  Delay and Sum (DAS), as the most common beamforming algorithm in
Photoacoustic Imaging (PAI), having a simple implementation, results in a
low-quality image. Delay Multiply and Sum (DMAS) was introduced to improve the
quality of the reconstructed images using DAS. However, the resolution
improvement is now well enough compared to high resolution adaptive
reconstruction methods such as Eigenspace- Based Minimum Variance (EIBMV). We
proposed to integrate the EIBMV inside the DMAS formula by replacing the
existing DAS algebra inside the expansion of DMAS, called EIBMV-DMAS. It is
shown that EIBMV-DMAS outperforms DMAS in the terms of levels of sidelobes and
width of mainlobe significantly. For instance, at the depth of 35 mm,
EIBMV-DMAS outperforms DMAS and EIBMV in the term of sidelobes for about 108
dB, 98 dB and 44 dB compared to DAS, DMAS, and EIBMV, respectively. The
quantitative comparison has been conducted using Full-Width-Half-Maximum (FWHM)
and Signal-to-Noise Ratio (SNR), and it was shown that EIBMV-DMAS reduces the
FWHM about 1.65 mm and improves the SNR about 15 dB, compared to DMAS.
