Patent Publication Number: US-2006004291-A1

Title: Methods and apparatus for visualization of quantitative data on a model

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application claims priority to and the benefit of the filing date of U.S. Provisional Application No. 60/581,675 filed on Jun. 22, 2004 and which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION  
      The present invention relates to diagnostic ultrasound methods and systems. In particular, the present invention relates to methods and systems for visualizing ultrasound data sets on a model.  
      Numerous ultrasound methods and systems exist for use in medical diagnostics. Various features have been proposed to facilitate patient examination and diagnosis based on ultrasound images of the patient. For example, certain systems offer various techniques for obtaining volume rendered data. Systems have been developed to acquire information corresponding to a plurality of two-dimensional representations or image planes of an object for three-dimensional reconstruction and surface modeling.  
      Heretofore, quantitative object time data has yet to be shown associated with the areas of a surface model. In the past, ultrasound methods and systems were unable to present quantitative time data with surface model rendering techniques.  
      A need exists for improved methods and systems that are able to implement surface model rendering techniques for the visualization of quantitative data.  
     BRIEF DESCRIPTION OF THE INVENTION  
      An ultrasound method for visualization of quantitative data on a surface model is provided. The ultrasound method acquires ultrasound information from an object. The information acquired defines ultrasound images along at least first and second scan planes through the object and is stored in a buffer memory. The method then constructs a surface model of the object based on the ultrasound information. Timing information associated with local areas on the object is determined. The surface model and timing information are displayed with the timing information being positioned proximate regions of the surface model corresponding to local areas on the object.  
      In accordance with an alternative embodiment, an ultrasound system is provided that includes a probe to acquire ultrasound information from an object and a memory for storing the ultrasound information along at least first and second scan planes through the object. A processor for constructing a surface model of the object based on the ultrasound information is included. The processor determines timing information associated with local areas on the object. The system includes a display for presenting a surface model and the timing information, with the timing information being positioned proximate regions of the surface model corresponding to the local areas on the object. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagram of an ultrasound system formed in accordance with an embodiment of the present invention.  
       FIG. 2  is a block diagram of an ultrasound system formed in accordance with an alternative embodiment of the present invention.  
       FIG. 3  is a flowchart of an exemplary method for mapping quantitative object timing information onto a surface model.  
       FIG. 4  illustrates an embodiment of a screen display of geometrical surface model showing tissue synchronization imaging (TSI) data.  
       FIG. 5  illustrates a top view of three scan planes through the surface model of  FIG. 4  used to generate the surface model.  
       FIG. 6  shows a Bull&#39;s Eye plot that maps TSI data in accordance with an alternative embodiment of the present invention.  
       FIG. 7  illustrates an embodiment of a view of a mitral ring in which three data planes intersect to generate a visualization of a dynamic mitral valve (MV) ring.  
       FIG. 8  illustrates a resultant ring that may be constructed when a spline is fitted through two points in each of the three planes of  FIG. 7 .  
       FIG. 9  illustrates longitudinal movement of two points on the mitral ring of  FIG. 8  and upward movement thereof in relation to each other. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIG. 1  is a block diagram of an ultrasound system  100  formed in accordance with an embodiment of the present invention. The ultrasound system  100  is configurable to acquire information corresponding to a plurality of two-dimensional (2D) representations or images of a region of interest (ROI) in a subject or patient. One such ROI may be the human heart or the myocardium of a human heart. The ultrasound system  100  is configurable to acquire 2D image planes in two or more different planes of orientation. The ultrasound system  100  includes a transmitter  102  that, under the guidance of a beamformer  110 , drives a plurality of transducer elements  104  within an array transducer  106  to emit pulsed ultrasound signals into a body. The elements  104  within the array transducer  106  are excited by an excitation signal received from the transmitter  102  based on control information received from the beamformer  110 . When excited, the transducer elements  104  produce ultrasonic waveforms that are directed along transmit beams into the subject. The ultrasound waves are back-scattered from density interfaces and/or structures in the body, like blood cells or muscular tissue, to produce echoes which return to the transducer elements  104 . The echo information is received and converted into electrical signals by the transducer elements  104 . The electrical signals are transmitted by the array transducer  106  to a receiver  108  and subsequently passed to the beamformer  110 . In the embodiment described below, the beamformer  110  operates as a transmit and receive beamformer.  
      The beamformer  110  delays, apodizes and sums each electrical signal with other electrical signals received from the array transducer  106 . The summed signals represent echoes from the ultrasound beams or lines. The summed signals are output from the beamformer  110  to an RF processor  112 . The RF processor  112  may generate in phase and quadrature (I and Q) information. Alternatively, real value signals may be generated from the information received from the beamformer  110 . The RF processor  112  gathers information (e.g. I/Q information) related to one frame and stores the frame information with time stamp and orientation/rotation information into an image buffer  114 . Orientation/rotation information may indicate the angular rotation one frame makes with another. For example, in a tri-plane situation whereby ultrasound information is acquired simultaneously for three differently oriented planes or views, one frame may be associated with an angle of 0 degrees, another with an angle of 60 degrees, and a third with an angle of 120 degrees. Thus, frames may be added to the image buffer  114  in a repeating order of 0 degrees, 60 degrees, 120 degrees, . . . 0 degrees, 60 degrees, 120 degrees . . . . The first and fourth frame in the image buffer  114  have a first common planar orientation. The second and fifth frames have a second common planar orientation and the third and sixth frames have a third common planar orientation. Alternatively, in a biplane situation, the RF processor  112  may collect frame information and store the information in a repeating frame orientation order of 0 degrees, 90 degrees, 0 degrees, 90 degrees, . . . . The frames of information stored in the image buffer  114  are processed by the 2D display processor  116 . Other acquisition strategies may include multi-plane variations of interleaving and frame rate decimation . . . . Also rotation of multi-plane to get higher spatial resolution by combining several beats.  
      The 2D display processors  116 ,  118 , and  120  operate alternatively and successfully in round-robin fashion processing image frames from the image buffer  114 . For example, the display processors  116 ,  118 , and  120  may have access to all of the data slices in the image buffer  114 , but are configured to operate upon data slices having one angular orientation. For example, the display processor  116  may only process image frames from the image buffer  114  associated with an angular rotation of 0 degrees. Likewise, the display processor  118  may only process 60 degree oriented frames and the display processor  120  may only process 120 degree oriented frames.  
      The 2D display processor  116  may process a set of frames having a common orientation from the image buffer  114  to produce a 2D image or view of the scanned object in a quadrant  126  of a computer display  124 . The sequence of image frames played in the quadrant  126  may form a cine loop. Likewise, the display processor  118  may process a set of frames from the image buffer  114  having a common orientation to produce a second different 2D view of the scanned object in a quadrant  130 . The display processor  120  may process a set of frames having a common orientation from the image buffer  114  to produce a third different 2D view of the scanned object in a quadrant  128 .  
      For example, the frames processed by the display processor  116  may produce an apical 2-chamber view of the heart to be shown in the quadrant  126 . Frames processed by the display processor  118  may produce an apical 4-chamber view of the heart to be shown in the quadrant  130 . The display processor  120  may produce frames to form an apical parasternal long-axis (PLAX) view of the heart to be shown in the quadrant  128 . All three views of the human heart may be shown simultaneously in real time in the three quadrants  126 ,  128 , and  130  of the computer display  124 .  
      A 2D display processor, for example the processor  116 , may perform filtering of the frame information received from the image buffer  114 , as well as processing of the frame information, to produce a processed image frame. Some forms of processed image frames may be B-mode data (e.g. echo signal intensity or amplitude) or Doppler data. Examples of Doppler data include color flow data, color power Doppler), or Doppler Tissue data. The display processor  116  may then perform scan conversion to map data from a polar to Cartesian coordinate system for display on a computer display  124 .  
      Optionally, a 3D display processor  122  may be provided to process the outputs from the other 2D display processors  116 ,  118 , and  120 . Processor  122  may combine the 3 views produced from 2D display processors  116 ,  118 , and  120  to form a tri-plane view in a quadrant  132  of the computer display  124 . The tri-plane view may show a 3D image, e.g. a 3D image of the human heart, aligned with respect to the 3 intersecting planes of the tri-plane. In one embodiment, the 3 planes of the tri-plane intersect at a common axis of rotation.  
      A user interface  134  is provided which allows the user to input scan parameters  136 . The scan parameters  136  may allow the user to designate what number of planes in the scan is desired. The scan parameters may allow for adjusting the depth and width of a scan of the object for each of the planes of the tri-plane. When performing simultaneous acquisition of scan data from three planes, the beamformer  110  in conjunction with the transmitter  102  signals the array transducer  106  to produce ultrasound beams that are focused within and adjacent to the three planes that slice the scan object. The reflected ultrasound echoes are gathered simultaneously to produce image frames that are stored in the image buffer  114 . As the image buffer  114  is being filled by the RF processor  112 , the image buffer  114  is being emptied by the 2D display processors  116 ,  118 , and  120 . The 2D display processors  116 ,  118 , and  120  form the data for viewing as 3 views of the scan object in corresponding computer display quadrants  126 ,  130 , and  128 . The display of the 3 views in quadrants  126 ,  130 , and  128 , as well as an optional displaying of the combination of the 3 views in quadrant  132 , is in real time. Real time display makes use of the scan data as soon as the data is available for display.  
       FIG. 2  is a block diagram of an ultrasound system  200  formed in accordance with an alternative embodiment of the present invention. The system includes a probe  202  connected to a transmitter  204  and a receiver  206 . The probe  202  transmits ultrasonic pulses and receives echoes from structures inside of a scanned ultrasound volume  208 . The memory  212  stores ultrasound data from the receiver  206  derived from the scanned ultrasound volume  208 . The volume  208  may be obtained by various techniques (e.g., 3D scanning, real-time 3D imaging, volume scanning, 2D scanning with transducers having positioning sensors, freehand scanning using a voxel correlation technique, 2D or matrix array transducers and the like).  
      The probe  202  is moved, such as along a linear or arcuate path, while scanning a region of interest (ROI). At each linear or arcuate position, the probe  202  obtains scan planes  210 . Alternatively, a matrix array transducer probe  202  with electronic beam steering may be used to obtain the scan planes  210  without moving the probe  202 . The scan planes  210  are collected for a thickness, such as from a group or set of adjacent scan planes  210 . The scan planes  210  are stored in the memory  212 , and then passed to a volume scan converter  214 . In some embodiments, the probe  202  may obtain lines instead of the scan planes  210 , and the memory  212  may store lines obtained by the probe  202  rather than the scan planes  210 . The volume scan converter  214  may process lines obtained by the probe  202  rather than the scan planes  210 . The volume scan converter  214  receives a slice thickness setting from a control input  216 , which identifies the thickness of a slice to be created from the scan planes  210 . The volume scan converter  214  creates a 2D frame from multiple adjacent scan planes  210 . The frame is stored in slice memory  218  and is accessed by a surface rendering processor  220 . The surface rendering processor  220  performs surface rendering upon the frame at a point in time by performing an interpolation of the values of adjacent frames. The output of the surface rendering processor  220  is passed to the video processor  222  and the display  224 . The position of each echo signal sample (voxel) is defined in terms of geometrical accuracy (i.e., the distance from one voxel to the next) and ultrasonic response (and derived values from the ultrasonic response). Suitable ultrasonic responses include gray scale values, color flow values, tissue velocity, strain rate and angio or power Doppler information, and combinations thereof. B-mode data may be utilized to outline the model. The surface of the model is defined through surface rendering. Once the surface of the model is defined, quantitative information is then mapped onto the surface. The mapping operation may be achieved between frames by interpolation of adjacent frames or planes at different depths in first and second scan planes that intersect with one another along a common axis.  FIG. 3  is a flowchart  300  of an exemplary method for mapping quantitative object timing information onto a model, e.g. a surface model, of the scanned object. At  302 , ultrasound scan information is acquired from an object. For example, the object may constitute the heart and ultrasound scan information may be acquired to produce a cine loop of frames that are gathered over at least one heart cycle.  
      At  304 , acquired ultrasound information is stored in a data memory  212  ( FIG. 2 ) that defines images of the object along at least first and second scan planes through the object. The stored information includes multiple images that are associated within a single scan plane through the object at different points in time, and multiple images from different scan planes at a common point in a cyclical motion of the object. In the example of first and second scan planes (a biplane scan), first and second scan planes may intersect with one another along a common axis through the object whereby the planes are oriented at a predetermined angle with respect to one another. Likewise, for an the example of three planes (a tri-plane scan), the three planes may intersect with one another along a common axis through the object whereby the planes are oriented at a predetermined angle with respect to one another.  
      At  306 , a model, for example a 3D surface model, a bull&#39;s eye model, or a heart mitral valve (MV) ring model is constructed of the object based on the ultrasound information acquired. An outline of the object may be manually determined by mouse clicking on a series of points (or mouse drawing of contours) in one of the planar images of the object at predefined times in the cyclical motion of the object. The mouse may be part of the user interface  134 . A manual determination of the outline may be done in each of the three data planes. In an alternative embodiment, the outline of the object/landmark may be determined automatically within the data planes by the 3D display processor  122  of  FIG. 1  detecting boundaries or landmarks of the object, such as for the example of a human heart, the AV plane, the mitral ring, and the apex.Color may be used to indicate the degree of time delay in TSI data. A color is assigned automatically by the system  100  to each designated ROI in the three frames depending on the movement of that particular ROI over time. A color may be associated with a ROI that indicates the time from a reference time of the ROI to a peak velocity. For example, the interval chosen for real time measurement of time delay may be from the time of QRS in the cardiac cycle to the time of peak tissue velocity within a given search interval. The search interval may, for example, be from aortic valve opening time to aortic valve closure time. The color assigned to each ROI is based on the color scale and the time to peak velocity for the ROI over time. For, example, an ROI having a short time delay is assigned a green color, an ROI having a medium time delay is assigned a yellow color, and an ROI having a long time delay is assigned a reddish orange color. Therefore, green indicates tissue with early motion and red indicates tissue with delayed motion. The color is mapped onto a gray scale image of each frame such that a particular color corresponds to an intensity level or brightness of the grayscale or B-mode frame. Once the color mapping of the grayscale image is accomplished, the system  100  automatically interpolates the colors of the three frames onto the surface model as it is generated.  
      At  308 , quantitative object timing information, such as one of tissue velocity, displacement, strain, and strain rate, associated with local areas on the object is determined. The object timing information associated with the local areas is relative to a reference time for the local areas. In the example of the human heart, the reference time may be the QRS point in the heart cycle. The timing information defines a time from the reference time to when the local area reaches a particular state in a series of states through which the object cycles. Quantitative object timing information may be used to detect malfunctioning of tissues of the object. For example, an area of tissue may be found in the human heart to lag in time from QRS to reach peak velocity in contrast to surrounding tissue areas. The lag in time to reach peak velocity may indicate the presence of diseased tissue.  
      At  310 , a model, e.g. a 3D surface model, bull&#39;s eye surface model, or mitral valve ring surface model, and object timing information are displayed. The timing information being displayed is positioned proximate regions of the model corresponding to the local areas on the object. The timing information may constitute at least one of color coding of, and vector indicia on, the regions of the model. Color coding with a range of colors indicating a range from normal to abnormal may be used to visualized the desired parameter of quantitative object timing data, e.g. time to peak tissue velocity, time to peak strain. Such color coding may visually identify asynchronous areas of tissue, for example in the heart, that are unhealthy.  
       FIG. 4  illustrates an embodiment of a screen display  400  of a geometrical surface model  408  showing tissue synchronization imaging (TSI) data to indicate tissue motion delay. The display  400  may be shown on the computer display screen  124  of  FIG. 1 . The three data planes  402 ,  404 , and  406  shown in the left side of the figure are based on the ultrasound information acquired  302  and stored  304 . The surface model  408  may be generated automatically from the data planes  402 ,  404 , and  406 . The user may manually trace an outline of the object by defining/marking  305  landmarks or ROIs, for example ROIs  410 ,  412 ,  414 ,  416 ,  418 , and  420  are designated in data plane  406  by a user mouse clicking on these areas. Likewise, landmarks and/or ROIs may be defined  305  to outline the object in frames or planes  402  and  404 . In an alternative embodiment, the system  100  may automatically define  305  the landmarks and/or ROIs from the ultrasound boundary interface data. For example, the system  100  of  FIG. 1  may detect the AV plane and apex points at a given time and make a spline surface through these points. Some shape factors such as wideness and skew may be included. Once the outlines are defined  305  in all three data planes  402 - 406 , the system  100  generates or constructs  306  the surface model  408 . The three data planes  402 ,  404 , and  406  are correspondingly shown in the surface model view  422  as planes  424 ,  426 , and  428 . In order to construct  306  the surface model  408 , interpolation of the data in the planes  424 ,  426 , and  428  is done to determine the points between the planes through which the constructed surface model  408  may be drawn. The contour of the surface of the object depends on the shape of the connected points. Depending where a landmark or ROI is manually or automatically determined, the contour may be circular or not, as shown in  FIG. 5 .  
      The geometrical surface model  408  may be color coded to determine  308  and to visually display  310  the mapping of quantitative object timing data. For example, a portion of the surface model  408 , for example portion  430 , may be colored red-orange, while the rest of the surface outline is colored green. The color coding of the surface model  408  may indicate the portion  430  having a reddish-orange color for mapped TSI data which indicates tissue with delayed motion, while the rest of the surface is colored in green to indicate tissue with early motion.  
       FIG. 5  illustrates a top view  500  of the three scan planes  424 ,  426 , and  428  of  FIG. 4 . Landmark or ROI points  502 ,  504 , and  506  may be manually defined  305  by the user as described for the ROIs  410 - 420  of  FIG. 4 , or automatically determined by the system  100 . A point  508  may be interpolated from the planar points  502  and  504  by the system  100 . Likewise, a point  510  may be interpolated from the planar points  504  and  506  by the system  100 . The points  502 ,  508 ,  504 ,  510  and  506  may when connected by the system  100  generate a circular contour  518 . Alternatively, if ROI point  516  is selected instead of ROI point  504  by the user, the points  512  and  514  may be interpolated in contrast to the corresponding points  508  and  510 . System  100  in this case may generate a non-circular contour  520  through the points  502 ,  512 ,  516 ,  514 , and  506 . In a similar manner, the complete surface model  408  may be generated/constructed  306  by the system  100  from points selected in the planes  424 - 428  and points interpolated between the planes.  
      Color coding is accomplished according to  308  and  310  in  FIG. 3 . The time interval chosen for the embodiment of  FIG. 4  is the time to peak velocity. Therefore, the interval chosen for real-time measurement of time delay is from the time of QRS in the cardiac cycle to the time of peak tissue velocity. A color scale  432  is shown with a color gradient ranging from green to yellow to red. At the one end of the scale, the color green corresponds to a short time delay starting at 60 milliseconds (ms). The other end of the scale is red and indicates a long time delay extending to a maximum of 509 ms.  FIG. 6  shows the generation of a Bull&#39;s Eye plot  600  that maps TSI data. The Bull&#39;s eye is a bottom or apical view of the heart that is projected onto a flat or 2D surface model or a plane. The center  602  of the Bull&#39;s eye where the crosshair is located is the apex of the heart. The middle ring area  604  is the middle segments of the left ventricle of the heart. The outer ring area  606  is the basal segments of the heart and includes the mitral valve ring. The numbers on the Bull&#39;s eye plot  600  represent quantitative data on time to peak velocity after QRS complex in different regions of the ventricle. In  FIG. 6 , the value  230  represents the area of maximum time to peak tissue velocity. Asynchrony in terms of TSI calculated indexes derived for these numbers include, septal lateral delay, septal posterior delay, maximum delay, standard deviation, etc. The numbers may be generated automatically as for a geometric surface model or they may be based on manual positioning of sampling regions. Manual measurement of time to time to peak velocity is determined  308  by single-clicking in each (basal and mid) segment. The result is presented or displayed  310  in a Bull&#39;s eye plot  600  as color coding and numbers therein. The numbers on the Bull&#39;s eye plot may be automatically generated or determined  308  as a function of the velocity measurements in different areas of the heart.  
       FIG. 7  illustrates an embodiment of a view  700  of a mitral ring in which three data planes  702 ,  710 , and  718  intersect the mitral ring valve at different angles to one another to generate a visualization of a dynamic mitral valve (MV) ring. The position of the mitral ring may be tracked throughout a whole heart cycle in a 3D data set. Then the tracking is visualized as a model which is an integrated image of all the mitral ring positions throughout the cycle. This can be used to extract information on heart function. The model is cylindrical for a heart where the walls are well-synchronized. The initial position of the mitral valve ring may either be manually defined or detected automatically by an AV-plane detector. Two points in each plane through the left ventricle may be selected in each of the three data planes of the left ventricle  704 ,  712 , and  720  in  FIG. 7 . In plane  702 , the points  706  and  708  are chosen on the mitral valve ring  726  of the left ventricle  704 . In plane  710 , the points  714  and  716  are chosen on the mitral valve ring  728  of the left ventricle  712 . In plane  718 , the points  722  and  724  are chosen on the mitral valve ring  730  of the left ventricle  720 . The six points  706 ,  708 ,  714 ,  716 ,  722 , and  724  are connected as shown in  FIG. 8 .  
       FIG. 8  illustrates the resultant ring  800  that may be constructed when a spline is fitted through the six points  706 ,  708 ,  714 ,  716 ,  722 , and  724  of  FIG. 7 . Upon detecting the location of the AV plane and the mitral ring and with the use of the apex, these three landmarks in the three planes may be used to construct an outline of the left ventricle. The MV ring  800 , which lies in the AV plane, may be visualized by looking at sequential sets of the six points over time. The longitudinal or up and down motion of the ring along the long axis of the ventricle in relation to the apex may be viewed over time as an index of synchronicity. The index of synchronicity of the points along the mitral valve ring structure may be used to obtain a dynamic view of the mitral ring valve function.  
       FIG. 9  illustrates longitudinal movement  900  of two points  902  and  904  on the mitral ring of  FIG. 8  and their upward movement in relation to each other. Point  902  may move a distance of delta, whereas point  904  may move a lesser distance of only delta over two in relation to point  902 . After the dynamic mitral ring model  800  is generated, several M&amp;A parameters may be extracted from the model data. The degree of asynchrony may (TSI), excursion of the six standard apical segments or E′ wave velocity of the six standard apical segments (relaxation) may be determined.  
      The tissue delay of different regions of interest may be compared to identify a degree of delay. For example, ROIs corresponding to segments within the left ventricle may be compared to identify the most delayed segment. Similarly, segments may be compared between the left and right ventricles. Although  FIG. 4  illustrates data representative of a left ventricle, thus quantifying the amount of synchrony within the left ventricle, it should be understood that the method of  FIG. 3  may be used to quantify and compare the time delay of samples in the left and right ventricles. In this way, the amount of synchrony between the left and right ventricles may be determined. In addition, the method of  FIG. 3  may be used to quantify and compare the time delay of regions in the left and right atria of the heart.  
      The system and method described herein include automatic detection of peaks, zero-crossings or other features of tissue velocity, displacement, strain rate and strain data as a function of time. By processing only the image frames within the selected time interval, the processing time is shortened and the possibility of false positives is lowered, such as may occur when an incorrect peak is identified. The system and method color codes the delay of samples in the image in relation to the onset of the QRS, and presents the data as a parametric image, both in live display and in replay. Thus, heart segments or other selected tissue with delayed motion might be more easily visualized than with other imaging modes. Therefore, patients who will respond favorably to cardiac resynchronization therapy (CRT) may be more easily selected, and the optimal position for the left ventricle pacing lead for a cardiac pacemaker may be located by identifying the most delayed site within the left ventricle. Furthermore, the effect of the various pacemaker settings, such as AV-delay and VV-delay, may be studied to find the optimal settings.  
      Optionally, the model may not be a surface model. Instead, the model may be a splat rendering, Bulls-Eye, a mitral ring model and the like.  
      While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.