Terry Peters
Many inter-cardiac interventions are performed either via open-heart surgery, or using minimally invasive approaches, where instrumentation is introduced into the cardiac chambers via the vascular system or heart wall. While many of the latter procedures are often employed under x-ray guidance, for some of these x-ray imaging is not appropriate, and ultrasound is the preferred intra-operative imaging modality. Two such procedures involves the repair of a mitral-valve leaflet, and the replacement of aortic valves. Both employ instruments introduced into the heart via the apex. For the mitral procedure, the standard of care for this procedure employs a 3D Trans-esophageal echo (TEE) probe as guidance, but using primarily its bi-plane mode, with full 3D only being used sporadically. In spite of the clinical success of this procedure, many problems are encountered during the navigation of the instrument to the site of the therapy. To overcome these difficulties, we have developed a guidance platform that tracks the US probe and instrument, and augments the US mages with virtual elements representing the instrument and target, to optimise the navigation process. Results of using this approach on animal studies have demonstrated increased performance in multiple metrics, including total tool distance from ideal pathway, total navigation time, and total tool path lengths, by factors of 3,4,and 5 respectively, as well as a 40 fold reduction in the number of times an instrument intruded into potentially unsafe zones in the heart. The aortic valve procedure primarily uses X-ray fluoroscopy guidance, but this suffers from the problem of high radiations dose, poor target visibility and potential kidney damage as a result of x-ray contrast administration. To overcome these limitations, we have adopted similar technology to that used for the mitral valve problem, to develop an ultrasound-only solution, again augmented with virtual models of instruments and key targets to guide aortic valve replacement procedures. Preliminary results of this approach on cardiac phantoms indicate that the US-only approach may be as accurate as the standard fluoroscopy-guided technique.