Real-Time Photoacoustic Imaging and Its Applications in Blood Oxygenation Measurements
Date Issued
2012
Date
2012
Author(s)
Hsu, Yung-Chieh
Abstract
In this study we discuss the feasibility of using dual-wavelength photoacoustic imaging, along with a high pulse repetition frequency laser for real-time measurements of blood oxygen level. Blood oxygen level is an important physiological parameter. Conventionally, there are two ways to measure the blood oxygen level. One is direct blood analysis and the other is using a pulse oximeter. The direct method, which draws blood from patients invasively, is the current gold standard for blood oxygen level measurement. Pulse oximeter, on the other hand, is a non-invasive and thus more convenient method. But the accuracy is inferior. The hypothesis of this research is that by combining photoacoustic imaging with blood oxygen level measurements, 2D functional imaging can be achieved. To this end, the goal of this research is to develop and implement a signal processing method, utilizing absorption spectrum difference between oxyhemoglobin and deoxyhemoglobin, to measure the blood oxygen level distribution in real time. In our experimental setup, a high PRF pulsed dye laser is used to achieve a frame rate up to 5 frames/sec. On the other hand, a Ti-Sapphire tunable laser, pumped by a 532nm Nd:YAG laser, is used for dual wavelength measurements. Due to system limitations, currently real-time imaging only with a single wavelength (722nm) is achieved. Various samples, including blue/red ink and gold nano-particles, were used to test our methods. Results show that the measured concentration of blue ink had a mean error of -24%, and a standard deviation of 32%. For gold nanoparticles, the mean error was -3.43%, and the standard deviation was 14.5%. For human blood, the calculated blood oxygen level for both gas-filled blood and no gas-filled blood was above 85%, but the oxygen level was higher for no gas-filled blood. It is suggested that 720nm and 800nm should be the two wavelengths used for future investigation.
Subjects
photoacoustic effect
blood oxygenation
dual-wavelength
real-time imaging
Type
thesis
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