Video gaming technology facilitates beating-heart surgery
Operating on a beating heart could enable surgeons to repair defects without having to perform cardiopulmonary bypass. But to work with fragile moving anatomic structures in the presence of blood would require novel imaging techniques. To achieve this, surgeons would need dependable three-dimensional visual feedback to guide them.
Researchers with Children’s Hospital Boston and with Harvard University in Cambridge, Mass., were evaluating a 3-D ultrasound imaging system in animal studies when they found that these images didn’t afford the maneuverability that they needed. “Although we had 3-D visualization, there was no depth perception,” said Dr. Nikolay V. Vasilyev of Children’s Hospital. To address thislimitation, they looked to an unlikely source of inspiration: the video gaming industry.
Taking a cue from video gaming technology, researchers have devised a means to perform beating-heart surgery. Using stereoscopic vision display technology (3-D glasses) they repaired atrial septal defects (ASDs) in pigs. As shown above, the technology renders volumetric data separately for the right and left eyes, skewing the images to provide the stereoscopic effect. LA = left atrium; RA = right atrium. Images reprinted with permission of The Journal of Thoracic and Cardiovascular Surgery.
The team, led by Dr. Pedro J. del Nido, chief of cardiac surgery at Children’s Hospital, recently turned to stereoscopic vision display technology — which is very similar to that used with gaming systems — to help them with 3-D echocardiography-guided beating-heart surgery. Such technology had been applied to other image-guided surgical interventions, but never to the cardiac procedures the researchers were using. “With the stereoscopic technology,” Vasilyev said, “we found it easier and safer to navigate inside the beating heart and repair the defects in question.”
To achieve this, they streamed data acquired live from a 3-D ultrasound imaging system made by Philips Medical Systems of Andover, Mass., to a computer with a commercially available graphics card, typically used for gaming applications. A custom algorithm implemented on this card immediately displays the streaming volumes on a conventional 19-in. cathode-ray tube monitor positioned directly in front of the surgeon.
The surgeon views the volumes with stereoscopic liquid crystal display shutter glasses made by eDimensional Inc. of Jupiter, Fla. Data is rendered separately for the right and left eyes, with both eyes receiving exactly the same image but skewed anywhere from 7° to 12° to produce the stereoscopic effect. So, when wearing the 3-D glasses, the surgeon actually has a sense of the depth.
The glasses offer a very high frame rate, Vasilyev added, so the clinician doesn’t experience any flickering — as might be the case with other approaches to stereoscopic vision, such as the red and blue glasses used to view 3-D movies.
The researchers tested the efficacy of the stereoscopic vision display system using an animal model of atrial septal defect closure. They created defects in six pigs and then used the vision display system for guidance in closing the defects using a catheter-based patch delivery system, affixing patches with tissue mini-anchors. For each anchor placement, task-performance measures such as completion time, trajectory of the tip of the anchor deployment device and accuracy of the anchor placement were compared with those recorded using a standard display for guidance.
To evaluate the efficacy of the technology, the researchers performed atrial septal defect closure in pigs using both the stereoscopic vision display and a standard display (postmortem photographs are shown here, on the left and right, respectively) — closing the defects using a catheter-based patch delivery system and affixing the patches with tissue mini-anchors. They found that the stereoscopic vision display outperformed the standard display in two of three task performance measures; the third measure — accuracy of placement — was roughly the same for the two displays.
The investigators found that the stereoscopic vision display allowed the surgeons to outperform the standard display in two of the three measures. The completion time was 44 percent shorter and the navigational accuracy, determined by trajectory deviation, showed a 38 percent improvement. The accuracy of anchor placement was roughly the same for the two groups.
The researchers are developing the technology further so that it can be used for 3-D guidance during beating-heart surgery. It could show 2-D slices of anatomical structures on the same display, for example, in case the surgeon needs additional information about a particular target spot. In addition, sometime early next year, after completing safety tests, they plan to assess the technology in human trials.
The Journal of Thoracic and Cardiovascular Surgery, June 2008, pp. 1334-1341.
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