Inhomogeneity in body fat distribution may result in inaccuracy in the measurement of vertebral bone mass

Automatic phantom-less QCT system with high precision of BMD measurement for osteoporosis screening: Technique optimisation and clinical validation

Background

Objective

Methods

Results

Conclusion

Translational potential statement

A review of menopause nomenclature

Menopause nomenclature varies in the scholarly literature making synthesis and interpretation of research findings difficult. Therefore, the present study aimed to review and discuss critical developments in menopause nomenclature; determine the level of heterogeneity amongst menopause definitions and compare them with the Stages of Reproductive Aging Workshop criteria. Definitions/criteria used to characterise premenopausal and postmenopausal status were extracted from 210 studies and 128 of these studies were included in the final analyses. The main findings were that 39.84% of included studies were consistent with STRAW classification of premenopause, whereas 70.31% were consistent with STRAW classification of postmenopause. Surprisingly, major inconsistencies relating to premenopause definition were due to a total lack of reporting of any definitions/criteria for premenopause (39.84% of studies). In contrast, only 20.31% did not report definitions/criteria for postmenopause. The present findings indicate that there is a significant amount of heterogeneity associated with the definition of premenopause, compared with postmenopause. We propose three key suggestions/recommendations, which can be distilled from these findings. Firstly, premenopause should be transparently operationalised and reported. Secondly, as a minimum requirement, regular menstruation should be defined as the number of menstrual cycles in a period of at least 3 months. Finally, the utility of introducing normative age-ranges as supplementary criterion for defining stages of reproductive ageing should be considered. The use of consistent terminology in research will enhance our capacity to compare results from different studies and more effectively investigate issues related to women's health and ageing.

Fat mass changes during menopause: a metaanalysis

OBJECTIVE

Data: Fat mass has been shown to increase in aging women; however, the extent to which menopausal status mediates these changes remains unclear. The purpose of this review was to determine (1) how fat mass differs in quantity and distribution between premenopausal and postmenopausal women, (2) whether and how age and/or menopausal status moderates any observed differences, and (3) which type of fat mass measure is best suited to the detection of differences in fat mass between groups.

STUDY

This review with metaanalyses is reported according to Metaanalysis of Observational Studies in Epidemiology guidelines.

STUDY APPRAISAL AND SYNTHESIS METHODS

Studies (published up to May 2018) were identified via PubMed to provide fat mass measures in premenopausal and postmenopausal women. We included 201 cross-sectional studies in the metaanalysis, which provided a combined sample size of 1,049,919 individuals and consisted of 478,734 premenopausal women and 571,185 postmenopausal women. Eleven longitudinal studies were included in the metaanalyses, which provided a combined sample size of 2472 women who were premenopausal at baseline and postmenopausal at follow up.

RESULTS

The main findings of this review were that fat mass significantly increased between premenopausal and postmenopausal women across most measures, which included body mass index (1.14 kg/m²; 95% confidence interval, 0.95-1.32 kg/m²), bodyweight (1 kg; 95% confidence interval, 0.44-1.57 kg), body fat percentage (2.88%; 95% confidence interval, 2.13-3.63%), waist circumference (4.63 cm; 95% confidence interval, 3.90-5.35 cm), hip circumference (2.01 cm; 95% confidence interval, 1.36-2.65 cm), waist-hip ratio (0.04; 95% confidence interval, 0.03-0.05), visceral fat (26.90 cm²; 95% confidence interval, 13.12-40.68), and trunk fat percentage (5.49%; 95% confidence interval, 3.91-7.06 cm²). The exception was total leg fat percentage, which significantly decreased (-3.19%; 95% confidence interval, -5.98 to -0.41%). No interactive effects were observed between menopausal status and age across all fat mass measures.

CONCLUSION

The change in fat mass quantity between premenopausal and postmenopausal women was attributable predominantly to increasing age; menopause had no significant additional influence. However, the decrease in total leg fat percentage and increase in measures of central fat are indicative of a possible change in fat mass distribution after menopause. These changes are likely to, at least in part, be due to hormonal shifts that occur during midlife when women have a higher androgen (ie, testosterone) to estradiol ratio after menopause, which has been linked to enhanced central adiposity deposition. Evidently, these findings suggest attention should be paid to the accumulation of central fat after menopause, whereas increases in total fat mass should be monitored consistently across the lifespan.

Quantitative CT assessment of bone mineral density in dogs with hyperadrenocorticism

Canine hyperadrenocorticism (HAC) is one of the most common causes of general osteopenia. In this study, quantitative computed tomography (QCT) was used to compare the bone mineral densities (BMD) between 39 normal dogs and 8 dogs with HAC (6 pituitary-dependent hyperadrenocorticism [PDH]; pituitary dependent hyperadrenocorticism, 2 adrenal hyperadrenocorticism [ADH]; adrenal dependent hyperadrenocorticism) diagnosed through hormonal assay. A computed tomogaraphy scan of the 12th thoracic to 7th lumbar vertebra was performed and the region of interest was drawn in each trabecular and cortical bone. Mean Hounsfield unit values were converted to equivalent BMD with bone-density phantom by linear regression analysis. The converted mean trabecular BMDs were significantly lower than those of normal dogs. ADH dogs showed significantly lower BMDs at cortical bone than normal dogs. Mean trabecular BMDs of dogs with PDH using QCT were significantly lower than those of normal dogs, and both mean trabecular and cortical BMDs in dogs with ADH were significantly lower than those of normal dogs. Taken together, these findings indicate that QCT is useful to assess BMD in dogs with HAC.

Skeletal effects of bariatric surgery: examining bone loss, potential mechanisms and clinical relevance

Bariatric surgery is the most effective therapeutic approach to morbid obesity, resulting in substantial weight loss and improved cardiometabolic profiles; however, a growing body of evidence suggests that bariatric procedures increase both skeletal fragility and the risk of related future fracture secondary to excessive bone loss. Prospective evidence shows that areal bone mineral density (BMD) assessed by dual energy X-ray absorptiometry (DXA) declines by as much as 14% in the proximal femoral regions, including the femoral neck and total hip, 12 months postoperatively. Lumbar spine areal BMD outcomes show greater 12-month postoperative variability across surgical procedures (-8 to +6%) and contrast with no change in volumetric BMD outcomes measured by quantitative computed tomography. Diminished mechanical loading, micronutrient deficiency and malabsorption, along with neurohormonal alterations, offer plausible underlying mechanisms to explain these observed post-bariatric bone changes, but most remain largely unsubstantiated in this population. Importantly, DXA-based skeletal imaging may have limited utility in accurately detecting bone change in people undergoing bariatric surgery; partly because excessive tissue overlying bone increases the variability of areal BMD outcomes. Moreover, a paucity of fracture and osteoporosis incidence data raises questions about whether marked post-bariatric surgery bone loss is clinically relevant or a functional adaptation to skeletal unloading. Future studies that use technology which is able to accurately capture the site-specific volumetric BMD and bone architectural changes that underpin bone strength in people undergoing bariatric surgery, that consider mechanical load, and that better quantify long-term fracture and osteoporosis incidence are necessary to understand the actual skeletal effects of bariatric surgery.

IL-17 mediates estrogen-deficient osteoporosis in an Act1-dependent manner

Estrogen-deficient osteoporosis may be an inflammatory disorder and we therefore asked if IL-17 participates in its pathogenesis. Deletion of the principal IL-17 receptor (IL-17RA) protects mice from ovariectomy (OVX)-induced bone loss. Further supporting a central role of IL-17 in its pathogenesis, OVX-induced osteoporosis is prevented by a blocking antibody targeting the cytokine. IL-17 promotes osteoclastogenesis by stimulating RANK ligand (RANKL) expression by osteoblastic cells, mediated by the IL-17RA SEFIR/TILL domain. Estrogen deprivation, however does not enhance IL-17RA mRNA expression by osteoblasts or in bone, but augments that of Act1, an IL-17RA-interacting protein and signaling mediator. Similar to IL-17RA(-/-) mice, those lacking Act1 are protected from OVX-induced bone loss. Also mirroring IL-17RA-deficiency, absence of Act1 in osteoblasts, but not osteoclasts, impairs osteoclastogenesis via dampened RANKL expression. Transduction of WT Act1 into Act1(-/-) osteoblasts substantially rescues their osteoclastogenic capacity. The same construct, however, lacking its E3 ligase U-box or its SEFIR domain, which interacts with its counterpart in IL-17RA, fails to do so. Estrogen deprivation, therefore, promotes RANKL expression and bone resorption in association with upregulation of the IL-17 effector, Act1, supporting the concept that post-menopausal osteoporosis is a disorder of innate immunity.

Obesity increases precision errors in dual-energy X-ray absorptiometry measurements

The precision errors of dual-energy X-ray absorptiometry (DXA) measurements are important for monitoring osteoporosis. This study investigated the effect of body mass index (BMI) on precision errors for lumbar spine (LS), femoral neck (NOF), total hip (TH), and total body (TB) bone mineral density using the GE Lunar Prodigy. One hundred two women with BMIs ranging from 18.5 to 45.9 kg/m(2) were recruited. Participants had duplicate DXA scans of the LS, left hip, and TB with repositioning between scans. Participants were divided into 3 groups based on their BMI and the percentage coefficient of variation (%CV) calculated for each group. The %CVs for the normal (<25 kg/m(2)) (n=48), overweight (25-30 kg/m(2)) (n=26), and obese (>30 kg/m(2)) (n=28) BMI groups, respectively, were LS BMD: 0.99%, 1.30%, and 1.68%; NOF BMD: 1.32%, 1.37%, and 2.00%; TH BMD: 0.85%, 0.88%, and 1.06%; TB BMD: 0.66%, 0.73%, and 0.91%. Statistically significant differences in precision error between the normal and obese groups were found for LS (p=0.0006), NOF (p=0.005), and TB BMD (p=0.025). These results suggest that serial measurements in obese subjects should be treated with caution because the least significant change may be larger than anticipated.

Femoral bone mineral density reflects histologically determined cortical bone volume in hemodialysis patients

We evaluated the associations between dual energy X-ray absorptiometry (DXA) and histologically determined cancellous and cortical bone volume by controlling for vascular calcifications and demographic variables in hemodialysis (HD) patients. Femoral bone mineral density (f-BMD) was associated with cortical porosity.

INTRODUCTION

Assessment of bone mass in chronic kidney disease patients is of clinical importance because of the association between low bone volume, fractures, and vascular calcifications. DXA is used for noninvasive assessment of bone mass whereby vertebral results reflect mainly cancellous bone and femoral results reflect mainly cortical bone. Bone histology allows direct measurements of cancellous and cortical bone volume. The present study evaluates the association between DXA and histologically determined cancellous and cortical bone volumes in HD patients.

METHODS

In 38 HD patients, DXA was performed for assessment of bone mass, anterior iliac crest bone biopsies for bone volume, and multislice computed tomography for vascular calcifications.

RESULTS

While lumbar bone mineral density (l-BMD) by DXA was not associated with histologically measured cancellous bone volume, coronary Agatson score showed a borderline statistically significant association (P = 0.055). When controlled for age and dialysis duration, f-BMD by DXA was associated with cortical porosity determined by histology (P = 0.005).

CONCLUSIONS

The usefulness of l-BMD for predicting bone volume is limited most probably because of interference by soft tissue calcifications. In contrast, f-BMD shows significant association with cortical porosity.

Phantom-less QCT BMD system as screening tool for osteoporosis without additional radiation

PURPOSE

Phantom-less bone mineral density (PLBMD) systems are easily integrated into the CT workflow for non-dedicated Quantitative CT (QCT) BMD measurements in thoracic and abdominal scans. This in vivo retrospective study aims to determine accuracy and precision of the PLBMD option located on the Extended Brilliance Workspace (Philips Medical Systems, Cleveland, OH, US) from both cross-sectional and longitudinal image data.

MATERIALS AND METHODS

The cross-sectional comparison with phantom-based QCT BMD was performed for 82 patients (61 female, 21 male) with a mean age of (63.0±11.8 SD) years on 197 vertebrae. This was followed by an interobserver variability analysis on 71 vertebrae. The longitudinal PLBMD study was carried out on 45 vertebrae from 10 patients (5 female, 5 male) with a mean age of (64.4±11.5 SD) years. They were re-scanned with standardized scan and contrast-injection protocols within a mean and median of (33±41 SD) and 8 days, respectively. All CT scans were acquired on an Mx8000 Quad (Philips) at Florence-Nightingale Hospital, Kaiserswerth, Germany, in a spiral acquisition mode.

RESULTS

A negligible BMD bias of -0.9mg/cm(3) for the PLBMD option was observed with respect to phantom-based QCT BMD. Applying CT number matching of muscle and fat ROIs, the analysis of cross-sectional interobserver and of longitudinal variability yielded precision values of 3.1mg/cm(3) (CV%=4.0) and 4.2mg/cm(3) (CV%=5.3), respectively.

CONCLUSION

Although the precision is inferior to phantom-based BMD systems, PLBMD is a robust clinical utility for the detection of lowered BMD in a large patient population. This can be achieved without additional radiation exposure from non-contrasted CT scans, to perform an ancillary diagnosis of osteopenia or osteoporosis.

Contribution of the vertebral posterior elements in anterior-posterior DXA spine scans in young subjects

Because DXA is a projection technique, anterior-posterior (AP) measurements of the spine include the posterior elements and the vertebral body. This may be a disadvantage because the posterior elements likely contribute little to vertebral fracture resistance. This study used QCT to quantify the impact of the posterior elements in DXA AP spine measures. We examined 574 subjects (294 females and 280 males), age 6-25 yr, with DXA and QCT. QCT measures were calculated for the cancellous bone region and for the vertebral body including and excluding the posterior elements. DXA data were analyzed for the entire L(3) vertebra and for a 10-mm slice corresponding to the QCT scan region. BMC and BMD were determined and compared using Pearson's correlation. The posterior elements accounted for 51.4 +/- 4.2% of the total BMC, with a significant difference between males (49.9 +/- 4.0%) and females (52.8 +/- 3.9%, p < 0.001). This percentage increased with age in younger subjects of both sexes (p < 0.001) but was relatively consistent after age 17 for males and 16 for females (p > 0.10). DXA areal BMD and QCT volumetric BMD correlated strongly for the whole vertebra including the posterior elements (R = 0.83), with BMC measures showing a stronger relationship (R = 0.93). Relationships were weaker when excluding the posterior elements. We conclude that DXA BMC provides a measure of bone that is most consistent with QCT and that the contribution of the posterior elements is consistent in young subjects after sexual maturity.

Vitamin D status and its relationship to body fat, final height, and peak bone mass in young women

CONTEXT

Vitamin D insufficiency has now reached epidemic proportions and has been linked to low bone mineral density, increased risk of fracture, and obesity in adults. However, this relationship has not been well characterized in young adults.

OBJECTIVE

The objective of the study was to examine the relationship between serum 25-hydroxyvitamin D (25OHD), anthropometric measures, body fat (BF), and bone structure at the time of peak bone mass.

DESIGN

This was a cross-sectional study. OUTCOME MEASURES AND SUBJECTS: Anthropometric measures, serum 25OHD radioimmunoassay values, and computed tomography and dual-energy x-ray absorptiometry values of BF and bone structure in 90 postpubertal females, aged 16-22 yr, residing in California were measured.

RESULTS

Approximately 59% of subjects were 25OHD insufficient (<or=29 ng/ml), and 41% were sufficient (>or=30 ng/ml). Strong negative relationships were present between serum 25OHD and computed tomography measures of visceral and sc fat and dual-energy x-ray absorptiometry values of BF. In addition, weight, body mass, and imaging measures of adiposity at all sites were significantly lower in women with normal serum 25OHD concentrations than women with insufficient levels. In contrast, no relationship was observed between circulating 25OHD concentrations and measures of bone mineral density at any site. Unexpectedly, there was a positive correlation between 25OHD levels and height.

CONCLUSIONS

We found that vitamin D insufficiency is associated with increased BF and decreased height but not changes in peak bone mass.

Quantitative CT reference values for vertebral trabecular bone density in children and young adults

PURPOSE

To determine normative reference values for vertebral trabecular bone density (TBD) obtained by using quantitative computed tomography (CT) in healthy white children, teenagers, and young adults of both sexes.

MATERIALS AND METHODS

The data presented in this HIPAA-compliant study are a compilation of data from multiple investigations on the determinants of bone acquisition in healthy children conducted at this institution from 1992 to 2006. The institutional review board for clinical investigations approved the protocols for each of these studies, and written informed consent was provided by all parents and/or participants. Quantitative CT measurements of TBD (in milligrams per cubic centimeter) were obtained at the first, second, and third lumbar vertebrae in 1222 healthy white male and female subjects aged 5-21 years (mean age for male subjects, 15.1 years +/- 3.6 [standard deviation]; range, 5.6-21.9 years; mean age for female subjects, 14.2 years +/- 3.9; range, 5.7-21.6 years; mean age for both sexes, 14.6 years +/- 3.8). Mean and standard deviations for TBD were determined for each age group in 1-year intervals, and Student t tests for unpaired data were performed to compare male subjects with female subjects.

RESULTS

TBD increased equally during growth in male and female subjects. Although the percentage increase in TBD was similar for both sexes (23.7% [57 of 241] for male subjects, 22.2% [54 of 243] for female subjects), the rise began and reached peak values at an earlier age in female subjects; increases in TBD occurred from 10-15 years of age in female subjects, whereas in male subjects, these increases were not observed until age 12 years and were completed at 17 years.

CONCLUSION

This study provides reference standards for quantitative CT bone measurements in children and young adults, which may aid in the diagnosis, prevention, and treatment of pediatric metabolic bone disorders.

Construction of the femoral neck during growth determines its strength in old age

Study of the design of the FN in vivo in 697 women and in vitro in 200 cross-sections of different sizes and shapes along each of 13 FN specimens revealed that strength in old age was largely achieved during growth by differences in the distribution rather than the amount of bone material in a given FN cross-section from individual to individual.

INTRODUCTION

We studied the design of the femoral neck (FN) to gain insight into the structural basis of FN strength in adulthood and FN fragility in old age.

MATERIALS AND METHODS

Studies in vivo were performed using densitometry in 697 women and in vitro using high-resolution microCT and direct measurements in 13 pairs of postmortem specimens.

RESULTS

The contradictory needs of strength for loading yet lightness for mobility were met by varying FN size, shape, spatial distribution, and proportions of its trabecular and cortical bone in a cross-section, not its mass. Wider and narrower FNs were constructed with similar amounts of bone material. Wider FNs were relatively lighter: a 1 SD higher FN volume had a 0.67 (95% CI, 0.61-0.72) SD lower volumetric BMD (vBMD). A 1 SD increment in height was achieved by increasing FN volume by 0.32 (95% CI, 0.25-0.39) SD with only 0.15 (95% CI, 0.08-0.22) SD more bone, so taller individuals had a relatively lighter FN (vBMD was 0.13 [95% CI, 0.05-0.20 SD] SD lower). Greater periosteal apposition constructing a wider FN was offset by even greater endocortical resorption so that the same net amount of bone was distributed as a thinner cortex further from the neutral axis, increasing resistance to bending and lowering vBMD. This was recapitulated at each point along the FN; varying absolute and relative degrees of periosteal apposition and endocortical resorption focally used the same amount of material to fashion an elliptical FN of mainly cortical bone near the femoral shaft to offset bending but a more circular FN of proportionally more trabecular and less cortical bone to accommodate compressive loads adjacent to the pelvis. This structural heterogeneity was largely achieved by adaptive modeling and remodeling during growth-most of the variance in FN volume, BMC, and vBMD was growth related.

CONCLUSIONS

Altering structural design while minimizing mass achieves FN strength and lightness. Bone fragility may be the result of failure to adapt bone's architecture to loading, not just low bone mass.

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.

Assessment of bone acquisition in childhood and adolescence

Availability, ease of use, relative low cost, and minimal radiation exposure have made dual-energy x-ray absorptiometry the most widely used technique worldwide to obtain bone measurements for both research and clinical purposes in pediatric populations. However, errors related to growth and maturity significantly diminish the accuracy of dual-energy x-ray absorptiometry bone measurements. Several investigators have found that dual-energy x-ray absorptiometry in children frequently leads to a misdiagnosis of osteoporosis and an underestimation of the amount of bone. In this regard, a recent official position paper by the International Society for Clinical Densitometry states that subjects <20 years of age should not be given a diagnosis of osteoporosis on the basis of dual-energy x-ray absorptiometry criteria. Nevertheless, the increased awareness that osteoporosis has its antecedents in childhood and the demand for examinations of bone acquisition and response to therapy stress the urgent need to improve the value of dual-energy x-ray absorptiometry measurements for children.

Photon absorptiometry, bone densitometry and the challenge of osteoporosis

During the lifetime of Physics in Medicine and Biology, osteoporosis has been recognized as the cause of a major health burden for societies, particularly within developed countries. The health detriment is associated with the consequences of bone fractures and the subsequent increases in morbidity and mortality. Much of the credit for the current availability of means for identifying groups of subjects at risk of fracture and the provision of means for the effective treatment of excessive bone loss can be attributed to the technique of dual photon absorptiometry. In this review, the history of the development of techniques based on the interactions of x- and gamma-rays with bone is considered and the ultimate dominance of x-ray based absorptiometry is described. The advantages and disadvantages of current absorptiometric techniques are presented and the likely future path for bone measurement is outlined.

The DXL Calscan heel densitometer: evaluation and diagnostic thresholds

The DXL Calscan (Demetech AB) is a new dual energy X-ray absorptiometry device for determining heel bone mineral density (BMD). The system is based on the standard technique of dual energy X-ray absorptiometry (DXA), using a fan beam configuration, but introduces an additional laser measurement of heel thickness intended to improve accuracy. We have examined the utility, in vitro and in vivo performance of the DXL Calscan and established triage thresholds based on the UK's National Osteoporosis Society guidelines on peripheral densitometry. The Calscan proved convenient, easy to use and was stable over time and within a range of operating temperatures. Short-term in vitro precision as %CV, with phantom repositioning, was 0.75% and long term precision 0.73%. Precision in vivo, determined from duplicate right heel scans of 67 subjects, was 1.19%. Effective radiation dose to the patient was <0.1 microSv per scan. 140 white females (70 osteoporotic and 70 non-osteoporotic), aged 55-70 years underwent scans of both heels. Subjects were defined as osteoporotic or non-osteoporotic on the basis of axial DXA (spine L2-L4 and total hip). Triage thresholds for reassurance-referral or referral-treatment were 0.391 g cm(-2) and 0.306 g cm(-2) for non-dominant and 0.395 g cm(-2), 0.294 g cm(-2) for dominant heel, respectively. The non-dominant heel proved slightly superior to the dominant for triage purposes. Of the seven non-osteoporotic subjects misclassified as osteoporotic by Calscan of either heel, six had severe axial osteopenia. If operated by trained personnel and used in appropriate populations exhibiting risk factors, the Calscan is well suited for use in the management of post-menopausal osteoporosis.

Dual energy x-ray laser measurement of calcaneal bone mineral density

In dual energy x-ray absorptiometry (DXA) the photon attenuation is assumed to be similar in soft tissue overlying, adjacent to and inside the measured bone. In the calcaneal dual energy x-ray laser (DXL) technique, this assumption is not needed as attenuation by soft tissues at the local bone site is determined by combining DXA and heel thickness measurements. In the present study, 38 subjects were measured with DXL Calscan, Lunar PIXI and Lunar DPX-IQ DXA instruments and Hologic Sahara ultrasound instrument, and the performance and agreement of the instruments were analysed. Furthermore, numerical simulations on the effect of non-uniform fat-to-lean tissue ratio within soft tissue in heel were conducted. In vivo short-term precision (CV%, sCV%) of DXL Calscan (1.24%, 1.48%) was similar to that of Lunar PIXI (1.28%, 1.60%). Calcaneal areal bone mineral densities (BMD, g cm(-2)) measured using DXL Calscan and Lunar PIXI predicted equally well variations in BMD of femoral neck (r2 = 0.63 and 0.52, respectively) or lumbar spine (r2 = 0.61 and 0.64, respectively), determined with Lunar DPX-IQ. BMD values measured with DXL Calscan were, on average, 19% lower (p < 0.01) than those determined with Lunar PIXI. Interestingly, the difference in BMD values between instruments increased as a function of body mass index (BMI) (r2 = 0.17, p < 0.02) or heel thickness (r2 = 0.37, p < 0.01). Numerical simulations suggested that the spatial variation of soft tissue composition in heel can induce incontrollable inaccuracy in BMD when measured with the DXA technique. Theoretically, in contrast to DXA instruments, elimination of the effect of non-uniform soft tissue is possible with DXL Calscan.

Patient-specific DXA bone mineral density inaccuracies: quantitative effects of nonuniform extraosseous fat distributions

Nonuniform extraosseous fat is shown to raise the magnitude of inaccuracies in DXA in vivo BMD measurements into the range of 20-50% in clinically relevant cases. Hence, DXA-based bone fragility diagnoses/ prognoses and evaluations of bone responsiveness to treatment can be unreliable. Patient-specific DXA in vivo bone mineral areal density (BMD) measurements have been demonstrated to be inherently inaccurate even when extraosseous fat (F) and lean muscle tissue (L) are uniformly distributed throughout the scan region of interest (ROI). The present work extends these investigations to quantitative evaluation of the extent to which clinically realistic soft tissue inhomogeneities external to the bone within the DXA scan ROI affect patient-specific in vivo BMD measurement inaccuracies. The results are particularly relevant to patient-specific lumbar vertebral and proximal femoral sites. Norland, Hologic, and Lunar DXA scans and corresponding DXA simulation studies of the same set of 225 different phantom arrays were carried out. The phantoms were specially fabricated absorptiometric replications of bone mineral material (B), red marrow (RM), and yellow marrow (YM) mixtures, and extraosseous F and L combinations spanning the anthropometric ranges encountered clinically. The three different DXA scanners yielded BMD results that effectively coincided, were in excellent agreement with the findings of the present corresponding DXA-simulation studies in each case, and confirmed the validity of the DXA BMD inaccuracy analysis formalism. It was found that only relatively small extraosseous soft tissue inhomogeneities within the ROI of DXA BMD scans can increase substantially the already sizable BMD inaccuracies shown earlier to pertain for uniformly distributed extraosseous soft tissues. The extent of these in vivo BMD inaccuracies (%) are shown to depend on the mean extraosseous F-to-L areal density ratio and its degree of nonuniformity within the local bone scan ROI, the marrow thickness and specific composition, and the actual BMD in any given case. It was found that patient-specific DXA-measured in vivo BMD inaccuracies can, in many clinically encountered cases, be as large as 20-50%, particularly so for osteopenic, osteoporotic, and elderly patients. It is concluded that, because these DXA in vivo BMD inaccuracies are unavoidable and clinically unpredictable, diagnoses/ prognoses of bone fragility and evaluations of bone responsiveness to treatment of individual patients based mainly on DXA in vivo BMD measurements can be unreliable.

Dual-energy X-ray absorptiometry in diagnosis of osteoporosis: basic principles, indications, and scan interpretation

Dual-energy x-ray absorptiometry is currently the most commonly used modality for the diagnosis of osteoporosis, allowing fast, accurate, and noninvasive measurements of bone mineral density. In this review we discuss the principles, applications, advantages, and limitations of this diagnostic technique.

Are soft tissue composition of bone and non-bone pixels in spinal bone mineral measurements by DXA similar? Impact of weight loss

Weight loss seems associated with a decrease in bone mineral density (BMD) as measured by absorptiometry, which may be the result of accuracy errors caused by differences in soft tissue between non-bone and bone pixels. The aim was to study the abdominal fat% and thickness in regions corresponding to non-bone, soft tissue-only and bone pixels for spinal BMD measurements by dual energy X-ray absorptiometry (DXA), and to calculate the theoretical errors in measurement of changes in BMD by DXA as a result of changes in soft tissue heterogeneity with weight loss. Abdominal computed tomography (CT) and DXA scans were performed in 34 obese subjects (42.1+/-10.1 years (mean +/- SD), wt: 102.1+/-12.8 kg and BMI: 36.6+/-3.8 kg m(-2)) before and after weight loss (11.3+/-6.9 kg after 1 year). There were some significant differences in fat% and thickness of soft tissue between abdominal regions corresponding to non-bone and bone pixels, respectively, for spinal BMD measurements by DXA, both before and after weight loss. With weight loss there were some changes in the soft tissue heterogeneity, which caused a minor theoretical error (apparent, but false decrease of 1-2%) of borderline significance for the anterior-posterior (AP) spinal BMD by DXA.

Bone turnover and density in obese premenopausal women during moderate weight loss and calcium supplementation

Bone turnover is increased during weight loss in postmenopausal women and can be suppressed with calcium supplementation. In this study, we assessed the influence of energy restriction with and without calcium supplementation (1 g/day) in premenopausal women. Thirty-eight obese premenopausal women (body mass index [BMI] of 35.0 +/- 3.9 kg/m2) completed a 6-month study of either moderate weight loss or weight maintenance. During weight loss, women were randomly assigned to either a calcium supplementation (n = 14) or placebo group (n = 14) and lost 7.5 +/- 2.5% of their body weight. The control group of women (n = 10) maintained their body weight. Total body and lumbar bone mineral density (LBMD) and content were measured by dual-energy X-ray absorptiometry (DXA) at baseline and after weight loss. Throughout the study, blood and urine samples were collected to measure bone turnover markers and hormones. During moderate energy restriction, dietary calcium intake decreased (p < 0.05) and the bone resorption marker deoxypyridinoline (DPD) increased slightly (p < or = 0.05) without evidence of bone loss. Calcium supplementation during weight loss tended to increase lumbar BMD by 1.7% (p = 0.05) compared with the placebo or weight maintenance groups. In contrast to our previous findings in postmenopausal women, premenopausal obese women who consume a low calcium diet do not lose bone over a 6-month period, whether their weight is stable or decreasing moderately.

Inaccuracies inherent in dual-energy X-ray absorptiometry in vivo bone mineral densitometry may flaw osteopenic/osteoporotic interpretations and mislead assessment of antiresorptive therapy effectiveness

New, anatomically realistic simulation studies based on a cadaveric lumbar vertebra and a broad range of soft tissue anthropometric representations have quantitatively delineated inaccuracies inherent in dual-energy X-ray absorptiometry (DXA) in vivo bone mineral density (BMD) methodology. It is found that systematic inaccuracies in DXA BMD measurements may readily exceed +/-20% at typical in vivo lumbar vertebral sites, especially for osteopenic/osteoporotic, postmenopausal, and elderly patients. These findings are quantitatively compared with extensive clinical evidence of strong, positive correlations between soft tissue anthropometrics and DXA in vivo BMD upon which prior significant bone biology interpretations and implications have been based. The agreement is found to be both qualitatively and quantitatively excellent. Moreover, recent extensive multicenter clinical studies have also exposed new facets of strong linkages between body mass/percent body fat/body mass index (BMI) and DXA-measured BMD that are particularly relevant to osteopenia/osteoporosis and remedial effectiveness of antiresorptive drug therapy. These seemingly disparate and unrelated diagnostic and prognostic aspects of clinically observed associations between soft tissue anthropometrics and measured vertebral BMD are, in this study, self-consistently shown to share the common origin of being manifestations of systematic inherent inaccuracies in DXA in vivo BMD methodology, without the need to invoke any underlying biologically causal mechanism(s). These inaccuracies arise principally from absorptiometric disparities between the intra- and extraosseous soft tissues within the DXA scan region of interest. The present evaluative comparisons are based exclusively on an incisive and diverse body of clinical data that appears difficult to dismiss or discount. Previous invocations of biologically causal mechanisms responsible for this broad range of observations linking body mass, percent body fat, and/or BMI to measured BMD now appear questionable. This doubtful status has also been extended in the present work to previously reported relationships between antiresorptive therapies and observed changes in DXA-derived BMD. These findings strongly indicate that critical and insightful reassessments of diagnostic/prognostic imputations underpinned by DXA in vivo BMD measurements are warranted. It is suggested that a good deal of what is known of bone fragility, bone densitometry, antiresorptive drug efficacy, and/or other therapeutic regimens, if based on patient-specific in vivo DXA methodology, may prove to be equivocal and tenuous.

Lumbar osteoarthritis, bone mineral density, and quantitative ultrasound

Low bone mass is a major risk factor for osteoporotic fractures. Thus, bone density evaluation, performed by Dual Energy X-ray Absorptiometry (DXA) is important for diagnosis and monitoring treatment of osteoporosis. The accuracy of DXA, particularly at the lumbar spine, can be affected by several factors such as degenerative diseases. To evaluate the effects of vertebral osteophytosis on densitometric measurements, we examined 198 women, aged 32-81 years, who had undergone lateral X-ray of the lumbar spine. We classified patients according to different grades of osteophytosis, and evaluated bone density at the lumbar spine and the proximal femur by DXA. We also performed quantitative ultrasound at the heel (QUS). Patients with severe osteophytosis were significantly older (p < 0.0005), and values were adjusted for this parameter. We observed a significant increase in lumbar bone density with worsening osteophytosis (p < 0.02). On the contrary, no significant differences were found at the femur and QUS. According to bone density at the femoral neck, we subdivided patients into two groups: osteoporotic (group A) and non-osteoporotic (group B). Both groups showed increasingly high bone density at the spine with worsening osteophytosis (A: p < 0.01; B: p < 0.02). No differences were found in all the other evaluations. In conclusion, lumbar spine measurement is dramatically influenced by osteophytosis, particularly in the elderly. Consequently, other strategies should be performed such as evaluation of the hip and also measurement of the heel by ultrasound, which could be an interesting approach in these cases.

Monte Carlo modelling of an extended DXA technique

The precision achieved in measuring bone mineral density (BMD) by commercial dual-energy x-ray absorptiometry (DXA) machines is typically better than 1%, but accuracy is considerably worse. Errors, due to inhomogeneous distributions of fat, of up to 10% have been reported. These errors arise because the DXA technique assumes a two-component model for the human body, i.e. bone mineral and soft tissue. This paper describes an extended DXA technique that uses a three-component model of human tissue and significantly reduces errors due to inhomogeneous fat distribution. In addition to two x-ray transmission measurements, a measurement of the path length of the x-ray beam within the patient is required. This provides a third equation, i.e. T = ts + tb + tf where T, ts, tb and tf are the total, lean soft tissue, bone mineral and fatty tissue thicknesses respectively. Monte Carlo modelling was undertaken to make a comparison of the standard and extended DXA techniques in the presence of inhomogeneous fat distribution. Two geometries of varying complexity were simulated. In each case the extended DXA technique produced BMD measurements that were independent of soft tissue composition whereas the standard technique produced BMD measurements that were strongly dependent on soft tissue composition. For example, in one case, the gradients of the plots of BMD versus fractional fat content were for standard DXA (-0.183+/-0.037) g cm(-2) and for extended DXA (0.027+/-0.044) g cm(-2). In all cases the extended DXA method produced more accurate but less precise results than the standard DXA technique.

A suggested methodology for the construction of national bone densitometry reference ranges: 1372 Caucasian women from four UK sites

This paper presents a simple methodology for combining bone densitometry data from different sites in the UK, having instruments from the same manufacturer (LUNAR Radiation). Additive normalization factors were used on all data prior to inclusion in a reference database which ultimately included data on 1372 Caucasian women, aged 20-70 years, of whom 749 were post-menopausal. Reference data for spine (L2-L4) and femoral neck bone mineral density are given in tabular form as 3 year moving averages for: (1) all women; (2) perimenopausal women grouped by menopausal status; and (3) post-menopausal women with respect to years since menopause. These data may be used to construct Z-score. T-score or percentile reporting ranges and may be adopted as the core for a UK reference range.

The benefit of hormone replacement therapy on bone mass is greater at the vertebral body than posterior processes or proximal femur

The aim of this study was to determine whether the higher vertebral bone mass in women receiving hormone replacement therapy (HRT) is confined to the trabecular rich vertebral body rather than the predominantly cortical posterior processes, and to determine whether the protective effect of HRT at the proximal femur, a predominantly cortical site, is less than at the spine. Bone mass (g) of the third lumbar vertebra (total, vertebral body and posterior processes, measured by lateral scanning), and bone mineral density (g/cm2) of the femoral neck, Ward's triangle, and trochanter were measured using dual X-ray absorptiometry in a cross-sectional study of 71 women receiving HRT for 5.7 +/- 0.4 years (mean +/- SEM), ranging from 1 to 21 years, 69 age-matched controls, and 42 premenopausal controls aged 20 to 40 years. Relative to untreated postmenopausal controls, total bone mass of the third lumbar vertebra (body plus posterior processes) by postero-anterior (PA) scanning was 0.4 +/- 0.1 SD or 9.6 +/- 3.0% higher in HRT treated women (p < 0.01). By lateral scanning, total bone mass was higher than age-matched controls (z score 0.4 +/- 0.1 SD or 11.2 +/- 3.4%, p < 0.01). This difference was confined to the vertebral body (z score 0.6 +/- 0.1 SD, p < 0.001), which was 17.1 +/- 3.3% higher than in age-matched controls (p < 0.001). Bone mass of the posterior processes was no higher [z score 0.1 +/- 0.1, not significant (NS)]. The deficit at the vertebral body in HRT-treated women, relative to premenopausal controls, was half the deficit at the vertebral body in untreated postmenopausal women (t score -0.7 +/- 0.1 vs. -1.4 +/- 0.1 SD, respectively; p < 0.001) but no less at the posterior processes (t score -1.6 +/- 0.2 vs. -1.9 +/- 0.2 SD, respectively; NS). Similarly, the deficit in the vertebral body in the HRT treated group was half the deficit at their posterior processes (t score -0.7 +/- 0.1 SD vs. -1.6 +/- 0.2, respectively; p < 0.001). In HRT-treated women, bone mass diminished significantly with age at the posterior processes (r = -0.31, p < 0.01), but not at the vertebral body (r = -0.21, p = 0.07). Bone mass diminished significantly with age at the vertebral body and posterior processes in untreated women (r = -0.55, p < 0.001; r = -0.45, p < 0.001, respectively). Bone density (g/cm2) diminished at all femoral sites with advancing age in HRT-treated women. A protective effect was seen at the femoral neck and Ward's triangle, but not trochanter (z score 0.2 +/- 0.1, p = 0.06; 0.3 +/- 0.1, p < 0.05; 0.0 +/- 0.1, NS, respectively). In conclusion, the protective effect of HRT against bone loss at the vertebral body, the site of fracture in osteoporosis, may be underestimated by PA scanning. The greater benefit at the vertebral body, and more modest effect at the proximal femur, suggests that HRT may be a more effective means of reducing the risk of spine than hip fractures.

Apparent pre- and postmenopausal bone loss evaluated by DXA at different skeletal sites in women: the OFELY cohort

We measured the bone mineral density (BMD) at various skeletal sites (total body, hip, anteroposterior [AP] and lateral [lat] spine, and forearm) in a large population-based cohort of women aged 31-89 years (the OFELY cohort), and results were analyzed according to age and postmenopausal years. A significant apparent bone loss was found before the menopause in cancellous bone, i.e., at the lat spine and Ward's triangle (-10%; p < 0.05-0.001). Cross-sectional analysis indicated that, after the menopause, apparent bone loss was accelerated within the 10 years following menopause, continued thereafter at all sites except the AP spine, and was again accelerated in elderly menopausal for more than 25 years. Between 30 and 80 years, BMD decreased by 15 to 44% (T score -1.6 to -3.4) according to the site. The amount of apparent bone loss was highest at the Ward's triangle when expressed in percentage (44%) and at the mid- and distal radius when expressed in number of standard deviations from the peak bone mass (-3.4). As a result, the percentage of women classified as osteoporotic according to the World Heath Organization, i.e., with a T score < or = -2.5, varied substantially from site to site and was highest at the radius (37% and 46%) and lateral spine (25-31%), intermediate at the Ward's triangle, AP spine, and whole body BMD, and lowest at the whole body bone mineral content, femoral neck, and trochanter (10-12%). In conclusion, this cross-sectional but large study suggests that there is a moderate apparent premenopausal bone loss that occurs only at cancellous bone sites and that apparent bone loss is accelerated at most skeletal sites after the age of 75 years. Because of the highly variable coefficient of variation of the peak bone mass at various skeletal sites, the percentage of postmenopausal women identified as being osteoporotic varies widely according to the site of measurement.

A longitudinal study of supine lateral DXA of the lumbar spine: a comparison with posteroanterior spine, hip and total-body DXA

We report a study to assess whether supine lateral dual-energy X-ray absorptiometry (DXA) scans of the lumbar spine provide better data for monitoring response to treatment than alternative measurement sites such as the posteroanterior (PA) spine, hip and total body. The study population was 152 women enrolled in a placebo-controlled clinical trial of cyclical etidronate therapy. All subjects were 1-10 years after the menopause with bone mineral density (BMD) between 0 and -2 SD of age-matched normal women. Paired PA and lateral spine, left hip and total-body DXA scans were performed at baseline, 1 year and 2 years on a Hologic QDR-2000. One hundred and thirty-one subjects completed the study. Mean percentage change from baseline at 2 years in the treated (n = 61) and control (n = 70) groups was calculated for vertebral body, width-adjusted (WA) vertebral body, mid-vertebral body and WA mid-vertebral body BMD measurement on the lateral scans and compared with the percentage changes in PA spine, femoral neck, trochanter, Ward's triangle and total-body BMD. The long-term precision for each BMD measurement site was obtained by linear regression analysis in subjects taking placebo. Overall treatment effect, defined as the difference in the percentage change in BMD in the two treatment groups at 2 years, was divided by long-term precision to give an index of the ability of each site to monitor response to treatment. Results (and standard errors) normalized to the ratio of treatment effect/ precision for PA spine BMD were as follows: PA spine, 1.00; vertebral body, 0.89 (0.14); WA vertebral body, 0.78 (0.14); mid-vertebral body, 0.65 (0.14); WA mid-vertebral body, 0.60 (0.13); femoral neck, 0.35 (0.15); trochanter, 0.45 (0.15); Ward's triangle, 0.59 (0.22); total body, 0.52 (0.19). Although treatment effect was larger for lateral than for PA spine BMD, this advantage was offset by the greater precision errors. PA spine BMD remains the optimum measurement for longitudinal studies in recently postmenopausal women.

Equivalent deficits in bone mass of the vertebral body and posterior processes in women with vertebral fractures: implications regarding the pathogenesis of spinal osteoporosis

Reduced bone mass of the spine in women with vertebral fractures is attributed to excessive trabecular bone loss from the vertebral body. However, the measurement obtained by posteroanterior (PA) scanning includes the posterior processes and the vertebral body, each comprising about 50% of the total vertebral mass. Thus, the deficit in bone mass by PA scanning may be due to deficits in one or both of these structures. We asked two questions: (1) In healthy women, is the age-related diminution in bone mass of the vertebral body greater than the diminution at the posterior processes? (2) In women with vertebral fractures, is the deficit in bone mass at the vertebral body, the fracture site in spinal osteoporosis, greater than at the posterior processes? Bone mass of the posterior processes and vertebral body of the third lumbar vertebra was measured by lateral scanning using dual-energy X-ray absorptiometry (DXA). Compared with 27 premenopausal women, deficits in 27 postmenopausal women at the posterior processes and vertebral body, respectively, were 35.9 +/- 3.7 and 25.2 +/- 4.1% (p < 0.05); t score, -1.5 +/- 0.2 and -1.1 +/- SD (p = 0.09). Compared with the postmenopausal (age-matched) women, deficits in 21 women with vertebral fractures at the posterior processes and vertebral body, respectively, were 22.6 +/- 4.9 and 24.5 +/- 8.3% (p = NS); Z score, -0.8 +/- 0.2 and -0.8 +/- 0.3 (p = NS). In vivo the bone mass of the vertebral body as a percentage of the whole vertebra was 45.7 +/- 0.1 in premenopausal women, 48.9 +/ 1.9 in postmenopausal women, 51.5 +/- 1.1 in women with low bone mass but no fractures, 52.7 +/- 2.4 in women with vertebral fractures, and 51.9 +/- 2.5% in vitro, based on autopsy specimens from 19 postmenopausal women aged 65 - 95 years. The lower spinal bone density measured using PA scanning in women with spine fractures may not be due to excessive or disproportionate trabecular bone loss from the vertebral body because comparable deficits are found at the posterior processes. Whether these deficits are due to reduced peak bone mass, trabecular bone loss, cortical bone loss, or varying combinations of these mechanisms remains to be established.