Nonlinear contrast-enhanced intravascular ultrasound imaging with a commercial catheter

Subharmonic intravascular ultrasound (IVUS) imaging is under development for the assessment of vascular disease. However, subharmonic IVUS typically requires broadband imaging catheters that are not yet available clinically. The goal of this work was to investigate the feasibility of subharmonic IVUS imaging with a commercial catheter. This study was performed using an iLab system (Boston Scientific/Scimed, Natick, MA) equipped with custom transmit and receive electronics, and an Atlantis PV imaging catheter (center frequency: 15-MHz, -3 dB fractional bandwidth: 26%). A tissue-mimicking vessel phantom perfused with an ultrasound contrast agent (Targestar-P ®, Targeson Inc., San Diego, CA) was visualized with standard short-burst pulses and long-duration chirp excitation. The detection sensitivity of imaging was assessed versus decreasing contrast agent concentration. The contrast agent-infused regions could not be detected in fundamental and subharmonic images produced using standard short-burst excitation. Perfused regions were detected clearly in subharmonic images obtained with long-duration excitation with contrast-to-tissue ratios of up to 14 dB. Flow channels with diameters ranging from 2.2 mm down to 0.8 mm were visualized for contrast agent dilutions ranging from 1:1000 to 1:8000. These results demonstrate that subharmonic IVUS imaging is achievable despite transducer bandwidth limitations.