System and method for providing variable ultrasound analyses in a post-storage mode

A system and method for accumulating ultrasound information from a region of interest during a storage period are disclosed. The accumulated ultrasound information is then processed during a post-storage operation to provide a number of various and selectable analysis and display modes. Ultrasound echo signal data comprising, for example, a complete set of raw RF signal samples (or the quadrature signals I & Q) are accumulated in a cinescan memory during a storage period for multiple range positions along one or more scan lines covering a region of interest. Line interleaving and multi-line acquisition techniques may be employed in data accumulation. The accumulated echo signal data is processed during a post-storage operation to provide a number of various and selectable analysis and display modes. During the post-storage playback operation, any known signal processing and data manipulation techniques, which have conventionally been carried out in real-time during a scanning session, may be employed. The various known parameters of signal processing and data manipulation may be selectably modified during post-storage playback to optimize the displayed output. For example, in an off-line playback mode, the system operator may select any scan line and Doppler gate location and width within the region of interest for spectral Doppler analysis or for color M-mode analysis. The system operator may also manually set and reset one or more beam/vessel angles during the off-line playback mode to provide quantitative velocity color mapping. Other parameters such as spectrum scale, Doppler dynamic range, Doppler gain, baseline and color mapping may also be modified during off-line playback. Other known signal processing operations such as noise suppression, filtering, low intensity rejection and/or fixed target canceling may be performed, and the parameters thereof adjusted, during the post-storage operation.

CROSS-REFERENCE TO RELATED APPLICATIONS
 None
 STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
 Not applicable.
 BACKGROUND OF THE INVENTION
 The present invention relates to ultrasound systems which image anatomical
 structures and the movement thereof. More particularly, the present
 invention relates to a method and apparatus for accumulating and storing a
 complete set of ultrasound information from a region of interest during a
 scanning period and then, in a post-scanning operation, processing the
 stored ultrasound information to provide a number of various and
 selectable analysis and display modes.
 Doppler ultrasound systems rely on the Doppler effect to detect movement by
 measuring the change in frequency between a transmitted ultrasound signal
 and the retuning echoes. If it is necessary or desirable to limit Doppler
 analysis only to echoes returned from a structure at a known depth, pulsed
 ultrasound is employed. Pulsed ultrasound allows the time for the
 ultrasound signal to make a round trip from the transmitter to the target
 and back to the receiver to be measured and the depth of reflecting
 structures calculated. In pulsed Doppler systems the operator has the
 opportunity of determining the depth from which Doppler signals are to be
 collected. In practice this is done by selectively ignoring signals
 returning to the receiver until a selected time interval after
 transmission of the ultrasonic pulse. The receiver is then switched on for
 a further short interval, during which Doppler information is collected.
 The duration of this collection interval determines the length of the data
 collection volume within the tissue. The sensitive zone created by this
 technique is commonly referred to as the "range gate" or "Doppler gate".
 Spectral Doppler uses pulsed Doppler techniques to measure the velocity of
 targets, such as blood cells within a vessel, at a predefined depth.
 Usually a two-dimensional B-mode ultrasound image is used to locate the
 vessel of interest. The system operator then sets the Doppler gate to
 correspond to the location (depth) and width of the vessel along the
 appropriate ultrasound beam or scan line. Once the Doppler gate is set, a
 number of clinically useful analyses can be made. For example, spectrum
 analysis of the Doppler shift frequencies provides information regarding
 the range of different velocities within a vessel. A blockage or stenosis
 within a blood vessel, for example, will create a wider range of
 velocities and, therefore, a broader spectrum of Doppler shift frequencies
 would be observed than in the case of a healthy vessel. A quantitative
 velocity analysis can be made if the angle between the ultrasound beam and
 long axis of the vessel is known. Many conventional ultrasound systems
 permit the operator to set the beam/vessel angle by tracing a line along
 the axis of the vessel under examination.
 Because of the rapidity and transient nature of abnormal blood flow
 patterns and other movements such as cardiac contractions, Doppler
 ultrasound systems may use recording systems to store a series of images.
 These images may then be played back at slow speed or frame by frame in a
 post-scanning operation. Video recorders or a digital memory (often
 referred to as a "cine loop") capable of recording a few seconds worth of
 images are incorporated into many conventional ultrasound systems. The
 information stored by and played back from a typical cine loop is
 generally limited by the analysis being performed during recording. The
 reason for this limitation is that a conventional cine loop receives data
 produced after the echo signals have been processed and prepared for
 display. Therefore, the cine loop stores only the data resulting from a
 particular processing operation carried out upon the echo signals. The
 processing operation is determined by the present mode of operation and
 parameter settings. The processed data may ignore and/or eliminate certain
 information from the echo signals. For example, if color flow imaging were
 being performed on one sub-region within a region of interest, the only
 information that is stored and available for playback may be the same
 color flow image from the same sub-region. Similarly, post-scanning
 playback of a spectral Doppler analysis is limited by the Doppler gate
 location and width set prior to initiating the cine loop recording.
 Information contained in echoes received outside the Doppler gate "window"
 or along non-selected scan lines is ignored and, therefore, lost forever.
 Also, the accuracy and usefulness of a quantitative velocity measurement
 would depend on the beam/vessel angle traced during the original scan.
 The above mentioned limitations of known cine loop schemes lead to several
 disadvantages. For example, each time a different kind of Doppler analyses
 is undertaken, a different Doppler gate location or width is set or a
 different sub-region is selected for color flow imaging, an additional
 scanning period must be initiated and new information must be stored in
 the cine loop. Analyses of different structures at multiple gate locations
 at the same moment in time is not possible. Also, an abnormality
 recognized in a recorded image after the patient has left, cannot be
 analyzed in greater detail unless the patient returns for a new scanning
 session (and then the abnormality present during the original scanning
 session may not reveal itself). Images that are recorded while inaccurate
 or less than optimal parameters are set may be useless. Anything that
 increases the length or number of ultrasound scanning sessions, may
 increase patient exposure time, patient discomfort and procedure costs.
 Furthermore, studies employing contrast agents are limited in the number
 of different analyses that can be performed during the rapid decay of the
 contrast agent.
 A need remains for an improved ultrasound system to overcome the
 above-identified difficulties and limitations. It is an object of the
 present invention to meet this need.
 SUMMARY OF THE INVENTION
 A system and method for accumulating unprocessed ultrasound information
 from a region of interest during a storage period is provided. The
 accumulated ultrasound information is then processed during a post-storage
 operation to provide a number of various and selectable ultrasound
 movement analysis and display modes.
 Ultrasound echo signal data comprising, for example, a complete set of RF
 signals (or the quadrature signals I & Q) are accumulated in a cinescan
 memory during a storage period for multiple range positions along a scan
 line. Line interleaving techniques may be used to simultaneously
 accumulate ultrasound information from multiple scan lines covering a
 region of interest. Optimally, the maximum available pulse repetition
 frequency (PRF) may be used. Multiple line acquisition (MLA) may be used
 to increase the size or density of the region of interest from which
 ultrasound information may be accumulated during the storage period.
 The accumulated echo signal data is then processed during a post-storage
 operation to provide a number of various and selectable ultrasound
 movement analysis and display modes. During the post-storage playback
 operation, any known signal processing and data manipulation techniques,
 which have conventionally been carried out in real-time during a scanning
 session, may be employed. The various known parameters of signal
 processing and data manipulation may be selectably modified during
 post-storage playback to optimize the displayed output. For example, in an
 off-line playback mode, the system operator may select any scan line and
 Doppler gate location and width within the region of interest for color
 M-mode analysis or for spectral Doppler analysis. The system operator may
 also select any sub-region within the region of interest for color flow or
 tissue velocity imaging. Other parameters such as spectrum scale, Doppler
 dynamic range, Doppler gain, baseline and color mapping may also be
 modified during off-line playback. Other known signal processing
 operations such as noise suppression, filtering (including wall motion
 filtering), low intensity rejection and/or fixed target canceling may be
 performed, and the parameters thereof adjusted, during the post-storage
 operation.
 The ultrasound system according to a preferred embodiment of the present
 invention may also provide manual beam/vessel angle correction during
 playback. Beam/vessel angle correction may be employed for a number of
 imaging modes such as spectral Doppler and color mapping of mean and/or
 maximum velocity. In the case of color mapping, a quantitative movement
 analysis is provided by angle correction for one or more vessels within
 the region of interest.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 A method and apparatus are described for accumulating and storing a
 complete set of ultrasound echo information from a region of interest
 during a scanning period and then, in a post-storage operation, performing
 one or more ultrasound movement analyses, such as Doppler analyses, on the
 stored echo information from a plurality of selectable ultrasound movement
 analyses. In the following description, numerous specific details are set
 forth in order to provide a thorough understanding of the preferred
 embodiment of the present invention. It will be apparent, however, to one
 of ordinary skill in the art that the present invention may be practiced
 without these specific details.
 A block diagram for an ultrasound system (generally indicated at 10)
 according to a preferred embodiment of the present invention is shown in
 FIG. 1. The ultrasound system 10 includes a transmitter 12 which drives
 transducers 14 within a probe 16 to emit pulsed ultrasonic signals into a
 body. The ultrasonic signals are backscattered from structures in the
 body, like blood cells or muscular tissue, to produce echoes which return
 to the transducers 14. The echoes are detected by a receiver 18. The
 received echoes are passed through a beamformer 19, which performs beam
 forming and outputs an RF signal. The RF signal then passes through an RF
 processor 20. According to a preferred embodiment of the present
 invention, the RF signal data may then be routed directly to a "cinescan"
 memory 22 for storage. The term "cinescan" is used to distinguish the
 cinescan memory 22 from a conventional cine loop memory. Alternatively,
 the RF processor 20 may include a complex demodulator (not shown) that
 demodulates the RF signal to form I, Q data pairs representative of the
 echo signals prior to storage in cinescan memory 22.
 Ultrasound system 10 also includes a signal processor 24 to process the
 received echo signal data (i.e., RF signal data or I, Q data pairs) and
 prepare an image for display on display 26. The signal processor 24 is
 adapted to perform one or more processing operations from a plurality of
 selectable processing operations on the received echo signal data. Echo
 signal data may be processed and displayed in real-time during a scanning
 session as the echo signals are received. Additionally or alternatively,
 according to a preferred embodiment of the present invention, the echo
 signal data may be stored in cinescan memory 22 during a scanning session
 and then, in a post-storage (off-line) operation, retrieved from cinescan
 memory 22, processed by signal processor 24 and displayed on display 26.
 Preferably the cinescan memory 22 is of sufficient capacity to store
 several seconds of echo signal data for multiple range positions along
 multiple scan lines. The echo signal data is stored in a manner to
 facilitate retrieval thereof according to scan line, range position and
 elapsed time from the start of the scanning period. Cinescan memory 22 may
 comprise any known data storage medium. Cinescan memory 22 may also allow
 the archiving of echo signal data from multiple scanning sessions and/or
 multiple patients.
 Ultrasound system 10 may also include a conventional cine loop memory 28
 for recording displayed images or post-processed echo signal data.
 The signal processor 24 may employ any known signal processing and data
 manipulation techniques to provide any known ultrasound mode or analysis
 that has conventionally been carried out in real-time during a scanning
 session. However, these signal processing and data manipulation techniques
 may be carried out in a post-storage (off-line) operation on stored echo
 signal data. Furthermore the various known parameters of signal processing
 and data manipulation may be selectably modified during off-line playback
 to optimize the displayed output. For example, the operator may select any
 sub-region within the region of interest for color flow or tissue velocity
 imaging or any scan line within the region of interest for color M-mode
 analysis or for spectral Doppler analysis. In the case of spectral Doppler
 analysis the operator may also select any Doppler gate location and width
 along the scan lines within the region of interest. Also signal processing
 operations such as noise suppression, filtering (including wall motion
 filtering), low intensity rejection and/or fixed target canceling may be
 performed, and the parameters thereof adjusted, during the post-storage
 operation. Parameters such as spectrum scale, Doppler dynamic range,
 Doppler gain, baseline and color mapping may also be modified during
 off-line playback.
 The ultrasound system according to a preferred embodiment of the present
 invention may also provide manual beam/vessel angle correction during
 playback. Beam/vessel angle correction may be employed for a number of
 imaging modes such as spectral Doppler and color mapping of mean and/or
 maximum velocity. In the case of color mapping, the operator may manually
 set the beam/vessel angle by tracing a line along the vessel axis while
 viewing a two-dimensional B-mode image or a qualitative color map of the
 region of interest. A single angle may be set or multiple angles may be
 set for multiple vessels within the region of interest. The angles may be
 set and reset during playback. The system operator is provided with the
 ability to select a desired vessel, select a desired Doppler gate location
 and width and to perform manual angle correction off-line. Angle
 correction may also be performed automatically in any known manner while
 the off-line playback mode.
 According to a preferred embodiment of the present invention, the storage
 of echo signal data in cinescan memory 22 may take place continuously when
 storage is initiated by the system operator. In this case, cinescan memory
 22 may be a cyclic memory storing N seconds of data in a
 first-in-first-out routine. As illustrated in FIG. 2b, the ultrasound
 system 10 receives ultrasound echoes (step 30) and the RF processor
 extracts echo signal data (step 31). The echo signal data may comprise,
 for example, raw RF signal data or I, Q data pairs. The echo signal data
 is routed to and stored in cinescan memory 22 (step 32). The echo signal
 data is simultaneously routed to the signal processor 24 for real-time (as
 opposed to-post storage) processing (step 33) and display on display 26
 (step 34) according to the current system parameter settings. An operator
 initiated command, such as a freeze command, may be used to end the
 storage period and "lock-in" the immediately previous N seconds of data
 for off-line playback and/or archiving (step 35).
 FIG. 2b illustrates a flow chart of an alternative process for accumulation
 and storage of echo signal data according to a preferred embodiment of the
 present invention. The ultrasound system 10 receives ultrasound echoes
 (step 36) and the RF processor extracts echo signal data (step 37). The
 echo signal data may comprise, for example, raw RF signal data or I, Q
 data pairs. If a cinescan storage period is initiated (step 38), the echo
 signal data is routed to and stored in cinescan memory 22 (step 39). The
 echo signal data is stored over a predetermined period of time of any
 length (only limited by the capacity of cinescan memory 22). During this
 storage period, the probe 16 is held stationary over the region of
 interest. Upon completion of the storage period, the ultrasound system 10
 may return to a real-time processing operation or may prompt the operator
 to select an off-line playback mode and related parameters. If a cinescan
 storage period has not been initiated (step 38), the echo signal data is
 processed in real-time by signal processor 24 (step 40) and then displayed
 on display 26 (step 41). Although not shown in FIG. 2, real-time (as
 opposed to post-storage) processing and display of echo signal data may
 proceed in parallel with the storage of echo signal data in cinescan
 memory 22.
 Alternatively, data may be collected serially from a number of segments of
 a region of interest during a storage period. In this manner, the storage
 period comprises a number of storage periods. During the first storage
 period, data from a first segment is stored. During a second storage
 period that may commence immediately following the first storage period,
 data from a second segment that may share a border with the first segment
 is stored. Further storage periods and segments may be similarly
 implemented. In this manner, data from a larger region of interest may be
 collected during a storage period. The number of segments may be increased
 or decreased to alter the area covered by the region of interest. While a
 composite image of the segments will represent data stored at different
 points in time, the image will still provide clinically useful information
 due to the cyclical or repetitive nature of most anatomical movements.
 An example of the accumulation and storage of echo signal data from a
 region of interest is described with respect to FIG. 3. As illustrated in
 FIG. 3, the region of interest 50 may comprise five scan lines 51, 52, 53,
 54 and 55 of a sector scan 60. After a storage period is initiated, the
 probe 16 is held over the region of interest 50 for the duration of the
 storage period. For illustrative purposes, the storage period of this
 example is 6 seconds. During this storage period, echo signal data is
 accumulated from the scan lines 51, 52, 53, 54 and 55 at a PRF of, for
 example, 10,000. If an interleave size of five is used and the number of
 samples per vector is 100, then the number of echo signal data samples
 stored for each line is 1,200,000. A total of 6,000,000 for the full
 region of interest. The echo signal data may be stored in a data table
 according to the scan line from which the echo signal data was collected.
 The echo signal data may also be indexed according to range position
 and/or elapsed time from the beginning of the storage period. P The size
 of the region of interest 50 may be changed by increasing or decreasing
 the number of scan lines from which data will be accumulated and stored.
 Line interleaving techniques may be used to allow simultaneous
 accumulation of echo signal data from multiple lines. The concept of line
 interleaving refers to an ultrasound firing sequence, in which a group of
 several lines is repeatedly scanned. Line interleaving can be used when
 the required minimum PRF (from a clinical view-point--determined by the
 required velocity range that is to be detected without aliasing) is
 smaller than the maximum PRF (determined by the depth of the scan). In
 this case the "dead" time between consecutive firings along one scan line
 is used to fire along other scan lines. According to a preferred
 embodiment of the present invention, this concept is employed during the
 storage period to continuously acquire multiple lines of echo signal data
 in a region of interest 50 defined by the interleaving size (number of
 interleaved lines).
 The size of the region of interest 50 may be further increased by applying
 multi-line acquisition MLA). This technique allows reception of more than
 one receiver beam for each transmitted pulse. Using this technique, a
 broader ultrasonic beam is transmitted, and the beam-former of receiver 18
 is set up to receive and separate the signals from two or more different
 beam directions within the transmit beam opening angle. Use of a broader
 ultrasonic beam allows the accumulation of echo signal data from a larger
 region of interest than could be covered without the use of MLA.
 FIG. 4 illustrates a flow chart of a post-storage, off-line playback
 operation that may be carried out by the ultrasound system 10 for
 processing the stored echo signal data. Playback may take place on the
 same ultrasound system as was used to accumulate and store the data set,
 another ultrasound system, or a separate workstation. At step 70, the
 off-line playback mode is initiated by the operator. At this point, the
 operator may be prompted to select an archived data set or the most
 recently stored data set for playback (step 72). Next, the playback mode
 or analysis is selected (step 74).
 The playback modes or analyses selected at step 74 of FIG. 4 may include,
 for example: standard Doppler analyses such spectral Doppler including
 Doppler Audio playback, color flow, tissue velocity imaging and/or color M
 mode; advanced Doppler color mapping analyses such as maximum velocity
 color mapping, pulsatility index color mapping, resistive index color
 mapping, spectral Doppler derivatives and/or statistical flow parameters;
 tailored clinical studies such as cartiod, renal, malignant
 neovascularization, feto placental and/or coronaries studies; and/or other
 advanced studies such as contrast agents and/or tissue elasticity studies.
 Some of the playback modes may take advantage of the fact that a complete
 data set for the entire region of interest and the entire storage period
 is available simultaneously. Also, for playback modes requiring intensive
 data processing that are difficult or impossible to accomplish in an
 on-line real-time operation due to processing limitations, processing may
 be performed on the stored data set without the speed requirements of
 real-time processing and display.
 At step 76, the various parameters of the selected playback mode or
 analysis are set. To facilitate the selection of such parameters as M-mode
 scan line, Doppler gate location and width and/or setting of beam/vessel
 angle, the ultrasound system 10 may be a duplex scanner that stores B-mode
 image information from the region of interest 50 during the storage
 period. A B-mode image of the region of interest 50 is then displayed
 during the post-storage playback operation. The operator may use this
 B-mode image to locate vessels and set parameters accordingly. All of the
 available parameters may be set and reset before or during the
 post-storage playback operation.
 The signal processor 24 then retrieves the portion of the stored echo
 signal data from the cinescan memory 22 that is appropriate for the
 selected mode and parameters (step 78). The retrieved echo signal data is
 then processed by signal processor 24 (step 80) and displayed on the
 display 26 (step 82).
 The stored echo signal data may be processed and displayed an unlimited
 number of times according to any of the available processing modes and
 parameter settings. For example, the echo signal data may first be
 processed and displayed according to a spectral Doppler mode and then,
 later, be processed and displayed according to a color mapping mode and/or
 M-mode. Also, for example, spectral Doppler may first be performed for one
 scan line, Doppler gate location, and Doppler gate width and then, later,
 spectral Doppler may be performed for a different scan line, Doppler gate
 location and/or Doppler gate width.
 In the foregoing specification the invention has been described with
 reference to specific exemplary embodiments thereof It will, however, be
 evident that various modifications and changes may be made thereto without
 departing from the broader spirit and scope of the invention as set forth
 in the appended claims. The specification and drawings are, accordingly,
 to be regarding in an illustrative rather than restrictive sense.