Yuichi FUKUI, Tsuyoshi YAMAMOTO¹, Toshinori KATO² and Eiji OKADA

Department of Electronics and Electrical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
¹Advanced Research Laboratory, Hitachi, Ltd., 2520 Akanuma, Hatoyama-machi, Hiki-gun, Saitama 350-0395, Japan
²Ogawa Laboratories for Brain Function Research, Hamano Life Science Research Foundation, 12 Daikyo-cho, Tokyo 160-0015, Japan

(Received February 17, 2003; Accepted May 16, 2003)

Near infrared topographic imaging is a novel non-invasive technique to obtain the activated region in the brain cortex. The light propagation in the head is strongly scattered and this causes results in poor spatial resolution and contrast in the topographic images. Adequate modelling of light propagation in the head in order to deduce the volume of tissue interrogated by a source-detector pair for topographic imaging is very important to improve the quality of image of brain activity. In this study, the light propagation in a three-dimensional realistic head model is calculated by the finite difference method. The geometry of the model is generated from axial slices of an MRI scan. The topographic image is obtained from the change in intensity detected by source-detector pairs caused by the brain activity. The images obtained by two types of source-detector arrangement are compared to evaluate the efficiency of source-detector arrangement. The results show that the double-density arrangement improves the quality of the topographic image of the brain activity.

Key words: biomedical optics, light propagation, finite difference method, topographic image