Kevin E. Wilson

Dual energy X-Ray absorptiometry body composition reference values from NHANES.

In 2008 the National Center for Health Statistics released a dual energy x-ray absorptiometry (DXA) whole body dataset from the NHANES population-based sample acquired with modern fan beam scanners in 15 counties across the United States from 1999 through 2004. The NHANES dataset was partitioned by gender and ethnicity and DXA whole body measures of %fat, fat mass/height2, lean mass/height2, appendicular lean mass/height2, %fat trunk/%fat legs ratio, trunk/limb fat mass ratio of fat, bone mineral content (BMC) and bone mineral density (BMD) were analyzed to provide reference values for subjects 8 to 85 years old. DXA reference values for adults were normalized to age; reference values for children included total and sub-total whole body results and were normalized to age, height, or lean mass. We developed an obesity classification scheme by using estabbody mass index (BMI) classification thresholds and prevalences in young adults to generate matching classification thresholds for Fat Mass Index (FMI; fat mass/height2). These reference values should be helpful in the evaluation of a variety of adult and childhood abnormalities involving fat, lean, and bone, for establishing entry criteria into clinical trials, and for other medical, research, and epidemiological uses.

Dual-Energy X-Ray Performs as Well as Clinical Computed Tomography for the Measurement of Visceral Fat

Visceral adipose tissue (VAT) is associated with adverse health effects including cardiovascular disease and type 2 diabetes. We developed a dual‐energy X‐ray absorptiometry (DXA) measurement of visceral adipose tissue (DXA‐VAT) as a low cost and low radiation alternative to computed tomography (CT). DXA‐VAT was compared to VAT assessed using CT by an expert reader (E‐VAT). In addition, the same CT slice was also read by a clinical radiographer (C‐VAT) and a best‐fit anthropomorphic and demographic VAT model (A‐VAT) was developed. Whole body DXA, CT at L4–L5, and anthropometry were measured on 272 black and white South African women (age 29 ± 8 years, BMI 28 ± 7 kg/m2, waist circumference (WC) 89 ± 16 cm). Approximately one‐half of the dataset (n = 141) was randomly selected and used as a training set for the development of DXA‐VAT and A‐VAT, which were then used to estimate VAT on the remaining 131 women in a blinded fashion. DXA‐VAT (r = 0.93, standard error of the estimate (SEE) = 16 cm2) and C‐VAT (r = 0.93, SEE = 16 cm2) were strongly correlated to E‐VAT. These correlations with E‐VAT were significantly stronger (P < 0.001) than the correlations of individual anthropometry measurements and the A‐VAT model (WC + age, r = 0.79, SEE = 27 cm2). The inclusion of anthropometric and demographic measurements did not substantially improve the correlation between DXA‐VAT and E‐VAT. DXA‐VAT performed as well as a clinical read of VAT from a CT scan and better than anthropomorphic and demographic models.

Abdominal Aortic Calcification Detected on Lateral Spine Images From a Bone Densitometer Predicts Incident Myocardial Infarction or Stroke in Older Women

Among a cohort of elderly women, abdominal aortic calcification scored on baseline lateral spine densitometric images intended for vertebral fracture assessment was associated with subsequent myocardial infarction or stroke over a median 4‐yr period, independent of clinical cardiovascular disease risk factors.

Detection of Aortic Calcification during Vertebral Fracture Assessment (VFA) Compared to Digital Radiography

Background Cardiovascular disease is the most common cause of mortality among post-menopausal women. Our objective was to determine whether or not lateral spine images obtained on a bone densitometer to detect prevalent vertebral fracture can also accurately detect radiographic abdominal aortic calcification (AAC), an important risk factor for cardiovascular disease independent of clinical risk factors. Methodology/Principal Findings One hundred seventy four postmenopausal women had bone densitometry, lateral spine densitometry imaging (called vertebral fracture assessment, or VFA), and lateral spine digital radiographs. Radiographs and VFA images were scored for AAC using a previously validated 24 point scale and a simplified, new 8 point scale (AAC-8). One hundred fifty six (90%) of the VFA images were evaluable for AAC. The non-parametric intraclass correlation coefficient between VFA and radiographic 24 point and AAC-8 readings, respectively, were 0.80 (95% C.I. 0.68–0.87) and 0.76 (95% C.I. 0.65–0.84). Areas under receiver operating characteristics (ROC) curves for VFA to detect those with a radiographic 24-point AAC score ≥5 were 0.86 (95% C.I. 0.77–0.94) using the 24 point scale and 0.84 (95% C.I. 0.76–0.92) using the AAC-8 scale. Conclusion/Significance VFA imaging intended to detect prevalent vertebral fracture can also detect radiographic AAC, an important cardiovascular disease risk factor. Since bone densitometry is recommended for all women age 65 and older, VFA imaging at the time of bone densitometry offers an opportunity to assess this risk factor in the post-menopausal female population at very little incremental time and expense.

Assessment of abdominal fat compartments using DXA in premenopausal women from anorexia nervosa to morbid obesity.

Objective: To test a newly developed dual energy X‐ray absorptiometry (DXA) method for abdominal fat depot quantification in subjects with anorexia nervosa (AN), normal weight, and obesity using CT as a gold standard.

Differences in structural geometrical outcomes at the neck of the proximal femur using two-dimensional DXA-derived projection (APEX) and three-dimensional QCT-derived (BIT QCT) techniques

SummaryStructural geometric parameters at neck of the proximal femur were obtained using DXA-derived hip structural analysis (APEX 3) and quantitative computed tomography-derived (BIT QCT) techniques in 237 elderly females. Linear correlations for parameters ranged from 0.45 to 0.90. The average value of the subperiosteal width, as determined by the two techniques, was the same; variables dependent on mass measurements were different.IntroductionThere has been increasing interest in using bone structural geometry to assess bone fragility to complement bone mineral mass. The objective of this study is to compare structural geometrical differences between “2D” DXA-derived and “3D” QCT-derived techniques in unselected clinical cases.MethodsAll 237 females had both DXA and QCT assessments of femoral neck structural geometry. Variables compared were areal bone mineral density, cross-sectional area (CSA), cross-sectional moment of inertia (CSMI), section modulus (Z), averaged cortical thickness (Ct), endosteal width (ESW), subperiosteal width (W), and buckling ratio (BR).ResultsCorrelation of femoral neck variables ranged from 0.45 for ESW to 0.90 for CSA. APEX 3 and BIT QCT-derived femoral neck W values were numerically similar. However CSA, CSMI, Z and Ct values measured by APEX 3 were higher and ESW and BR values were lower than corresponding BIT QCT.Conclusions2D DXA structural analysis of neck of femur is related to but different from same parameters calculated from true 3D images obtained by CT. Femoral neck size values are similar for DXA and QCT, but structural geometrical variables dependent on mass calibration standards, location of neck ROI and mathematical derivation techniques are different.

Abdominal Aortic Calcification Identified on Lateral Spine Images From Bone Densitometers Are a Marker of Generalized Atherosclerosis in Elderly Women

Objective— Dual-energy x-ray absorptiometry is a low-cost, minimal radiation technique used to improve fracture prediction. Dual-energy x-ray absorptiometry machines can also capture single-energy lateral spine images, and abdominal aortic calcification (AAC) is commonly seen on these images. Approach and Results— We investigated whether dual-energy x-ray absorptiometry–derived measures of AAC were related to an established test of generalized atherosclerosis in 892 elderly white women aged >70 years with images captured during bone density testing in 1998/1999 and B-mode carotid ultrasound in 2001. AAC scores were calculated using a validated 24-point scale into low (AAC24 score, 0 or 1), moderate (AAC24 scores, 2–5), and severe AAC (AAC24 scores, >5) seen in 45%, 36%, and 19%, respectively. AAC24 scores were correlated with mean and maximum common carotid artery intimal medial thickness (r s=0.12, P<0.001 and r s=0.14, P<0.001). Compared with individuals with low AAC, those with moderate or severe calcification were more likely to have carotid atherosclerotic plaque (adjusted prevalence ratio (PR), 1.35; 95% confidence interval, 1.14–1.61; P<0.001 and prevalence ratio, 1.94; 95% confidence interval, 1.65–2.32; P<0.001, respectively) and moderate carotid stenosis (adjusted prevalence ratio, 2.22; 95% confidence interval, 1.39–3.54; P=0.001 and adjusted prevalence ratio, 4.82; 95% confidence interval, 3.09–7.050; P<0.001, respectively). The addition of AAC24 scores to traditional risk factors improved identification of women with carotid atherosclerosis as quantified by C-statistic (+0.075, P<0.001), net reclassification (0.249, P<0.001), and integrated discrimination (0.065, P<0.001). Conclusions— AAC identified on images from a dual-energy x-ray absorptiometry machine were strongly related to carotid ultrasound measures of atherosclerosis. This low-cost, minimal radiation technique used widely for osteoporosis screening is a promising marker of generalized extracoronary atherosclerosis.

3D structural measurements of the proximal femur from 2D DXA images using a statistical atlas

A method to obtain 3D structural measurements of the proximal femur from 2D DXA images and a statistical atlas is presented. A statistical atlas of a proximal femur was created consisting of both 3D shape and volumetric density information and then deformably registered to 2D fan-beam DXA images. After the registration process, a series of 3D structural measurements were taken on QCT-estimates generated by transforming the registered statistical atlas into a voxel volume. These measurements were compared to the equivalent measurements taken on the actual QCT (ground truth) associated with the DXA images for each of 20 human cadaveric femora. The methodology and results are presented to address the potential clinical feasibility of obtaining 3D structural measurements from limited angle DXA scans and a statistical atlas of the proximal femur in-vivo.

Bone analysis apparatus and method for calibration and quality assurance of an ultrasonic bone analysis apparatus

A method of calibrating an ultrasound bone analysis apparatus having a pair of transducer assemblies. Each transducer assembly has a transducer and a coupling pad, and is movable relative to the other so that a face of each pad can be moved to a position in which they mutually contact at a first compression and to a position where the faces contact body parts at a second compression different than the first compression. The method according to the present application includes transmitting an ultrasound signal from one transducer and receiving a signal corresponding to the transmitted ultrasound signal through the other transducer when the transducer assemblies are in the first position and the second position. A time for the ultrasound signal to pass through the body part is determined, and a width of the body part based on positions of the transducers is determined. Then, using the time and width values a speed of sound of the ultrasound signal passing through the body part with squish compensation is calculated.

Long-term atherosclerotic vascular disease risk and prognosis in elderly women with abdominal aortic calcification on lateral spine images captured during bone density testing: a prospective study

Lateral spine images are captured using bone densitometers for vertebral fracture assessment (VFA) in older women. Abdominal aortic calcification (AAC) is commonly seen on these images; however, the long‐term prognosis in women with AAC remains uncertain. In a prospective study of 1052 community‐dwelling ambulant white women over 70 years old abdominal aortic calcification 24 scale (AAC24) scores were calculated from digital lateral spine images captured during bone density testing in 1998 or 1999. Cardiovascular risk factors were assessed in 1998, whereas 14.5‐year atherosclerotic vascular disease (ASVD)‐related hospitalizations and deaths (events) were available through linked health records. Using established cut points for AAC 471 women (45%) had low AAC (AAC24 score 0 or 1), 387 (37%) moderate AAC (AAC24 score 2–5), and 197 (19%) had high AAC (AAC24 score ≥6). Over 14.5 years, 420 women experienced an ASVD event. Increasing severity of AAC was associated with increased absolute risk of ASVD events (37%, 39%, and 49%, respectively, p = 0.008 for trend), ASVD deaths (15%, 21%, and 27%, respectively, p < 0.001 for trend), and all‐cause mortality (30%, 38%, and 44%, respectively, p < 0.001 for trend). After adjusting for Framingham risk scores, women with high AAC had increased relative hazard for ASVD events, HR 1.37 (95% CI, 1.07 to 1.77; p = 0.013) compared to women with low AAC. Similarly, women with moderate AAC and high AAC had increased relative hazards for ASVD deaths HR 1.41 (95% CI, 1.03 to 1.94; p = 0.034) and HR 1.80 (95% CI, 1.26 to 2.57; p = 0.001), or any deaths HR 1.30 (95% CI, 1.03 to 1.64; p = 0.026) and HR 1.53 (95% CI, 1.17 to 2.00; p = 0.002), compared to women with low AAC. In conclusion, more advanced AAC on images captured for VFA is associated with long‐term ASVD hospitalizations and deaths before and after adjusting for Framingham risk scores. AAC assessment could be considered in addition to VFA to identify individuals who may benefit for more aggressive cardiovascular primary prevention strategies.