Photoacoustic imaging(PAI),as an emerging biomedicine diagnostic technique that has been developed quickly in the past decade,inherits the high spatial resolution of ultrasonography in imaging deep tissue and the high sensitivity of optical imaging in evaluating tissue chemical and physiological information.In this paper,after introducing the basic principles of PAI including both photoacoustic tomography and photoacoustic microscopy,we will review some recent progress of PAI in biomedicine and demonstrate the capability of PAI in detecting the chemical compositions and in evaluating the histological microstructures in biological tissue.
The speed-of-sound variance will decrease the imaging quality of photoacoustic tomography in acoustically inhomogeneous tissue. In this study, ultrasound computed tomography is combined with photoacoustic tomography to enhance the photoacoustic tomography in this situation. The speed-of-sound information is recovered by ultrasound computed tomography. Then, an improved delay-and-sum method is used to reconstruct the image from the photoacoustic signals. The simulation results validate that the proposed method can obtain a better photoacoustic tomography than the conventional method when the speed-of-sound variance is increased. In addition, the influences of the speed-of-sound variance and the fan-angle on the image quality are quantitatively explored to optimize the image scheme. The proposed method has a good performance even when the speed-of-sound variance reaches 14.2%. Furthermore, an optimized fan angle is revealed,which can keep the good image quality with a low cost of hardware. This study has a potential value in extending the biomedical application of photoacoustic tomography.
Pulse decomposition has been proven to be efficient to analyze complicated signals and it is introduced into the photo-acoustic and thermo-acoustic tomography to eliminate reconstruction distortions caused by negative lobes.During image reconstruction,negative lobes bring errors in the estimation of acoustic pulse amplitude,which is closely related to the distribution of absorption coefficient.The negative lobe error degrades imaging quality seriously in limited-view conditions because it cannot be offset so well as in full-view conditions.Therefore,a pulse decomposition formula is provided with detailed deduction to eliminate the negative lobe error and is incorporated into the popular delay-and-sum method for better reconstructing the image without additional complicated computation.Numerical experiments show that the pulse decomposition improves the image quality obviously in the limited-view conditions,such as separating adjacent absorbers,discovering a small absorber despite disturbance from a big absorber nearby,etc.
