Double Minimum Variance Beamforming Method to Enhance Photoacoustic Imaging

Mahdi Orooji

doi:10.34297/ajbsr.2019.01.000518

Abstract

One of the common algorithms used to reconstruct photoacoustic (PA) images is the non-adaptive Delay-and-Sum (DAS) beamformer. However, the quality of the reconstructed PA images obtained by DAS is not satisfying due to its high level of sidelobes and wide mainlobe. In contrast, adaptive beamformers, such as minimum variance (MV), result in an improved image compared to DAS. In this paper, a novel beamforming method, called Double MV (D-MV) is proposed to enhance the image quality compared to the MV. It is shown that there is a summation procedure between the weighted subarrays in the output of the MV beamformer. This summation can be interpreted as the non-adaptive DAS beamformer. It is proposed to replace the existing DAS with the MV algorithm to reduce the contribution of the off-axis signals caused by the DAS beamformer between the weighted subarrays. The numerical results show that the proposed technique improves the full-width-half-maximum (FWHM) and signal-to-noise ratio (SNR) for about 28.83 \mu m and 4.8 dB in average, respectively, compared to MV beamformer. Also, quantitative evaluation of the experimental results indicates that the proposed D-MV leads to 0.15 mm and 1.96 dB improvement in FWHM and SNR, in comparison with MV beamformer.

Highlights

Photoacoustic imaging (PAI) is a non-invasive medical imaging modality which is fast growing [1]
diagonal loading (DL) is applied to the spatial covariance matrixes in each stage of applying DMV with the assumption of ∆ = 1/100L and ∆D = 1/100LD in the first and the second stage, respectively
In minimum variance (MV), as an adaptive beamformer, the calculated weights are changed depending on the characteristics of the signals

Summary

Introduction

Photoacoustic imaging (PAI) is a non-invasive medical imaging modality which is fast growing [1]. It combines the physics of the ultrasound (US) and the optical imaging modalities and provides the resolution of US and contrast of the optical imaging [2,3]. Compared to the optical imaging, the advantage of PAI is its high penetration depth. It does not have the speckle noise appeared in US imaging [4]. Delay-Multiply-and-Sum (DMAS), introduced by Matrone et al [20] was proposed in order to improve the quality of the reconstructed images compared to DAS [20]

Methods

Results

Discussion

Conclusion