“Creation of a Novel Ex Vivo Human Liver Model for Microwave Ablation Investigation” will be presented during the Closing Plenary Session on Wednesday, March 27, at 10:30 a.m. MT.
“One of the big problems that we have right now in translational research for microwave ablation is that we use healthy animal models,” said Carlos B. Ortiz, MD, lead author of “Creation of a Novel Ex Vivo Human Liver Model for Microwave Ablation Investigation.”
“Whether it’s porcine or bovine, sometimes they’re not perfused and if it’s an in vivo animal such as a pig, the porcine livers are pretty small, and their lobes are really thin.
It’s a known issue within IR, Dr. Ortiz said, and while ablation system manufacturers provide guidelines for how to achieve a specific size burn, those data may not be entirely accurate because it wasn’t tested on human models.
“When you have an ex vivo nonperfused organ, it’s going to create a larger microwave ablation zone than if you compare it to an organ with perfusion. That’s because you have the heat sink effect or perfusion-mediated tissue cooling, which decreases the size of your burn, especially the closer you are to large vessels, because those will dissipate the heat,” said Dr. Ortiz. “Microwave ablation is frequently touted as superior to radiofrequency ablation because it’s less susceptible to the heat sink effect. And while that is true, there is still a significant amount of heat sink effect that happens for microwave ablations.”
That is why it’s crucial to have data that more accurately reflect real-world scenarios, Dr. Ortiz said.
The research utilized 12 human livers declined for organ transplantation to develop an ex vivo perfusion model and study microwave ablation in human tissue.
Researchers used a fluoroscopic compatible ex vivo dual arterial and portal perfusion system to obtain normothermic conditions. According to the abstract, digital subtraction angiography of the arterial, portal and biliary system was performed before and after MWA, which was performed using an MWA system at 140 Watts for 6 minutes. After perfused and nonperfused MWAs were performed, MWA zones were segmented along the MWA trajectory to obtain maximal short axis diameter (SAD) and long axis diameter (LAD) measurements.
“Essentially, we warmed our organs up to physiologic temperatures, performed the microwave ablations and then we halted perfusion,” Dr. Ortiz said. “Then, at the same temperature, we performed microwave ablations in a nonperfused state.”
This shows that the model can produce a heat sink effect, Dr. Ortiz said, which provided clearer data when comparing different conditions in perfused human organs.
Additional analysis by tissue type was performed, demonstrating a statistically significant increase in perfused MWA zones for livers with cirrhosis compared to livers with macrosteatosis.
“If you are looking at nonperfused data, you might get misled into thinking you’re going to create a larger ablation zone in a patient when in reality, the heat sink effect is there. And if you have a smaller burn, that will increase the risk for recurrence,” said Dr. Ortiz.
According to Dr. Ortiz, he is also interested in utilizing the basis of this model to gain more precise measurements of tissue dielectric properties. “Right now, we can send tissue to pathology and get their assessment, but we really want to know what is happening within the tissue and better understand the dielectric properties during MWA,” he said.
“Our future goal is to use more research organs of various tissue types—cirrhosis, fatty and normal livers—and then compare the ablation sizes by tissue type. Our current model is capable of producing the heat sink effect and normothermic conditions,” said Dr. Ortiz.
Dr. Ortiz said that he hopes to integrate a dielectric probe into this model to improve the significance of his research. “This may help us see if we can better predict what ablation zones we get based on the existing tissue,” he said.
All of this will have clinical applications in helping IRs to be more precise in their ablations, Dr. Ortiz said. “You can’t just look at the number on the chart,” he said. “You have to understand how the data are created and translate that directly to the patient.”
