Volumetric Ultrasound Localization Microscopy With Diverging Cylindrical Waves

Area of Science:

• Medical Imaging
• Ultrasound Technology
• Neuronanotechnology

Background:

• Transcranial ultrasound has limitations in neuroradiology, including low resolution and user dependency.
• Volumetric ultrasound localization microscopy (ULM) offers potential to overcome these limitations by breaching the diffraction limit.
• High-frame-rate 3-D ultrasound imaging for microbubble tracking through the skull remains challenging, particularly with portable systems.

Purpose of the Study:

• To develop and evaluate a ULM sequence for volumetric transcranial imaging.
• To address the challenges of high frame rate, signal-to-noise ratio (SNR), and portability in transcranial ULM.
• To assess the efficacy of cylindrical emissions for microbubble tracking through the skull.

Main Methods:

• Simulations, hydrophone measurements, and flow phantom experiments were used to evaluate the ULM sequence.
• Cylindrical emissions on multiplexed matrix probes were employed for volumetric transcranial imaging.
• Comparison of performance metrics between cylindrical and spherical emission geometries.

Main Results:

• Cylindrical emissions doubled peak acoustic pressure (up to 400 kPa) and improved volume rate (up to 180 Hz) compared to spherical emissions.
• ULM saturation rate improved by 60% through a skull phantom using cylindrical emissions.
• Microbubble velocity assessment error reduced from 33% with spherical waves to 5% with cylindrical waves.

Conclusions:

• The developed cylindrical volumetric ULM sequence enhances SNR and 3-D imaging capabilities for transcranial applications.
• Despite limitations in field of view and isotropic sensitivity, this method shows promise for ULM as a portable diagnostic tool.
• The technique could significantly benefit human diagnostics in neuroradiology, especially in portable settings.