Title

Spread spectrum pulse compression in ultrasonic tissue imaging

Date of Completion

January 1997

Keywords

Engineering, Biomedical|Engineering, Electronics and Electrical

Degree

Ph.D.

Abstract

Ultrasound has become a major medical imaging modality whose performance continues to improve among technological advances. Existing systems could benefit from the enhanced system performance in such essential areas as signal-to-noise ratio (SNR), peak power requirements, and minimum detectable signal. Acoustic peak pressure levels are limited in medical ultrasound due to safety concerns. This dissertation explored how pulse compression techniques can affect a reduction in ultrasound acoustic peak pressure levels by spreading the power spectrum over a longer time duration. While maintaining system range resolution, it accomplished this by improving the SNR, and thus sensitivity, for a given transmit power.^ For this research, a digital, real-time, Barker Coded, bi-phase modulator was designed and constructed, as well as a simple ultrasonic test tank containing both synthetic targets and excised goat's liver parenchyma. A practical Barker coded ultrasonic pulse compression system with correlation sidelobe suppression was not realized prior to this research. The motivating theory of this prototype system, as well as physical performance results, are presented here. It was found that for 13 bit Barker code compression, the expected increase in signal-to-noise ratio of 11 dB was realized, while at the same time maintaining greater than 30 dB of instantaneous dynamic range. ^