Effects of Element Directivity in Linear-Array Photoacoustic Imaging

Photoacoustic imaging (PAI) is an emerging medical imaging modality with a steady growth in both pre-clinical and clinical applications. In linear-array PAI, beamformers play a significant role in the image reconstruction procedure. Generally, beamformers assume a point- like model for the elements of the array, and the elements are assumed to be omnidirectional. In this study, we investigated the effects of receiver element directivity on the Photoacoustic (PA) image formation procedure where delay-andsum (DAS) and delay-multiply-and-sum (DMAS) algorithms have been used as beamformers. The proposed method is evaluated experimentally (wire phantom and ex vivo imaging). It has been shown that the contribution of the directivity of the transducer elements improves the PA image quality. The results show that using the directivity, the sidelobes of the formed image (wire phantom) by DAS are attenuated about 20 %, compared to when directivity is not used. Moreover, signal-to-noise ratio achieved by DAS and DMAS is improved by about 12.5 % and 11.3 %, respectively.

Abbreviations: PAI: Photo Acoustic Imaging; PA: Photo Acoustic; DAS: Delay-And-Sum; DMAS: Delay-Multiply-And-Sum; MV: Minimum variance; DS-DMAS: Double stage- Delay-Multiply-And-Sum; MCF: Modified Version of the Coherence Factor; US: Ultrasound