Investigation on THz Spectra of Ex vivo and In vivo Blood
Date Issued
2015
Date
2015
Author(s)
Tseng, Tzu-Fang
Abstract
Blood is the most complicated body fluid in the world which sends many kinds of biomolecules such as cholesterol, triglyceride, glucose, and proteins to organs and tissues. These molecules are related to many diseases such as coagulating problem and hyperlipidemia, that can only be examined ex vivo in nowadays. For the most common used biochemical and optical examination methods, blood centrifuge is needed to separate blood cells and plasma. In the past two decades THz has been indicated to be sensitive to the vibrational and rotational motions of many kinds of biomolecules. Comparing to the existing examination methods, THz waves is one of the candidates to noninvasively observe the molecular behaviors in whole blood. To develop futuristic applications in blood examination in THz region, we first need to find out the molecules of which the motions dominantly affect the THz spectrum of the whole blood. Since the concentrations of many biomolecules differ among individuals, it is necessary to collect a number of blood samples and have statistical analysis to efficiently find out these dominant molecules. In this thesis we have collected 58 ex vivo whole blood samples following 8-hours fasting guideline, 29 without adding anticoagulant and another 29 with heparin added, to have immediate and time-dependent THz spectra acquisition and analyze the correlation between the refractive indices and absorption coefficients to the examined hematological and biochemical factors. We have observed that the THz absorption coefficient of the whole blood without anticoagulant had a positive correlation to platelet count. This positive correlation is attributed to the platelet induced biochemical reactions including platelet deformation, platelet aggregation, and protein activations, in the beginning of blood coagulation. However, during the clotting process that change blood from the fluidic to the solid phase, no significant correlation between THz absorptions and time was found, indicating that THz is not sensitive to this phase transition. On the other hand, in the whole blood samples with heparin added to block the coagulation process, we have found that their absorption coefficients in the low sub-THz frequency region were dominated by the red blood cell count with a negative correlation. At high sub-THz frequency region, their absorption coefficients were dominated by the concentration of triglyceride with also a negative correlation. For futuristic non-invasive application, we have built a sub-THz in vivo near-field system for vessel imaging, adopting waveguided illumination and near–field scanning detection with a subwavelength aperture, to investigate the in vivo blood absorption coefficient and refractive index. Nearby blood vessels could be clearly resolved in our THz images, with a lateral resolution of around 0.5mm. The near-field pattern of the power transmittance through the vessel has also been numerical simulated and was found to have good correspondence to the measured results. According to the refractive indices of the tissue and the blood obtained in previous researches, as well as the well-known upper limit of the absorption coefficient of blood and the lower limit of the absorption coefficient of living tissue, our study indicated a small refractive index difference (at most 0.3) and a large absorption coefficient difference (at least 80 cm-1) between blood and surrounding tissues. The relationship between the power transmittance variation and the absorption coefficient variation of blood was also quantified with the help of numerical simulation. These works help in developing futuristic blood examination applications in THz region.
Subjects
THz
blood
spectroscopy
near-field imaging
Type
thesis
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