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3 Results

We designed and implemented a pilot surgical navigation system to support the surgeons to perform the HoLEP. Our system required a-priori trans-rectal US acquisition and a subsequent realization of the patient specific 3D model of the prostate (capsule and adenoma). Our system provides a view showing a 3D rendering scene in which the instruments and the prostate with the planned cutting surface are visualized. Figure 7 shows the 3D prostate model obtained by segmenting US trans-rectal images and the outlines of the adenoma and the external prostate capsule. Our system is able to support different types of visualization.

Fig. 7. Ultrasound scan of the prostate phantom and 3D model; a), b), d) show the prostate in the three anatomical planes; c) shows the 3D model built up and e) is a zoom of prostate capsule and adenoma from axial view in respect of the transducer

We conducted a feasibility study by using a prostate phantom containing a benign hyperplasia. Firstly we investigated the mechanical features and the acoustic impedance of a massive number of materials. Our studied led us to the agar/psyllium solution. The US investigation was acceptable but the densities between central and peripheral zones were too different. Consequently the surgical simulation performed

to the phantom resulted not comparable with real cases. Then we availed ourselves of one urologist expert advices in order to find the materials and the right composition of those to obtain a plausible prostate phantom. We focused our attention to duplicate the stiffness that surgeons contend with. We found an optimal solution: it exploits cornstarch, corned beef and beets: the cited work is cheap and permits the recognition of the anatomical structures. Although the echogenicity achieved by this latter solution was not exactly the one of the real diagnostic scenario, the phantom simulated well the prostate and the adenoma in terms of density and stiffness.

4 Conclusions

We implemented a virtual reality navigation system for HoLEP. Surgeons currently use only endoscopic images to advance with medical instrumentation during HoLEP. Our solution is a preliminary surgical navigator that helps surgeons to orientate the laser fiber used during the intervention and to follow the hyperplasia borders. Our navigation system provides surgeons a virtual scene showing in real time the relationship between the anatomy and the instrument tip. Different types of visualization are provided. We are designing a validation study to evaluate also the best visualization.

To validate the navigation system we studied different ways to build up a plausible US prostate phantom, taking into account the acoustic impedance, the mechanical features and the stiffness ratio between the adenoma and the external prostatic capsule. Future works are required to validate the proposed solution by urologists.

Acknowledgment. This work has been supported by Regione Toscana within the Scientific Project “MILoRDS” (PAR FAS 2007-2013 Azione 1.1 P.I.R. 1.1.B).


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