Neuro-navigation techniques visualize boundaries between sick and healthy tissue in the brain-pan

Utrecht 26 March 1999 At the University Hospital in Utrecht (UMC), physicians apply so-called neuro-navigation techniques to distinguish healthy tissue from cancer tumours during brain surgery. The combination of information technology with mechanics allows to accurately determine the boundaries between sick and healthy tissue in medical imaging. As a result, the most deeply seeded tumours can be removed with great precision. The coordinates of the various surgical instruments in motion are projected upon the Magnetic Resonance Imaging (MRI) scan which visualizes the tumour to be eliminated. The doctor can navigate the operational microscope in such a way that the surgical field remains visible at any moment.

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At the University Hospital in Utrecht (UMC), physicians apply so-called neuro-navigation techniques to distinguish healthy tissue from cancer tumours during brain surgery. The combination of information technology with mechanics allows to accurately determine the boundaries between sick and healthy tissue in medical imaging. As a result, the most deeply seeded tumours can be removed with great precision. The coordinates of the various surgical instruments in motion are projected upon the Magnetic Resonance Imaging (MRI) scan which visualizes the tumour to be eliminated. The doctor can navigate the operational microscope in such a way that the surgical field remains visible at any moment.

Before, the surgeon had to rely on the MRI-scans in combination with his own intuitive anatomical knowledge. Just one single coordinate was determined by means of a stereotactic frame, a metal construction screwed onto the patient's skull. The innovative technique allows to calculate several coordinates interactively in real time. The surgeon can dispose of a device to interconnect between the MRI and the surgical field, according to researcher Peter Willems. The current system applies a probe with infrared LEDs and a infrared camera. This enables the doctor to make more accurate and smaller incisions in the skull and to minimize the damaging of tissue.

The new techniques have been optimized for almost fifteen years. Initially, the Utrecht team applied acoustic signals for the navigation. The inserted probes were equipped with an audible source. The computers calculated the delay of the returning echo in order to three-dimensionally define the exact location of the tumour. The method guaranteed an accuracy between 1 and 4 millimetre. The heat radiating from the operating lamps had an important impact on the conductive qualities of the sound, however. In a further stage, the team used electro-magnetic fields, which in turn were disturbed by large metal objects, such as the operating table. With the new system, the doctor is far less dependent from air streams, temperature influences, and so on.

Neuro-navigation is equally used in surgical treatment of epilepsy, in order to map brain areas which are difficult to recognize. Digital imaging allows to detect tissue connected with vital brain functions, like language and motion. Dr. Willems stresses that the boundaries of sick tissue might be dislocated, which makes it hard to rely on the knowledge gained in the study of healthy tissue. In the pre-operative phase, the vital brain functions are visualized by means of functional MRI (fMRI). The blood perfusion within the brain parts indicates which parts are activated in different tasks. The mechanical arm of the microscope acquires a micro-metrical precision within the novel system. This proves that the technique has reached a mature stage.

Currently, the team studies the effects of the neuro-navigation techniques on the life expectancy of patients, submitted to brain surgery. Each year, about 750 malignant brain tumours are diagnosed in The Netherlands. This is why the other university hospitals are in a hurry to use the navigation techniques as well. In turn, the UMC cherishes great ambitions with regard to the area of digital radiology. In the next four years, the university hospital will switch to a system of digital image storage, distribution and interpretation. Images will be directly available on the physician's workstation via FTP.

At present, a broadband network is being installed, based on a 622 megabit-ATM-backbone with a series of 100 megabit subconnections to the individual workstations. The investments to be made are estimated at f 11 million, on top of the current costs for exploitation. At the University Medical Center in Utrecht, about 170.000 radiological examinations are being carried out each year. The news source for this article is the Automatisering Gids.


Leslie Versweyveld

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