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PubMed1998

Analytic and quantitative exposition of patient-specific systematic inaccuracies inherent in planar DXA-derived in vivo BMD measurements.

An extensive analytic exposition is developed of systematic inaccuracies inherent in planar dual-energy x-ray absorptiometry (DXA) in vivo bone mineral density (BMD) measurements arising directly from the dual-energy facet of this methodology. Generalized and specific criteria governing these BMD inaccuracies are derived for the presence of relevant absorptiometrically distinguishable extra- and intra-osseous soft tissues (lean muscle tissue, interposed adipose, marrow, and cerebrospinal fluid). These analytic findings are utilized in comprehensive quantitative simulation studies which evaluate the magnitude and stipulate the direction (under- or over-estimate) of such systematic errors for typical, realistic DXA in vivo lumbar vertebral BMD scans over the ranges of soft tissue parameters and trabecular bone volumes (TBV) encountered clinically. It is shown that inherent systematic inaccuracies as high as +/- approximately 20% may be anticipated in typical patient-specific planar DXA vertebral BMD scans, particularly so for older, osteoporotic-prone, and osteoporotic individuals. These inaccuracies exceed considerably the DXA precision error and may mask or exaggerate clinically significant true changes in BMD. Both the scale and trends of patient-specific inaccuracies found to pertain in the present work are in keeping with those observed by recent investigators in actual specimen-specific in situ and in vitro DXA scans of given cadaveric bones. Insofar as the range of BMD inaccuracies found here is comparable to that of variations in the DXA-measured interpatient, age-moderated BMD of normal individuals, the intrinsic specificity of planar DXA for screening/diagnostic purposes is examined critically. It is shown that these inherent inaccuracies may prompt erroneous diagnoses, assessments, and interpretations of DXA-derived BMD measurements undertaken to screen, monitor, and help evaluate patient-specific predictive bone fragility, and to assess the efficacy of drug and other therapeutic regimens.

Absorptiometry, Photon↗
PubMed1999

Comparison of accuracy and cost effectiveness of clinical criteria and BUA for referral for BMD assessment by DXA in osteoporotic and osteopenic perimenopausal subjects.

A pilot study of 107 women aged 60-69 years recently suggested that the measurement of broadband ultrasound attenuation (BUA) provides a superior cost effective pre-screen referral method for bone mineral density (BMD) measurement by DXA (dual-energy X-ray absorptiometry) than can be achieved by clinical criteria (CC). The aim of this study was to compare the accuracy and cost effectiveness of BUA and clinical criteria in a younger cohort. 599 women aged 50-54 years (52.18 +/- 1.35) had previously been measured by DXA at lumbar spine and right femoral neck, along with BUA measurement of the right calcaneus. Each subject had also completed an extensive clinical and social questionnaire to ascertain those who would have met one or more of the six general clinical criteria adopted by our Centre. Each subject was classified by DXA using the WHO criteria as normal, osteopenic or osteoporotic, defined at lumbar spine or femoral neck. Sensitivity, specificity and accuracy were calculated for BUA and the clinical criteria, noting that analysis was undertaken with and without the oestrogen deficiency clinical criterion (CC1): "Any oestrogen deficient woman who would want to be treated or would want to continue treatment if found to be osteopenic or osteoporotic". The accuracy for identifying osteoporotic subjects was 72.8% for BUA (at the point of matched sensitivity and specificity, 75 dB MHz(-1)), 30.7% for CC(1-6) and 64.3% for CC(2-6). When osteopenic subjects were incorporated, the accuracies were 63.8% for BUA (at the point of matched sensitivity and specificity, 82 dB MHz(-1)), 60.3% for CC(1-6) and 55.7% for CC(2-6). The minimum cost per osteoporotic subject correctly identified was pound sterling 573.50 by DXA alone, pound sterling 325 by BUA, pound sterling 458 by CC(1-6) and pound sterling 416 by CC(2-6). When osteopenic subjects were incorporated, the costs were pound sterling 87, pound sterling 83.50, pound sterling 78 and pound sterling 74, respectively. The overall cost, dependent upon the prevalence of osteoporosis (or osteopenia) within the population, more accurately indicates the feasibility of a population-based screening programme. For the identification of either osteoporotic or osteopenic subjects from the general population by DXA, the prevalence-compensated cost (cost per subject correctly identified multiplied by prevalence) is pound sterling 45, irrespective of age cohort. If CC(2-6) were adopted for the identification of osteoporotic subjects alone, the prevalence-compensated cost would be pound sterling 32 and pound sterling 42 for the 50-54 and 60-69 aged cohorts, respectively. For BUA, the prevalence-compensated cost falls to pound sterling 25 and pound sterling 43 for the 50-54 and 60-69 aged cohorts, respectively. If osteoporotic or osteopenic subjects were to be identified in the 50-54 aged cohort, both CC(2-6) (pound sterling 38) and BUA (pound sterling 43) perform similarly to DXA alone. BUA appears to provide a valuable population pre-screen for the identification of osteoporotic subjects, less so for osteopenic. It is suggested that if both osteopenic and osteoporotic women are to be identified for clinical management incorporating DXA, then neither BUA nor clinical criteria are satisfactory referral methods. An unanswered question from this study, however, is whether ultrasound has an independent role in the assessment of fracture risk for perimenopausal women who do not have the benefit of referral for DXA.

Absorptiometry, Photon↗
PubMed2000

Cost effectiveness analysis of BMD referral for DXA using ultrasound as a selective pre-screen in a group of women with low trauma Colles' fractures.

Measurements of bone density (BMD) are central to the World Health Organisation (WHO) approach to the definition of osteoporosis. Dual energy X- ray absorptiometry (DXA) remains the gold standard technique for measuring the bone mineral density (BMD) but Quantitative Ultrasound (QUS) is an attractive alternative method of bone assessment because it is easy to use and relatively inexpensive. It has been suggested that QUS could be used as a selective population pre-screen, to maximise the cost effectiveness of referral for DXA assessment of BMD. We set out to examine how such an approach might perform in the assessment of women with low trauma Colles' fracture. In 46 women aged 50-80 (mean 67) years we used DXA to measure BMD at lumbar spine and hip, and heel bone ultrasound to measure Broad Band Attenuation (BUA) and Velocity of Sound (VOS). We calculated local costs of pounds sterling 45 for DXA and pounds sterling 15 for QUS. We identified a BUA threshold of 60 dB/MHz as most cost effective as pre-screen, and calculated a sensitivity of 93% and specificity of 84% in identifying those subjects who were subsequently identified as having osteoporosis by DXA. DXA assessment of all patients had a cost of pounds sterling 77 per osteoporotic subject identified. We examined the cost-effectiveness of using QUS as a pre-screen, only referring subjects for more expensive DXA assessment if BUA was less than 60 dB/MHz. However this approach had no advantage, still costing pounds sterling 78 per osteoporotic subject identified. QUS assessment does not appear cost-effective as a pre-screen for DXA, even in this high risk group of women with low trauma Colles' fracture. A QUS pre-screen would only be cost-effective if the scan could be performed at a substantially lower cost.

Absorptiometry, Photon↗
PubMed2006

Pediatric DXA: technique and interpretation.

This article reviews dual X-ray absorptiometry (DXA) technique and interpretation with emphasis on the considerations unique to pediatrics. Specifically, the use of DXA in children requires the radiologist to be a "clinical pathologist" monitoring the technical aspects of the DXA acquisition, a "statistician" knowledgeable in the concepts of Z-scores and least significant changes, and a "bone specialist" providing the referring clinician a meaningful context for the numeric result generated by DXA. The patient factors that most significantly influence bone mineral density are discussed and are reviewed with respect to available normative databases. The effects the growing skeleton has on the DXA result are also presented. Most important, the need for the radiologist to be actively involved in the technical and interpretive aspects of DXA is stressed. Finally, the diagnosis of osteoporosis should not be made on DXA results alone but should take into account other patient factors.

Absorptiometry, Photon↗
PubMed2003

Potential clinical relevance of digital radiogrammetry for quantification of periarticular bone demineralization in patients suffering from rheumatoid arthritis depending on severity and compared with DXA.

The aim of this study was to investigate a new bone densitometric technology based on digital radiogrammetry (DXR) with respect to its ability to measure severity-dependent variations of bone mineralization in patients with rheumatoid arthritis. One hundred six randomly selected patients suffering from verified rheumatoid arthritis underwent digitally performed plain radiographs of the non-dominant hand and measurements of dual-energy X-ray absorptiometry (DXA) regarding total femur and lumbar spine. Using DXR the radiographs were analyzed retrospectively for bone mineral density (BMD) calculation. The severity was classified using Larsen score and Steinbroker stage blinded by two radiologists. A third radiologist reviewed the incongruently scored cases. Mean values of calculated parameters changed as follows from Larsen 1 to Larsen 5: Bone mineral density (DXR-BMD) decreased from 0.55 to 0.44 g/cm2 (p=0.000), DXR-MCI decreased from 0.44 to 0.33 (p=0.001), DXA-BMD (total femur) decreased from 0.92 to 0.78 g/cm2 (p=0.090) and DXA-BMD (lumbar spine) decreased from 0.91 to 0.84 g/cm2 (p=0.595). Similar results were verified for the Steinbroker stage. The relative decrease of BMD measured by DXR between the highest and lowest score was 20% for Steinbroker stage and Larsen score (p<0.05). The relative decrease of BMD using DXA revealed not such a significant result. Similar results were verified for metacarpal index (estimated by DXR). Correlations between BMD determined by DXR and by DXA were all significant (R=0.45 for lumbar spine and R=0.59 for total femur). Consequently, less than 35% of the DXR-BMD value is explainable by corresponding DXA values. The DXR-based BMD calculation seems to be able to distinguish severity and progress of the disease in contrast to those of DXA at lumbar spine and total femur.

Absorptiometry, Photon↗
PubMed2005

Percentage fat in overweight and obese children: comparison of DXA and air displacement plethysmography.

OBJECTIVE: To compare percentage body fat (percentage fat) estimates from DXA and air displacement plethysmography (ADP) in overweight and obese children. RESEARCH METHODS AND PROCEDURES: Sixty-nine children (49 boys and 20 girls) 14.0+/-1.65 years of age, with a BMI of 31.3+/-5.6 kg/m2 and a percentage fat (DXA) of 42.5+/-8.4%, participated in the study. ADP body fat content was estimated from body density (Db) using equations devised by Siri (ADP(Siri)) and Lohman (ADP(Loh)). RESULTS: ADP estimates of percentage fat were highly correlated with those of DXA in both male and female subjects (r=0.90 to 0.93, all p<0.001; standard error of estimate=2.50% to 3.39%). Compared with DXA estimates, ADP(Siri) and ADP(Loh) produced significantly (p<0.01) lower estimates of mean body fat content in boys (-2.85% and -4.64%, respectively) and girls (-2.95% and -5.15%, respectively). Agreement between ADP and DXA methods was further examined using the total error and methods of Bland and Altman. Total error ranged from 4.46% to 6.38% in both male and female subjects. The 95% limits of agreement were relatively similar for all percentage fat estimates, ranging from +/-6.73% to +/-7.94%. DISCUSSION: In this study, conversion of Db using the Siri equation led to mean percentage fat estimates that agreed better with those determined by DXA compared with the Lohman equations. However, relatively high limits of agreement using either equation resulted in percentage fat estimates that were not interchangeable with percentage fat determined by DXA.

Absorptiometry, Photon↗
PubMed2004

Body composition in patients with short bowel syndrome: an assessment by bioelectric impedance spectroscopy (BIS) and dual-energy absorptiometry (DXA).

OBJECTIVE: To describe body composition in patients with short bowel syndrome (SBS) by using bioelectric impedance spectroscopy (BIS), dual-energy X-ray absorptiometry (DXA) measurements and anthropometrical-derived estimates. SUBJECTS: In all, 19 patients were included, mean age 54 y, range 36-77 (F/M=11/8). Mean BMI was 21.5 kg/m(2). Eight patients were on home parenteral nutrition (HPN). METHODS: Total body water (TBW), intracellular water and extracellular water were assessed by BIS. TBW were derived from DXA. Fat-free mass (FFM) was assessed by BIS and DXA. TBW and FFM were predicted according to an empirical formula. Differences were analysed using the Bland-Altman method. RESULTS: The mean difference between TBW (DXA) and TBW (BIS) was -1.1 l in women and -1.8 l in men. For FFM, the mean difference between FFM (DXA) and FFM (BIS) was -1.7 kg in women and -2.5 kg in men. The mean difference between TBW (DXA) and TBW (BIS) for all patients was -1.2 l and limits of agreement were (-7.80-5.40). Hydration of FFM assessed by BIS gave a mean of 0.75 (0.08). CONCLUSION: The limits of agreement (Bland-Altman) between DXA and BIS were wide, indicating that methods are not interchangeable, which limits its clinical utility. Most of our patients with SBS were maintained in a stable clinical condition within normal limits of body weight and BMI. FFM and TBW did not appear to be altered in ileostomates or those on HPN.

Absorptiometry, Photon↗
PubMed2004

Comparison of anthropometry to DXA: a new prediction equation for men.

OBJECTIVE: This study compared three professionally recommended anthropometric body composition prediction equations for men to dual energy X-ray absorptiometry (DXA), and then developed an updated equation, DXA Criterion (DC) from DXA. DESIGN: Cross-sectional. SETTING: Exercise Physiology Lab. University of Missouri-Columbia, USA. SUBJECTS: A total of 160 men aged 18-62 y old. INTERVENTIONS: Percent body fat (%BF) by anthropometry was compared to DXA on the same day. RESULTS: Although %BF was significantly correlated (r=0.923-0.942) (P<0.01) with DXA for all three equations, each equation underestimated %BF (range=3.1-3.3%) (P<0.01) compared to DXA. The following DC equation for men was created: %BF=0.465+0.180(Sigma7SF)-0.0002406(Sigma7SF)(2)+0.06619(age); (Sigma7SF=sum of chest, midaxillary, triceps, subscapular, abdomen, suprailiac, thigh; age=years). The predicted residual sum of squares (PRESS) R(2) was high (0.90) and the PRESS standard error of estimates was excellent (2.2% at the mean) for the DC equation when applied to our sample of 160 men. CONCLUSIONS: The currently recommended anthropometric equations for men underestimate %BF compared to DXA. The DC equation yields a more accurate estimation of %BF in men aged 18-62 y old. The results from this study support the need for the current %BF standards and norms for men to be adjusted upward.

Absorptiometry, Photon↗
PubMed2006

Timing of peak bone mass: discrepancies between CT and DXA.

CONTEXT: The time of life in which peak bone mass in the axial skeleton is attained has been the subject of considerable controversy, with estimates ranging from the time of sexual and skeletal maturity to the fifth decade of life. OBJECTIVE: The objective was to examine whether dual energy x-ray absorptiometry (DXA) and computed tomography (CT) values for bone mass and bone density (BD) in the axial skeleton increase after sexual and skeletal maturity. DESIGN/PARTICIPANTS: Measurements of vertebral bone mineral density and bone mineral content (BMC) by DXA and vertebral BD and BMC by CT were obtained in 50 sexually and skeletally mature white females at baseline and 3 yr later. CT BMC values were calculated through analysis of vertebral volume in relation to density (BMC = vertebral volume x BD). RESULTS: Although neither CT BD nor BMC measures changed with time, DXA bone mineral density and BMC values were significantly higher at follow-up (P < 0.0001). Despite strong correlations between DXA and CT bone measures, DXA yielded greater changes in bone values in 47 of 50 subjects. CONCLUSIONS: Bone acquisition in the lumbar spine as measured by CT reaches its peak by sexual and skeletal maturity. In contrast, bone values by DXA continue to increase after puberty and cessation of longitudinal growth. Increases in DXA measures are likely a reflection of inhomogeneous changes in soft tissues around the spine or of disproportionate increases in the posterior elements of the vertebrae rather than of changes within the vertebral body.

Absorptiometry, Photon↗
PubMed2002

Comparison of DXA and MRI methods for interpreting femoral neck bone mineral density.

The aim of the study was to improve the practical implementation of the dual X-ray absorptiometry (DXA) by converting the areal bone mineral density BMD (BMD(areal)) to volumetric BMD using magnetic resonance (MR) imaging (MRI) because a failure to control for the femoral neck size can lead to erroneous interpretation of BMD values. We also evaluated the feasibility of MR T2* relaxation time in assessing bone mineral status of the femoral neck. Twenty-eight randomly selected 47- to 64-yr-old healthy men were studied. The men had neither unilateral nor bilateral hip osteoarthritis according to radiographs. Bone width, mineral content (BMC), BMD(areal), and apparent volumetric BMD (BMD(vol)) of the right femoral neck were measured with DXA. The BMD(vol) was calculated by approximating the femoral neck to be cylindrical with a circular cross-section (Vol(dxa)). Volumetric measurements from MR (Vol(mri)) images of the femoral neck were also used to create a BMD measure that was corrected for the femoral neck volume (BMD(mri)). T2* measurements were performed with a 1.5-T scanner (Siemens Magnetom 63SP, Erlangen, Germany). A single 10-mm-thick coronal slice was generated on the femur with a repetition time of 60 ms, and nine echo times (4-20 ms) were used to derive T2* values. Vol(mri) correlated positively (r = 0.828, p < 0.001) with Vol(dxa). However, the Vol(mri) of the femoral neck was 18% lower than the Vol(dxa). Similarly, the BMD(mri) was related to the BMD(vol) (r = 0.737, p < 0.001). Because of the difference in the volumetric measures, the BMD(mri) of the femoral neck was 21% higher than the BMD(vol) (p < 0.001). T2* relaxation time showed a significant negative correlation with BMC, BMD(areal), BMD(vol), and BMD(mri) (r = -0.423 to -0.757, p < 0.05-0.001). In conclusion, these results are evidence that DXA-derived volume approximations by the cylinder with circular cross-section geometry may lead to lower DXA-derived BMD(vol) values, as compared to true MRI-derived volumetric bone mineral density. Thus, the BMD(vol) may not be an accurate method to calculate the true volumetric BMD in the femoral neck. Our results also suggest that the MRI-derived T2* method may be used to approximate the BMD in the proximal femur.

Absorptiometry, Photon↗
PubMed2005

Training requirements for DXA technologists in the United States.

The purposes of this study were to determine, by state, the requirements for dual-energy X-ray absorptiometry(DXA) operators' training, knowledge of these state requirements, and factors that predicted state and International Society of Clinical Densitometry (ISCD) certification of DXA technologists. Seventeen states required registered technologist (RT) certification or authorized/licensed limited certification for DXA operators, 16 had no certification requirements, 12 required RT certification, and 5 had state-specific requirements. There were 9745 surveys mailed toDXA users including 50% Hologic Inc., 50% GE Lunar, and 100% Norland; 3148 surveys are included in this analysis. Among responders who indicated that their state did not have any certification requirements (n=1673), 1095(65.5%) were incorrect; there were requirements. Possession of state and ISCD certification was significantly correlated with the number of patients scanned per week (p<or=0.05), the number of technologists employed within a center (p<0.01), and the subspecialty of the practitioner (p<or=0.02). Our study uncovered a lack of uniformity amongstates with respect to central DXA operator training requirements. Additionally, in those states with requirements, DXA operators were often unaware of these requirements. Uniform national training requirements for central DXA operators to ensure adequate DXA scan quality are urgently needed.

Absorptiometry, Photon↗
PubMed2006

QCT versus DXA in 320 survivors of childhood cancer: association of BMD with fracture history.

PURPOSE: To assess agreement on diagnosis of diminished bone mineral density (BMD) and correlation between BMD values obtained by dual-energy X-ray absorptiometry (DXA) and quantitative computed tomography (QCT) in childhood cancer survivors. PATIENTS AND METHODS: We retrospectively reviewed lumbar spine QCT and DXA studies for BMD in patients who underwent both imaging studies within a 24-hr period. We determined correlation between BMD values and agreement on diagnosis of diminished BMD obtained by both modalities. Diminished BMD was defined as two or more SDs below mean for age- and gender-matched reference values. We evaluated the relationship of BMD values determined by each modality to self-reported fracture history in the 160 (50%) patients with available reports. RESULTS: Of 320 patients, 56% (178) were male; 87% (277) were white. Median age was 16.4 (range, 5.1-36.0) years. Median BMD Z-score was -1.43 (range, -5.96 to 3.20) by QCT and -1.30 (range, -5.50 to 2.80) by DXA. Correlation between QCT- and DXA-determined BMD values was significant but low, and agreement on diminished BMD was fair (kappa = 0.32). There was no association between BMD measured by either QCT or DXA and self-reported traumatic fracture history. Male gender was associated with doubling the traumatic fracture risk (P = 0.0499). CONCLUSIONS: Quantitative computed tomography and DXA may give discrepant results when used to assess bone health in childhood cancer survivors, especially in those of non-white race. This inconsistency in indicators of BMD deficiency may complicate clinical decision-making. Consecutive use of a single modality is recommended to provide reliable longitudinal information.

Absorptiometry, Photon↗
PubMed2003

Evaluation of the possibility to assess bone age on the basis of DXA derived hand scans-preliminary results.

The classical method of skeletal age assessment is based on the recognition of changes in the radiographic appearance of the maturity indicators in hand-wrist radiographs by comparison with a reference atlas. The purpose of this study was the evaluation of the possibility to assess bone age using a less invasive method such as dual-energy X-ray absorptiometry (DXA). Bone ages of 50 children free of any chronic diseases (5-18 years old) and ten with multihormonal pituitary deficiency (MPD) (8-20 years old) were assessed using an Expert-XL densitometer. Hand scans and classical hand-wrist radiographs were evaluated by two independent observers for bone age by visual comparison with reference standards of skeletal development published in the atlas. The precision errors of duplicate bone age ratings were low both for radiographs (<1%) and DXA hand scans (<0.9%). A high degree of agreement between bone age ratings done by two observers was assessed by intraclass correlation coefficients. The same bone age based on radiographs and DXA hand scans was assessed in 44 of 60 cases (73.3%); in 16 cases the differences between bone age were no higher than 0.5 year. No significant difference between mean bone age based on radiographs and DXA hand scans was observed ( P>0.05). Moreover, there was a very strong correlation between bone age results ( r=0.998; r(2)=0.996; P<0.0001), indicating agreement of bone age assessments based on DXA and radiographic images. Remarkable differences (up to 3 years) between bone age and chronological age were observed in healthy subjects, probably reflecting the effect of the secular trend towards earlier maturation or alterations in pubertal development. The study indicates that evaluation of skeletal maturity using DXA images is less invasive (up to 8 micro Sv) than radiography, giving results comparable to the classical method.

Absorptiometry, Photon↗
PubMed2004

Accuracy of DXA scanning of the thoracic spine: cadaveric studies comparing BMC, areal BMD and geometric estimates of volumetric BMD against ash weight and CT measures of bone volume.

Biomechanical studies of the thoracic spine often scan cadaveric segments by dual energy X-ray absorptiometry (DXA) to obtain measures of bone mass. Only one study has reported the accuracy of lateral scans of thoracic vertebral bodies. The accuracy of DXA scans of thoracic spine segments and of anterior-posterior (AP) thoracic scans has not been investigated. We have examined the accuracy of AP and lateral thoracic DXA scans by comparison with ash weight, the gold-standard for measuring bone mineral content (BMC). We have also compared three methods of estimating volumetric bone mineral density (vBMD) with a novel standard-ash weight (g)/bone volume (cm3) as measured by computed tomography (CT). Twelve T5-T8 spine segments were scanned with DXA (AP and lateral) and CT. The T6 vertebrae were excised, the posterior elements removed and then the vertebral bodies were ashed in a muffle furnace. We proposed a new method of estimating vBMD and compared it with two previously published methods. BMC values from lateral DXA scans displayed the strongest correlation with ash weight (r=0.99) and were on average 12.8% higher (p<0.001). As expected, BMC (AP or lateral) was more strongly correlated with ash weight than areal bone mineral density (aBMD; AP: r=0.54, or lateral: r=0.71) or estimated vBMD. Estimates of vBMD with either of the three methods were strongly and similarly correlated with volumetric BMD calculated by dividing ash weight by CT-derived volume. These data suggest that readily available DXA scanning is an appropriate surrogate measure for thoracic spine bone mineral and that the lateral scan might be the scan method of choice.

Absorptiometry, Photon↗
PubMed2002

Usefulness of lumbar AP spine DXA for measuring the percentage of perilumbar regional fat and predicting visceral fat in obese postmenopausal women.

We investigated whether measurement of the perilumbar regional fat amount by lumbar spine DXA is as good a predictor of visceral fat in obese postmenopausal women. Twenty-two obese (BMI 30-383 kg/m(2)) and 18 nonobese (BMI 20.1-24.7 kg/m(2)) postmenopausal women with similar age were recruited. Lumbar AP spine DXA for measuring the percentage of perilumbar regional fat and CT scanning for estimation of the abdominal visceral fat areas were performed. In obese subjects, visceral fat areas as measured by CT were significantly correlated with BMI, waist circumference, WHR, and DXA-measured perilumbar regional fat percentage. In nonobese subjects, visceral fat areas measured with CT were correlated with BMI, waist circumference, WHR, and DXA-measured perilumbar regional fat percentage. The results of multiple regression analysis were that the perilumbar regional fat percent by DXA was the best predictor of visceral fat amount in obese postmenopausal women (R(2) = 0.750) and BMI predicted visceral fat amount in nonobese postmenopausal women (R(2) = 0.343). This study suggests that lumbar regional fat percentage, as measured by DXA, is a better predictor of abdominal visceral fat amount than waist circumference, WHR, or BMI in obese postmenopausal women.

Abdomen↗
PubMed2000

Usefulness of anthropometry and DXA in predicting intra-abdominal fat in obese men and women.

OBJECTIVE: To investigate the usefulness of anthropometry and DXA in predicting intra-abdominal fat (IAF) in obese men and women. RESEARCH METHODS AND PROCEDURES: Observational, cross sectional study of 22 women and 18 men with a body mass index of 30 or above. IAF from 20 cm above and 10 cm below the L4 to L5 intervertebral disc was measured by magnetic resonance imaging (MRI) as a reference method. Central abdominal fat was measured from the upper border of L2 to the lower border of L4 by DXA. Waist and hip circumferences were also measured. RESULTS: In obese women DXA, waist circumference and waist-hip ratio were equally well correlated with IAF (r = 0.74, 0.75, and 0.70, respectively). In obese men DXA was moderately correlated with IAF measured by MRI (r = 0.46), whereas waist circumference and waist-hip ratio were not significantly correlated with IAF. DISCUSSION: The prediction of IAF in obese subjects was highly dependent on sex more than in non-obese persons. Anthropometry and DXA were equally useful in obese women, whereas anthropometry had no predictive power and DXA was the only acceptable predictor of IAF in obese men.

Abdomen↗
PubMed2004

Assessing body composition among 3- to 8-year-old children: anthropometry, BIA, and DXA.

OBJECTIVE: To examine the inter-relationships of body composition variables derived from simple anthropometry [BMI and skinfolds (SFs)], bioelectrical impedance analysis (BIA), and dual energy x-ray (DXA) in young children. RESEARCH METHODS AND PROCEDURES: Seventy-five children (41 girls, 34 boys) 3 to 8 years of age were assessed for body composition by the following methods: BMI, SF thickness, BIA, and DXA. DXA served as the criterion measure. Predicted percentage body fat (%BF), fat-free mass (FFM; kilograms), and fat mass (FM; kilograms) were derived from SF equations [Slaughter (SL)1 and SL2, Deurenberg (D) and Dezenberg] and BIA. Indices of truncal fatness were also determined from anthropometry. RESULTS: Repeated measures ANOVA showed significant differences among the methods for %BF, FFM, and FM. All methods, except the D equation (p = 0.08), significantly underestimated measured %BF (p < 0.05). In general, correlations between the BMI and estimated %BF were moderate (r = 0.61 to 0.75). Estimated %BF from the SL2 also showed a high correlation with DXA %BF (r = 0.82). In contrast, estimated %BF derived from SFs showed a low correlation with estimated %BF derived from BIA (r = 0.38); likewise, the correlation between DXA %BF and BIA %BF was low (r = 0.30). Correlations among indicators of truncal fatness ranged from 0.43 to 0.98. DISCUSSION: The results suggest that BIA has limited utility in estimating body composition, whereas BMI and SFs seem to be more useful in estimating body composition during the adiposity rebound. However, all methods significantly underestimated body fatness as determined by DXA, and, overall, the various methods and prediction equations are not interchangeable.

Absorptiometry, Photon↗
PubMed2005

Comparison of DXA, QCT and trabecular structure in beta-thalassaemia.

Osteopathy, as a major feature of homozygous beta-thalassaemia, is a multifactorial disorder, not fully understood. We studied the lumbar vertebrae of 48 patients using Dual-Energy X-ray Absorptiometry (DXA) and Quantitative Computed Tomography (QCT), and we focused on structural properties, assessed by High Resolution Computed Tomography (HRCT). Bone Mineral Density (BMD) values were expressed as Z-scores and the results were correlated. The effect of age, sex, and type of thalassaemia and hormonal factors on BMD was assessed. We estimated, with HRCT, the cortex integrity and the number and thickness of trabeculae; the latter were classified to a three-grade scale. Our results showed the overall prevalence of osteoporosis to be 44% with DXA and 6% with QCT. Both techniques revealed an inverse correlation between age and BMD, whereas hormonal factors demonstrated associations with QCT and DXA measurements. The correlation coefficient between DXA's BMD and QCT's trabecular BMD was 0.545 (P < 0.001) whereas the corresponding value for Z-scores was r = 0.491 (P < 0.001). The classification of the patients into normal, osteopenic and osteoporotic categories, using QCT's Z, was in better agreement with the assignment based on trabecular number (K = 0.209, P = 0.053) than the classification using DXA's Z (K = 0.145, P = 0.120). Cortex evaluation by HRCT showed discontinuity in 15 patients. Both methods indicate a progression of osteoporosis with age. Hormonal deficiency is associated with thalassaemic osteoporosis whereas the visual estimation of cortex indicates that Thalassaemia Intermedia (TI) patients could be more affected than Thalassaemia Major (TM). Using the trabecular number as an indicator of osteoporosis, it seems that QCT may evaluate osteopathy better than DXA. Since the former has the ability to measure trabecular and cortical BMD separately, it could give early indication of which changes more rapidly and to what degree.

Absorptiometry, Photon↗