Static and mobile DXA scanner in-vivo cross-calibration study

Abstract

Cross calibration of DXA scanning equipment with phantom subjects has been recommended for assessing agreement between devices co-located within DXA scanning services.This study evaluated in-vivo and in-vitro cross calibration of a static and a mobile DXA scanner within the same service in their individual clinical settings. 50 individuals from a volunteer group were recruited to take part in this study and had DXA measurements made on two GE Lunar Prodigy Advance (GE Lunar, Bedford, UK) scanners.Results in this study showed that the scanners agreed, with no statistically significant differences in BMD measurements made at the same site on the individual devices used in this study. The in-vivo cross calibration of the instruments was a useful experience, which demonstrated closely calibrated systems and raised the profile of the bone densitometry service within the hospital.3 Introduction Central dual energy x-ray absorptiometry (DXA) of the spine and hip is the current preferred method for the diagnosis of osteoporosis [1]. DXA scanners have good long term precision due to stable calibration and effective instrument quality control procedures to detect long term drift [1]. However, the results from DXA scanners produced by different manufacturers and even the same make of scanner made by the same manufacturer cannot be directly compared due to potential differences in calibration [2]. When introducing additional or replacing DXA scanners it is therefore recommended to perform cross calibration whether the new machine is from the same manufacturer or not [3]. While cross calibration between two machines of the same manufacturer and using the same manufacture's phantom has been reported to have good agreement of 0.2%, in vivo measurements may differ by more than 2%[4] The increased errors in-vivo can be partly attributed to the increased precision errors introduced by virtue of scanning an individual who has in-homogeneity within their tissue, meaning that the x-ray photons may not pass though the same structures on both scans. Precision errors within DXA are also important for the characterisation of it's ability to assess bone mineral density and detect longitudinal change. Monitoring measurement errors within a service is also dependant on QA systems to detect scanner changes [5]. When introducing a new scanner, it is recommended to undertake a cross-calibration of the scanners within a service. The optimum technique for undertaking a cross-calibration study of DXA scanners is to use in-vivo measurements since this is how DXA scanners are used in clinical practice [4,6].In 2009, a GE Lunar Prodigy DXA scanner (GE Healthcare, Bedford, UK) was purchased and commissioned to operate in a mobile vehicle, alongside the existing static GE Lunar Prodigy within the Healthy Bones Service at Derriford Hospital (Plymouth UK). While it is not good practice to make longitudinal measurements of