Cross-Calibration of GE Healthcare Lunar Prodigy and iDXA Dual-Energy X-Ray Densitometers for Bone Mineral Measurements

Table 4

Mean (SD) values and linear correlation coefficients () of the in vivo dual-energy X-ray absorptiometry (DXA) measurements with Prodigy and iDXA (). Bland and Altman analysis results with relative mean differences % as well as limits of agreement [  ±  (1.96 × SD)]. Simple linear regression analysis of Prodigy (dependent) versus iDXA (independent) BMD data with standard error (SE) and standard errors of estimates (SEE). Regional total body BMD values differed considerably between Prodigy and iDXA. BMD discrepancy was smaller but significant at total body region of interest. After linear regression correction equations were applied the differences were negligible.

	Prodigy; mean (SD)	iDXA; mean (SD)		%	Intercept (SE)	Slope (SE)	SEE	SEE (%)	Limits of agreement
Arms	0.936 (0.091)	0.827 (0.093)	0.848	−11.6	0.251 (0.056)	0.828 (0.067)	0.049	5.5	−0.208 to −0.009
Trunk	0.891 (0.068)	0.932 (0.095)	0.945	4.6	0.263 (0.028)	0.674 (0.030)	0.022	2.5	−0.034 to 0.116
Spine	0.995 (0.102)	1.037 (0.112)	0.922	4.2	0.128 (0.047)	0.836 (0.045)	0.040	3.9	−0.044 to 0.128
Pelvis	1.101 (0.096)	0.979 (0.114)	0.928	−11.0	0.331 (0.040)	0.785 (0.041)	0.036	3.5	−0.206 to −0.036
Legs	1.233 (0.099)	1.154 (0.104)	0.979	−6.4	0.162 (0.029)	0.929 (0.025)	0.020	1.7	−0.121 to −0.037
Total body	1.162 (0.078)	1.146 (0.095)	0.962	−1.3	0.257 (0.033)	0.789 (0.029)	0.021	1.9	−0.073 to 0.041

Formula for relative mean difference (%): [(iDXA − Prodigy) × 100/Prodigy].
Significantly different () mean difference ( = Prodigy − iDXA, paired -test or nonparametric Wilcoxon signed-rank test in Ward’s triangle BMD, BMC, or area ROIs).
Correction equation: Prodigy (BMD) = Slope × iDXA (BMD) + intercept.
Formula for SEE (%): [SEE × 100/((Prodigy + iDXA)/2)].