Jessie Libber

Spine Trabecular Bone Score Subsequent to Bone Mineral Density Improves Fracture Discrimination in Women

Bone mineral density (BMD) measured by dual-energy X-ray absorptiometry (DXA) is used to diagnose osteoporosis and assess fracture risk. However, DXA cannot evaluate trabecular microarchitecture. This study used a novel software program (TBS iNsight; Med-Imaps, Geneva, Switzerland) to estimate bone texture (trabecular bone score [TBS]) from standard spine DXA images. We hypothesized that TBS assessment would differentiate women with low trauma fracture from those without. In this study, TBS was performed blinded to fracture status on existing research DXA lumbar spine (LS) images from 429 women. Mean participant age was 71.3 yr, and 158 had prior fractures. The correlation between LS BMD and TBS was low (r = 0.28), suggesting these parameters reflect different bone properties. Age- and body mass index-adjusted odds ratios (ORs) ranged from 1.36 to 1.63 for LS or hip BMD in discriminating women with low trauma nonvertebral and vertebral fractures. TBS demonstrated ORs from 2.46 to 2.49 for these respective fractures; these remained significant after lowest BMD T-score adjustment (OR = 2.38 and 2.44). Seventy-three percent of all fractures occurred in women without osteoporosis (BMD T-score > -2.5); 72% of these women had a TBS score below the median, thereby appropriately classified them as being at increased risk. In conclusion, TBS assessment enhances DXA by evaluating trabecular pattern and identifying individuals with vertebral or low trauma fracture. TBS identifies 66-70% of women with fracture who were not classified with osteoporosis by BMD alone.

Dual-Energy X-Ray Absorptiometry Measured Regional Body Composition Least Significant Change: Effect of Region of Interest and Gender in Athletes

Dual-energy X-ray absorptiometry (DXA) is widely used to evaluate body composition in athletes. Knowledge of measurement precision is essential for monitoring body composition changes over time. This study begins characterizing DXA body composition precision in 60 (30 males and 30 females) Division 1 athletes focusing on gender, regional, and tissue type differences. Two total body scans with repositioning between were performed on the same day. Least significant change (LSC) for the root-mean-square deviation (LSCRMSD) and the percent coefficient of variation (LSC%CV) for total, lean, and fat mass was calculated for 6 regions of interest. The effect of gender, region, tissue type, and mass on the standard deviation (SD) and percent coefficient of variation (%CV) between the 2 scans was evaluated using repeated measures regression analysis. Statistically significant effects of gender, region, tissue type, and mass on SD and %CV were noted. To generalize, a nonlinear positive relationship between LSCRMSD and mass and a nonlinear negative relationship between LSC%CV and mass were observed. In conclusion, DXA body composition LSC varies among genders, regions, tissues, and mass. As such, when evaluating serial body composition in athletes, especially if assessing regional change, knowledge of precision in individuals of similar body size and gender to the population of interest is needed.

Clinical Observations in Total Body DXA: Technical Aspects of Positioning and Analysis

Total body (TB) dual-energy X-ray absorptiometry (DXA) can assess regional body composition, which may necessitate greater attention to patient positioning and analysis than required for whole body assessment. This report describes technical challenges experienced in performing TB DXA, explores the frequency with which autoanalysis inaccuracies occur, assesses their effect on regional body composition results, and describes a uniform clinical approach for TB DXA positioning and analysis. Patient positioning followed manufacturer recommendations with additional facility-imposed procedures. On visual inspection, it was apparent that automated analysis often did not meet manufacturer guidelines, thus requiring manual alteration. To explore the frequency with which manual adjustments were needed, and the impact on results, TB scans were obtained in 20 men and 20 women aged 18-93 yr. The head line was altered in 98%, one or both shoulder lines in 93%, and the lateral hip boundary in 40%. Manual and automated TB analyses were highly correlated (r(2)=0.98-1.00). However, regional result correlation was less robust, that is, automated and manual appendicular lean mass differed by more than our least significant change in 33%. In conclusion, manual correction of automated TB DXA scan analysis is often needed. Such alterations do not affect TB measures but may affect regional body composition results.

A DXA Whole Body Composition Cross-Calibration Experience: Evaluation With Humans, Spine, and Whole Body Phantoms

New densitometer installation requires cross-calibration for accurate longitudinal assessment. When replacing a unit with the same model, the International Society for Clinical Densitometry recommends cross-calibrating by scanning phantoms 10 times on each instrument and states that spine bone mineral density (BMD) should be within 1%, whereas total body lean, fat, and %fat mass should be within 2% of the prior instrument. However, there is limited validation that these recommendations provide adequate total body cross-calibration. Here, we report a total body cross-calibration experience with phantoms and humans. Cross-calibration between an existing and new Lunar iDXA was performed using 3 encapsulated spine phantoms (GE [GE Lunar, Madison, WI], BioClinica [BioClinica Inc, Princeton, NJ], and Hologic [Hologic Inc, Bedford, MA]), 1 total body composition phantom (BioClinica), and 30 human volunteers. Thirty scans of each phantom and a total body scan of human volunteers were obtained on each instrument. All spine phantom BMD means were similar (within 1%; <-0.010 g/cm2 bias) between the existing and new dual-energy X-ray absorptiometry unit. The BioClinica body composition phantom (BBCP) BMD and bone mineral content (BMC) values were within 2% with biases of 0.005 g/cm2 and -3.4 g. However, lean and fat mass and %fat differed by 4.6%-7.7% with biases of +463 g, -496 g, and -2.8%, respectively. In vivo comparison supported BBCP data; BMD and BMC were within ∼2%, but lean and fat mass and %fat differed from 1.6% to 4.9% with biases of +833 g, -860 g, and -1.1%. As all body composition comparisons exceeded the recommended 2%, the new densitometer was recalibrated. After recalibration, in vivo bias was lower (<0.05%) for lean and fat; -23 and -5 g, respectively. Similarly, BBCP lean and fat agreement improved. In conclusion, the BBCP behaves similarly, but not identical, to human in vivo measurements for densitometer cross-calibration. Spine phantoms, despite good BMD and BMC agreement, did not detect substantial lean and fat differences observed using BBCP and in vivo assessments. Consequently, spine phantoms are inadequate for dual-energy X-ray absorptiometry whole body composition cross-calibration.

Does the Precision of Dual-Energy X-ray Absorptiometry for Bone Mineral Density Differ by Sex?

Given larger bone size in men, bone mineral density (BMD) precision might differ between sexes. This study compared dual-energy X-ray absorptiometry BMD precision of 3 International Society for Clinical Densitometry-certified technologists in older men and women. Each technologist scanned a cohort of 30 men and 30 women (total n = 180) by using a Lunar iDXA densitometer (GE Healthcare, Madison, WI). Each volunteer had 2 lumbar spine and bilateral hip scans with repositioning between examinations. BMD least significant change was calculated. Age and body mass index did not differ between men and women. Mean height and weight were greater in men, 174.6 cm ± 6.9 and 81.6 kg ± 11.1 respectively, (p < 0.0001) than in women, 161.5 cm ± 5.9/69.1 kg ± 14.2, respectively. Bone area was greater in men (p < 0.0001) at all sites. BMD least significant change was statistically better (p < 0.05) in women at the mean total femur (0.014 vs 0.018 g/cm(2)) and left femoral neck (0.025 vs 0.038 g/cm(2)), but not different at either total femur, the right femoral neck, or lumbar spine (all p > 0.05). In conclusion, statistically significant male/female differences in BMD precision were observed at the mean total femur and left femoral neck. Given the small magnitude of difference in g/cm(2) and inconsistent pattern, that is, no right femoral neck difference, there is virtually no clinical difference in BMD precision between sexes. These data do not support a need for sex-specific precision analyses.