Block-switching in ultrasound imaging
Systems of generating and manipulating an ultrasound beam are disclosed. The system uses selective sets of ultrasound elements to generate an ultrasound beam, scanning the beam over a series of ultrasound elements in order to collected echo data covering an area, and generating an image from the resulting data. The scanning process includes shifting the set of ultrasound elements used to form the ultrasound beam by more than one ultrasound element (block-switching) between each step in the scanning process. This is accomplished without loss of image resolution by using area-forming techniques. The block-switching technique enables use of cross-correlation methods during image construction.
The present application is a continuation and claims the priority benefit of U.S. patent application Ser. No. 10/893,085 entitled “Block-Switching in Ultrasound Imaging” filed Jul. 16, 2004, which is a continuation and claims the priority benefit of U.S. patent application Ser. No. 10/039,922 entitled “Block-Switching in Ultrasound Imaging” filed Oct. 20, 2001 now U.S. Pat. No. 6,773,399; the disclosures of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention is related to medical devices and more particularly to ultrasound imaging.
2. Background
Ultrasound imaging is a common method of analysis used for examining a wide range of materials. The method is especially common in medicine because of its relatively non-invasive nature, low cost, and fast response times. Typically, ultrasound imaging is accomplished by generating and directing ultrasonic sound waves into a material under investigation in a transmit phase and observing reflections generated at the boundaries of dissimilar materials in a receive phase. For example, reflections are generated at boundaries between a patient's tissues. The reflections are converted to electrical signals by receiving devices (transducers) and processed, using beam-forming techniques known in the art, to determine the locations of echo sources. The resulting data is displayed using a display device such as a monitor.
Typically, the ultrasonic signal transmitted into the material under investigation is generated by applying continuous or pulsed electronic signals to a transducer. The transmitted ultrasound is commonly in the range of 1 MHz to 15 MHz. The ultrasound propagates through the material under investigation and reflects off of structures such as boundaries between adjacent tissue layers. As it travels, the ultrasonic energy may be scattered, resonated, attenuated, reflected, or transmitted. A portion of the reflected signals are returned to the transducers and detected as echoes. The detecting transducers convert the echo signals to electronic signals and furnish them to a beamformer. The beamformer calculates locations of echo sources along a line (beam), and typically includes simple filters. After beam-forming, an image scan converter uses the calculated positional information resulting from several beams, to generate two dimensional data that can be presented as an image. In prior art systems, the image formation rate (i.e., the frame rate) is limited by at least a pulse round trip time. The pulse round trip time is the time between the transmission of ultrasonic sound into the media of interest and the detection of the last reflected signals.
As an ultrasound pulse propagates through a material under investigation, additional harmonic frequency components are generated. These additional harmonic frequency components continue to propagate and, in turn, reflect off of, or interact with, other structures in the material under investigation. Both fundamental and harmonic signals are detected. The analysis of harmonic signals is generally associated with the visualization of boundaries or image contrast agents designed to re-radiate ultrasound at specific harmonic frequencies.
Ultrasound system 100 sends a series of ultrasound beam 170 through different paths to form an image with a cross-sectional area greater than the width of each individual ultrasound beam 170. Multiple beams are directed from ultrasound system 100 in a scanning or steering process. An ultrasound scan includes transmission of more than one distinct ultrasound beam 170 in order to image an area larger than each individual ultrasound beam 170. Between each transmit phase a receive phase occurs during which echoes are detected. Since each ultrasound beam 170, included in the ultrasound scan, requires at least one transmit/receive cycle, the scanning processes can require many times the pulse round trip time. Optionally, an ultrasound beam 170 is transmitted in several transmit/receive cycles before another ultrasound beam 170 is generated. If ultrasound transducers 110A-110H move relative to the material under investigation during the scanning process undesirable artifacts can be generated.
Some prior art systems use electronically controlled switches 410 and multiplexer 145 (
An ultrasound system including an array of ultrasound transducer elements configured to produce ultrasound beams is provided. The beams are generated using subsets of the ultrasound transducer elements, wherein the subsets differ by a shift of more than one transducer element. This “block-switching” is enabled by a block-switching multiplexer, and reduces the number of transmit/receive cycles required to generate an image of a given area without reducing the resolution of the image.
DETAILED DESCRIPTION OF THE INVENTIONThe invention uses broad-beam technologies to determine locations of echo sources and form an image. Detected echoes are processed using area-forming techniques to generate data that is optionally used to produce an image. In broad-beam technologies, the processes that determine lateral spatial resolution (focusing) occur during data processing of the detected signals. Thus, this method is different from prior art that accomplished focusing merely through timing of transducer element 110 (
In one embodiment of the invention, subsets 320A, 320C, and 320E of transducer array 310 are sequentially excited such that subset 320C is the only subset 320 of transducer elements 110A-110H operative between a time subset 320A is operative and a time subset 320E is operative. Each of the sequentially excited subsets 320A, 320C, and 320E is displaced by a shift of more than one transducer element 110. Thus, each subset 320A, 320C, and 320E differs by the addition of more than one transducer element 110 and the removal of more than one of the transducer element 110. The method of displacing sequentially excited subsets 320A, 320C, and 320E by a shift of more than one transducer element 110 is called “block-switching” and a transmit/receive switch 515 configured to execute this method is called a “block-switching switch.”
In the switching scheme shown in
The subsets 320A, 320C, and 320E of transducer array 310 used to generate each ultrasound beam 710A-710C are optionally differentiated by a displacement equal to or greater than a number of transducer elements 110A-110H in each subset 320A, 320C, or 320E. In various embodiments, this displacement is more than four or more than eight transducer elements. However, if the shift (displacement) is greater than the number of elements in each subset 320A, 320C, or 320E, image resolution, uniformity, and continuity may be degraded.
Differentiating subsets 320A, 320C, and 320E, used to form ultrasound beams 710A-710C, by a displacement of more than one transducer element 110 reduces the number of transmit/receive cycles required to image an area in comparison with prior art methods. For example, the prior art method illustrated in
The block-switching methods describe above are representative. Ultrasound system 500 should not be construed as being limited by or to the number of transducer elements 110A-110H shown in any of
Block-switching reduces the complexity of transmit/receive switch 515 and multiplexer 517 in comparison to the prior art. This reduced complexity occurs in embodiments wherein each output of beam transmitter 150 is not coupled to some transducer element 110 of transducer array 310. In contrast with the prior art, each transducer element 110 is optionally used to generate no more than two ultrasound beams 710A-710C. In various embodiments, each output from transmit/receive switch 515 is coupled to less than three or less than eight inputs to transmit/receive switch 515. In another embodiment, each output from transmit/receive switch 515 is coupled to less than eighty-seven percent of inputs to transmit/receive switch 515.
In one embodiment, each of the excited subsets 320A-320E overlap by a small number of transducer elements 110A-110H. This overlap is typically less than fifty percent and sometimes less than thirty-three percent of the size of subsets 320A-320E, and is optionally as small as one or two of transducer elements 110A-110H. A small overlap enables comparison between data generated using different ultrasound beams 710A-710C. In one embodiment, this comparison includes a cross-correlation calculation used to detect correlated changes in echo positions resulting from relative movement between scan head 510 and the material under investigation. These changes in echo positions potentially cause artifacts in images generated using different ultrasound beams 710A-710C. Cross-correlation results are used by computer code 540 to reduce the effect of the relative movement on the quality of the resulting image.
The cross-correlation technique and artifact reduction methods disclosed using
From the description of the various embodiments of the process and apparatus set forth herein, it will be apparent to one of ordinary skill in the art that variations and additions to the embodiments can be made without departing from the principles of the present invention. For example, transducer elements 110A-110H can be replaced by alternative ultrasound generating elements; transmit/receive switch 515 can be replaced by separate transmit and receive switches; and subsets 320 can be used to generate ultrasound beams 710 in various sequences.
In other embodiments, the methods and apparatus disclosed herein are applied to two-dimensional transducer arrays. In these embodiments, a “block” optionally includes a one-dimensional or a two-dimensional subset of the two-dimensional transducer array. The block switching technique can be extended to three and four-dimensional imaging systems, such as systems that include volume-forming and multidimensional-forming techniques.
Claims
1. A method for three-dimensional ultrasound imaging, comprising:
- exciting a first, second, and third subset of ultrasound transducer elements, wherein the second subset is displaced by more than one transducer element from the first subset and the third subset is displaced by more than one transducer element from the second subset, the sequential excitation of each subset generating consecutive ultrasound beams;
- directing the consecutive ultrasound beams into a material under investigation;
- detecting echoes generated by each of the three consecutive ultrasound beams; and
- generating three-dimensional echo location data using the detected echoes.
2. The method of claim 1, wherein two of the three subsets have no ultrasound transducer elements in common.
3. The method of claim 1, wherein each subset differs in position by at least fifty percent of the number of ultrasound transducer elements in the second subset.
4. The method of claim 1, wherein the second subset is the only subset of a plurality of ultrasound transducer elements operative between a time the first subset is operative and a time the third subset is operative.
5. The method of claim 1, wherein the center of the first subset is displaced from the center of the second subset by a distance greater than or equal to the width of two ultrasound transducer elements from the plurality of ultrasound transducer elements.
6. The method of claim 1, wherein the center of the second subset is displaced from the center of the third subset by a distance greater than or equal to the width of two ultrasound transducer elements in the plurality of ultrasound transducer elements.
7. The method of claim 1, wherein generating the three-dimensional echo location data includes area-forming.
8. The method of claim 1, further comprising generating an image using the three-dimensional echo location data.
9. The method of claim 8, wherein the resolution of the image is independent of overlaps between the first, second, and third ultrasound beams.
10. A method for three-dimensional ultrasound imaging comprising:
- directing three consecutive ultrasound beams into a material under investigation,
- wherein a second ultrasound beam overlaps with a first ultrasound beam by less than eighty-seven percent of the width of the second ultrasound beam, and a third ultrasound beam overlaps with the second ultrasound beam by less than eighty-seven percent of the width of the second ultrasound beam;
- detecting echoes generated by each of the three consecutive ultrasound beams; and
- generating three-dimensional echo location data using the detected echoes.
11. The method of claim 10, wherein generating the three-dimensional echo location data includes area-forming.
12. The method of claim 10, further comprising generating an image using the three-dimensional echo location data.
13. The method of claim 12, wherein the resolution of the image is independent of overlaps between the first, second, and third ultrasound beams.
14. A method for executing a three-dimensional ultrasound scan, comprising:
- selecting a first subset of ultrasound transducer elements for excitation from an array of ultrasound transducer elements;
- exciting the first subset of ultrasound transducer elements;
- generating a first ultrasound beam from the first excited subset of ultrasound transducer elements;
- transmitting the first ultrasound beam into a material under investigation;
- receiving a generated echo;
- selecting a second subset of ultrasound transducer elements from the array of transducers, the second subset differing from the first subset by a displacement of more than one transducer element when the three-dimensional ultrasound scan is determined to not be completed.
15. The method of claim 14, wherein the subsets have no ultrasound transducer elements in common.
16. The method of claim 14, further comprising:
- generating a second ultrasound beam from the second subset of ultrasound transducer elements;
- transmitting the second ultrasound beam into the material under investigation; and
- receiving a new generated echo.
17. The method of claim 14, further comprising selecting the subset of ultrasound transducer elements and executing a second three-dimensional ultrasound scan.
18. A method for executing a three-dimensional ultrasound scan, comprising:
- selecting a subset of ultrasound transducer elements for excitation from an array of ultrasound transducer elements;
- exciting the subset of ultrasound transducer elements;
- generating an ultrasound beam from the excited subset of ultrasound transducer elements;
- transmitting the ultrasound beam into a material under investigation;
- receiving a generated echo; and
- continuing to a query when the scan is determined to be complete.
19. The method of claim 18, further comprising selecting the subset of ultrasound transducer elements and executing a second three-dimensional ultrasound scan.
20. A method for forming a three-dimensional ultrasound image, comprising:
- executing a transmit/receive cycle for an ultrasound beam;
- generating echo data from the ultrasound beam;
- generating positional data from the echo data using area forming;
- storing the positional data;
- creating a composite set of positional data; and
- generating a three-dimensional image from the composite set of positional data.
21. The method of claim 20, further comprising executing a cross-correlation and adjusting the positional data in response to the cross-correlation.
22. The method of claim 20, further comprising displaying the three-dimensional ultrasound image.
Type: Application
Filed: Apr 9, 2008
Publication Date: Dec 25, 2008
Inventors: Xufeng Xi (Mountain View, CA), Glen McLaughlin (Saratoga, CA), Umit Tarakci (Hayward, CA)
Application Number: 12/082,412
International Classification: G01S 3/80 (20060101);