Open source tools for validation of deformable registration

Abstract

International audienceDeformable image registration is of considerable interest to the radiation therapy community. It is considered a key enabling technology for applications such as adaptive radiotherapy, contour propagation in 4D CT images, atlas-based segmentation, breathing motion modeling, dose accumulation and many more. Deformable registration is slowly finding its way to commercial software packages. However, validation of the estimated deformation fields remains challenging because no ground truth is available. In general, validation of deformable registration relies on manually generated data, often in the form of hand-clicked landmarks or handdrawn contours. Obtaining such data is a laborious and time-consuming task. Strictly speaking, the resulting validation should be considered as partial, due to the high number of degrees of freedom of the system. In addition, the ill-posed nature of the problem implies the procedure needs to be repeated when dealing with images of different quality, nature or modality. Open-source and open-data concepts constitute an approach where source code and data are provided for free usage, within the limits of a defined agreement, and with a strong concern on users' feedback and participation. It has proved to be an efficient strategy to accelerate scientific advances in a difficult field, based on distributed and collaborative effort, in particular by enabling evaluation and comparison. Many initiatives exist for the application of validating deformable registration, several of which have had a considerable impact in the field. In this presentation, we will describe some open-source and open-data tools that have been proposed and used for validation of deformable image registration. We will review some freely available image processing toolkits (e.g. ITK, elastix), publicly accessible databases of annotated images (e.g. Dir-Lab, POPI), visualization freeware (e.g. VTK, Osirix, VV) and implementation contests or challenges (EMPIRE10). Advantages and limitations of each will also be discussed