Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
  • G01S7/52017—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 particularly adapted to short-range imaging
  • G01S7/52085—Details related to the ultrasound signal acquisition, e.g. scan sequences
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
  • G01S15/88—Sonar systems specially adapted for specific applications
  • G01S15/89—Sonar systems specially adapted for specific applications for mapping or imaging
  • G01S15/8906—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques
  • G01S15/8909—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques using a static transducer configuration
  • G01S15/8913—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques using a static transducer configuration using separate transducers for transmission and reception
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
  • G01S15/88—Sonar systems specially adapted for specific applications
  • G01S15/89—Sonar systems specially adapted for specific applications for mapping or imaging
  • G01S15/8906—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques
  • G01S15/8995—Combining images from different aspect angles, e.g. spatial compounding
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
  • G01S7/52017—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 particularly adapted to short-range imaging
  • G01S7/52023—Details of receivers
  • G01S7/52025—Details of receivers for pulse systems
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
  • G01S7/52017—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 particularly adapted to short-range imaging
  • G01S7/5205—Means for monitoring or calibrating
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
  • G01S7/52017—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 particularly adapted to short-range imaging
  • G01S7/52053—Display arrangements
  • G01S7/52057—Cathode ray tube displays
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
  • G01S7/52017—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 particularly adapted to short-range imaging
  • G01S7/52053—Display arrangements
  • G01S7/52057—Cathode ray tube displays
  • G01S7/5206—Two-dimensional coordinated display of distance and direction; B-scan display
  • G01S7/52065—Compound scan display, e.g. panoramic imaging
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
  • G01S7/52017—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 particularly adapted to short-range imaging
  • G01S7/52023—Details of receivers
  • G01S7/52034—Data rate converters
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
  • G01S7/52017—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 particularly adapted to short-range imaging
  • G01S7/52023—Details of receivers
  • G01S7/52036—Details of receivers using analysis of echo signal for target characterisation
  • G01S7/52038—Details of receivers using analysis of echo signal for target characterisation involving non-linear properties of the propagation medium or of the reflective target

Definitions

• This invention relates to ultrasonic diagnostic imaging systems and, in particular, to ultrasonic diagnostic imaging systems which produce spatially compounded images by combining a variable number of received images.
• Spatial compounding is an imaging technique in which a number of ultrasound images of a given target that have been obtained from multiple vantage points or angles (look directions) are combined into a single compounded image by combining the data received from each point in the compound image target which has been received from each angle. Examples of spatial compounding may be found in US Patents 4649927; 4319489; and 4159462.
• Real time spatial compound imaging is performed by rapidly acquiring a series of partially overlapping component image frames from substantially independent spatial directions, utilizing an array transducer to implement electronic beam steering and/or electronic translation of the component frames. The component frames are combined into a compound image by summation, averaging, peak detection, or other combinational means.
• the acquisition sequence and formation of compound images are repeated continuously at a rate limited by the acquisition frame rate, that is, the time required to acquire the full complement of scanlines over the selected width and depth of imaging.
• the compounded image typically shows lower speckle and better specular reflector delineation than conventional ultrasound images from a single viewpoint. Speckle is reduced (i.e. speckle signal to noise ratio is improved) by the square root of N in a compound image with N component frames, provided that the component frames used to create the compound image are substantially independent and are averaged.
• speckle is reduced (i.e. speckle signal to noise ratio is improved) by the square root of N in a compound image with N component frames, provided that the component frames used to create the compound image are substantially independent and are averaged.
• Several criteria can be used to determine the degree of independence of the component frames (see, e.g., O'Donnell et al. in IEEE Trans. UFFC v.35, no.4, pp 470-76 ( ⁇ .
• One of the problems associated with real time spatial compound imaging is that several image acquisitions are needed to produce each new compound image frame.
• the time needed to acquire a spatial compound image consisting of N component frames is approximately N times longer than that of each individual component frame. It is generally desirable to acquire a large number of component frames to maximize the image quality of the compound image.
• the number of different look directions of a target which are compounded is variable in accordance with changes in ultrasound system operating parameters, either singly or in combination, which improves the performance of the spatial compounding system.
• the steering angle(s) of the look directions are varied in response to changes in the image depth.
• an ultrasonic transducer scans a target from a number of different perspectives. For example, several sector images can be sequentially acquired by a phased array transducer, each with an apex located at a different point in relation to the array.
• a steered linear array can be used to image the target with a sequence of groups of beams, each group steered at a different angle with respect to the axis of the array.
• beams having no particular relationship to a frame or image format can interrogate targets in a region of the body from multiple directions, by the transmission of individual beams or multiple beams simultaneously. In either case the received images are processed in the usual way by beamforming and detection and stored in a memory.
• the component frames or target echoes to be combined are spatially aligned (if not already aligned by a common beam steering reference) by scan conversion or resampling. The common spatial locations in the image field are then compounded by averaging or summing and the resultant compound image is displayed.
• FIGURE 1 illustrates in block diagram form an ultrasonic diagnostic imaging system constructed in accordance with the principles of the present invention
• FIGURE 2 illustrates in block diagram form a preferred implementation of the spatial compounding processor of FIGURE 1;
• FIGURES 3a-3b illustrate the effects of increasing and decreasing the number of acquired frames which are compounded to form a spatially compounded ultrasonic image.
• a scanhead 10 including an array transducer 12 transmits beams at different angles over an image field denoted by the dashed rectangle and parallelograms.
• Three groups of scanlines are indicated in the drawing, labeled A, B, and C with each group being steered at a different angle relative to the scanhead.
• the transmission of the beams is controlled by a transmitter 14 which controls the phasing and time of actuation of each of the elements of the array transducer so as to transmit each beam from a predetermined origin along the array and at a predetermined angle.
• the echoes returned from along each scanline are received by the elements of the array, digitized as by analog to digital conversion, and coupled to a digital beamformer 16.
• the digital beamformer delays and sums the echoes from the array elements to form a sequence of focused, coherent digital echo samples along each scanline.
• the transmitter 14 and beamformer 16 are operated under control of a system controller 18, which in turn is responsive to the settings of controls on a user interface 20 operated by the user of the ultrasound system.
• the system controller controls the transmitter to transmit the desired number of scanline groups at the desired angles, transmit energies and frequencies.
• the system controller also controls the digital beamformer to properly delay and combine the received echo signals for the apertures and image depths used.
• the scanline echo signals are filtered by a programmable digital filter 22, which defines the band of frequencies of interest.
• a programmable digital filter 22 defines the band of frequencies of interest.
• the passband of the filter 22 is set to pass harmonics of the transmit band.
• the filtered signals are then detected by a detector 24.
• the filter and detector include multiple filters and detectors so that the received signals may be separated into multiple passbands, individually detected and recombined to reduce image speckle by frequency compounding.
• the detector 24 will perform amplitude detection of the echo signal envelope.
• Doppler imaging ensembles of echoes are assembled for each point in the image and are Doppler processed to estimate the Doppler shift or Doppler power intensity.
• the digital echo signals are processed by spatial compounding in a processor 30.
• the digital echo signals are initially pre-processed by a preprocessor 32.
• the pre-processor 32 can preweight the signal samples if desired with a weighting factor.
• the samples can be preweighted with a weighting factor that is a function of the number of component frames used to form a particular compound image.
• the pre-processor can also weight edge lines that are at the edge of one overlapping image so as to smooth the transitions where the number of samples or images which are compounded changes.
• the pre-processed signal samples may then undergo a resampling in a resampler 34.
• the resampler 34 can spatially realign the estimates of one component frame to those of another component frame or to the pixels of the display space.
• the image frames are compounded by a combiner 36.
• Combining may comprise summation, averaging, peak detection, or other combinational means.
• the samples being combined may also be weighted prior to combining in this step of the process.
• post-processing is performed by a post-processor 38.
• the post-processor normalizes the combined values to a display range of values. Post-processing can be most easily implemented by look-up tables and can simultaneously perform compression and mapping of the range of compounded values to a range of values suitable for display of the compounded image.
• the compounding process may be performed in estimate data space or in display pixel space.
• scan conversion is done following the compounding process by a scan converter 40.
• the compound images may be stored in a Cineloop memory 42 in either estimate or display pixel form. If stored in estimate form the images may be scan converted when replayed from the Cineloop memory for display.
• the scan converter and Cineloop memory may also be used to render three dimensional presentations of the spatially compounded images as described in U.S. Patents 5,485,842 and 5,860,924, or displays of an extended field of view by overlaying successively acquired, partially overlapping images in the lateral dimension.
• the spatially compounded images are processed for display by a video processor 44 and displayed on an image display 50.
• FIGURE 2 illustrates a preferred implementation of the spatial compounding processor 30 of FIGURE 1.
• the processor 30 is preferably implemented by one or more digital signal processors 60 which process the image data in various ways.
• the digital signal processors 60 can weight the received image data and can resample the image data to spatially align pixels from frame to frame, for instance.
• the digital signal processors 60 direct the processed image frames to a plurality of frame memories 62 which buffer the individual image frames.
• the number of image frames capable of being stored by the frame memories 62 is preferably at least equal to the maximum number of image frames to be compounded such as sixteen frames.
• the digital signal processors are responsive to changes in system control parameters including image display depth, number of scanlines or line density, number of transmit focal zones, amount of deadtime per pulse repetition interval (PRI), number of transmissions per image line, depth of region of greatest compounding, clinical application, number of simultaneous modes, size of region of interest, mode of operation, and acquisition rate for determining the number of component frames to compound at a given point in time.
• the digital signal processors select component frames stored in the frame memories 62 for assembly as a compound image in accumulator memory 64.
• the compounded image formed in the accumulator memory 64 is weighted or mapped by a normalization circuit 66, then compressed to the desired number of display bits and, if desired, remapped by a lookup table (LUT) 68.
• the fully processed compounded image is then transmitted to the scan converter for formatting and display.
• the digital signal processors 60 determine the number of frames which are to be compounded to improve image quality while still providing an acceptable realtime compound image frame rate. Increasing the number of component frames does not lead to a proportional or unlimited increase in the image quality of the compound image. There is, therefore, a practical maximum number of frames, each steered by a minimum angle, that can be usefully employed to improve image quality in spatial compound scanning. This number o can vary widely depending on the transducer design and size of the active aperture, but can be as large as 16 component frames per compound image for an array with a large acceptance angle and small active apertures. The maximum useful number of frames will also depend on the mixture of speckle and anisotropic scatterers in the tissue of interest, and therefore on the clinical application.
• the present invention has particular utility when the clinician is changing between "survey" and "target” modes of operation.
• the clinician is rapidly maneuvering the scanhead to quickly ascertain the presence of prominent physiological landmarks or features.
• the compounding of a large number of component frames when the scanhead is in motion will result in blurred images. Consequently the number component frames being compounded is reduced during the survey mode.
• the scanning motion is slowed down or stopped completely to image the features of interest ("targeted" or "study” mode). At this point, the image features within the component frames are more highly correlated, and motion blurring in the compound image is substantially reduced or completely eliminated as long as the scanhead is substantially stationary.
• the target mode the number of component frames being compounded is increased to produce high quality images without the consequence of blurring.
• the frame rate of an image with a given line density is dependent upon the maximum display depth of the image, because the speed of sound in tissue (-1.54 millimeters per microsecond) imposes a minimum round trip propagation delay of 13 microseconds for every centimeter of image depth.
• additional delay time is also added to prevent reverberation artifacts, that is the receipt of echoes at the beginning of one image line which are returning from deep depths of a previous image line.
• the acquisition frame rate can be 100 frames per second or greater, but for an 8 centimeter image depth the frame rate can drop to 25 frames per second.
• Compound scanning with a steered linear array results in a pattern of overlapping component frames such that the region of maximum image quality (RMIQ) where all N frames overlap is a trapezoidal or an inverted triangular region with its base at the top of the compound image.
• RMIQ region of maximum image quality
• this region of maximum image quality extends deep into the compound image.
• the RMIQ is relatively shallow. This is illustrated by FIGURES 3a-3c, which show three different compound scan geometries, each consisting of several partially overlapping steered linear component frames scanned from a linear array scanhead 10.
• the minimum steering angle was chosen as 15° between component frames.
• FIGURE 3a shows three component frames A, B, and C which are compounded, and the RMIQ extends the full 4.0 cm height of the image.
• FIGURE 3b shows an image which compounds five component frames A, B, C, D and E, and the RMIQ now extends only 2.3 cm from the top of the compound frame.
• FIGURE 3c shows that for seven component frames A-G, the RMIQ of the compound image only extends 1.3 centimeters in depth.
• the system controller 18 responds by decreasing the number of frames which are acquired and compounded to form the displayed compound image.
• the ultrasound system responds by decreasing the number of frames of the compounded display.
• the acquisition frame rate declines the number of frames compounded is also decreased.
• the ultrasound system will respond by decreasing the number of compounded frames in a displayed image.
• the look directions of the acquired image frames is varied by steering the transmit beams in a number of different look directions the angle of the sides of the trapezoidal-shaped image decreases with increases in the number of images which are compounded.
• FIGURES 3a-3c illustrates how a greater maximum steering angle will more effectively cover a shallow imaging depth, whereas a lesser maximum steering angle is more effective for greater imaging depths.
• the number of look directions compounded in the compound image is decreased, as is the maximum steering angle.
• the number of look directions is also decreased when the number of lines or line density of the image is increased; when the number of transmit focal zones is increased; when the amount of deadtime per PRI is increased; when the number of transmissions per image line is increased (e.g., for synthetic aperture, pulse inversion harmonic imaging), when the number of simultaneous modes is increased (e.g., spectral Doppler together with 2D imaging), the size of the region of interest is increased (e.g., image zoom is decreased or turned off), the clinical application (e.g., changing from abdominal or peripheral vascular imaging to cardiac imaging), or changing from target to survey mode.
• the number of look directions can be increased. It will be apparent to one skilled in the art that other changes in imaging parameters by the user, or various changes in a combination of the above parameters, should also be responded to by a change in the number of look directions which are compounded.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Computer Networks & Wireless Communication (AREA)
• General Physics & Mathematics (AREA)
• Acoustics & Sound (AREA)
• Ultra Sonic Daignosis Equipment (AREA)
• Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)

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Cited By (7)

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Citations (4)

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• 1999
  • 1999-06-17 US US09/335,058 patent/US6210328B1/en not_active Expired - Lifetime
  • 1999-09-30 DE DE69923430T patent/DE69923430T2/de not_active Expired - Lifetime
  • 1999-09-30 JP JP2000574949A patent/JP4694692B2/ja not_active Expired - Lifetime
  • 1999-09-30 EP EP99952523A patent/EP1046061B1/en not_active Expired - Lifetime
  • 1999-09-30 WO PCT/EP1999/007473 patent/WO2000020884A1/en not_active Ceased
• 2010
  • 2010-10-29 JP JP2010242898A patent/JP4828651B2/ja not_active Expired - Lifetime

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