Dual-energy X-ray Absorptiometry Technology Research Articles

Use of dual-energy x-ray absorptiometry for body composition in chronic disease management

As individuals age or contend with chronic diseases, shifts in body composition often emerge, characterized by a loss of muscle mass and an increase in fat mass, even among those with stable body weight. Both obesity and sarcopenia are key drivers of frailty, disability, and heightened morbidity and mortality. The simultaneous decline in skeletal muscle and accumulation of visceral fat can work synergistically, magnifying their detrimental effects on physical function and metabolic health. Today, dual-energy x-ray absorptiometry (DEXA) is widely recognized as one of the most versatile imaging techniques for assessing not only osteoporosis but also sarcopenia and obesity. Whole-body DEXA facilitates comprehensive analysis, offering detailed insights into fat mass, non-bone lean mass, and bone mineral content at both total and regional levels. DEXA is highly valued for its accuracy, reproducibility, speed, affordability, and low radiation exposure. Furthermore, advancements in DEXA technology and software now allow for precise estimation of visceral adipose tissue. This review underscores the clinical applications of whole-body DEXA, focusing on the use of muscle and fat mass indices in diagnosing low muscle mass, sarcopenia, and sarcopenic obesity, aligned with the latest research and guidelines.

Open, Active-Controlled Clinical Study to Evaluate the Correlation between Whole Body DEXA and BIA Muscle Measurements.

Dual energy X-ray absorptiometry (DXA) is the gold standard for diagnosing sarcopenia. However, comparative studies using bioelectrical impedance analysis (BIA) would be required in the Korean population. This study aimed to evaluate the correlation between total-body bone density measuring devices (Hologic and GE Lunar) and a bioelectrical impedance measurement device (InBody 970) as well as the correlation between upper body muscle mass. A total of 119 participants were involved in this study, aged 20 to 70 years, with specific body mass index ranges and no severe health conditions used both DXA (or DEXA) and BIA technologies to assess body composition. The participants were scanned using a Hologic QDR-4500W DXA scanner and GE-Lunar Prodigy DXA systems, and the InBody 970 type of multi-frequency BIA machine. Statistical analysis was performed to determine the correlation between the devices, with a coefficient of at least 0.8. The muscle mass measurement comparisons between the InBody 970 and Hologic devices demonstrated remarkably high correlation coefficients (exceeding 0.9) across all limbs. Similarly, the muscle mass comparison between the Inbody 970 and GE Lunar devices also revealed substantial correlation coefficients, ranging from 0.83 upwards, across all limbs. Limb muscle mass measurements using Hologic and GE Lunar whole-body DXA and Inbody 970 BIA demonstrated particularly high levels of concordance. In addition, a conversion formula that bridges limb muscle mass measurements from two widely used whole-body DXA machines and a BIA machine will facilitate sarcopenia research and patient management.

In vivo assessment of body composition and growth potential of modern broiler using dual-energy X-ray absorptiometry

Context Genetic improvements in modern strains have led to continuous increments in broiler growth rates, which, as a consequence, have resulted in higher economic returns for broiler producers over the last decades. Aim The present study was conducted to characterise the potential growth of the body and feathers of Cobb 500, Hubbard Flex and Ross 308 male and female broilers, as well as to assess the changes in chemical composition that occur up to 16 weeks of age. Methods Birds were fed isoenergetic diets divided in four phases and formulated to marginally exceed the nutritional requirements of the strains throughout the growing period. They were maintained in a controlled environment so as not to limit growth. A dual energy X-ray absorptiometry (DXA) scanner was used to follow the in vivo body composition of 12 broilers of each strain and sex (total of 72 broilers), and the feather weight and composition was determined in four birds of each strain and sex selected at intervals during the growing period (total of 288 broilers) through comparative slaughter with later chemical analysis. Key results Parameters of Gompertz growth curve to describe the strains were estimated for body and feather weight as well as for the growth of their chemical components. Conclusion Differences in the growth rates between strains were evident, indicating the possible differences in selection methods used by geneticists in the different breeding companies. These genetic parameters would explain part of the variation on broiler´s performance which impacts on the way they should be fed and housed during growth. Implications The accurate description of genetic growth potential is useful information to be associated with factorial models that predict nutritional and feed intake requirements of birds. The main advantage of DXA technology is to decrease the variation of body deposition on the Gompertz model, resulting from the use of the same bird throughout its life. Despite the speed of obtaining chemical values of the body, the method is unsuitable for measuring the growth of feathers, which is also important data to be collected and related to the broiler strains.

A Cross-Sectional Analysis of Body Composition Among Healthy Elderly From the European NU-AGE Study: Sex and Country Specific Features.

Body composition (BC) is an emerging important factor for the characterization of metabolic status. The assessment of BC has been studied in various populations and diseases such as obesity, diabetes, endocrine diseases as well as physiological and paraphysiological conditions such as growth and aging processes, and physical training. A gold standard technique for the assessment of human BC at molecular level is represented by dual-energy X-ray absorptiometry (DXA), which is able to precisely assess the body mass (and areal bone mineral density-aBMD) on a regional and whole-body basis. For the first time, within the framework of the NU-AGE project, BC has been assessed by means of a whole-body DXA scan in 1121 sex-balanced free-living, apparently healthy older adults aged 65–79 years enrolled in 5 European countries (Italy, France, United Kingdom, Netherlands, and Poland). The aim of this analysis is to provide a complete profile of BC in healthy elderly participants from five European countries and to investigate country- and sex-related differences by state-of-the-art DXA technology. To compare BC data collected in different centers, specific indexes and ratios have been used. Non-parametric statistical tests showed sex-specific significant differences in certain BC parameters. In particular, women have higher fat mass (FM) (Fat/Lean mass ratio: by 67%, p < 2.2e-16) and lower lean mass (Lean Mass index: by -18%, p < 2.2e-16) than men. On the other hand, men have higher android FM than women (Android/gynoid FM ratio: by 56%, p < 2.2e-16). Interesting differences also emerged among countries. Polish elderly have higher FM (Fat/Lean mass ratio: by 52%, p < 2.2e-16) and lower lean mass (Skeletal Mass index: by -23%, p < 2.2e-16) than elderly from the other four countries. At variance, French elderly show lower FM (Fat/Lean mass ratio: by -34%, p < 2.2e-16) and higher lean mass (Skeletal Mass index: by 18%, p < 2.2e-16). Moreover, five BC profiles in women and six in men have been identified by a cluster analysis based on BC parameters. Finally, these data can serve as reference for normative average and variability of BC in the elderly populations across Europe.

Rapid and non-destructive determination of lean fat and bone content in beef using dual energy X-ray absorptiometry

Dual energy X-ray absorptiometry (DXA) was evaluated for its accuracy in predicting total lean, fat and bone in beef carcass sides and primal cuts. Left carcass sides (n = 316) were broken down into primal cuts, scanned using DXA and then dissected to fat, lean and bone. The DXA estimates for bone, lean and fat from the primals (n = 237) were used to calibrate partial least squares regression (PLSR) models for predicting tissue weights. Models were validated using 79 additional carcass sides, which were broken into primals, scanned using DXA, and subsequently dissected to fat, lean and bone. Models were highly accurate for predicting tissue weights for the entire carcass side (lean R2 = 0.991, fat R2 = 0.985 and bone R2 = 0.941) and within most primal cuts. Results suggest DXA technology can be utilized to accurately predict carcass tissue composition for whole carcass sides and within most primals.

Potential of near infrared (NIR) spectroscopy and dual energy X-ray absorptiometry (DXA) in predicting pork belly softness

Pork bellies (n = 198) were scanned with dual energy X-ray absorptiometry (DXA). Visible and near-infrared reflectance (Vis-NIR) spectra were collected from the lean (latissimus dorsi), subcutaneous fat and intermuscular fat layers. Belly-flop angle and subjective belly scores were collected as measures of pork belly softness. Vis-NIR spectra from a single fat layer could explain between 72.7 and 81.1% of the variation in pork belly softness (43.6–72.4% in validation set). The combination of the lean and subcutaneous layers improved the calibration model fit to 79.7–99.9% (66.3–71.5% in validation set). The DXA estimates explained 62.3% of variation in pork belly softness (65.2% in validation set). Results indicated that DXA and NIR technologies could potentially be utilized for pork belly softness sorting in the pork industry.

Evaluation of Total Lean and Saleable Meat Yield Prediction Equations and Dual Energy X-Ray Absorptiometry for a Rapid, Non-Invasive Yield Prediction in Beef

ObjectivesThe objective of this study was to evaluate the beef yield equations currently used in North America and the potential use of the Dual energy X-ray absorptiometry (DXA) technology to predict either total or saleable yield of beef carcasses.Materials and MethodsA total of 316 left carcass sides over a wide range of weight (192 to 453 kg) and backfat thickness (1 to 29 mm) were fabricated into primal and retail cuts. Carcass break points were identified following Institutional Meat Purchase Specifications (IMPS) for Fresh Beef Products, Series 100. The primals collected from the left fabricated carcass side were the chuck (IMPS #113), rib (IMPS #103), brisket (IMPS #118), flank (IMPS #193, non-trimmed), foreshank (IMPS #117), loin (IMPS #172A), round (IMPS #158A) and plate (IMPS #121) primal cuts. All the cuts were scanned with an iDXA unit (GE Lunar Prodigy Advance, General Electric, Madison, WI) and then for the chuck, rib, loin and round, broken into closely trimmed retail cuts. Cuts were then fully dissected into fat [subcutaneous (SQ), intermuscular (IM) and body cavity (BC)], lean and bone and weighed.ResultsRegressing total lean meat yield predicted using the Canadian grade ruler versus dissected total lean meat yield resulted in an R2 of 0.56 (i.e., the equation predicted 56% of the variation). Regressing USDA calculated meat yield estimation (saleable yield) versus actual saleable yield of the boneless, closely trimmed round, loin, rib and chuck retail cuts resulted in an R2 of 0.34. Regressing total lean meat yield versus saleable meat yield yielded a moderate R2 (0.63). DXA was able to accurately predict total lean and total fat content in the carcass (R2 = 0.98) using partial least squares regression (PLSR). Predictions of saleable yield for each of the four major primals, using DXA technology were slightly lower (R2 ranged from 0.70 to 0.87) than those for total carcass lean and fat estimations.ConclusionAccurate prediction of beef yield is required to provide fair settlements for producers, and to help guide genetic improvements. This database provides important knowledge regarding the prediction accuracy and relationships between total lean meat yield and saleable meat yield necessary to support North American grade harmonization. In addition, DEXA technology may have the potential to estimate beef carcass traits such as total or saleable yield performance.

Dual Energy X-Ray Absorptiometry as a Rapid and Non-Destructive Method for Determination of Lean, Fat and Bone Content in Livestock

ObjectivesTo implement dual energy X-ray absorptiometry (DXA) as a platform technology, calibrations and development of robust equations to attain precision and accuracy are required before using for routine predictions of carcass yields in livestock. This manuscript summarized results of ongoing research where DXA has been used to estimate lean, fat, and bone carcass composition in beef, pork and lamb.Materials and MethodsFrom a wide range of carcasses, a total of 334 beef (230 crossbred finished steers and 104 cows), 212 pork and 155 lamb carcasses were used to build calibration equations within each population. Left carcass sides were scanned with a Lunar iDXA unit and then dissected into lean, fat, and bone and weighed. Partial least square regression was used to carry out the prediction equations for lean, fat and bone values from primal cuts scans (independent) and actual lean, fat and bone obtained through the full dissection (dependent). The predictive ability of the models was evaluated in terms of coefficient of determination (R2) and root mean square error of calibration (RMSE).ResultsThe PLSR results between actual and DXA estimated lean and fat values showed high relationship (R2 > 0.97) across all the species. Within beef, the present results suggest that DXA capacity to estimate carcass composition is independent of maturity. With regard to the bone predictions, PLSR analyses also improved the relationship for bone predictions compared to simple regression models previously developed at this institution or single pass scans for pork and lamb. Observed R2 values for predicting bone were slightly lower than those for lean and fat estimations, particularly in those carcasses with smaller bone sizes such as pork (R2 = 0.889) and lamb (R2 = 0.870).ConclusionThe results suggest that DXA technology can reliably estimate carcass composition in livestock, particularly for lean and fat estimations. Using PLSR analyses, suitable models for research have been developed from main primal scan data. However, further studies to externally validate the prediction accuracy and to obtain calibration curves for specific retail cuts or carcass cut-outs specifications are needed. Prediction accuracies for industry applications using single pass scans will also be needed.

Practical Considerations for Body Composition Assessment of Adults with Class II/III Obesity Using Bioelectrical Impedance Analysis or Dual-Energy X-Ray Absorptiometry.

The purpose of this review is to explore the practical considerations for body composition assessment of adults with class II/III obesity. Studies assessing adults (18-64years) with a body mass index (BMI) ≥35kg/m2 with bioelectrical impedance analysis (BIA) and/or dual-energy X-ray absorptiometry (DXA) were included. Twelve studies met inclusion criteria. Five considerations were identified: variances in equipment and technology, equipment weight capacity, subject positioning, tissue penetration, and total body hydration. In subjects with BMI ≥35kg/m2, BIA overestimated fat-free mass with scaling errors as BMI increased. DXA provided accurate and reliable body composition measures, but equipment-related barriers prevented assessment of some taller, wider, and heavier subjects. BIA is an unreliable method to assess body composition in class II/III obesity. Advancements in DXA technology (e.g., iDXA), methodology (e.g., subject positioning, longer scan times), and more inclusive testing criteria (e.g., use equipment limits not just BMI) may improve access and understanding of body composition in this cohort.

Contribution of Heritability and Epigenetic Factors to Skeletal Muscle Mass Variation in United Kingdom Twins.

Context:Skeletal muscle mass (SMM) is one of the major components of human body composition, with deviations from normal values often leading to sarcopenia.Objective:Our major aim was to conduct a genome-wide DNA methylation study in an attempt to identify potential genomic regions associated with SMM.Design:This was a mixed cross-sectional and longitudinal study.Setting:Community-based study.Participants:A total of 1550 middle-aged United Kingdom twins (monozygotic [MZ] and dizygotic [DZ]), 297 of which were repeatedly measured participated in the study.Main Outcome Measure:Appendicular lean mass assessed using dual-energy X-ray absorptiometry technology, and methylated DNA immunoprecipitation sequencing DNA methylation profiling genome-wide were obtained from each individual.Results:Heritability estimate of SMM, with simultaneous adjustment for covariates obtained using variance decomposition analysis, was h2 = 0.809 ± 0.050. After quality control and analysis of longitudinal stability, the DNA methylation data comprised of 723 029 genomic sites, with positive correlations between repeated measurements (Rrepeated = 0.114–0.905). Correlations between MZ and DZ twins were 0.51 and 0.38 at a genome-wide average, respectively, and clearly increased with Rrepeated. Testing for DNA methylation association with SMM in 50 discordant MZ twins revealed 36 081 nominally significant results, of which the top-ranked 134 signals (P < .01 and Rrepeated > 0.40) were subjected to replication in the sample of 1196 individuals. Seven SMM methylation association signals replicated at a false discovery rate less than 0.1, and these were located in or near genes DNAH12, CAND1, CYP4F29P, and ZFP64, which have previously been highlighted in muscle-related studies. Adjusting for age, smoking, and blood cell heterogeneity did not alter significance of these associations.Conclusion:This epigenome-wide study, testing longitudinally stable methylation sites, discovered and replicated a number of associations between DNA methylation at CpG loci and SMM. Four replicated signals were related to genes with potential muscle functions, suggesting that the methylome of whole blood may be informative of SMM variation.

DXA: Technical aspects and application

The key role of dual-energy X-ray absorptiometry (DXA) in the management of metabolic bone diseases is well known. The role of DXA in the study of body composition and in the clinical evaluation of disorders which directly or indirectly involve the whole metabolism as they may induce changes in body mass and fat percentage is less known or less understood. DXA has a range of clinical applications in this field, from assessing associations between adipose or lean mass and the risk of disease to understanding and measuring the effects of pathophysiological processes or therapeutic interventions, in both adult and paediatric human populations as well as in pre-clinical settings. DXA analyses body composition at the molecular level that is basically translated into a clinical model made up of fat mass, non-bone lean mass, and bone mineral content. DXA allows total and regional assessment of the three above-mentioned compartments, usually by a whole-body scan. Since body composition is a hot topic today, manufacturers have steered the development of DXA technology and methodology towards this. New DXA machines have been designed to accommodate heavier and larger patients and to scan wider areas. New strategies, such as half-body assessment, permit accurate body scan and analysis of individuals exceeding scan field limits. Although DXA is a projective imaging technique, new solutions have recently allowed the differential estimate of subcutaneous and intra-abdominal visceral fat. The transition to narrow fan-beam densitometers has led to faster scan times and better resolution; however, inter- or intra-device variation exists depending on several factors. The purposes of this review are: (1) to appreciate the role of DXA in the study of body composition; (2) to understand potential limitations and pitfalls of DXA in the analysis of body composition; (3) to learn about technical elements and methods, and to become familiar with biomarkers in DXA.

Osteoporosis Imaging in the Geriatric Patient.

Given the expected rapid growth of the geriatric world population (=individuals aged >65 years) to 1.3 billion by 2050, age-related diseases such as osteoporosis and its sequelae, osteoporotic fractures, are on the rise. Areal bone mineral density (aBMD) by dual-energy X-ray absorptiometry (DXA) is the current gold standard to diagnose osteoporosis, to assess osteoporotic fracture risk, and to monitor treatment-induced BMD changes. However, most fragility fractures occur in patients with normal or osteopenic aBMD, indicating that factors beyond BMD impact bone strength. Recent developments in DXA technology such as TBS, VFA, and hip geometry analysis are now available to assess some of these non-BMD parameters from the DXA image. This review will discuss the use of DXA and DXA-assisted technologies and their respective advantages and disadvantages. Special attention is given to if and how each method is indicated in the geriatric population, and the latest ISCD 2015 guidelines have been incorporated.

Using Dual Energy X-Ray Absorptiometry technology for rapid and non-invasive fat and lean predictions in beef carcasses

Using Dual Energy X-Ray Absorptiometry technology for rapid and non-invasive fat and lean predictions in beef carcasses

Epidemiology of bone and joint disease - the present and future - . Diagnosis of sarcopenia : techniques for assessing muscle mass

Diagnosis of sarcopenia is operationally based on having a low skeletal muscle mass in combination with poor physical functioning. Currently, several techniques are available for assessing regional or whole-body muscle mass noninvasively. Among these techniques, dual-energy X-ray absorptiometry (DXA) is regarded as a most reliable and practical method for both clinical and research settings. This article will review the current understanding of techniques for assessing muscle mass, focusing on DXA technology.

Quality Assurance in Bone Densitometry

Dual energy X-ray absorptiometry (DXA) is a well-established method for the diagnosis of osteoporosis and monitoring of treatment. Recent advances in DXA technologies have improved accuracy and precision. Nevertheless, errors in bone mineral density measurement and interpretation could occur and negatively affect the diagnosis and management of patients. These errors can result from improper equipment installation and maintenance, inadequate education and training in bone densitometry, and insufficient knowledge of current clinical guidelines. This review describes the current procedures of quality assurance in bone densitometry and emphasizes strict adherence of technicians and clinicians to manufacturers’ recommendations and current clinical guidelines.

Factors that determine body composition of female systemic lupus erythematosus (SLE) patients in Sri Lanka: a comparative study using dual-energy x-ray absorptiometry

Studies on body composition and its determinants among SLE patients are limited. Estimation of body composition, analysis of determinants and associations of different body compartments are important in planning long-term care of these patients. The aim of the study was to identify the changes in body composition among SLE patients and assess the effect of corticosteroid use, patient and disease-related variables on body composition. We compared lean mass, fat mass, bone mineral density (BMD), and bone mineral content (BMC) determined by dual-energy x-ray absorptiometry technology, in a group of premenopausal women with SLE (n = 27) and an age-matched healthy group of women (n = 27). The median (IQR) duration of SLE was 3 (2-5) years while median (IQR) duration and dose of prednisolone therapy were 108 (88 - 172) weeks and 9730 (6160-15360) mg, respectively. No significant difference was observed in body mass index (BMI) or total fat mass between the two groups. SLE patients, however, had significantly lower lean mass (p < 0.001), BMD (p < 0.001) and BMC (p < 0.005) than healthy controls. Among cases, compared with lean mass, total body fat content showed stronger associations with total body BMD (r = 0.49, p < 0.01) and total body BMC (r = 0.63, p < 0.01). When a stepwise regression model was fitted, lean mass among controls and total fat mass among cases emerged as the best predictors of BMC/BMD. No significant correlations were found between the disease duration or cumulative glucocorticosteroid dose and total body BMD, total body BMC, lean mass or total fat content in SLE patients.

Examining the Link Between Bariatric Surgery, Bone Loss, and Osteoporosis: a Review of Bone Density Studies

As the popularity of bariatric surgery to treat morbid obesity has risen, so has a concern of increased skeletal fragility secondary to accelerated bone loss following bariatric procedures. We reviewed cross-sectional and prospective literature reporting bone density outcomes following bariatric surgical treatment for morbid obesity. Prospective research provides evidence of hip and lumbar spine areal bone mineral density (aBMD) reductions primarily in women despite calcium and vitamin D supplementation. Femoral neck aBMD declines of 9-11% and lumbar spine aBMD reductions up to 8% were observed at the first post-operative year following malabsorptive procedures. Mean T- and Z-scores up to 25years following surgery remained within normal and healthy ranges. Of those studies reporting development of osteoporosis following gastric bypass, one woman became osteoporotic after 1year. Despite observed bone loss in the hip region post-surgery, data do not conclusively support increased incidence of osteoporosis or increased fracture risk in post-bariatric patients. However, given the limitations of dual energy X-ray absorptiometry technology in this population and the relative lack of long-term prospective studies that include control populations, further research is needed to provide conclusive evidence regarding fracture outcomes in this population.

The Accuracy Of Selected Field Measures For Predicting Body Fat Percentage In Female Athletes

There are numerous techniques that measure body fat percentage (BF%), and recently dual-energy x-ray absorptiometry (DEXA) has emerged as the criterion method for assessing body fat percentage in laboratory settings. However, most athletes do not have access to DEXA technology. Bioelectrical impedance analysis (BIA) and the skinfold technique (SF) are two popular field techniques that can predict BF% in field settings. There is limited research available that has cross-validated these measures in female athletes using DEXA. PURPOSE: The purpose of this investigation was to determine the accuracy of BIA and SF for estimating body fat percentage (BF%) in college-age female athletes using DEXA as the criterion method. METHODS: Forty female athletes from the National Association for Intercollegiate Athletics (NAIA) volunteered to participate in this study. For each participant, BF% was obtained via DEXA, hand-to-hand BIA, and a popular SF model (Jackson et al., 1980). The mean predicted BF% value by BIA and SF were compared to the criterion DEXA measure. RESULTS: The DEXA strongly correlated to the BIA (r=0.74, p<0.01) and SF (r=0.85, p<0.01). The mean values for each of the BF% techniques were as follows: DEXA = 27.6 ± 5.3%, BIA = 22.5 ± 3.5%, and the SF = 19.9 ± 4.2%. Bland-Altman Plots showed that the mean difference between the criterion and predicted values was -5.1% for BIA and -7.7% for SF. Furthermore, the 1.96 SD of the differences ranged from -12.3% to 2.1% for BIA and -2.1% to -13.3% for SF. Last, the standard error of estimate was 3.6% for BIA and 2.8% for SF. CONCLUSIONS: The results of this investigation indicate that BIA and SF significantly underestimated BF% in female athletes when compared to the criterion DEXA. There also appears to be large individual differences in the criterion vs. predicted BF% values. Therefore, it appears that BIA and SF techniques are not valid field measures, when compared to the DEXA, for estimating BF% in female athletes. Inaccurate body composition estimates could have consequences well worth noting, such as prompting body image concerns and/or misclassifying an athlete with an acceptable body fat category as over or underweight.

An in vivo comparison of hip structure analysis (HSA) with measurements obtained by QCT

SummaryIn a population of elderly women, bone cross-sectional area (CSA), cross-sectional moment of inertia (CSMI), section modulus (Z), femoral neck axis length (FNAL), and width measured with hip structure analysis (HSA) on dual-energy x-ray absorptiometry (DXA) images in the femoral neck and trochanteric regions are highly correlated to quantitative computed tomography (QCT) measurements.IntroductionHSA is a method of obtaining measurements of proximal femur structure using 2D DXA technology. This study was designed to examine the correlations between HSA measurements and 3D QCT.MethodsForty-one women (mean age, 82.8 ± 2.5 years) were measured using DXA and a 64-slice CT scanner (1 mm slice thickness, 0.29 mm in plane resolution). HSA parameters were calculated at the narrow neck (NN) and trochanteric (IT) regions on the DXA image. These regions were then translated to anatomically equivalent regions on the QCT dataset by co-registering the DXA image and QCT dataset using four DXA images acquired at different angles.ResultsAt the NN and IT regions, high linear correlations were measured between HSA and QCT for CSA r = 0.95 and 0.93, CSMI r = 0.94 and 0.93, and Z r = 0.93 and 0.89, respectively. All correlations were highly significant (p < 0.001), but there were differences in slope and offset between the two techniques, at least in part due to differences in calibration between the two techniques. FNAL and width of the bone at the NN and IT regions, physical measurements independent of the calibration, were highly correlated (r = 0.90–0.95, p < 0.001) and had slopes close to 1.0 (range, 0.978 to 1.003).ConclusionCSA, CSMI, Z, FNAL, and width measured by HSA correlate highly to high-resolution QCT.

Bone Density Distribution Patterns in the Rostrum of Delphinids and Beaked Whales: Evidence of Family‐Specific Evolutive Traits

Toothed whales have undergone a profound telescopic rearrangement of the skull, with elongation of facial bones and formation of a hollow rostrum, filled in vivo by the mesorostral cartilage. In most species of the family Ziphiidae, this latter cartilage becomes secondarily ossified, producing in some cases the densest bone existing in nature. Starting from this observation, we wanted to investigate the patterns of distribution of bone mineral density (BMD) in the rostrum of two families of toothed whales with different ecological and behavioral traits: Delphinidae and Ziphiidae. We analyzed BMD non invasively by means of the dual energy X-ray absorptiometry technology, and found two different density distribution patterns that distinctly set the two families apart. Namely, BMD values decrease from the proximal to the distal region of the rostrum in delphinids, whereas the beaked whales show a BMD peak in the central region. Possible functions such as ballast or protection against clashes might be likely, although more data about the species of both families is needed to give better evidence.