Third harmonic imaging using pulse inversion

The pulse inversion (PI) technique can be utilized to separate and enhance harmonic components of a waveform for tissue harmonic imaging. While most ultrasound systems can perform pulse inversion, only few image the 3rd harmonic component. PI pulse subtraction can isolate and enhance the 3rd harmonic component for imaging on any ultrasound system capable of PI. PI was used to perform 3rd harmonic B-mode scans of a water-filled wire phantom on an experimental ultrasound system. The 3rd harmonic scans were compared to fundamental and 2nd harmonic scans on the same system. The 3rd harmonic image showed a 46% improvement in the lateral FWHM resolution compared to fundamental B-mode imaging at 75 mm depth and a 28% improvement compared to 2nd harmonic B-mode imaging. The axial FWHM resolution was improved by 35% and 30% for 3rd harmonic imaging compared to fundamental and 2nd harmonic imaging respectively. The improvements in spatial resolution and the fact that PI can isolate the 3rd harmonic suggest that it is advantageous to implement 3rd harmonic imaging on ultrasound systems capable of PI.