In Vivo Imaging Using a Copolymer Phased Array

Abstract

Phased-array images have been obtained in vivo with a steered copolymer array operating at 2.5 MHz. The array was fabricated using 28 μm copolymer film, λ/4 resonant at 21 MHz, which was bonded to a glass ceramic backing with a thin film bond. The 32 array elements were created by laser ablation of the continuous gold electrode on one side of the film. The transducer was driven by 200 V shock excitation, and the received signal was processed by 32 custom IC preamplifiers that were mounted to the array connector. The amplifiers had a high input impedance compared to that of the array elements and their output impedance matched that of the coaxial cable that connected to the scanner. Because the copolymer transducer had a broad bandwidth, the spectrum of the pulse echo image was modified by the frequency dependent attenuation of tissue and the bandpass of the ultrasound scanner, resulting in a center frequency of 2.5 MHz. The performance of the copolymer array was compared to that of a 3 MHz, PZT array with similar dimensions. On the Duke phased-array scanner, the copolymer sensitivity was 28 dB less than that of PZT. The copolymer elements had a 6 dB pulse-echo angular response of 30°, and the interelement cross-coupling was −35 dB. Phased-array images were made of the heart of a 25 year-old normal male.