The reliability and validity of a clinical 3D freehand ultrasound system Francesco Cenni a,b, *, Davide Monari a,b , Kaat Desloovere b,c , Erwin Aertbeliën a , Simon-Henri Schless b,c , Herman Bruyninckx a a Department of Mechanical Engineering, KU Leuven, Celestijnenlaan 300b, 3001 Leuven, Belgium b Clinical Motion Analysis Laboratory, University Hospital, Pellenberg, Weligerveld 1, 3212 Pellenberg, Belgium c Department of Rehabilitation Sciences, KU Leuven, Tervuursevest 101, 3001 Leuven, Belgium ARTICLE INFO Article history: Received 13 May 2016 Received in revised form 28 August 2016 Accepted 2 September 2016 ABSTRACT Background and Objective: Acquiring large anatomical volumes in a feasible manner is useful for clinical decision-making. A relatively new technique called 3D freehand ultrasonography is capable of this by combining a conventional 2D ultrasonography system. Currently, a thorough analysis of this technique is lacking, as the analyses are dependent on the software imple- mentation details and the choice of measurement systems.Therefore this study starts by making this implementation available under the form of an open-source software library to perform 3D freehand ultrasonography. Following that, reliability and validity analyses of extracting volumes and lengths will be carried out using two independent motion-tracking systems. Methods: A PC-based ultrasonography device and two optical motion-tracking systems were used for data acquisition. An in-house software library called Py3DFreeHandUS was devel- oped to reconstruct (off-line) the corresponding data into one 3D data set. Reliability and validity analyses of the entire experimental set-up were performed by estimating the volumes and lengths of ground truth objects.Ten water-filled balloons and six cross-wires were used. Repeat measurements were also performed by two experienced operators. Results: The software library Py3DFreeHandUS is available online, along with the relevant documentation. The reliability analyses showed high intra- and inter-operator intra-class correlation coefficient results for both volumes and lengths. The accuracy analysis re- vealed a discrepancy in all cases of around 3%, which corresponded to 3 ml and 1 mm for volume and length measurements, respectively. Similar results were found for both of the motion-tracking systems. Conclusions: The undertaken analyses for estimating volume and lengths acquired with 3D freehand ultrasonography demonstrated reliable design measurements and suitable per- formance for applications that do not require sub-mm and -ml accuracy. © 2016 Elsevier Ireland Ltd. All rights reserved. Keywords: 3D freehand ultrasonography Volume and length measurements Reliability and validity analysis Open source software 1. Introduction Over the past 30 years, medical imaging modalities acquiring large anatomical 3D data sets have been routinely used to explore features useful for clinical decision-making [1]. These modalities, such as computed tomography (CT) and mag- netic resonance imaging (MRI), provide a high image quality with a large field of view. However, these systems are expen- sive, time consuming and uncomfortable for patients. In more * Corresponding author. Department of Mechanical Engineering, KU Leuven, Celestijnenlaan 300b, 3001 Leuven, Belgium. Fax: +32 16338012. E-mail address: francesco.cenni@kuleuven.be (F. Cenni). http://dx.doi.org/10.1016/j.cmpb.2016.09.001 0169-2607/© 2016 Elsevier Ireland Ltd. All rights reserved. computer methods and programs in biomedicine 136 (2016) 179–187 journal homepage: www.intl.elsevierhealth.com/journals/cmpb