Abstract: The time-resolved reflectance of photons from a homogeneous tissue was modeled using a Monte Carlo simulation. The data was then converted by fast Fourier transform (FFT) into the frequency domain. In the frequency domain, the phase, $Phi@, and modulation, M, of collected light from a frequency-modulated light source was determined. A comparison of Monte Carlo and diffusion theory was made for various separation distances between the source and collector on the tissue surface. The results showed that Monte Carlo and diffusion theory agreed in the time domain only for times larger than 500 ps after injection of an impulse of photons. In the frequency domain, Monte Carlo and diffusion theory agreed only if the probe separation, r, was at least 2 cm apart for $mu$-s$/$PRM $EQ $mu$-s$/(1 $MIN g) $EQ 5 cm$+$MIN@1$/, or in dimension less units r$mu$-s$/$PRM $GRT 10. The effect of buried absorbed is also tested in the time and frequency domains. A semi-infinite volume of absorber is placed at 0, 3 mm, 6 mm, or $INF from the surface of a nonabsorbing tissue. The presence of a deep absorber on the time and frequency domain data show that attenuation of longer pathlength photons causes the phase of collected photons to reduce and the modulation of collected photons to increase. Both effects are indicative of the net shorter pathlength of the ensemble of collected photons. !8
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机译：摘要：使用蒙特卡洛模拟法模拟了来自均匀组织的光子的时间分辨反射率。然后通过快速傅立叶变换（FFT）将数据转换到频域。在频域中，确定了来自调频光源的所收集光的相位$和调制M。对组织表面上源和收集器之间的各种分离距离进行了蒙特卡洛和扩散理论的比较。结果表明，在注入光子脉冲后，Monte Carlo和扩散理论仅在大于500 ps的时间域中一致。在频域中，蒙特卡洛和扩散理论仅在探头间距r至少相距2 cm且$ mu $ -s $ / PRM $ EQ $ mu $ -s $ /（1 $ MIN g）时同意。 $ EQ 5 cm $ + $ MIN @ 1 $ /，或尺寸较小的单位r $ mu $ -s $ / $ PRM $ GRT10。还在时域和频域中测试了掩埋吸收的影响。将半无限体积的吸收剂放置在距离非吸收性组织表面0、3 mm，6 mm或$ INF处。在时域和频域数据上存在深吸收体表明，更长的路径长度光子的衰减会导致收集的光子的相位减少，并且收集的光子的调制增加。两种效应都表明所收集的光子集合的净较短路径长度。 ！8
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