Ultrasonic Synthetic-Aperture Interface Imaging.

Area of Science:

• Acoustics
• Biomedical Imaging
• Signal Processing

Background:

• Synthetic-aperture (SA) imaging visualizes acoustic impedance contrast but assumes constant mass density and weak contrast, limiting its use for large objects.
• The band-limited nature of recorded data causes spatial blurring in SA volume imaging, quantified by the point spread function.
• SA volume imaging is typically valid under the Born approximation, suitable for weak contrasts.

Purpose of the Study:

• To introduce Synthetic-aperture (SA) interface imaging as an alternative to SA volume imaging.
• To characterize SA interface imaging for visualizing acoustic impedance discontinuities at tissue interfaces.
• To compare the performance of SA interface imaging and SA volume imaging.

Main Methods:

• Developed SA interface imaging, assuming constant wave speed and validity under the Kirchhoff approximation for small wavelengths relative to interface dimensions.
• Derived the interface spread function to quantify spatial blurring in SA interface imaging.
• Compared SA interface imaging with SA volume imaging using synthetic and experimental data of a large gelatin cylinder.

Main Results:

• SA interface imaging produces a vector image of acoustic impedance discontinuities at interfaces.
• SA interface imaging is blurred by an interface spread function (a tensor).
• Experimental results showed SA interface imaging peaking at the gelatin-water interface, unlike SA volume imaging which showed a peak and trough.

Conclusions:

• SA interface imaging provides a valuable alternative for visualizing acoustic impedance discontinuities, particularly for large objects where SA volume imaging is less effective.
• The method accurately localizes interfaces by imaging discontinuities in acoustic impedance.
• SA interface imaging demonstrates superior performance over SA volume imaging for large-scale interfaces.