Dynamic Optical Tomography: A New Concept for Non-Invasive Human Brain Mapping

Hideaki Koizumi, Prof., Ph.D.

We have been studying for a considerable time how the concept of spectroscopic optical computed tomography (CT) using transmitted light might be applied to various fields (1)(2). This technique is turning out to be impractical for application to a human adult head because of the heavy light scattering caused by the brain tissue. We recently developed a way to observe the active area on the brain cortex by using light transmitted through the skull and reflected by the cortex (3)-(7). This technique, which we call optical topography, is a completely non-invasive method for measuring and analyzing the higher-order brain functions. With optical topography, dynamic functional mapping is possible because the signal-to-noise ratio is much higher than with optical CT. Optical topography allows us to obtain both spatial and temporal information about the oxy- and deoxy-hemoglobin by focusing on the cerebral cortices just behind the skull, i.e., non-invasive cortical optical topography.

Apparatus based on this concept has been developed by applying multi-wavelength frequency modulation.  Optical topography is the only imaging methodology available that allows the study of higher-order brain functions in infants without sedation. In optical topography, the measurement coordinates can be fixed on the brain, unlike with conventional methods for brain-function imaging such as PET, fMRI and MEG. This represents a breakthrough.

Noninvasive dynamic optical topography has a wide variety of applications from basic science to clinical medicine. We have applied noninvasive dynamic optical topography by working with various collaborators. Several applications, such as the study of the Broca and Wernicke language areas, the assessment of the dominant hemisphere of the brain, epilepsy focus determination, and sleep studies will be reported soon in the special issue of the Journal of Biomedical Optics.

References

(1) H. Koizumi: Chemistry and Chemical Industry, 33, 49 (1980).

(2) F. Kawaguchi, et al.: Med. Biol. Eng. Comp., 29(S2), 959 (1991).

(3) H. Koizumi, et al.: Proceedings of BMED '95 & MEBC '95, 46 (1995).

(4) A. Maki, et al.: Med. Phys., 22, 1997 (1995).

(5) Y. Yamashita, et al.: Rev. Sci. Instrum., 67, 730 (1996).

(6) Y. Yamashita, et al.: Opt. Eng., 35, 1046 (1996).

(7) E. Watanabe, et al.: Neurosci. Lett., 205, 41 (1996).