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The Department of Neurological Surgery at St. Louis University has partnered with the university's School of Engineering to begin quantifying how advanced manufacturing practices such as 3D printing can enhance the training as well as the surgical practice for neurosurgeons. The ongoing study, which focuses on specifically saving a patient who is experiencing a brain aneurysm, compares 3D printing against traditional training methodologies such as cadavers (human, animal), foam models, and other conventional practices.

Saleem Abdulrauf, MD, trains a surgeon using a 3D printed brain.

The 3D printing study was spearheaded by Saleem Abdulrauf, MD, professor and chairman of the Department of Neurological Surgery and neurosurgeon-in-chief at the St. Louis University Hospital. He is also president of The Walter E. Dandy Neurosurgical Society, a premier forum for neurosurgical surgeons that provides education and training to surgeons on cutting-edge practices that improve patient outcomes. Dr. Abdulrauf's mission is to improve patient outcomes during the most complicated neurosurgical operations using all the innovative tools available to him.

“I personally perform a lot of brain aneurysm surgeries. It is a complex operation given the number of anatomical issues that we're dealing with under the microscope. I knew if there was a way of simulating those complications before the operation using the same tools and under the same microscope, we'd have a higher positive impact on the procedure outcome for the patient,” he says.

Challenge

Brain aneurysms differ minutely from patient to patient. During the operation, a surgeon is tasked with determining how to reach the aneurysm with minimal effect on surrounding tissue. The surgeon must calculate, in real time, the optimum angle to get into the area while factoring in the depth at which the aneurysm occurs and the size of the clip needed to close the aneurysm area.

“Every aneurysm is different in size, contour, and location. We have hundreds of clips sizes and types we can use, and we're typically making the decision on clip size during surgery. If I can make that decision beforehand by practicing on a model using the same tools and clips I plan to use in the final operation, it really makes a difference during surgery,” explains Dr. Abdulrauf.

Developing a method to simulate an individual patient's specific brain aneurysm presented a few challenges. Because the simulation would be most effective as a physical model on which the surgeon could practice the procedure, the models therefore needed to be a 1:1 scale of the patient's brain. If the models could additionally mimic the look and feel of brain matter so that surgeons could use the same equipment on the model as they would on the patient, it would be even more beneficial to surgeons.

Achieving simulation models with those parameters first requires an accurate high resolution map of the patient's brain translated into a 3D CAD model. Next, an extremely fast manufacturing method is needed because patients would be suffering from the aneurysm in real time. Lastly, for the models to truly demonstrate potential as a future business model viable for doctors, a fast and a cost-effective production method is required. Ideally, each model would be created as a one-off part unique to each patient's particular brain abnormality. Therefore, conventional production, with high costs for single tools that are dedicated to large volumes of identical parts, would be unsustainable for the low-volume needs pertinent to a patient case-by-case creation.

Solution

One of the fastest and most cost-effective production methods for one-of-a-kind parts is 3D printing, and so it was quickly considered as a viable solution for creating the brain models. From the selection of additive manufacturing technologies, PolyJet stood out as the most ideal 3D printing process because it is capable of meeting the time, cost, and material challenges Dr. Abdulrauf's team faced. Additionally, PolyJet is one of the only 3D printing processes capable of printing a range of durometers into a single part, a significant boon to achieving the best feel for the skull of the model.

A 3D printed model simulates the procedure to assist in planning the surgery.

To create the models for the preliminary patients, scans of the patients’ brains were sent to the St. Louis University School of Engineering. The engineering students translated the scans into high-resolution models that were exported as stereolithography (STL) files compatible with 3D printing. Although the university had its own PolyJet machine, to achieve the quality and materials diversification necessitated by the project the team chose to outsource the models. They sent multiple CAD files of the brain, skull, and aneurysm to Stratasys Direct Manufacturing, Poway, CA, for printing. Together with Stratasys Direct, the engineering and medical students noted the critical area of the aneurysm. The Stratasys Direct team focused on maintaining flawless accuracy and detail on the aneurysm area throughout the entire production process.

Stratasys Direct was chosen as the 3D printing provider for the project for a few key reasons: its capacity, expertise, and dedicated anatomical department. The Stratasys Direct anatomical department is one of the leading innovators in revolutionary manufacturing methods in the field of anatomical training models. Some of its key achievements include providing 3D printing and urethane components for birthing simulators, as well as dental, heart, bone, and kidney models. Stratasys Direct collaborated with the university to build the scans of the brains, aneurysms, and skulls using PolyJet and urethane casting.

The combined teams from Stratasys Direct and the university chose PolyJet Rigid VeroYellow for the skull and an over-molded TangoPlus material with a durometer of Shore 27A for the brain. The TangoPlus brain was built as a multifunctional piece. Initially, it served as the solid brain. Within the CAD design, the aneurysm was 3D printed according to the aneurysm pattern experienced by the actual patient. Finally, the skull was built with the inner support material that hugged the grooves and depressions of the sulci and gyri likeness of the patient's brain. This support material served as the pattern for creating the inner brain matter.

The interior of the TangoPlus brain was filled with a specially formulated gelatinous colloid material that mimics the feel of the spongey sulci and gyri in the brain. The ure-thane material filled in around the anatomically correct PolyJet printed aneurysm. The mixture cured within the TangoPlus and, with the aneurysm intact and in place according to the patient's exact brain map, resulted in a completed, multi-material piece ready for operation.

The Stratasys team focused on ensuring the accuracy and detail of the aneurysm area throughout the entire production process.

Results

These preliminary surgeries using a 3D printed model to simulate the procedure prior to operation provided valuable feedback for Dr. Abdulrauf and his team. “Having the 3D printed model here has a very positive impact on the procedure results,” says Dr. Abdulrauf. “The model has helped to identify and overcome surgical challenges, like optimum access to the aneurysm or the depth and angle of the approach, before surgery begins.”

With these positive preliminary results, the next step is to measure the success of 3D printed models through blind studies. Dr. Abdulrauf has proposed a two-arm study with resident neurosurgeons. All of the residents will be asked to perform a procedure on a cadaver. Half of the residents will receive a 3D printed model of the cadaver's brain prior to surgery while the other half will prepare for the surgery without a 3D model. The two groups will then be compared blind. The assessors will not know which group received the 3D printed model. The success of one group over the other will be measured by the time undertaken during the process, absence of errors, and the ability of the groups to keep the circumference of the surgery as minimally invasive into healthy tissue as possible. From this study, Dr. Abdulrauf hopes to quantify the use of 3D printed models in presurgical planning.

A second study will involve measuring the outcomes of patients who receive the traditional gold standard of care during surgery and patients who receive the gold standard plus their neurosurgeons receive a 3D printed model of their brain to practice on prior to surgery. The recovery time of patients and overall patient comfort post-surgery will be carefully monitored in both groups. By studying actual patient outcomes, Dr. Abdulrauf hopes to gain measurable insight into the benefits of 3D printing for surgical procedures.

“The future of medicine is all based on measuring outcomes. The most important thing is quantifying what's better for patients and improving the lives of patients. To do that, we must know the absolute best measures we can take using the tools we have to improve their lives,” explains Dr. Abdulrauf.

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