Cemil Göksu

Depth-map-based scene analysis for active navigation in virtual angioscopy

This work presents an approach dealing with virtual exploratory navigation inside vascular structures. It is based on the notion of active vision in which only visual perception drives the motion of the virtual angioscope. The proposed fly-through approach does not require a premodeling of the volume dataset or an interactive control of the virtual sensor during the fly-through. Active navigation combines the on-line computation of the scene view and its analysis, to automatically define the three-dimensional sensor path. The navigation environment and the camera-like model are first sketched. The basic stages of the active navigation framework are then described: the virtual image computation (based on ray casting), the scene analysis process (using depth map), the navigation strategy, and the virtual path estimation. Experimental results obtained from phantom model and patient computed tomography data are finally reported.

Finite-Element-Based Matching of Pre- and Intraoperative Data for Image-Guided Endovascular Aneurysm Repair

Endovascular repair of abdominal aortic aneurysms is a well-established technique throughout the medical and surgical communities. Although increasingly indicated, this technique does have some limitations. Because intervention is commonly performed under fluoroscopic control, 2-D visualization of the aneurysm requires the injection of a contrast agent. The projective nature of this imaging modality inevitably leads to topographic errors, and does not give information on arterial wall quality at the time of deployment. A specially adapted intraoperative navigation interface could increase deployment accuracy and reveal such information, which preoperative 3-D imaging might otherwise provide. One difficulty is the precise matching of preoperative data (images and models) and intraoperative observations affected by anatomical deformations due to tool-tissue interactions. Our proposed solution involves a finite-element-based preoperative simulation of tool-tissue interactions, its adaptive tuning regarding patient specific data, and the matching with intraoperative data. The biomechanical model was first tuned on a group of ten patients and assessed on a second group of eight patients.

Fluid/Structure Interaction applied to the simulation of Abdominal Aortic Aneurysms

Aneurysms are a local dilatation of a vessel wall of at least twice the normal diameter (commonly accepted definition). They are asymptomatic and rupture is often lethal. Thus, prediction of rupture is an important stake. Aiming at a diagnosis tool relying on patient specific data and general physiological values, we created a virtual aneurysm model based on real imaging data. Fluid/structure interaction (FSI) simulations were made to compute the displacement and stress for the wall. For the fluid, the only in vivo measures used were for the inlet velocity. The mandatory output boundary condition has been implemented with the first order Windkessel model equations. Structure has been much more complicated to handle because of the association of a realistic geometry (no symmetry) and a full fluid/structure interaction approach. We used surface elements to stabilize the structure and to model surrounding organs. Validation parameters are the displacement, the Von Mises stress and the pressure profile at the outlet. The main difference with other studies relies on the association of all these elements in order to prepare industrial applications as the main goal of this study was to build an automated tool easy to use by people who are not experts in numerical simulation

Influencing factors of sac shrinkage after endovascular aneurysm repair

Objective: Sac shrinkage is considered a reliable surrogate marker of success after endovascular aneurysm repair (EVAR). Whereas sac shrinkage is the best expected outcome, predictive factors of sac shrinkage remain unclear. The aim of this study was to identify the role of preoperative and postoperative influencing factors of sac reduction after EVAR. Methods: Online searches across MEDLINE, Embase, and Cochrane Library medical databases were simultaneously performed. Study effects were pooled using a random‐effects model, and forest plots were generated for every potential influencing factor. Results: A total of 24 studies with 14,754 patients were included (mean age, 73.4 years; 76% male). At a mean follow‐up of 24 months, the pooled shrinkage proportion was 47%. Random‐effects meta‐analysis revealed that renal impairment (odds ratio [OR], 0.74; 95% confidence interval [CI], 0.57‐0.96), type I endoleaks (OR, 0.17; 95% CI, 0.08‐0.39), type II endoleaks (OR, 0.21; 95% CI, 0.14‐0.33), and combined type I and type II endoleaks (OR, 0.32; 95% CI, 0.22‐0.47) were found to prevent sac shrinkage, whereas hypercholesterolemia (OR, 1.24; 95% CI, 1.02‐1.51) and smoking (OR, 1.32; 95% CI, 1.17‐1.49) have a significant positive impact on sac shrinkage. In addition, there was a trend toward the association between shrinkage and statin therapy (OR, 4.07; 95% CI, 1.02‐16.32) and nearly significant negative impacts of coronary artery disease (OR, 0.84; 95% CI, 0.70‐1.01), diabetes (OR, 0.79; 95% CI, 0.60‐1.04), and sac thrombus (OR, 0.88; 95% CI, 0.77‐1.01) on sac shrinkage. Conclusions: In this large meta‐analysis of patients undergoing EVAR, we found that several comorbidity and postoperative factors were associated with postoperative sac shrinkage. These findings may contribute to a better understanding of the shrinkage process of patients undergoing EVAR.

Estimation of 2D/3D rigid transformation for Computer-assisted Endovascular Navigation

Minimally invasive vascular interventions require the exact location and orientation of the endovascular tools (i.e., balloon, stent graft) with respect to the patient in the surgical environment. While a 3D image is often available preoperatively (typically an angio-CT scan) the practitioner mainly relies on the 2D images provided by the mobile fluoroscopic device (C-arm) to obtain a real-time feedback of the intravascular tool location as well as of the therapeutic actions. The main objective of this work is the study of an endovascular navigation system that enables the surgeon to improve the accuracy of the procedure along with a minimum use of the intra-operative 2D acquisitions, leading to less radiation exposure and less contrast agent injection. With the aim of exploiting the whole available information at the different observation stages through a cooperative approach, this paper focuses on the definition of the different rigid geometrical transformations implied in the 3D preoperative / 2D intraoperative images matching, as well as on the estimation of the transformation parameters based on the use and combination of different types of data and methods (calibration, 3D tracking, image registration).

A Study of Dosimetric Evaluation and Feasibility of Image Guided Intravascular Brachytherapy in Peripheral Arteries

This work involves the conception of the experimental dosimetric testing setup of an image based procedure for intravascular brachytherapy by 192Ir seed in peripheral arteries. After making sure of the suitability of the basis dosimetry data used for dose calculation, the treatment sequence as a whole has been tested in a customized tissue-equivalent phantom. The method is based on the use of CT preoperative images and 2D intra-operative radiographs. Experimental dosimetric results agree with the planning and demonstrate the feasibility of the procedure.

Systematic Review and Meta-Analysis of Preoperative Risk Factors of Type II Endoleaks after Endovascular Aneurysm Repair

BACKGROUND Type II endoleaks (T2Es) remain the Achilles heel of endovascular aneurysm repair (EVAR), involving a close follow-up and sometimes leading to reintervention. Identifying risk factors impacting T2Es is of concern to improve decision making and optimize follow-up. However, it has led to contradictory results, with supporting evidence for the majority of factors being weak. METHODS A systematic review and meta-analysis was conducted to study risk factors of T2Es following EVAR to identify risk factors and measure their dedicated strength of association. Using a literature search of MEDLINE, EMBASE, and the Cochrane Library, 31 retrospective studies including a total of 15,793 patients were identified and fulfilled the strict specified inclusion criteria. Random-effects meta-analysis was conducted for each factor to combine effect estimate across studies. A total of 21 factors related to demography, preoperative treatment, comorbidity, and morphology were statistically pooled. RESULTS On the basis of the pooled odds ratios and their 95% confidence intervals, patency of aortic side branches, represented by the patency of the inferior mesenteric artery, lumbar arteries, or total number of aortic side branches, were found to be significant harmful risk factors of T2Es. Women were also found to have nearly significant higher risk of developing T2Es than men. On the contrary, the following were found to have a significant protective role: smoking, peripheral artery disease, and thrombus load, represented by the maximum thickness at the maximum aneurysm diameter, the presence of circumferential thrombus, or the presence of thrombus at the level of inferior mesenteric artery. CONCLUSION Identifying significant risk factors of development of T2Es is mandatory to improve decision making and optimize surveillance planning in EVAR.