Research On Thermal-based Deeper Photoacoustic Tomography

Photoacoustic Tomography(PAT) is a kind of laser-based imaging mode, by using target distribution difference of optical absorption coefficient to induce ultrasound wave of different frequency, to receive ultrasound by ultrasonic transducer, to reconstruct image by utilizing reconstruction algorithm. Thus, PAT has the advantage of high resolution and high contrast which come from ultrasonic imaging and optical imaging separately. However, PAT’s image quality remains to be strengthened, furthermore, it cannot satisfy the large size and high resolution imaging of biological tissue clinically. Although photoacoustic imaging mode opens up to avoid light scattering effect which is different from the pure optical imaging, a new imaging method, but photoacoustic signals especially signals of high frequency or photoacoustic signals come from deeper biological tissue are often difficult to detect because of strong attenuation, this limits the photoacoustic imaging for the high quality of deeper tissue imaging. On account of this, this paper presents a new type of PAT based on thermal effect, Utilizing external excitation source(laser, focused ultrasound and microwave) heating target to produce one area which its temperature is different from the surrounding media, temperature differences lead to sound velocity differences, then form a thermal lens. Reuse the lens focusing effect to get deep photoacoustic signal, thus achieve the purpose of deepening imaging depth and improve the imaging quality. This paper graft the thermal effect into PAT for the first time, specific contents as follows:1. Analyzes the advantages of PAT and current problems in the development of PAT, presents current methods to deal with the exsiting problems. Emphasis is put forward in this paper, also, solutions to these problems and the research significance of this article are proposed.2. Combing the theory of PAT, analyzes the physical process of photoacoustic signal, makes a meticulous research of the factors affecting the quality of PAT.3. From theory and experiment on the thermal effect were analyzed and validated. Analyzed High Intensity Focused Ultrasound(HIFU), high intensity focus ultrasound) produced by the thermal effect. Theoretical part mainly analyses the physical process of heating and heat effect on the target medium physical properties especially the influence of the acoustic properties. Emphatically analyzed and verified the experimental section produced by high intensity focused ultrasound irradiation target medium heat effect, which is generated by the focal spot size and focal spot of the beam focusing ability.4. Based on the depth of the thermal effect of photoacoustic imaging technology has carried on the experimental study. Set the photoacoustic imaging experimental hardware system, photoacoustic imaging experiment was carried out, thermal-based effect of photoacoustic imaging experiments, experimental verification and confirmed the heating effect of the light.