U.S. patent application number 13/149417 was filed with the patent office on 2012-12-06 for system and method for collimation in diagnostic imaging systems.
Invention is credited to Yaron Hefetz, Floribertus P.M. Heukensfeldt Jansen.
Application Number | 20120305781 13/149417 |
Document ID | / |
Family ID | 47145934 |
Filed Date | 2012-12-06 |
United States Patent
Application |
20120305781 |
Kind Code |
A1 |
Jansen; Floribertus P.M.
Heukensfeldt ; et al. |
December 6, 2012 |
SYSTEM AND METHOD FOR COLLIMATION IN DIAGNOSTIC IMAGING SYSTEMS
Abstract
A system and method for collimation in diagnostic imaging
systems is provided. One collimator includes a plurality of
parallel hole segments and a plurality of collimator bores within
each of the plurality of parallel hole segments. Additionally, all
of the plurality of collimator bores in at least one of the
plurality of parallel hole segments have a first pointing direction
and all of the plurality of collimator bores in at least one other
of the plurality of parallel hole segments have a second pointing
direction, wherein the plurality of parallel hole segments are
arranged in a fanbeam collimation configuration. Further, the first
pointing direction is different than the second pointing
direction.
Inventors: |
Jansen; Floribertus P.M.
Heukensfeldt; (Ballston Lake, NY) ; Hefetz;
Yaron; (Kibbutz alonim, IL) |
Family ID: |
47145934 |
Appl. No.: |
13/149417 |
Filed: |
May 31, 2011 |
Current U.S.
Class: |
250/363.04 ;
250/363.1; 29/428 |
Current CPC
Class: |
G21K 1/02 20130101; G21K
1/025 20130101; G02B 27/30 20130101; Y10T 29/49826 20150115 |
Class at
Publication: |
250/363.04 ;
250/363.1; 29/428 |
International
Class: |
G01T 1/166 20060101
G01T001/166; B23P 11/00 20060101 B23P011/00; G21K 1/02 20060101
G21K001/02 |
Claims
1. A collimator for a radiation imaging detector, the collimator
comprising: a plurality of parallel hole segments; and a plurality
of collimator bores within each of the plurality of parallel hole
segments, wherein all of the plurality of collimator bores in at
least one of the plurality of parallel hole segments have a first
pointing direction and all of the plurality of collimator bores in
at least one other of the plurality of parallel hole segments have
a second pointing direction, the first pointing direction being
different than the second pointing direction, such that the
plurality of parallel hole segments are arranged in a fanbeam
collimation configuration.
2. The collimator of claim 1, wherein the fanbeam collimation
configuration defines a cone-beam arrangement, wherein a field of
view of the plurality of segments is smaller than a field of view
of the collimator.
3. The collimator of claim 1, wherein the first pointing direction
defines at least a first slant angle and the second pointing
direction defines at least a second slant angle, the first slant
angle being greater than the second slant angle, and the plurality
of parallel hole segments having the first pointing direction
located closer to a collimator body edge than the plurality of
parallel hole segments having the second pointing direction.
4. The collimator of claim 1, wherein one of the first or second
pointing directions is ninety degrees relative to a front face of
one of the plurality of parallel hole segments.
5. The collimator of claim 1, wherein a difference between the
first and second pointing directions is the same as a gantry
rotation step, an integer multiple thereof or a sub-multiple
thereof.
6. The collimator of claim 1, wherein the plurality of parallel
hole segments are formed from angle cut parallel hole collimator
sections.
7. The collimator of claim 1, further comprising a shielding member
in a gap between at least two of the plurality of parallel hole
segments.
8. The collimator of claim 1, wherein at least two of the plurality
of parallel hole segments have collimator bores with the first
pointing direction and at least two of the plurality of parallel
hole segments have collimator bores with the second pointing
direction.
9. The collimator of claim 1, wherein the plurality of collimator
bores are pointed along a length of a collimator body.
10. The collimator of claim 1, wherein the plurality of collimator
bores in different ones of the plurality of parallel hole segments
have different lengths.
11. A nuclear medicine (NM) imaging system comprising: a gantry; at
least one imaging detector supported on the gantry and configured
to rotate about the gantry defining an axis of rotation; and a
collimator coupled to the at least one imaging detector, the
collimator having a plurality of parallel hole segments, wherein a
plurality of collimator bores are within each of the plurality of
parallel hole segments, with all of the plurality of collimator
bores in at least one of the plurality of parallel hole segments
having a first pointing direction and all of the plurality of
collimator bores in at least one other of the plurality of parallel
hole segments having a second pointing direction, the first
pointing direction being different than the second pointing
direction, such that the plurality of parallel hole segments are
arranged in a fanbeam collimation configuration.
12. The NM imaging system of claim 11, wherein the fanbeam
collimation configuration defines a cone-beam arrangement, wherein
a field of view of the plurality of parallel hole segments is
smaller than a field of view of the collimator.
13. The NM imaging system of claim 12, further comprising an image
reconstruction module configured to iteratively reconstruct an
image based on acquired image data received by the at least one
imaging detector.
14. The NM imaging system of claim 11, wherein a difference between
the first and second pointing directions is the same as a rotation
step of the gantry, an integer multiple thereof or a sub-multiple
thereof.
15. The NM imaging system of claim 11, further comprising an image
reconstruction module configured to reconstruct an image from data
acquired from the at least one imaging detector, wherein the image
reconstruction module is configured to rebin the acquired data into
aligned multiple parallel projections.
16. The NM imaging system of claim 11, further comprising a
controller configured to control movement of the at least one
imaging detector.
17. The NM imaging system of claim 11, wherein the at least one
imaging detector comprises a Single Photon Emission Computed
Tomography (SPECT) camera.
18. A method for manufacturing a collimator of an imaging system,
the method comprising: coupling tubes together to form a stack of
parallel hole collimator segments or forming a corrugated
collimator core; cutting the stack or the corrugated collimator
core at one or more pointing directions to form a plurality of
slanted collimator segments; and coupling the plurality of slanted
collimator segments together to form a segmented type collimator,
wherein at least two of the slanted collimator segments have
collimator bores with different pointing directions and are
arranged in a fanbeam collimation configuration.
19. The method of claim 18, wherein at least one of the pointing
directions is ninety degrees relative to a front face of the
parallel hole collimator segment.
20. The method of claim 18, wherein the cutting comprises providing
angular increments that are the same as a gantry rotation step, an
integer multiple thereof or a sub-multiple thereof.
21. The method of claim 18, further comprising providing a
shielding member in a gap between at least two of the plurality of
slanted collimator segments.
22. The method of claim 18, further comprising coupling at least
one non-slanted collimator segment together with the plurality of
slanted collimator segments.
Description
BACKGROUND
[0001] The subject matter disclosed herein relates generally to
diagnostic imaging systems, and more particularly to detector
collimation in Nuclear Medicine (NM) imaging systems.
[0002] In NM imaging, radiopharmaceuticals are taken internally and
then detectors (e.g., gamma cameras), typically mounted on a
gantry, capture and form images from the radiation emitted by the
radiopharmaceuticals. The NM images primarily show physiological
function of, for example, a patient or a portion of a patient being
imaged.
[0003] Collimation may be used to focus the field of view of the
detectors. For example, parallel hole collimators may be used.
Additionally, converging fanbeam collimators can be used to improve
the sensitivity of the detectors over a limited field of view.
However, current fanbeam collimators are constructed using a
precision cast process that is difficult to perform and expensive.
The precise construction is needed because image quality depends on
the alignment of tens of thousands of collimator bores that point
in slightly different directions. Additionally, because every
collimator bore points in a unique direction, reconstruction
algorithms that use certain rebinning techniques may cause loss of
resolution.
BRIEF DESCRIPTION
[0004] In accordance with an embodiment, a collimator for a
radiation imaging detector is provided that includes a plurality of
parallel hole segments and a plurality of collimator bores within
each of the plurality of parallel hole segments. Additionally, all
of the plurality of collimator bores in at least one of the
plurality of parallel hole segments have a first pointing direction
and all of the plurality of collimator bores in at least one other
of the plurality of parallel hole segments have a second pointing
direction. Further, the first pointing direction is different than
the second pointing direction, such that the plurality of parallel
hole segments are arranged in a fanbeam collimation
configuration.
[0005] In accordance with another embodiment, a nuclear medicine
(NM) imaging system is provided that includes a gantry and at least
one imaging detector supported on the gantry and configured to
rotate about the gantry defining an axis of rotation. The NM
imaging system also includes a collimator coupled to the at least
one imaging detector, with the collimator having a plurality of
parallel hole segments. A plurality of collimator bores are within
each of the plurality of parallel hole segments, with all of the
plurality of collimator bores in at least one of the plurality of
parallel hole segments having a first pointing direction and all of
the plurality of collimator bores in at least one other of the
plurality of parallel hole segments having a second pointing
direction. Additionally, the first pointing direction is different
than the second pointing direction, such that the plurality of
parallel hole segments are arranged in a fanbeam collimation
configuration.
[0006] In accordance with yet another embodiment, a method for
manufacturing a collimator of an imaging system is provided. The
method includes coupling tubes together to form a stack of parallel
hole collimator segments or forming a corrugated collimator core,
and cutting the stack or the corrugated collimator core at one or
more pointing directions to form a plurality of slanted collimator
segments. The method also includes coupling the plurality of the
slanted collimator segments together to form a segmented type
collimator, wherein at least two of the slanted collimator segments
have collimator bores with different pointing directions and are
arranged in a fanbeam collimation configuration.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a schematic block diagram illustrating a Nuclear
Medicine (NM) imaging system formed in accordance with various
embodiments.
[0008] FIG. 2 is a diagram of a collimator formed in accordance
with various embodiments.
[0009] FIG. 3 is a diagram illustrating tubes used to form a
collimator in accordance with various embodiments.
[0010] FIG. 4 is a diagram illustrating the cutting of stacks of
tubes to form slanted parallel hole collimator segments in
accordance with various embodiments.
[0011] FIG. 5 is a diagram of slanted parallel hole collimator
segments formed in accordance with various embodiments.
[0012] FIG. 6 is a diagram of a collimator formed in accordance
with various embodiments.
[0013] FIG. 7 is a diagram illustrating a cross-sectional view in
the transverse plane of a symmetric multi-section collimator for
cardiac imaging in accordance with various embodiments.
[0014] FIG. 8 is a diagram illustrating a coronal plane
cross-section of a symmetric multi-section collimator for cardiac
imaging in accordance with various embodiments.
[0015] FIG. 9 is a diagram illustrating a transverse plane
cross-section of an asymmetric multi-section collimator for brain
imaging in accordance with various embodiments.
[0016] FIG. 10 is a diagram illustrating a coronal plane
cross-section of an asymmetric multi-section collimator for brain
imaging in accordance with various embodiments.
[0017] FIG. 11 is a diagram illustrating tilting operation of a
detector in accordance with various embodiments.
[0018] FIG. 12 is a diagram illustrating gantry rotation steps.
[0019] FIG. 13 is a diagram of a sinogram illustrating a sampling
scheme for rebinning in accordance with various embodiments.
[0020] FIG. 14 is a diagram of another sinogram illustrating a
sampling scheme in accordance with various embodiments.
[0021] FIG. 15 is a perspective view of an exemplary NM imaging
system formed in accordance with various embodiments.
[0022] FIG. 16 is a flowchart of a method in accordance with
various embodiments for manufacturing a collimator for use in
collimating a detector of an imaging system.
DETAILED DESCRIPTION
[0023] The foregoing summary, as well as the following detailed
description of certain embodiments, will be better understood when
read in conjunction with the appended drawings. To the extent that
the figures illustrate diagrams of the functional blocks of various
embodiments, the functional blocks are not necessarily indicative
of the division between hardware circuitry. Thus, for example, one
or more of the functional blocks (e.g., processors, controllers or
memories) may be implemented in a single piece of hardware (e.g., a
general purpose signal processor or random access memory, hard
disk, or the like) or multiple pieces of hardware. Similarly, the
programs may be stand alone programs, may be incorporated as
subroutines in an operating system, may be functions in an
installed software package, and the like. It should be understood
that the various embodiments are not limited to the arrangements
and instrumentality shown in the drawings.
[0024] As used herein, an element or step recited in the singular
and proceeded with the word "a" or "an" should be understood as not
excluding plural of said elements or steps, unless such exclusion
is explicitly stated. Furthermore, references to "one embodiment"
are not intended to be interpreted as excluding the existence of
additional embodiments that also incorporate the recited features.
Moreover, unless explicitly stated to the contrary, embodiments
"comprising" or "having" an element or a plurality of elements
having a particular property may include additional such elements
not having that property.
[0025] Various embodiments provide a system and method for
collimation in diagnostic imaging systems, such as a Nuclear
Medicine (NM) imaging system. For example, a collimator arrangement
may be provided for use in a Single Photon Emission Computed
Tomography (SPECT) imaging system. The collimator arrangement in
various embodiments is formed from sections of parallel hole
collimators, such that a fanbeam collimator is approximated. By
practicing at least one embodiment, one technical effect is reduced
cost and reduced complexity for precision collimator manufacturing.
Additionally, at least one other technical effect is the ability to
use a simpler reconstruction algorithm.
[0026] Some embodiments provide a segmented collimator that
includes slanted parallel hole collimator segments. The segmented
collimator provides fanbeam type collimation, such as for use with
detectors of an NM imaging system, for example, a SPECT system. An
NM imaging system 20 may be provided as illustrated in FIG. 1
having an NM camera configured as a SPECT detector 22. It should be
noted that the various embodiments are not limited to the NM
imaging system 20 having a single detector 22 operable to perform
SPECT imaging. For example, the NM imaging system 20 optionally may
include one or more additional detectors 22 (an additional detector
22 is illustrated in dashed lines) such that a pair of detectors 22
is provided having a central opening 24 therethrough. An object,
such as a patient 26, is positioned in proximity to the one or more
detectors 22 for imaging.
[0027] It should be noted that number of detectors 22 may be
greater than two, for example three or more. In a multi-detector
camera, the position of the detectors 22 may be substantially at 90
degrees to each other as illustrated in FIG. 1, or in different
configurations as known in the art. It also should be noted that in
a multi-detector camera configuration, some of the collimators may
optionally be a standard collimator, for example a parallel hole
collimator or a standard fan-beam collimator, or a cone-beam
collimator, or a pinhole collimator, while at least one of the
collimators is a segmented collimator according to one or more of
the various embodiments. Alternatively, all of the collimators may
be segmented collimators according to one or more of the various
embodiments.
[0028] The detectors 22 may be pixelated detectors that may
operate, for example, in an event counting mode. The pixelated
detectors 22 may be configured to acquire SPECT image data. The
detectors 22 may be formed from different materials, particularly
semiconductor materials, such as cadmium zinc telluride (CdZnTe),
often referred to as CZT, cadmium telluride (CdTe), and silicon
(Si), among others. In some embodiments, a plurality of detector
modules is provided, each having a plurality of pixels. In other
embodiments, the detector 22 may be made of a scintillation crystal
such as NaI coupled to an array of Photo-Multiplier Tubes (PMTS).
However, it should be noted that the various embodiments are not
limited to a particular type or configuration of detectors, and any
suitable imaging detector may be used.
[0029] The detectors 22 are fitted with (e.g., have coupled
thereto) collimators 28 that include a plurality segments 30, which
in various embodiments are parallel hole collimator segments, at
least some of which are slanted parallel hole collimator segments.
For example, four segments 30 are illustrated that define four
different parallel hole collimator sections where the pointing
direction of the bores within at least some of the individual
segment 30 are different. However, some of the segments 30 may have
bores that are pointed the same. Accordingly, while one or more the
segments 30 may have bores provided at the same pointing direction,
at least one segment 30 has bores at a different pointing direction
than the bores of another segment 30, which may be adjacent or
non-adjacent segments 30, as described in more detail herein.
[0030] It should be noted as used herein, pointing direction refers
to one or more angles that define a direction that the bore extends
through the collimator 28. For example, the pointing direction
defines a tilt direction in various embodiments that may be defined
by an azimuth and elevation. In various embodiments, the tilt is
defined by two angles, such as an axial angle and a transaxial
angle. Thus, the pointing direction may be a pointing vector that
is not normal to a face of the collimator 28.
[0031] The detectors 22 may be provided in different
configurations, for example, in single planar imaging mode
(illustrated in FIG. 1), a two detector 22 "L" mode configuration
(illustrated in FIG. 1 with the dashed line detector 22), an "H"
mode configuration, or a three headed camera, among others.
Additionally, a gantry (not shown) supporting the detectors 22 may
be configured in different shapes, for example, as a "C" and the
detectors 22 may be arranged in different configurations.
[0032] The imaging system 20 also includes a detector controller 32
that operates to control the movement of the detectors 22 around
the central opening 24 and about the patient 26. For example, the
detector controller 32 may control movement of the detectors 22,
such as to rotate the detectors 22 around a patient, and which may
also include moving the detectors closer or farther from the
patient 26 and pivoting the entire detector 22.
[0033] The imaging system 20 also includes an image reconstruction
module 34 configured to generate images from acquired image
information 36 received from the detectors 22. For example, the
image reconstruction module 34 may operate using NM image
reconstruction techniques, such as SPECT image reconstruction,
techniques to generate SPECT images of the patient 26, which may
include an object of interest, such as the heart 38 of the patient.
As described in more detail herein, in one embodiment, with the
pointing directions of the segments 30 at projection pointing
direction steps (e.g. gantry rotation steps) of the imaging system
20, the image information 36 can be rebinned into parallel
projections without a loss of resolution.
[0034] Variations and modifications to the various embodiments are
contemplated. For example, in a dual headed system, namely one with
two detectors 22, one detector 22 may include the collimator 28
with the segments 30 while the other detector 22 includes a
parallel hole collimator. In this embodiment, the parallel hole
collimator can obtain information for an entire field of view
(FOV), while the detector 22 with the collimator 28 operates to
focus on a smaller region of interest (ROI) to provide higher
quality information (e.g., more accurate photon counting).
Accordingly, the collimator 28 with the segments 30 provides
fanbeam or converging type of operation.
[0035] The image reconstruction module 34 may be implemented in
connection with or on a processor 40 (e.g., workstation) that is
coupled to the imaging system 20. Optionally, the image
reconstruction module 34 may be implemented as a module or device
that is coupled to or installed in the processor 40. Accordingly,
the image reconstruction module 34 may be implemented in software,
hardware or a combination thereof. In one embodiment, the image
reconstruction may be performed on a remote workstation (e.g., a
viewing and processing terminal) having the processing components
and not at the imaging scanner.
[0036] It should be noted that in various embodiments, the image
reconstruction (e.g., generating a 3D image from a plurality of
acquired 2D projections) is performed using one or more iterative
algorithms (e.g., a maximum-likelihood expectation maximization
(MLEM) algorithm or an ordered-subset expectation maximization
(OSEM) algorithm or other suitable algorithm) taking into account
the known tilts of the various sections of the collimator 28.
Specifically, when axial tilt is involved, direct (non-iterative)
reconstruction algorithms such as filtered back projection (FBP)
may not be used.
[0037] The image information 36 received by the processor 40 may be
stored for a short term (e.g., during processing) or for a long
term (e.g., for later offline retrieval) in a memory 42. The memory
42 may be any type of data storage device, which may also store
databases of information. The memory 42 may be separate from or
form part of the processor 40. A user input 44, which may include a
user interface selection device, such as a computer mouse,
trackball and/or keyboard is also provided to receive a user
input.
[0038] Thus, during operation, the output from the detectors 22,
which may include the image information 36, such as projection data
from a plurality of detector or gantry angles is transmitted to the
processor 40 and the image reconstruction module 34 for
reconstruction and formation of one or more images.
[0039] As illustrated in FIG. 2, the collimator 28 may include four
segments 30 (S.sub.1-S.sub.4), with each having a plurality of
collimator bore 50. It should be noted that the bores 50 may
include, for example, any shape or size of hole or opening. The
pointing direction of the bores 50 in each of the segments 30 may
be different, such as pointed for focusing on an ROI. However, two
or more of the segments 30 may have parallel bores 50 pointed
inwardly (toward the middle of the detector 22) to the same degree.
For example, segments S.sub.1 and S.sub.4 may have bores 50 pointed
the same while the bores 50 of segments S.sub.2 and S.sub.3 are
pointed the same, such as +/-10 degrees and +/-20 degrees,
respectively. Thus, the bores 50 for each of the segments 30 are
pointed the same, but the pointing direction is different for at
least two of the segments 30, to define different projection
pointing directions in the different segments 30. Thus, the
segments 30 define fixed slanted parallel hole collimator sections
which together can provide fanbeam type operation, for example,
approximate fanbeam collimation.
[0040] However, the bores 50 may be pointed at different angles
than as described herein, for example, as desired or needed. For
example, the pointing direction may define an angle relative to a
face of the collimator 28 of between about 30 degrees and about 45
degrees. In one embodiment, such as in a five segment 30 collimator
28, the segments may have pointing directions with the following
angle degrees: -40, -20, 0, +20, +40. For example, for a 3.times.5
array of segments 30, for a 40.times.50 cm detector 22 may have the
following angulations:
[0041] [(-40,-30),(-20,-30), (0,-30), (+20,-30) (+40, -30)];
[0042] [(-40,0),(-20,0), (0,0), (+20,0) (+40, 0)]; and
[0043] [(-40,+30),(-20,+30), (0,+30), (+20,+30) (+40, +30)].
[0044] Thus, the tilt of a peripheral section can be less than
about 30 degrees and more than about 45 degrees such that the focal
point (or line) is near the center of the body or ROI. This may be
optimized to the particular application. In a small body part, such
as a brain, the focal point may be set to the center of the brain,
for example, which is about 15 cm deep. With a 50 cm detector
width, the angle is more than 45 degrees.
[0045] It should be noted that the rectangular shape of the bores
50 in FIG. 2 is for illustration only, and other shapes, for
example hexagonal or round collimator bores may be used.
Additionally, it should be noted that the segments 30 need not be
shaped as strips and may be arranged in a two-dimensional
configuration. For example, a 3.times.3 array of 9 segments 30 may
be used. Further, some segments 30 may be wedge shaped, have a
curved outline, or may be provided in different shapes.
[0046] It should be noted that the segments 30 and bores 50 may be
formed from any suitable collimator material, for example, lead or
tungsten. It also should be noted that different segments 30 may be
formed having different parameters such as bore size, shape,
angulations and length.
[0047] Thus, in the various embodiments, the bores 50 are generally
parallel bores 50, namely openings through the collimator 28, such
that the plurality of parallel hole segments 30 form a fanbeam type
arrangement, which may have different focal lengths. In one
embodiment, the bores 50 in each segment have a different degree of
slanting. However, the bores 50 in one or more segments 30 or may
be perpendicular to the surface of the detector 22. For example, in
one or more segments 30, the bores 50 may be slanted such that the
bores 50 are pre-focused to a typical point of offset based on the
location of the segment 30 along the collimator 28. Thus, the
collimator 28 formed in accordance with various embodiments may
have different configurations.
[0048] Modifications and variations are contemplated to the various
embodiments. For example, each of the segments 30 may have
different sizes of bores 50 or different bore lengths. In some
embodiments, the bores 50 that are usually further from the ROI
(near the edge of the detector 22) may be longer bores to
compensate for the greater distance to the ROI (at the expense of
sensitivity, but maintaining some resolution). In other
embodiments, the segments 30 may be incrementally converging or
diverging along the axis of rotation of the imaging system 20
(shown in FIG. 1), which effectively reduces or increases,
respectively, the FOV in the direction along the axis of rotation
and increases the sensitivity. When the FOV is known to be quite
small (e.g., in the heart) this additional convergence in each of
the respective segments 30 can provide additional improvement in
sensitivity. In still other embodiments, the bores 50 in each of
the segments 30 may be pointed different from one segment 30 to
another along the short or long axis of the segment 30.
[0049] The collimator 28 in various embodiments is a single
collimator unit defining a single collimator body formed from
several segments 30. For example, the collimator 28 is constructed
from several segments 30 of parallel hole collimator sections that
are coupled together to form the single collimator 28. Accordingly,
once the segments 30 are coupled together, the segments 30 move
together as a single unit (and also move with the detectors 22 when
coupled thereto). In one embodiment, the segments 30 are formed
from lead tubes 60 (also referred to as lead straws) as shown in
FIG. 3, which may be tubes 60 of lead stacked in parallel and then
coupled together, such as with epoxy or other suitable glue. The
lead tubes 60 may have one or more channels or bores therethrough.
In one embodiment, the segments 30 are cut out of stack of lead
straw, which are formed using, any suitable method for constructing
a single parallel hole collimator. The tubes 60 may have bores with
different cross-sectional shapes, such as circular, square or
hexagonal, among others.
[0050] With the lead tubes 60 coupled together into a stack 62,
pointed parallel hole segments 30 are formed. In particular, the
stack 62 of lead tubes 60 is cut at one or more pointing directions
as illustrated by the cut lines 64 in FIG. 4. Alternatively, a
thick collimator may be formed as described below. It should be
noted that the pointing direction of the cuts to form the parallel
hole segments 30 may be varied as desired as needed, such as based
on the particular pointing direction for one or more segments 30.
The cutting and finishing of the segments 30 from the stack 62 of
lead tubes 60 is performed using any suitable collimator cutting
technique, such as any suitable parallel hole collimator cutting
technique. The cutting of the stack 62 of lead tubes 60 results in
a series of slanted parallel hole collimator sections 66 having
parallel bores 50 as shown in FIG. 5 and that define the segments
30 as shown in FIG. 6. It should be noted that while the parallel
hole collimator sections 66 are shown as having constant thickness,
wedge like sections (or other configurations) may be provided by
cutting along non-parallel cut lines, thereby resulting in sections
66 with variable bore length. The cutting may be performed, for
example, using a wire saw, which allows for curved cut lines to be
made.
[0051] The segments 30 are joined together using any suitable
coupling means, such as with epoxy or other suitable glue, to form
the collimator 28. As can be seen, each of the segments 30 has
bores 50 within that segment 30 pointed to the same degree, with
the bores 50 in at least two segments 30 pointed differently. It
should be noted that one or more segments 30 may have non-slanted
bores 50 as illustrated by the segment 30c. Additionally, in this
embodiment, the bores 50 in segments 30a and 30e are pointed
inwardly at the same slant of the pointing direction and the bores
50 in segments 30b and 30d are pointed inwardly at the same
pointing direction. However, as should be appreciated, the pointing
directions for the set of bores 50 in each segment 30 may be
different.
[0052] It should be noted that the formation or construction of the
collimator 28 may be provided using any suitable method. For
example, the collimator 28 may be formed by a method for forming
corrugated collimators, such as described in U.S. Pat. No.
3,936,340 entitled "Method for Making Corrugated Collimators for
Radiation Imaging Devices." However, it should be appreciated that
there are variations to the described method. As another example,
the collimator 28 may be formed using a tube assembly process. It
should be noted that the process described below is described
generally for forming a single segment and when forming a
multi-segment collimator different steps may be used as further
described. The process, in one embodiment, includes:
[0053] a. Forming a plurality of lead tubes, for example, about 20
cm long, about 2 mm bore diameter, about 0.2 mm wall, and having a
hexagonal cross-section. However, other dimensions and parameters
may be used, as well as other cross-sectional shapes, such as
square cross-sections were made. In one embodiment, a high pressure
punch is used.
[0054] b. Applying glue on the outer surface of the lead tubes.
[0055] c. Stacking the tubes (e.g., in a frame to maintain
parallelism and shape) and curing the glue forming a thick
"honeycomb" structure. It should be noted that the stacking may be
performed while tubes are on a wedge, thereby crating a structure
similar to FIG. 5.
[0056] d. Filling the bores with wax to provide rigidity.
[0057] e. Sawing or cutting the structure to create "collimator
cores" (e.g., 10 cores of 2 cm bore length). For a multi-segment
collimator, a plurality of sections is cut with desired angulations
(namely, the collimator core is cut to slanted segments).
[0058] f. Mounting each core in a collimator holder. For a
multi-segment collimator, a set of segments are mounted/positioned
on the holder based on desired angulations or pointing directions.
It should be noted that optionally different segments may be
separately cut.
[0059] g. Removing the wax (e.g., by heat and/or solvent). It
should be noted that steps f and g may be reversed in some
embodiments.
[0060] Variations are also contemplated. For example, for a
corrugated collimator, a thick or tilted corrugated collimator core
is formed or prepared, and then step d through g are performed as
described above.
[0061] Thus, using segments 30 having parallel bores 50 to form the
collimator 28, a fan beam type collimation arrangement is provided.
It should be noted that shielding also may be provided in the
region or gap between the collimator segments 30 (or behind the
segments) to reduce or prevent high count rates caused by radiation
penetrating through the gap between adjacent segments 30. As
illustrated in FIG. 6, a wedge shaped shielding member 68 may be
provided between adjacent segments 30 that fills the gap
therebetween. It should be noted that the amount of spacing between
the segments 30 may be varied based on the different pointing
directions for adjacent segments 30. It also should be noted that
the shielding members 68 may be formed from any type of collimator
or photon blocking material, such as lead or tungsten.
Alternatively, radiation leaks may be reduced or prevented by
applying a material with a high stopping power such as an epoxy
mixed with lead or tungsten powder.
[0062] Additionally, different varying pointing direction
configurations may be provided. For example, a first pointing
direction of one of the segments 30 may be greater than a second
pointing direction of another one of the segments 30 such that the
segments 30 having the greater pointing directions are located
closer to ends or an edge 76 of the body of the collimator 28.
Thus, a converging fanbeam collimator may be provided. However,
other configurations may be provided by changing the pointing
directions, such as to form a diverging fanbeam collimator.
[0063] Thus, a single collimator 28 is formed from a plurality of
parallel bore segments 30 and that may be coupled to one or more
detectors 22 (shown in FIG. 1). In one embodiment, the orientation
of the bores 50 is rotated about an axis parallel to the short axis
of the collimator 28.
[0064] In operation, the detector 22 (or detectors 22) with the
collimator 28 coupled or mounted thereto move around the patient 26
(both shown in FIG. 1). Additionally, the detectors 22 may be
tilted to provide a level of adjustment as described in more detail
herein.
[0065] Image data may be acquired at a plurality of angular
increments of the detector 22 about the patient 26. It should be
noted that the positioning of the detector(s) 22 can be automatic
based on prior information (e.g., CT information), emission
information (adapting during the scan), atlas-based information
(e.g., all hearts are roughly in a particular location), user
interaction (e.g., based on initial emission data, a user may
select a desired ROI), information based on the reconstructed image
(another form of adaptive acquisition and reconstruction), among
other information or factors. Additionally, suitable proximity
sensors or other means for measuring a patient outline or detecting
a patient may be provided.
[0066] The segments 30 of the collimator 28 define different
focused fields-of-view (FOVs) 72 as shown in FIG. 6. It should be
noted that one or more of the segments 30 may have an overlapping
portion 74 of the FOVs 72, such as adjacent segments 30. The
detector 22 (shown in FIG. 1) is positioned to focus the FOVs 72 on
an ROI. Thus, the bores 50 in different ones of the fixed segments
30 may be pointed differently such that each set of bores 50
corresponding to different segments 30 are focused onto the ROI
from different pointing directions. It should be noted that at
least two sets of the different segments 30 (e.g., segments 30a and
30e, and 30b and 30d) may be tilted the same amount.
[0067] The detector 22 with collimator 28 may be provided in
different configurations. For example, FIG. 7 is a diagram
illustrating a cross-sectional view in the transverse plane (also
referred to as the horizontal plane, axial plane or transaxial
plane, which is perpendicular to the coronal and sagittal planes)
of a symmetric multi-section collimator 28 formed in accordance
with various embodiments that may be used for cardiac imaging. The
detector 22 rotates about a detector rotation axis 51.
[0068] In one embodiment, the detector 22 is a general purpose
gamma camera having dimensions of, for example, 50 cm by 40 cm
(trans-axial and axial dimensions respective to the axis of gantry
rotation). In contrast, the human heart 38 is much smaller (less
than 20.times.20.times.20 cm). Thus, most of the detector 22 is not
viewing the heart and is "wasted". Using the segments 30, a greater
area of the detector 22 is viewing the heart 38 (or other organ of
interest), thus contributing to the useful image data, increasing
image quality, reducing imaging time, and/or enabling reduction of
injected isotope dose (thereby reducing patient radiation exposure
and mutagenic risk to the patient and operator).
[0069] FIG. 8 is a diagram illustrating a coronal plane
cross-section of the symmetric multi-section collimator 28 (taken
along the line A-A in FIG. 7) that may be used for cardiac imaging
in accordance with various embodiments. The detector 22 rotates
about the patient 26 along the radius R and about the detector
rotation axis 51.
[0070] FIG. 9 is a diagram illustrating of a transverse plane
cross-section of an asymmetric multi-section collimator 28 that may
be used for brain imaging in accordance with various embodiments.
In brain imaging, the patient's shoulders require asymmetric
placement of the detector(s) 22 in order to achieve close proximity
of the face of the collimator 28 to the imaged organ (as resolution
degrades with distance). The asymmetric collimator construction
illustrated may provide, for example, for efficient utilization of
the detector surface. In one embodiment, as illustrated, collimator
segments 30 that are further from the brain optionally may be made
with longer bores 50 (which may vary in length) to maintain a
similar resolution even with the larger detector-patient
distance.
[0071] FIG. 10 is a diagram illustrating a coronal plane
cross-section of the asymmetric multi-section collimator 28 (taken
along the line A-A in FIG. 9) that may be used for brain imaging in
accordance with various embodiments. The detector 22 rotates about
the patient 26 along the radius R and about the detector rotation
axis 51
[0072] Additionally, the detector 22 may be moved or tilted to
focus on the ROI. For example, as shown in FIG. 11, the entire
detector 22 may be tilted at an angle. The detector 22 is tilted,
for example, relative to an axis of rotation such that a different
portion of the ROI (e.g., a head of the patient 26) may be imaged
and not just the center of rotation. The detector 22 may be tilted
using any suitable drive mechanism. The detector 22 also may rotate
around a gantry (not shown) and about the ROI.
[0073] The tilting shown in FIG. 11 puts the "focus" of the
collimator 28 on the brain and allows the collimator surface to be
positioned close to the head, which would not be possible due to
the collision of the collimator 28 with the shoulders of the
patient. In one embodiment, in order to avoid collision with the
shoulders, the detector 22 rotates at a much greater radius around
the head. In this embodiment, a collimator 28 with longer "focal
length" is used (in this case, the "focal length" is approximately
equal to the radius of rotation). It should be noted that
resolution degrades with distance as the sensitivity of a fan beam
reduces with the "numerical aperture" of the collimator (defined as
the width of the collimator divide by its focal length). Thus, with
the tilting, a wide collimator 28 with strongly angulated segments
30 that are pointed at the brain, to a short distance from the
brain, without colliding with the shoulders of the patient, is
provided.
[0074] It should be noted the one movement is not exclusive of
other movements. Accordingly, one or more of the movements
described herein may be performed simultaneously, concurrently,
consecutively, or otherwise, such as rotation about the patient 26
and tilting of the detector 22.
[0075] It should be noted that although an odd number of segments
30 are illustrated, namely five, a different number, such as an
even number of segments 30 may form the collimator 28. Thus
although, five segments 30a-e may be provided as shown in FIG. 6,
with the center segment 30c having no slant (with perpendicular
bores 50), and the outer segments 30a, 30b, 30d and 30e have bores
50 that are pointed as described herein, the center segment 30c may
be removed resulting in a collimator 28 formed from four segments
30. For example, in one embodiment, an asymmetric collimator as
described herein may be provided in which an untilted segment 30
(being perpendicular to a face of the collimator 28) is not the
central segment 30 of the collimator 28, which may be used, for
example, in cardiac imaging. The collimator 28 may have bores 50
with segments 30 having pointing directions defined by the
following angles (in degrees): -10, 0, +10, +20.
[0076] In operation, prior to acquiring or during acquisition of an
image of a structure of interest, the detector(s) 22 may be
adjusted, such as the orientation, positioning and/or placement of
the detector 22 relative to a structure or object of interest.
Additionally, a patient table or gantry also may be moved. With the
collimator 28 with fixed segments 30, the patient table may be
moved during acquisition such that an object of interest is
adequately or sufficiently imaged. Image data is then acquired by
each the detector(s) 22, which may be combined and reconstructed
into a composite image that may comprise two-dimensional (2D)
images, a three-dimensional (3D) volume or a 3D volume over time
(4D).
[0077] Thus, the detector(s) 22 may be moved to also adjust the
effective field of view for one or more of the detectors 22, such
that the FOV is reoriented or decreased/increased, such as by
pivoting one or more of the detectors 22 and or translating one or
more of the detectors 22. It should be noted that in some
embodiments cone beam collimation may be provided with the acquired
data reconstructed using a suitable iterative reconstruction
technique.
[0078] In some embodiments, fanbeam type operation, which may be
used for approximate fanbeam rebinning may be provided. For
example, in one embodiment, the angular increments of the fanbeam
are equal to the rotation steps S.sub.1, S.sub.2, S.sub.3 . . .
S.sub.N (or multiples or fractions thereof) of a gantry as shown in
FIG. 12. In this embodiment, with the angular increments of the
fanbeam equal to the rotation steps of the gantry (namely
rotational movements of the gantry), subsequent segments 30 of the
collimator 28 are parallel in subsequent views and are rebinned
into single parallel projections (which simplifies the
reconstruction algorithm). For example, a plurality of bins may be
provided wherein each of the bins represents a different location
along the gantry and is used to reconstruct an image based on the
different views. The data in the bins are time stamped to allow for
rebinning into the single parallel projections used to reconstruct
an image.
[0079] It should be noted that in various embodiments a difference
between pointing directions of the various segments 30 may be the
same as a gantry rotation step, an integer multiple thereof or a
sub-multiple thereof. For example, in various embodiments, for
.alpha. angle increments and .beta. rotation steps,
M.alpha.=N.beta. for some integer values of M and N.
[0080] Thus, in one embodiment, the detectors 22 with the
collimators 28 are rotated about a center of rotation (as defined
by the detector rotation axis 51) such that the step size is
defined so that the segments 30 of the collimator 28 end up
pointing in the same direction in successive views (or after an
integer number of steps). For example, as illustrated in FIG. 12, a
first step is illustrated by the detector 22 in position 1 with
views 61 then the detector 22 is moved to position 2 providing
detector views 63.
[0081] Thus in operation, a segmented collimator 28 may produce
three differently oriented projections at orientations .phi.1;
.phi.2; .phi.3 at the same time. When the detector is rotated, for
example by an angle .alpha., three more projections are produced:
.phi.1+.alpha.; .phi.2+.alpha.; .phi.3+.alpha.. After another
rotation by angle .alpha., three more projections are produced:
.phi.1+2.alpha.; .phi.2+2.alpha.; .phi.3+2.alpha., etc. Optionally,
some of the orientations may be the same (for example if
.phi.1=n*.alpha.; where n is a non-zero integer), these projections
may be grouped and combined. The combining may be performed, for
example, by summing or performing weighted summation of the
acquired data.
[0082] It should be noted that this is the case for the tangential
angulations of the segments 30. In a collimator 28 where the
segments 30 are axially angulated, the rotation of the gantry does
not produce overlapping of the segments 30 having different
pointing directions (e.g., axially angled). In this case, the data
set is composed of projections characterized by d(X,Y,.phi.,
.gamma.) wherein .gamma. is the axial angulations. For example in
the embodiment of FIG. 7, .gamma. can be .gamma.1; .gamma.2=0; and
.gamma.3=-.gamma.1. Assuming that the angulations of the segments
30 seen in FIG. 8 are .phi.1=30O; .phi.2=0.degree.; and
.phi.=-30.degree., and the gantry rotation step is
.alpha.=3.degree., the following results:
[0083] 1. Only one of the data of the axially central sections can
be combined (.gamma.2=0);
[0084] 2. after 10 rotation steps (10.alpha.=30.degree.) section
three assumes the orientation of 10.alpha.+.phi.3=0.degree. to have
the same initial orientation of the central section, (.gamma.=0;
.theta.=0)
[0085] In various embodiments, as shown in FIGS. 13 and 14, a
sinogram 140 or 150, respectively, is formed that represents
responses from the one or more detectors 22, such as radionuclide
emissions from the patient 26, wherein .theta. corresponds to a
gantry angle and .gamma. corresponds to emission data. Thus, the
sinogram 140 is binned (or sorted) data measured by the detectors
22. FIGS. 13 and 14 illustrate different embodiments of sampling
schemes. Using the sinogram 140 or 150, the emission data is then
rebinned into parallel projections represented by the aligned data
142 or 152. Accordingly, the acquired data line up over time, which
can simplify image reconstruction. It should be noted that the
sorted data may generally represent a plurality of projections.
[0086] In particular, in the sinogram 140, the gantry motion step
is equal to the alignment step of the segments 30 (namely the
change in pointing direction). In the sinogram 150 the gantry
motion step is half of the alignment step of the segments 30. Thus,
while in the sinogram 140, after each gantry step the pointing
direction for a segment 30 is the same as the pointing direction of
the previous segment 30 in the previous gantry step, in the
sinogram 150, the same pointing direction occurs after two steps of
the gantry. Thus, a staircase type of collimation is provided
wherein each segment 30 "jumps" in pointing direction, which in
various embodiments is based on or relative to the gantry steps. It
should be noted that each segment 30 may not encompass or "see" the
entire FOV (e.g., the organ of interest), such as when the segments
30 are pointed beyond the FOV. After rebinning the data, each
projection view will encompass a larger FOV than is seen by an
individual segment. In this manner the segmented collimator has a
FOV larger than the size of the segments. It should be noted that
in some embodiments that use iterative reconstruction, the process
of rebinning may not be performed. For example, rebinning in some
embodiments is used for rearranging data in a structure fit for a
FBP or other direct algorithm.
[0087] The detectors 22 with collimators 28 of the various
embodiments may be provided as part of different types of imaging
systems, for example, NM imaging systems such as SPECT imaging
systems having different detector configurations. For example, FIG.
15 is a perspective view of an exemplary embodiment of a medical
imaging system 200 constructed in accordance with various
embodiments, which in this embodiment is a SPECT imaging system.
The system 210 includes an integrated garitry 212 that further
includes a rotor 214 oriented about a gantry central bore 232. The
rotor 214 is configured to support one or more NM cameras 218 (two
cameras 218 are shown). The NM cameras 218 may be provided similar
to the detectors 22 with the collimators 28. It should be noted
that the detectors, for example, the detectors 22 or NM cameras 218
are generally equipped with interchangeable collimators. For
example, the detector 22 or NM camera 218 is supplied with a
plurality of collimators (or collimator pairs for dual head
cameras) wherein each collimator type is used for one type or a few
different types of medical imaging procedures. According to some
embodiments, fixed-segment collimators are supplied with the
detector 22 or NM camera 218 to be used for one or more different
imaging applications. The fixed-segment collimators may have
segments 30 with different parallel hole pointing directions as
described herein, such as based on the type of imaging scan to be
performed. In some embodiments, the fixed-segment collimator or
collimators are used for applications where more expensive fan-beam
or cone beam collimators can be used. In operation, in some
embodiments, one of the collimators may be a standard collimator,
such as a parallel hole collimator.
[0088] In various embodiments, the cameras 218 may be formed from
pixelated detectors or a continuous detector material (e.g., NaI;Tl
scintillator). The rotors 214 are further configured to rotate
axially about an examination axis 219.
[0089] A patient table 220 may include a bed 222 slidingly coupled
to a bed support system 224, which may be coupled directly to a
floor or may be coupled to the gantry 212 through a base 226
coupled to the gantry 212. The bed 222 may include a stretcher 228
slidingly coupled to an upper surface 230 of the bed 222. The
patient table 220 is configured to facilitate ingress and egress of
a patient (not shown) into an examination position that is
substantially aligned with examination axis 219. During an imaging
scan, the patient table 220 may be controlled to move the bed 222
and/or stretcher 228 axially into and out of a bore 232. The
operation and control of the imaging system 200 may be performed in
any suitable manner. It should be noted that the various
embodiments may be implemented in connection with imaging systems
that include rotating detectors (where a gantry having a stator and
a rotor coupled the detectors includes rotation of the stator) or
stationary detectors.
[0090] Thus, various embodiments provide fanbeam type collimation
of detectors using collimators with slanted parallel hole
collimator segments.
[0091] Additionally, various embodiments provide a method 250 as
illustrated in FIG. 16 for manufacturing a collimator for use in
collimating a detector of an imaging system, such as an NM imaging
system as described in more detail above. The method 250 includes
coupling at 252 a plurality, of tubes (with a channel or bore
therethrough) together to form a stack for a parallel hole
collimator segment. For example, a plurality of tubes formed from
collimator suitable material, for example, lead in an NM
application, are joined together using a suitable adhesive to form
a parallel hole section. Thereafter, the formed stack is cut at one
or more pointing directions at 254 as described herein. For
example, the stack is cut along one or more non-perpendicular lines
relative to the length of the stack. However, it should be noted
that in one embodiment, at least one cut is along a line
perpendicular to the length of the stack. It also should be noted
that the pointing direction for all of the cuts for a single stack
may be the same or some may be different.
[0092] The cut tubes that form slanted segments are coupled
together to form a fanbeam type collimator at 256, such as by
joining the segments together with a suitable adhesive. In
particular, the slanted segments used to form the collimator
include at least two segments having bores slanted at different
pointing directions. It should be noted that one of the segments
may have non-slanted bores, which may be referred to as bores
having a ninety degree or perpendicular slant relative to a front
face of the collimator 28. The coupled slanted segments form a
fanbeam type collimator wherein different segments provide
different collimator focusing. It should be noted that a shield
member may be provided in a gap between the joined segments. For
example, a filling material may be added between the joined
segments to fill in gaps (or partial gaps) between the
segments.
[0093] Thereafter, the collimator is coupled to an imaging detector
of an imaging system at 258. For example, the collimator may be
mounted to a front surface of one or more SPECT gamma cameras. With
the collimator coupled to the imaging detector, a controller may be
used to move the collimated detector to image a particular FOV. The
movement may include a defined scan pattern based on prior
information such that an optimized scan of a particular organ is
performed.
[0094] The various embodiments and/or components, for example, the
modules, or components and controllers therein, also may be
implemented as part of one or more computers or processors. The
computer or processor may include a computing device, an input
device, a display unit and an interface, for example, for accessing
the Internet. The computer or processor may include a
microprocessor. The microprocessor may be connected to a
communication bus. The computer or processor may also include a
memory. The memory may include Random Access Memory (RAM) and Read
Only Memory (ROM). The computer or processor further may include a
storage device, which may be a hard disk drive or a removable
storage drive such as an optical disk drive, solid state disk drive
(e.g., flash RAM), and the like. The storage device may also be
other similar means for loading computer programs or other
instructions into the computer or processor.
[0095] As used herein, the term "computer" or "module" may include
any processor-based or microprocessor-based system including
systems using microcontrollers, reduced instruction set computers
(RISC), application specific integrated circuits (ASICs), logic
circuits, and any other circuit or processor capable of executing
the functions described herein. The above examples are exemplary
only, and are thus not intended to limit in any way the definition
and/or meaning of the term "computer".
[0096] The computer or processor executes a set of instructions
that are stored in one or more storage elements, in order to
process input data. The storage elements may also store data or
other information as desired or needed. The storage element may be
in the form of an information source or a physical memory element
within a processing machine.
[0097] The set of instructions may include various commands that
instruct the computer or processor as a processing machine to
perform specific operations such as the methods and processes of
the various embodiments of the invention. The set of instructions
may be in the form of a software program, which may form part, of a
tangible non-transitory computer readable medium or media. The
software may be in various forms such as system software or
application software. Further, the software may be in the form of a
collection of separate programs or modules, a program module within
a larger program or a portion of a program module. The software
also may include modular programming in the form of object-oriented
programming. The processing of input data by the processing machine
may be in response to operator commands, or in response to results
of previous processing, or in response to a request made by another
processing machine.
[0098] As used herein, the terms "software" and "firmware" are
interchangeable, and include any computer program stored in memory
for execution by a computer, including RAM memory, ROM memory,
EPROM memory, EEPROM memory, and non-volatile RAM (NVRAM) memory.
The above memory types are exemplary only, and are thus not
limiting as to the types of memory usable for storage of a computer
program.
[0099] It is to be understood that the above description is
intended to be illustrative, and not restrictive. For example, the
above-described embodiments (and/or aspects thereof) may be used in
combination with each other. In addition, many modifications may be
made to adapt a particular situation or material to the teachings
of the various embodiments of the invention without departing from
their scope. While the dimensions and types of materials described
herein are intended to define the parameters of the various
embodiments of the invention, the, embodiments are by no means
limiting and are exemplary embodiments. Many other embodiments will
be apparent to those of skill in the art upon reviewing the above
description. The scope of the various embodiments of the invention
should, therefore, be determined with reference to the appended
claims, along with the full scope of equivalents to which such
claims are entitled. In the appended claims, the terms "including"
and "in which" are used as the plain-English equivalents of the
respective terms "comprising" and "wherein." Moreover, in the
following claims, the terms "first," "second," and "third," etc.
are used merely as labels, and are not intended to impose numerical
requirements on their objects. Further, the limitations of the
following claims are not written in means-plus-function format and
are not intended to be interpreted based on 35 U.S.C..sctn.112,
sixth paragraph, unless and until such claim limitations expressly
use the phrase "means for" followed by a statement of function void
of further structure.
[0100] This written description uses examples to disclose the
various embodiments of the invention, including the best mode, and
also to enable any person skilled in the art to practice the
various embodiments of the invention, including making and using
any devices or systems and performing any incorporated methods. The
patentable scope of the various embodiments of the invention is
defined by the claims, and may include other examples that occur to
those skilled in the art. Such other examples are intended to be
within the scope of the claims if the examples have structural
elements that do not differ from the literal language of the
claims, or if the examples include equivalent structural elements
with insubstantial differences from the literal languages of the
claims.
* * * * *