The liver is a squishy, slippery organ that often shifts tumors and life-preserving blood vessels from the time the tumors are discovered through a CT scan, to when the patient is on the operating table.
Surgeons can swab and expose the liver lightly on the surface with a special stylus, capture the shape of the organ during surgery and a computer can match the image with the CT scan on a screen. This GPS-like technology is better than guessing where the tumor and vessels are or feeling for them. However, this map could be off by centimeters, which could mean life or death when scraping the liver.
This graphic represents the mismatch between the liver shape based on a CT scan of the liver (in green) and the shape traced by the intraoperative tracking device during surgery (black dots). Image credit: Vanderbilt University
Michael Miga from Vanderbilt University, Harvie Branscomb, a professor of biomedical engineering, and his team have found a new potential solution to this problem. This team has developed surgery-tested software that better marries the CT scan image to the tracked tool image. This is an advance that could help more than half a million liver cancer patients each year.
The study done with this technology used blinded, randomized 20-patient bystanders over two years at Memorial Sloan Kettering Cancer Center in New York. Surgeons said the new technology improved the registration in more than 70 percent of cases.
"Deformation happens," said Miga, who developed the Pathfinder stylus system that was sold to Analogic Corporation in 2014. "The way the liver is configured in the body at the time of diagnostic imaging and the way it's presented for surgery are very different. If you're trying to get to a tumor the size of a dime and avoid a blood vessel, you need to avoid errors. The problem is, by the time a surgeon can access the organ for surgery, the CT-derived GPS map could be off by centimeters. That's dangerous, especially if resecting close to a major vessel."
This method fixes the error without investing in expensive equipment, by using software that makes a computer model out of the original image of the liver. This technology stimulates the forces being applied during surgery, like packed gauze lifting the liver upward. The computer adjusts the CT-derived GPS map to better match the exposed organ shape in the OR.
During the study, surgeons were shown six or seven CT images, depending on time, for each of the 20 tumor patients in the operating room with a total of 125 images. The CT map would be aligned to the original Pathfinder or Miga’s new CT map that corrected for deformations. The surgeons were not told which display was being presented and they would assess the alignment by touching the stylus on the liver and looking at the display. The surgeons provided a score on a scale of +3 or -3 relative to the previous display presented. The display order was randomized and could go from enhanced to original, original to enhanced or held constant. The surgeon was able to detect the variations correctly in 73 percent of the 125 evaluations.
This new deformation correction technology is available to be integrated into image-guided surgery systems. The study on this new technology is titled “Deformation Correction for Image Guided Liver Surgery: An Intraoperative Fidelity Assessment” and was published in the journal, Surgery.
