Motivation: Spinal needle injections are technically demanding procedures. The use of ultrasound image guidance without prior CT and MR imagery promises to improve the efficacy and safety of these procedures in an affordable manner. Methodology: We propose to create a statistical shape model of the lumbar spine and warp this atlas to patient-specific ultrasound images during the needle placement procedure. From CT image volumes of 35 patients, statistical shape model of the L3 vertebra is built, including mean shape and main modes of variation. This shape model is registered to the ultrasound data by simultaneously optimizing the parameters of the model and its relative pose. Ground-truth data was established by printing 3D anatomical models of 3 patients using a rapid prototyping. CT and ultrasound data of these models were registered using fiducial markers. Results: Pairwise registration of the statistical shape model and 3D ultrasound images led to a mean target registration error of 3.4 mm, while 81% of all cases yielded clinically acceptable accuracy below the 3.5 mm threshold.
Evaluation of the algorithm is performed on 10 clinical patient datasets. The registration approach was able to align CT and US datasets from initial misalignments of up to 25 mm, with a mean TRE of 1.37 mm. These results suggest that the proposed approach has the potential to offer a sufficiently accurate registration between clinical CT and US data.
The Ilizarov method is used to correct bone deformities by using an adjustable frame to simultaneously perform alignment and distraction of an openwedge osteotomy. We have adapted the idea of fixation-based surgery, which requires computer-assisted planning and guidance, to the Ilizarov method with the Taylor frame. This work incorporates the kinematics of the Taylor frame (a Stewart platform) into the planning and application phases of surgery. The method has been validated in laboratory studies. The study shows that the method requires almost no intraoperative X-ray exposure and that complex corrections can easily be achieved.
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