Significance: The application of near-infrared spectroscopy (NIRS) to determine the concentrations of tissue chromophores has typically relied on three alternative technological approaches: continuous-wave, frequency-domain, and time-domain. It is often the case that uncertain and variable coupling of light into and out of the skin surface renders absolute measurements unreliable, and NIRS methods are mostly used to measure changes of chromophore concentrations and of physiological parameters such as blood volume and oxygenation. Aim: The aim has been to investigate whether an approach based on a wavelength-modulated source may enable measurements to be acquired, which are independent of surface coupling and may facilitate derivation of absolute values of tissue parameters. Approach: An analysis is performed using the modified Beer–Lambert law. Results: It is shown that the relative modulation in detected intensity resulting from a wavelength-modulated source could be used to estimate absolute concentrations of chromophores if unknown surface coupling losses and geometrical factors are insensitive to small changes in wavelength. Conclusions: Wavelength modulated NIRS could be an effective tool for quantitative in vivo analysis of tissues, although it may be technically challenging.

中文翻译：

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探索波长调制近红外光谱的可行性

意义：应用近红外光谱 (NIRS) 来确定组织生色团的浓度通常依赖于三种替代技术方法：连续波、频域和时域。通常情况下，进出皮肤表面的光的不确定和可变耦合使得绝对测量不可靠，近红外光谱方法主要用于测量发色团浓度和生理参数（如血容量和氧合）的变化。目的：目的是研究基于波长调制源的方法是否可以获取测量值，这些测量值与表面耦合无关，并且可以促进组织参数绝对值的推导。方法：使用修改后的 Beer-Lambert 定律进行分析。结果：结果表明，如果未知的表面耦合损耗和几何因素对波长的微小变化不敏感，则由波长调制源产生的检测强度的相对调制可用于估计发色团的绝对浓度。结论：波长调制 NIRS 可能是组织体内定量分析的有效工具，尽管它在技术上可能具有挑战性。