Nonlinear intravascular ultrasound contrast imaging

Area of Science:

• Medical Imaging
• Ultrasound Technology
• Biomedical Engineering

Background:

• Intravascular ultrasound (IVUS) is crucial for visualizing coronary arteries.
• Enhancing contrast-agent imaging in IVUS can improve diagnostic accuracy.
• Nonlinear imaging techniques offer potential for better signal differentiation.

Purpose of the Study:

• To investigate nonlinear contrast agent imaging using a prototype intravascular ultrasound (IVUS) system.
• To evaluate the feasibility of second harmonic (H40) and subharmonic (SH20) imaging with a small bubble contrast agent.
• To assess the potential applications in coronary lumen boundary detection and vasa vasorum imaging.

Main Methods:

• Utilized a prototype IVUS system with a mechanically scanned single-element transducer.
• Operated at 20 MHz (F20) for second harmonic imaging (H40) and 40 MHz (F40) for subharmonic imaging (SH20).
• Employed pulse-inversion and bandpass filtering to suppress tissue signals; conducted characterization and coronary phantom experiments.

Main Results:

• Second harmonic imaging (H40) improved contrast-to-tissue signal ratio (CTR) by up to 22 dB compared to fundamental frequency (F20).
• H40 imaging showed susceptibility to tissue propagation harmonics at pressures >0.3 MPa.
• Subharmonic imaging (SH20) was feasible across a pressure range (0.25-1.8 MPa) with significant tissue signal suppression.
• Successfully detected contrast agent within 1 mm vessels outside a 4 mm vessel in coronary phantom experiments.

Conclusions:

• Harmonic IVUS contrast imaging is feasible and demonstrates significant improvements in contrast detection.
• Subharmonic imaging offers robust tissue signal suppression, enhancing contrast visualization.
• This technique holds potential for improved coronary lumen boundary detection and vasa vasorum imaging.