Ultrasound and CT Registration Quality: Elastography vs. Classical B-Mode

Ultrasound and computed tomography registration is a valuable tool for interventional imaging and navigation, but current methods are limited in reliability or usefulness, requiring large fields of view, large ultrasound penetration depth, distinct image features, or contours of the investigated organs. Computationally cheap, small-field- of-view registration proved elusive so far. We propose the use of interventional ultrasound elastography imaging to perform limited-field-of-view, limited-features registration reliably, examining the image acquisition and registration in the example application of partial nephrectomies. Furthermore, the benefits of elastography vs. conventional B-Mode ultrasound imaging are investigated

A 3D-elastography-guided system for laparoscopic partial nephrectomies

We present an image-guided intervention system based on tracked 3D elasticity imaging (EI) to provide a novel interventional modality for registration with pre-operative CT. The system can be integrated in both laparoscopic and robotic partial nephrectomies scenarios, where this new use of EI makes exact intra-operative execution of pre-operative planning possible. Quick acquisition and registration of 3D-B-Mode and 3D-EI volume data allows intra-operative registration with CT and thus with pre-defined target and critical regions (e.g. tumors and vasculature). Their real-time location information is then overlaid onto a tracked endoscopic video stream to help the surgeon avoid vessel damage and still completely resect tumors including safety boundaries. The presented system promises to increase the success rate for partial nephrectomies and potentially for a wide range of other laparoscopic and robotic soft tissue interventions. This is enabled by the three components of robust real-time elastography, fast 3D-EI/CT registration, and intra-operative tracking. With high quality, robust strain imaging (through a combination of parallelized 2D-EI, optimal frame pair selection, and optimized palpation motions), kidney tumors that were previously unregistrable or sometimes even considered isoechoic with conventional B-mode ultrasound can now be imaged reliably in interventional settings. Furthermore, this allows the transformation of planning CT data of kidney ROIs to the intra-operative setting with a markerless mutual-information-based registration, using EM sensors for intraoperative motion tracking. Overall, we present a complete procedure and its development, including new phantom models - both ex vivo and synthetic - to validate image-guided technology and training, tracked elasticity imaging, real-time EI frame selection, registration of CT with EI, and finally a real-time, distributed software architecture. Together, the system allows the surgeon to concentrate on intervention completion with less time pressure