Laser speckle contrast imaging (LSCI) is a non-scanning full-field hemodynamic imaging technology, which has the advantages of real-time, non-invasive, and high spatiotemporal resolution. It has become a widely used optical imaging technology for vascular visualization and dynamic blood flow monitoring. The Reflect-LSCI (R-LSCI) system is mostly used for the imaging of superficial blood vessels, exhibiting poor image quality when it comes to deep vascular visualization. Some studies have shown that Transmissive-LSCI (T-LSCI) has advantages in deep tissue imaging. At the same time, adaptive window space direction (awsdK) method has better imaging quality for deep blood vessels in R-LSCI. In this study, we used several LSCI methods processed in the spatial domain to compare the speckle images acquired by the R-LSCI system and the T-LSCI system. The results of comparative experiments show that in the T-LSCI, the awsdK also has the ability to improve the visualization of deep blood vessels without changing the relative velocity information. At the same time, the reflection speckle images and transmission speckle images were compared. The results showed that the T-LSCI was better than the R-LSCI in deep tissue imaging for a certain thickness of tissue
For specific cerebrovascular diseases such as epilepsy and Alzheimer's disease, it is urgent to detect the chronic changes of regional cerebral blood flow (rCBF) for a long time. interferometric diffusing wave spectroscopy (iDWS) based on optical heterodyne detection is expected to improve the detection sensitivity and reduce the interference of scalp blood flow. However, iDWS technology is difficult to achieve two-dimensional blood flow imaging. Therefore, this research proposes a interferometric diffusing speckle contrast imaging (iDSCI) system for monitoring rCBF, which combines an improved diffusion speckle contrast analysis method with iDWS technology. The dynamic phantom experiment demonstrated a good linear relationship between the reconstructed relative blood flow index and the actual flow velocity, and multi-parameter analysis validated the effectiveness of the iDSCI system in monitoring rCBF velocity, improving detection accuracy from 0.82 to 0.97. Therefore, the iDSCI system has the potential to provides a new theoretical basis for the early diagnosis and treatment of cerebrovascular diseases in the future.
Cerebral blood flow (CBF) is the main basis for clinical diagnosis of cerebrovascular diseases such as cerebral infarction and cerebral hemorrhage. The local cerebral blood flow (rCBF) detection method based on optical heterodyne detection (OHD) is expected to achieve high-precision detection of rCBF. The purpose of this study is to study the polarization state distribution characteristics of polarized light in the scattering medium by Monte Carlo simulation method, and to guide the optimization of measurement position and source-detector separation when OHD method is used to detect rCBF, and improve the measurement sensitivity. The Monte Carlo simulation result shows that the proportion of photons maintaining polarization state in the weak scattering medium is greater than in the strong scattering medium, and the proportion of photons maintaining polarization state is inversely proportional to the source-detector separation. Among them, The photon ratio that maintains the polarization state is best when the scattering angle is 0 or π. This study is of great significance for optimizing the source-detector separation and improving the sensitivity of OHD method for detecting rCBF.
We present a floating reference position (FRP)-based drift correction method for near-infrared (NIR) spectroscopy-based long-term blood glucose concentration (BGC) monitoring. Previously, we reported that it is difficult to quantify the systematic drift caused by the fluctuation of incident light intensity at different source–detector (SD) separations based on the absolute FRP change. We use the relative FRP change as a baseline reference to quantitatively characterize the signal drift at different SD separations. For the wavelengths that were used, a uniform equation was developed to describe the relationship between the drift and the relative FRP change. With the help of this equation, the correction can easily be performed by subtracting the systematic drift estimated by the equation. A theoretical analysis and an experimental phantom study demonstrated that our method could be used for systematic drift correction in NIR spectroscopy for long-term BGC monitoring. Moreover, the analysis method can also be referenced to reduce drifts from multiple sources.
Position-based reference measurement method is taken as one of the most promising method in non-invasive measurement of blood glucose based on spectroscopic methodology. Selecting an appropriate source-detector separation as the reference position is important for deducting the influence of background change and reducing the loss of useful signals. Our group proposed a special source-detector separation named floating-reference position where the signal contains only background change, that is to say, the signal at this source-detector separation is uncorrelated with glucose concentration. The existence of floating-reference position has been verified in a three layer skin by Monte Carlo simulation and in the in vitro experiment. But it is difficult to verify the existence of floating-reference position on the human body because the interference is more complex during in vivo experiment. Aiming at this situation, this paper studies the determination of the best reference position on human body by collecting signals at several source-detector separations on the palm and measuring the true blood glucose levels during oral glucose tolerance test (OGTT) experiments of 3 volunteers. Partial least square (PLS) calibration model is established between the signals at every source-detector separation and its corresponding blood glucose levels. The results shows that the correlation coefficient (R) between 1.32 mm to 1.88 mm is lowest and they can be used as reference for background correction. The signal of this special position is important for improving the accuracy of near-infrared non-invasive blood glucose measurement.
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