All is not what it seems

Precision in imaging, often referred to as reproducibility, describes the ability of a quantitative measurement technique to reproduce the same numerical result when repeatedly performed in an identical fashion. In DXA, precision is the ability of a DXA system to obtain consistent bone mineral density (BMD) values upon repeated measurements of the same patient over a short time. In order to monitor bone loss or the efficacy of treatment, good precision (ie small variations in serial measurements) is crucial.

Precision error depends on many confounders. In vivo error is usually greater than in vitro, long-term (over period of study) is usually greater than short-term (same day), and inter-observer (different operators) is usually greater than intra-observer (same operator). Precision is worse in elderly patients and patients with low BMD.

Equipment changes, different dual energy methods, different calibration, different detectors, different edge detection software and different regions of interest will all increase precision error.

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