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A research done to promote the use of open-source tools in turn hoping to reduce the medical costs incurred by patients undergoing cardiovascular surgeries.
During my bachelor’s at MIT, Manipal I was involved in an academic project, where I got to work as a research lead focused on helping to promote open-source tools. The main goal was to understand the existing tools used in performing the fluid-structure interaction studies of arterial systems in the human body and compare these results with the latest open-source packages released in the market. For this a section of the arterial system specifically, the coronary artery was chosen and used for analysis. With near to similar initial parameters the artery was modeled from, DICOM images obtained through an MRI scan, on both tools. The final results were then compared to understand the effectiveness of the open-source tool and room for future improvements.
In this research, we have used an open-source tool SimVascular: a cardiovascular modeling and simulation package by SImTk. This software was developed at the University of California, Berkeley, and Stanford.
*This work is being published hence the specifics are not disclosed*
ABSTRACT
Image-based modeling is one of the most extensively used methods for analyzing patient anatomy in medical diagnostics. It has seen great advancements in recent years. It helps in identifying any anatomical or physiological abnormalities and charting a database of normal patients for future reference for doctors. With the help of vascular imaging, we would have clear data for treating a patient-specific problem.
In a medical case, the most important thing doctors require for evaluating the options and planning the treatment is the medical data of the patient in analogy to a normal. In this work, we have concentrated on the cardiovascular study using the medical image model created using patient-specific MRI data and evaluating the parameters using the results from the Fluid-Structure interaction results. In cardiovascular diseases, the important evaluating factor is the high blood pressure in the aorta and other blood vessels.
In recent years, it is observed that cardiovascular health has started to deteriorate due to increased hypertension, smoking, inactivity, etc. Many researchers have suggested it would likely increase due to the increasing population and aging. Recent statistics have also stated an increase in mortality rate by 26.6% in 2019 compared to the numbers in 2010. With the substantial advancements in the medical field and the use of evidence-based treatments, doctors are trying to reduce the death count attributed to heart diseases.
This whole study is highlighted to promote the use of open-source tools in place of the standard methods being followed for obtaining the required flow parameter results. In present medical cases, the normal method of evaluation is using mimics for modeling and ansys fluent for simulations. But it has turned out to be not feasible in all cases due to the requirements of high computational power and heavy price tag which in turn increases the cost to the patient. So, recently a fully open-source package, SimVascular was developed for medical image modeling and simulations. It has systematically laid out tools for the construction and evaluation of medical data making it an easy tool for quick learning and use. It is found to have great value in medical image research, medical device modeling, and even educational purposes.
DATA SET USED
During the research, the shown DICOM images from MRI were used to create a model as shown in the next picture. The inlet conditions like the physiological values and the inlet waveform were taken straight from the literature.
GRUNTWORK
Now for developing the outlet boundary conditions, the biological system was translated into an electrical system considering a resistor, capacitor, and current flow within the system. With these, the outlet boundaries were estimated and used in the system. This Boundary condition is called the RCR windkessel model. Some data was adapted from the literature.
WORKFLOW
The shown steps were taken to model the system. In the open-source tool: Simvascular the workflow is similar to any cad package. we start by drawing a sketch and creating profiles which are then used to create a 3D part. Similarly here first the path is created to represent the arteries and then the profiles are created to finally form a 3D model. Next, the model was meshed using the 3D Delaunay triangulation method to generate a smooth tetrahedral mesh.
While on the other side, using software like Mimics and CATIA the model was created and cleaned to achieve the final model. Here ANSYS workbench was used to prepare the model for simulation.
ROADBLOCKS
Since the open-source tool was still under development there were several steps unclear during usage. The lack of easily accessible resources to learn or debug an issue was the biggest drawback. Of all those instances the two important ones were the lack of a units system for the whole package and the lack of the right simulation packages for all windows platforms.
The lack of a units system caused tremendous troubles as most of the data available was in the CGS units while the model was in MKS units. Hence, to solve this problem I had to develop a program to scale the model with respect to the center point of the model. I developed a python script that would take a model, here the model.vtp file, and the scaling factor as the input to provide you with the scaled model. Then this was imported into the GUI.
Secondly, due to the lack of the right solver for windows, I had to find an external solver and configure the wireframes to match that with the tool. This was explained on the developers’ page of simvascular, but unclear. It was recently observed that this was resolved by their new version which was compatible with all platforms.
RESULTS
*Final results are not disclosed*
SimVascular can provide us with vital data after simulation which was found to be useful to make the required decisions on the patient's cardiovascular health. By comparison with known literature resources and results obtained from standard software, SimVascular can provide comparable results with the requirements of minimal computational power and is mainly cost-efficient. With this, I conclude the software has a high scope for betterment and advancement in the mere future leading to a significant addition to the medical world.
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