Koichiro SAKAGUCHI, Shunsuke FURUKAWA, Satoshi MATSUO, Naotaka SAKASHITA, Takushige KATSURA¹, Kyoko YAMAZAKI¹, Hideo KAWAGUCHI¹, Atsushi MAKI¹, and Eiji OKADA

Department of Electronics and Electrical Engineering, Keio University, Yokohama 223-8522, Japan
¹Advanced Research Laboratory, Hitachi, Ltd., Akanuma, Saitama 350-0395, Japan

(Received August 25, 2008; Accepted December 18, 2008)

The simplified cranial window, which is transparent thinned skull, has been used for the optical imaging of cortical tissue of small animals to measure the concentration change in haemoglobin as an intrinsic signal of brain activation. The multi-spectral images of the cortical tissue of guinea pigs through the skull cranial window were compared with those of the exposed cortex to evaluate the influence of the scattering and absorption properties of the skull on the measurement of the concentration change in haemoglobin. Although skull thickness affects the sensitivity of the optical signal due to a decrease in mean optical path length in the cortical tissue, the influence of the skull cranial window on the wavelength dependence of optical path length can be ignored when the skull thickness is less than approximately 100 μm. Accurate concentration changes in oxygenated and deoxygenated haemoglobins can be calculated from the optical signal measured through a skull cranial window and the wavelength dependence of optical path length for the exposed cortex.

Key words: biomedical optics, multi-spectral imaging, brain activity, optical intrinsic signal, cranial window, thinned skull, optical path length