Dalhousie University

Katherine Latham

Jeremy Brown

Christopher Samson

Robert Adamson

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 N×N 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.

Systems and methods of sparse orthogonal diverging wave ultrasound imaging

Fresnel elevation focusing at a selected elevation angle is performed by transmitting a sequential set of Fresnel-focused ultrasound pulses, where a different Fresnel phase pattern is used for each pulse, and where the receive signals are coherently compounded. The different Fresnel patterns cause the secondary lobe energy to be reduced via averaging of variations of the pressure fields in the secondary lobe regions. In some embodiments, the method of coherently compounded Fresnel focusing is combined with coherently compounded defocused wave (e.g. plane wave or diverging wave) imaging in the azimuth direction. Each of the elevation slices are collected by changing the Fresnel patterns respectively employed when the sequence of plane waves or diverging waves are transmitted, such that the coherent compounding can benefit both planes simultaneously. Hadamard receive encoding and subsequent dynamic receive beamforming may be employed to further improve performance in the elevation direction.

Systems and methods for ultrasound beamforming using coherently compounded Fresnel focusing

Systems and methods are disclosed for performing imaging with a crossed-electrode ultrasound transducer array, where ultrasound transducer array is configured for focusing in one direction via conventional time-delay phased array beamforming, and for focusing in a second direction via a Fresnel aperture formed via the application of bias voltages. The ultrasound transducer array connections are switched between transmit and receive operations, such that the Fresnel aperture is generated in the first direction upon transmit, and in the second direction upon receive. One or both of the transmit Fresnel aperture and the receive Fresnel aperture are configured as a set of delay-corrected Fresnel sub-apertures, where the delay associated with each Fresnel sub-aperture is selected to compensate for variations in path lengths between the Fresnel sub-apertures and the focal point. The use of multiple Fresnel sub-apertures and time delay corrections overcomes problems associated with steering-induced bandwidth degradation.

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Dartmouth, Canada

Katherine Latham