Frequency-Dependent Spatial Coherence in Conventional and Chirp Transmissions.

Area of Science:

• Medical Imaging
• Biomedical Engineering
• Acoustics

Background:

• Adaptive ultrasound imaging requires accurate characterization of image quality at various frequencies.
• Current methods for assessing frequency-dependent tissue properties are time-consuming.
• Improving target conspicuity in ultrasound relies on balancing resolution, signal-to-clutter, and speckle.

Purpose of the Study:

• To investigate the use of broadband linear frequency-modulated transmissions (chirps) for efficient characterization of frequency-dependent tissue spatial coherence.
• To evaluate the ability of chirps to replicate coherence measurements obtained by conventional single-frequency pulses.
• To assess the feasibility of using chirps for real-time adaptive imaging strategies.

Main Methods:

• Chirps were used to interrogate frequency-dependent spatial coherence.
• Coherence measurements from chirps were compared to those from conventional pulses across fundamental and harmonic frequencies.
• Simulations and experimental measurements were performed using uniform phantoms, porcine abdominal models, and human liver models.

Main Results:

• Chirps accurately replicated the mean coherence and its distribution over frequency in uniform phantoms.
• Prediction accuracy of coherence improved with increasing chirp length.
• Chirps successfully predicted frequency-dependent coherence decreases in porcine and human liver models for both fundamental and harmonic imaging.

Conclusions:

• Broadband chirps offer an efficient and viable strategy for variable frequency coherence mapping.
• This approach facilitates real-time implementation of frequency-based adaptive ultrasound imaging.
• Chirp-based coherence mapping can enhance target conspicuity by optimizing imaging parameters dynamically.