Instrumentation Design for Ultrasonic Imaging

The purpose of this chapter is to show how piezoelectric transduction, sound wave propagation, and interaction with scattering targets are taken advantage of in image formation with an ultrasound instrument. These instruments have evolved over the last 40 years from relatively simple handmoved scanners built around an off-the-shelf oscilloscope to rather sophisticated imaging computers. Much technology has been perfected during this evolution. For example, transducers have grown from circular single-element probes to precision arrays with more than 1000 elements. With better frontend electronics, the operating frequencies have increased as weaker echoes can be handled. As the gate counts of VLSI ASICs* have increased, the numbers of processing channels in array-based systems have risen. With the introduction of reasonably low cost high-speed (20 to 40 MHz) 8to 12bit analog-to-digital converters, digital beam formation has become the standard. The organization of this chapter is based on the discussion of a block diagram of a generalized ultrasound system. Each component of the block diagram will be reviewed in considerable detail. Different design approaches for the various blocks will be reviewed and their advantages and disadvantages discussed. Finally those areas of the block diagram that are targets of significant current research are summarized.