ANSYS Fluent Saves Infant Lives
BCPA surgery simulation of contrast medium injection into superior vena cava. Color-coded to velocity.
Around the world, children are born with a heart condition known as hypoplastic left heart syndrome (HLHS). The congenital heart defect allows only one ventricle to work. In the US, 960 newborns are affected by this condition every year. This to correct this condition and survive, children need three surgeries (Norwood, BCPA & TCPC) before the age of three.
These surgeries have risks and many don’t survive between operations. However, by testing surgical options using ANSYS Fluent CFD simulations, doctors can gain more information to select the optimal surgical option is chosen. These simulations can increasing patient survival and reduce complications.
| Surgery | Age | Goal |
|---|---|---|
| Norwood | Days | Connect circulatory system to working ventricle |
| Bidirectional Cavopulmonary Anastomosis (BCPA) | 4-6 months | Blood flow to lungs increased |
| Total Cavopulmonary Connection (TCPC) | 2-3 years | Venous return rerouted to lungs creating a healthy blood flow sequence where de-oxygenated blood moves to lungs and oxygenated blood to the body. |
This new wave of medical simulations is called In silico testing. It involves bioengineers translating bio-scans into CAD models which are then used to simulate patient-specific treatments. Thierry Marchal, Industry Director for Healthcare at ANSYS, said “Interacting with surgeons, being in the operating room, and watching a valve replacement reminds me of why we work so hard to produce our simulation software.”
Dr. Gilles Eggenspieler, Sr. Fluid Product Line Manager at ANSYS, added “When people ask me: ‘is simulation accurate, or can we rely on it?’ I tell them the story about these children. If the simulations are good enough for these good doctors to test a surgery that save lives, then it’s probably good enough for their products as well.”
Setting up the Life Saving CFD Simulation
3D model of pre-operated stage 2 BCPA coupled with an LPM simplified model of the body’s circulatory system. Patient anatomy courtesy of Lucile Packard Children’s Hopsiptal, Palo Alto, Calif., USA.)
With the help of ANSYS Fluent and Marchal’s simulation experts, doctors and surgeons as well as a network of research specialists through University Politecnico di Milano, are using In silico testing to help treat HLHS patients.
Currently, the simulation process is too complicated for doctors to perform on their own. The engineers will modify the geometry in the software to investigate each surgical option defined by the doctor.
These experts can take any biomedical scan and convert it into 3D geometry specific to the patient. The scans come out as a black and white picture. The varying levels of grey can then be used to identify the shape of the object (organs, arteries, etc.) in the image. By calibrating to the grey spectrum of the image, an accurate 3D representation of the image can be produced. “This is called segmentation,” said Marchal. “There are a few software options bioengineers can use to process bio-scans into CAD including Simpleware and Materialise.”
Once the heart and major cardiac arteries are modeled, the engineer then sets up a multi-domain simulation to model the blood flow.
Much of the circulatory system can be simplified to a lumped parameter network (LPN) to create proper boundary conditions. Additionally, this simplification will reduce the calculation time needed to process the simulation allowing for more surgical options to be tested.
“Quite often we are told simulations over simplify the body. We don’t take blood cells, and minor arteries into account. But it isn’t important to mimic the whole body; our goal is to save lives. If we can do it we will simplify the model. If we need it to be more complex, we will make it more complex. But at the end of the day, we want to do minimal calculation to get the maximum certainty that a life will be saved,” expressed Marchal.
To that end, the LPN can be made as complex or simple as needed. It is used by the engineers to represent the body and feed the simulation’s boundary conditions. The LPN can also be modified to simulate different patient activities including running, biking, and working. This means that the doctor will be able to assess which activities the patient can participate in post-surgery.
“The LPN will not be accurate around the body but will be accurate at the boundary condition,” explained Marchal. “The legs and brain are not important to a heart surgeon. But, you cannot neglect them or the model will miss that blood must be send there. The circulatory system will affect the boundary conditions of the simulation so it cannot be ignored.”
Thanks to these simplifications and improved computing software, the simulations are calculated faster. For HLHS patients, the first surgery must be performed days after birth. Each day wasted will add risk to the patient. A few years ago, this simulation would have taken days to perform. However, with cloud computing and simulation optimizations, it takes only a few minutes.
Will doctors set up their own CFD simulations?
TCPC surgery simulation of contrast medium injection into superior and interior vena cava. Color-coded to velocity.
One challenge with the early stage of In silico testing is to get doctors on board. “We need to educate doctors that this is a viable option. Many surgeons will only trust other surgeons. However, we are working with a few pioneers that value our results. Once we have doctors convinced, we can create a simplified version of the software so they can investigate in silico surgeries on their own,” explained Marchal.
As such, ANSYS plans to transfer the knowledge of their simulation experts into an environment doctors can use without training. To do this, the CFD simulation setup must be completely automated.
“The doctors don’t have time to learn. They are saving lives. Unfortunately, it’s hard to produce software that can’t make mistakes. Especially since humans are so complicated. So we are putting a lot of work into developing an interface specific for the pathology. Maybe in a few years we will see some doctors using simulation software to treat a specific illness or plan a certain surgery. But it will have to pass regulations first,” said Marchal.
He added, “We want to give doctors a tool to recommend and optimize procedures. However, we are never making the decisions. Simulations give additional information; our experts are not trained for medical decisions. But with a standalone medical program, powered by ANSYS Fluent, doctors and surgeons can make better, faster, decisions.”
It is the hope that this software will also allow doctors to perform a virtual surgery on their patient. Unfortunately, this will be difficult as they will have to manipulate the geometry of the patient’s arteries and heart, though Marchal is convinced that one day there will be virtual surgeries.
For the simulation technology to mature to a standalone tool for medical professionals, Marchal suggests that we need to convince more students to become bioengineers. “Our challenge is a lack of bioengineering workforce. This is especially true for females. We have too many doctors but not enough bioengineers. It would be very impactful if some of these would-be doctors did a similar job, but as a bioengineer. I suggest they would save even more lives.”
At the End of the Day, Simulations Saves Lives
“By collecting hundreds of samples of patient geometry, we can revolutionize healthcare by accurately testing procedures before they are performed on real patients. We may not solve HLHS and cardiovascular disease, but we will be able to work on them faster and easier,” said Marchal.
ANSYS has sponsored promotion of their Fluent software on ENGINEERING.com. They have no editorial input to this post - all opinions are mine. Shawn Wasserman