Diffraction Effects and Compensation in Passive Acoustic Mapping.

Area of Science:

• Acoustics
• Medical Imaging
• Biomedical Engineering

Background:

• Noninvasive monitoring of therapeutic ultrasound relies on sensing acoustic emissions.
• Diagnostic ultrasound arrays are used to detect, localize, and quantify nonlinear sources like cavitation.
• Existing beamforming algorithms often assume ideal array element diffraction, which differs from reality.

Purpose of the Study:

• To identify discrepancies between ideal and actual element diffraction patterns in diagnostic arrays.
• To quantify the effect of diffraction correction on the performance of cavitation mapping beamformers.
• To improve the accuracy of quantitative analyses in therapeutic ultrasound safety and efficacy assessments.

Main Methods:

• Performed calibration measurements on a diagnostic linear array to obtain real element diffraction data.
• Calculated diffraction correction terms based on measured diffraction patterns.
• Applied these corrections to cavitation emission data from soft tissue phantom experiments.

Main Results:

• Measured diffraction patterns significantly deviated from ideal element forms, especially at higher frequencies and shorter distances.
• Diffraction compensation increased cavitation energy estimates by up to a factor of 5.
• Bias between two beamforming algorithms was substantially reduced after applying diffraction corrections.

Conclusions:

• Measured array responses are crucial for validating analytical models and minimizing biases in ultrasound imaging.
• Diffraction compensation is essential for accurate quantitative analysis in therapeutic ultrasound monitoring.
• Implementing diffraction correction enhances the reliability of safety and efficacy assessments for therapeutic ultrasound procedures.