Study design

Our investigation of operator positioning variability and its contribution to measurement precision errors in HR-pQCT followed two complimentary study procedures (Figure 2). First, we performed an in vivo scan-rescan reproducibility study to compare the true total precision error for HR-pQCT bone measurements (including scan positioning variability) to precision error as it has previously been measured for HR-pQCT (excluding scan positioning variability). Specifically, we compared precision errors for bone parameters measured in the entire volumes acquired for each repeat scan, to those measured in volume of interest constrained to overlapping slices between scan and rescan. Second, we isolated the error produced by operator positioning variability by calculating bone parameters in sub volumes corresponding to variable operator-defined scan positions. We performed retrospective positioning experiments using custom scan simulation software and the scout view images collected for this second study in order to evaluate: (i) short-term intra-operator, (ii) long-term intra-operator, and (iii) inter-operator positioning precision. Based on the positioning experiments, we quantified the absolute reference line position precision and the corresponding precision errors for bone parameters. This second study was performed in (i) a group of experienced operators, and (ii) a group of operators without previous HR-pQCT experience, who performed custom software training and evaluation exercises prior to their reproducibility experiments.

Design of our study. First we investigated the contribution of HR-pQCT operators to total acquisition precision, and then we decomposed operator precision in intra- and inter-operator precision. In the last case, we also tested the efficacy of our training tool at reducing operator precision errors.