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Cross-Calibration of iDXA and pQCT Scanners at Rural and Urban Research Sites in The Gambia, West Africa.

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Ó Breasail, Mícheál  ORCID logo
Janha, Ramatoulie 


Between-scanner differences in measures of bone and body composition can obscure or exaggerate physiological differences in multi-site studies or the magnitude of changes in longitudinal studies. We conducted a cross-calibration study at two bone imaging centres in The Gambia, West Africa where DXA (dual-energy X-ray absorptiometry) and pQCT (peripheral Quantitative-Computed Tomography) are routinely used. Repeat scans were obtained from 64 Gambian adults (58% Male) aged Mean(SD) 30.9 (13.5) years with Mean(SD) body mass index (BMI) 21.7 (4.0) kg/m2, using DXA (GE Lunar iDXA, whole body [WB], total hip [TH], lumbar spine [LS]) and pQCT (Stratec XCT2000L/XCT2000, tibia 4%, 50% sites). Between-scanner differences were tested using paired t tests (p < 0.05). Between-scanner correlation was explored with linear regression, and cross-calibration equations derived. Bland-Altman analysis investigated machine trend/bias. When differences were detected (p < 0.05), cross-calibration equations were applied to urban values, with t tests and Bland Altman analysis repeated. Between-scanner differences exceeded the predefined level of statistical significance (p < 0.05) for WB aBMD and BA; all pQCT measures vBMD, BMC, cortical cross-sectional area (CSA) and stress-strain index (SSI). Between-scanner correlation was high (R2:0.92-0.99), except pQCT Mu.Den (R2 = 0.51). Bland Altman plots indicated bias increased with increasing BMD. Cross-calibration equations attenuated all between-scanner differences and systematic bias. Cross-calibration, particularly of pQCT scanners, is an important consideration in multi-site studies particularly where between population comparisons are intended. Our experiences and findings may be generalisable to other resource-limited settings where the logistics of sourcing parts and in-country repair may result in lengthy scanner downtime.


Acknowledgements: The authors wish to acknowledge the contribution of the participants who took part in this study. We thank the men and women of Kiang West and the Kombos, The Gambia, who patiently participated in the study. We acknowledge the enthusiastic work of the study team, especially the research and bone imaging staff, who tirelessly collected the data, and the drivers who transported the participants between facilities. The support of the data management team was greatly appreciated both during and after data collection. We are grateful to Michael Mendy and Mustapha Ceesay for their senior oversight of the bone imaging team. We also thank Dr. Sarah Dalzell for her help in planning the study. This research was jointly funded by the MRC (programme codes U105960371, U123261351, MCA760-5QX00) and the Department for International Development (DFID) under the MRC/DFID Concordat agreement. For the purposes of Open Access, the authors (KAW, AP) have applied a Creative Commons Attribution (CC BY) licence to any Author Accepted Manuscript version arising.


Body composition, Cross-calibration, DXA, Densitometry, pQCT, Adult, Male, Humans, Aged, Female, Bone Density, Gambia, Calibration, Absorptiometry, Photon, Lumbar Vertebrae, Africa, Western

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Calcif Tissue Int

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Springer Science and Business Media LLC
Medical Research Council (MC_U123261351)
Medical Research Council (MC_U105960371)