News
Video game technology gives surgeons 3-D vision
for operating on beating hearts
24 June 2008
Stereo glasses and video game hardware can give surgeons the fast,
highly sophisticated real-time 3-D imaging needed to do complex
operations on the beating heart using keyhole surgery.
In a study published in the June Journal of
Thoracic and Cardiovascular Surgery, cardiac surgeons from
Children’s Hospital Boston, US, report good results with the technology.
The researchers, led by Pedro del Nido, MD, and Nikolay Vasilyev, MD,
of the Children’s Hospital Department of Cardiac Surgery, had already been testing a
three-dimensional ultrasound imaging system. But although the images are
3D and displayed in real time, they give little indication of depth. In
animal tests, surgeons trying to navigate surgical tools inside the
heart became disoriented when guided by these images.
Del Nido, chief of Cardiac Surgery at the Children’s Hospital,
realised that what they needed was stereoscopic vision. Watching the
flat picture on the computer screen was like watching a baseball game on
TV, he says. “It’s good enough to follow what's happening in the game,
but you could never grab a ball in mid-flight,” del Nido explains.
So collaborator Dr Robert Howe, of Harvard University, borrowed a
solution from video games — splitting computer images in two and cocking
them at slightly different angles. When wearing gamers’ flickering
glasses, users can see ultrasound images of the beating heart as a
hologram. “You definitely have depth perception,” says Vasilyev. “You
feel like you’re inside the heart chamber.”
Vasilyev tested the glasses while operating on pigs with an atrial
septal defect, a common form of congenital heart disease in which there
is a hole in the wall dividing the heart’s upper chambers. Vasilyev
closed each defect using a catheter carrying a tiny patch, threaded into
the heart through a vein. Using another device, he fastened the patch
around the hole with tiny anchors. In all, he placed 64 anchors: 32
under standard 3D ultrasound guidance, and 32 using the stereoscopic
vision display.
Using the stereoscopic display, Vasilyev was able to place the
anchors 44% faster than with the standard display (9.7 versus 17.2
seconds). The tip of the anchoring device also navigated more
accurately.
The accuracy of anchor placement didn’t differ significantly between
the two sets of tests. However, the speed of the anchor
placement improved significantly. The researchers believe that the
ability to precisely navigate tools inside the beating heart will
minimize risk to neighbouring heart structures.
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Stereo vision (above)
Volumetric data on an atrial septal defect
(arrowheads) are streamed in real time from an ultrasound
system to a graphics station computer, which renders
left-eye and right-eye views by alternating the position and
orientation of the image, skewed by angle %u03B1.
The rendered volumes, immediately
displayed on a conventional monitor, are synchronized with
flickering shutter glasses worn by the surgeon, yielding
stereo-rendered 3D ultrasound images. This imaging
technology provides surgeons with significantly better
spatial information and depth perception for making repairs
inside the beating heart. (LA, left atrium; RA, right
atrium.) |
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Beatring heart repair of
atrial septal defects
When surgeons patched holes guided by
ordinary 3-D ultrasound, they anchored their patches askew
(left). Aided by stereoscopic vision (middle), they secured
the patches with more evenly-spaced anchors (middle),
results nearly as good as those with open-heart surgery. |
Clinical trials of beating-heart surgery with the patching system
could begin in children with ASDs this year, Vasilyev says.
Del Nido believes that stereoscopic imaging, coupled with recent
advances in catheter-based surgical tools, will eventually allow
surgeons to do much more complex operations on beating hearts, such as
closing more complicated holes, shaving away excess tissue or repairing
fast-moving structures like mitral or aortic valve leaflets. “We look at
some very unusual cardiac anatomy,” he says. “Half the battle is
figuring out what the structure is without opening up the heart.”
For children, being able to do beating-heart surgery is a real
advantage, del Nido adds. The large incisions can scar the heart and
disrupt its rhythm, occasionally requiring a pacemaker. Opening the
heart invites infection, and air bubbles can slip into the bloodstream
and damage the brain. Running blood through a bypass machine can
sometimes launch an inflammatory response, damaging organs throughout
the body. And even in uncomplicated open-heart surgeries, recovery times
are weeks to months.
The real-time stereoscopic visualization system was designed to
handle and render 30MB of data every second. The renderer was
implemented on a GeForce FX 7800 computer video card from nVidia Corp.
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