A model for Stent Graft Planning

1. Hulusi Baysal, Semih Utku, Alp Kut A model for Stent Graft Planning Abdominal Aortic Aneurysms Abdominal AorticAneurysms (AAA) occur when a weak section on the wall of aorta expands or bulges. The blood pressure in abdominal aorta may cause the weakened part of the aorta to bulge likea balloon.If the weakened part is stretched beyond the safetylimits, aorta may burst or rupture resultingin life-threatening bleeding. This may lead to shock or even death. Medical Images To diagnose and treat abdominal aortic aneurysms, CT images are used. They are stored as DICOM file format. DICOM (Digital Imaging and Communications in Medicine) is a standard for handling, storing, printing, and transmitting information in medical imaging. 3D Aorta Model & Measurements Predication of stent type, size and location are crucial factors for stent graft planning. Determination of these factors is a time-consuming task. Experts should get these values easily in a faster way. We constructed a 3D model of aorta using the data which we get from aorta segmentation. Generated model is shown below. • Treatment • There are two well-known treatments to cure the abdominal aortic aneurysms: • Open (Surgical) Aneurysm Repair • Endovascular Aneurysm Repair (EVAR) • Nowadays, endovascular aneurysm repair is fairly popular since it is less invasive. This method allows patients to leave hospital sooner and recover more quickly. Stent grafts are used during endovascular repair. CT Images There are different intensity levels in CT images. According to these differences body organs should be distinguished. To determine the status of aneurysm nearly 300 CT images are used for a patient. An Aortic Aneurysm Aorta Segmentation Image segmentation plays a very important role in medical applications by extracting the part of region of interest. There are different segmentation methods in digital imaging such as thresholding approaches, clustering approaches, and region-growing approaches. At the moment, we have already implemented aorta segmentation by using region-growing approach on DICOM data. Region growing is a technique for extracting a region of the image that is based on some predefined criteria. This criteria can be based on intensity information and/or edges in the image. 3D Aorta Model • We also implemented user-interactive measurement feature on 3D aorta model.User can click on the model to get the desired values. Measurements, such as aortic diameter, common iliac diameter, length from lower renal, plays a key role in during stent selection. • This tool is capable to do the following steps currently: • Downloading DICOM data from PACS • Loading DICOM Files • User-interactive Aorta Segmenation • 3D Reconstruction & Visualization • User-interactive Measurement • There are several tools which segment medical data and visualize them. Our tool combines these features and provides experts faster decision during stent selection process. Stent Graft Selection & Repair An endovascular stent graft is a device which is placed inside the weakened part of the aorta in order to reinforce or strengthen it. The stent graft is positioned into aorta through long, thin tubes called catheters that are threaded through blood vessels. Expert only makes a small incision in groin area to thread the catheters. Aorta segmentation is provided by a user-interactive feature. User makes a single click on the slice where the aorta resides. Aorta data are detected in all other slices. Stent Graft Stent graft selection is a major difficulty of the method due to less visual feedback. The stent must have same dimensions such as length and diameter, with the part of aorta where aneurysm occurs. If a small stent is selected, there exists a leakage between stent and aorta wall. On the other hand, if it is too large, it will be impossible to place the stent. Another major difficulty in stent graft repair operation is to place the selected stent into correct position in aorta. For example, there are two renal vessels that are connected to aorta and they supply blood to kidneys. Stent graft should not block these vessels. Aorta Segmentation References Pham D. L., Xu C. ,Prince J. L. Current Methods in Medical Image Segmentation. Annual Review of Biomedical Engineering, 2000; 315-338. Haralick R. M., Shapiro L. G. Image segmentation techniques Computer Vision, Graphics Image Processing,1985; 29:100-132. Zhao M., Tian J., Zhu X., Xue J., Cheng Z., Zhao H. The Design and Implementation of a C++ Toolkit for Integrated Medical Image Processing and Analyzing,Procedings.Of SPIE:Medical Imaging,2004; 5367:39-47 Future Work We plan to propose the appropriate stent model according to gathered measurements using a stent graft database. In this database, grafts will be classified according to their characteristics. Also we plan to model selected stent and apply it to aneurysm virtually. The completed model aims to (1) reduce time-waste in stent selection process, (2) propose the most appropriate stent for the aneurysm and (3) see the complications on model before real surgery.