| Massive blood loss is the most important cause of soldier deaths in war。Therefore, timely blood transfusion provides an effective measure to reduce death rate of soldiers. In recent years, transfusion of blood components has gained wide application. Compared with transfusing whole blood, component transfusion has many advantages, including efficient use of blood, improved patient care, reduced side effects, ease of storage and transporting. Clinical practices indicate that transfusing red blood cell(RBC) suspension is an effective measurement to treat the patients who have acute blood loss.The quality of RBC suspensions in storage is influenced by storage time, temperature, long vibration during transportation and other factors under various field conditions. These causes can cause the breakdown of RBCs or hemolysis and lead to the increase of the concentration of free hemoglobin in RBC suspension. Transfusing the whole blood or RBC suspension with high degree of hemolysis will directly affect metabolic function of important organs, induce the occurrence of multiple organ dysfunction syndrome and even endanger the lives of the wounded. Accordingly, detection of the concentration of free hemoglobin in RBC suspensions is the key parameter to evaluate the quality of blood bag.At present, the standard method to detect the concentration of free hemoglobin in the blood bag is to use a chemical method with reagents. This method needs to take blood from the blood bag and will lead to blood pollution inevitably. Therefore, development of new methods which allow noninvasive detection of the concentration of free hemoglobin in a blood bag rapidly in field is of great significance. This thesis research is designed to study and develop a new method for determination of multiple optical parameters of RBC suspension which provides a foundation for future instrumentation development.Spectrophotometric measurement and analysis of turbid samples could yield an important way to realize noninvasive dection of hemolysis in blood samples.Since blood is strongly turbid,it can be characterized by anisotropy factor, scattering coefficient, andabsorption coefficient according to the radiative transfer theory.The most often used methods of blood measurement require the use of integrating spheres to measure light signals and Carlo Monte or other inverse models to determine optical parameters and their spectra. This approach has many drawbacks such as complex sysem design, high cost of construction and maintenance, which hinder its applications in fields and similar environment.In this thesis, we aim to develop a multi-parameter spectrophotometric system of RBC suspension with multiple single detectors of photodiodes and no integrating sphere. By measuring the scattered light signal from a turbid orblood sample in different directions and positions, we can obtain the measured values of collimated transmittance, diffuse transmittance and diffuse reflectance. The measured data results are imported into a Monte Carlo based software to inversely determine the anisotropy factor, scattering coefficient and absorption coefficient of the sample using a new perturbation method. The relatively simple measurement system combined with the accurate and fast inverse calculation software lays a solid foundation for future instrumentation development to rapidly determine multiple optical parameters of blood sample and determine the degree of hemolysis.In this thesis research, we carried out the following studies:1. A new multi-parameter spectrophotometric system has been constructed with multiple single detectors of photodiodes without the use of integrating spheres. The system includes a signal amplification unit, an optical unit, a signal acquisition and digital filtering software and the inverse calculation software based on Monte Carlo simulations. The optical unit including a xenon light source, an optical chopper,a monochromator, and a sample holder. The continuous wide-wavelength-band light output beam from the xenon light lamp turns into monochromatic light beam by a monochromater and modulated at a selected frequency of 1k Hz by a mechanical chopper. We measured the values of collimated transmittance,diffuse transmittance and diffuse reflectancefrom different directions and position by multiple single detectors of photodiodes. The incident light is turned about 80° from horizontal to close to vertical direction by a plane mirror. The signal amplification unit consists of photoelectric detectors, impedance amplifier circuit and a high precision 16-bit A/D converter. The photodiode detectors work in photovoltaic mode which has the characteristics of zero bias, no dark current and accurate linear response. A variety of noise-suppression measures were used to reduce ambient light backgroun and electrical noise to improve the SNR of the measured signals.After amplification, the output analog signal is converted to digital signal by the 16-bit A/D converter and the component of the modulation frequency point is extracted by digital demodulation and filtering method, which further improves the accuracy of signal measurement.The inverse calculation software of Carlo Monte simulation is the key partof our method for determination of multiple optical parameters and their spectra for RBC suspensions. Based on the single photon tracking and GPU parallel acceleration calculation, Monte Carlo simulation gives the calculated values of characteristic signal rapidly by changing the ratio of ua, us and g between the reference sample and perturbation sample, which forms the acceleration solution of i MC-GPU inverse calculation.2. After establishing multi-parameter spectrum measurement system for erythrocyte suspension, we calibrated and normalized the parameters of optical elements and multi-channel amplifier to ensure the accuracy and consistency of the measurement results between different elements and different channels.3. To verify the accuracy of results measured by the system of multiple optical parameters,we measure the optical parameters of 0.9um and 2.6um polystyrene microsphere suspension respectively and comparing with the results of Mie theoretical calculation. The results are basically consistent. Through above experiments, we verify the feasibility and the reliability of the method in measuring the multiple spectrum parameters of turbid medium.4. Further, we measure the optical parameters of 5 different erythrocyte suspension which hematocrit is 7.1% by using the method mentioned in this paper.After the data were processed, we compare with the literature’s results which was obtained by integrating sphere with Monte Carlo simulation model. The results are basically consistent and there are specific absorption peaks in the wavelengths of 420 nm, 560 nm and 580 nm.Therefore, the feasibility and the reliability of the method in measuring the multiple spectrum parameters of erythrocyte suspension is verified.5. Based on the multiple optical spectra of 7.1% erythrocyte suspension, we explore and establish the quantitative relationship between the concentration of free hemoglobin and the multiple optical parameters of erythrocyte suspension by keeping the red blood cell concentration unchanged, and the concentration of free hemoglobin was different. We measure the optical parameters of 10 different erythrocyte suspension each of which have six levels of concentration and choose the specific absorption wavelength point of erythrocyte suspension as the measuring wavelength. Through measuring the quantitative relationship between the concentration of free hemoglobin and the red blood cell suspension, we provide a new method which lay a foundation for further study of the non-invasive measurement of free hemoglobin.Finally, we conclude the advantages of this system compared with the existing method of measuring multiple optical parameters of turbid media.(1)Based on the multiple single detectors of photodiodes without the use of integrating sphere device, the structure is of simple structure, easy operating and realize instrumentation easily.(2)By using GPU acceleration and perturbation iteration algorithm, the inverse calculation speed of Carlo Monte simulation is increased by nearly 300 times, which is one of the key factors to determine whether the instrument can be realized in this paper.(3)IMC-GPU inverse calculation model can also output the absorption coefficient, scattering coefficient and anisotropy factor simultaneously, which lay a foundation for further study of the non-invasive measurement of free hemoglobin.(4)Through a large number of experimental studies, the feasibility and reliability of this method in measuring the multiple optical spectra of erythrocytesuspension are preliminarily verified.There are some problems in the system.(1)As the attenuation coefficient is one of input parameters in IMC-GPU inverse calculation model, its measuring accuracy has a great influence on the simulation results.(2)When the absorption coefficient is very small(less than 0.1), the i MC-GPU inverse calculation model has no output results. Low resolution of absorption coefficient. The resolution of absorption coefficient is low.(3)Due to the weak light intensity and other reasons, we measure the erythrocyte suspension with lower hematocrit. We have not studied the higher hematocrit erythrocyte suspension.According to the problems existing in the system, we make a plan about the next step of research.(1)To optimize the i MC-GPU inverse calculation model and to improve the accuracy of simulation inverse calculation. To obtain the absorption coefficient, scattering coefficient and anisotropy factor by taking the diffuse reflectance Rd, the diffuse transmittance Td and the collimation transmission Tc as input parameters simultaneously.(2)To further improve the SNR of weak optical signal measurement and the output resolution of the i MC-GPU inverse calculation model, so the system can measure the lower concentration of free hemoglobin.(3)To develop a clear and quantitative relationship between the concentration of lower free hemoglobin and red blood cell suspension, and to lay the foundation for the rapid analysis of blood quality in blood bags. |
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