Linear synthetic aperture modes for ultrasonic pulse-echo imaging

A unified approach is developed to characterize and compare the most widely used two-dimensional ultrasound pulse-echo imaging procedures. The methods of monostatic, bistatic and multistatic time-domain holography are theoretically investigated with regard to line spread functions, resolution capabilities, and the effects of multiple scattering and object inhomogeneities. Analytical derivations and computer simulations show the superiority of monostatic holography in applications such as nondestructive testing, where in most cases the assumptions generally made in the calculation of the inverse scattering formulae are justified. However, if higher order scattering and/or the spatial variations of the sound speed play a significant role, then multistatic imaging is more advantageous. A modification of this latter mode, with fixed focus on transmission, is commonly used in medical imaging B-scan systems, but implementation of the full algorithm would offer improved resolving power and reduced side lobe levels throughout the image plane.