Low-artifact And Long Depth-of-field Photoacoustic Microscopy By Using Gaussian Weighted Annular Array

As an emerging non-invasive biomedical imaging technology,photoacoustic imaging combines the advantages of optical imaging and acoustic imaging.It has the characteristics of high imaging depth,high resolution,high contrast,fast and safe and has attracted widely attention in recent years.Photoacoustic microscopy is an embodiment of Photoacoustic imaging,which has broad development prospects.In this study,a Gaussian-weighted concentric annular ultrasonic transducer array is innovatively proposed to overcome the imaging problems in clinical situations.On the one hand,by applying Gaussian weighting on each ring,the sensitivity of the transducer can be adjusted.Benefiting from the no side-lobe property of the Gaussian field,the annular array suppresses the side lobes by about 18 d B compared to the conventional focused transducer,the “X”-shaped artifacts are significantly reduced in reconstructed photoacoustic images.On the other hand,due to the shallow depth-offield of the conventional focused transducer,image quality drops and distortion becomes serious as the imaging area deviate from the focal region.However,by controlling the delay time of the photoacoustic signals received by each ring,the annular array can dynamically focus at different depths,thus achieving a much longer depth of field.The thesis analyzes and discusses the imaging theory of the Gaussian weighted annular array,numerical simulations and experiments are also performed which demonstrate that the proposed scheme can significantly improve the imaging performance of photoacoustic microscopy.