GB2493902A

GB2493902A - Multiple scan-plane ultrasound imaging apparatus and method suitable for the assessment of wall motion abnormalities of the heart

Info

Publication number: GB2493902A
Application number: GB1111124.2A
Authority: GB
Inventors: Bja Rn A J Angelsen
Original assignee: Surf Technology AS
Current assignee: Surf Technology AS
Priority date: 2011-06-28
Filing date: 2011-06-29
Publication date: 2013-02-27
Also published as: GB201111124D0

Abstract

A method for detection and assessment of wall motion abnormalities in the left ventricle (LV) 100 is given. The method comprises simultaneous imaging of the LV from the LV apex with 3 or more 2D scan planes 103, 104, 105 in real time, and selecting at least one depth 110, 111, 112, 113, along the ultrasound beams that provides image data from a cross section of the left ventricle, and presenting the image data in coordinate location for each 2D scan plane on a display screen. The image data may be displayed in a three dimensional display. A wireframe and / or shaded display may be generated.

Description

Multiple scan-plane ultrasound apparatus and method suitable for the assessment of wall motion abnormalities of the heart

Field of the invention

The present invention is directed towards a method and apparatus suitable for real time ultrasound imaging of the heart. The method and apparatus of embodiments can provide images for analysis of wall motion abnormalities of the heart.

Background of the invention

Detection and analysis of wall motion abnormalities of the heart is useful for assessing regional cardiac function. Both two-dimensional (2D) and three-dimensional (3D) ultrasound imaging of the heart can be used for this purpose. 3D imaging provides the best overview of the heart, but has slow frame rate, so that beat by beat analysis has reduced quality.

US Pat 7,758,509 discloses a method of automatic ultrasound imaging of the heart in three or four discrete scan planes that provides a frame rate advantage over full 3D imaging methods.

Summary of the invention

According to an aspect of the present invention there is provided an apparatus for ultrasound imaging. The apparatus comprises an ultrasound transducer arranged to acquire ultrasound signals from only a discrete number of 2D scan planes, a signal processor arranged to process said signals by selecting signals originating from a predetermined distance from the receiver and a display arranged to display image data of the beating heart for a cross-section of the heart at said distance.

The number of 2D scan planes may be a finite number of 2D scan planes, for example a number not exceeding 10 scan planes. Preferably 3, 4 or 5 scan planes are chosen.

According to another aspect of the present invention there is provided an apparatus for ultrasound imaging. The apparatus comprises an ultrasound transducer arranged to acquire ultrasound signals from only a discrete number of 2D scan planes, a signal processor arranged to process said signals by selecting signals originating from a number predetermined distances from the receiver and to select a point within each intersection of a 2D scan plane with the heart wall at each of the distance according to a selection rule and a display arranged to display the selected points in a three dimensional display.

Although image data from 3 or 4 multiple 2D scan planes can be obtained by known methods in real time, it is still a challenge to analyze the data to detect and assess the degree of wall motion abnormalities. The present invention addresses this problem by taking the image data obtained with such multi-plane imaging of the heart, and presenting a display of the data that simplifies the analysis for detection and assessment of location and degree of potential wall motion abnormalities.

According to another aspect of the present invention there is provided a method for detection of wall motion abnormality in the left ventricle (LV) of the heart is given. The method comprises simultaneous imaging in real time of the heart with 3 or more discrete 20 scan planes that are rotated around a common axis, and selecting at least one depth along the ultrasound beams that provides image data from at least one cross section of the heart, and presenting the image data of the beating heart in spatial coordinate location for each said at least one cross section of the heart from all 2D scan planes on an image display.

The method further comprises selecting characteristic points of the wall image of each cross section in the image display, and connecting said characteristic points for each cross section with a continuous curve, and displaying said continuous curve on said image display. Said characteristic points can for example be one of edges of the wall images, the mid-point of the wall images, and the center of gravity of the wall images.

The method further comprises highlighting said continuous curves with largest area as the end diastolic curve (EDC), and smallest area as the end systolic curve (ESC) for each of said cross sections on the image display. The distance as a function of angular location between said ESC and said EDC is used to quantif' the degree of wall motion abnormality for each cross section.

The method can also vary the distance between the cioss sections so that the cross sections follow material points in the heart wall. This can for example be achieved by the operator marking the material points in 20 images at different times during the cardiac cycle, or the instrument can time-integrate velocity information of the wall in each image location to obtain the time variable distance of material points of the wall in the different images during the cardiac cycle, and said at least one cross section moves with the material points of the heart wall during the cardiac cycle.

The method further comprises connecting said characteristic points of the same cross sections from different neighboring depths are in combination with the distance between the cross sections along the beams, into a 3D wire frame model for display of the beating heart, for assessment of 3D location and magnitude of the wall motion abnormality.

Said wire frame model can also be used to calculate the end diastolic volume (EDV), the end systolic volume (ESV), the stroke volume SV = EDV -ESV, and the ejection fraction EF = SV/EDV of the LV.

The method further comprises continuing said 3D wire frame model to a surface, and the distance between the ESC and the EDC for each cross section is interpolated across the surface and coded into the display along the surface to show areas of wall motion abnormality.

Brief description of the drawings

FIG. 1 shows a schematic overview of a left ventricle (LV) with an ultrasound transducer array that provides three two-dimensional ultrasound scan planes that crosses the LV walls.

FIG. 2 shows a display according to an embodiment of the invention of the image data obtained with the multi-planar imaging method of the LV shown in Figure 1.

FIG. 3 illustrates a method of interpolating curves between characteristic points within the ventricular wall cross section to improve detection and to quantify wall motion abnormalities.

FIG. 4 shows a 3D model of the beating heart based on the characteristic points shown in Figure 3.

Detailed description

Example embodiments according to the invention, are presented in the following. It is clear that this presentation is meant for illustration purposes only, and by no means represents limitations of the invention, which in its broadest aspect is defined by the claims appended hereto.

FIG. 1 shows a schematic illustration of the left ventricle (LV) of the heart as 100 with the LV wall illustrated as 101. An ultrasound transducer array 102 is shown to scan ultrasound beams from the apex of the heart within three 2D scan planes 103, 104, 105, for example according to the methods described in US Pat 7,758,509. The beam density is selected within each of the 2D scan planes so that adequate imaging of the LV wall is obtained with adequate spatial resolution and frame rate to assess wall motion abnormalities. The beam density within a scan plane may, for example, vary dependent on the region of the ventricle that is being imaged. A first beam density may, for example be used in areas known (for example from a preceding pilot scan) to contain myocardium, while a second, lower beam density may be used for areas of the LV known not to contain myocardium.

in the embodiment, image data is selected at least one depth along the beams, where FIG. 1 shows a set of 4 depths 110, 111, 112, and 113, which hence presents cross sectional image information from regions of the LV wall. The image data can typically be the amplitude of the backscattered signals, motion, strain, or strain velocity analysis of the regions of the LV wall.

A typical real time display of the image data from the beating heart, according to an embodiment, is shown in FIG. 2, where the data from the cross sectional depths 110-113 is shown in the cross sectional displays 210, 211, 212, 213. Each of the displays 210-213 has the same structural relation to the data from the scan planes, where the lines 203, 204, 205 correspond to the scan planes 103- 104 of FIG. 1 in a cross sectional view. Reference numerals 215, 216, 217, 218, 219, 220 represents the image data from the LV wall in the three scan plane 203, 204 and 205. image data that is displayed could for example be the magnitude of the backscattered signal, velocity information in the back scattered signal, strain or strain velocity information in the back scattered signal, or a combination of these, all obtained according to known methods. The data could be displayed as a grey scale or color scale with a width along the scan planes for example relating to the spatial resolution in the imaging system, or selectable by the instrument operator.

The display can be real time. In this case the images displayed could move to display the movement of the beating heart, as measured by the ultrasound probe. The respective distances between the ultrasound probe and one or more of the cross-sections 210 -213 may be adjusted by the ultrasound apparatus so that the one or more cross-sections 210-213 are locked to a fixed/material point in the heart. Such locking may be achieved by the operator marking the material points in the 2D images versus time, or automatically by obtaining radial velocity information along the beams of the wall echoes 215-220 from the back scattered ultrasound signal and by time-integrating to vary the distance between the cross sectional depths 110-113 during the cardiac cycle. The lower cross section 113 can then for example be made to follow the aortic-mitral valve plane during the cardiac cycle.

The display could also include further multiple sets similar to 210 -213 where different image data is shown in the different sets, or the different sets show images under different degrees of physical or pharmacologic stress (exercise) during the examination, or different sets show recalled images from earlier examinations.

To detect and assess the location and degree of the wall motion abnormality, one embodiment presents an analysis that is demonstrated with reference to FIG. 3. This Figure shows by example one of the cross section displays in FIG. 2, where the shape of the LV wall motion is distorted in the region 300 due to a wall motion abnormality. Characteristic points 301 -306 are selected for each of the wall areas 307 -313, either automatically or manually, or through a combination of both. Said characteristic points can for example be selected as one of i) the wall edges, and ii) the mid-point, and iii) the center of gravity of the walls. Said characteristic points are then connected through interpolation by a continuous curve 314. Such interpolation can for example be done using spline techniques of any order, Fourier interpolation, or direct connection by straight lines between said characteristic points.

If the selection criterion for selecting the characteristic point within each of the intersections of the three scan planes with the LV wail remains the same over a series of images obtained, that is if the characteristic points remain at the same relative position with regard to the inside or outside wall of the LV, then the continuous curve will move with the beating heart. To quantify the movement, the curves 315 at maximal area (end diastolic curve -EDC) and 316 minimal area (end systolic curve -ESC) would typically be high-lighted on the screen, with distance indications 317 between the ESC and the EDC. Regions of low distance would then indicate a region of low wall motion shown as 300 in the Figure. The distance indications could typically be color coded to indicate degree of motion, and especially be shown in a different color (for example red) if the direction of motion is opposite to contraction, which would indicate an anneurysmic function of parts of the LV. For better location and quantification of the reduced wall motion, the distance 317 versus angle coffid be shown in a Cartesian plot versus angle as shown in 318.

For clarity it is emphasizes that, while Figure 3 shows image data 307 to 312, the image data illustrated in this figure is merely provided to illustrate, by way of example, that the characteristic points 301 to 306 may be chosen so that they lie at the inner edge of the LV wall. The EDC characteristic curve 315 and the ESC characteristic curves 3 16 have not been obtained from image data 307 to 312 but has instead been obtained from other image data obtained earlier or later in the cardiac cycle than image data 307 to 312.

Connecting the characteristic points for each scan plane between the different depth displays for a given set of image data/point in time, one obtains a 3D wire frame model of the LV at that time point, illustrated as 400 in FIG. 4. An indication of wall motion may be superimposed over this wireframe, for example by colour coded shading, or any other means deemed suitable for illustrating wall motion. The wireframe model can be rotated to be examined from different view directions to better assess the location and magnitude of the wall motion abnormality.

The wire-frame model can through interpolation be continued between the wires into a continuous surface, and the deviation distance indications, 317, can be interpolated between the measured cross sections and coded into grey or color scale onto the surface, illustrated by example as 401 in the Figure. Additionally or alternatively the wireframe display may be updated in real time to indicate the motion of the LV wall in this manner.

When the characteristic points 301-306 are chosen as the inner wall edges, the wire frame model can be used to calculate the instantaneous volume of the LV, and obtain the stroke volume (SV) as the difference between the end diastolic volume (EDV) and the end systolic volume (ESV), and the ejection fraction (EF) can be calculated as EF = SV/EDV.

We should note that when the outer wall edges are used for the characteristic points, we would still obtain the SV as the difference between the EDV and ESV, because the LV muscle volume is constant. The EDV and ESV would then be too high by the magnitude of the LV wall volume.

Similar statements holds approximately true also when the characteristic points are the mid points or center of gravity of the wall echoes.

In one embodiment, once an area of potential concern has been detected, say for example an area of reduced wall motion or an area where the direction of wall motion is opposite to the direction of wall motion in other parts of the heart, the cross-sectional planes may be moved so that they all lie within the area of potential concern or so that two of the cross-sections lie close to the area of potential concern, with the remaining cross-sections being provided within the area of potential concern. An addition to moving the cross-sections, or alternative to such movement, additional cross-sections may be provided within the area of potential concern. An area of potential concern may either be identified by the ultrasound apparatus or an associated image processing device or may be indicated by way of user interaction. Once the area of potential concern has been identified, the cross-sections may automatically or manually be moved to the above discussed positions or additional cross-sections may be provided in an automated manner, or through user interaction.

It will be appreciated that, while the above description makes reference to measurements obtained from the left ventricle, the apparatus and method described herein may equally find use in analysis of the right ventricle or indeed of the entire heart or of more localized/smaller parts of the heart.

Claims

<claim-text>Claims: 1. An apparatus for ultrasound imaging comprising: an ultrasound transducer arranged to acquire ultrasound signals from only a number of 2D scan planes; a signal processor arranged to process said signals by selecting signals originating from a predetermined distance from the receiver; and a display arranged to display image data of the beating heart for a cross-section of the heart at said distance.</claim-text> <claim-text>2. An apparatus according to Claim 1, wherein the signal processor is further arranged to select a point within each intersection of a 2D scan plane with the heart wall according to a selection rule and to connect the selected points for the cross section using a continuous curve.</claim-text> <claim-text>3. An apparatus according to Claim I or 2, wherein the signal processor is further arranged to process said signal for more than one predetermined depths.</claim-text> <claim-text>4. An apparatus according to Claim 3, wherein the signal processor is further arranged to select a point within each intersection of a 20 scan plane with the heart wall at each of the depth according to a selection rule and to connect the selected points within a cross section using a continuous curve.</claim-text> <claim-text>5. An apparatus for ultrasound imaging comprising: an ultrasound transducer arranged to acquire ultrasound signals from only a number of 20 scan planes; a signal processor arranged to process said signals by selecting signals originating from a number predetermined distances from the receiver and to select a point within each intersection of a 20 scan plane with the heart wall at each of the distance according to a selection rule; and a display arranged to display the selected points in a three dimensional display.</claim-text> <claim-text>6. An apparatus according to Claim 5, wherein the signal processor is further arranged to connect the selected points at each distance with a characteristic curve and to display the characteristic curves at the number of distances in a wireframe andlor shaded display.</claim-text> <claim-text>7. An apparatus according to Claim 5 or 6, further comprising updating the three dimensional display in real time.</claim-text> <claim-text>8. An apparatus according to any of claims 5 to 7, wherein the signal processor is further arranged to select said predetermined distances so that over one or more heart beats all of the selected signals originate from the same cross-section of the heart.</claim-text> <claim-text>9. An apparatus according to any of Claims 5 to 8, wherein the signal processor is further arranged to track the movement of a selected point at a selected depths over time.</claim-text> <claim-text>10. An apparatus according to claim 9, wherein said display is further arranged to display an indication of the motion of said point as part of or in addition to the three dimensional display.</claim-text> <claim-text>11. An apparatus according to Claim 10, as dependent from claim 6, wherein the signal processor is further arranged to repeatedly determine a said characteristic curve for successive measurements in time and to provide interpolated indications of movement in areas between said 20 scan planes.</claim-text> <claim-text>12. A method for detection and assessment of wall motion abnormality in the left ventricle (LV) of the heart, comprising -simultaneous imaging in real time of the LV from the LV apex with 3 or more 2D scan planes that are rotated around a common axis, and -selecting at least one depth along the ultrasound beams that provides image data from at least one cross section of the LV, and -presenting the image data of the beating heart in spatial coordinate location for each said at least one cross section of the LV from all 20 scan planes on an image display.</claim-text> <claim-text>13. A method according to claim 12, further comprising -selecting characteristic points of the LV wall image of each cross section in the image display, and -connecting said characteristic points for each cross section with a continuous curve, and -displaying said continuous curve on said image display.</claim-text> <claim-text>14. A method according to claim 13, where said characteristic points are one of edges of the LV wall images, and the mid-point of the LV wall images, and the center of gravity of the LV wall images.</claim-text> <claim-text>15. A method according to claim 13, further comprising -highlighting said continuous curves with largest area as the end diastolic curve (EDC), and smallest area as the end systolic curve (ESC) for each of said cross sections on the image display.</claim-text> <claim-text>16. A method according to claim 14, further comprising using the distance as a function of angular location between said ESC and said EDC to quantify the degree of wall motion abnormality for each cross section.</claim-text> <claim-text>17. A method according to claim 12, where velocity information of the LV wall in each image location is time-integrated to obtain the time variable distance of material points of the LV wall in the different images during the cardiac cycle, and said at least one cross section moves with the material points of the LV during the cardiac cycle.</claim-text> <claim-text>18. A method according to claim 13, where said characteristic points of the same cross sections from different neighboring depths are in combination with the distance between the cross sections along the beams, connected into a 3D wire frame model for display of the beating heart, for assessment of 3D location and magnitude of the wall motion abnormality.</claim-text> <claim-text>19. A method according to claim 18, where velocity information of the LV wall in each image location is time-integrated to obtain the time variable distance of material points of the LV wall in the different images during the cardiac cycle, and said time variable distance is used in the formation of the wire frame model.</claim-text> <claim-text>20. A method according to claim 18, where said 3D wire frame model is continued to a surface, and the distance between the ESC and the EDC for each cross section is interpolated across the surface and coded into the display along the surface to show areas of wall motion abnormality.</claim-text> <claim-text>21. A method according to claim 18, said wire frame model is used to calculate the end diastolic volume (EDV), the end systolic volume (ESV), the stroke volume SV = EDV -ESV, and the ejection fraction EF = SV/EDV of the LV 22. A method according to claim 12, where the instrument operator allocates material points in the 2D images at different times in the cardiac cycle, and said at least one cross section moves with the material points of the LV during the cardiac cycle.23. A method according to claim 18, where the instrument operator allocates material points with time variable distance in the 2D images at different times in the cardiac cycle, and said time variable distance is used in the formation of the wire frame model.</claim-text>