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. Apr-Jun 2016;19(2):220-5.
doi: 10.1016/j.jocd.2015.04.003. Epub 2015 Jun 10.

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

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Free PMC article

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

Diane Krueger et al. J Clin Densitom. .
Free PMC article

Abstract

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.

Keywords: Cross-calibration; dual-energy X-ray absorptiometry; in vivo; spine phantom; whole body phantom.

Figures

Figure 1
Figure 1. Encapsulated spine phantoms
Three spine phantoms were evaluated for cross-calibration, A. GE Lunar (Madison, WI), B. Hologic (Bedford,MA) and C. BioClinica Bona Fide Phantom (Princeton, NJ)
Figure 2
Figure 2. Body Composition Phantom
BioClinica Body Composition Phantom Prototype (BBCP). Whole body phantom designed to emulate bone, lean and fat mass for the purpose of monitoring DXA scanners for body composition. The phantom measures 60 × 36 × 9 cm and weighs ~16 kg.
Figures 3
Figures 3. a-d: Bland-Altman Plots of Lean and Fat BioClinica Body Composition Phantom Data Before and After Recalibration
Lean and fat differed between instruments by 4.6% & 7.8% with biases of +463 g & −496 g (3a-b). After recalibration, instrument agreement improved to 2.6% for lean and 4.8% in fat, with biases of +265 g and −298 g respectively (3c-d).
Figure 4
Figure 4. a-b: Lean and Fat In Vivo Data Before and After Recalibration
Figure 4a depicts the total body lean mass agreement as assessed by linear regression and Bland-Altman plots prior to (open circles) and following densitometer re-calibration (closed circles). Figure 4b depicts the same evaluations for total body fat mass prior to (open diamonds) and following recalibration (closed symbols). Pre-recalibration the regression equations were y = 1.0037x + 637.37 for lean and y = 0.9953x – 774.61 for fat. Following re-calibration the regression equations were y = 0.9948x = 259.91 and y = 1.0034x – 64.702 respectively. There was a change in the slope and bias of 0.009 and 855.6 g respectively in lean and −0.008 and −855.6 g respectively in fat.

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