CARS Preview 2018

Mati ja Ciganovi c i s a PhD student in the lab of Professor Orcun Goksel at the Computer -assi sted Appl i cations in Medi c ine (CAiM) group at ETH Zur i ch, whi ch i s a joint venture wi th the Balgr i st Universi ty Hospi tal , al so located in Zur i ch. Registration of 3D Freehand Ultrasound to a Bone Model for Orthopaedic Procedures of the Forearm Matija Ciganovic Matija speaks to us ahead of this year’s CARS conference about work he completed as a result of his Master’s thesis: Registration of 3D Freehand Ultrasound to a Bone Model for Orthopaedic Procedures of the Forearm . He was supervised by Firat Ozdemir . Matija tells us that the work focused on registration between ultrasound and a different imaging modality, looking at registration algorithms that were used by other people and considering how easy they were to use with his own data. Could they be used out of the box or was additional work necessary to make them work reliably? Three kinds of registration algorithms were investigated: ICP – Iterative Closest Point (“the classical registration algorithm”); CPD – Coherent Point Drift ; and the third one doesn’t have its own name but like CPD is based on modelling the surfaces with Gaussian mixture models. Matija says that the main challenge is that no algorithm works out of the box. If you have two bone surfaces, one from ultrasound and one from another modality, how can you help the algorithm? He explains that essentially you can run an algorithm multiple times and in between each time move the surfaces into a different relative position. The idea is that as soon as the surfaces are close enough to a good alignment, running a registration algorithm from that alignment can then lead to a successful registration. The data set was bones in the forearm. Using principal component analysis and a few different tweaks, they were able to find a set of initial alignments of the surfaces, one of which was close enough so that a registration algorithm could function properly. “ It turns out that the solution that works best is in fact simpler than all the other alternatives that you had in mind! ” 20 CARS 2018 Preview Presentation