Image Enhancement and Noise Reduction Using Modified Delay-Multiply-and-Sum Beamformer: Application to Medical Photoacoustic Imaging

摘要

Photoacoustic imaging (PAI) is an emerging biomedical imaging modalitycapable of providing both high contrast and high resolution of optical andUltraSound (US) imaging. When a short duration laser pulse illuminates thetissue as a target of imaging, tissue induces US waves and detected waves canbe used to reconstruct optical absorption distribution. Since receiving part ofPA consists of US waves, a large number of beamforming algorithms in US imagingcan be applied on PA imaging. Delay-and-Sum (DAS) is the most commonbeamforming algorithm in US imaging. However, make use of DAS beamformer leadsto low resolution images and large scale of off-axis signals contribution. Toaddress these problems a new paradigm namely Delay-Multiply-and-Sum (DMAS),which was used as a reconstruction algorithm in confocal microwave imaging forbreast cancer detection, was introduced for US imaging. Consequently, DMAS wasused in PA imaging systems and it was shown this algorithm results inresolution enhancement and sidelobe degrading. However, in presence of highlevel of noise the reconstructed image still suffers from high contribution ofnoise. In this paper, a modified version of DMAS beamforming algorithm isproposed based on DAS inside DMAS formula expansion. The quantitative andqualitative results show that proposed method results in more noise reductionand resolution enhancement in expense of contrast degrading. For thesimulation, two-point target, along with lateral variation in two depths ofimaging are employed and it is evaluated under high level of noise in imagingmedium. Proposed algorithm in compare to DMAS, results in reduction of lateralvalley for about 19 dB followed by more distinguished two-point target.Moreover, levels of sidelobe are reduced for about 25 dB.