Fundamental Study And Application On Photoacoustic Tomography For Biomedical Imaging

In photoacoustic tomography(PAT), a short-pulsed laser is used to irradiate biological tissue samples to generate acoustic wave. Photoacoustic image reconstructed from the photoacoustic(PA) signal reveals the spatial optical absorption distribution at a certain wave length and has the advantage of both high imaging resolution and contrast. In this dissertation, the optical and acoustic properties of biological tissue is firstly summarized. Then, several factors that influences the spatial resolution is researched by numerical simulation. The relationship between the transducer frequency response and imaging contrast is researched both by numerical simulation and experiment. The corresponding signal processing method is also proposed. A photoacoustic imaging system based on the linear acoustic transducer array is developed and the imaging speed had been improved. A photoacoustic imaging system based on unfocused needle acoustic transducer is developed and the photoacoustic image with high contrast and resolution of the blood vessel network inside mouse brain in-vivo and the porcine eyeball ex-vivo is acquired. The main contents in this dissertation is as follows:1. Taking the Point-Spread-Function(PSF) as the criteria, the relationship between the spatial resolution and the several influencing factors such as the band-width and upper cutoff frequency of the filter, the diameter of the transducer active detecting surface and the transducer detecting radius is researched numerically. The results shows that the full width at half maximum(FWHM) of PSF decreases exponentially with the increase of the band-width and the upper cutoff frequency of the filter. The PSF diffuses linerly with the increase of the active detecting diameter of the transducer. With the same active detecting diameter of the transducer, the PSF diffuses with the decrease of the transducer scanning radius. The numerical simulation provides the theoretical basis for the improvement of the spatial resolution of PA image.2. The deconvolution algorithm with wiener filter based on the transducer point source response is presented. The method had avoided the determination of the band-width and the cutt-off frequency of the band-pass filter manually during deconvolution. The frequency spectrum of the wide-band PA signal had been restored preferably and the imaging contrast had been improved. 3. The trial photoacoustic tomography for ophthalmology is performed. The two dimensional optical absorption image of the entire porcine eyeball was reconstructed with high imaging contrast.4. The relationship between the spatial position of the transducer and the PA image quality is researched. The accumulated spatial position error of pixels in PA image is founded to be the main factor that causes the distortion on the edge of the PA image. The distortion can be eliminated by the increase of transducer scanning radius.