■尽管在漫射光学条件下已经很好地表征了空间频率域成像(SFDI),在扩散状态之外进行的组织测量可以提供新的诊断信息。在这些测量结果变得具有临床相关性之前,然而,必须评估亚扩散SFDI的行为及其对导出组织参数准确性的影响。
■我们的目的是表征假定的散射相位函数(SPF)和照明光源的偏振状态在扩散或亚扩散条件下运行时对SFDI衍生光学特性的准确性的影响,分别。
■通过使用一组特征良好的光学体模,在四个波长(395、545、625和850nm)和两个不同的空间频率(0.3和1.0mm-1)下评估SFDI精度。提供了广泛的扩散和次扩散条件,使用三个不同的SPF。为了确定极化的影响,使用非偏振和交叉偏振照明评估SFDI的准确性。
■发现假定的SPF对SFDI衍生的光学性质的准确性有直接而显着的影响,SPF的最佳选择由极化状态决定。由于非极化SFDI保留了信号的子扩散部分,当使用包括正向和反向散射分量的全SPF时,发现光学性质更准确。相比之下,当使用前向散射SPF时,交叉极化SFDI产生了准确的光学特性,匹配交叉极化的行为,以衰减亚漫反射的立即反向散射。使用正确的SPF和偏振对启用的反射率标准,而不是更主观的幻影,作为参考测量。
■这些结果为更透彻地了解SFDI提供了基础,并使这种技术的新应用成为可能,其中亚扩散条件占主导地位(例如,需要μaμs\')或高空间频率。
UNASSIGNED: Although spatial frequency domain imaging (SFDI) has been well characterized under diffuse optical conditions, tissue measurements made outside the diffuse regime can provide new diagnostic information. Before such measurements can become clinically relevant, however, the behavior of sub-diffuse SFDI and its effect on the accuracy of derived tissue parameters must be assessed.
UNASSIGNED: We aim to characterize the impact that both the assumed scattering phase function (SPF) and the
polarization state of the illumination light source have on the accuracy of SFDI-derived optical properties when operating under diffuse or sub-diffuse conditions, respectively.
UNASSIGNED: Through the use of a set of well-characterized optical phantoms, SFDI accuracy was assessed at four wavelengths (395, 545, 625, and 850 nm) and two different spatial frequencies (0.3 and 1.0 mm - 1 ), which provided a broad range of diffuse and sub-diffuse conditions, using three different SPFs. To determine the effects of
polarization, the SFDI accuracy was assessed using both unpolarized and cross-polarized illumination.
UNASSIGNED: It was found that the assumed SPF has a direct and significant impact on the accuracy of the SFDI-derived optical properties, with the best choice of SPF being dictated by the
polarization state. As unpolarized SFDI retains the sub-diffuse portion of the signal, optical properties were found to be more accurate when using the full SPF that includes forward and backscattering components. By contrast, cross-polarized SFDI yielded accurate optical properties when using a forward-scattering SPF, matching the behavior of cross-
polarization to attenuate the immediate backscattering of sub-diffuse reflectance. Using the correct pairings of SPF and
polarization enabled using a reflectance standard, instead of a more subjective phantom, as the reference measurement.
UNASSIGNED: These results provide the foundation for a more thorough understanding of SFDI and enable new applications of this technology in which sub-diffuse conditions dominate (e.g., μ a ≮ μ s \' ) or high spatial frequencies are required.