U.S. patent application number 16/004137 was filed with the patent office on 2018-10-11 for x-ray mammography with tomosynthesis.
This patent application is currently assigned to Hologic, Inc.. The applicant listed for this patent is Hologic, Inc.. Invention is credited to Kenneth DeFreitas, Baorui Ren, Christopher RUTH, Ian SHAW, Andrew P. SMITH, Jay A. STEIN.
Application Number | 20180289347 16/004137 |
Document ID | / |
Family ID | 63710575 |
Filed Date | 2018-10-11 |
United States Patent
Application |
20180289347 |
Kind Code |
A1 |
DeFreitas; Kenneth ; et
al. |
October 11, 2018 |
X-RAY MAMMOGRAPHY WITH TOMOSYNTHESIS
Abstract
A method and system for producing tomosynthetic images of a
patient's breast. An x-ray source that delivers x-rays through a
breast immobilized and compressed between a compression paddle and
a breast platform and form an image at a digital x-ray receptor
panel. Multiple x-ray images are taken as the x-ray source and the
receptor move relative to the immobilized breast. In one preferred
embodiment, the x-ray source travels from -15.degree. to
+15.degree.. The source can travel in an arc around the breast
while the receptor travels linearly while remaining parallel and at
the same distance from the breast platform. The sets of x-ray image
data taken at different angles are combined to form tomosynthetic
images that can be viewed in different formats, alone or as an
adjunct to conventional mammograms.
Inventors: |
DeFreitas; Kenneth;
(Patterson, NY) ; Ren; Baorui; (Andover, MA)
; SHAW; Ian; (Yorktown Heights, NY) ; RUTH;
Christopher; (Danvers, MA) ; SMITH; Andrew P.;
(Lexington, MA) ; STEIN; Jay A.; (Boston,
MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hologic, Inc. |
Marlborough |
MA |
US |
|
|
Assignee: |
Hologic, Inc.
Marlborough
MA
|
Family ID: |
63710575 |
Appl. No.: |
16/004137 |
Filed: |
June 8, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13896828 |
May 17, 2013 |
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16004137 |
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12879807 |
Sep 10, 2010 |
8452379 |
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13896828 |
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10723486 |
Nov 26, 2003 |
7831296 |
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12879807 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 6/025 20130101;
A61B 6/481 20130101; A61B 6/502 20130101; A61B 6/482 20130101; A61B
6/464 20130101; A61B 6/12 20130101 |
International
Class: |
A61B 6/00 20060101
A61B006/00; A61B 6/02 20060101 A61B006/02 |
Claims
1.-56. (canceled)
57. A breast x-ray imaging system to obtain two types of breast
images of a patient's breast in a single breast compression,
wherein a first type of the multiple types of breast images is a
mammogram image and a second type of the multiple types of breast
images are a plurality of tomosynthesis images: a breast platform
and a compression paddle configured to compress therebetween the
patient's breast for the single breast compression; a flat panel
digital x-ray receptor; an x-ray source disposed opposite the
breast platform and the compression paddle and configured to be
selectively energized to emit x-rays at at least three positions
over an angular range, wherein one of the at least three positions
is substantially normal to the breast platform; an electronic
control system configured for interaction with the x-ray source,
wherein the electronic control system is configured to selectively
energize the x-ray source at the at least three positions over the
angular range; and an anti-scatter grid positioned between the
breast platform and the flat panel digital x-ray receptor, the
anti-scatter grid configured for selective retraction between a
first grid position and a second grid position; wherein the x-ray
source is configured for emission of x-rays at each of the at least
three positions over the angular range to obtain the second type of
breast images, and wherein the x-ray source is configured for
emission of x-rays at only the substantially normal position to
obtain the first type of breast images, wherein an x-ray dose to
the patient's breast at each of the at least three positions to
obtain the second type of breast images is lower than an x-ray dose
to the patient's breast at the only the substantially normal
position to obtain the first type of breast images, and wherein the
two types of breast images are obtained in the single breast
compression.
58. The system of claim 57, wherein the electronic control system
is configured to move the x-ray source continuously along the
angular range during energizing of the x-ray source in the at least
three positions.
59. The system of claim 57, wherein the x-rays emitted to obtain
the first type of breast images are emitted at a kV less than the
x-rays emitted to obtain the second type of breast images.
60. The system of claim 57, wherein when in the first grid
position, the anti-scatter grid is disposed between the x-ray
source and the flat panel digital x-ray receptor, and the x-ray
source is configured to emitted the x-ray only so as to obtain the
first type of breast images.
61. The system of claim 57, further comprising a display configured
to display at least one of the multiple types of breast images.
62. The system of claim 57, wherein the second type of the multiple
types of breast images comprise an adjustable image thickness.
63. The system of claim 57, wherein the x-ray source comprises
Tungsten.
64. The system of claim 57, wherein the electronic control system
is configured to maintain the x-ray source in a stationary position
when emitting the x-rays.
65. The system of claim 57, wherein the electronic control system
is configured to maintain the flat panel digital x-ray receptor in
a stationary position when the x-ray source is emitting x-rays in
the at least three positions.
66. The system of claim 57, wherein the electronic control system
is configured to position the x-ray source approximately one degree
apart in each of the at least three positions.
67. An x-ray system for acquiring multiple types of breast images,
including a conventional mammogram image and a tomosynthesis image
in a single compression of a breast, the x-ray system comprising:
an x-ray source disposed on a rotatable arm; a breast platform; a
digital x-ray receptor disposed below the breast platform; a
compression paddle disposed between the x-ray source and the
receptor; at least one processor communicatively coupled to the
x-ray system; and memory storing executable instructions that, when
executed by the at least one processor, perform a method
comprising: compressing the breast between the compression paddle
and the breast platform; rotating automatically the x-ray source
along a range of angular positions; emitting x-rays at each of the
angular positions of the x-ray source along the range, wherein the
angular positions include (i) a conventional mammogram position,
and (ii) a plurality of tomosynthesis positions, wherein at least
one of the plurality of tomosynthesis positions is the same as the
conventional mammogram position, taken during the single
compression of the breast; and receiving image data when the x-ray
source is emitting x-rays at the conventional mammogram position
and at the plurality of tomosynthesis positions.
68. The method of claim 67, further comprising processing the image
data to obtain the conventional mammogram image and the
tomosynthesis image.
69. The system of claim 67, wherein the method further comprises:
emitting a conventional mammogram image dose when the x-ray source
is at the conventional mammogram position; and emitting a
tomosynthesis image dose when the x-ray source is at the plurality
of tomosynthesis positions.
70. The system of claim 67, wherein the system further comprises an
anti-scatter grid movably disposed between the breast platform and
the receptor, and wherein the method further comprises positioning
automatically the anti-scatter grid based at least in part on a
type of x-ray dose emitted.
71. The system of claim 70, wherein the anti-scatter grid is
disposed between the breast platform and the receptor when the
x-ray is emitted at the conventional mammogram position.
72. The system of claim 67, wherein compressing the breast between
the compression paddle and the breast platform comprises releasing
the breast from compression after emitting x-rays at the angular
positions.
73. The system of claim 67, wherein rotating automatically the
x-ray source along the range of angular positions is performed
substantially simultaneously with emitting x-rays at the angular
positions, while the breast remains in compression between the
breast platform and the compression paddle.
74. The system of claim 67, wherein the tomosynthesis image
comprises a plurality of tomosynthesis images, and wherein
processing the image data comprises reconstructing a plurality of
tomosynthesis projection images into the plurality of tomosynthesis
images.
75. The system of claim 67, further comprising an anti-scatter grid
and a grid support wherein the grid support is configured to place
the anti-scatter grid in the path of x-rays from the breast to the
receptor while receiving image data when the x-ray source is
emitting x-rays at the conventional mammogram position but out of
the path to the receptor while receiving image data when the x-ray
source is emitting x-rays at the plurality of tomosynthesis
positions.
76. The system of claim 67, wherein the method further comprises
energizing the x-ray source to emit an x-ray dose for each of the
plurality of tomosynthesis positions that is less than an x-ray
dose for the conventional mammogram position.
77. The system of claim 67, wherein the method further comprises to
placing the x-ray source in the conventional mammogram position
after obtaining image data at some of the plurality of
tomosynthesis positions but before taking image data for others of
the plurality of tomosynthesis positions.
78. The system of claim 67, wherein the method further comprises
energizing the x-ray source at each of the plurality of
tomosynthesis positions at a higher x-ray source kV than an x-ray
source kV energized by the x-ray source at the conventional
mammogram position.
79. An x-ray system for acquiring multiple types of breast images,
including a conventional mammogram image and a tomosynthesis image
in a single compression of a breast, the x-ray system comprising:
an x-ray source disposed on a rotatable arm; a breast platform; a
digital x-ray receptor disposed below the breast platform; a
compression paddle disposed between the x-ray source and the
receptor; means for automatically compressing and releasing the
breast between the compression paddle and the breast platform;
means for rotating automatically the x-ray source along a range of
angular positions; means for emitting x-rays at angular positions
of the x-ray source along the range of angular positions, wherein
the angular positions include (i) a conventional mammogram
position, and (ii) a plurality of tomosynthesis positions, wherein
at least one of the plurality of tomosynthesis positions is the
same as the conventional mammogram position, taken during the
single compression of the breast; means for receiving image data
when the x-ray source is emitting x-rays at the conventional
mammogram position and at the plurality of tomosynthesis positions;
and means for processing the image data to obtain the conventional
mammogram image and the tomosynthesis image.
80. A method of acquiring multiple types of breast images,
including a conventional mammogram image and a tomosynthesis image
of a breast using the same equipment, the method comprising;
compressing the breast between a compression paddle and a breast
platform; automatically placing an x-ray source in a plurality of
positions along a range of angular positions while the breast
remains compressed; automatically moving an x-ray receptor that
receives x-rays from the x-ray source through the breast when the
x-ray source is energized; energizing the x-ray source in the
plurality of positions; receiving image data from the receptor in
response to x-rays from the x-ray source impinging thereon after
passing through the breast; processing the image data to obtain the
conventional mammogram image and the tomosynthesis image; and
automatically releasing the breast from compression after
selectively energizing the x-ray source in the plurality of
positions.
81. The method of claim 80, wherein the plurality of positions
comprises a conventional mammogram position and a plurality of
tomosynthesis positions.
82. The method of claim 80, wherein processing the image data
comprises reconstructing at least some of the image data.
83. The method of claim 80, wherein an x-ray dose to the breast at
each of the plurality of the tomosynthesis positions is
substantially less than that for a conventional mammogram.
84. The method of claim 83, wherein at least one of the plurality
of tomosynthesis positions is the same as the conventional
mammogram position.
85. The method of claim 83, further comprising positioning
automatically an anti-scatter grid based at least in part on the
dose emitted from the x-ray source.
86. The method of claim 85, further comprising removing
automatically from a path of the x-ray the anti-scatter grid when
the x-ray source emits a dose of a conventional mammogram.
Description
FIELD
[0001] This patent specification is in the field of x-ray imaging
of the breast and, more specifically, obtaining and processing
x-ray data for tomosynthesis.
BACKGROUND
[0002] Breast cancer remains an important threat to women's health.
X-ray mammography currently is the most widely used breast imaging
tool for early detection, and is the modality approved by the Food
and Drug Administration to screen for breast cancer in women who do
not show symptoms of breast disease. A typical mammography system
takes a projection image of the compressed breast, using a
collimated x-ray source at one side and a film/screen unit at the
other side of the breast. In the United States, typically two views
are taken of each breast, one from above (cranial-caudal, or CC)
and one from the side (mediolateral-oblique, or MLO). The x-ray
source is an x-ray tube typically operating at 25-40 kVp, using a
molybdenum or rhodium rotating anode with a focal spot of about
0.3-0.4 mm and, in some cases, 0.1 mm or less. An anti-scatter grid
between the breast and the film/screen unit reduces the effects of
x-ray scatter. The screen converts x-ray energy to visible light to
which the film is exposed to record the image. In each view, the
breast is compressed to reduce patient motion and also for reasons
such as reducing scatter, separating overlapping structures in the
breast, making the thickness of the imaged breast more uniform, and
providing more uniform x-ray exposure. Currently, flat panel array
receptors are replacing the film/screen units in mammography
systems. The Selenia.TM. digital mammography system with such a
flat panel x-ray receptor is offered by Lorad, a subsidiary of the
assignee Hologic, Inc. of Bedford, Mass. Digital mammography has
significant advantages and in time may fully supplant film/screen
systems. Additional information regarding digital mammography
systems and processes offered by the common assignee can be found
at <www.hologic.com>.
[0003] Mammograms, whether from film/screen units or from digital
systems, are particularly difficult to read, and the rate of false
negatives and false positives is significant. Many advances have
been made in recent years in image acquisition and in image
processing, but a need still remains to reduce the rates of false
negatives and positives, at least in screening mammography.
Additional information can be gained through modalities such as CT
and MRI, but examination and interpretation time and cost and other
factors have limited their use in screening for breast cancer.
Ultrasound breast examination has been proposed as an adjunct to
x-ray examination, with synthesized ultrasound images of thick
slices of the breast as they would appear in the same projection
view as an x-ray view displayed together with the x-ray view, and a
unit taking both x-ray and ultrasound images has been proposed.
See, e.g., Patent Application Publication No. U.S. 2003/0007598 A1
and U.S. Pat. No. 5,983,123. Digital tomosynthesis has been
proposed for x-ray breast imaging, and a laboratory unit is
believed to have been installed at the Massachusetts General
Hospital (more than a year before the filing date hereof), as
reported in Wu, Tao, 2002, Three-Dimensional Mammography
Reconstruction Using Low Dose Projection Images, PhD thesis,
Brandeis University, incorporated here by reference. See, also,
Patent Application Publication No. 2001/0038681 A1 and PCT
application International Publication No. WO 03/020114 A2 published
Mar. 13, 2003, both incorporated herein by reference. Digital
tomosynthesis in more general contexts also has been proposed. See,
e.g., U.S. Pat. Nos. 6,289,235 and 5,051,904, commonly assigned
U.S. Pat. No. 4,496,557, and Digital Clinical Reports,
Tomosynthesis. GE Brochure 98-5493, 11/98, all incorporated herein
by reference. Reference markers can be used in x-ray imaging for
purposes such as checking the rotation angle and unwanted shift of
center of rotation of an x-ray source and receptor, and fiducial
phantoms can be used in 3D angiography to calibrate for irregular
scan geometries. See, e.g., U.S. Pat. Nos. 5,051,904, 5,359,637,
and 6,289,235, N. Navab, et al., Dynamic geometrical calibration
for 3D cerebral angiography, SPIE Vol. 2708, pp. 361-370, and said
PCT published application WO 03/020114 A2, all incorporated by
reference here.
[0004] It is believed that no breast tomosynthesis systems are
commercially available currently for clinical use in breast
imaging, and that improvements in x-ray imaging and tomosynthesis
are a desired goal. Accordingly, it is believed that a need remains
for improved and practical tomosynthesis mammography.
SUMMARY
[0005] In a typical x-ray imaging according to preferred
embodiments disclosed in this patent specification, a patient's
breast is immobilized, at the same or lower compression than in
conventional mammography, between a breast platform and a
compression paddle. The platform and paddle, and the breast between
them, in turn are between an x-ray source and a digital imaging
receptor. Unlike conventional x-ray mammography, in which typically
a breast is imaged from only one angle at a given compression, here
the immobilized breast is imaged with x-rays from the source that
pass through the breast and impinge on the receptor, from a greater
number of different positions of the source and receptor relative
to the breast while maintaining the breast immobilized, to derive
image data for the respective positions. To do this, the x-ray
source moves around the immobilized breast, typically but not
necessarily in an arc, and the receptor also moves relative to the
breast, but in a motion that allows it to remain substantially
parallel to the same plane. The x-ray data taken at each of a
number of positions of the receptor relative to the breast is
processed to form images where each of a number of the images is
formed from image data acquired from two or more of the different
positions, e.g., to form tomosynthetic images. The x-ray dose to
the breast can be different for the different imaging positions.
One or more of the imaging positions can use an x-ray dose
comparable to that used for conventional mammography. These
positions may be the same or similar to the source/receptor
positions for the typical views used in conventional mammography,
e.g., the CC view and the MLO view. Fiducial markers can be used to
help assess the positions of the x-ray source and x-ray receptor
relative to each other and/or the breast being imaged, and for
other calibration purposes. The fiducial markers can be integrated
with the compression paddle and/or the breast platform, or can be
positioned otherwise to serve the intended purpose. The immobilized
breast can be imaged at angular positions extending over a selected
range around the immobilized breast, for example .+-.15.degree.,
although other ranges can be used in other examples. The motion can
be continuous over some or all of the imaging positions, or can be
intermittent such that the x-ray source and/or the x-ray receptor
stop for taking and image and then move to the next position for
the next image.
[0006] An antiscatter grid can be used, positioned between the
breast platform and the x-ray receptor while x-ray image data are
taken. One example is the grid available from Lorad under the
tradename HTC.RTM. grid. Alternatively, the image data at some or
all of the imaging positions can be taken without an antiscatter
grid that is external to the x-ray receptor. Rather than using the
currently conventional materials for the x-ray emitting target in
an x-ray tube serving as the x-ray source, in one of the preferred
embodiments the target is made essentially of Tungsten, to provide
x-rays at energies that are believed more suitable for breast x-ray
tomosynthesis. Geometries other than an x-ray source that rotates
around the immobilized breast and an x-ray receptor that moves
relative to the breast and the source but remains in substantially
parallel to the same plane, can be used.
[0007] Image data taken at the different imaging positions can be
processed to generate tomosynthetic images of selected slices of
the breast. The images can be of thin slices, essentially planar
sections through the breast, as in CT slices. Alternatively, they
can be of thick slices of the breast, e.g., slices that are about
0.5 cm to about 1.0 cm thick, and simulate projection images of
slices of that thickness, projected on one or more selected image
planes. In one example, the image plane or planes of the thick
slice images are the same as those of the typical conventional
mammograms, and can be displayed for viewing in appropriate
groupings. For example, projection-like tomosynthetic images of
thick slices on a plane parallel to that of a conventional CC image
can be displayed together with a conventional CC image of a breast,
on the same screen or adjacent screens or other displays.
Similarly, projection-like tomosynthetic images of thick slices on
plane parallel to that of an MLO image can be displayed on the same
display or on adjacent displays with a conventional MLO mammogram
of the same breast. In the alternative, the image planes of the
tomosynthetic images can be at one or more selected angles to the
image planes of the typical images used in screening x-ray
mammography.
[0008] Tomosynthetic images can be formed using a form of filtered
backprojection modified by using a filter function that is
significantly different from a conventional ramp filter used in CT
technology backprojection. The novel filter function is believed to
be uniquely suited to breast tomosynthesis. In particular, in the
frequency domain the novel filter function at low spatial
frequencies is much steeper than a CT technology ramp function, it
is close to an all-pass filter at intermediate frequencies, and at
higher frequencies it falls off to suppress fine detail noise.
BRIEF DESCRIPTION OF THE DRAWING
[0009] FIG. 1 illustrates schematically a front view of an x-ray
source, a breast immobilized between a compression paddle and a
breast platform, an antiscatter grid and an image receptor, where
the x-ray source and the x-ray receptor move relative to the breast
for imaging the breast at different angles according to a preferred
embodiment.
[0010] FIG. 2 illustrates a side view of the system illustrated in
FIG. 1 and additional components of a system according to a
preferred embodiment.
[0011] FIG. 3 illustrates a display arrangement showing both images
that are the same or similar to conventional mammograms and
tomosynthetic images according to a preferred embodiment.
[0012] FIG. 4 illustrates in graph form a backprojection filter in
the frequency domain used in a preferred embodiment, compared with
a conventional ramp filter used in CT technology and an all-pass
filter.
[0013] FIG. 5 illustrates coordinate values of a backprojection
filter according to a preferred embodiment as control point values
in the frequency domain in log scale.
[0014] FIG. 6 illustrates the use of fiducial markers.
[0015] FIGS. 7 and 8 are similar to FIGS. 1 and 2, respectively,
but illustrate another preferred embodiment.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0016] FIG. 1 schematically illustrates in front view an x-ray
source 100 in three different positions 100a, 100b and 100c,
between which source 100 moves in an arc centered at the top center
of a patient's breast 102 immobilized between a compression paddle
104 and a breast platform 106. An antiscatter grid 108 is
immediately below breast platform 106, and an x-ray receptor 110 is
below grid 108, and is shown in three different positions, 110a,
110b, and 110c, corresponding to the illustrated positions of
source 100. Receptor 110 moves relative to immobilized breast 102
along a path substantially parallel to breast platform 106 and
maintains substantially the same distance from platform 106, as
indicated by the arrows in FIG. 1. In operation, source 100 moves
from one of its illustrated position to another, and so does
receptor 110. At each position of source 100 and receptor 110,
source 100 is energized to emit a collimated x-ray beam, of which
only the center ray is illustrated. The beam irradiates breast 102
and some of the radiation that has passed through the breast also
passes through grid 108 and is received by receptor 110. As in
known in the art, receptor 110 and associated electronics generate
image data in digital form for each pixel of a rectangular grid of
pixels at each of the illustrated angular position of source 100
and translation positions of receptor 110 relative to immobilized
breast 102. While only three positions are illustrated in FIG. 1,
in practice image data is taken at each of a much greater number of
positions, for example, at every 1.degree. of an arc of
.+-.15.degree. of source 100 around immobilized breast 102. The
taking of image data can be while source 100 and receptor 110 are
stopped at their respective positions, after moving from one
position to the next. In a different preferred embodiment, the
motion of one or both of source 100 and receptor 110 can be
continuous, with a respective set of image data being accumulated
over a small increment of continuous motion, say a 0.1.degree. to
0.5.degree. arc of motion of source 100. These parameters are only
an example. Different preferred embodiments can use different
ranges of motion of source 100 and receptor 110, and can use a
motion of source 100 that is arcuate and centered at a different
point, such as in immobilized breast 102 or at breast platform 106
or at grid 108 or at receptor 110, or a motion that is not arcuate
but is translational or is a combination of different types of
motions, such as partly translational and partly rotational. In the
most preferred embodiment, the source 100 motion is arcuate and the
receptor 110 motion is translational. As described further below,
in practice source 100 can be integrated in a C-arm that is the
same or similar to the C-arm used in the commercially available
Selenia.RTM. or MIV mammography systems available from Lorad, and
receptor 110 can be the same receptor as used in such commercially
available systems but mounted differently so that it translates in
a plane substantially parallel to breast platform 106 while
maintaining a substantially constant distance from platform 106
rather that rotating as a unit with source 100, as in Lorad
commercially available systems.
[0017] FIG. 2 schematically illustrates a side view of a
mammography system using the arrangement of FIG. 1. In FIG. 2,
x-ray source 100 is at one end 200a of a C-arm 200 that is
supported for selective rotation about an axis 202, independently
of a support 204 for compression paddle 104 and breast platform
106. Support 204 also selectively rotates about the same axis 202.
The other end 200b of C-arm 200 interacts with x-ray receptor 110
through a motion translator schematically illustrated at 206 that
translates the rotational motion of the end 200b about axis 202 to
a substantially translational motion of receptor 110 that
substantially maintains the distance of receptor 110 from breast
platform 106 while x-ray data is being taken. FIG. 2 is not to
scale, and receptor 110 can be spaced further from member 200b than
illustrated, to allow more space for motion translator 206, and
also to allow for receptor 110 to be moved selectively further from
or closer to breast platform 104 and thus allow for x-ray image
magnification. In operation, C-arm 200 and support 204 are rotated
to desired angular positions, either manually or by motor drives,
patient breast 102 is positioned on platform 106 and is immobilized
by bringing paddle 104 toward platform 106 and compressing breast
102, with typically the same or less force than for a typical
conventional mammogram, such as between one to one-third the
conventional force. With breast 102 immobilized, and with C-arm at
a selected angle relative to a normal to platform 106 and receptor
110, such as +15.degree., imaging starts, and a projection image is
taken for each of a number of selected angular positions of source
100 while C-arm 200 rotates, continuously or intermittently,
through a selected angle, such as an angle of 30.degree., is from
+15.degree. to -15.degree.. Of course, the motion can be in the
opposite direction, from -15.degree. to +15.degree., or can be over
a different angular interval, such as over less than a total of
30.degree., e.g. 25.degree., 20.degree., etc., or more than
30.degree., such as 35.degree., 40.degree., etc. Currently, the
preferred range is .+-.15.degree.. A set of image data can be taken
at selected angular positions, such as every degree, or every
fraction of a degree, or every several degrees of angle. The
angular increments between the different positions for sets of
image data need not be the same. For example, the increments around
0.degree. can be less than those at the extremes of the angular
positions, or vice versa. Currently, the preferred angular
increment is 3.degree.. The sets of image data can be taken after
an incremental motion from one angular position of source 100 to
another, and from one translational position of receptor 110 to
another, such that source 100 and receptor 110 are stationary while
a set of image data is being taken. Alternatively, one or both of
source 100 and receptor 110 can move continuously while sets of
image data are being taken, one set for each increment of
continuous motion. In the currently preferred embodiment, in the
example of continuous motion while taking image data both source
100 and receptor 110 move while image data are being taken.
[0018] FIG. 2 also illustrates schematically an
electrical/electronic system 208 that interacts with the components
discussed above. System 208 includes a control 210 for selectively
energizing and otherwise controlling x-ray source 100, an arm
rotation control 212 for selectively rotating C-arm 200 and support
204, a breast compression control 214 for selectively moving
compression paddle 104 toward and away from breast platform 106,
data readout electronics 216 coupled with x-ray receptor 110 to
read out the sets of image data at the respective positions of
source 100 and receptor 110 relative to immobilized breast 102, and
an image reconstruction and display unit 218 coupled with data
readout electronics 216 to receive the sets of image data from
electronics 216 and to process the image data for reconstruction
and other purposes and display images.
[0019] For a given position of breast 102, such as a position that
is the same or similar to the CC position for a conventional
mammogram, source. 100 and receptor 110 can be positioned relative
to immobilized breast 102 such that at the 0.degree. position a
center ray of the x-ray beam from source 100 would be substantially
normal to receptor breast platform 106 and receptor 110. For a
first set of image data, source 100 is at +(or -) 15.degree. in a
preferred example, and is gradually moved, continuously or
intermittently to -(or +) 15.degree., with a set of image data
taken every 3.degree.. The angular range and the increment over
which data sets are taken can each be selectively set by the
operator, depending of characteristics of the breast being imaged
and the screening and diagnostic needs, and can be different for
different patients or from one to the other breast of the same
patient. For example the source can move through angles that range
from a fraction to a degree to several degrees from one imaging
position to the next. Each set of image data is supplied by image
readout 216 for processing at image reconstruction and display unit
218. Each set of image data can be taken at the same x-ray dose to
the breast, and the dose at any one of the different imaging
positions can be substantially less than that for a conventional
mammogram. The x-ray dose can be substantially the same for each
imaging position, but preferably the dose at one of the position,
e.g., at or close to the 0.degree. position, is the same or similar
to dose for a conventional mammogram while the dose at the each of
the other positions is less, preferably much less. Alternatively,
the scan can begin with or end with an exposure close to the
0.degree. position at a dose similar to a conventional mammogram,
and the rest of the set of image data can be over the angular range
with each exposure at an x-ray dose that is substantially less than
that for a conventional mammogram. Thus, two types of images can be
produced in accordance with the currently preferred embodiment
while breast 102 is immobilized in the same position. One type is
the same or is at least similar to a conventional mammogram, which
can be read and interpreted in the manner familiar to health
professionals. The other type is tomosynthetic images reconstructed
from the image data and displayed either separately or as an
adjunct to the display of the image that is the same or similar to
a conventional mammogram. The process described above for one
position of breast 102 can be repeated for another position. For
example one process can be for a breast position in a manner that
is the same or similar to positioning the breast for a conventional
CC view, the breast can then be released, the support 204 and C-arm
200 rotated to other angular positions and the breast repositioned
in a manner that is the same and similar to the position for an MLO
view, and the procedure repeated.
[0020] FIG. 3 illustrates schematically a display according to a
preferred embodiment, where 300 is a display that is the same or
similar to a display for a conventional CC mammogram of two breasts
and 302 is a similar display for a conventional MLO view. Another
display 304 is close to display 300 and can display any one or more
of several types of tomosynthetic images reconstructed from the
image data taken at the different imaging positions. For example,
if display 300 shows views of a right breast taken at or close to
the 0.degree. position in one imaging sequence of a total rotation
of source 100 over the .+-.15.degree. range, display 304 can show,
at the option of the user, any one or more of the following views
of the right breast: (1) one or more of the projection views taken
at the different imaging positions; (2) one or more of several
tomosynthetic views of thick slices of the right breast simulating
projection views of the right breast taken at the same or similar
angle as the view at display 300, with the slices having effective
thicknesses selected by the user, such as from several mm to
something less than the thickness of the immobilized breast,
typically from several mm to about 1 cm; (3) one or more
tomosynthetic views of thin slices of the right breast, each
simulating a slice through the breast in a respective plane
parallel to that of the view at display 300, where each thin slice
has an effective thickness of about a mm or less; (4) thin and/or
thick slices corresponding to planes that are not parallel to that
of the view at display 300; (5) a scrolling image through any of
the slices discussed above; and (6) a selected combination of the
above displays. A similar display 306 can be associated with
display 302, and show a similar selected views related to the
images at display 302. FIG. 3 illustrates only one example
according to preferred embodiments. Other arrangements also are
contemplated, such as different windows on the same display for the
different images, differently positioned displays, etc. The user
can select the type of images for display, the thickness of a thick
slice or a thin slice, the orientation of the slices for display,
which slices to display where and in what order, whether to display
thick or thin slices as static slides or to scroll through slice
images as in movie, etc. Controls 306 can be coupled to each of the
displays, and can include manual inputs such as a joystick and/or
other known interface devices and a suitably programmed computer to
allow a user to control the images that are displayed. For example,
the controls can include: (1) selecting one or more areas or
volumes of interest at one or more of the displayed images and
further processing the image data to form and display additional
images of the area or volume of interest (for example, if a lesion
is identified that is between tomosynthetic thin slices 32 and 37,
the user can manually designate the corresponding area or volume
and command the display of the thin slices in that area or volume,
and other parameters such as the orientation of the thin slices);
(2) identifying the position of an area or region of interest for
use in additional procedures such as needle biopsy (for example,
the user can designate with a cursor or in some other way a point
in or an outline of a suspected lesion in the breast, and the xyz
coordinates of the designated point, area, or volume); (3) the user
can manually designate the desired thickness, arrangement, and
other parameters of slices whose images are to be displayed, to
thereby display images of slices that have user-selected
thicknesses and other parameters, such as orientation, so that
images of slices of different thicknesses and/or orientations can
be displayed concurrently; and (4) the user can point to an area of
interest in one of the displayed images and the system can
automatically display one or more markers at corresponding or at
least related locations in one or more of the other images that are
being concurrently displayed.
[0021] At each imaging position, receptor 100 generates respective
digital values for the pixels in a two-dimensional array. In one
example, receptor 110 has a rectangular array of approximately 4096
by 3328 pixels, with a pixel size of approximately 70 micrometers
in each of the column and row directions. The image data of a set
(for a respective imaging position) can be processed either at the
full spatial resolution of receptor 110, or at a lower effective
spatial resolution, e.g., by binning several original pixel value's
into a single, combined pixel value. For example, each set of
2.times.2 adjacent pixels can be combined into a single respective
pixel value, thus achieving an effective spatial resolution of 140
micrometers in each direction. The binning can be in some other
combination of original pixels, such as 2.times.3, and can be done
by data readout electronics 216 or image reconstruction and display
unit 218 (FIG. 2).
[0022] Image reconstruction is done using backprojection in the
spatial domain or in the frequency domain as in CT technology but
with a novel filter that differs from the ramp filter (in the
frequency domain) used in CT reconstruction. See, e.g., G.
Lauritsch, et al., A theoretical framework for filtered
backprojection in tomosynthesis, SPIE Medical Imaging Conference,
Vol. 3338, 1998, and U.S. Pat. No. 6,442,288, both incorporated
here by reference. Referring to FIG. 4, the novel filter is
represented by graph 400, while a graph 402 represents a
conventional CT ramp filter, and a graph 404 represents an all-pass
filter. As seen in FIG. 4, the novel filter according to a
preferred embodiment rises sharply in amplitude at lower
frequencies, between points a and c (in the range indicated at b),
as compared with the conventional ramp filter, then levels off at
intermediate frequencies to become the same as or close to an
all-pass filter between points c and d, and then gradually drops
off at higher frequencies. Using the novel filter produces
significantly better breast images compared to using a conventional
CT technology ramp filter.
[0023] FIG. 5 gives a sense of the values of the low, intermediate
and high frequencies discussed in connection with FIG. 5. In FIG.
5, the frequency axis is plotted on log scale, and typically is
related to spatial resolution of a few mm or more, i.e., it affects
mainly to overall impression and flatness of the reconstructed
image. With suitable suppression of low frequency content through
frequency dependent weights defined by the shape of the novel
filter, and gradual suppression of high frequency noise, a
tomographic image with good image contrast at all frequency scales
can be reconstructed and presented in accordance with a preferred
embodiment. Preferably, the filtered backprojection reconstruction
of tomographic images is carried out in the frequency domain, using
well known processes with the novel filter. However, comparable
filtered backprojection can be carried out in the spatial domain,
as in known in CT technology, using direct convolution of image
data with the spatial domain representation of the filter
represented in the frequency domain in FIGS. 4 and 5. In either the
frequency domain or in the spatial domain the novel filter can be
applier to the image data to generate filtered data for
backprojection, or backprojection can be carried out first,
followed by a filtering operation. The reconstruction process
preferably uses the direct fan-beam backprojection method known in
CT technology, but with the novel filter, although it may be
possible to use the image data to simulate sets of parallel beam
paths for backprojection. The reconstructed thin slice images form
a three-dimensional image of the breast, comprising voxel values
for respective incremental volumes. These voxel values can then be
combined as known in CT technology to synthesize any selected thin
slice or thick slice in any selected orientation, and in any
selected projection plane.
[0024] In a preferred embodiment, while each of all or most of the
imaging positions uses lower x-ray dose than that of a conventional
mammogram, higher KV can be used as compared with a conventional
mammogram in order to boost signal levels from receptor 110 and
improve signal-to-noise (SNR) ratios. In addition, preferable an
x-ray tube with a Tungsten target is used to further exploit the
advantage of higher kVp imaging of the breast, such as between 25
and 50 kVp with different x-ray beam filtration. A small focal
spot, of the order of 1 mm or less, is preferred, although a larger
focal spot of several mm can be used.
[0025] In other preferred embodiments, contrast enhanced breast
tomosynthesis can be carried out, by obtaining tomosynthetic images
as described above before injecting a contrast agent such as Iodine
into the patient, then repeating the process after injection, and
subtracting images of the pre-injection and post-injection sets.
Another preferred embodiment involves time subtraction
tomosynthesis, related to subtracting comparable images obtained at
different times. Yet another is dual-energy breast tomosynthesis,
whereby two tomosynthetic images at low and high energies are
acquired and then subtracted, the two images being acquired through
a process such as using successive scans at two different x-ray
energy ranges or by alternating x-ray pulses of low and high energy
to create the two images. Another other preferred embodiment
involves obtaining and displaying both x-ray tomosynthetic images
of a breast and ultrasound images of the same breast. Computer
aided diagnosis, as known to those skilled in the art and as
commercially used currently in the United States, can be applied to
selected tomosynthetic images generated as described above.
[0026] Fiducial markers are used in preferred embodiments for
off-line (without a breast) mechanical positioning and calibration
and/or on-line (while imaging a breast with x-rays) image based
positioning encoding of moving components. The fiducial markers can
be made of a material such as lead or another metal, and can be in
the form of points or lines or arrows or crosses, at locations that
would be imaged by the x-ray beam at receptor 110 simultaneously
with the imaging of a breast 102 but outside the area of the breast
image. The fiducial markers are integrated with compression paddle
104, or they can be at or near breast platform 106, or they can be
supported separately from paddle 104, for example on a separate
member that can be selectively brought into the path of the imaging
x-ray beam or taken out of that path, e.g., to take an image that
is the same or similar to a conventional mammogram. Different
patterns or types of fiducial markers can be provided, for
selection by the user. FIG. 6 illustrates an example of arranging
fiducial markers 601, 602, 603 and 604 relative to an image of
breast 102a on receptor 110, as seen in a top plan view when
receptor 110 is horizontal and the fiducial markers are integrated
in compression paddle 104.
[0027] An alternative embodiment, illustrated schematically in a
front view in FIG. 7 and in side view in FIG. 8, is similar to the
embodiment illustrated in FIGS. 1 and 2 except that receptor 110 is
affixed to the end 200b of C-arm 200 that is opposite x-ray source
100. In this embodiment, receptor 110 moves relative to immobilized
breast 102 along an arcuate path from one imaging position to
another. Because the change in angle between receptor 110 and
breast platform is small, it can be disregarded in processing the
sets of x-ray image data. Alternatively, a geometric correction
known to those skilled in the art can be applied to each set of
image data to convert it to interpolated pixel values that would
correspond to those that would have been obtained if receptor 110
had been parallel to and at the same distance from platform 106 at
all imaging positions. The so corrected sets of image data can then
be used in filtered back projections as described above.
[0028] In each of the embodiments of FIGS. 1-2 and FIGS. 7-8,
antiscatter grid 108 may be selectively retractable, so that the
user may take any selected set of x-ray image data with or without
using grid 108. As in known in the art, grid 108 can be made to
move relative to the x-ray beam during the taking of a set of image
data. Similarly, the distance between breast platform 106 and
receptor 110 can be selectively changed to effect magnification of
the breast image recorded at receptor 110.
* * * * *