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July 10, 1997

Team Develops World's First Light-based Procedure for Examining Epileptic Brain Sites

- Non-invasive method subjects patients to less stress -

Examinations are conducted with the new method to determine the location of blood flow increase during an epileptic episode. The results were in close agreement with those obtained by conventional examinations. The new method will make it possible to carry out such examinations without subjecting the patient to stress and discomfort during diagnostic procedures.

When epilepsy is not readily treatable with drugs, treatment currently consists of the surgical removal of epileptic focus, for which it is necessary to pinpoint the exact location of the focus. Normally such an examination is based on various electroencephalographic measurements. However, the low spatial resolution of such methods makes it difficult to establish the exact location.

At present, two methods are used to determine the location of an epileptic focus. One method involves opening the cranium to place electrodes on the surface of the brain or to insert electrodes into deeper portions of the brain which enables measuring epileptic discharges during seizures. The other method utilizes single photon emission computed tomography (SPECT(*3)), in which a radioactive isotope is injected into the blood. This discloses the blood flow increase in the epileptic focus during seizures.

Since both of these methods subject the patient to considerable stress, discomfort and radioactive insult, there has been a growing need for a method of performing such an examination without subjecting the patient to such distress.

It was to achieve that goal that Tokyo Metropolitan Police Hospital and Hitachi started working together on a method of using near-infrared light spectroscopy to determine the location of epileptic sites. Near-infrared beams can pass relatively easily through the scalp and cranium, and can be efficiently detected after being reflected by the cerebrum. By utilizing differences in the absorption index of the hemoglobin in the blood, it is possible to measure changes in blood flow accompanying brain activities. Hitachi developed a multichannel measuring system based on this operating principle that can measure changes in blood flow in both sides of the brain arising during an epileptic seizure, and display this information visually on a realtime basis.

At Tokyo Metropolitan Police Hospital this system was used to detect blood flow changes that occurs during seizures to thereby determine the location of an epileptic focus. An analysis of the technology compared to conventional methods conducted in respect of seven cases showed the clinical efficacy of the new method.

Specifically, when the new method was used to determine the location of blood flow increase accompanying epileptic episodes, the results obtained were in close agreement with focus locations determined by conventional methods such as intracranial EEG recording or SPECT. It was also confirmed that the new technology can be used to measure the chronological changes of blood flow that take place in the brain during a seizure. The results of the seven cases are listed in Table 1.

The new technology makes it possible to non-invasively determine whether an epileptic focus is on the right or left side. It also has the potential to locate the focus within a hemisphere where measured more broadly to examine the whole brain. This method replaces the invasive electrode technologies. Moreover, the ability to analyze time-based changes in cerebral blood flow during an epileptic seizure is something that was not possible with conventional methods, making this an important pathological tool.

Looking to the future, Hitachi plans to apply the features and benefits of optical topography to the examination of other brain diseases and functions.

The new technology will be presented at the Annual Meeting of the Japan Neuroscience Society that opens July 16 in Sendai.

Notes
*1 Optical topography
A technique of using light to obtain two-dimensional images of the cerebral cortex. Optical fibers are used to project light and pick up reflected light. To produce images of brain functions, optical fibers are arranged in a two- dimensional array and reflected light corresponding to each point is measured simultaneously. Since the apparatus is portable and simple to operate, it can be used to carry out examinations virtually anywhere, including at the bed-side.

*2 Near infrared light
This refers to light having a wavelength of 800 nm to 2000 nm. While it varies from person to person, light of around 800 nm is perceived as being a faint red. Near infrared light is more readily transmitted by the body than visible or infrared light.

*3 SPECT: single photon emission computed tomography
This is a technique in which a patient is injected with a substance labelled with a radio-isotope, enabling the amount of the substance that accumulates at a prescribed place inside the body to be measured by an external radiation detection device.

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