Evolution of ultrasound beamformers

Real-time ultrasonic imaging systems have been available for more than thirty years. During this time much has occurred to the basic architecture and functions of these clinical systems and their beamformers, which are, in many ways, the most important components of these systems. This talk will review some of the changes that have occurred and will discuss current trends in beamformer design. Throughout most of the 30 years of real time imaging, analog beamformers have been the mainstay of all instruments. The common methods for the implementation of analog beamformers for annular, linear/curved arrays, and phased arrays will be reviewed and the distinguishing characteristics identified. At the present time the industry is undergoing a major shift toward digital beamformation with the introduction of several commercial systems. Given that the earliest digital systems were available roughly 15 years ago, it is fair to say that the introduction of digital beamformers has been relatively slow. Today this shift seems to be gaining momentum. Some of the factors causing these shifts will be reviewed along the the common types of designs and implementations. The ongoing search for improved imaging performance will continue to introduce new challenges for beamformer designers. Among already proposed imaging methods and techniques are elevation focusing (1.5D arrays), synthetic apertures, 2D and sparse arrays, phase aberration correction, and others. The most common complication introduced by these is a significant increase in channel count. Further, there will also be beamformer design issues related to signal processing. These include not only Doppler processing but also the processing of signals due to novel contrast agents. Finally, with advances in computer and microelectronics technologies, the way we view beamformation may have to undergo sizeable changes. These topics will be reviewed not only as technical challenges but also in light of the constraints introduced by today's marketplace.