Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1998-11-25
2001-05-01
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06224556
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an ultrasound system and method for obtaining ultrasound data with an array of transducer elements. In particular, the transducer elements are spaced to create a sparse ultrasonic phased array.
Ultrasound systems include a beamformer and an image processor. The beamformer generates transmit waveforms and coherently sums reflected receive signals. The beamformer also filters the information. The filtering may be selectable between a harmonic and a fundamental frequency. For example, the filter isolates information associated with a second harmonic frequency of a fundamental transmit frequency. The coherently summed information is processed by the image processor to generate an image on a display.
The transmit waveforms from the beamformer are converted to acoustical energy, and the reflected acoustical energy is converted into receive signals by an array of transducer elements. In order to avoid grating lobes in steered transducer arrays, the distance from the center of a transducer element to the center of adjacent transducer elements is maintained at around one-half a wavelength of a transmit and receive center frequency. In non-steered arrays, this distance is on the order of one wavelength. Increasing the lateral resolution by using a larger transducer extent in the lateral dimension would require a greater number of transducer elements. However, increasing the number of elements increases the cost and complexity of the transducer and the associated beamformer. For example, the number of beamformer transmit and receive channels is increased.
BRIEF SUMMARY
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the preferred embodiment described below includes a method and system for obtaining ultrasound data with a sparse array of transducer elements. The transducer elements are spaced. About one to two wavelengths of a highest operating frequency (i.e., the transmit fundamental or the harmonic receive frequency) separates the center of each transducer element from the center of any adjacent transducer element for a steered array. For a non-steered array, the separation is about two to four wavelengths of the highest operating frequency, such as a second harmonic receive frequency. While this spacing may generate grating lobes, the beamformer of the ultrasound system is configured to transmit at a fundamental frequency and to filter and isolate receive information at a harmonic of the fundamental transmit frequency. The resulting two-way beam pattern is effected less by the grating lobes. The image generated as a function of the harmonic information has little or no artifacts created as a function of the sparse spacing of the transducer elements.
Given a set number of beamformer transmit channels, the sparse spacing may allow for a larger aperture. A larger aperture generates a narrower beam in the azimuthal dimension of a one-dimensional transducer. By generating a narrower beam, better azimuthal resolution is obtained. Alternatively, the number of transmit channels may be reduced by one-half to provide a beam width that is the same or similar to a beam generated with transducer elements having a one-half wavelength spacing of the highest operating frequency for a steered array. By using fewer transmit channels to obtain the same beam width, the space required by the number of individual electrical traces connecting each transducer element to the beamformer is reduced. The reduced required space is beneficially used in catheter or intravascular transducers.
In one aspect of the embodiments described below, acoustic energy is generated at a fundamental frequency. Using a steered array of transducer elements that are spaced by at least about one wavelength of a highest operating frequency, such as a second harmonic of the fundamental transmit frequency, information is obtained at a harmonic of the fundamental transmit frequency from reflected acoustic energy. In another aspect, a non-steered array has transducer elements that are spaced by at least about two wavelengths of the highest operating frequency.
Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments.
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Jackson John I.
Plugge Jay S.
Schwartz Jodi L.
Acuson Corporation
Brinks Hofer Gilson & Lione
Lateef Marvin M.
Patel Maolin
Summerfield, Esq. Craig A.
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