Windowing of wide-band ultrasound transducers

A high performance ultrasound imaging system requires precise control of the amplitude of the elements in its aperture, as well as the time delays between them. The authors describe results in imaging with and without such apodizing, and describe a method for controlling channel amplitude which preserves the autonomy between channels characteristic of digital beamformers. As part of the study, the authors investigate how the classical results on windowing transfer to a high-bandwidth system such as an ultrasound scanner. The algorithm allows the array to be dynamically windowed while its aperture grows in proportion to the time after a transmit excitation. Linear and curved arrays, where the phase center changes with beam position, are also accommodated. A surprisingly versatile system is needed to provide a satisfactory apodizing function in all cases. The simulations from a bit-level model of the VLSI implementation of the algorithm show its value in improving beam quality.