U.S. patent application number 10/666188 was filed with the patent office on 2004-04-08 for radiation imaging system and method of collimation.
Invention is credited to Claus, Bernhard Erich Hermann, Eberhard, Jeffrey Wayne, Hewes, Ralph Allen, Jenkins, Harold John JR., Wirth, Reinhold Franz.
Application Number | 20040066904 10/666188 |
Document ID | / |
Family ID | 24744570 |
Filed Date | 2004-04-08 |
United States Patent
Application |
20040066904 |
Kind Code |
A1 |
Eberhard, Jeffrey Wayne ; et
al. |
April 8, 2004 |
Radiation imaging system and method of collimation
Abstract
A radiation imaging system comprises a movable radiation source
adapted to be disposed in a plurality of respective radiation
source positions; a radiation detector and a collimator assembly
configured to displace a collimator in a plurality of respective
collimator positions, each of the collimator positions being
coordinated with at least one of the radiation source positions
such that a radiation beam emanating from the radiation source is
collimated to limit radiation incident on the detector to a
predetermined exposure area. Another radiation imaging system
comprises a movable radiation source; a radiation detector; and a
collimator comprising an adjustable geometry aperture assembly
configured such that an adjustment of the aperture geometry is
synchronized with the movement of the radiation source and
coordinated with the radiation source position so as to limit the
incident radiation to a predetermined exposure area at the
detector.
Inventors: |
Eberhard, Jeffrey Wayne;
(Albany, NY) ; Wirth, Reinhold Franz; (Ballston
Spa, NY) ; Claus, Bernhard Erich Hermann; (Niskayuna,
NY) ; Hewes, Ralph Allen; (Burnt Hills, NY) ;
Jenkins, Harold John JR.; (Amsterdam, NY) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY
GLOBAL RESEARCH CENTER
PATENT DOCKET RM. 4A59
PO BOX 8, BLDG. K-1 ROSS
NISKAYUNA
NY
12309
US
|
Family ID: |
24744570 |
Appl. No.: |
10/666188 |
Filed: |
September 10, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10666188 |
Sep 10, 2003 |
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09683564 |
Jan 18, 2002 |
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6647092 |
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Current U.S.
Class: |
378/147 |
Current CPC
Class: |
G21K 1/04 20130101 |
Class at
Publication: |
378/147 |
International
Class: |
G21K 001/02 |
Goverment Interests
[0001] The invention was made with Government support under
contract number DAMD17988109 awarded by the U.S. Army. The
Government has certain rights in the invention.
Claims
1. A radiation imaging system comprising: a movable radiation
source configured to be displaced in a plurality of respective
radiation source positions; a radiation detector; a collimator
assembly, said assembly comprising a collimator, said assembly
further being configured to displace the collimator in a plurality
of respective collimator positions, each of said collimator
positions being coordinated with at least one of said radiation
source positions such that a radiation beam emanating from said
radiation source is collimated to limit radiation incident on said
detector to a predetermined exposure area.
2. The imaging system of claim 1 wherein said collimator assembly
further comprises a collimator positioning apparatus for displacing
said collimator in respective ones of said collimator positions,
each of said collimator positions corresponding to a respective
spatial relationship with said radiation source and said
detector.
3. The imaging system of claim 2 wherein said collimator
positioning apparatus further comprises a displacement mechanism
comprising: a rotational displacement mechanism adapted to position
the collimator axially with respect to the radiation source and the
detector.
4. The imaging system of claim 2 wherein said collimator
positioning apparatus further comprises a translational
displacement mechanism adapted to position the collimator
horizontally with respect to the radiation source and the
detector.
5. The imaging system of claim 2 wherein said collimator
positioning apparatus further comprises a multi-axis displacement
mechanism adapted to position the collimator both axially and
horizontally with respect to the radiation source and the
detector.
6. The imaging system of claim 1, wherein each one of said
collimator positions corresponds to exactly one of said radiation
source positions.
7. The imaging system of claim 1, wherein said collimator further
comprises an aperture assembly, said aperture assembly being
configured to provide an adjustable geometry aperture.
8. The imaging system of claim 1, wherein said collimator further
comprises an aperture assembly comprising radiation absorbing
material and adapted to provide an adjustable geometry aperture to
limit radiation incident on said detector to said predetermined
exposure area.
9. The imaging system of claim 7, wherein said aperture assembly
comprises a plurality of movable sides.
10. The imaging system of claim 7, wherein said aperture assembly
comprises at least one movable side.
11. The imaging system of claim 7, wherein said aperture assembly
comprises multiple independently positionable sections with
different boundary shapes.
12. The imaging system of claim 11, wherein said multiple sections
have linear boundaries.
13. The imaging system of claim 10, wherein said plurality of sides
comprise rotationally and translationally movable sides.
14. The imaging system of claim 1, wherein said collimator further
comprises an aperture of fixed geometry.
15. The imaging system of claim 14, wherein said fixed geometry
aperture has a rectangular cross-section.
16. The imaging system of claim 15, wherein movement of said
radiation source relative to said detector is the same as the
movement of said radiation source relative to said aperture.
detecting the radiation beam on a radiation detector.
17. A method for radiation imaging, comprising: positioning a
radiation source in a plurality of respective radiation source
positions; displacing a collimator in a plurality of respective
collimator positions, each of said collimator positions
corresponding to a respective one of said radiation source
positions such that a radiation beam emanating from said radiation
source is collimated to limit the incident radiation to a
predetermined exposure area; and
18. The method of claim 17, wherein displacing said collimator
comprises: displacing said collimator such that each of said
collimator positions corresponds to a respective spatial
relationship with said radiation source and said radiation
detector.
19. The method of claim 18, wherein displacing said collimator
comprises positioning the collimator axially with respect to the
radiation source and the detector.
20. The method of claim 18, wherein displacing said collimator
comprises positioning the collimator horizontally with respect to
the radiation source and the detector.
21. The method of claim 18, wherein displacing said collimator
comprises positioning the collimator both axially and horizontally
with respect to the radiation source and the detector.
22. The method of claim 17, wherein displacing said collimator in
said plurality of collimator positions is done such that each one
of said collimator positions corresponds to exactly one of said
radiation source positions.
23. The method of claim 17, wherein displacing said collimator
further comprises adjusting the geometry of an aperture.
24. The method of claim 23, wherein adjusting the geometry of the
aperture comprises moving a plurality of sides of an aperture
assembly of said collimator.
25. The method of claim 23, wherein adjusting the geometry of the
aperture comprises moving of at least one side of an aperture
assembly of said collimator.
26. The method of claim 17, wherein displacing said collimator
further comprises adjusting the geometry of an aperture for
limiting radiation incident on said detector to said predetermined
exposure area.
27. The method of claim 21, wherein the collimator comprises an
aperture, and wherein positioning the radiation source and
displacing the collimator are performed to provide movement of said
radiation source relative to said detector that is the same as
movement of said radiation source relative to said aperture.
28. A radiation imaging system comprising: a movable radiation
source adapted to be disposed in a plurality of respective
radiation source positions; a radiation detector; a collimator
assembly, said assembly comprising a collimator comprising an
aperture assembly configured to provide an aperture and a
collimator positioning apparatus for displacing said collimator in
a plurality of respective collimator positions, each of said
collimator positions being coordinated with at least one of said
radiation source positions such that a radiation beam emanating
from said radiation source is collimated through the aperture to
limit radiation incident on said detector to a predetermined
exposure area.
29. The imaging system of claim 28, wherein each of said collimator
positions corresponds to a respective spatial relationship with
said radiation source and said radiation detector.
30. The imaging system of claim 28, wherein each one of said
collimator positions corresponds to exactly one of said radiation
source positions.
31. The imaging system of claim 28, wherein said aperture assembly
is configured to provide an adjustable geometry aperture.
32. The imaging system of claim 31, wherein said aperture assembly
comprises a plurality of movable sides.
33. The imaging system of claim 31, wherein said aperture assembly
comprises at least one movable side.
34. The imaging system of claim 28, wherein said aperture assembly
is configured to provide an aperture of fixed geometry.
35. The imaging system of claim 34, wherein the aperture of fixed
geometry has a rectangular cross-section.
36. A radiation imaging system comprising a movable radiation
source; a radiation detector; a collimator comprising an adjustable
geometry aperture assembly configured such that an adjustment of
the aperture geometry is synchronized with the movement of said
radiation source and coordinated with the radiation source position
so as to limit the incident radiation to a predetermined exposure
area at said detector.
37. The imaging system of claim 36, wherein said aperture assembly
is configured for adjusting at least one of the position of the
aperture and the shape of the aperture.
38. The imaging system of claim 36, further comprising a collimator
assembly comprising a collimator positioning apparatus for
positioning said collimator.
39. The imaging system of claim 36, wherein said aperture assembly
comprises a plurality of movable sides.
40. The imaging system of claim 36, wherein said aperture assembly
comprises at least one movable side.
41. The imaging system of claim 36, wherein said aperture assembly
comprises multiple independently positionable sections with
different boundary shapes.
42. The imaging system of claim 41, wherein said multiple sections
have linear boundaries.
43. The imaging system of claim 39, wherein said plurality of sides
comprise rotationally and translationally movable sides.
44. A method for radiation imaging, comprising: moving a radiation
source in a plurality of radiation source positions; adjusting an
aperture by synchronizing the aperture geometry adjustment with the
movement of said radiation source and coordinating at least one of
the position and the shape of said aperture with the respective
position of said radiation source such that a radiation beam
emanating from said radiation source is collimated to limit the
incident radiation to a predetermined exposure area; and detecting
the radiation beam on a radiation detector.
Description
BACKGROUND OF INVENTION
[0002] The present invention relates generally to X ray radiation
imaging systems and more particularly to a method and apparatus for
collimating X rays to avoid excess dosage to the patient.
[0003] Collimators are used in applications where it is desirable
to permit only beams of radiation emanating from the radiation
source in a particular direction to pass beyond a selected path or
a plane. In radiation imagers, collimators are used to ensure that
no radiation beams emanating along a direct path from the radiation
source miss the detector and hit unintended parts of the object.
Collimators are positioned to substantially absorb the undesired
radiation. Collimators are traditionally made of a material that
has a relatively high atomic number. Collimator design affects the
field of view of the imaging system. With the introduction of new
imaging applications, the conventional collimators have a
disadvantage that excess X rays can spill past the edge of the
detector surface (or other predetermined exposure area), or that
not the entire detector surface (or other predetermined exposure
area) is exposed to incident X rays.
[0004] In the conventional imaging systems, collimators are used
for standard examinations. One such configuration of a collimator
comprises an X ray opaque metal with a simple aperture. In another
collimator embodiment the aperture is formed by blades that are
motor driven to fixed opening sizes. During the course of an X ray
exam, typical in tomosynthesis, stereotaxy, stereo imaging and
mammography where the X ray source travels in a prescribed arc (or
other prescribed trajectory) around the object (patient), it is
important to prevent any unnecessary X ray dose to reach the
object. Presently the limitation of radiation exposure to the
object is governed by US regulation CDRH 21 CFR 1020.30(k).
[0005] In such advanced imaging systems, it is desirable to
minimize the radiation exposure to the patient, minimize the
complexity of the collimator in terms of its mechanical, electrical
and software implementation, assure high speed of response of the
system so that multiple images can be acquired in rapid succession,
control the movement of the collimator with respect to other motion
in the imaging system, and assure maximum field of view at the
detector consistent with system constraints.
SUMMARY OF INVENTION
[0006] Briefly, in accordance with one embodiment of the invention,
a radiation imaging system comprises a movable radiation source
adapted to be disposed in a plurality of respective radiation
source positions, a radiation detector and a collimator assembly.
The collimator assembly comprises a collimator and a collimator
positioning apparatus which is configured to displace the
collimator in a plurality of respective collimator positions.
Further, each of the collimator positions is coordinated with at
least one of the radiation source positions such that a radiation
beam emanating from the radiation source is collimated to limit
radiation to a predetermined exposure area on the detector.
[0007] In accordance with another embodiment of the present
invention, a method for radiation imaging comprises positioning a
radiation source in a plurality of respective radiation source
positions; displacing a collimator in a plurality of respective
collimator positions where each of the collimator positions
corresponds to a respective one of the radiation source positions
such that a radiation beam emanating from the radiation source is
collimated to limit the incident radiation to a predetermined
exposure area on the detector; and detecting the radiation beam on
the radiation detector.
[0008] In accordance with another embodiment of the present
invention, a radiation imaging system comprises a movable radiation
source, a radiation detector and a collimator comprising an
adjustable geometry aperture assembly configured such that an
adjustment of the aperture geometry is synchronized with the
movement of the radiation source and coordinated with the radiation
source position so as to limit the incident radiation to a
predetermined exposure area at the detector.
[0009] In accordance with another embodiment of the present
invention, a method for radiation imaging, comprises moving a
radiation source in a plurality of radiation source positions;
adjusting an aperture by synchronizing the aperture geometry
adjustment with the movement of the radiation source and
coordinating at least one of the position and the shape of the
aperture with the respective position of the radiation source such
that a radiation beam emanating from the radiation source is
collimated to limit the incident radiation to a predetermined
exposure area; and detecting the radiation beam on a radiation
detector.
BRIEF DESCRIPTION OF DRAWINGS
[0010] These and other features, aspects, and advantages of the
present invention will become better understood when the following
detailed description is read with reference to the accompanying
drawings in which like characters represent like parts throughout
the drawings, wherein:
[0011] FIG. 1 illustrates a system block diagram of an imaging
system according to one embodiment of the present invention.
[0012] FIG. 2 illustrates a plurality of radiation source positions
according to one embodiment of the present invention.
[0013] FIG. 3 illustrates a collimator assembly including a
collimator in one embodiment of the invention.
[0014] FIG. 4 illustrates use of a traditional collimator in a
Mammography system, depicting the different field of views at the
detector for different radiation source positions and respective
collimator aperture geometry configurations.
[0015] FIG. 5 illustrates the shape of the collimated beam falling
onto the detector plane, relative to the detector, for a fixed
rectangular aperture, according to one embodiment of the invention
corresponding to the system geometry depicted in FIG. 2 and a
stationary (i.e., not moving) collimator.
[0016] FIG. 6 illustrates the shape of the collimated beam falling
onto the detector plane, relative to the detector, for a fixed
rectangular aperture, according to another embodiment of the
invention corresponding to the system geometry depicted in FIG. 2
for a translatable collimator.
[0017] FIG. 7 illustrates one embodiment of the invention wherein
projection of the collimator aperture coincides exactly with the
active area of the detector.
[0018] FIG. 8 illustrates one embodiment of the invention where the
movement of the radiation source with respect to the detector is
the same as the movement of the radiation source with respect to
the aperture and shows the geometric relationships for a vertical
position of the X Ray source.
[0019] FIG. 9 illustrates another embodiment of the invention where
the movement of the radiation source with respect to the detector
is the same as the movement of the radiation source with respect to
the aperture and shows the geometric relationships with the
radiation source rotated at an angle.
[0020] FIG. 10 is a top view of an embodiment of the invention
wherein an aperture assembly is configured to provide an adjustable
geometry aperture.
DETAILED DESCRIPTION
[0021] One embodiment of the present invention is a radiation
imaging system 1, as illustrated in FIG. 1, comprising a movable
radiation source 2, a radiation detector 3, and a collimator
assembly 4. As the radiation source moves relative to an object 14,
it assumes a plurality of radiation source positions resulting in
the radiation beam emanating from the radiation source intersecting
the object at various angles, as shown in FIG. 2. The collimator
assembly 4, which is typically in a fixed spatial relationship to
the X ray source has flexibility to be configured to position the
collimator to limit the radiation incident on the detector to a
predetermined exposure area. The predetermined exposure area
typically comprises a region of interest for a particular imaging
task, an active area of the detector, or the area of the X ray
image receptor. The radiation source is configured to be displaced
in a plurality of radiation source positions with respect to the
object 14, by a radiation source positioner 17, fed by a generator
16 and a system controller 15, comprising an electromechanical
system 13 and embedded software. "Movable radiation source" means
that the source is free to travel in any direction typical in
tomosynthesis and related applications. Non-limiting examples of
imaging systems wherein embodiments of the present invention are
particularly useful include tomosynthesis, stereotaxy, stereo
imaging, for example in mammographic imaging systems.
[0022] FIG. 1 also illustrates the collimator assembly 4 according
to one embodiment, which includes a collimator 5, and a collimator
positioning apparatus 6. The collimator positioning apparatus is
configured to displace the collimator to have a plurality of
collimator positions such that each collimator position is
coordinated with at least one of the radiation source positions.
The collimator positioning apparatus is configured to provide
movement to the collimator so that each of the collimator positions
relates to at least one specific radiation source position at any
given time during the imaging process. Further, the movement of the
collimator and the radiation source are synchronized such that
movement of the collimator occurs in the same time interval as the
movement of the radiation source, and both are moving in a
coordinated fashion.
[0023] In one embodiment, the movement of the collimator is also
controlled so that each collimator position corresponds to a
specific spatial relationship with radiation source and detector.
Spatial relationship is defined as the relationship of the
collimator position with the position of the radiation source and
the radiation detector in the three dimensional space containing
the source, collimator and detector. This coordination of the
collimator position with the positions of the radiation source and
the detector results in collimating and limiting the radiation beam
from the radiation source to a predetermined exposure area on the
detector and thus avoiding exposure of the object 14 to x-rays that
do not contribute to the image formed at the detector. Spillage is
defined as X rays emanating from the radiation source, which pass
through the collimator aperture along a direct path from the
radiation source, and do not hit the detector or the predetermined
exposure area on the detector. That is, these X rays do not
contribute to the image formed at the detector.
[0024] In one embodiment, the movement of the collimator assembly
and coordination of the collimator position with at least one of
the radiation source positions is achieved through a collimator
positioning apparatus 6, as shown in FIG. 1, which comprises an
electro-mechanical system 13 and a software program of a system
controller which computes the positions on the basis of input
signals and generates an output signal for providing the desired
movement of the collimator.
[0025] The displacement by the collimator positioning apparatus
results in different configurations of the collimator assembly.
Each configuration corresponds to a specific collimator position.
Further, the collimator assembly is configured to displace the
collimator in a plurality of collimator positions with respect to
the radiation source, each one of the collimator positions
corresponding to one of the radiation source positions.
[0026] Typically the collimator positioning apparatus 6 has a
displacement mechanism 7. In one embodiment the displacement
mechanism comprises a rotational displacement mechanism, for
positioning the collimator axially as shown in FIG. 7, that is, at
an angle, with respect to the radiation source and the detector to
achieve a rotational displacement. In another embodiment, the
displacement mechanism comprises a translational displacement
mechanism, for positioning the collimator horizontally with respect
the radiation source and the detector to achieve a translational
displacement. In still another embodiment, the displacement
mechanism comprises a multi-axis displacement mechanism, for
positioning collimator both axially and horizontally with respect
to the radiation source and the detector to achieve multi axis
displacement.
[0027] The imaging system is typically coupled to a system
controller, which includes a software program to calculate the
various displacements and positions of the movable elements of the
imaging system including the radiation source, the collimator
assembly and the collimator. The system controller is programmed to
control the collimator positioning apparatus so as to displace the
collimator in plurality of collimator positions. In a more specific
embodiment, the displacement of the collimator position with
respect to the radiation source corresponds to the respective
displacement of the radiation source with respect to the
detector.
[0028] In one embodiment, the aperture assembly has a fixed
geometry aperture, that is an aperture made of fixed sides 18. In a
more specific embodiment, as shown in FIG. 3, the fixed geometry
aperture has a rectangular cross-section. In an even more specific
embodiment, aperture 11 is positioned within an aperture plate 23
which is movably mounted relative to a base plate 25 via guide
wheels 27, drive belt 21, and stepper motor 20. If the base plate
opening 29 is sized such that movement of aperture plate 23
potentially exposes X-rays through opening 29, it is useful to
mechanically couple sliding plates 31 to aperture plate 23 to
prevent such exposure.
[0029] In another embodiment, the collimator further comprises an
aperture assembly 10, configured to provide an adjustable geometry
aperture 11 as shown in FIG. 10. In a more specific embodiment, the
aperture assembly has at least one side 19 movable rotationally,
translationally, or a combination thereof.
[0030] Alternatively or additionally, the aperture assembly
comprises a plurality of movable sides 19. In another embodiment
the aperture assembly comprises multiple sections, with different
boundary shapes that can be independently positioned to form an
adjustable geometry aperture. Further in another embodiment the
multiple sections can have linear boundaries that can be
independently positioned. Another embodiment comprises a plurality
of sides movable both rotationally and translationally. The
aperture assembly typically comprises a radiation absorbing
material such as tungsten or some other high atomic number (greater
than about 74, for example) material and is adapted to adjust
aperture geometry to limit radiation incident on the detector to
the predetermined exposure area.
[0031] When the radiation source moves from one position to the
next, the aperture is adjusted accordingly. The movement of
radiation source and adjustment of aperture are synchronized, that
is, their timing is coordinated. Furthermore, at least one of the
position and the shape of the aperture during exposure (i.e., at
the instant an image is acquired) is coordinated relative to the
position of the radiation source, and relative to the position of
the detector. The fact that the position of the aperture is
appropriately coordinated with the position of source and detector
ensures that no radiation spills beyond the edge of the detector
(or active area/predetermined exposure area). In one embodiment,
synchronization and position coordination are controlled by the
stepper motor 20 and drive belt 21 (such as shown in FIG. 3, for
example), driven by system controller 15 and a generator 16 (shown
in FIG. 1).
[0032] The collimator is typically mounted as close to the focal
spot as possible, to minimize size and weight and maximize speed of
operation. One use of such a collimator assembly is in a
mammography system, where the rotation axis of the tube arm is
about 22 cm above the face of the detector. In this geometry, the X
ray beam is not centered on the detector except for exposures taken
at the vertical (0 degree) position.
[0033] The intersection of the center of the X-ray beam with the
image receptor at various angles of tube inclination is shown in
FIG. 4. The width of a conventional adjustable collimator aperture,
which is symmetric with respect to the center of the beam, has to
be decreased with increasing tube inclination angle, in order to
avoid any spill beyond the edge of the detector. As shown in FIG.
4, the resulting area of exposure on the detector is very small
(about 35 mm in width or smaller, for example) for high tube angles
(greater than about 24 degrees, for example) and is not practical.
In one embodiment of the present invention one uses a translatable
collimator with a fixed rectangular aperture. Using this
embodiment, one can achieve almost optimal coverage of the
detector, without any spill beyond the edge of the detector. FIGS.
5 and 6 show the shape of the collimated beam falling onto the
detector, for a fixed rectangular aperture. FIG. 5 illustrates a
stationary (i.e., not moving) collimator, with spill beyond the
edge of the detector. FIG. 6 illustrates a translatable collimator,
with no spill, and for every angle of inclination of the tube,
almost all of the detector surface is irradiated by the beam.
[0034] In one embodiment of the invention, at least one of the
shape of the collimator aperture and the movement of the collimator
is controlled such that the relative position of the radiation
source with respect to the collimator aperture is the same (meaning
identical up to a magnification or scaling factor) as the relative
position of the radiation source with respect to the detector. The
advantages are that there is no spill of X rays beyond the edge of
the active area of the detector and there is no shadow of the
collimator falling on the active area of the detector, which
results in an optimal field of view. FIG. 7 illustrates the
relative positions of radiation source (FS) and the position of the
collimator 5 (with an aperture defined by points AB) with respect
to the detector 3 (defined at points CD) and a rotation point P. In
this embodiment, the generalized pyramid defined by the set of
points [FS,C,D] is a magnified or scaled version of the generalized
pyramid defined by the set of points [FS,A,B]. In one embodiment of
the invention the magnification or scaling is kept constant for
plurality of radiation source positions. In FIG. 7, the desired
scaling is achieved when distance A1 B1 equals distance A2B2, and
they are both equal to "s" times the distance CD, where "s" is the
magnification or scaling factor. In one embodiment, an essentially
similar mechanical arrangement, a scaled down version in size by a
factor "1/s" as defined earlier is used to move the collimator
relative to the radiation source, as is used to move the radiation
source relative to the detector. Referring to FIGS. 8 and 9, the
geometry of the set of points [FS,A,B,Q] is a magnified or scaled
version of the geometry of the points [FS,C,D,P] and rotation of
the radiation source around point P corresponds to the rotation of
the collimator around point Q to optimally position the collimator.
One geometry being a magnified or scaled version of the other
geometry means that any point in the first geometry has a
corresponding point in the second geometry; further, that the
distance between any two points in the first geometry is equal to
"s" times the distance between the corresponding points in the
second geometry, where "s" is the magnification or scaling factor,
and that the line passing through the two points in the first
geometry has the same orientation as the line passing through the
corresponding two points in the second geometry. FIG. 8 illustrates
one embodiment of the invention where the movement of the radiation
source with respect to the detector is the same (up to a
magnification or scaling factor) as the movement of the radiation
source with respect to the aperture and shows the geometric
relationships for a vertical position of the X Ray source, and FIG.
9 illustrates another embodiment of the invention where the
movement of the radiation source with respect to the detector is
the same (up to a magnification or scaling factor) as the movement
of the radiation source with respect to the aperture and shows the
geometric relationships with the radiation source rotated at an
angle. For ease of interpretation, in FIG. 9 the radiation source
is drawn in the same position as in FIG. 8, with the radiation
detector and the collimator rotated correspondingly.
[0035] Another embodiment of the present invention is a method of
radiation imaging, which includes positioning of a radiation source
in a plurality of radiation source positions, displacing the
collimator in a plurality of respective collimator positions such
that each collimator position corresponds to a respective one of
the radiation source position to collimate and limit the radiation
beam emanating from the radiation source to a predetermined
exposure area and detecting the radiation beam on a radiation
detector.
[0036] In another embodiment of the present invention, a radiation
imaging system comprises: a movable radiation source; a radiation
detector; and a collimator comprising an adjustable geometry
aperture assembly configured such that an adjustment of the
aperture geometry is synchronized with the movement of said
radiation source and coordinated with the radiation source position
so as to limit the incident radiation to a predetermined exposure
area at said detector. The above described more specific aperture
assembly embodiments are also applicable in this embodiment. The
adjustable aperture geometry embodiment can be used to obviate the
need for changing collimator positions as described above with
respect to the displaceable collimator embodiment and may be used
independently of or in combination with the displaceable collimator
embodiment.
[0037] As described above, adjustment of the aperture geometry is
synchronized with the movement of said radiation source by
coordinating their timing, and the aperture geometry adjustment is
further coordinated (i.e., at the instant an image is acquired)
relative to the position of the radiation source, and relative to
the position of the detector. The fact that the position of the
aperture is appropriately coordinated with the position of source
and detector ensures that no radiation spills beyond the edge of
the detector (or active area / predetermined exposure area). In one
embodiment, synchronization and position coordination are
controlled by the stepper motor and drive belt mechanism driven by
a system controller and a generator.
[0038] Another embodiment of the present invention is a method for
radiation imaging, which includes moving a radiation source in a
plurality of radiation source positions, adjusting an aperture by
synchronizing the aperture geometry adjustment with the movement of
the radiation source and coordinating at least one of the position
and the shape of the aperture with the respective position of the
radiation source such that a radiation beam emanating from the
radiation source is collimated to limit the incident radiation to a
predetermined exposure area and detecting the radiation beam on a
radiation detector.
[0039] While only certain features of the invention have been
illustrated and described herein, many modifications and changes
will occur to those skilled in the art. It is, therefore, to be
understood that the appended claims are intended to cover all such
modifications and changes as fall within the true spirit of the
invention.
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