Double vision

The computer makes brain surgery a lot easier

 
Published: Saturday 04 July 2015

Operating in stereo: with MAGI (Credit: arvind yadav / cse)saying brain surgery is a delicate business would be an understatement. Cut a little bit more here and the patient might end up blind, deaf or perhaps even paralysed. So knowing what lies beneath the tissue surface could be a life-saver. But right now, the only way surgeons can do this is to look away from what they are doing on the operating table and examine the brain scans of the patient taken prior to the operation. But this, is about to change.

Very soon, brain surgeons will be able to operate with their confidence boosted by a new microscope imaging technique that will allow them to 'see' beneath the brain surface they are working on. The Microscope Assisted Guiding Imaging ( magi ) technique, developed at the London-based Guy's Hospital, reduces risks of accidental damage to critical structures and helps ensure complete and accurate extraction of tumours. magi combines data from two types of scan: magnetic resonance imaging ( mri ), which shows photon density, and computerised tomography ( ct ) -- which integrates the cross-sectional x -ray images. The two image types are combined to form a three-dimensional ( 3d ) computerised model of the patient's brain that is then fed into the microscope and appears as an overlay on the microscope image ( New Scientist , Vol 160, No 2160).

"The advantage of viewing the image through the microscope in that it is stereo. You have a different image for each eye," says Philip Edwards, a computer scientist working on the project. The overall effect is what he calls augmented reality: a 3d model of the parts of the brain laid over the top.

To avoid holding the patient's head stationary with a clamp, magi shifts the computer image with every tiny movement of the patient's head, so that it always corresponds exactly to where the surgeon is looking. To do this, markers are placed on the patient's upper teeth and then these are monitored by cameras. Movements as small as 0.9 millimetres can be detected and compensated for. One of the main difficulties in developing the tool was matching the size of the computer model from the scans with the microscope's image of the actual organ.

The researchers are currently testing different formats for the stereo image to discover which one suits the surgeons' needs. Options include outlines, silhouettes and wire-frame overlays.

"In a way, the magi project is ahead of its time," says Michael Gleeson, a senior surgeon at Guy's, "because many of the ways of treating these skull-based tumours are still in their infancy." Gleeson has operated several times using magi in its various stages of development. "It's comfortable to be able to see where the tumour is," he says.

So far, the system has been tested on seven patients undergoing procedures such as skull-based surgery and ear, nose and throat operations. The researchers hope to develop it further for other forms of surgery that use binocular microscopes and endoscopes.

They are now fine tuning the stereo effect. The three-year project has two more years to run.

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