Design And Implementation Of The Photoacoustic Imaging System

Photoacoustic imaging is a new nondestructive medical imaging technology. It's based on photoacoustic effect of biological tissue and the different optical absorption of various biological tissues, so it has both the benefits of pure ultrasound imaging and pure optical imaging on getting high-resolution and high contrast images.In this paper, we firstly discuss the theory and the process of photoacoustic imaging. On this basis, an integration photoacoustic imaging device was designed, including a photoacoustic signal generation device, a signal preprocessing circuit, a data acquisition and transmission circuit and image reconstruction algorithm. First of all, expose the tissue to the pulsed laser. Then, use a linear array ultrasound detector by side to collect the photoacoustic signal and convert them into electrical signal. The electrical signal is then sampled by the data acquisition circuit after filtered and amplified. Finally, the data will be transferred to PC via USB port and reconstructed to image.Secondly, we studied the image reconstruction algorithm. According to the characteristics of noise in photoacoustic signal, a new de-noising method based on EMD and wavelet is presented. After that the phase-controlled focusing algorithm is used to reconstruct photoacoustic image. In order to overcome the problem that the image have many artifacts and is lateral resolution is very low, a multi-angle observations based on spatial compound imaging method is presented to reduce the image artifacts and improves the resolution photoacoustic images.At last we discussed the application of compressed sensing theory in photoacoustic imaging. For photoacoustic imaging systems with a single-element detector, we introduced a new imaging device and reconstruction algorithm based on compressed sensing theory so that there is no need to rotate the detector, which greatly reducing the imaging time. Subsequently, considering that there is always much noise in the photoacoustic signal, we presented a new reconstruction algorithm based Bayesian analysis, which can inhibit the noise while image reconstruction, reduce the reconstruction error and improve the image.