Photoacoustic quantitative thermal imaging for laser-induced thermotherapy
Date Issued
2009
Date
2009
Author(s)
Wang, Shiou-Han
Abstract
This study applied the ultrasound (US) and laser for the non-invasive photoacoustic (PA) technology to monitor the temperature during laser-induced photothermotherapy. The US and PA images were also combined for imaging purpose, and technology for quantitative thermal imaging was developed. PA signal can be used to research the thermal reaction of the surface plasmon resonance of the gold nanoparticles irradiated with the continuous wave mode laser. The safety and efficacy of the laser-assisted plasmonic photothermal therapy were kept by combining the US and PA signals to elucidate the anatomical structure of the tumor, and to monitor the tissue temperature during therapy. Many kinds of energy may trigger PA signal. We selected the pulsed laser to produce the PA signal and used the high-frequency ultrasonic transducer to obtain PA images with high resolution.A signal may be used for non-invasive tissue imaging. The amplitude of the PA pressure P(z) is governed by the equation . Under the stable laser system, the amplitude is affected by the Grüneisen parameter Γ and the absorption coefficient μa. However, the absorption coefficient is independent to temperature change, and the Grüneisen parameter Γ for water is a linear relationship to the temperature. The soft tissue is composed of more than 70% of water, and thus we can use the Grüneisen parameter Γ of water to measure the temperature of the water-contained tissue during the thermotherapy.emperature may not only have influence on the amplitude of PA signal, but also cause the echo-shift of the ultrasound signal. With the correction of the speed of sound and thermal expansion according to the temperature change, the ultrasound radiofrequency signals can be adjusted to the same position. Though thermal expansion and speed of sound affect the ultrasound echo time shift, they are independent to the amplitude of PA signal. We may use the PA signal to measure the temperature change for a large range.he quality of PA imaging system is related to our spatial resolution. By increasing the central frequency of the ultrasound transducer, the spatial resolution is able to be improved. We used the 20MHz high frequency transducer to approach the spatial resolution of 200-300 μm.e can increase the accuracy of temperature measurement by improving the stability of output energy of the pulsed laser. This system can respond to the heat flux quickly and produce change of the amplitude of PA signal immediately according to the output power of the CW laser. It may secure the safety and efficacy of the thermotherapy.he gold nanoparticles and irradiation of CW laser can increase the amplitude of the PA signal. Compared to the intrinsic chromophores of soft tissue, the gold nanoparticles may trigger higher PA amplitude after absorption the energy of the pulsed laser and thus are suitable for contrast agent during PA imaging. Before and after the laser-induced thermotherapy, this system can combine the UA and PA images to locate the position of the tumor and the nanoparticles to facilitate better treatment plan and therapeutic quality.hotoacoustic technology for temperature measurement has the potential to monitor the thermotherapy and is suitable for gold nanoparticle-assisted laser-induced plasmonic photothermal therapy. We can also use the technique of quantitative thermal imaging for real-time monitoring during the laser-induced thermotherapy.
Subjects
gold nanoparticles
laser-induced thermotherapy
photoacoustic effect
quantitative thermal imaging
surface plasmon resonance
temperature measurement
Type
thesis
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