ULTRASONIC-IMAGING USING OPTOELECTRONIC TRANSMITTERS

Conventional ultrasound scanners utilize electronic transmitters and r eceivers at the scanner with a separate coaxial cable connected to eac h transducer element in the handle. The number of transducer elements determines the size and weight of the transducer cable assembly that c onnects the imaging array to the scanner. 2-D arrays that allow new im aging modalities to be introduced significantly increase the channel c ount making the transducer cable assembly more difficult to handle. Th erefore, reducing the size and increasing the flexibility of the trans ducer cable assembly is a concern. Fiber optics can be used to transmi t signals optically and has distinct advantages over standard coaxial cable to increase flexibility and decrease the weight of the transduce r cable for large channel numbers. The use of fiber optics to connect the array and the scanner entails the use of optoelectronics such as d etectors and laser diodes to send and receive signals. In transmit, op toelectronics would have to be designed to produce high-voltage wide-b andwidth pulses across the transducer element. In this paper, we descr ibe a 48 channel ultrasound system having 16 optoelectronic transmitte rs and 32 conventional electronic receivers. We investigated both sili con avalanche photodiodes (APD's) and GaAs lateral photoconductive sem iconductor switches (PCSS's) for producing the transmit pulses. A Siem ens SI-1200 scanner and a 2.25 MHz linear array were used to compare t he optoelectronic system to a conventional electronic transmit system. Transmit signal results and images in tissue mimicking phantoms of cy sts and tumors are provided for comparison.