Università di Pisa – Dottorato di Ricerca In Ingegneria dell’Informazione
PhD Candidate: Roberta PiazzaTutor: Ph.D. Vincenzo Ferrari
Supervisor(s): Ph.D. Sara Condino, Prof. Enzo Pasquale Scilingo
Doctoral Thesis: DESIGN OF NEW ENDOVASCULAR PROTOTYPES FOR THE 3D
COMPUTER-ASSISTED IN SITU LASER FENESTRATION PROCEDURE Summary
EndoVascular Aneurysm Repair (EVAR) is a minimally invasive surgical procedure which involves, under fluoroscopic guidance, the deployment of an endograft within the aneurismal sac to prevent its rupture. However, exclusion of an aneurysm involving renal, visceral, and/or supra-aortic branches remains a challenge in case of complex anatomical configurations. Indeed, the deployment of the endoprosthesis can require prolonged surgical time and enhanced amount of X-ray radiation in order to obtain a proper anchorage, maintaining a continuous blood flow through the branched vessel.
For this reason, custom-made fenestrated stent grafts have been developed. However, these devices are expensive, depend on accurate preoperative imaging and their implantation is technically challenging and time-consuming since fenestrations, which are customized holes on the endograft wall, should be aligned with the collateral vessels’ origins. Moreover, patient-specific stent grafts are not available for acute syndromes and for emergency situations (their fabrication requires several months).
Alternative procedure, such as the in situ fenestration of a standard stent grafts, has been proposed in order to find a rapid, simple, accurate and cost-effective intraoperative way to obtain fenestrated stent grafts and preserve blood flow to essential visceral arteries. The reliability of this procedure is today principally limited by difficulties in targeting the proper fenestration site under fluoroscopic control and by the lack of a safe method to perforate the graft.
This thesis proposes an innovative fenestration system consisting of the integration of a laser technology into a three-dimensional (3D) electromagnetic (EM) navigation platform to overcome the limitations of the current in situ fenestration technique, providing the surgeon with a selective fenestration tool whose position and orientation can be accurately tracked in real-time within a 3D virtual model of the patient vasculature. In addition, the endovascular navigator would allow avoidance of the need for real-time fluoroscopy and angiography, thus reducing X-ray exposure
and contrast agent injection.
In particular, this work deals with the ad hoc design process of sensorized endovascular prototypes: 1) a guiding catheter system to easily navigate 2) a laser tool at the correct fenestration site, offering support to perform the 3D computer-guided antegrade in situ laser fenestration of a standard endoprosthesis.
A description of medical and technical background is reported; then, the main mechanical requirements for the fabrication of endovascular prototypes are discussed, and different design strategies to accomplish the desired specifications are described.
Experimental testing for the evaluation of the new endovascular instrumentation are detailed. More in particular, in vitro tests and a clinical trial were carried out to explore different laser irradiation conditions for a successful endograft fenestration and to evaluate the harmless effects of diode laser irradiation on human aortic tissue, providing a selective and safe laser fenestration tool. As regards the guiding catheter system, different methods were employed to evaluate the desired specifications. Preliminary in vitro test on the first design solutions has been carried out to direct the design process toward an optimal configuration. Mechanical simulations were performed with a design software system for the development of composite tubing for endovascular catheters. Lastly, a revised version of first design project has been tested in vitro in order to perform the EM guided antegrade in situ laser fenestration procedure within two in vitro setups with different level of complexity.
The final prototypes of the guiding catheter system consist of two sensorized endovascular catheters: a steerable catheter has been developed to properly orient the fenestration tool toward the fenestration site and a stabilizing catheter has been designed to offer mechanical support and stability during in situ fenestration. Regarding the laser tool prototype, it consists of a sensorized laser fiber integrated within a custom-made hollow strand guidewire.
The proposed trackable instrumentation has the potential to expand the indications for EVAR to aneurysms previously considered ineligible, also to cases of acute syndromes. Moreover, the proposed approach paves the way to use the in situ fenestration as a bailout technique for restoring patency to branched arteries after inadvertent coverage during EVAR, avoiding permanent failure of vital organs.
