Study on Key Problems of Non-invasive Optical Bilirubin Sensing
|Keywords||Bilirubin Non-invasive optical sensing Hemoglobin Floating-Reference Theory (FRT) Monte Carlo simulation|
Abnormal metabolism of bilirubin may cause a range of diseases, and it’s a seriously threat to human health. Therefore, daily serum bilirubin concentration is considered as an important physiological index of the liver and gall bladder function. Currently, invasive serum bilirubin concentration detection is the most important method in clinical human bilirubin test. However, blood sample needs to be taken with this method, thus it may cause the pain. This method will increase the risk of infection and cannot monitor bilirubin concentration in real-time. Non-invasive optical bilirubin measurement plays an important role in clinical bilirubin test with its non-invasive, rapid and simple features. But currently, the products of non-invasive optical bilirubin measurement in the market such as transcutaneous bilirubinometry (TcB) general has a poor accuracy. It only can be used for initial screening of neonatal jaundice, which hinders the promotion and the use of the products.This thesis studies the characteristics of non-invasive optical bilirubin measurement, in order to improve its accuracy with the Floating-Reference Theory (FRT). The skin model’s optical parameters associated with the bilirubin concentration are calculated and summarized. Then the Monte Carlo simulation is used and the distribution of the diffuse reflection light in different radial locations with the change of bilirubin concentration are obtained. The result shows that no radial reference location of the bilirubin measurement appears because of the strong absorption of bilirubin in the visible band. Based on the floating reference wavelength method of pure absorbing medium, the result shows that there exist a reference wavelength at 524nm after calculating and experimentally verifying. Spectral data at 524nm are further used for spectral calibration. In the actual bilirubin measurement, absorbance at this wavelength is expected to remove the background noise and environmental interference, thus it could improve the accuracy of bilirubin measurement.In addition, this thesis also studies the optical properities of hemoglobin, and then analyzes the influence of hemoglobin to the optical bilirubin measurement, especially to Partial Least Squares Regression ( PLS ) Modeling. Result demonstrates that the adding of hemoglobin brings the absorption noise of hemoglobin in PLS modeling. The adding of hemoglbin also increases the number of principal components and changes the position of the greatest contribution wavelength of PLS model. Hemoglobin increases the Root Mean Square Error of Prediction( RMSEP) by 24.90% and decreases the correlation coefficient by 0.29%. This means hemoglobin reduces the fitting ability of PLS models and its prediction ability to the bilirubin concentration. Therefore, the effect of hemoglobin should be considered, in order to further improve the accuracy of clinical bilirubin measurement, and make the transcutaneous bilirubin measurement suitable for a wider population.