Study On Basis And Application Of Floating Reference Method For Non-Invasive Blood Glucose Sensing With Near-Infrared Spectroscopy

The background changes of the testee is an important interferential factor in near-infrared (NIR) non-invasive blood glucose measurement. The floating reference measuring method is helpful to solve this problem. However, it’s not a mature technique which is also in the preliminary researching stage. Aiming at this problem, the thesis studies the measuring method based on the floating reference through theoretical derivation, simulation analysis and experimental verification.First of all, the research progress of near-infrared non-invasive blood glucose measurement is introduced, as well as the current technical difficulties in this field are discussed. How to eliminate the interference of measuring background changes is the key problem. In the in vitro glucose sensing experiment, the background subtraction method is usually adopted as an effective method, but the substitutable substances as the background do not exist in the in vivo measurement. The floating-reference measuring method proposed by our studying team could solve this problem.The measuring method based on the floating reference is exposited with two directions, i.e. positional floating reference point and wavelength floating reference point. The theory of the floating reference method is derived according to the sensitivity of diffuse reflection spectrum variation with the glucose concentration, and the existence characteristic of the positional floating reference point and wavelength floating reference point are analyzed on the condition of the Boltzmann transport equation (BTE) and the analytical solution to the stationary diffusion equation in an infinite medium.The existence characteristic of the positional floating reference point of the glucose in the fat emulsion injection is studied through Monte Carlo simulation. The results show that the distribution of positional floating reference point is nearly consistent with the theoretical calculation at different wavelength. In the three-layer skin model, impact factors concerning both the optical and structural features of the tissue is analyzed which provides evidence to the optical probe design in vivo.The optical probe which could receive the diffuse reflectance at different radial positions by changing light shading cylinders for proving the existence of the positional floating reference point in vitro experiment is designed. And a near-infrared spectrometer based on the acousto-optic tunable filter (AOTF) is built to validate the existence characteristic of positional floating reference point at different wavelength for the first time. The experiment result shows that the positional floating reference point exists 1.3-1.6mm away from the source center in 10% Intralipid solution at the wavelength of 1200~1600nm.Meanwhile, for the first time, research plan about the acquisition of the wavelength floating reference point in the turbid medium is put forward and simulated results of the wavelength floating reference point of the glucose are presented, based on which the impact factors concerning the optical features of the tissue is discussed. The simulated result in the three-layer skin model has proved that the wavelength reference point will move toward short-wavelength as the radial distance increases and the epidermis thickens.Finally, a data processing method based on the floating reference point is studied to establish the calibration model by means of partial least squares method, which shows a great effectiveness to enhance the stability and the prediction precision of the calibration model. Compare to the background subtraction method, this method reduces the interference induced by background changes during the measurement process effectively.