Kexin Xu

Influence of contact state on NIR diffuse reflectance spectroscopy in vivo

In the practice of non-invasive blood glucose measurement by near-infrared (NIR) diffuse reflectance spectroscopy, an optical probe usually directly contacts skin in order to eliminate specular reflection. In this paper, the influence of contact state on the diffuse reflectance in vivo and the variation trend of diffuse reflectance with contact time under the same contact pressure, are investigated at wavelengths ranging from 1100 to 1700 nm. The result shows that the diffuse reflectance decreases with increasing contact pressure under the contact state. At a certain applied pressure, the diffuse reflectance fluctuates significantly at the beginning of contact, and the fluctuation becomes stable with elapsing contacting time. It is our aim in this paper to find out the optimal contact state and optimal measuring time, in order to reduce the influence of contact pressure on diffuse reflectance measurements. It is found from our experiments that, for in vivo measurement, the optimal contact state appears when the skin is pressed to about 0.5 mm by the probe, where the probe contacts the palm entirely, and that the optimal measuring time is at the 30th second since the probe contacting with the measuring site. Putting the above conclusions into practice, the repeatability of spectra is improved greatly.

A photoacoustic tomography system for imaging of biological tissues

Non-invasive laser-induced photoacoustic tomography (PAT) is a promising imaging modality in the biomedical optical imaging field. This technology, based on the intrinsic optical properties of tissue and ultrasonic detection, overcomes the resolution disadvantage of pure-optical imaging caused by strong light scattering and the contrast and speckle disadvantages of pure ultrasonic imaging. Here, we report a PAT experimental system constructed in our laboratory. In our system, a Q-switched Nd : YAG pulse laser operated at 532 nm with a 8 ns pulse width is used to generate a photoacoustic signal. By using this system, the two-dimensional distribution of optical absorption in the tissue-mimicking phantom is reconstructed and has an excellent agreement with the original ones. The spatial resolution of the imaging system approaches 100 µm through about 4 cm of highly scattering medium.

Discussion on Floating-Reference Method for Noninvasive Measurement of Blood Glucose with Near-Infrared Spectroscopy

Weak signal and great background variation have been the major challenges for noninvasive measurement of blood glucose. Two kinds of noise are analyzed, and it is found out that, when instruments achieve a high level of signal to noise ratio, physiological variation other than glucose concentration becomes the dominant over instrument noise. After analyzing the sensitivity of glucose concentration on diffuse reflectance spectroscopy at different source-detector separation, floating-reference method is proposed firstly. This method discusses how to extract signal relating to glucose and signal only relating to background variation respectively, by making use of two special points, reference point and measuring point. Experiments on phantom and Monte Carlo simulations have been performed to validate the feasibility of floating-reference method.

Prediction of blood glucose using interstitial fluid extracted by ultrasound and vacuum

Prediction of blood glucose using interstitial fluid extracted by ultrasound and vacuum is proposed by the paper. Low-frequency ultrasound with 55 KHz is applied for about 30 seconds to enhance the skin permeability to interstitial fluid by disrupting the stratum corneum lipid bilayers and then interstitial fluid is extracted out of skin successfully by 10in.Hg vacuum for 15 minutes. The glucose concentration in the interstitial fluid is measured by an instrument with immobilized enzyme sensor. And then a method of data analysis is set up to prediction the glucose concentration in the blood by the measurement of the glucose concentration in the interstitial fluid. At last, Clarke Error Grid analysis is performed to assess if the prediction accuracy could satisfy the requirements of clinical application. The whole method and experimental system above is set up in the article and the feasibility of this way for blood glucose detecting is primarily validated for clinical application with the requirements of bloodless, painless, continuous glucose monitoring. Additional a prototype of miniature diabetes monitoring device with the technique of surface plasma resonance to measure the glucose concentration in the interstitial fluid is also being developed.

Study on optical measurement conditions for noninvasive blood glucose sensing

Utilizing Near-infrared Spectroscopy for non-invasive glucose concentration sensing has been a focusing topic in biomedical optics applications. In this paper study on measuring conditions of spectroscopy on human body is carried out and a series of experiments on glucose concentration sensing are conducted. First, Monte Carlo method is applied to simulate and calculate photons’ penetration depth within skin tissues at 1600 nm. The simulation results indicate that applying our designed optical probe, the detected photons can penetrate epidermis of the palm and meet the glucose sensing requirements within the dermis. Second, we analyze the influence of the measured position variations and the contact pressure between the optical fiber probe and the measured position on the measured spectrum during spectroscopic measurement of a human body. And, a measurement conditions reproduction system is introduced to enhance the measurement repeatability. Furthermore, through a series of transmittance experiments on glucose aqueous solutions sensing from simple to complex we found that though some absorption variation information of glucose can be obtained from measurements using NIR spectroscopy, while under the same measuring conditions and with the same modeling method, choices toward measured components reduce when complication degree of components increases, and this causes a decreased prediction accuracy. Finally, OGTT experiments were performed, and a PLS (Partial Least Square) mathematical model for a single experiment was built. We can easily get a prediction expressed as RMSEP (Root Mean Square Error of Prediction) with a value of 0.5-0.8mmol/dl. But the model’s extended application and reliability need more investigation.

Applying the floating-reference method to improve the precision of noninvasive blood glucose measurement

A new method, floating-reference, can efficiently reduce the influence of the physiological background variations on the blood glucose measurement by differentially processing two signals from reference point and measuring point. In this paper, the reference point, where the diffuse reflected light is not sensitive to the variation of glucose concentration, is theoretically proved. Then Monte Carlo simulations are applied to study the radial distribution of the diffuse reflectance at different glucose concentrations for the skin. Moreover, the experiments are constructed to measure the radial distribution of the diffuse reflectance by the intralipid solutions with different glucose concentrations. Both the results from simulation and experiment validate the existence of floating-reference point. By theoretically analyzing the background noises and their disturbing mode on the blood glucose detection, a novel data processing method based on the reference point is proposed to effectively extract the blood glucose information. And it is found from our preliminary experiments with intralipid samples that, this data processing method can reduce the influence of background variation on the extraction of real glucose signal and thus enhance the resolving capability on glucose concentration.

Influence and correction of temperature on optical measurement for fat and protein contents in a complex food model system

Near infrared spectroscopy has been proposed as an effective way for measuring complex component compositions noninvasively. However temperature-induced spectral variation can cause accuracy problems if not taken care of in a proper manner. The influence of temperature on optical measurements has been studied for determining fat and protein contents in complex food systems. A model system consisting of mixtures of fat, protein, water and emulsion was developed to create an imitation of complex food systems. The changes in optical properties, including the absorbance coefficients and reduced scattering coefficients, of the system from 25°C to 40°C were measured in the wavelength from 1100 to 1670 nm. Complex changes in the absorbance coefficient and decreasing changes in the reduced scattering coefficients with the increasing temperature were founded. The mechanisms of the influences were analyzed. In order to correct the effect, a statistical method was needed. Then, a method called global robust temperature calibration model is proposed. Accordingly, the validating experiments using the samples made up of 54 complex food systems were executed. The experimental results indicated that the method can significantly reduce the temperature effect on optical measurement.

The feasibility investigation of non-invasive blood glucose sensing based on near-infrared spectroscopy

We have performed transcutaneous measurement and vessel bypass measurement to obtain the skin spectra and the blood vessel spectra respectively over the 1100-1700nm in the animal trial. The aim of this study is to validate the feasibility of the near-infrared (NIR) spectroscopy as a non-invasive blood glucose monitoring method, in particular during clinically relevant fluctuation in blood glucose. Two steps are adopted to evaluate the correlation between the skin diffusion spectra and the blood vessel transmission spectra. First, the variation tendencies of the skin and the blood vessel spectra were evaluated, and the partial least square (PLS) regression was adopted to establish the calibration model between the skin spectra, the vessel spectra and the corresponding concentration respectively. Then, the correlation analysis method is used to describe the relationship between the two kinds of spectra mentioned above. The correlation between the skin and the vessel spectra will be a powerful proof to demonstrate the correlation between the skin spectra and the blood glucose concentration.

Automatic quantitative study on the vibrational wave of human vocal folds via videokymography

Videokymography (VKG) is a powerful and cost-friendly method to observe the variability of the vocal fold vibration. A new quantitative method based on image processing, which introduces snakes model and genetic algorithm to improve precision and speed, is presented to analyze the vibration information in VKG automatically. To verify the precision of the proposed algorithm, an indirect simulation setup of vocal folds has been performed. One hundred and twenty images from twelve subjects have been analyzed, and the result shows that the vibration characteristics of vocal folds can be recognized more exactly, and the diseases in vocal fold can be diagnosed quantitatively.

Methodology of effective glucose-specific signal extraction in complicated sample

In the area of noninvasive human blood glucose concentration detecting, it has always been a critical task to extract the glucose-specific signal from the highly overlapped and disturbed near-infrared spectrum. In this paper, the methodology of effective glucose-specific signal extraction in complicated non-scattering sample is studied. By analyzing the impact of water displacement upon dissolution of glucose, the relationship between glucose concentration and absorption coefficient of the sample is deduced. Then, the reference wavelength where the absorption coefficient is insensitive to the changes of glucose concentration is put forward theoretically. Accordingly, the validating experiments in aqueous glucose solutions are executed. Both the theoretical and laboratorial results show that the reference wavelength of glucose appears at 1525nm. Based on the reference wavelength, an effective method for extracting the glucose-specific signal in complicated non-scattering samples is proposed and the corresponding validating experiments are constructed with different glucose and albumin concentration. Two different methods, traditional and the novel reference wavelength method are used to extract glucose signal and the corresponding root mean square error of prediction are 19.86mg/dl and 9.87mg/dl respectively. The experiment results indicate that the reference wavelength method can effectively eliminate the influence of various noises on the glucose-specific signal extraction, and thus can remarkably improve the measuring precision in noninvasive near-infrared glucose detecting.