Knowledge integration in ultrasound-guided medical interventions

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The objective of this research program is to improve computer assisted medical interventions by providing image analysis tools to extract useful guidance information for the clinician from intra-operative imagery. Ultrasound (US) being flexible, portable, safe and low cost, emerges as a promising intra-operative modality, with freehand 3D US allowing the acquisition of 3D data using a conventional 2D probe widely available in the clinic. The challenges involved in exploiting these data pertain to simultaneous tracking of US transducer motion and tissue deformations, tissue characterisation, segmentation and registration to pre-operative patient imagery. The new tools will solve these problems by integrating information from the images themselves with measurements from position tracking devices as well as prior knowledge regarding the US data acquisition protocol, patient anatomy and tissue biomechanical properties. A key hypothesis is that by explicitly modelling the different sources of knowledge, including application-specific ones, and quantifying their respective reliability, optimal data fusion can be performed, leading to more accurate intra-operative guidance as well as safer and shorter interventions. New algorithms will be developed to track the position and orientation of an ultrasound transducer in 3D while compensating for tissue deformations arising from varying probe pressure. Through a collaboration with the Musculo-Skeletal Deformation Research Group at Sainte-Justine Hospital, these new algorithms will be applied to the context of minimally invasive spine discectomy, where an articulated 3D spine model derived from pre-operative MRI or bi-planar X-ray data must be updated and displayed to reflect global changes in spine shape caused by localised surgical manoeuvres. Here, freehand 3D US offers a non-invasive and practical alternative to landmark digitisation. The model updates thus obtained will assist the surgeon in adapting his strategy, improving the quality of patient treatment and cost to the healthcare system. Additionally, the methods developed within this research program will be adaptable to other types of interventions like image-guided needle biopsy and radiotherapy.