Improved scatterer size estimation from ultrasound backscatter using coded excitation and pulse compression

Abstract

Scatterer size estimation from ultrasound backscatter has been used to improve the detection and classification of cancer. Estimates of scatterer size from tissues come from ultrasound backscattered signals that often have low signal-to-noise ratio (SNR). Coded excitation was explored as a means to increase the SNR of signals used in scatterer size estimation. The normalized backscatter coefficient was measured from tissue mimicking phantoms containing glass beads. The diameters of the glass beads were estimated by fitting the normalized backscatter coefficient to models for scattering from spheres [J. Acoust. Soc. Am. 23, 405–418 (1951)]. Two weakly-focused, single-element transducers (f0=5 MHz, −6 dB BW=4.2 MHz, f/3, and f0=10 MHz, −6 dB BW=9.1 MHz, f/4) were used in the measurements. For coded excitation, a linear FM chirp with a time bandwidth product of 40 was used. Three phantoms with average glass bead diameters of 30, 45, and 82 μm were scanned. Preliminary results indicated that estimate bias was reduced versus penetration depth for the coded excitation compared to conventional pulsing. In addition, estimate variance using the coded excitation technique was reduced because the SNR was increased. [Work supported by start-up funds from the University of Illinois at Urbana-Champaign.]