Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1999-03-31
2001-01-30
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06179781
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a medical diagnostic ultrasound system and method for improving Doppler processing, such as color flow imaging. In particular, increasing the accuracy of Doppler estimates is provided by using signals at multiple frequency bands.
Doppler imaging comprises receiving signals in a single frequency band, such as at a fundamental frequency band or at a second harmonic frequency band of the fundamental frequency band. Typically, the frequency band is narrowly defined within the available broadband system bandwidth, increasing the amount of transmitted power and the signal to noise ratio (SNR).
One ensemble of received signals is processed to estimate motion at each point in space along an ultrasound line. This process is repeated over many ultrasound lines within an image frame.
Doppler imaging of tissue and blood is a qualitative diagnostic tool. The tool remains qualitative partly due to the inaccuracies of estimates. The demand for adequate frame rates, diagnostic resolution, and reasonable interrogated areas dictate that an ultrasound system typically only transmit 2 to 16 pulses to insonify any distinct point in space. This constraint may create estimate drop-outs in flow fields and demand extensive spatial and/or temporal averaging of estimates resulting in inaccurate differentiation between flow and tissue.
Some processes to increase sensitivity to Doppler velocities above conventional maximum velocity detection limits use signals at two different frequency bands. Conventional Doppler systems may not provide for accurate detection of velocities beyond a maximum value determined primarily by the center frequency within a single receive band. The sensitivity to velocities above this limit (the aliasing limit) is increased by using two different frequency bands. The difference between Doppler frequencies obtained from two separate narrow frequency bands is calculated. Since this difference Doppler frequency is less than the Doppler frequency from either of the two frequency bands independently, the maximum detect able Doppler frequency is extended.
For example, Powers describes in U.S. Pat. No. 4,534,357 a system that transmits broad, single band, pulses and then processes receive signals from two narrow receive bands for each broadband pulse transmitted. In other examples, Fehr in U.S. Pat. No. 5,046,500 and Burckhardt in U.S. Pat. No. 5,183,047 describe systems that transmit pulses composed of two separate narrow frequency bands and then process signals from a corresponding two narrow receive bands for each transmitted pulse. However, methods extend the maximum detectable velocities only.
In Ultrasound Imaging Enhancement Methods and Systems, by Ismayil Guracar et. al., U.S. application Ser. No. 08/838,920, now U.S. Pat. No. 5,961,460, filed Apr. 11, 1997, imaging enhancements using two different frequency bands are disclosed. In one embodiment, two different types of scan-converted images are combined into a single image by using a two-dimensional look-up-table (LUT). For example, an image of contrast agents corresponding to a harmonic frequency band is combined with an image corresponding to a fundamental frequency band. In one further embodiment in the above referenced application, “either or both of the fundamental and harmonic images are generated from signals detected by the Doppler detector 22 with no clutter filtering” (page 16).
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 Doppler processing of information at two different frequency bands.
Signals from two or more unique frequency bands are processed separately to detect motion. The resulting Doppler values of each parameter, such as velocity, energy, and variance parameters, are averaged or otherwise combined. One of the average, the Doppler values at each frequency band and a null value are selected for further processing and display. The resulting Doppler images may have improved accuracy and precision, without a loss in frame rate, resolution or displayed area. Further, the parameter selection process can be used to further improve differentiation between blood flow and clutter.
Using signals at different frequency bands allows for more effective use of unused bandwidth to increase information content and improve estimation accuracy. One of or more of the two or more receive frequency bands may be within the transmitted fundamental frequency band or within harmonic frequency bands of the transmitted fundamental frequency band. The increased information content generated by using two separate narrow receive frequency bands is used to improve many aspects of motion detection, not just the sensitivity to velocities beyond the conventional maximum detectable velocities.
In one embodiment, signals at two different frequency bands are used to further improve detection of velocities beyond the conventional limit. Energies of one narrow frequency band at higher frequencies is exposed to more significant attenuation than energies of a lower frequency band, contributing to inferior SNR and potentially poor velocity estimates in some cases. Energy estimates are used to identify inferior SNR. Energy estimates are screened to determine application of an algorithm to detect velocities beyond the individual conventional maximum velocity limits for either of the two narrow frequency bands.
In a first aspect, a medical diagnostic ultrasound method and system for Doppler processing are provided. First and second receive signals at first and second frequency bands, respectively, are obtained. The first frequency band is different than the second frequency band. First and second Doppler values of a same type of Doppler parameter are determined from the first and second receive signals, respectively. A value is selected from a group consisting of two or more of: the first Doppler value, the second Doppler value and a third Doppler value that is a combination of the first and second Doppler values. A Doppler display responsive to the selected value is generated.
In a second aspect, other medical diagnostic ultrasound systems and methods for Doppler processing are provided. First and second receive signals at first and second frequency bands, respectively, are obtained, where the first frequency band is different than the second frequency band. First and second Doppler values of a same type of Doppler parameter from the first and second receive signals, respectively, are generated. The first and second Doppler values are combined, where the combination is responsive to a function selected from the group consisting of: addition, multiplication, division and combinations thereof An image responsive to the combination is generated.
In a third aspect, yet another medical diagnostic ultrasound method for Doppler processing is provided. A plurality of pulses are transmitted along a first scan line. The plurality comprises a flow sample count. A plurality of samples responsive to the plurality of pulses, respectively, are received. The plurality of samples are separated into first and second sets of receive signals responsive to respective first and second frequency bands where a number of the first and second receive signals for each depth is at least about twice the flow sample count for a single frequency band. First and second sets of Doppler values of a same parameter responsive to the first and second sets of receive signals, respectively, are determined. The first and second sets of Doppler values are combined, wherein the combination increases an accuracy of the combined Doppler values.
In a fourth aspect, a medical diagnostic ultrasound method for Doppler processing is provided. First and second Doppler velocity values at first and second frequency bands, respectively, are obtained where the first frequency band is different than the second frequency band. First and second Doppler e
Acuson Corporation
Brinks Hofer Gilson & Lione
Imam Ali M.
Lateef Marvin M.
Summerfield Craig A.
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