of the reference whole-body scan, although differences were small (0.17 kg, -0.02 kg, and -0.10% for BMC, LST, and FM, respectively). The alternative procedure explained more than 99% of the reference scan variance with low limits of agreement (BMC: -13.8 to 23.9 g [athletes] and -6.3 to 18.0 g [nonathletes]; LST: -0.11 to 0.45 kg; FM: -0.22 to 0.17 kg). Regardless of body mass index, athletic status, and gender, RS is a useful and simple solution to be used in individuals wider than the DXA scan area. However, individual errors for BMC may be higher in athletes engaged in lateral dominant sports practice.

A Novel Morphological Analysis of DXA-DICOM Images by Artificial Neural Networks for Estimating Bone Mineral Density in Health and Disease.

One of the best methods for diagnosing bone disease in humans is site-specific and total bone mineral density (BMD) measurements by Dual-energy X-ray Absorptiometry (DXA) machines. The basic disadvantage of this technology is inconsistent BMD measurements among different DXA machines from different manufacturers due to different image analysis algorithms. The objective of the present study was to apply artificial neural networks (ANNs) to estimate total BMD for diagnosing a population of Egyptians with and without pathology, using extracted features from DXA-DICOM images based on the Histogram and Binary algorithms as compared to reference BMD measurements by DXA machine. The sample size comprised 3000 male and female participants with an age range 22-49 years, who were referred to us for diagnosis and/or treatment and for DXA total body scans in the period from January 2016 till December 2017. We constructed an entry computer data-logging visible unit, where we applied morphological operations to get a specific bone image, and used their extracted feature vectors as inputs to ANNs with cascade training, gathering, and testing for DXA-DICOM image processing. The multilayer feed-forward ANN set up its initial weights, carried out training and initiated the recall mode, and finally observed its decision and interaction based on estimated BMD. The ANN construction was carried out using a 3-layer architecture, with one hidden layer of 85 neurons. The input layer has neuron numbers equal to 256 for the Histogram and 77,365 for Binary algorithms, respectively. Total BMD estimation performance based on the Binary algorithm was capable of identifying all DXA-DICOM images with an accuracy of 100% for the training, cross-validation, and testing of the ANN phases. We believe this strategy will represent the means for standardizing bone measurements of all DXA machines, regardless of the manufacturer.

The impact of analytical variation of hemoglobin measurement on blood donors' hemoglobin and deferral rates.

BACKGROUND: Donors' hemoglobin (Hb) level must be tested before blood donation. Low Hb is the leading reason for donor deferral. Many donor-related and external factors associated with low Hb are known, but no studies have been conducted concerning the effects of analytical variation on donor Hb measurements and deferrals. STUDY DESIGN AND METHODS: The effects of donors' age, the seasonal and daily distribution of donations, and batch-to-batch variation in HemoCue Hb 201+ cuvettes on donors' capillary Hb (cHb) measurements and deferrals were analyzed for more than 1.7 million donor visits in 2010 to 2016 at a national blood establishment. Furthermore, approximately 3.1 million cHb measurements from the years 2000 to 2009 were included in analyses to correlate measured cHb value and Hb deferral rate. RESULTS: A significant correlation between the mean annual cHb and Hb deferral rate was observed in both women and men. The season of the donation was the strongest explanatory factor for the monthly variation of predonation cHb (explaining 25 and 31% of the variation in women and men, respectively). Batch-to-batch variation in HemoCue cuvettes explained 6.8% of monthly variation in women and 7.4% in men. Monthly changes in donors' age distribution explained 2.5% of monthly variation in women and 2.4% in men. CONCLUSION: Small and, in most clinical settings, negligible analytical variation in Hb measurement methods can have significant consequences when used for Hb screening of blood donors. This should be minimized by using methods in which analytical variation is under control and kept as low as possible.

Agreement between dual x-ray absorptiometers using pencil beam and fan beam: indicators of bone health and whole-body plus appendicular tissue composition in adult athletes.

OBJECTIVE: The current study was aimed to examine intra-individual variation on indicators of bone health in addition to whole-body plus appendicular tissue measurements using two concurrent assessments based on pencil beam and fan beam dual energy X-ray absorptiometry (DXA) systems in adult athletes from several sports. METHOD: Thirty-two male participants (27.6±10.1 years) were measured on anthropometry including multifrequency bioelectric impedance and air-displacement plethysmography. Bone mineral content (BMC), bone area, fat and lean soft tissue were derived using pencil beam (Lunar DPX-MD+) and fan beam (Lunar iDXA) absorptiometry. Bone mineral density (BMD) was obtained for the femoral neck, trochanter and triangle of ward. Finally, the right thigh was defined as a region of interest (ROI). Analyses comprised intra-class correlation (ICC), Effect size (d) from mean differences of repeated measurements, coefficient of variation (CV). RESULTS: ICC were >0.900 for all measurements. Intra-individual differences were large for BMC (d=1,312; CV=2,7%), bone area (d=1,761; CV=2,7%), fat tissue (d=1,612; CV=11%) and all indicators of appendicular lean soft tissue (d=1,237-1687; CV=2,0-4,1%). A very large difference (d=4,014; CV=8.4%) was diagnosed for lean soft tissue of the ROI. CONCLUSION: Although differences among concurrent instruments for BMC and bone area, the effect size of mean differences was negligible for BMD. Fat and lean soft tissue derived from DXA should be interpreted as reference values (not criterion) due to equipment-related variation, more apparently in the ROI values.

Calibration of an on-line dual energy X-ray absorptiometer for estimating carcase composition in lamb at abattoir chain-speed.

This experiment assessed the ability of an on-line dual energy x-ray absorptiometer (DEXA) installed at a commercial abattoir to determine carcase composition at abattoir chain-speed. 607 lamb carcases from 7 slaughter groups were DEXA scanned and then scanned using computed tomography to determine the proportions of fat (CT fat%), lean (CT lean%), and bone (CT bone%). Data between slaughter groups were standardised relative to a synthetic phantom consisting of Nylon-6. Models were then trained within each dataset using hot carcase weight and DEXA value to predict CT composition, and then validated in the remaining datasets. Results from across-dataset validation tests demonstrated excellent precision for predicting CT fat%, with RMSE and R2 values of 1.32 and 0.89, compared to values of 1.69 and 0.69 for CT lean%, and 0.81 and 0.68 for CT bone% which had less precision. Accuracy across datasets was also robust, with average bias values of 0.66, 0.83, and 0.51 for CT fat%, lean%, and bone%.

Evaluation of Bone Mineral Density Using DXA and cQCT in Postmenopausal Patients Under Thyrotropin Suppressive Therapy.

Purpose: This study aimed to examine the discrepancy in osteoporosis diagnoses between central quantitative computed tomography (cQCT) and dual-energy X-ray absorptiometry (DXA) and evaluated correlations among volumetric bone mineral density (vBMD), areal bone mineral density (aBMD), and trabecular bone score(TBS) in postmenopausal women who were undergoing TSH suppressive therapy. Methods: We enrolled a total of 81 postmenopausal patients [median age: 58 years; interquartile range (IQR): 57 to 60 years] receiving TSH suppressive therapy with levothyroxine after undergoing total thyroidectomy for papillary thyroid cancer. Patients were diagnosed by their bone mineral density (BMD) T-score and categorized according to a vBMD threshold of 120 mg/cm3 for osteopenia and a threshold of 80 mg/cm3 for osteoporosis. Results: When DXA and cQCT were compared, the BMD evaluation results differed in 76% of patients (n = 62; P < 0.001), and the detection rate of osteoporosis was 30.9% for cQCT and 21.0% for DXA. Sixty-two patients had discordant results; in 46 of these patients (74%) whose DXA T-scores were normal, the diagnosis shifted to osteopenia (n = 35) and osteoporosis (n = 11) according to the vBMD on cQCT (P < 0.001), and their vBMD values were significantly correlated with TBS (r = 0.293; P = 0.008). However, aBMD was not significantly correlated with TBS (r = 0.080; P = 0.480). TBS was significantly lower in patients with osteopenia (median: 1.35; IQR: 1.18 to 1.47) and osteoporosis (median: 1.28; IQR: 1.07 to 1.47) than in those with a normal BMD value (median: 1.37; IQR: 1.25 to 1.49; P = 0.041) on cQCT. There was no significant difference in TBS according to DXA BMD status (P = 0.200). Conclusions: DXA and cQCT yielded inconsistent results, and detection of osteopenia and osteoporosis was higher using cQCT. TBS showed a more significant correlation with vBMD than with aBMD.

Increasing soft tissue thickness does not affect trabecular bone score reproducibility: a phantom study.

PURPOSE: Trabecular Bone Score (TBS) provides an indirect score of trabecular microarchitecture from lumbar spine (LS) dual energy X-ray absorptiometry. Increasing soft tissue thickness artifactually reduces TBS values; we evaluated the effect of a fictitious increase of soft tissue thickness on TBS and bone mineral density (BMD) reproducibility on a phantom model. METHODS: A Hologic spine phantom was scanned with a QDR-Discovery W Hologic densitometer. Fresh pork rind layers of 5 mm were used to simulate the in-vivo soft tissues. For each scan mode (fast array [FA], array, high definition [HD]), 25 scans were consecutively performed without phantom repositioning, at 0 (no layers), 1 cm, 3 cm, and 6 cm of thickness. BMD and TBS reproducibility was calculated as the complement to 100% of least significant change. RESULTS: Both BMD and TBS reproducibility slightly decreased with increasing soft tissue; this difference was statistically significant only for BMD using HD modality (reproducibility decreased from 99.4% at baseline to 98.4% at 6-cm of thickness). TBS reproducibility was slightly lower compared to that of BMD, and ranged between 98.8% (array, 0 cm) and 97.4% (FA, 6 cm). Without taking into account manufacturer BMI optimization, we found a progressive decrease of TBS mean values with increasing soft tissue thickness. The highest TBS difference between baseline scan and 6 cm was -0.179 (-14.27%) using HD. CONCLUSIONS: Despite being slightly lower than that of BMD, TBS reproducibility was not affected up to 6 cm of increasing soft tissue thickness, and was even less influenced by fat than BMD reproducibility.

Agreement between dual x-ray absorptiometers using pencil beam and fan beam: indicators of bone health and whole-body plus appendicular tissue composition in adult athletes

SUMMARY OBJECTIVE: The current study was aimed to examine intra-individual variation on indicators of bone health in addition to whole-body plus appendicular tissue measurements using two concurrent assessments based on pencil beam and fan beam dual energy X-ray absorptiometry (DXA) systems in adult athletes from several sports. METHOD: Thirty-two male participants (27.6±10.1 years) were measured on anthropometry including multifrequency bioelectric impedance and air-displacement plethysmography. Bone mineral content (BMC), bone area, fat and lean soft tissue were derived using pencil beam (Lunar DPX-MD+) and fan beam (Lunar iDXA) absorptiometry. Bone mineral density (BMD) was obtained for the femoral neck, trochanter and triangle of ward. Finally, the right thigh was defined as a region of interest (ROI). Analyses comprised intra-class correlation (ICC), Effect size (d) from mean differences of repeated measurements, coefficient of variation (CV) RESULTS: ICC were >0.900 for all measurements. Intra-individual differences were large for BMC (d=1,312; CV=2,7%), bone area (d=1,761; CV=2,7%), fat tissue (d=1,612; CV=11%) and all indicators of appendicular lean soft tissue (d=1,237-1687; CV=2,0-4,1%). A very large difference (d=4,014; CV=8.4%) was diagnosed for lean soft tissue of the ROI. CONCLUSION: Although differences among concurrent instruments for BMC and bone area, the effect size of mean differences was negligible for BMD. Fat and lean soft tissue derived from DXA should be interpreted as reference values (not criterion) due to equipment-related variation, more apparently in the ROI values.

RESUMO OBJETIVO: O presente estudo examinou a concordância entre os indicadores de saúde óssea e composição tecidual resultantes da aplicação de equipamentos concorrentes de absorciometria de raios X de dupla energia (DXA). MÉTODO: A amostra (n = 32), com 27,6 ± 10,1 anos de idade avaliados antropometricamente, inclui impedância bioelétrica com multifrequência e pletismografia de ar deslocado. O conteúdo mineral ósseo (CMO), a área de tecido ósseo, o tecido magro e o tecido gordo de corpo inteiro foram obtidos considerando o modo pencil beam (Lunar DPX-MD+) e o fan beam (Lunar iDXA). Para cada um dos equipamentos, foi efetuado um scanner proximal do fêmur, sendo produzida informação sobre a densidade mineral óssea (DMO) do colo, nomeadamente triângulo de Ward, trocanter e haste. Na fase de processamento, foi definida uma região de interesse (ROI; coxa direita). As análises compreenderam a diferença de médias de medidas repetidas com cálculo da magnitude de efeitos (d), coeficiente de correlação intraclasse (CCI), coeficiente de variação (CV). RESULTADOS: Foram obtidos CCI>0,900 para todas as medidas, com diferenças intraindividuais largas apenas para CMO (d = 1,312; CV = 2,7%), área de tecido ósseo (d = 1,761; CV = 2,7%), tecido gordo total (d = 1,612; CV = 11%) e tecido magro em todos os segmentos (d = 1,237-1,687; CV = 2,0-41%). A massa magra da ROI apresentou uma variaçāo intraindividual muito larga (d = 4,014; CV = 8,4%). CONCLUSÃO: Foram encontradas diferenças negligenciáveis para a DMO de corpo todo. As medidas de massa gorda e massa magra obtidas por DXA nāo devem ser tidas como critério, mas antes como referenda, muito especialmente quando se delimita uma ROI.

Denoising images of dual energy X-ray absorptiometry using non-local means filters.

BACKGROUND: In general, the image quality of high and low energy images of dual energy X-ray absorptiometry (DXA) suffers from noise due to the use of a small amount of X-rays. Denoising of DXA images could be a key process to improve a bone mineral density map, which is derived from a pair of high and low energy images. This could further improve the accuracy of diagnosis of bone fractures and osteoporosis. OBJECTIVE: This study aims to develop and test a new technology to improve the quality, remove the noise, and preserve the edges and fine details of real DXA images. METHODS: In this study, a denoising technique for high and low energy DXA images using a non-local mean filter (NLM) was presented. The source and detector noises of a DXA system were modeled for both high and low DXA images. Then, the optimized parameters of the NLM filter were derived utilizing the experimental data from CIRS-BFP phantoms. After that, the optimized NLM was tested and verified using the DXA images of the phantoms and real human spine and femur. RESULTS: Quantitative evaluation of the results showed average 24.22% and 34.43% improvement of the signal-to-noise ratio for real high and low spine images, respectively, while the improvements were about 15.26% and 13.55% for the high and low images of the femur. The qualitative visual observations of both phantom and real structures also showed significantly improved quality and reduced noise while preserving the edges in both high and low energy images. Our results demonstrate that the proposed NLM outperforms the conventional method using an anisotropic diffusion filter (ADF) and median techniques for all phantom and real human DXA images. CONCLUSIONS: Our work suggests that denoising via NLM could be a key preprocessing method for clinical DXA imaging.

Estimates of the precision of regional and whole body composition by dual-energy x-ray absorptiometry in persons with chronic spinal cord injury.

STUDY DESIGN: Repeated measures design. OBJECTIVES: To determine the reproducibility of total-body and regional-body composition assessments from a total-body scan using dual-energy x-ray absorptiometry (DXA) in persons with spinal cord injury (SCI). METHODS: Twenty-four individuals with SCI completed within-day short-term precision testing by repositioning study participants between scans. An additional and separate cohort of 22 individuals with SCI were scanned twice on a GE-Lunar DXA scanner separated by a 4-week interval to assess the long-term precision assessment. The root mean square coefficient of variation percent (RMS-CV%) values for the regional and total body composition was calculated. RESULTS: For the same day, short-term precision assessment, the RMS-CV% for each region did not exceed 5.6, 2.7, 3.8, 6.5, 5.8, and 2.3% for arms, legs, trunk, android and gynoid regions, and total body mass, respectively. In the long-term precision assessment, the RMS-CV% for each region did not exceed 6.0, 3.0, 4.4, 8.2, 3.4, and 2.0% for arms, legs, trunk, android, gynoid, and total body mass. Moreover, the interclass-correlation coefficient in the long-term precision group demonstrated excellent linear agreement between repeat scans for all regions (r > 0.97). CONCLUSIONS: The precision error of the total body composition variables in our SCI cohort was similar to those reported in the literature for nondisabled individuals, and the precision errors of the regional body composition compartments were notably higher, but similar to the regional precision errors reported in the general population.

Short term in vivo precision of whole body composition measurements on the Horizon A densitometer.

INTRODUCTION: Dual-energy X-ray absorptiometry (DXA) is increasingly being used to assess abnormalities in body composition associated with a wide variety of conditions including obesity, sarcopenia, diabetes, anorexia, human immunodeficiency virus lipodystrophy, malabsorption and neuromuscular disorders. The objective of this study was to determine the short-term in vivo precision and least significant change in serial body composition measurements provided by the Hologic Horizon A densitometer as there is no published, peer reviewed body composition precision data on Horizon scanners in the medical literature. METHODS: After acquiring two new Hologic Horizon A densitometers, short term precision scanning was performed on the two scanners using different groups of 30 volunteers, who had duplicate scans with all scans performed by the same operator. Using the International Society of Clinical Densitometry's advanced precision tool, the scan data were recorded and the coefficient of variation (CV) and least significant change (LSC) determined for total fat, lean and bone mineral content (BMC) and bone mineral density (BMD). RESULTS: Coefficients of variation of 0.78% and 0.77% were achieved for total fat (LSC at 95% confidence 2.15%) and 0.52% and 0.40% for total lean (LSC at 95% confidence 1.45% and 1.11%). CONCLUSIONS: These results indicate that the two Horizon A scanners in this study exceeded the minimum acceptable precision values by roughly a factor of four and are therefore capable of detecting small differences in lean and fat mass of 1-2% between two measurements at 95% confidence.

Enhanced Precision of the New Hologic Horizon Model Compared With the Old Discovery Model Is Less Evident When Fewer Vertebrae Are Included in the Analysis.

The International Society for Clinical Densitometry guidelines recommend using locally derived precision data for spine bone mineral densities (BMDs), but do not specify whether data derived from L1-L4 spines correctly reflect the precision for spines reporting fewer than 4 vertebrae. Our experience suggested that the decrease in precision with successively fewer vertebrae is progressive as more vertebrae are excluded and that the precision for the newer Horizon Hologic model might be better than that for the previous model, and we sought to quantify. Precision studies were performed on Hologic densitometers by acquiring spine BMD in fast array mode twice on 30 patients, according to International Society for Clinical Densitometry guidelines. This was done 10 different times on various Discovery densitometers, and once on a Horizon densitometer. When 1 vertebral body was excluded from analysis, there was no significant deterioration in precision. When 2 vertebrae were excluded, there was a nonsignificant trend to poorer precision, and when 3 vertebrae were excluded, there was significantly worse precision. When 3 or 4 vertebrae were reported, the precision of the spine BMD measurement was significantly better on the Hologic Horizon than on the Discovery, but the difference in precision between densitometers narrowed and was no longer significant when 1 or 2 vertebrae were reported. The results suggest that (1) the measurement of in vivo spine BMD on the new Hologic Horizon densitometer is significantly more precise than on the older Discovery model; (2) the difference in precision between the Horizon and Discovery models decreases as fewer vertebrae are included; (3) the measurement of spine BMD is less precise as more vertebrae are excluded, but still quite reasonable even when only 1 vertebral body is included; and (4) when 3 vertebrae are reported, L1-L4 precision data can reasonably be used to report significance of changes in BMD. When 1 or 2 vertebrae are reported, precision data for 1 or 2 vertebrae, respectively, should be used, because the exclusion of 2-3 vertebrae significantly worsens precision.

Assessment of the effect of strontium, lead, and aluminum in bone on dual-energy x-ray absorptiometry and quantitative ultrasound measurements: A phantom study.

PURPOSE: Dual-energy X-ray absorptiometry (DXA) is the gold standard technique to measure areal bone mineral density (aBMD) for the diagnosis of osteoporosis. Because DXA relies on the attenuation of photon to estimate aBMD, deposition of bone-seeking metallic elements such as strontium, lead, and aluminum that differ in atomic numbers from calcium can cause inaccurate estimation of aBMD. Quantitative ultrasound (QUS) is another technique available to assess bone health by measuring broadband ultrasound attenuation (BUA), speed of sound (SOS), and an empirically derived quantity called stiffness index (SI). Because the acoustic properties are not prone to significant change due to changes in microscopic atomic composition of bone, it is hypothesized that QUS is unaffected by the presence of bone-seeking elements in the bone. The objective of this study was to investigate the effect of strontium, lead, and aluminum on DXA-derived aBMD and QUS parameters using bone-mimicking phantoms compatible with both techniques. METHODS: Bone-mimicking phantoms were produced by homogeneously mixing finely powdered hydroxyapatite compounds that contain varying concentrations of strontium, lead, or aluminum with porcine gelatin solution. Seven strontium-substituted phantoms were produced with varying molar ratio of Sr/(Sr + Ca) ranging from 0% to 2%. Four lead-doped phantoms and four aluminum-doped phantoms were constructed with the respective analyte concentrations ranging from 50 to 200 ppm. An additional 0 ppm phantom was produced to be used as a baseline for the lead and aluminum phantom measurements. All phantoms had uniform volumetric bone mineral density (vBMD) of 200 mg/cm3 , and were assessed using a Hologic Horizon® DXA device and a Hologic Sahara® QUS device. Furthermore, theoretical aBMD bias for mol/mol% substitution of calcium with the three bone-seeking elements was calculated. RESULTS: Strong positive linear relationship was found between aBMD measured by DXA and strontium concentration (P < 0.001, r = 0.995). From the measurement of lead and aluminum phantoms using DXA, no statistically significant relationship was observed between aBMD and the analyte concentrations. For the QUS system, with an exception of BUA and lead concentration that exhibited statistically significant relationship (P < 0.038, r = 0.899), no statistically significant change was observed in all QUS parameters with respect to the clinically relevant concentration of all three elements. The calculated theoretical aBMD bias induced by 1 mol/mol% substitution of calcium with strontium, lead, and aluminum were 10.8%, 4.6%, and -0.7%, respectively. CONCLUSION: aBMD measured by DXA was prone to overestimation in the presence of strontium, but acoustic parameters measured by QUS are independent of strontium concentration. The deviation in aBMD induced by the clinically relevant concentrations of lead and aluminum under 200 ppm could not be detected using the Hologic Horizon® DXA device. Furthermore, the SI measured by the QUS system was not affected by lead or aluminum concentrations used in this study.

Direct Comparison of the Precision of the New Hologic Horizon Model With the Old Discovery Model.

Previous publications suggested that the precision of the new Hologic Horizon densitometer might be better than that of the previous Discovery model, but these observations were confounded by not using the same participants and technologists on both densitometers. We sought to study this issue methodically by measuring in vivo precision in both densitometers using the same patients and technologists. Precision studies for the Horizon and Discovery models were done by acquiring spine, hip, and forearm bone mineral density twice on 30 participants. The set of 4 scans on each participant (2 on the Discovery, 2 on the Horizon) was acquired by the same technologist using the same scanning mode. The pairs of data were used to calculate the least significant change according to the International Society for Clinical Densitometry guidelines. The significance of the difference between least significant changes was assessed using a Wilcoxon signed-rank test of the difference between the mean square error of the absolute value of the differences between paired measurements on the Discovery (Δ-Discovery) and the mean square error of the absolute value of the differences between paired measurements on the Horizon (Δ-Horizon). At virtually all anatomic sites, there was a nonsignificant trend for the precision to be better for the Horizon than for the Discovery. As more vertebrae were excluded from analysis, the precision deteriorated on both densitometers. The precision between densitometers was almost identical when reporting only 1 vertebral body. (1) There was a nonsignificant trend for greater precision on the new Hologic Horizon compared with the older Discovery model. (2) The difference in precision of the spine bone mineral density between the Horizon and the Discovery models decreases as fewer vertebrae are included. (3) These findings are substantially similar to previously published results which had not controlled as well for confounding from using different subjects and technologists.