BRAIN surgeons will soon be able to operate with more confidence thanks to a
microscope imaging technique that allows them to 鈥渟ee鈥� beneath the surface of
the brain they are working on. The Microscope Assisted Guided Intervention
technique (MAGI), developed at Guy鈥檚 Hospital in London, lessens the risk of
damage to critical structures and helps ensure complete extraction of
tumours.
Brain surgery is a delicate business. Cut a little bit too deep and a surgeon
could pierce a blood vessel or sever a nerve. So knowing what lies beneath the
surface of tissue can be a life-saver. But the only way to do this at present is
to look away from the surgical microscope and examine brain scans of the patient
that were taken before the operation.
MAGI addresses this problem by marrying data from two types of scan: magnetic
resonance imaging (MRI), which shows proton density, and computerised tomography
(CT), which integrates cross-sectional X-ray images. The two image types are
combined to form a three-dimensional computerised model of the patient鈥檚 brain
that is then fed into the microscope and appears as an overlay on the microscope
image.
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鈥淭he advantage of viewing the image through the microscope is that it is
stereo. You have a different image for each eye,鈥� 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 having to hold the patient鈥檚 head stationary with a clamp, MAGI
shifts the computer image with every tiny movement of the patient鈥檚 head, so
that it always exactly corresponds to where the surgeon is looking. To achieve
this, markers are placed on the patient鈥檚 upper teeth and 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鈥檚 image of the actual
organ.
The researchers are currently testing different formats for the stereo image
to discover which one surgeons find most helpful. Options include outlines,
silhouettes and wire-frame overlays.
鈥淚n a way, the MAGI project is ahead of its time,鈥� says Michael Gleeson, a
senior surgeon at Guy鈥檚, 鈥渂ecause many of the ways of treating these skull-based
tumours are still in their infancy.鈥� Gleeson has operated several times using
MAGI in its various stages of development. 鈥淚t鈥檚 comforting to be able to see
where the tumour is,鈥� 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 still has
two years to run.