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Blood coagulation is a very complex process that can cause some serious complications, such as resulting in the formation of thrombosis and embolism in the human circulation system. It is crucial to develop effective techniques to early detecting the process of blood coagulation in clinical diagnosis. Optical coherence tomography （OCT） based on the principle of low-coherence interferometry measurement, with a non-invasive and real-time monitoring, is different from traditional optical imaging methods. OCT has some advantages in highly scattering media （eg biological tissues） tomographic imaging and optical property measurements.OCT signal slope （OCTSS） and 1/e light penetration depth (D1/e) were explored to reflect the changes in the optical properties during blood coagulation. To improve the sensitivity and accuracy of the detection, the OCT system with the center wavelength of 1310 nm, the light source bandwidth of 95 nm, and output power of 8 mW was used. Blood coagulation was induced by addition of 0.25M calcium chloride solution with volume ratio of 9:1.Experimental results indicated that OCTSS and D1/e could clearly distinguish different stages of coagulation process. In the process of blood coagulation, the refractive index of plasma increased firstly and then kept stable, while the refractive index of red blood cells remained unchanged. The refractive index matching between the blood and environment was improved significantly and then remained invariable. OCT signal slope （OCTSS） and 1/e light penetration depth (D1/e) against time were obtained from the profiles of reflectance vs depth. Results showed that both OCTSS and d1/e were able to sensitively differentiate various stages of blood properties during coagulating. After 1 h clotting, OCTSS decreased by 47.0%, 15.0%, 13.7%, and 8.5%, D1/e increased by 34.7%, 29.4%, 24.3%, and 22.9%, and the clotting time was 1969±92s, 375±12s, 455±11s and 865±47s for the blood samples at HCT of 25, 35, 45, and 55%, respectively. However, OCTSS and D1/e vs time curve were abnomalies in the process 25% HCT blood coagulation, which can be divided into three sections. OCTSS and D1/e vs time curves only can be divided into two sections in the process of 35%, 45% and 55% HCT blood coagulation. Different pH of the blood can affect the optical properties in the process of blood coagulation. When pH value deviated from 7.35, the optical parameters vs time curve was abnomalies during the blood clotting process. In a word, the results showed that the clotting time, HCT and pH all had a certain influence on OCTSS and D1/e. Especially for HCT, it’s one of the important factors of the blood clotting mechanism. The blood coagulation process was abnormal when the HCT was low or pH deviated from 7.35. In the normal range of the HCT, the lower of the HCT, the shorter time of blood clotting , the stronger change of the light scattering and transmission depth before and after solidification.Moreover, we also studied the feasibility of OCT to investigate optical properties of dynamic blood during coagulation. The experimental results showed that the most appropriate experimental program is the opened circulation system. And diameter of silicone tube is 3mm, when scanning mode is signal A-scan. Considering to OCT imaging depth, resolution, contrast ratio, the glass tube is better. Under these conditions, the change of D1/e in the process of dynamic blood coagulation is similar to static blood coagulation. This provides a possibility for further research.
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