Development of a technique to measure local scattering in turbid media using backscattered light at the surface for noninvasive turbidity evaluation of blood in subcutaneous blood vessels

A large open access dataset of transillumination imaging the toward realization of optical computed tomography

Transillumination imaging is commonly used in medicine and biometrics to provide non-invasive insights into internal structures. However, the prevalent image blurring resulting from scattering effects poses a significant challenge to the effective application of transillumination. Artificial intelligence algorithms have gained prominence for enhancing transillumination images and addressing challenges such as scattering suppression, depth estimation, and three-dimensional structure reconstruction. These advances require high-quality input images to optimize model performance. Acquiring a large-scale transillumination image dataset for practical AI applications is difficult due to subjective imaging conditions. This study aimed to overcome this obstacle by introducing a comprehensive dataset of transillumination images. Methods and algorithms for generating depth-dependent point-spread function and transillumination images were presented. The dataset comprised 12,000 pairs of images of clear and scattered media, each associated with the corresponding depth information. This study is valuable for advancing AI-based solutions in transillumination imaging and provides a foundation for further research on image deblurring, depth perception, and 3D reconstruction.

Optical parameters estimation in inhomogeneous turbid media using backscattered light: for transcutaneous scattering measurement of intravascular blood

In our earlier research, a technique was developed to estimate the effective attenuation coefficient of subcutaneous blood vessels from the skin surface using the spatial distribution of backscattered near-infrared (NIR) light. The scattering effect in surrounding tissues was suppressed through the application of a differential principle, provided that the in vivo structure is known. In this study, a new method is proposed enabling the separate estimation of both scattering and absorption coefficients using NIR light of different wavelengths. The differential technique is newly innovated to make it applicable to the subcutaneous structure without requiring explicit geometrical information. Suppression of the scattering effect from surrounding tissue can be incorporated into the process of estimating the scattering and absorption coefficients. The validity of the proposed technique can be demonstrated through Monte Carlo simulations using both homogeneous and inhomogeneous tissue-simulating models. The estimated results exhibit good coherence with theoretical values (r2 = 0.988-0.999). Moreover, the vulnerability and robustness of the proposed technique against different measurement errors are verified. Optimal conditions for practical measurement are specified under various light-detection conditions. Separate estimation of scattering and absorption coefficients improves the accuracy of turbidity measurements and spectroscopy in biomedical applications considerably, particularly for noninvasive measurements and analysis of blood, lipids, and other components in subcutaneous blood vessels.

Quantification of the Phenomena Affecting Reflective Arterial Photoplethysmography

Photoplethysmography (PPG) is a widely emerging method to assess vascular health in humans. The origins of the signal of reflective PPG on peripheral arteries have not been thoroughly investigated. We aimed to identify and quantify the optical and biomechanical processes that influence the reflective PPG signal. We developed a theoretical model to describe the dependence of reflected light on the pressure, flow rate, and the hemorheological properties of erythrocytes. To verify the theory, we designed a silicone model of a human radial artery, inserted it in a mock circulatory circuit filled with porcine blood, and imposed static and pulsatile flow conditions. We found a positive, linear relationship between the pressure and the PPG and a negative, non-linear relationship, of comparable magnitude, between the flow and the PPG. Additionally, we quantified the effects of the erythrocyte disorientation and aggregation. The theoretical model based on pressure and flow rate yielded more accurate predictions, compared to the model using pressure alone. Our results indicate that the PPG waveform is not a suitable surrogate for intraluminal pressure and that flow rate significantly affects PPG. Further validation of the proposed methodology in vivo could enable the non-invasive estimation of arterial pressure from PPG and increase the accuracy of health-monitoring devices.