Frequency-Dependent F-Number Suppresses Grating Lobes and Improves the Lateral Resolution in Coherent Plane-Wave Compounding

Ultrafast imaging modes, such as coherent plane-wave compounding (CPWC), increase image uniformity and reduce grating lobe artifacts by dynamic receive apertures. The focal length and the desired aperture width maintain a given ratio, which is called the F -number. Fixed F -numbers, however, exclude...

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Bibliographic Details
Published in:IEEE transactions on ultrasonics, ferroelectrics, and frequency control ferroelectrics, and frequency control, 2023-09, Vol.PP (9), p.1-1
Main Authors: Schiffner, Martin F., Schmitz, Georg
Format: Article
Language:English
Subjects:
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Algorithms
Apertures
Beamforming
Compounding
Directivity
dynamic aperture
Far fields
Focusing
Fourier-domain beamforming
frequency-dependent apodization
grating lobes
Gratings
Heuristic algorithms
Imaging
Lobes
Plane waves
RF signals
ultrafast ultrasound imaging
Wires
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Summary:Ultrafast imaging modes, such as coherent plane-wave compounding (CPWC), increase image uniformity and reduce grating lobe artifacts by dynamic receive apertures. The focal length and the desired aperture width maintain a given ratio, which is called the F -number. Fixed F -numbers, however, exclude useful low-frequency components from the focusing and reduce the lateral resolution. Herein, this reduction is avoided by a frequency-dependent F -number. This F -number derives from the far-field directivity pattern of a focused aperture and can be expressed in closed form. The F -number, at low frequencies, widens the aperture to improve the lateral resolution. The F -number, at high frequencies, narrows the aperture to avoid lobe overlaps and suppress grating lobes. Phantom and in-vivo experiments with a Fourier-domain beamforming algorithm validated the proposed F -number in CPWC. The lateral resolution, which was measured by the median lateral full widths at half maximum of wires, improved by up to 46.8% and 14.9% in a wire and a tissue phantom, respectively, in comparison to fixed F -numbers. Grating lobe artifacts, which were measured by the median peak signal-to-noise ratios of wires, reduced by up to 9.9 dB in comparison to the full aperture. The proposed F -number thus outperformed F -numbers that were recently derived from the directivity of the array elements.
ISSN:0885-3010
1525-8955
DOI:10.1109/TUFFC.2023.3291612