The acoustic and thermal effects of using multiplexers in small invasive probes

Invasive ultrasound procedures have advanced at two size scales. Intraluminal transducer arrays placed on catheters with diameters of one to several millimeters have become very important for vascular imaging. Larger arrays for endoscopic, gastroscopic, and laparoscopic probes have been built on scopes with diameters ranging from about 10 to 14 mm. While there are many applications that could benefit from probes with diameters in between these two ranges, the fabrication approaches used make it quite difficult to accommodate the intermediate range by scaling. The catheter arrays use multiplexers that are limited to very small elements and a synthetic aperture approach which will result in unacceptable frame rate for applications requiring deeper penetration. The larger probes are directly wired using individual coaxes and can not be scaled to smaller probes. The solution is to develop miniature multiplexers built into the ultrasound array. However, these multiplexers can affect the acoustic performance and increase the power dissipation at the probe. Here, the authors examine the multiplexer specification using the KLM model. Acoustic performance and thermal heating due to power dissipation are both considered. A modification of the KLM model in described which allows the power dissipation to be calculated for each component including the multiplexer. The components are then considered to be heat sources in a finite element thermal model. It is concluded that multiplexers are possible which meet the requirements for achieving good imaging performance with tolerable power dissipation in invasive probes of intermediate size.