U.S. patent number RE37,088 [Application Number 09/078,378] was granted by the patent office on 2001-03-06 for method for generating anatomical m-mode displays.
This patent grant is currently assigned to Vingmed Sound A/S. Invention is credited to James Ashman, Eivind Holm, Bjorn Olstad.
United States Patent |
RE37,088 |
Olstad , et al. |
March 6, 2001 |
**Please see images for:
( Certificate of Correction ) ** |
Method for generating anatomical M-mode displays
Abstract
A method for generating anatomical M-Mode displays for
ultrasonic investigation of living biological structures during
movement of the structure, for example a heart function, employing
an ultrasonic transducer (21) comprises the acquisition of a time
series of 2D or 3D ultrasonic images (22), arranging said time
series so as to constitute data sets, providing at least one
virtual M-Mode line (23) co-registered with said data sets,
subjecting said data sets to computer processing on the basis of
said at least one virtual M-Mode line, whereby interpolation along
said at least one virtual M-Mode line is effected, and displaying
the resulting computed anatomical M-Mode display (24) on a display
unit.
Inventors: |
Olstad; Bjorn (Ranheim,
NO), Holm; Eivind (Horten, NO), Ashman;
James (Braunstone, GB) |
Assignee: |
Vingmed Sound A/S (Horten,
NO)
|
Family
ID: |
26648522 |
Appl.
No.: |
09/078,378 |
Filed: |
May 13, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
379205 |
Jan 27, 1996 |
05515856 |
May 14, 1996 |
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Foreign Application Priority Data
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Aug 30, 1994 [NO] |
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94.3214 |
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Current U.S.
Class: |
600/440 |
Current CPC
Class: |
A61B
8/486 (20130101); G01S 7/52066 (20130101); G01S
7/52074 (20130101); G01S 15/8993 (20130101); G01S
7/52071 (20130101) |
Current International
Class: |
G01S
15/89 (20060101); G01S 15/00 (20060101); G01S
7/52 (20060101); A61B 008/00 () |
Field of
Search: |
;600/440,441,463,454,455,448,449,450,451,453,456 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Foley, et al., "Computer Graphics: Principles And Practice,"
Addison Wesley USA (1990) (only bibliographic pages included).
.
Olstad, B., "Maximizing Image Variance In Rendering Of Columetric
Data Sets", Journal Of Electronic Imaging, 1:256-265, Jul. 1992.
.
Borgefors, G., "Distance Transformations In Digital Images".,
Computer Vision, Graphics And Image Processing 34, 1986, pp.
344-371. .
Seitz, P., "Optical Superresolution Using Solid State Cameras And
Digital Signal Processing", Optical Engineering 27(7) Jul. 1998,
pp. 535-540. .
R. Omoto, Y. Yokote, et al. "B/M Conversion System With Free
Setting Of Cursor Line: Clinical Applications Thereof", 41-PA-31,
3pgs. (Saitama Medical School). .
R. Omoto, Y. Yokote, et al. "New System for Converting From
Tomogram Echocardiography To M-Mode Freely Set Cursor Line",
40-C-51, 2pgs. (Saitama Medical School). .
"New Transforming System From Tomogram Echocardiography To M-Mode",
40-C-5.1, 7pgs. .
R. Omoto, Y. Yokote, et al. "B/M Conversion System with Free
Setting of Cursor Line: Clinical Applications Thereof ", 41-PA-31,
3pp. .
R. Omoto, Y. Yokote, et al. "New System For Converting From
Tomogram Echocardiography To M-Mode Freely Set Cursor Line",
40-C-51, 2pp..
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Primary Examiner: Manuel; George
Attorney, Agent or Firm: Blakely, Sokoloff, Taylor &
Zafman, LLP
Claims
We claim:
1. A method for generating anatomical M-Mode displays in ultrasonic
investigation of living biological structures during movement
employing an ultrasonic transducer the method comprising the steps
of:
acquiring a time series of ultrasonic images;
arranging said time series so as to constitute data sets obtained
by multiple ultrasound beams;
providing at least one virtual M-Mode line positioned in
relationship to said data sets so as not to coincide with any
ultrasonic beam direction of said transducer;
subjecting said data sets to computer processing on the basis of
said at least one virtual M-Mode line, whereby interpolation along
said at least one virtual M-Mode line is effected using values from
said multiple ultrasound beams; and
displaying the resulting computed anatomical M-Mode display on a
display unit.
2. The method according to claim 1, further comprising the step of
moving the position and orientation of said at least one virtual
M-Mode line in response to rhythmic movement of the biological
structure.
3. The method according to claim 2, further comprising the step of
associating a reference point with said ultrasonic images and
fixing a corresponding reference point at a chosen vertical
coordinate in the resulting anatomical M-Mode display based upon
said reference point.
4. The method according to claim 3, employed for investigating the
left ventricle wall of the heart, the method further comprising the
steps of:
computing anatomical M-Modes associated with each position on the
left ventricle wall surface in ultrasonic images so as to represent
a differential time evolution of the cardiac cycle, and
characterizing each of the computed anatomical M-Modes for color
encoding at each said position on the left ventricle wall
surface.
5. The method according to claim 3, further comprising the steps
of:
computing anatomical M-Modes associated with each position on the
left ventricle wall surface in ultrasonic images limited to the
difference between two image frames, and
characterizing each of the computed anatomical M-Modes for color
encoding at each said position on the left ventricle wall
surface.
6. The method according to claim 3, further comprising the steps
of:
computing anatomical M-Modes associated with each position on the
left ventricle wall surface in ultrasonic images so as to represent
a time interval, and
characterizing each of the computed anatomical M-Modes for color
encoding at each said position on the left ventricle wall
surface.
7. The method according to claim 1, employed for investigating the
left ventricle wall of the heart, the method further comprising the
steps of:
computing anatomical M-Modes associated with each position on the
left ventricle wall surface in ultrasonic images so as to represent
a differential time evolution of the cardiac cycle, and
characterizing each of the computed anatomical M-Modes for color
encoding at each said position on the left ventricle wall
surface.
8. The method according to claim 7, further comprising the step of
measuring local or global thickening of said left ventricle wall
along said at least one virtual M-Mode line and utilizing the
result of the measurement for said color encoding.
9. The method according to claim 7, further comprising the step of
measuring temporal intensity variations along said at least one
virtual M-Mode line and utilizing the result of the measurement for
said color encoding.
10. The method according to claim 7, further including the step of
determining the direction of said at least one virtual M-Mode line
as the direction determined in the distance transform from an
arbitrary position to the closest position on the left ventricle
wall.
11. The method according to claim 1, further comprising the steps
of:
computing anatomical M-Modes associated with each position on the
left ventricle wall surface in ultrasonic images limited to the
difference between two image frames, and
characterizing each of the computed anatomical M-Modes for color
encoding at each said position on the left ventricle wall
surface.
12. The method according to claim 1, further comprising the steps
of:
computing anatomical M-Modes associated with each position on the
left ventricle wall surface in ultrasonic images so as to represent
a time interval, and
characterizing each of the computed anatomical M-Modes for color
encoding at each said position on the left ventricle wall
surface.
13. The method according to claim 12, further comprising the step
of measuring local or global thickening of said left ventricle wall
along said at least one virtual M-Mode line and utilizing the
result of the measurement for said color encoding.
14. The method according to claim 12, further comprising the step
of measuring temporal intensity variations along said at least one
virtual M-Mode line and utilizing the result of the measurement for
said color encoding.
15. The method according to claim 1, further comprising the step of
subjecting the result of said computer processing with
interpolation to image processing for edge enhancement, thus
producing said resulting computed anatomical M-Mode display.
16. The method according to claim 1, wherein the step of acquiring
a time series of ultrasonic images occurs after a desired virtual
M-Mode line has been defined, such that only the ultrasound data
necessary to generate the said virtual M-Mode line are acquired,
thereby increasing the time-resolution of said time series and
hence the said computed anatomical M-Mode display.
17. The method according to claim 1, further comprising the step of
moving the position and orientation of said at least one virtual
M-Mode line in response to rhythmic movement of the biological
structure.
18. The method according to claim 1, further comprising the step of
associating a reference point with said ultrasonic images and
fixing a corresponding reference point at a chosen vertical
coordinate in the resulting anatomical M-Mode display based upon
said reference point.
19. The method according to claim 1, wherein said time series of
ultrasonic images is three dimensional..Iadd.
20. An ultrasound imaging apparatus comprising:
a memory to store ultrasonic information associated with a set of
ultrasound beams; and
a computer processing device, coupled to said memory, said
processing device to generate a virtual M-mode line that is
distinct from said ultrasound beams, and to generate image data
based on said M-Mode line..Iaddend..Iadd.
21. The apparatus of claim 20, wherein said virtual M-mode line is
non-coincident with said set of ultrasound
beams..Iaddend..Iadd.
22. The apparatus of claim 21, further comprising:
a transducer, coupled to said memory, to provide said ultrasonic
information associated with said set of ultrasound
beams..Iaddend..Iadd.
23. The apparatus of claim 21, further comprising:
a display, coupled to said processing device, to display an image
based on said image data..Iaddend..Iadd.
24. The apparatus of claim 23, wherein said image includes color
encoded information, based on a predetermined
variable..Iaddend..Iadd.
25. The apparatus of claim 24, wherein said predetermined variable
depends on temporal variation along said virtual M-mode
line..Iaddend..Iadd.
26. The apparatus of claim 24, wherein said predetermined variable
depends on a thickness of an anatomical
structure..Iaddend..Iadd.
27. The apparatus of claim 26, wherein said structure comprises an
anatomical structure having motion..Iaddend..Iadd.
28. The apparatus of claim 21, wherein said ultrasonic information
comprises a time series of ultrasonic
information..Iaddend..Iadd.
29. The apparatus of claim 21, wherein said processing device is
operable to vary at least one of a position and an orientation of
said virtual M-mode line..Iaddend..Iadd.
30. The apparatus of claim 29, wherein said processing device is
further operable to vary at least one of said position and said
orientation of said virtual M-mode line based on motion of a
structure indicated by said ultrasonic
information..Iaddend..Iadd.
31. A system for providing ultrasound imaging, said system
comprising:
a first means for providing ultrasonic information based on a set
of ultrasound beams; and
a second means for generating image data based at least in part on
a virtual M-mode line means which is distinct from said ultrasound
beams..Iaddend..Iadd.
32. The system of claim 31, wherein:
said first means includes a transducer means for generating said
set of ultrasound beams upon which said ultrasonic information is
based; and
said M-mode line which is non-coincident with said set of
ultrasound beams..Iaddend..Iadd.
33. The system of claim 31, further comprising:
a display means for displaying an image associated with said image
data..Iaddend..Iadd.
34. The system of claim 33, wherein said image includes color
encoded information, based on a predetermined
variable..Iaddend..Iadd.
35. The system of claim 34, wherein said predetermined variable
depends on temporal variation with respect to said virtual
reference means..Iaddend..Iadd.
36. The system of claim 34, wherein said predetermined variable
depends on a thickness of an anatomical
structure..Iaddend..Iadd.
37. The system of claim 31, wherein said ultrasonic information
comprises a time series of ultrasonic
information..Iaddend..Iadd.
38. The system of claim 31, wherein said second means comprises
means for varying at least one of a position and an orientation of
said virtual M-mode line means..Iaddend..Iadd.
39. The system of claim 38, wherein said second means provides for
varying at least one of said position and said orientation of said
virtual M-mode line means based on motion of a structure indicated
by said ultrasonic information..Iaddend..Iadd.
40. A method for use in an ultrasound imaging system, said method
comprising:
storing ultrasonic data associated with a set of ultrasonic beams;
and
generating a virtual M-mode line to generate image data based on
said ultrasonic data, wherein said virtual M-mode line is distinct
from said set of ultrasonic beams..Iaddend..Iadd.
41. The method of claim 40, further comprising:
displaying an image based on an interpolation of said ultrasonic
data along said reference..Iaddend..Iadd.
42. The method of claim 41, further comprising:
color encoding said image based on a predetermined
criteria..Iaddend..Iadd.
43. The method of claim 42, wherein said predetermined criteria is
associated with a temporal intensity variation with respect to said
virtual reference, which comprises a virtual M-mode
line..Iaddend..Iadd.
44. The method of claim 42, wherein said predetermined criteria is
associated with thickening of an anatomical
structure..Iaddend..Iadd.
45. The method of claim 40, wherein said virtual M-mode line
non-coincident with said set of ultrasound
beams..Iaddend..Iadd.
46. The method of claim 40, further comprising:
acquiring a time series of ultrasonic information; and
arranging said time series of ultrasonic information to generate
said ultrasonic data, which represents data sets obtained by said
set of ultrasonic beams..Iaddend..Iadd.
47. The method of claim 46, wherein said time series of ultrasonic
information is three-dimensional (3D)..Iaddend..Iadd.
48. The method of claim 40, further comprising:
moving at least one of a position and orientation of said virtual
M-mode line..Iaddend..Iadd.
49. The method of claim 48, wherein moving said at least one of
said position and orientation of said virtual M-mode line depends
on movement of an object represented by said ultrasonic
data..Iaddend..Iadd.
50. The method of claim 40, further comprising:
performing edge enhancement image processing upon said ultrasonic
data; and
displaying an image based on said edge enhanced ultrasonic data,
said image representing an interpolation of said ultrasonic data
along said virtual M-mode line..Iaddend.
Description
BACKGROUND OF THE INVENTION
This invention relates to a method for generating anatomical M-Mode
displays in ultrasonic investigation of living biological
structures during movement, for example a heart function, employing
an ultrasonic transducer.
The invention describes a technique for obtaining anatomically
meaningful M-Mode displays by data extraction from 2D (two
dimensional) and 3D (three dimensional) ultrasonic imaging.
Conventional M-Mode is acquired along one acoustical beam of an
ultrasonic transducer employed, displaying the .[.tide-variant.].
.Iadd.time-variant .Iaddend.data in a display unit with time along
the x-axis and depth along the y-axis. The localization of the
M-Mode line in conventional M-Mode is limited to the set of beam
directions that can be generated (scanned) by the transducer.
In cardiology, the use of the M-Mode method is fairly standardized,
requiring specific cuts through the heart at standard positions and
angles. To be able to perform a good M-Mode measurement, important
criteria are:
1. Image quality. The borders and interfaces between different
structures of the heart must be clearly visible. One of the most
important factors to achieve this, is to position the ultrasound
transducer on the body concerned at a point where the acoustic
properties are optimum. These places are often referred to as
"acoustic windows". On older patients, these windows are scarce,
and hard to find.
2. Alignment. The standardized M-Mode measurements require that the
recording is taken at specific angles, usually 90 degrees relative
to the heart structure being investigated.
3. Motion. As the heart moves inside the chest during contraction
and relaxation, a correct M-Mode line position at one point in the
heart cycle may be wrong at another point in the same heart cycle.
This is very difficult to compensate for manually, since the probe
must be moved synchronous to the heartbeats. Therefore, most
sonographers settle for a fixed, compromise direction of the M-Mode
line, i.e. transducer beam.
4. Wall thickening analysis. With coronary diseases, an important
parameter to observe is the thickening of the left ventricular
muscle at various positions.
In many cases there can be problems getting the correct alignment
at a good acoustical window. Often, the good acoustic windows give
bad alignment, and vice versa. Hence, the sonographer or user
spends much time and effort trying to optimize the image for the
two criteria (alignment, image quality).
SUMMARY OF THE INVENTION
With the advent of high-performance digital front-end control for
phased transducer array probes, the possibility exists for
acquiring 2D images at very high framerates (<10 ms per 2D
image). These 2D data are stored in a computer RAM, with storage
capacity enough to hold one or more full heart cycles worth of 2D
data recordings. M-Mode displays can be generated based on these
recordings with an adequate temporal resolution. According to the
present invention this allows for complete flexibility in the
positioning of the M-Mode lines. The invention describes how this
flexibility can be utilized to improve the anatomical information
content in the extracted M-Mode displays.
The invention also applies to extraction of M-Mode displays from a
time series with 3D images. In 3D it is possible to compensate for
the true 3D motion of the ventricle. Based on 2D recordings the
operator will be limited to compensate for the movements that can
be measured in the imaged plane. The invention also describes how
local M-Mode information extracted from 3D acquisitions can be
utilized to obtain a color encoding of the ventricle wall providing
information about wall thickening.
The anatomical M-Mode displays can be generated in real-time during
scanning of a 2D image or during real-time volumetric scanning. The
invention then describes how multiple M-Mode displays can be
maintained together with the live 2D or 3D image. These M-Mode
displays can also be freely positioned and even allowed to track
the location and direction of the ventricle wall during the cardiac
cycle. During real-time scanning, time resolution of anatomical
M-Mode displays may be increased by constraining the 2D or
volumetric scanning to the area defined by the ultrasound probe and
the M-Mode line. This requires complete control of the ultrasound
scanner front-end.
The anatomical M-Mode can also be used as a post-processing tool,
where the user acquires the 2D/3D image sequence at super-high
framerates, without making any M-Mode recordings. As long as the 2D
data includes an adequate cut/view through the heart, the user may
use the anatomical M-Mode to do the M-Mode analysis later.
The computer processing of data sets are previously known, as for
example described in: J. D. Foley, A van Dam, S. K. Seiner, J. F.
Hughes "Computer Graphics: Principles and Practice", Addison Wesley
U.S.A. (1990). Among other things line drawing algorithms are
described in this reference. Thus, such computer processing,
operations and steps are not explained in detail in the following
description. Other references relating more specifically to
techniques of particular interest here are the following:
B. Olstad, "Maximizing image variance in rendering of volumetric
data sets," Journal of Electronic Imaging, 1:245-265, July
1992.
E. Steen and B. Olstad, "Volume rendering in medical ultrasound
imaging". Proceedings of 8th Scandinavian Conference on Image
Analysis. Troms.o slashed., Norway May 1993.
G. Borgefors, "Distance transformations in digital images",
Computer vision, graphics and image processing 34, 1986, pp.
344-371.
Peter Seitz, "Optical Superresolution Using Solid State Cameras and
Digital Signal Processing", Optical Engineering 27(7) July
1988.
On the background of known techniques this invention takes as a
starting-point methods for computation of conventional M-Mode and
established clinical procedures for utilization of M-Mode imaging.
The invention includes new techniques for the computation of
anatomical M-Mode displays based on a time series of 2D or 3D
ultrasonic images. The anatomical M-Mode is derived as a virtual
M-Mode measurement along an arbitrary or virtual, tilted M-Mode
line. What is novel and specific in the method according to the
invention is defined more specifically in the appended claims.
Some of the advantages obtained with this invention can be
summarized as follows: Multiple M-Mode displays with arbitrary
positioning can be computer on the basis of a 2D or 3D acquisition.
The position of the M-Mode line is not limited to the scanning
geometry and can be freely positioned. Global heart movements can
be compensated for by moving the M-Mode line according to the
motion of the heart during the cardiac cycle. Wall thickening
analysis is improved due to the possibility of keeping the M-Mode
line perpendicular to the ventricle wall during the entire cardiac
cycle. Reference points in the scene can be fixed at a given
y-coordinate in the M-Mode display, hence improving the visual
interpretability of relative motion/thickening phenomenons. 3D
acquisitions can be visualized by mapping properties extracted from
local M-Mode lines in a color encoding of the ventricle wall.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention shall be described in more detail in the following
description of various embodiments with reference to the drawings,
in which:
FIG. 1 schematically illustrates the computation of M-Mode displays
according to the prior art.
FIG. 2 schematically illustrates the inventive concept of a tilted
anatomical or virtual M-Mode line for computation of corresponding
M-Mode displays.
FIG. 3 indicates a setting with multiple M-Mode lines, according to
an embodiment of this invention.
FIG. 4 illustrates how movement of the position of the M-Mode line
as a function of the position in the cardiac cycle can be used to
obtain motion correction.
FIG. 5 illustrates an anatomical M-Mode whereby no reference point
is specified.
FIG. 6 illustrates an anatomical M-Mode line when a reference point
has been specified and fixed to given vertical position in the
display of the anatomical M-Mode.
FIG. 7 illustrates wall thickening analysis in a setting with 3
simultaneous anatomical M-Mode displays.
FIG. 8 indicates how the anatomical M-Mode displays are computed in
a situation where the position of the M-Mode line is fixed during
the cardiac cycle.
FIG. 9 schematically illustrates how a color encoding of the
ventricle wall representing wall thickening can be computed in 4D
ultrasonic imaging.
FIG. 10 schematically illustrates how the acquisition of the
ultrasound data can be optimized for used in anatomical M-Mode,
reducing the amount of data used for each image, enabling more
images to be acquired during a given time span.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates conventional M-Mode imaging. An ultrasound
transducer 11 is schematically indicated in relation to an
ultrasonic image 12 obtained by angular scanning of the acoustical
beam of the transducer. In this conventional method by the M-Mode
line or corresponding acoustical beam 13 is fixed at a given
position and the ultrasonic signal along the beam is mapped as a
function of time in the M-Mode display 14. Extreme temporal
resolution can be achieved with this prior art because a new time
sample can be generated as soon as the data for one beam has been
gathered. This prior art for M-Mode imaging will on the other hand
limit the positioning of the M-Mode line 13 according to the
acoustic windows and scanning geometry.
TILTED M-MODE LINES
This invention relates to how M-Mode images can be generated by
extraction of interpolated displays from time series of 2D or 3D
images. The concept of a "tilted" M-Mode display 24 is illustrated
in FIG. 2. The "virtual" M-Mode line 23 is in this case freely
moveable, not being restricted to coincide with one acoustic beam
(transducer 21) originating at the top of the 2D image(s) 22.
MULTIPLE M-MODE LINES
FIG. 3 illustrates an example where two tilted M-Mode displays 34A,
34B have been computed or calculated from a single 2D sequence or
image 32, with corresponding virtual, tilted M-Mode lines indicated
at 33A and 33B respectively. Basing the generation of M-Mode
displays on 2D or 3D images, any sector number of M-Mode displays
can be generated, enabling analysis of various dimensions from the
same heartbeat. Thus, acquired time series as indicated at 1, 2, 3,
4 in FIG. 2 are arranged to constitute data sets, at least one
virtual M-Mode line 23 or 33A, 33B in FIG. 3, are provided and
co-registered with the data sets, and these are then subjected to
computer processing with interpolation along the virtual M-Mode
line concerned. The importance of interpolation will be explained
further below.
MOTION CORRECTION
As the heart moves inside the chest during contraction and
relaxation, a correct M-Mode line position at one point in the
heart cycle may be wrong at another point in the same heart cycle.
This is very difficult to compensate for manually, the probe must
be moved synchronous to the heartbeats.
The anatomical M-Modes according to this invention can compensate
for this motion. FIG. 4 illustrates this concept. The user defines
the position of the M-Mode line 43A and 43B respectively, at
different points in the heart cycle such as by scrolling a 2D
cineloop and fixing a new M-Mode line position. Appropriate
computer operations or software are available and known to those of
ordinary skill in this field, as shown in the above references, is
utilized to interpolate the M-Mode line positions between the
"fixed" M-Mode lines 43A and 43B, and generates an M-Mode display
44 where each vertical line in the M-Mode display is extracted
along the local definition of the M-Mode line.
In this manner the position and/or orientation of the virtual
M-Mode line can be movable in response to other rhythmic movements
in the biological structure or body concerned, other than the
heartbeats referred to in the description of FIG. 4.
MOTION REFERENCE POINTS
When studying an organ's time-variant dimensions in a living body,
there is often a wish to study the different structures' dimensions
relative to each other, without observing the whole organ's
displacement inside the body. This is especially interesting when
looking at the heart's ventricular contractions and relaxations,
where the thickening of the muscle tissue is the important
parameter to observe.
To enhance the relative variations, according to an embodiment of
this invention, the user can define a reference point on the
"fixed" M-Mode lines described in the previous paragraph on motion
correction. Typically, this point will correspond to an easily
defined clinical structure. FIGS. 5 and 6 illustrate M-Mode
generation without and with a fixation of a given reference point
66 in the imaged scene 62. Thus, on the basis of the reference
point 66 associated with the interpolated M-Mode line positions 63A
to 63B shown in FIG. 6, there is generated a M-Mode display 64 with
this point 66 appearing as a straight line 67 (no motion) i.e. at a
chosen vertical coordinate in the display. Alternatively, a given
y-coordinate can be tracked in the M-Mode display and the M-Mode
display regenerated by sliding the position of the M-Mode lines at
the various time locations such that the tracked image structure
appears as a horizontal structure in the final M-Mode display.
WALL THICKENING ANALYSIS
With coronary diseases, an important parameter to observe is the
thickening of the left ventricular muscle at various positions.
Combining the techniques described in previous paragraphs, this
invention provides a specially useful tool for left ventricle
thickening analysis, as illustrated by FIG. 7.
Each M-Mode display 74A, 74B and 74C represents the regional wall
thickening and contraction of one part of the ventricle 70, each
part being penetrated by a corresponding virtual M-Mode line 73A,
73B and 73C respectively. FIG. 7 shows a short axis view of the
left ventricle 70 and three anatomical M-Mode displays 74A, 74B,
74C generated with the techniques described in the previous
paragraphs.
IMPLEMENTATION
The sequence of 2D/3D frames is stored in the scanner/computer
employed as a 3- or 4-dimensional array or data set(s) of
ultrasound samples. This array may have different geometric
properties, depending on the transducer probe geometry used, and
whether images have been scanconverted to a rectangular format
prior to storing. For illustration, in the setting shown in FIG. 8,
we use an example where the 2D sector data have been scanconverted
previously (typically using an ultrasound scanner's hardware
scanconverter) and stored to disk/memory in a rectangular data set
format, as a 3D-array 82 of samples with the dimensions being
[x,y,t].
Generating an M-Mode display 84 can then be viewed upon as cutting
a plane 88 through the 3D data set 82, interpolating and resampling
the data to fit into the desired display rectangle 84. The motion
correction techniques described above will modify the cutting plane
88 to a curved surface that is linear in the intersections with the
[x,y] planes. It is of primary importance that adequate
interpolation techniques are applied both in the spatial and
temporal dimension. Such interpolation can to some extent
compensate for inferior resolution compared with conventional
M-Mode along the acoustical beams generated by the transducer as
shown in FIG. 1.
Temporal resolution of the M-Mode displays may be increased by
controlling the image acquisition to encompass only the necessary
area. In FIG. 10, the virtual M-Mode line 101 defines the minimum
necessary image area 104. By controlling the front-end of the
ultrasound scanner to only acquire the necessary acoustical beams
102, and not acquiring the data 103 outside the virtual M-Mode
line, the ultrasound scanner uses less time for acquiring the
image, and this time is used to improve the temporal resolution of
the time series. This special enhancement can be done at the cost
of freely positioning other virtual M-Mode lines during
post-processing.
According to an embodiment of the invention it is an additional and
advantageous step to let the result of the above computer
processing including interpolation, be subjected to an image
processing as known per se for edge enhancement, to produce the
resulting computed anatomical M-Mode display.
3D ULTRASONIC IMAGING
All the techniques described here apply both to a sequence of 2D
and a sequence of 3D ultrasonic images. 3D acquisitions further
improves the potential of motion correction described, because the
true 3D motion of the heart can be estimated.
In addition to the actual generation of M-Mode displays the
techniques according to this invention can be further utilized to
extract anatomical M-Modes for all points across the endocard
surface in the left ventricle. This setting is illustrated with an
example in FIG. 9. A 4 dimensional ultrasound data set 92 is
assumed consisting of m short axis planes and n 3D cubes recorded
during the cardiac cycle. For simplicity in the figure only three
virtual M-Mode lines 93A, 93B, 93C with the associated M-Mode
displays 94A, 94B and 94C, respectively, have been drawn, but
similar M-Mode displays should be associated with every point or
position on the endocard surface in the ventricle 90.
Each of the individual M-Mode displays 94A, 94B, 94C . . . , are
then processed in order to obtain a characterization that can be
visualized as a color encoding of the associated location on the
ventricle wall. The mapping strategy is illustrated in FIG. 9 and
is similar to the approach found in ref. B. Olstad, "Maximizing
image variance in rendering of volumetric data sets," Journal of
Electronic Imaging, 1:245-265, July 1992 and E. Steen and B.
Olstad, "Volume rendering in medical ultrasound imaging".
Proceedings of 8th Scandinavian Conference on Image Analysis.
Troms.o slashed., Norway May 1993 identified previously. The
characterization routine thus operates on an anatomical M-Mode
display and generates a single value or a color index that reflects
physiological properties derived in the M-Mode image. One of these
properties is a quantification of wall thickening by estimation of
thickening variations during the cardiac cycle. Each of the
anatomical M-Mode displays 94A, 94B and 94C are in this case
analyzed. The wall is located in the said M-Mode displays methods
such as those described in Peter Seitz, "Optical Superresolution
Using Solid State Cameras and Digital Signal Processing", Optical
Engineering 27(7) July 1988 for superresolution edge localization
at the various time instances in the M-Mode displays and the
thickness variations are used to define the said estimated
quantification of wall thickening. A second property is given by a
characterization of the temporal signal characteristics at a given
spatial coordinate or for a range of spatial coordinates in the
M-Mode displays 94A, 94B and 94C.
A second alternative is to use only two cubes that are either
temporal neighbors or that are located at End-Systole and
End-Diastole. The associated M-Modes will in this case reduce to
simply two samples in the temporal direction. This approach is more
easily computed and will provide differential thickening
information across the ventricle wall if the cubes are temporal
neighbors. The wall thickening analysis is in this case a
comparison of two one dimensional signals where thickenings can be
estimated with the methods described in Peter Seitz, "Optical
Superresolution Using Solid State Cameras and Digital Signal
Processing", Optical Engineering 27(7) July 1988 for
superresolution edge localization.
The color encodings described for 3D also applies to 2D imaging,
but the color encodings are in this case associated with the
boundary of the blood area in the 2D image. FIG. 7 illustrates such
a 2D image sequence. The figure includes only three virtual M-Mode
lines 73A, 73B and 73C with the associated M-Mode displays 74A, 74B
and 74C, respectively, but similar M-Mode displays should be
associated with every point or position on the endocard surface in
the ventricle 70. Each of the individual M-Mode displays 74A, 74B
and 74C are then processed with the same techniques as described
above for the corresponding M-Mode displays 94A, 94B and 94C in the
three-dimensional case.
The M-Mode lines in this embodiment of the invention are associated
with each point or position identified on the surface of the
ventricle wall and the direction is computed to be perpendicular to
the ventricle wall. The direction of the local M-Modes are computed
as the direction obtained in a 2- or 3-dimensional distance
transform of a binary 2- or 3-dimensional binary image representing
the position of the points on the ventricle wall. See ref. G.
Borgefors, "Distance transformations in digital images", Computer
vision, graphics and image processing 34, 1986, pp. 344-371 for
information on a suitable distance transform.
In summary this invention as described above provides a method for
computation of anatomical M-Mode displays based on a time series of
2D or 3D ultrasonic images. The method is used for the
investigation of living biological structures during movement, for
example a heart function. The main application will be in hospitals
and the like. The anatomical M-Mode displays can be computed in
real-time during the image acquisition or by postprocessing of a 2D
or 3D cineloop. The anatomical M-Mode is derived as a virtual
M-Mode measurement along an arbitrary tilted M-Mode line. Multiple,
simultaneous M-Mode lines and displays can be specified. The
arbitrary positioning of the M-Mode line allows for anatomically
meaningful M-Mode measurements that are independent of acoustic
windows that limit the positioning of M-Modes in the prior art. The
positioning of the M-Mode line can be changed as a function of time
to compensate for global motion. The M-Mode line can in this way be
made perpendicular to the heart wall during the entire heart cycle.
This property increases the value of M-Modes in wall thickening
analysis because erroneous thickenings caused by inclined
measurements can be avoided. Furthermore, reference points in the
image scene can be fixed in the M-Mode display such that the visual
interpretation of relative variations can be improved. In 3D
cineloops the M-Modes can be computed locally at all points in the
ventricle wall along M-Mode lines that are perpendicular to the
endocard surface. These local M-Modes are exploited to assess wall
thickening and to utilize these measurements in a color encoding of
the endocard surface.
* * * * *