The liver is a particularly squishy, slippery organ, prone to shifting both deadly tumors and life-preserving blood vessels by inches between the time they’re discovered on a CT scan and when the patient is lying on an operating room table.
Surgeons can swab the exposed liver lightly on the surface with a special stylus, capturing the shape of the organ during surgery, and a computer can match that image with the CT scan on a screen. This GPS-like ability is far better than feeling for tumor and blood vessel location, but even this road map can be off by centimeters.
Michael Miga, Harvie Branscomb Professor of Biomedical Engineering, and his team published the potential solution: surgery-tested software that better marries images from the CT scan and the tracked tool. The advance stands to help more than a half-million liver cancer patients worldwide each year.
Their paper, “Deformation Correction for Image Guided Liver Surgery: An Intraoperative Fidelity Assessment,” appears this month in the journal Surgery.
Used in a blinded, randomized 20-patient bystander study over the past 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 for abdominal surgeries. It sold to Analogic Corporation in 2014 and is in use at top cancer centers.
“If you’re trying to get to a tumor the size of a dime and avoid a blood vessel, you need to avoid errors,” he said. “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.”
Software that makes a computer model out of the original image of the liver and simulates the forces being applied during surgery – such as packed gauze lifting the liver upward – addresses the problem without investing in additional expensive equipment is. The computer adjusts the CT-derived GPS map to better match the exposed organ shape in the OR.
In the study, surgeons were shown six or seven CT images, depending on time, for each of 20 liver tumor patients in the operating room, for a total of 125 images. The CT map would be aligned to either the original Pathfinder or Miga’s new enhanced CT map that corrected for deformations. Surgeons were not told which display was presented and would assess the alignment by touching the stylus on the patient’s liver and looking at the display.
Each surgeon then provided a score on a scale of +3 to -3 relative to the previous display presented. Display order was randomized and could go from enhanced to original, original back to enhanced, or held constant. Surgeons were able to detect the variations correctly in 73 percent of the 125 different evaluations.
Current procedures force surgeons to use as much art as science to locate tumors and decide how much to resect while retaining enough organ tissue to allow the liver to grow back.
Miga said the new research, in particular the type of study they performed, represents a major advance in soft-tissue, image-guided surgery for the abdomen. This new deformation correction technology can be integrated into image-guided surgery systems.
The lead author on the paper is Logan W. Clements, research assistant professor of biomedical engineering. Miga is an affiliate of the Vanderbilt Institute for Surgery and Engineering. Their work was supported by National Institutes of Health grant R01-CA162477.
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