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Publication Number
US-9675316-B2
Publication Date
2017-06-13
Expiration Date
Abstract
Ultrasound diffraction-grating transducers produce beams at an angle to their face, which makes them useful for Doppler measurement of scattering fluids such as blood. The present invention discloses a diffraction-grating transducer, with the capability to focus transmitting or receiving beams to a desired point in space. This focusing capability leads to greater sensitivity when the diffraction-grating transducer is used as a receiver, and greater concentration of ultrasound energy when used as a transmitter. The focusing is achieved by using curved elements instead of the straight ones in conventional diffraction-grating transducers, and by using non-uniform spacing among these elements rather than the uniform spacing of conventional diffraction-grating transducers. Methods of computing the proper curvature of the elements and their spacing for a desired focal point in space are provided.
Core Innovation
The invention relates to an ultrasound diffraction-grating transducer (DGT) configured to focus transmitting and/or receiving ultrasound beams to a desired spatial focal point. A focused DGT (F-DGT) uses curved diffraction-grating elements and non-uniform spacing between elements, instead of the uniform spacing used in conventional DGTs, so that wavefronts converge to the desired focal point to concentrate ultrasound energy and improve sensitivity for receiving.
A key geometric condition is that the difference in distances from the desired focal point to neighboring circular segment elements is λ/2, where λ is the wavelength of the ultrasound beam. The element curvature and element placement are calculated for a chosen focal point using this λ/2 path-length relationship together with an alternating-phase excitation concept.
The F-DGT is implemented with a fan shape transmitter/receiver using circular segment elements disposed around a common center point at a radius from that common center point. The document further describes Doppler blood-velocity measurement using the focused transmitting and receiving behavior and determining blood velocity based on shifted frequency caused by scatterers flowing through a lumen.
In the example use case, blood velocity in a radial artery is measured at varying depths beneath a skin surface using one or two F-DGTs that provide different focal depths. The disclosure also discusses bus-bar interconnection of alternating-phase elements and notes optional imaging using focused transmit/receive behavior and reciprocity.
Claims Coverage
The independent claims cover three related inventive setups: an ultrasound transducer for measuring flow velocity using a transmitter and a fan shape receiver DGT with non-uniformly spaced circular segment elements focused to a desired focal point, a method of measuring blood velocity using similar DGT focusing and determining velocity from shifted frequency in received signals, and a specialized radial-artery configuration using first and second DGTs with different focal depths below the skin. Across these independent claims, the core inventive features are the non-uniform spacing of circular segment elements arranged around a common center point to satisfy a λ/2 distance difference to a desired focal point, beam forming with wavefront convergence, and beam perpendicularity to the lumen axis, with specialized structural and interconnect constraints in dependents.
Fan shape receiver DGT with non-uniformly spaced circular segment elements focused with λ/2 to a desired focal point
A diffraction-grating transducer (DGT) disposed adjacent to a transmitter, the DGT comprising a fan shape receiver that forms a receiving beam, the receiver comprising an array of circular segment elements disposed around a common center point at a radius, wherein any two neighboring circular segment elements are spaced at a non-uniform spacing, wherein a difference in distances from a desired focal point inside the lumen to each of the neighboring circular segment elements is λ/2, and wherein wavefronts of the receiving beam converge to the desired focal point.
Perpendicular ultrasound beam excitation relative to lumen axis
A transmitter configured to excite an ultrasound beam perpendicular to the axis of the lumen, with the DGT disposed adjacent to the transmitter such that the receiving beam and wavefront convergence relate to the desired focal point inside the lumen.
Blood-velocity determination from shifted frequency in received signals with a focused DGT
A method comprising exciting from a transmitter an ultrasound beam with wavelength λ perpendicular to the axis of the lumen; receiving signals from the DGT; and determining the velocity of blood based on shifted frequency in the received signals, where the shifted frequency is caused by the scatterers flowing through the lumen, the DGT having a fan shape receiver with an array of circular segment elements having non-uniform spacing and a λ/2 distance difference to a desired focal point with wavefront convergence.
First and second DGTs with different desired focal point depths below skin for radial artery flow-velocity measurement
An ultrasound transducer for measuring velocity of flow in a lumen of a radial artery beneath a skin surface, with a transmitter exciting an ultrasound beam perpendicular to the lumen axis, a first DGT disposed adjacent to one side of the transmitter with a first fan shape receiver and a first array of circular segment elements focused to a first desired focal point via non-uniform spacing and a λ/2 distance difference, and a second DGT disposed adjacent to the opposite side of the transmitter with a second fan shape receiver and a second array of circular segment elements focused to a second desired focal point via non-uniform spacing and a λ/2 distance difference, wherein the first and second desired focal points are at different distances below the skin surface.
Across the independent claims, the inventive coverage centers on DGTs with fan-shaped receivers/transmitters using circular segment elements arranged around a common center point with non-uniform spacing, where neighboring elements differ in distance to a desired focal point by λ/2 to enforce wavefront convergence, combined with excitation perpendicular to the lumen axis and velocity determination based on shifted frequency caused by flowing scatterers. A further independent claim adds a radial-artery configuration using two DGTs that produce different focal depths below a skin surface.
Stated Advantages
Improves sensitivity (receiver) and concentrates ultrasound energy (transmitter) by using curved diffraction-grating elements and non-uniform spacing to focus to a desired spatial focal point.
Documented Applications
Doppler blood-velocity measurement in a radial artery at varying depths beneath a skin surface using one or two focused DGTs with different focal depths.
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