Comparison of contrast-enhanced fundamental imaging, second-harmonic imaging, and pulse-inversion harmonic imaging

RATIONALE AND OBJECTIVES. To investigate the feasibility of recent contrast -specific ultrasound techniques in depicting vascular flow and the effects of changing the output power of the transducer and insonation mode on contr ast enhancement, the authors performed an experimental study with a flow ph antom. METHODS. While changing the mechanical index and the sound insonation mode (continuous and intermittent), images were obtained with three contrast-enh anced ultrasound techniques: fundamental, second-harmonic, and pulse-invers ion harmonic imaging (PIHI) after a bolus injection of microbubble contrast agent. The images were compared on a time-intensity curve. RESULTS. In assessing fixed flow (10 cm/s), PIHI showed the best depiction of flow signal. In intermittent scanning, increases in the mechanical index caused stronger flow signals and longer enhancement duration in all techni ques. However, continuous scanning revealed poor depiction of flow signal r egardless of the technique or changes in the mechanical index because of si gnificant bubble destruction. CONCLUSIONS. Microbubble-enhanced PIHI with intermittent scanning at a high mechanical index can depict vascular flow highly effectively without short ening the duration of enhancement.