Cardiovascular disease is a leading cause of premature death, killing around 900,000 people per year in the USA alone, with ruptured aneurysms forming a significant part of these deaths. In this context, a novel index called Finite Element Analysis Rupture Index (FEARI) was created to help the surgical decision making process by expressing the rupture potential of an aneurysm. As during the surgical intervention the correct sizing of the medical device is of utmost importance to avoid complications, the two aims of this study were (1) to examine FEARI’s effectiveness and (2) to show how 3D reconstructions created in the Mimics Innovation Suite can be a useful surgical guidance tool.
Using Mimics® to Quickly Turn CT Data into 3D Reconstructions
For this study, CT data were collected from 10 patients suffering from abdominal aortic aneurysms (AAA) and imported in Mimics. Within only a few steps a 3D reconstruction was generated. First, a thresholding technique was applied to the data in order to highlight the areas of interest. Second, these areas were segmented with different colors being assigned to specific features, for example, the diseased aorta. Finally, with the segmentation done, a 3D model was quickly and easily created. In the case of the aorta, reconstruction times ranged from 2 minutes for basic models where minor details were ignored, to one hour for a model where all details were included, such as intraluminal thrombus and surface indentations. As CT scans are taken a considerable time prior to the actual operation and thanks to the possibility to quickly create 3D reconstructions, surgeons can easily afford to examine a 3D model without sacrificing the health status of the patient.
3D Reconstruction Plays Key Role in Calculating FEARI
The FEARI involves an equation based on a simple engineering definition of material failure, that is, failure will occur when the stress acting on the material exceeds the strength of the material. As such, the value of FEARI is calculated by dividing the Finite Element Analysis (FEA) Wall Stress by the Experimental Wall Strength. The result is a value between 0 and 1, with 0 indicating a low rupture potential, and values close to 1 indicating a very high rupture potential. While the Experimental Wall Strength values were obtained from previous research, the FEA Wall Stress values were obtained by using the ten 3D reconstructions generated in Mimics. The 3D reconstructions were imported in an FEA program for stress analysis, the resulting values being used in the FEARI calculation.
After analyzing the values obtained during this study, it was concluded that FEARI could indeed serve as a useful tool for surgical decision making when used in conjunction with current procedures.
“3D reconstruction of AAAs, using Mimics, is a powerful and useful tool. It allows the surgeon to obtain measurements useful for the sizing of stent grafts, and also allows for the visualization of the aneurysm prior to surgery. Reconstructions are also necessary for further use with FEA, which has been shown to be a good method of determining wall stress in the diseased aorta. Because of this, 3D reconstruction could aid surgeons in improving the treatment of AAAs”
- Doyle and McGloughin, University of Limerick, Ireland
Greatly Improved Surgical Planning and Outcome
When the decision is made to operate, the preferred surgical intervention is endovascular aneurysm repair (EVAR). Many benefits were found when EVARs were planned using the Mimics Innovation Suite and 3D reconstructions. The sophisticated measurement tools in Mimics provide accurate dimensions of complex geometries, allowing for accurate measurements and greater insight into the morphology of the diseased aorta. This is important as nowadays surgeons are tackling more challenging anatomy than ever with EVAR. The valuable information from the 3D reconstructions ensures that the surgeons don’t encounter any unforeseen problems during surgery; this in turn increases confidence in the procedure. Additionally, the precise measurements which can be determined using the Mimics Innovation Suite, aid in the choice of the most appropriate stent graft. Furthermore, it means that new medical devices can also be conceived and designed for a better fit to patients. Finally, post-operative 3D reconstructions can also help the surgeon to observe the outcome of the EVAR procedure at regular intervals, allowing for a quick identification and treatment of complications.
In conclusion, the Mimics Innovation Suite’s powerful 3D reconstruction tool has proven highly useful. It serves a role in calculating FEARI, which has the potential to aid in the surgical decision making process. Furthermore, 3D reconstruction is performant and could not only help to standardize the measurement and size stent grafts, but also to support surgeons in improving AAA treatment.
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