Majaron Boris, Milanic Matija
Jozef Stefan Institute, Jamova 39, SI 1000 Ljubljana, Slovenia.
Phys Med Biol. 2007 Feb 21;52(4):1089-101. doi: 10.1088/0031-9155/52/4/015. Epub 2007 Jan 25.
Spectral variation of the sample absorption coefficient in mid-infrared (muIR) demands caution in photothermal radiometric measurements, because a constant muIR is regularly assumed in inverse analysis of the acquired signals. Adverse effects of such approximation were recently demonstrated in numerical simulations of pulsed photothermal radiometric (PPTR) temperature profiling in soft biological tissues, utilizing a general-purpose optimization code in the reconstruction process. We present here an original reconstruction code, which combines a conjugate gradient minimization algorithm with non-negativity constraint to the sought temperature vector. For the same test examples as in the former report (hyper-Gaussian temperature profiles, InSb detector with 3-5 microm acquisition band, signal-to-noise ratio SNR=300) we obtain markedly improved reconstruction results, both when using a constant value mueff and when the spectral variation muIR(lambda) is accounted for in the analysis. By comparing the results, we find that the former approach introduces observable artefacts, especially in the superficial part of the profile (z<100 microm). However, the artefacts are much less severe than previously reported and are almost absent in the case of a deeper, single-lobed test profile. We demonstrate that the observed artefacts do not result from sub-optimal selection of mueff, and that they vary with specific realizations of white noise added to the simulated signals. The same holds also for a two-lobed test profile.
中红外（mid - IR）区域样本吸收系数的光谱变化要求在光热辐射测量中保持谨慎，因为在对采集信号进行反演分析时通常假定吸收系数为常数。最近在软生物组织中脉冲光热辐射测量（PPTR）温度分布的数值模拟中，利用重建过程中的通用优化代码证明了这种近似的不利影响。我们在此展示一种原创的重建代码，它将共轭梯度最小化算法与对所求温度向量的非负性约束相结合。对于与前一份报告相同的测试示例（超高斯温度分布、采集波段为3 - 5微米的InSb探测器、信噪比SNR = 300），无论使用常数值μeff，还是在分析中考虑光谱变化μIR(λ)，我们都获得了显著改善的重建结果。通过比较结果，我们发现前一种方法会引入可观测的伪影，尤其是在分布的表层部分（z < 100微米）。然而，这些伪影比之前报告的要轻得多，并且在较深的单峰测试分布情况下几乎不存在。我们证明观测到的伪影并非源于μeff的次优选择，并且它们会随添加到模拟信号中的白噪声的具体实现而变化。对于双峰测试分布也是如此。
