For Photoacoustic Imaging Of Binary Acoustic Lens

Optoacoustic tomography is an imaging technique for biomedical tissue diagnosis with high optical contrast and ultrasonic resolution, which has become a popular research subject in recent ten years. Optoacoustic imaging methods include using some reconstruction algorithms to form an image and using an acoustic lens system to form an image directly. In the first case, all the methods have in common that the original absorption distribution can only be obtained to form an image by reconstruction algorithms, which will be time consuming and may introduce reconstruction artifacts. But the second case to use an acoustic lens to image can not only provide an image in real time but also offer a unique possibility to visualize the object at the depth of 4cm in optically turbid or opaque tissues by the sensitive time-resolved technique, which will provide more information of tissue structure valuable for biomedical diagnosis.In 2002, we reported that the lateral resolution is up to 4mm, and the depth resolution is 0.45mm to use an acoustic lens system to realize real-time optoacoustic imaging. In 2004, M. Frenz etc. al. had got 3-D real-time optoacoustic image with much higher optical contrast and ultrasonic resolution by using an acoustic lens system and CCD system. But the resolution of images got by the acoustic lens system is not good as images got by reconstruction algorithms. To make up for the lateral resolution, we increase the caliber of the acoustic lens. But with the increasing of the sensitivity and resolution, the chromatism and aberration being induced by the broadband of the optoacoustic signal will be increased at the same time. So the image will not be very good. This paper have done the research for these, main contents are as follows:1. It has designed a refractive-diffractive hybrid acoustic lens system based on binary acoustics for the better optoacoustic image. Namely, to use the refractive sphere surface of the hybrid acoustic lens to focus and the diffractive binary phase zone structure surface to improve the axial chromatism.2. Discussed the achromatic principle of our hybrid acoustic lens system by deducing the point spread function of a point source with a bandwidth through the different imaging system.3. Simulated the point spread function of the point source through the single acoustic lens system and through the hybrid acoustic lens system by computer and compared them through their normalized figures. By comparison, it could be clearly seen that the central dispersion of the point spread function through our hybrid acoustic lens system was improved better in evidence than the one through the single acoustic lens system. The result of lateral resolution being greatly increased and imaging quality being greatly improved is very significant to the optoacoustic imaging study.