Algorithm labels images of individual vertebrae during spine surgery

22 December 2016
The researchers were funded by the National Institute of Biomedical Imaging and Bioengineering (NIBIB), part of the National Institutes of Health in Bethesda, Maryland. New work recently published by the team demonstrates the accuracy, feasibility, and advantages of having the technology in the operating room.

Careful assurance

Spine surgery requires careful assurance that surgeons are operating at the right level of the spine. But, because of obesity, low bone density, or anatomical abnormalities, the spine—twenty-four separated vertebrae, the sacrum, and the tailbone—can be difficult to distinguish and number. To prevent mistakes, time and money are spent to ensure operations are performed at the right locations; sometimes an extra procedure is done before surgery to label the target vertebra. Still, in about one out of 3,000 procedures, a mistake is made and the wrong level is operated on, causing unnecessary damage and requiring an additional, corrective surgery.

The LevelCheck algorithm does more than help preventing this from happening, Steven Krosnick, M.D. explains. According to the director of the NIBIB program in Image-Guided Interventions, LevelCheck actually provides assurance to the surgeon, so it means they can be more confident. “It just makes for a better procedure. It fits into the surgical workflow and doesn’t require much additional time during surgery,” Krosnick says.

When a surgeon looks at a radiograph, like an x-ray, of the spine, it is difficult to say with 100 percent certainty they are looking at. The potential for human error is one that an algorithm could help to avoid,  Jeffrey Siewerdsen Ph.D., professor of biomedical engineering and computer science at Johns Hopkins University and senior author of the recent paper, believes. “Surgeons spend a lot of time, energy, and stress to get it right, and we wanted to provide some decision support for that.”

Algorithm uses routine images

The US and German researchers first described the algorithm in 2012. It takes advantage of two types of routinely taken images: a computerized tomography (CT) scan taken prior to surgery and a radiograph taken at the beginning of surgery.

The CT is three-dimensional, more detailed than a radiograph, and can be used to accurately define and label the vertebrae. When surgery is set to begin, LevelCheck compares the current radiograph to the previously labeled CT, matches positions and landmarks, and projects the labels onto the radiograph. Using high-speed computing, the algorithm makes its comparison and provides labels in the span of 20 to 40 seconds.

Usefulness LevelCheck

In the new work, published in the Oct. 15, 2016, issue of the journal Spine, the researchers examined the usefulness of the LevelCheck algorithm by applying it to nearly 400 images previously taken from spinal surgery patients.

Three spine surgeons evaluated both the algorithm’s accuracy and how useful they thought such a tool would be during surgery. LevelCheck labeled the vertebrae correctly in every case and the surgeons judged it to be helpful in 42 percent of the cases and to improve confidence in 31 percent. The algorithm turned out to be particularly advantageous when anatomical landmarks usually used to count spine segments, such as the sacrum or twelfth rib, were missing, obscured, or abnormal; when spine segments were not easily distinguishable; and when the image quality of the radiographs was poor. As for the additional time spent waiting for the labels to appear, the surgeons said they’d be willing to wait up to a minute for the extra assurance.

Independent check

Even though surgeons are accurate the vast majority of the time, an independent check can still help, especially since it doesn’t require additional work. In this, Jeffrey Siewerdsen compares LevelCheck to GPS in cars; you rely on it when you’re driving somewhere new, but you might also use it as a check or confirmation even when going places you’ve been before.

“Most of the time it is just confirming something that you would have gotten right anyway. But decision support can help you reach that decision a bit faster, with a bit more certainty. And every once in a while, it could even help prevent an error.”

The team also designed a version to be used when only preoperative MRIs, rather than CT scans, are available. Siewerdsen also sees potential for the technology to track and guide devices during surgery and to provide easier ways to collect quantitative data about surgeries.

Clinical trials

The current work is retrospective—the researchers added the labels to images after surgery. Clinical trials that use the technology during operations are now underway. Still, Siewerdsen thinks LevelCheck could one day be commonplace in the operating room, installed into imaging systems so labels—and the precision and confidence they provide—are just a button push away.