Study On The Proper Contact Pressure Range In Diffuse Reflective Contact Measurement

Contact measurement is a common in vivo measuring method.In the process of measurement,the change of contact pressure will affect the stability of diffuse reflectance spectrum,thus causing interference to the measurement results.The paper mainly studies the influence of contact pressure on the diffuse reflectance spectrum by MC(Monte Carlo)simulation and the proper range of contact measure pressure was determined.What's more,the results were validated by the result of in vivo experiment.Firstly,the contact force between human skin and probe and the deformation of human skin is simulated by finite element method.What's more,the results of finite element simulation are verified by human experiment.The results of simulation and experiment show that the thickness strain of human skin tissue increases linearly with the contact pressure in a small contact pressure range(< 10 kPa).When 10 kPa contact pressure is applied,the average thickness strain is 2.5mm.The deformation data under different contact pressures lay the foundation for the establishment of MC simulation skin model.Secondly,the diffuse reflectance intensity under different contact pressures is simulated based on MC program.It is found that the diffuse reflectance intensity increases with the increase of contact pressure.The diffuse reflectance intensity caused by the deformation,absorption and scattering of the tissue induced by contact pressure was investigated,and the effects and mechanism of the deformation,absorption and scattering on the light intensity were clarified.The results show that the light intensity increases with the contact pressure in three stages.In the range of 5-7 kPa,the change of light intensity with the contact pressure is small,which is proper for measuring the contact pressure range.In this range,the light intensity remains stable due to the combined action of absorption,scattering and deformation.Finally,a human near-infrared spectroscopy detection system was built,and in vivo experiment was carried out.The experimental results show that the skin tissue reaches a stable state after 6 seconds under 10 kPa contact pressure.With the increase of contact pressure,the diffuse reflectance spectrum increases and shows three distinct stages;At the pressure range of 5 kPa-7 kPa,the variation coefficient of diffuse reflectance signal is the smallest,and the spectral signal is the most stable,which is the appropriate pressure range of measurement.Through OGTT(Oral glucose tolerance test)experiments of three volunteers,diffuse reflectance spectroscopy data and blood glucose measurements were modeled under different contact pressures.The results showed that 6 kPa contact pressure had the best modeling effect.It was preliminarily verified that 6 kPa contact pressure was proper for near-infrared blood glucose measurement.Three volunteers were tested with OGTT to model the diffuse reflectance spectroscopy data and blood glucose measurements under different contact pressures.The results showed that the modeling effect was the best under 6 kPa contact pressures.The corrected standard deviation(RMSECV)of interactive verification was less than 1.0 mmol/L and the correlation coefficient R is greater than 0.9.It is preliminarily verified that the contact pressure of 6 kPa is proper for the contact pressure of near infrared blood glucose measurement.