Spatial coherence of backscatter for the nonlinearly produced second harmonic for specific transmit apodizations

Area of Science:

• Ultrasound physics
• Medical imaging
• Acoustics

Background:

• Correlation-based phase aberration correction in ultrasound imaging relies on high signal correlation.
• Spatial coherence differs between fundamental and second harmonic components in harmonic imaging.
• Understanding these differences is crucial for optimizing imaging techniques.

Purpose of the Study:

• To investigate the impact of transmit apodization on the spatial coherence of backscatter at the second harmonic.
• To compare the spatial coherence at the second harmonic versus the fundamental frequency.
• To identify optimal apodization strategies for improved harmonic imaging.

Main Methods:

• Experimental and simulation-based determination of effective apodizations for fundamental and second harmonic frequencies.
• Acquisition of 2D transverse cross-sections of ultrasonic fields using a hydrophone.
• Application of linear angular spectrum backpropagation and the Van Cittert-Zernike theorem for coherence prediction.

Main Results:

• Effective apodization at the second harmonic (2f) was consistently narrower than the transmit apodization.
• Three apodization functions (uniform, Riesz, trapezoidal) were analyzed.
• Specific transmit apodizations were shown to yield greater spatial coherence at the second harmonic compared to the fundamental.

Conclusions:

• Transmit apodization significantly influences the spatial coherence of backscatter at the second harmonic.
• Tailoring transmit apodization can enhance spatial coherence for improved phase aberration correction in harmonic ultrasound.
• This research provides insights into optimizing ultrasound imaging parameters for better diagnostic quality.