Optical Coherence Tomography Imaging To Study The Optical Properties Change With The Biological Macromolecules In The Blood

Fibrinogen is an important plasma protein that plays a significant role in theblood coagulation and red blood cell aggregation. The existing methods for thedetection of plasma fibrinogen focused on physical-chemical, immunoassay, andoptical approaches. However, all above mentioned methods need phlebotomy frompatients in laboratory, which increase the risk of infection and patients’ suffering andcannot reflect the real-time parameters in blood. Recently, a new biomedicaltechnique named optical coherence tomography (OCT) has got more and moreinterest and develops rapidly, with its noninvasive, real time, and high resolutioncapabilities. Similar to fibrinogen, dextran also can induce the aggregation of redblood cells (RBCs), which will lead to changes in optical properties of blood. Thethesis first studied the effect induced by dextran to determine the proper OCTparameter for measuring the changes in blood optical property. Then the feasibility ofoptical coherence tomography for determination of plasma fibrinogen in flowingblood was investigated. The results are as follows:1. Two optical parameters-OCT signal slope (OCTSS) and the reflectance (R)from the bottom surface-are determined in the study of dextran in blood by OCT.The results showed that the addition of dextran in plasma increased the refractiveindex matching between red blood cell cytoplasma and blood plasma, and induced theaggregation in RBCs, leading to the decrease in blood scattering. Therefore, theOCTSS had a decrease with the dextran concentration, whereas R had an increase.But when dextran concentration exceeds a certain level, the two parameters appearedopposite changes. Furthermore, the elevated hematocrit (HCT) increased the surfaceof scattering, which made the increase of OCTSS and decrease of R.2. To determine the optimal method for removing intrinsic plasma fibrinogen, theeffect of addition of dextran in plasma without fibrinogen on changes of blood opticalproperties was investigated. The results showed that the blood optical parametersperformed abnormal changes with dextran concentrations when plasma was treated bychemical precipitation, whereas those from freeze-thawing treated-plasma had normal changes with dextran concentrations. Freeze-thaw method was determined to be theoptimal approach for removing intrinsic fibrinogen.3. After treated by freeze-thaw method, the blood samples were prepared ofdifferent fibrinogen concentrations by exogenous human fibrinogen powder. Theresults showed that the optical properties of porcine blood had no significant changeswith the fibrinogen concentrations. This may be due to the weak activity betweenfibrinogen powder and porcine blood cells. But the experiments in human bloodshowed that the OCTSS had a salient decrease with the fibrinogen concentrations.The OCTSS of blood with higher plasma fibrinogen levels has a considerably lowervalue compared with the blood with a normal fibrinogen concentration (2-4g/L inhuman plasma). Moreover, our results also demonstrated that the OCTSS is alsodependent on other blood properties, e.g. HCT, blood flow and red blood cell-specificfactors.Overall, it is evident that the OCT signal slope has the potential to reflect theaccurate plasma fibrinogen in dynamic blood with proper calibration on individualdifference in hematocrit and other blood properties. Furthermore, the quantitativecorrelation between OCTSS and plasma fibrinogen level may deserve furtherinvestigation on in vivo measurements by OCT combined with the conventionalfibrinogen assays.