In 2018, 80,000 people in the U.S. will be diagnosed with a brain tumor, according to the American Brain Tumor Association. Many will undergo chemotherapy and major surgery to help combat the tumor, and out of those 80,000, 16,000 will not survive.
As an alternative treatment, doctors have increased their use of radiofrequency ablation (RFA) treatments as a new way to fight these tumors. RFA is a minimally invasive procedure that uses electrical energy to destroy cancer cells with heat. A thin needle is inserted into the brain and delivers radiofrequency waves directly to the tumor. This in turn heats the tumor to 140℉ until the tumor is destroyed. While this method is less invasive and becoming more popular, doctors are still lacking a method for monitoring the procedure in real-time.
However, the University of Southern California’s Viterbi School of Engineering has developed a new imaging method to help RFA become a more standard practice. “Although ablation is becoming increasingly popular, there is still no thermal imaging technology in regular clinical use to monitor these procedures in real time and ensure that the correct thermal dose is delivered the first time,” said Research Assistant Professor John Stang of the Ming Hsieh Department of Electrical Engineering.
Stang co-authored the study published in IEEE Transactions on Biomedical Engineering, along with Mahta Moghaddam, director of the Microwave Systems, Sensors, and Imaging Lab (MiXIL); Guanbo Chen, from the University of Southern California; Mark Haynes, from the NASA-Jet Propulsion Laboratory; and Eric Leuthardt, from Washington University in St. Louis. Stang and Moghaddam have developed a real-time thermal imaging method and device that will aid in the accurate delivery of RFA treatments.
The graph above shows how the method records the increase in thermal activity in the brain.
The method uses continuously transmitted microwaves to image changes in the dielectric properties of tissue with changing temperature. Instead of the precomputed linear Born approximation that was used in prior work to speed up the frame-to-frame inversions, the method uses nonlinear distorted Born iterative method (DBIM) to solve the electric volume integral equation (VIE) to image the temperature change.
This is made possible by using a recently developed graphic processing unit which has an accelerated conformal fixed difference time domain method to solve the forward problem and update the electric field in the monitored region in each DBIM iteration. From the signals and information collected during the transmissions, a 3D thermal image of the region is produced in real-time, providing the doctors a quantitative temperature map of the region. The new method provides a better approximation of the electric field within the VIE, and thus yields a more accurate reconstruction of tissue temperature change.
“In in vitro experimental validation studies, our system was able to achieve 1°C accuracy at a refresh rate of one frame per second,” Stang said. Today, doctors rely on CT or MRI scans to perform the RFA treatments. The problem is that with every new scan, doctors have to stop the RFA treatment, perform the scan, and then repeat the RFA treatment. Each repeated RFA introduces new risk of infection or other complications. The new thermal imaging method opens the opportunity for non-interrupted RFA treatments.
The next phase for this method is to create higher-resolution images and undergo animal testing. The researchers will specifically look towards imaging liver cancer, with the support from the USC Alfred E. Mann Institute for Biomedical Engineering and in collaboration with the Keck School of Medicine of USC. “Assuming we get good results, we may be three to five years away from clinical trials,” said Moghaddam.
