Numerical accuracy in finite difference time domain (FDTD) analysis in three-dimensional(3-D) optical scattering medium is described. Power of an isotropic point source located at 1/ μ_s ' below the surface is assigned to the Yee grid points at the bodi ends. When source power is assigned to a Yee grid point of k=1 in z ordinate, one fourth of the power is re-assigned to the surface grid point. 3-D homogeneous scattering medium was discretized into 0.5~3(mm~3) grids and backscattered power and time-resolve reflectance have been calculated by the FDTD analysis. The numerical results agree with the analytical solutions quite well, which justifies the FDTD analysis. Then, FDTD analysis to an adult head including non-scattering regions was applied, and the validity is verified.%積分型光拡散方程式に新境界条件を適用したFDTD 法を用いた点波源励起3次元散乱体の光伝搬解析 精度を述べている.等価散乱係数μ_s'は連続な値をとるため,波源の散乱点z_0=1/μ_s'は一般的にはYee 格子間に配置されるので,Z_0 に隣接するYee 格子の距離に反比例した波源の按分を行う.但し,Yee 格子座標た=1に按分された波源は,その1/4をk=1/4のYee 格子に再按分する.その結果,μ_s′=1~3mm~(-1)の範囲で100×120×40m~3の散乱体を△z=0.5mm で離散化したFDTD 定常解と解析解との誤差は6%以内に収まった.△z=0.5mm の後方散乱光パルス波形の相対振幅誤差も波形立ち上がり部を除けば,光パワと同等な解析精度が得られた.△z=1.0mm に拡大してもμ_s’=1~2.5mm(-1)の範囲で△z=0.5mm と同等の解析精度が実現されている.この解析法を,非散乱体を含むヒ ト頭部光パルス伝搬解析に適用したところ平均遅延時間は実測値と良く一致した.
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