Study On Pressure-Insensitive Position In Diffuse Reflective Contact Measurement

Nowadays,the variation of measurement condition is one of the main problems in the non-invasive blood glucose sensing by near-infrared(NIR).In the diffuse contact measurement,the variation of probe-tissue contact pressure will lead to poor measurement accuracy and stability in the in vivo measurement signal.After analyzing the influence of pressure on the distribution of diffuse reflectance varying with the radial position,this thesis proposes the pressure-insensitive radial position to collect the diffuse reflectance to minimize the measurement error caused by contact pressure.The existence of pressure-insensitive radial position and the validity of the noninvasive blood glucose sensing based on pressure-insensitive radial position are verified by Monte Carlo simulation and in vivo experiments.Firstly,based on the solid-liquid two-phase mechanic feature of skin tissue,the relationships between contact pressure and the variations in tissue thickness,and optical parameters were deduced.Monte Carlo simulation was used to study the distribution of diffuse reflectance caused by contact pressure varying with the radial position.The results showed that there was a radial position from which the diffuse reflectance variation was approximately 0 within the wavelength of 1000-1320 nm when contact pressure changed.That's,there is the pressure-insensitive radial positions.Further,the contact pressure on the skin model with different glucose concentrations were randomly matched to study the effectiveness of measurement based on pressure-insensitive position on the detection of glucose sensing when pressure changed.The results showed that the correlation coefficient between the diffuse reflectance received from pressure-insensitive position and the glucose concentration had lower decrease than that from other radial positions,which demonstrated that the measurement method based on pressure-insensitive position can significantly reduce the influence of pressure variation on diffuse reflectance.The effect of individual difference on the pressure-insensitive position was simulated by changing the thickness of epidermis and dermis.The results showed that the change of thickness of the epidermis had a great influence on the pressure-insensitive position.Secondly,the multi-radial position diffuse reflectance detection system was built.After evaluating the stability of the system,the reliability of model in MC simulation was verified by Intralipid experiments.Then,in vivo verification experiments were conducted to verify the existence of pressure-insensitive position.The results showed that the pressure-insensitive radial positions could be found in the wavelength of 1050,1219 and 1314 nm,and they were located within the radial distance of 0.78-1.0 mm.Then the stability of the diffuse reflectance received from different radial positions was evaluated.The results showed that the diffuse reflectance from pressureinsensitive position had higher signal to noise ratio.At last,clinical experiments validated the effectiveness of the measurement method based on pressure-insensitive position.After evaluating the accuracy of the system,in vivo OGTT experiments were conducted to detect the glucose concentration non-invasively,and the calibration model based on partial least square was established by relating the diffuse reflectance with the blood glucose concentration.Experiment results indicated that the measurement method based on pressure-insensitive position is helpful to improve the accuracy of contact measurement by non-invasive NIR diffuse reflectance.