U.S. patent application number 10/326020 was filed with the patent office on 2004-06-24 for cast collimators for ct detectors and methods of making same.
Invention is credited to Hoffman, David Michael.
Application Number | 20040120464 10/326020 |
Document ID | / |
Family ID | 32593918 |
Filed Date | 2004-06-24 |
United States Patent
Application |
20040120464 |
Kind Code |
A1 |
Hoffman, David Michael |
June 24, 2004 |
Cast collimators for CT detectors and methods of making same
Abstract
Cast collimators for use in CT imaging systems are described, as
are methods of making them. Such collimators may comprise
pre-patient collimators, pre-patient filter/collimator assemblies,
and/or post-patient collimators. The filters and/or collimators may
be made of any suitable high-density, high atomic number material
such as lead, a lead alloy, tantalum, tungsten, tungsten suspended
in an epoxy matrix, tungsten suspended in a slurry, or the like.
Embodiments of these collimators comprise specially-designed
channels and vanes that allow them to be precision cast to the
necessary degree of accuracy. These channels and vanes are
preferably tapered. These collimators and filter/collimator
assemblies help minimize the x-ray dose to the patient by
minimizing the scattered radiation creation mechanism and by
collimating out much of the scattered radiation that would
otherwise be subjected to the patient. These collimators may be
cast as either single piece structures, or multiple pieces that can
be operatively connected together.
Inventors: |
Hoffman, David Michael; (New
Berlin, WI) |
Correspondence
Address: |
Tracey R. Loughlin
DOUGHERTY, CLEMENTS & HOFER
1901 Roxborough Road, Suite 300
Charlotte
NC
28211
US
|
Family ID: |
32593918 |
Appl. No.: |
10/326020 |
Filed: |
December 19, 2002 |
Current U.S.
Class: |
378/147 |
Current CPC
Class: |
G21K 1/025 20130101 |
Class at
Publication: |
378/147 |
International
Class: |
G21K 001/02 |
Claims
What is claimed is:
1. A collimator for a CT imaging system, the collimator comprising:
a two-dimensional honeycomb structure, wherein the two-dimensional
honeycomb structure is made via a casting process, the
two-dimensional honeycomb structure comprises channels of a
predetermined shape running between channel walls of a
predetermined thickness, and the two-dimensional honeycomb
structure is capable of meeting predetermined precision
requirements.
2. The collimator of claim 1, wherein the collimator is utilized as
a pre-patient collimator and further comprises a filter operatively
coupled thereto.
3. The collimator of claim 2, wherein the filter comprises a
suitable high-density, high atomic number material.
4. The collimator of claim 3, wherein the suitable high-density,
high atomic number material comprises at least one of: lead, a lead
alloy, tantalum, tungsten, tungsten suspended in an epoxy matrix,
and tungsten suspended in a slurry.
5. The collimator of claim 2, wherein the filter comprises a
three-dimensional insert that is operatively positioned within the
channels of the two-dimensional honeycomb structure.
6. The collimator of claim 5, wherein the filter comprises a
suitable high-density, high atomic number material.
7. The collimator of claim 6, wherein the suitable high-density,
high atomic number material comprises at least one of: lead, a lead
alloy, tantalum, tungsten, tungsten suspended in an epoxy matrix,
and tungsten suspended in a slurry.
8. The collimator of claim 1, wherein the two-dimensional honeycomb
structure comprises a suitable high-density, high atomic number
material.
9. The collimator of claim 8, wherein the suitable high-density,
high atomic number material comprises at least one of: lead, a lead
alloy, tantalum, tungsten, tungsten suspended in an epoxy matrix,
and tungsten suspended in a slurry.
10. The collimator of claim 1, wherein the collimator is utilized
as a post-patient collimator.
11. The collimator of claim 10, wherein the predetermined shape of
the channels comprises at least one of: rectangular, circular,
ovular, trapezoidal, hexagonal, and square.
12. The collimator of claim 10, wherein the channels are tapered to
create a first aperture proximate an x-ray entry surface of the
collimator that is larger than a second aperture proximate an x-ray
exit surface of the collimator.
13. The collimator of claim 10, wherein the two-dimensional
honeycomb structure comprises a suitable high-density, high atomic
number material.
14. The collimator of claim 13, wherein the suitable high-density,
high atomic number material comprises at least one of: lead, a lead
alloy, tantalum, tungsten, tungsten suspended in an epoxy matrix,
and tungsten suspended in a slurry.
15. A filter for use in pre-patient filter/collimator assemblies in
CT imaging systems, the filter comprising a suitable high-density,
high atomic number material that is capable of absorbing x-ray
radiation.
16. The filter of claim 15, wherein the suitable high-density, high
atomic number material comprises at least one of: lead, a lead
alloy, tantalum, tungsten, tungsten suspended in an epoxy matrix,
and tungsten suspended in a slurry.
17. A pre-patient filter and collimator assembly for use in CT
imaging systems, the assembly comprising: a filter component; and a
collimator component, wherein the filter component is operatively
coupled to the collimator component and the collimator component
comprises a two-dimensional honeycomb structure comprising channels
of a predetermined shape running between channel walls of a
predetermined thickness.
18. The pre-patient filter and collimator assembly of claim 17,
wherein the filter component comprises a suitable high-density,
high atomic number material.
19. The pre-patient filter and collimator assembly of claim 18,
wherein the suitable high-density, high atomic number material
comprises at least one of: lead, a lead alloy, tantalum, tungsten,
tungsten suspended in an epoxy matrix, and tungsten suspended in a
slurry.
20. The pre-patient filter and collimator assembly of claim 17,
wherein the collimator component comprises a suitable high-density,
high atomic number material.
21. The pre-patient filter and collimator assembly of claim 18,
wherein the suitable high-density, high atomic number material
comprises at least one of: lead, a lead alloy, tantalum, tungsten,
tungsten suspended in an epoxy matrix, and tungsten suspended in a
slurry.
22. The pre-patient filter and collimator assembly of claim 17,
wherein the filter component comprises a three-dimensional insert
that is operatively positioned within the channels of the
two-dimensional honeycomb structure.
23. A post-patient collimator for use in CT imaging systems, the
collimator comprising: a two-dimensional honeycomb structure
comprising channels of a predetermined shape running between
channel walls of a predetermined thickness, wherein the
two-dimensional honeycomb structure is capable of meeting
predetermined precision requirements.
24. The post-patient collimator of claim 23, made via a casting
process.
25. The post-patient collimator of claim 23, wherein the
predetermined shape of the channels comprises at least one of:
rectangular, circular, ovular, trapezoidal, hexagonal, and
square.
26. The post-patient collimator of claim 23, wherein the channels
are tapered to create a first aperture proximate an x-ray entry
surface of the collimator that is larger than a second aperture
proximate an x-ray exit surface of the collimator.
27. The post-patient collimator of claim 23, wherein the
two-dimensional honeycomb structure comprises a suitable
high-density, high atomic number material.
28. The post-patient collimator of claim 27, wherein the suitable
high-density, high atomic number material comprises at least one
of: lead, a lead alloy, tantalum, tungsten, tungsten suspended in
an epoxy matrix, and tungsten suspended in a slurry.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to collimators for
use in computed tomography (CT) imaging systems. More specifically,
the present invention relates to cast collimators for use in CT
imaging systems, and methods of making same. This invention also
relates to filters for use with such collimators, and the choice of
material(s) for making such filters and/or collimators.
BACKGROUND OF THE INVENTION
[0002] In CT imaging systems, pre-patient filters and collimators
are used to shape an x-ray beam so that a fan-shaped x-ray beam
lies within the X-Y plane, or the imaging plane, before its
transmission through a patient. These pre-patient filters are
generally used to shape the intensity of the x-ray beam in the
X-direction, and are commonly enclosed in a housing (i.e.,
collimator) that determines the width of the x-ray beam in the
Z-direction. The filtered and collimated x-ray beam is attenuated
by the object being imaged (i.e., the patient having the CT scan
performed on them), and the x-rays are then detected by an array of
radiation detectors. Often times, the x-rays pass through a
post-patient collimator prior to being detected by the array of
radiation detectors. These post-patient collimators generally
comprise a number of various parts that can be very difficult to
accurately align and assemble.
[0003] The pre-patient collimators often generate significant
scattered radiation that subjects the patient to x-ray dose that is
not useful in the CT imaging process. Such scatter is becoming an
increasing problem as CT manufacturers open up the fan-shaped x-ray
beam more and more in the Z-direction to accommodate detectors with
more slices and coverage in the Z-direction, thereby increasing the
need for better pre-patient and post-patient collimator designs. As
CT systems are becoming increasingly dose sensitive, it would be
desirable to have systems and methods for making pre-patient
filter/collimator assemblies that minimize the scattered radiation
created therein and exiting therefrom so as to lower the x-ray dose
the patient is exposed to.
[0004] The post-patient collimators are generally complicated
structures comprising combs, rails, plates and wires. Currently,
each comb must be attached to a rail, each plate must be
individually inserted into appropriate slots in the combs and be
attached thereto, and then wires must be individually strung and
attached to the appropriate slots on each plate. This is a very
time consuming, labor-intensive process, often requiring reworking
if the components are not properly aligned. Therefore, it would be
desirable to have systems and methods for making post-patient
collimators in an easier, more efficient, and more economical
manner than currently possible.
[0005] Filters used with such collimators could also be better
designed to minimize the scattered radiation created therein and
exiting therefrom so as to help further lower the x-ray dose the
patient is exposed to.
[0006] It would be desirable to have collimators, both pre-patient
and post-patient, that lower the x-ray dose the patient is exposed
to by minimizing the scattered radiation created therein or exiting
therefrom. It would be further desirable to have such collimators
that can be more easily, more accurately, and more efficiently made
than currently possible. It would also be desirable to have filters
that minimize the scattered radiation created therein and exiting
therefrom, for use in combination with such collimators, so as to
help further reduce the x-ray dose the patient is exposed to. It
would be still further desirable to have such filters and/or
collimators be made of one or more cast pieces of a suitable high
density, high atomic number material. Finally, it would be
desirable to have such collimators to allow improved x-ray dose
efficiency. Many other needs will also be met by this invention, as
will become more apparent throughout the remainder of the
disclosure that follows.
SUMMARY OF THE INVENTION
[0007] Accordingly, the above-identified shortcomings of existing
systems and methods are overcome by embodiments of the present
invention, which relates to collimators, both pre-patient and
post-patient, that lower the x-ray dose the patient is exposed to
by minimizing the scattered radiation created therein or exiting
therefrom. Many embodiments of these collimators can be made more
easily, more accurately, and more efficiently than currently
possible. Embodiments of this invention also comprise filters that
minimize the scattered radiation created therein and exiting
therefrom, for use in combination with such collimators, so as to
help further reduce the x-ray dose the patient is exposed to. Such
filters and/or collimators are preferably made of one or more cast
pieces of a suitable high density, high atomic number material.
These collimators may allow improved x-ray dose efficiency to be
achieved.
[0008] Embodiments of this invention comprise collimators for use
in CT imaging systems. These collimators may comprise a
two-dimensional honeycomb structure that comprises channels of a
predetermined shape running between channel walls of a
predetermined thickness. This two-dimensional honeycomb structure
is preferably made via a casting process, and is capable of meeting
predetermined precision requirements. When used as a pre-patient
collimator, there may be a filter operatively coupled thereto,
wherein the filter is preferably made of any high-density, high
atomic number material such as lead, a lead alloy, tantalum,
tungsten, tungsten suspended in an epoxy matrix, tungsten suspended
in a slurry, or the like. The filter may be positioned in front of
the collimator, or it may comprise a three-dimensional insert that
is operatively positioned within the channels of the
two-dimensional honeycomb structure. When used as a post-patient
collimator, there may be channels running through the
two-dimensional honeycomb structure. These channels could be of any
shape, such as rectangular, circular, ovular, trapezoidal,
hexagonal, square, or the like. Preferably, these channels are
tapered to create a first aperture proximate an x-ray entry surface
of the collimator that is larger than a second aperture proximate
an x-ray exit surface of the collimator. The collimator itself may
also be made of any high-density, high atomic number material such
as lead, a lead alloy, tantalum, tungsten, tungsten suspended in an
epoxy matrix, tungsten suspended in a slurry, or the like.
[0009] Other embodiments of this invention comprise filters for use
in pre-patient filter/collimator assemblies in CT imaging systems,
or for use in conjunction with post-patient collimators, if so
desired. These filters preferably comprise any suitable
high-density, high atomic number material that is capable of
absorbing x-ray radiation, such as lead, a lead alloy, tantalum,
tungsten, tungsten suspended in an epoxy matrix, tungsten suspended
in a slurry, or the like.
[0010] Yet other embodiments of this invention comprise pre-patient
filter and collimator assemblies for use in CT imaging systems.
These assemblies may comprise: a filter component; and a collimator
component, wherein the filter component is operatively coupled to
the collimator component and the collimator component comprises a
two-dimensional honeycomb structure comprising channels of a
predetermined shape running between channel walls of a
predetermined thickness. The filter and/or the collimator may be
made of any suitable high-density, high atomic number material,
such as lead, a lead alloy, tantalum, tungsten, tungsten suspended
in an epoxy matrix, tungsten suspended in a slurry, or the like.
The filter may be positioned in front of the collimator or anywhere
else in suitable proximity to the collimator, or it may comprise a
three-dimensional insert that is operatively positioned within the
channels of the two-dimensional honeycomb structure.
[0011] Still other embodiments of this invention comprise
post-patient collimators for use in CT imaging systems. These
collimators preferably comprise: a two-dimensional honeycomb
structure comprising channels of a predetermined shape running
between channel walls of a predetermined thickness, wherein the
two-dimensional honeycomb structure is capable of meeting
predetermined precision requirements. Ideally, these collimators
are made via a casting process. The channels in these collimators
may comprise any suitable shape, such as rectangular, circular,
ovular, trapezoidal, hexagonal, and/or square. Preferably, these
channels are tapered to create a first aperture proximate an x-ray
entry surface of the collimator that is larger than a second
aperture proximate an x-ray exit surface of the collimator. The
two-dimensional honeycomb structure may comprise any suitable
high-density, high atomic number material, such as for example
lead, a lead alloy, tantalum, tungsten, tungsten suspended in an
epoxy matrix, tungsten suspended in a slurry, or the like.
[0012] Further features, aspects and advantages of the present
invention will be more readily apparent to those skilled in the art
during the course of the following description, wherein references
are made to the accompanying figures which illustrate some
preferred forms of the present invention, and wherein like
characters of reference designate like parts throughout the
drawings.
DESCRIPTION OF THE DRAWINGS
[0013] The systems and methods of the present invention are
described herein below with reference to various figures, in
which:
[0014] FIG. 1 is perspective view of an exemplary CT imaging
system;
[0015] FIG. 2 is a perspective view of a high aspect ratio
pre-patient collimator as utilized in embodiments of this
invention;
[0016] FIG. 3 is a portion of a cross-sectional side view showing
some non-tapered, rectangular-shaped vanes and channels as cast in
embodiments of this invention; and
[0017] FIG. 4 is a portion of a cross-sectional side view showing
some 2-dimensionally tapered, trapezoidal-shaped vanes and channels
as cast in other embodiments of this invention.
DETAILED DESCRIPTION OF THE INVENTION
[0018] For the purposes of promoting an understanding of the
invention, reference will now be made to some preferred embodiments
of the present invention as illustrated in FIGS. 1-4, and specific
language used to describe the same. The terminology used herein is
for the purpose of description, not limitation. Specific structural
and functional details disclosed herein are not to be interpreted
as limiting, but merely as a basis for the claims as a
representative basis for teaching one skilled in the art to
variously employ the present invention. Any modifications or
variations in the depicted support structures and methods of making
same, and such further applications of the principles of the
invention as illustrated herein, as would normally occur to one
skilled in the art, are considered to be within the spirit of this
invention.
[0019] FIG. 1 shows an exemplary CT imaging system 10. Such systems
generally comprise a gantry 12, a gantry opening 48, and a table 46
upon which a patient 22 may lie. Gantry 12 comprises an x-ray
source 14 that projects a beam of x-rays 16 toward an array of
detector elements 18. Generally, the array of detector elements 18
comprises a plurality of individual detector elements that are
arranged in a side-by-side manner in the form of an arc that is
essentially centered on x-ray source 14. In multi-slice imaging
systems, parallel rows of arrays of detector elements 18 can be
arranged so that each row of detectors can be used to generate a
single thin slice image through patient 22 in the X-Y plane. Each
detector element in the array of detector elements 18 senses and
detects the x-rays 16 that pass through an object, such as patient
22. While this figure shows the x-ray source 14 and the array of
detector elements 18 aligned along the X-axis, some CT imaging
systems may align the x-ray source 14 and the array of detector
elements 22 differently, such as along the Y-axis or anywhere else
in the X-Y plane.
[0020] In many CT imaging systems, pre-patient filters and
collimators are utilized between x-ray source 14 and patient 22 to
shape the x-ray beam 16 coming from x-ray source 14 before its
transmission through patient 22. The filters in these assemblies
tend to shape the intensity of the x-ray beam in the X-direction
across the patient 22, and are commonly enclosed in a housing that
determines the width of the x-ray beam in the Z-direction.
Generally, the housing collimation in Z is achieved by using
adjustable collimator blades or jaws to adjust the total area
exposed in Z. However, one major drawback to current pre-patient
filter/collimator assemblies is that they often generate
significant scattered radiation that subjects the patient to x-ray
dose that is not useful in the CT imaging process. As previously
mentioned, scatter is becoming an increasing problem as CT
manufacturers open up the fan-shaped x-ray beam more and more in
the Z-direction to accommodate detectors with more slices and
coverage in the Z-direction, thereby increasing the need for better
pre-patient and post-patient collimator designs. The increase in
such scatter seems to be linear with the increase in the
Z-direction beam width. As CT imaging systems become more and more
dose sensitive, it would be desirable to have pre-patient
filter/collimator assemblies that minimize the scattered radiation
created therein or exiting therefrom, so as to lower the x-ray dose
the patient 22 is exposed to. This invention may reduce the
scattered x-ray radiation creation mechanism in pre-patient
filter/collimator assemblies, as well as provide for the
collimation and subsequent minimization of the scattered radiation
that is created therein.
[0021] Utilizing specific materials for the filters in these
pre-patient filter/collimator assemblies may help minimize the
scattered radiation generated within the pre-patient
filter/collimator assemblies. Typically, these filters are made of
plastics, Teflon.RTM., Flexan.RTM. and/or other low density, low
atomic number materials that have a high Compton to total cross
section ratio (i.e., their primary attenuation mechanism is via
scattering, not via photo-electric absorption). Choosing materials
for the filters that have a high photo-electric to total cross
section ratio may help minimize the radiation scattered within the
filter by reducing or eliminating the scattered radiation creation
mechanism. Such materials may include any high atomic number, high
density material that is good for absorbing x-rays to minimize
x-ray scatter, such as for example, lead, a lead alloy, tantalum,
tungsten, tungsten suspended in an epoxy matrix, tungsten suspended
in a slurry, or any other high density, high atomic number material
that is capable of optimizing X-ray absorption. The collimators may
also benefit from being made from the same high density, high
atomic number materials as the filters. The filters and collimators
may comprise a single material, a stack of materials, or a
composite material.
[0022] The pre-patient scattered radiation could be further reduced
by positioning a honeycomb-shaped collimator 200 proximate a
filter, to filter out even more of the scattered radiation,
especially the forward scattered radiation that is directed at the
patient. Such a structure may be highly desirable since the
pre-patient filter/collimator assemblies currently available do not
have much of an aspect ratio, thereby allowing significant
quantities of forward scattered radiation to escape and be
subjected to the patient. In preferred embodiments, this
pre-patient filter/collimator assembly may comprise utilizing a
three-dimensional insert in the Z-slice width collimator that has
small holes in it, which effectively acts as a high aspect ratio
collimator to absorb the scattered radiation that may be generated
in the filter positioned in front of the pre-patient collimator.
Such an assembly would preferably be made by a casting process,
which would allow honeycomb structures having very thin walls or
vanes to be made. High density, high atomic number materials could
be used to make such honeycomb structures to further help minimize
the scattered radiation, and thereby reduce the x-ray dose to the
patient.
[0023] In embodiments, the filter material could be positioned
within the honeycomb structure itself, similar to honey in a
honeycomb. In yet other embodiments, instead of casting these
pre-patient collimators, stacked etched foils could be used, or
plate-plate egg crate assemblies could be used.
[0024] In one preferred embodiment, the pre-patient
filter/collimator assemblies comprise a specially-selected, high
atomic number, high density material for the filter, and a high
aspect ratio collimator having small channels therein operatively
coupled to the filter. This collimator 200 may comprise a cast
2-dimensional honeycomb structure, such as that shown in FIG. 2,
where the honeycomb structure comprises small rectangular-shaped
channels 211 running throughout the depth 220 of the collimator
200. Casting such a structure is preferable because it allows small
apertures in between very thin walls to be created. It will be
apparent to those skilled in the art that there are numerous other
suitable ways to make such a structure, such as by stacking etched
foils, using plate-plate egg crate assemblies, and the like, and
all such variations are deemed to be within the scope of this
invention. These cast structures may comprise a single cast piece,
or multiple cast pieces that may be joined together. As is well
known to those skilled in the art, all pre-patient and post-patient
collimators comprise radial assemblies that are focused at the
x-ray tube focal spot.
[0025] Many CT imaging systems also utilize post-patient
collimators between the patient 22 and the array of detector
elements 18 to focus the attenuated x-rays 16 that pass through
patient 22 onto the various detector elements in the array of
detector elements 18. Current post-patient collimators comprise
numerous precision or semi-precision machined or fabricated parts
that must be precisely positioned and assembled, one at a time, by
hand. As evidenced by the fact that some current post-patient
collimators comprise as many as 2 rails, 2 combs that must each be
attached to a rail, 944 plates that must be individually inserted
into appropriate slots in the combs and be attached thereto, and 17
tungsten wires that must be individually strung and attached to the
appropriate slots on each plate, this is a very labor-intensive,
time consuming process. Therefore, it would be desirable to have
systems and methods for making such collimators in an easier, more
efficient, and more economical manner than currently possible.
[0026] The post-patient collimators of this invention are
preferably made via casting, which allows thin, tapered vanes to be
created, thereby reducing non-linearities and image artifacts
commonly caused by misaligned collimator vanes in existing
post-patient collimators. Non-linearities in existing post-patient
collimators may be caused when the x-ray source moves slightly
during operation, as is common due to the heat generated by the
rotating anode within the x-ray generation source, thereby causing
the x-ray beams to be aligned in a non-parallel manner with respect
to the channels in the collimator, resulting in shadowing at the
x-ray exit surface 215 of the collimator. Such non-linearities are
often corrected in existing post-patient collimators by skewing the
vanes to slightly misalign the plates in the collimator; this
greatly reduces the channel-to-channel nonlinearities induced by
focal spot motion of the x-ray beam during operation. Casting these
post-patient collimators may help improve x-ray dose utilization
and efficiency by allowing thinner, tapered vanes to be used
therein, thereby eliminating the need to skew the vanes. It would
be almost inconceivable to create tapered vanes in any manner other
than casting.
[0027] While cast collimator assemblies are currently utilized in
nuclear and/or gamma camera systems, such collimators are not as
accurate as those needed for CT collimators, nor are they
thin-walled structures. However, recent advances in casting
technology have made casting more attractive for the manufacture of
low-cost precision CT collimators. The casting process lends itself
to some novel advantages when applied to the manufacture of CT
collimators, for both pre-patient and post-patient collimators.
Casting allows collimators having very thin walls with very small
channels or apertures therebetween to be formed. Casting also
allows tapered vanes to be created in such collimators. For
example, in the honeycomb structure described above in pre-patient
collimators, the channels were merely rectangular-shaped channels
211 in the imaging plane. However, by utilizing casting technology,
it may be possible to form tapered channels of varying shapes in
both pre-patient and post-patient collimators, if tapering is so
desired.
[0028] These cast channels could be tapered in one dimension or
two, whichever is desired. For example, these channels may be
tapered in only the X-direction or the Y-direction (i.e., 1-D
taper), or they could be tapered in both the X-direction and the
Y-direction (i.e., 2-D taper). While many embodiments utilize
rectangular-shaped vanes and channels, casting allows various other
shaped vanes and channels to be formed therein, such as for example
round channels or hexagonal channels, both of which could also be
tapered in one dimension or two, whichever may be desired. A
portion of a cross-sectional side view showing some non-tapered,
rectangular-shaped vanes 210 and rectangular-shaped channels 211,
as cast in embodiments of this invention, can be seen in FIG. 3. A
portion of a cross-sectional side view showing some tapered,
trapezoidal-shaped vanes 212 and trapezoidal-shaped channels 213,
as cast in other embodiments of this invention, is shown in FIG. 4.
It will be apparent to those skilled in the art that numerous other
shaped channels could be created in these collimators, and all such
variations are deemed to be within the scope of this invention.
[0029] Tapering the vanes in these post-patient collimators allows
the exacting precision required of such collimators to be required
on only one surface of the collimator, for example, on the x-ray
exit surface 215, but not on the x-ray entrance surface 216. If the
vanes are tapered in such collimators, the non-precision surface of
such collimators (i.e., the x-ray entrance surface 216), may be
hidden behind or within the shadow of the precision surface (i.e.,
the x-ray exit surface 215), thereby reducing the need for
precision accuracy on both surfaces since the shadow created by the
non-precision surface can move around a bit as long as it stays
within the shadow created by the precision surface. As creating
precision dimensions on only one surface is much easier than
creating precision dimensions on multiple surfaces, this greatly
improves the probability of being able to apply the much more cost
effective casting technology to the manufacture of CT collimators.
Tapering the vanes may also eliminate the varying shadowing effects
that are commonly caused by misaligned collimator vanes in existing
post-patient collimators. Furthermore, tapering the vanes
eliminates the need to skew the vanes, as is commonly done in
existing post-patient collimators to improve x-ray dose
efficiency.
[0030] While tapering these vanes and channels provides many
advantages, the vanes and channels in these pre-patient and
post-patient collimators do not have to be tapered. Furthermore,
the honeycomb structure of these collimators can be made with
2-dimensional septa, 1-dimensional septa, or the equivalent of the
current plates and wires used in such collimators. As will be
apparent to those skilled in the art, numerous cast designs of
these collimators are possible. The collimators may be cast as
single piece structures, or they may be cast as multiple pieces
that are capable of being operatively coupled together.
[0031] As described above, the systems and methods of the present
invention allow both the pre-patient and post-patient collimators
to be made via a casting process, allowing very accurate
collimators to be made much easier and more economically than
currently possible. Advantageously, these collimators also help
minimize scattered x-ray radiation, thereby reducing the x-ray dose
that patients are exposed to. The materials selected for making
such collimators may help minimize the scattered radiation that is
being created within such collimator assemblies or scattered
therefrom, and the honeycomb structures may help further reduce the
scattered radiation that patients are subjected to. This is
particularly advantageous since CT imaging systems are becoming
more dose sensitive, and it is desirable to expose the patient to
no more radiation than necessary.
[0032] Various embodiments of this invention have been described in
fulfillment of the various needs that the invention meets. It
should be recognized that these embodiments are merely illustrative
of the principles of various embodiments of the present invention.
Numerous modifications and adaptations thereof will be apparent to
those skilled in the art without departing from the spirit and
scope of the present invention. For example, while tapered vanes
are described in relation to cast post-patient collimators, they
could also be used in cast pre-patient collimators if desired.
Thus, it is intended that the present invention cover all suitable
modifications and variations as come within the scope of the
appended claims and their equivalents.
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