Fundamental resolution limits of a coded-excitation system for real-time pulse-echo imaging

A general analytical formula for image formation in a phased array system employing conventional beamforming, matched filtering, or pseudoinverse filtering with coded excitation is presented. Range and lateral resolution limits for the matched filtering approach are derived and compared with the well known diffraction limits encountered in conventional beamforming and super-resolution limits achievable with the pseudoinverse filters in the noise-free case. Experimental data is obtained to support the validity of the analytical results. It is shown that, even in the presence of noise, the regularized PI operator produces lateral resolution that exceeds the diffraction limit. This is achieved at practical SNR values for the imaging system and does not result in sacrificing contrast resolution.