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Image guided brain surgery
Imageologists are today concentrating on the functioning brain. The result is a whole gamut of imaging techniques like Trans Cranial Doppler, Intra Operative Ultrasound, PET, SPECT, MEG (Magneto Encephalography), SQUID (Semi Conductive Quantum Interference Device) and so on. To see the unseen, or to quote the star trekkers “To go where no man had ever gone before” it has become an obsession with brain cartographers. Today, it is possible to image every wrinkle on the face and every fold on the scalp of an individual, using interactive multimedia kits and sophisticated visual graphics. The face and the skull can be viewed from any direction. No longer is it simple antero posterior or lateral views. Studying images of the brain today involves team work and powerful computer work stations. The raw digitized data can be manipulated as per the need of the clinician.

3D reconstruction in color gives a perspective which has been totally unavailable before. The skull can be made transparent so that the internal structures can be visualized in relation to the exterior. On a giant screen AP, lateral, oblique and 3D views can be seen. The gray scale can be altered to highlight the particular area to be studied. The use of color for different anatomical structures helps display in 3D whether a tumor is literally touching a critical structure close by.

Conventionally, the neurosurgeon takes the CT or MRI pictures into the theatre and based on his knowledge of anatomy and imaging tries to picture where the lesion is and the best method of approaching it. Easier said than done. In real life, experienced surgeons have got lost on the way! Unfortunately, hitherto, there was no one to ask directions. The question “Where am I” is one which the surgeon keeps asking himself every few minutes, as he proceeds towards his destination in the brain. The gray matter and white matter of the brain do not carry sing posts like “No way traffic”, “Sharp turn ahead”, “Watch out – dangerous double hairpin bend” and so on. In the abdomen, one can always look around. In the brain, this can be disastrous and the effects can be of a permanent nature.

Today, thanks to the operating microscope, the road to the tumor is beautifully illuminated. Thanks to laser, ultrasound aspirator and other instruments, any road blocks can be removed – once they are encountered. However, damage can be done before they are encountered, as soon as the journey has commenced. Based on one’s knowledge of brain anatomy and physiology, a path is chosen, to reach the goal. Often, however, the terrain is forbidding and the weather incremental (torrential deluge from blood vessels cut on way). To make matters worse, the wipers on the windscreen stop working, reducing visibility (failure of the instrument used to coagulate bleeding vessels). Even the most experienced brain (brainy as well!) surgeon often gets lost, asking himself “where am I?” Any one would concede the traveling to Antarctica without a detailed map is bordering on foolhardiness. Trying to distinguish different areas in the brain, even with magnification, is like trying to distinguish one penguin from another! Yet one has to navigate in the sanctum sanatorium, with only a diagnostic film for assistance.

Even a few decades ago, the brain was indeed a dark continent – unmapped and unknown. To see the unseen, became an obsession with brain cartographers. Working overtime, they are slowly producing a truly comprehensive map which can be updated in real time. Tomorrows brain surgeon will have maps, precise as that in the Voyager mission.

Digital technology will make description of a surgeon of yesteryear – “Eyes of a hawk and the heart of a lion” obsolete. Familiarity with a mouse will be the order of the day. “Point and click”, “Single click, double click”, “Left button, middle button and right button”, “Drag and drop” these will be the jargon of the surgeon in the operation theatre.

The last few years have witnessed a tremendous growth in interactive image guided brain surgery – a detailed road map at last. The added advantage is, that this map is updated in real time. The presence of landslides and road blocks ahead are broadcast as in a citizens band radio. Reversing one’s path will almost never take place. How is this done?

Today with real time interactive image guided surgical tool like “The Viewing Wand” it is possible to achieve a navigation as precise as that in the Voyager mission. After all the intricacies and the consequences are none the less initial MRI or CT scanning is done with markers placed on the patients scalp which serve as reference points. A powerful computer workstation gives a 3D reconstruction of the face. The tumor is always related to the external skin markers. The “Viewing Wand” is a commercially available system consisting of an image processing computer and a mechanical arm, consisting of four movable joints. Each join consists of a potentiometer that constantly feeds back its position to a personal computer. Thus the computer knows the position in the space, of the end of the arm. Probes of different lengths and shapes can be attached to the end of the arm. This can act as pointer or even as biopsy forceps.

Using the wand software, the position of recognizable skin features on the patients scalp and skin makers, are registered into the 3D reconstructed image on the powerful computer workstation. After the patient’s head is fixed firmly, the wand is moved around the head. The tip of the wand is always seen on the computer screen relative to the tumor image. The scan data can be reconstructed in the direction that the image is pointing. This allows precise placement of the skin incision. The amount of underlying done opened will also be less due to precise placement.

The Viewing Wand is particularly useful when constant reference to the preoperative image is necessary. Locating small lesions no longer requires large exposures. After inputting all the diagnostic images into the work station, the wand is simply pointed at the head, the lesion located, the approach and trajectory planned and a minimally invasive approach option chosen. As one proceeds into the brain using the wand the exact present location in terms of the diagnostic image, is displayed on the computer screen. It will be possible to eventually input a host of data like physiological functions, angiograms and so on. Thus, one can avoid dangerous areas. There is minimal disruption of normal brain, while approaching the tumor. This technique ensures accuracy and precision in the ability of a device to locate a point in space. Precision is the ability to return to a specific location. Constant checking and rechecking is possible. Like a spacecraft checking its position continuously by the Global Position Satellite, one knows exactly where one is at any point of time.

Tomorrow’s surgeon may or may not be familiar with different types of blades and suture materials. If he or she cannot point, click and drag with a computer mouse he/she will soon fade into oblivion. In an ever increasingly competitive world, one has to keep running just to stay in the same place! The difference between the haves (internet access) and the have nots will be so much, that natural selection will result in survival of the fittest!