Analysis of Light Propagation in a Realistic Head Model by a Hybrid Method for Optical Brain Function Measurement
Near infrared spectroscopy (NIRS) is used to measure the change in blood volume and oxygenation in the brain cortex induced by functional brain activation. The development of an adequate model to calculate light propagation in the head is very important because the light is strongly scattered in the tissue and this causes ambiguity in the volume of tissue interrogated with a source–detector pair of the NIRS instrument. In this study, a two-dimensional realistic head model is generated from a MRI scan of a human adult head. The light propagation in the head model is calculated by the hybrid Monte Carlo–diffusion method to obtain the change in detected intensity caused by a focal absorption change in the grey matter or in the white matter to discuss the relationship between the depth of the activated region and the sensitivity of the NIRS signal. The sensitivity to the activated region in the white matter steeply decreases with an increase of the depth of the activated region because the spatial sensitivity profile is mainly confined to the grey matter. The contribution of the focal brain activity to the NIRS signal is determined by not only the depth of the activated region from the head surface but also the depth of the activated region from the brain surface.
Key wordsbiomedical optics light propagation brain function measurement Monte Carlo simulation diffusion equation
Unable to display preview. Download preview PDF.
- 4).H. Koizumi, Y. Yamashita, A. Maki, T. Yamamoto, Y. Ito, H. Itagaki and R. Kennan: J. Biomed. Opt. 4 (1999) 403.Google Scholar
- 5).D. A. Boas, T. Gaudette, G. Strangman, X. Cheng, J. J. A. Marota and J. B. Mandeville: Neurolmage 13 (2001) 76.Google Scholar
- 7).E. Okada, M. Firbank, M. Schweiger, S. R. Arridge, M. Cope and D. T. Delpy: Appl. Opt. 36 (1997) 21.Google Scholar
- 9).S. R. Arridge and M. Schweiger: Appl. Opt. 34 (1995) 8026.Google Scholar
- 11).D. A. Boas, J. P. Culver, J. J. Stott, A. K. Dunn: Opt. Express 10 (2002) 159.Google Scholar
- 14).T. Hayashi, Y. Kashio and E. Okada: Opt. Rev. 10 (2003) 501.Google Scholar
- 17).P. van der Zee, M. Essenpreis and D. T. Delpy: Proc. SPIE 1888 (1993) 454.Google Scholar