Sparse Orthogonal Encoding for Diverging Wave Ultrasound Imaging
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Solution Overview
Problem
Existing ultrafast ultrasound imaging techniques, such as diverging wave and synthetic aperture imaging, face challenges in achieving high frame rates while maintaining signal-to-noise ratio (SNR) and directivity, due to the limited aperture excitation and increased effective element size.
Innovation Solution
The use of sparse orthogonal encoding with diverging waves, where a subset of rows from an invertible orthogonal matrix, such as a Hadamard matrix, is employed to encode transmit signals, allowing for reduced insonifications while maintaining a large aperture for improved SNR and directivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If diverging wave imaging with virtual point sources is used, then frame rate is improved, but signal-to-noise ratio deteriorates due to limited aperture excitation
Solution Approach 1:
The aperture is segmented into multiple sub-apertures, each associated with a virtual point source. By dividing the full aperture into N sub-apertures and using orthogonal encoding across M virtual sources, the system achieves both high frame rates (through efficient sampling) and maintains SNR (through coherent combination of segmented aperture data).
Solution Approach 2:
The patent introduces a temporal dimension through orthogonal encoding sequences. Instead of simply using spatial aperture segmentation, it applies orthogonal codes across multiple transmit events, transforming a 2D spatial problem into a 3D space-time problem. This allows M virtual sources to be achieved with only N insonifications when M<N, by exploiting the additional temporal dimension.
2Productivity
If the number of insonifications is reduced for ultrafast imaging, then frame rate is improved, but image quality deteriorates
Solution Approach 1:
The patent changes the encoding parameter space by applying orthogonal codes to the transmit signals. This transforms the imaging problem from direct spatial sampling to coded excitation, where image quality is recovered through correlation processing. The orthogonal encoding allows fewer insonifications to carry equivalent information content to more traditional scans.
Solution Approach 2:
The patent creates virtual copies of the transmit aperture through orthogonal encoding. Each virtual point source represents a copied and coded version of the full aperture, allowing the system to synthesize multiple virtual sources (M) from fewer physical transmit events (N). This copying approach in the encoded domain enables ultrafast imaging with maintained image quality.
3Loss of time
If a subset of orthogonal matrix rows is used for encoding, then number of insonifications is reduced, but aperture coverage is limited
Solution Approach 1:
The patent employs feedback through correlation processing during image reconstruction. The orthogonal codes provide a known reference pattern that enables coherent integration and aperture synthesis. By correlating the received signals with the transmitted orthogonal codes, the system recovers full aperture coverage information even when using a subset of encoded transmit events.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables higher frame rates exceeding 1000 fps, improved SNR, and a broader angular insonification profile with enhanced directivity, effectively addressing the limitations of conventional ultrafast imaging techniques.
Implementation Method 1
transmit a plurality of encoded diverging acoustic waves into a medium... each diverging acoustic wave is generated by transmitting a respective set of encoded transmit signals
Implementation Method 2
detect a plurality of sets of acoustic signals back from the medium with a plurality of receive elements of the ultrasound array
Data Source
Figure 1A~2D
Figure 3A~3B
Figure 4
AI summary
Encoded transmit signals are provided to an ultrasound array such diverging ultrasound waves are sequentially transmitted. Each diverging ultrasound wave is generated by a respective set of encoded transmit signals, where each set of encoded transmit signals is encoded by a respective row of an NxN invertible orthogonal matrix. Only a selected subset of M rows, with N<M, is employed to encode the transmit signals. Sets of receive signals detected in response to the transmitted diverging ultrasound waves are decoded via a transposed matrix generated based on the invertible orthogonal matrix, with each set of decoded receive signals being associated with insonification via a subset of the ultrasound array elements in the fixed aperture. Synthetic aperture beamforming is performed on the decoded receive signals to generate an ultrasound image.