Photoacoustic (PA) signals encode information about the optical absorption and spatial distribution of absorbing chromophores as well as the light distribution in the medium. The wavelength dependence of the latter affects the accuracy in chromophore quantification, including estimations of oxygen saturation (sO₂) with depth. We propose the use of the ratio of the PA radiofrequency (RF) spectral slopes (SS) at different optical wavelengths to generate frequency filters which can be used to match the fluence profiles across separate images generated with different optical wavelengths.

Proof-of-principle experiments were carried on a plastic tube with blood of a known oxygenation inserted into a porcine tissue. The algorithm was tested in-vivo in the hind leg of six CD1 mice, each under three different breathing conditions (100 % O₂, room air and 100 % CO₂). Imaging was done using the VevoLAZR system at the wavelengths 720 and 870 nm. The SS was calculated from the linear fit of the ratio of the photoacoustic RF power spectra at the two wavelengths. An ultrasound frequency filter was designed and applied to each segmented PA signal in the frequency domain and inversely transformed into the time domain to correct for the differences in the fluence profiles at both wavelengths. Linear spectral unmixing was used to estimate sO₂ before and after applying the ultrasound frequency filter.

The estimated blood sO₂ in the plastic tube for the porcine tissue experiment improved by 10.3% after applying the frequency filter when compared to the sO₂ measured by a blood gas analyzer. For the in-vivo mouse experiments, the applied sO₂ correction was 2.67, 1.33 and -3.33% for every mm of muscle tissue for mice breathing 100% O₂, room air and 100% CO₂, respectively. The approach presented here provides a new approach for fluence matching that can potentially improve the accuracy of sO₂ estimates by removing the fluence depth dependence at different optical wavelengths.

光声 (PA) 信号对有关吸收发色团的光吸收和空间分布以及介质中的光分布的信息进行编码。后者的波长依赖性影响发色团定量的准确性，包括随深度的氧饱和度 (sO ₂ ) 的估计。我们建议使用不同光波长下的 PA 射频 (RF) 光谱斜率 (SS) 之比来生成频率滤波器，该滤波器可用于匹配不同光波长生成的单独图像的注量分布。

原理验证实验是在塑料管上进行的，其中将已知氧合的血液插入猪组织中。该算法在六只 CD1 小鼠的后腿上进行了体内测试，每只小鼠在三种不同的呼吸条件下（100% O ₂ 、室内空气和 100% CO ₂ ）。使用 VevoLAZR 系统在 720 和 870 nm 波长下进行成像。 SS 是根据两个波长的光声射频功率谱之比的线性拟合计算得出的。设计了超声波频率滤波器，并将其应用于频域中的每个分段 PA 信号，然后将其逆变换到时域，以校正两个波长下注量分布的差异。使用线性光谱分解来估计应用超声频率滤波器之前和之后的SO ₂ 。

与血气分析仪测量的sO ₂相比，应用频率滤波器后，猪组织实验的塑料管中估计的血液sO ₂提高了10.3%。对于体内小鼠实验，对于呼吸100% O ₂ 、室内空气和100% CO _{2 的}小鼠，每毫米肌肉组织所应用的sO ₂校正分别为2.67、1.33和-3.33%。这里提出的方法提供了一种新的注量匹配方法，该方法可以通过消除不同光波长下的注量深度依赖性来潜在地提高 sO ₂估计的准确性。