U.S. patent application number 14/433065 was filed with the patent office on 2015-09-10 for extremity imaging apparatus for cone beam computed tomography.
The applicant listed for this patent is Carestream Health, Inc.. Invention is credited to Nathan J. Packard, Jeffrey H. Siewerdsen, John Yorkston.
Application Number | 20150250431 14/433065 |
Document ID | / |
Family ID | 49354989 |
Filed Date | 2015-09-10 |
United States Patent
Application |
20150250431 |
Kind Code |
A1 |
Yorkston; John ; et
al. |
September 10, 2015 |
EXTREMITY IMAGING APPARATUS FOR CONE BEAM COMPUTED TOMOGRAPHY
Abstract
An apparatus for cone beam computed tomography can include a
support structure, a scanner assembly coupled to the support
structure for controlled movement in at least x, y and z
orientations, the scanner assembly can include a DR detector
configured to move along at least a portion of detector path that
extends at least partially around a scan volume with a distance D1
that is sufficiently long to allow the scan volume to be positioned
within the detector path; a radiation source configured to move
along at least a portion of a source path outside the detector
path, the source path having a distance D2 greater than the
distance D1, the distance D2 being sufficiently long to allow
adequate radiation exposure of the scan volume for an image
Inventors: |
Yorkston; John; (Penfield,
NY) ; Siewerdsen; Jeffrey H.; (Baltimore, MD)
; Packard; Nathan J.; (Rochester, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Carestream Health, Inc. |
Rochester |
NY |
US |
|
|
Family ID: |
49354989 |
Appl. No.: |
14/433065 |
Filed: |
October 7, 2013 |
PCT Filed: |
October 7, 2013 |
PCT NO: |
PCT/US2013/063670 |
371 Date: |
April 2, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61710832 |
Oct 8, 2012 |
|
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|
Current U.S.
Class: |
378/12 |
Current CPC
Class: |
A61B 6/4233 20130101;
A61B 6/035 20130101; A61B 6/025 20130101; A61B 6/4085 20130101;
A61B 6/50 20130101; A61B 6/4452 20130101; F04C 2270/041 20130101;
A61B 6/4429 20130101; A61B 6/461 20130101; A61B 6/4405 20130101;
A61B 6/0492 20130101; A61B 6/527 20130101; A61B 6/541 20130101;
A61B 6/032 20130101; A61B 6/548 20130101; A61B 6/4441 20130101;
A61B 6/467 20130101; A61B 6/04 20130101; A61B 6/4447 20130101; A61B
6/4482 20130101 |
International
Class: |
A61B 6/03 20060101
A61B006/03 |
Claims
1. An apparatus for cone beam computed tomography, the apparatus
comprising: a support structure; a scanner assembly coupled to the
support structure, comprising: a digital radiation detector, the
detector configured to move along at least a portion of a detector
path, the at least a portion of the detector path extending so that
the detector is configured to move at least partially around a scan
volume, the detector path having a distance D1 that is sufficiently
long to allow the scan volume to be positioned within the detector
path; a radiation source, the source configured to move along at
least a portion of a source path outside the detector path, the
source path having a distance D2 greater than the distance D1, the
distance D2 being sufficiently long to allow adequate radiation
exposure of the scan volume for an image capture by the detector; a
gap in the detector path and the source path to provide radial
access to the scan volume; and a control panel coupled to the
support structure to provide an operator interface for entering
instructions for operation of the apparatus; where a first mode of
the imaging apparatus is configured to perform CBCT imaging of the
scan volume and a second mode of the imaging apparatus is
configured to perform tomography imaging of the scan volume.
2. The apparatus according to claim 1, where in the second
tomography imaging mode an extremity is longitudinally oriented in
the scan volume and gap or the extremity is radially oriented in
the scan volume and the gap.
3. The apparatus according to claim 1, wherein the radiation source
has a radiation source actuator that is operable independently and
separate from a detector actuator to reduce weight.
4. The apparatus according to claim 1, where in the second
tomography imaging mode the source and the detector travel at least
a corresponding 30 degree path.
5. The apparatus according to claim 1, where the scanner assembly
comprises a retractable door to cover a detector path gap, where in
the second tomography imaging mode the door is retracted or where
the scanner assembly comprises a removable door to cover a detector
path gap, where in the second tomography imaging mode the door is
removed from the scanner assembly.
6. The apparatus according to claim 1, where in the second
tomography imaging mode a subset of the CBCT projections are
exposed to generate a topographic imaging data set to reduce metal
artifacts.
7. The apparatus according to claim 1, further comprising: a first
device configured to move the scanner assembly along a vertical
direction of the support column; a second device configured to
revolve the scanner assembly to a vertical or other angular
orientation; and a third device configured to orient the scanner
assembly by revolving the scanner assembly about a different axis
that the second device.
8. The apparatus according to claim 1, wherein radiation absorbent
shielding is added to at least portions of surfaces of the housing
or a door for absorbing radiation during exposure, wherein the
detector is coupled to a radiation-absorbent backing plate.
9. The apparatus according to claim 1, wherein the detector is
coupled to a radiation-absorbent backing plate, where the weight of
the radiation-absorbent backing plate is configured to position a
center of mass for the gantry is on the beta axis.
10. An imaging apparatus for cone beam computed tomography imaging
of an extremity, the apparatus comprising a scanner that scans a
scan volume about a .beta. axis, the scanner comprising: a) a
housing that defines an opening for patient extremity access to the
scan volume; b) a detector for acquiring image data from the scan
volume according to received radiation, wherein the detector has a
detector actuator and is translatable to orbit the scan volume
along a detector path that lies at a first radius R1 about the
.beta. axis; c) a radiation source that is energizable to direct
radiation through the scan volume and toward the detector, wherein
the radiation source has a radiation source actuator that is
operable independently of the detector actuator and wherein the
radiation source is moveable to orbit the scan volume at a second
radius R2 about the .beta. axis.
11. The imaging apparatus of claim 1, where the independent
operation of the radiation source actuator and the detector
actuator operate to position the source and the detector in a first
relative position before imaging and in a second relative position
during imaging.
12. An apparatus for cone beam computed tomographic imaging of one
extremity, the apparatus comprising: a digital radiation detector;
a detector mechanism attached to the detector and configured to
move the detector along a detector path, a shape of the detector
path comprising a first circular arc, the detector path defining a
detector axis whereat at least a portion of the one extremity is
positioned to be imaged by the apparatus; a radiation source; and a
source mechanism separate from the detector mechanism, the source
mechanism attached to the source and configured to move the source
along a source path, the source mechanism controllable to move the
source independent of the detector movement, a shape of the source
path comprising a second circular arc, the source path defining a
source plane and a source axis, the source axis coaxial with the
detector axis, wherein a distance from the detector path to the
detector axis is shorter than a distance from the source path to
the source axis.
13. The apparatus of claim 12, wherein the source mechanism and the
detector mechanism are configured to position the source and
detector, respectively, in a first relative position before
imaging, and in a second relative position while performing
imaging.
14. The apparatus of claim 13, wherein the apparatus is configured
to position the extremity at the detector axis while the source and
detector are disposed in the first relative position.
15. The apparatus of claim 14, wherein the apparatus is configured
to image the extremity at the detector axis while the source and
detector are disposed in the second relative position.
16. The apparatus of claim 13, wherein the source and detector are
diametrically opposite the detector axis in the second relative
position.
17. The apparatus of claim 12, wherein the source mechanism
includes a rigid C-shaped assembly to provide mechanical support
for the source as the source is moved along the source path.
18. The apparatus of claim 17, wherein the detector mechanism
includes the rigid C-shaped assembly to provide mechanical support
for the detector as the detector is moved along the detector
path.
19. The apparatus of claim 18, wherein the source mechanism further
includes a source support arm, a proximate end of the source
support arm attached to the C-shaped assembly and a distal end of
the source support arm attached to the source to provide mechanical
support for the source as the source is moved along the source
path.
20. The apparatus of claim 12, further comprising a C-shaped
housing to enclose the source and the source mechanism as the
source moves along the source path and to enclose the detector and
the detector mechanism as the detector moves along a portion of the
detector path.
Description
FIELD OF THE INVENTION
[0001] The invention relates generally to diagnostic imaging and in
particular to cone beam imaging systems used for obtaining volume
images of extremities.
BACKGROUND OF THE INVENTION
[0002] 3-D volume imaging has proved to be a valuable diagnostic
tool that offers significant advantages over earlier 2-D
radiographic imaging techniques for evaluating the condition of
internal structures and organs. 3-D imaging of a patient or other
subject has been made possible by a number of advancements,
including the development of high-speed imaging detectors, such as
digital radiography (DR) detectors that enable multiple images to
be taken in rapid succession.
[0003] Cone beam computed tomography (CBCT) or cone beam CT
technology offers considerable promise as one type of diagnostic
tool for providing 3-D volume images. Cone beam CT systems capture
volumetric data sets by using a high frame rate digital radiography
(DR) detector and an x-ray source, typically affixed to a gantry
that rotates about the object to be imaged, directing, from various
points along its orbit around the subject, a divergent cone beam of
x-rays toward the subject. The CBCT system captures projections
throughout the rotation, for example, one 2-D projection image at
every degree of rotation. The projections are then reconstructed
into a 3D volume image using various techniques. Among well known
methods for reconstructing the 3-D volume image from the 2-D image
data are filtered back projection approaches.
[0004] Although 3-D images of diagnostic quality can be generated
using CBCT systems and technology, a number of technical challenges
remain. In some cases, for example, there can be a limited range of
angular rotation of the x-ray source and detector with respect to
the subject. CBCT Imaging of legs, arms, and other extremities can
be hampered by physical obstruction from a paired extremity. This
is an obstacle that is encountered in obtaining CBCT image
projections for the human leg or knee, for example. Not all imaging
positions around the knee are accessible; the patient's own anatomy
often prevents the radiation source and image detector from being
positioned over a portion of the scan circumference.
[0005] To illustrate the problem faced in CBCT imaging of the knee,
the top view of FIG. 1 shows the circular scan paths for a
radiation source 22 and detector 24 when imaging the right knee R
of a patient as a subject 20. Various positions of radiation source
22 and detector 24 are shown in dashed line form. Source 22, placed
at some distance from the knee, can be positioned at different
points over an arc of about 200 degrees; with any larger arc the
paired extremity, left knee L, blocks the way. Detector 24, smaller
than source 22 and typically placed very near subject 20, can be
positioned between the patient's right and left knees and is thus
capable of positioning over the full circular orbit.
[0006] A full 360 degree orbit of the source and detector is not
needed for conventional CBCT imaging; instead, sufficient
information for image reconstruction can be obtained with an
orbital scan range that just exceeds 180 degrees by the angle of
the cone beam itself, for example. However, in some cases it can be
difficult to obtain much more than about 180 degree revolution for
imaging the knee or other joints and other applications. Moreover,
there can be diagnostic situations in which obtaining projection
images over a certain range of angles has advantages, but patient
anatomy blocks the source, detector, or both from imaging over that
range. Some of the proposed solutions for obtaining images of
extremities under these conditions require the patient to assume a
position that is awkward or uncomfortable. The position of the
extremity, as imaged, is not representative of how the limb or
other extremity serves the patient in movement or under
weight-bearing conditions. It can be helpful, for example, to
examine the condition of a knee or ankle joint under the normal
weight load exerted on that joint by the patient as well as in a
relaxed position. But, if the patient is required to assume a
position that is not usually encountered in typical movement or
posture, there may be excessive strain, or insufficient strain, or
poorly directed strain or tension, on the joint. The knee or ankle
joint, under some artificially applied load and at an angle not
taken when standing, may not behave exactly as it does when bearing
the patient's weight in a standing position. Images of extremities
under these conditions may fail to accurately represent how an
extremity or joint is used and may not provide sufficient
information for assessment and treatment planning.
[0007] Still other difficulties with conventional solutions for
extremity imaging relate to poor image quality. For image quality,
the CBCT sequence requires that the detector be positioned close to
the subject and that the source of the cone beam radiation be at a
sufficient distance from the subject. This provides the best image
and reduces image truncation and consequent lost data. Positioning
the subject midway between the detector and the source, as some
conventional systems have done, not only noticeably compromises
image quality, but also places the patient too near the radiation
source, so that radiation levels are considerably higher.
[0008] CBCT imaging represents a number of challenges that also
affect other types of volume imaging that employ a radiation source
and detector orbiting an extremity over a range of angles. There
are various tomographic imaging modes that can be used to obtain
depth information for a scanned extremity.
[0009] In summary, for extremity imaging, particularly for imaging
the lower paired extremities, a number of improvements are needed,
including the following: [0010] (i) improved placement of the
radiation source and detector relative to the imaged subject to
provide acceptable radiation levels and image quality throughout
the scanning sequence, with the capability for at least coarse
automated setup for examining an extremity under favorable
conditions; [0011] (ii) system flexibility for imaging at different
heights with respect to the rotational axis of the source and
detector, including the flexibility to allow imaging with the
patient standing or seated comfortably, such as with a foot in an
elevated position, for example; [0012] (iii) capability to adjust
the angle of the rotational axis to suit patient positioning
requirements; [0013] (iv) improved patient accessibility, so that
the patient does not need to contort, twist, or unduly stress limbs
or joints that may have been injured in order to provide images of
those body parts; [0014] (v) improved ergonomics for obtaining the
CBCT image, allowing the patient to stand or sit with normal
posture, for example. This would also allow load-bearing
extremities, such as legs, knees, and ankles, to be imaged under
the normal load exerted by the patient's weight, rather than under
simulated loading conditions and provide options for supporting the
patient; and [0015] (vi) adaptability for multi-use imaging,
allowing a single imaging apparatus to be configurable for imaging
any of a number of extremities, including knee, ankle, toe, hand,
elbow, and other extremities. This also includes the capability to
operate the imaging system in different imaging modes, including
CBCT, two-dimensional (2-D) projection radiography, fluoroscopy,
and other tomography modes.
[0016] In summary, the capability for straightforward configuration
and positioning of the imaging apparatus allows the advantages of
CBCT imaging to be adaptable for use with a range of extremities,
to obtain volume images under a suitable imaging modality, with the
image extremity presented at a suitable orientation under both
load-bearing and non-load-bearing conditions, and with the patient
appropriately standing or seated.
SUMMARY OF THE INVENTION
[0017] An aspect of this application is to advance the art of
medical digital radiography.
[0018] Another aspect of this application is to address, in whole
or in part, at least the foregoing and other deficiencies in the
related art.
[0019] It is another aspect of this application to provide, in
whole or in part, at least the advantages described herein.
[0020] It is another aspect of this application to advance the art
of diagnostic imaging of extremity body parts, particularly jointed
or load-bearing, paired extremities such as knees, legs, ankles,
fingers, hands, wrists, elbows, arms, and shoulders.
[0021] It is another aspect of this application to provide
apparatus and/or method embodiments that adapt to imaging
conditions suitable for a range of extremities and/or allows the
patient to be in a number of positions for suitable imaging of the
extremity.
[0022] It is another aspect of this application to provide
apparatus and/or method embodiments that provide a radiation source
actuator that is operable independently of a detector actuator
within a scanner housing for a CBCT imaging apparatus.
[0023] It is another aspect of this application to provide
apparatus and/or method embodiments that provide radiation
absorbent shielding to at least portions of surfaces of the housing
or a door for absorbing radiation during exposure for a CBCT
imaging apparatus.
[0024] It is another aspect of this application to provide
apparatus and/or method embodiments that provide a first mode of
the imaging apparatus to perform CBCT imaging of a scan volume and
a second mode of the imaging apparatus to perform tomography
imaging of the scan volume for a CBCT imaging apparatus.
[0025] From one aspect, the present invention provides an apparatus
for cone beam computed tomography that can include a support
structure; a scanner assembly coupled to the support structure that
can include a digital radiation detector, the detector configured
to move along at least a portion of a detector path, the at least a
portion of the detector path extending so that the detector is
configured to move at least partially around a scan volume, the
detector path having a distance D1 that is sufficiently long to
allow the scan volume to be positioned within the detector path; a
radiation source, the source configured to move along at least a
portion of a source path outside the detector path, the source path
having a distance D2 greater than the distance D1, the distance D2
being sufficiently long to allow adequate radiation exposure of the
scan volume for an image capture by the detector; a gap in the
detector path and the source path to provide radial access to the
scan volume; and a control panel coupled to the support structure
to provide an operator interface for entering instructions for
operation of the apparatus. In one embodiment, a first mode of the
imaging apparatus performs CBCT imaging of the scan volume and a
second mode of the imaging apparatus performs tomography imaging of
the scan volume.
[0026] These objects are given only by way of illustrative example,
and such objects may be exemplary of one or more embodiments of the
invention. Other desirable objectives and advantages inherently
achieved by the disclosed invention may occur or become apparent to
those skilled in the art. The invention is defined by the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The foregoing and other objects, features, and advantages of
the invention will be apparent from the following more particular
description of the embodiments of the invention, as illustrated in
the accompanying drawings. The elements of the drawings are not
necessarily to scale relative to each other.
[0028] FIG. 1 is a schematic view showing the geometry and
limitations of CBCT scanning for portions of the lower leg.
[0029] FIG. 2 shows a top and perspective view of the scanning
pattern for an imaging apparatus according to an embodiment of the
application.
[0030] FIG. 3A is a perspective view showing patient access to an
imaging apparatus according to an embodiment of the
application.
[0031] FIG. 3B is a top view showing a sequence of steps for
enclosing the extremity to be imaged within the path of the
detector transport.
[0032] FIG. 4 show portions of the operational sequence for
obtaining CBCT projections of a portion of a patient's leg at a
number of angular positions when using the imaging apparatus
according to an embodiment of the application.
[0033] FIG. 5 is a perspective view that shows a CBCT imaging
apparatus for extremity imaging according to an embodiment of the
application.
[0034] FIG. 6A shows internal components used for imaging ring
translation and positioning.
[0035] FIG. 6B shows reference axes for rotation and
translation.
[0036] FIG. 6C is a schematic diagram that shows components of the
positioning system for the imaging scanner.
[0037] FIG. 6D is a perspective view showing some of the components
of a vertical translation apparatus.
[0038] FIG. 6E shows the CBCT imaging apparatus with covers
installed.
[0039] FIG. 7A shows translation of the imaging ring with respect
to a vertical or z-axis.
[0040] FIG. 7B shows rotation of the imaging ring about an
.alpha.-axis that is orthogonal to the z-axis.
[0041] FIG. 7C shows rotation of the imaging ring about a
.gamma.-axis that is orthogonal to the .alpha.-axis.
[0042] FIG. 7D shows the position of operator controls for
fine-tune position of the imaging scanner.
[0043] FIG. 7E shows an enlarged view of the positioning
controls.
[0044] FIG. 8 is a perspective view that shows the extremity
imaging apparatus configured for knee imaging with a standing
patient.
[0045] FIG. 9 is a perspective view that shows the extremity
imaging apparatus configured for foot or ankle imaging with a
standing patient.
[0046] FIG. 10 is a perspective view that shows the extremity
imaging apparatus configured for knee imaging with a seated
patient.
[0047] FIG. 11 is a perspective view that shows the extremity
imaging apparatus configured for foot or ankle imaging with a
seated patient.
[0048] FIG. 12 is a perspective view that shows the extremity
imaging apparatus configured for toe imaging with a seated
patient.
[0049] FIG. 13 is a perspective view that shows the extremity
imaging apparatus configured for hand imaging with a seated
patient.
[0050] FIG. 14 is a perspective view that shows the extremity
imaging apparatus configured for elbow imaging with a seated
patient.
[0051] FIG. 15A is a top view of the scanner components of an
extremity imaging apparatus according to an embodiment of the
application.
[0052] FIG. 15B is a perspective view of a frame that supports
scanner components of an extremity imaging apparatus according to
an embodiment of the application.
[0053] FIG. 15C is a perspective view of a frame that supports
scanner components of an extremity imaging apparatus with added
counterweight according to an embodiment of the application.
[0054] FIG. 16A is a top view of the imaging scanner showing the
door open position.
[0055] FIG. 16B is a perspective view of the imaging scanner
showing a door closing position.
[0056] FIG. 16C is a top view of the imaging scanner showing the
door closed position.
[0057] FIG. 16D is a perspective view showing the door in closed
position.
[0058] FIG. 17A is a top view of the imaging scanner with a number
of its internal imaging components shown, at one extreme end of the
imaging scan.
[0059] FIG. 17B is a top view of the imaging scanner with a number
of its internal imaging components shown, at the opposite extreme
end of the imaging scan from that shown in FIG. 17A.
[0060] FIG. 17C is a top view of the imaging scanner with its
housing shown.
[0061] FIG. 17D is a top view of the imaging scanner with internal
imaging components and central arc angles shown.
[0062] FIG. 18 shows partial paths of scanner components within the
housing for separate actuation of the source and detector for orbit
about the scan volume.
[0063] FIG. 19 is a top view showing the scanning sequence when
using two separate actuators for detector and radiation source.
[0064] FIG. 20 shows shielding provided for internal components of
the scanner housing.
[0065] FIG. 21 shows shielding provided along the gantry, including
a backing plate behind the detector.
[0066] FIG. 22 is a diagram that shows another exemplary embodiment
for tomosynthesis imaging conducted by a CBCT imaging apparatus
according to embodiments of the application.
[0067] FIG. 23 is a diagram that shows another exemplary embodiment
for tomosynthesis imaging conducted by a CBCT imaging apparatus
according to embodiments of the application.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0068] The following is a description of exemplary embodiments of
the invention, examples of which are illustrated in the
accompanying drawings. Wherever possible, the same reference
numbers will be used throughout the drawings to refer to the same
or like parts.
[0069] For illustrative purposes, principles of the invention are
described herein by referring mainly to exemplary embodiments
thereof. However, one of ordinary skill in the art would readily
recognize that the same principles are equally applicable to, and
can be implemented in, all types of radiographic imaging arrays,
various types of radiographic imaging apparatus and/or methods for
using the same and that any such variations do not depart from the
true spirit and scope of the application. Moreover, in the
following description, references are made to the accompanying
figures, which illustrate specific exemplary embodiments.
Electrical, mechanical, logical and structural changes can be made
to the embodiments without departing from the spirit and scope of
the invention.
[0070] In the context of the application, the term "extremity" has
its meaning as conventionally understood in diagnostic imaging
parlance, referring to knees, legs, ankles, fingers, hands, wrists,
elbows, arms, and shoulders and any other anatomical extremity. The
term "subject" is used to describe the extremity of the patient
that is imaged, such as the "subject leg", for example. The term
"paired extremity" is used in general to refer to any anatomical
extremity wherein normally two or more are present on the same
patient. In the context of the application, the paired extremity is
not imaged unless necessary; only the subject extremity is imaged.
In one embodiment, a paired extremity is not imaged to reduce
patient dose.
[0071] A number of the examples given herein for extemporary
embodiments of the application focus on imaging of the load-bearing
lower extremities of the human anatomy, such as the leg, the knee,
the ankle, and the foot, for example. However, these examples are
considered to be illustrative and non-limiting.
[0072] In the context of the application, the term "arc" or,
alternately, or arcuate has a meaning of a portion of a curve,
spline or non-linear path, for example as being a portion of a
curve of less than 360 degrees or, considered alternately, of less
than 2.pi. radians for a given radius or distance from a central
bore.
[0073] The term "actuable" has its conventional meaning, relating
to a device or component that is capable of effecting an action in
response to a stimulus, such as in response to an electrical
signal, for example.
[0074] As used herein, the term "energizable" relates to a device
or set of components that perform an indicated function upon
receiving power and, optionally, upon receiving an enabling
signal.
[0075] In the context of the application, two elements are
considered to be substantially orthogonal if their angular
orientations differ from each other by 90 degrees, +/- no more than
about 10 degrees.
[0076] It is instructive to observe that the mathematical
definition of a cylinder includes not only the familiar
"can-shaped" right circular cylinder, but also any number of other
shapes. The outer surface of a cylinder is generated by moving a
first straight line element along a closed curve or other path
along a base plane, while maintaining the first straight line
element parallel to a second, fixed straight line that extends out
from the base plane, wherein the moving first straight line
intersects a fixed closed curve or base in the base plane. A cube,
for example, is considered to have a cylindrical shape according to
this definition. A can-shaped cylinder of revolution, for example,
is generated when the moving first straight line intersects a
circle in the base plane at a right angle. An object is considered
to be substantially cylindrical when its overall surface shape is
approximated by a cylinder shape according to this definition, with
allowance for standard edge rounding, protruding or recessed
mechanical and electrical fasteners, and external mounting
features.
[0077] Certain exemplary embodiments according to the application
address the difficulties of extremity imaging by providing an
imaging apparatus that defines coordinated non-linear source and
detector paths (e.g., orbital, curved, concentric about a center
point), wherein components that provide the source and detector
paths are configured to allow patient access prior to and following
imaging and configured to allow the patient to sit or stand with
normal posture during the CBCT image capture series. Certain
exemplary embodiments provide this capability by using a detector
transport device that has a circumferential access opening allowing
positioning of the extremity, wherein the detector transport device
is revolved about the positioned extremity once it is in place,
enclosing (e.g., partially, substantially, fully) the extremity as
it is revolved through at least a portion of the scan.
[0078] It is instructive to consider dimensional attributes of the
human frame that can be considerations for design of CBCT equipment
for scanning extremities. For example, an adult human patient of
average height in a comfortable standing position has left and
right knees generally anywhere from about 10 to about 35 cm apart.
For an adult of average height, exceeding about 35-40 cm (14-15.7
inches) between the knees becomes increasing less comfortable and
out of the range of normal standing posture. It is instructive to
note that this constraint makes it impractical to use conventional
gantry solutions for obtaining the needed 2-D image sequence. For
certain exemplary embodiments, either the source or the detector
must be able to pass between the legs of a standing patient for
knee CBCT imaging, a capability not available with gantry or other
conventional solutions.
[0079] The perspective and corresponding top views of FIG. 2 show
how the scanning pattern is provided for components of CBCT imaging
apparatus 10 according to an embodiment of the application. A
detector path 28 of a suitable radius R1 from a central axis .beta.
provided for a detector device by a detector transport 34. A source
path 26 of a second, larger radius R2 is provided for a radiation
source by a source transport 32. In one embodiment, a non-linear
source path 26 is greater in length than a non-linear detector path
24. According to an embodiment of the application, described in
more detail subsequently, the same transport system provides both
detector transport 34 and source transport 32. The extremity,
subject 20, is preferably substantially centered along central axis
.beta. so that central axis .beta. can be considered as a line
through points in subject 20. In one embodiment, an imaging bore or
the CBCT apparatus can include or encompass the central axis
.beta.. The limiting geometry for image capture is due to the arc
of source transport 32, blocked by gap 38 (e.g., for patient
anatomy, such as by a paired limb), and thus limited typically to
less than about 220 degrees, as noted previously. The
circumferential gap or opening 38 can occupy the space between the
endpoints of the arc of source path 26. Gap or opening 38 gives
space for the patient a place to stand, for example, while one leg
is being imaged.
[0080] Detector path 28 can extend through circumferential gap 38
to allow scanning, since the detector is not necessarily blocked by
patient anatomy but can have a travel path at least partially
around an imaged extremity that can extend between the standing
patient's legs. Embodiments of the present invention allow
temporary restriction of the detector path 28 to allow access for
the patient as part of initial patient positioning. The perspective
view in FIG. 2, for example, shows detector transport 34 rotated to
open up circumferential gap 38 so that it extends from the axis
.beta. (e.g., beyond a source path or housing). With detector
transport 34 translated to the open position shown in FIG. 3A, the
patient can freely move in and out of position for imaging. When
the patient is properly in position, detector transport 34 is
revolved about axis .beta. by more than 180 degrees; according to
an embodiment of the application, detector transport 34 is revolved
about axis .beta. by substantially 200 degrees. This patient access
and subsequent adjustment of detector transport 34 is shown in
successive stages in FIG. 3B. This orbital movement confines the
extremity to be imaged more effectively and places detector 24, not
visible in FIGS. 2-3B due to the detector transport 34 housing, in
position near subject 20 for obtaining the first projection image
in sequence. In one embodiment, a detector transport 34 can include
shielding or a door over part of the detector path, and/or the gap
38.
[0081] Circumferential gap or opening 38 not only allows access for
positioning of the subject leg or other extremity, but also allows
sufficient space for the patient to stand in normal posture during
imaging, placing the subject leg for imaging in the central
position along axis .beta. (FIG. 2) and the non-imaged paired leg
within the space defined by circumferential gap 38. Circumferential
gap or opening 38 extends approximately 180 degrees minus the fan
angle (e.g., between ends of the source path), which is determined
by source-detector geometry and distance. Circumferential gap or
opening 38 permits access of the extremity so that it can be
centered in position along central axis .beta.. Once the patient's
leg or other extremity is in place, detector transport 34, or a
hooded cover or hollow door or other member that defines this
transport path, can be revolved into position, closing the detector
portion of circumferential gap or opening 38.
[0082] By way of example, the top views of FIG. 4 show portions of
the operational sequence for obtaining CBCT projections of a
portion of a patient's leg at a number of angular positions when
using a CBCT imaging apparatus. The relative positions of radiation
source 22 and detector 24, which may be concealed under a hood or
chassis, as noted earlier, are shown in FIG. 4. The source 22 and
detector 24 can be aligned so the radiation source 22 can direct
radiation toward the detector 24 (e.g., diametrically opposite) at
each position during the CBCT scan and projection imaging. The
sequence begins at a begin scan position 50, with radiation source
22 and detector 24 at initial positions to obtain an image at a
first angle. Then, both radiation source 22 and detector 24 revolve
about axis .beta. as represented in interim scan positions 52, 54,
56, and 58. Imaging terminates at an end scan position 60. As this
sequence shows, source 22 and detector 24 are in opposing positions
relative to subject 20 at each imaging angle. Throughout the
scanning cycle, detector 24 is within a short distance D1 of
subject 20. Source 22 is positioned beyond a longer distance D2 of
subject 20. The positioning of source 22 and detector 24 components
on each path can be carried out by separate actuators, one for each
transport path, or by a single rotatable member, as described in
more detail subsequently. It should be noted that scanning motion
in the opposite direction, that is, clockwise with respect to the
example shown in FIG. 4, is also possible, with the corresponding
changes in initial and terminal scan positions.
[0083] Given this basic operation sequence in which the source 22
and detector 24 orbit the extremity, the usefulness of an imaging
system that is adaptable for imaging patient extremities with the
patient sitting or standing and in load-bearing or non load-bearing
postures can be appreciated. The perspective view of FIG. 5 shows a
CBCT imaging apparatus 100 for extremity imaging according to an
embodiment of the application. Imaging apparatus 100 has a
gimballed imaging ring or scanner 110 that houses and conceals
source 22 and detector 24 within a housing 78. FIG. 5 shows their
supporting transport mechanisms. Scanner 110 is adjustable in
height and rotatable in gimbaled fashion about non-parallel axes,
such as about substantially orthogonal axes as described in
subsequent figures, to adapt to various patient postures and
extremity imaging conditions. A support column 120 supports scanner
110 on a yoke, or bifurcated or forked support arm 130, a rigid
supporting element that has adjustable height and further provides
rotation of scanner 110 as described subsequently. Support column
120 can be fixed in position, such as mounted to a floor, wall, or
ceiling. According to portable CBCT embodiments such as shown in
FIGS. 6A and elsewhere, support column 120 mounts to a support base
121 that also includes optional wheels or casters 122 for
transporting and maneuvering imaging apparatus 100 into position. A
control panel 124 can provide an operator interface, such as a
display monitor, for entering instructions for apparatus 100
adjustment and operation. Support column 120 can be of fixed height
or may have telescoping operation, such as for improved visibility
when apparatus 100 is moved.
Vertical and Rotational Movement
[0084] FIG. 6A shows portions of exemplary internal imaging and
positioning mechanisms (with covers removed) for scanner 110 that
allow imaging apparatus 100 the capability for imaging extremities
with a variety of configurations. FIG. 6B shows rotation axes
definitions for scanner 110 positioning. The .alpha.-axis and the
.gamma.-axis are non-parallel, to allow gimbaled action. According
to an embodiment of the applications shown in FIG. 6A, the
.alpha.-axis and the .gamma.-axis are mutually orthogonal. The
.alpha.-axis is substantially orthogonal to the z-axis. The
intersection of the .alpha.-axis and the .gamma.-axis can be offset
from support column 120 by some non-zero distance.
[0085] First considering the z-axis, FIG. 6A shows an exemplary
embodiment to achieve vertical motion. Within support column 120, a
vertical carriage translation element 128 is actuated in order to
travel upwards or downwards along column 120 within a track 112 in
a vertical direction. Carriage translation element 128 has a
support shaft 132 that is coupled to an actuator 136 for providing
.alpha.-axis rotation to forked or C-shaped support arm 130. Forked
support arm 130, shown only partially in FIG. 6A to allow a better
view of underlying components, is coupled to support shaft 132.
X-ray source 22 and receiver 24 are mounted on a rotatable gantry
36 for rotation about a scan or central axis, designated as the
.beta. axis. Axis .beta. is orthogonal to the .alpha.-axis and the
.gamma.-axis.
[0086] It can be appreciated that z-axis translation can be
effected in a number of ways. Challenges that must be addressed by
the type of system that is used include handling the weight of
forked support arm 130 and the imaging scanner 110 that arm 130
supports. This can easily weigh a few hundred pounds. In addition,
precautions must be provided for handling conditions such as power
loss, contact with the patient, or mechanical problems that hamper
positioning movement or operation. According to an embodiment of
the application, as shown schematically in FIG. 6C and in the
perspective view of FIG. 6D, a vertical actuator 129 rotates a
threaded shaft 123. Vertical carriage translation element 128
employs a ball screw mount apparatus 125 to translate rotational
motion to the needed linear (e.g., z-direction) motion, thus urging
vertical carriage translation element 128 upward or allowing
vertical carriage translation element 128 to move downward. Ball
screw translation devices are advantaged for handling high weight
loads and are typically more efficient than other types of
translators using threaded devices. The use of a ball screw
arrangement also allows a small motor to drive the shaft that lifts
scanner 110 into position and can help to eliminate the need for a
complex and bulky counterweight system for allowing control of
vertical movement. An encoder 145, such as a linear encoder
element, can provide feedback signals that are used to indicate the
vertical position of vertical carriage translation element 128.
[0087] Vertical carriage translation element 128 travels inside
track 112 formed in support column 120 (FIG. 6A); wheels 138 help
to guide translation element 128 within the slots. Paired wheels
138 can be orthogonal to each other to provide centering within
column 120.
[0088] A braking system can also be provided for support column
120. Spring-loaded brakes 142 (FIG. 6D) are positioned to actuate
and grip shaft 123 or other mechanical support when mechanical
difficulties, power failure, or other conditions are detected. A
sensor 144, such as a load cell, is configured to sense rapid
movement or interference conditions that are undesirable and to
cause brake 142 actuation.
[0089] Other features of support column 120 for vertical
translation include built-in redundancy, with springs to absorb
weight and impact, the load cell to sense a mechanical problem
including obstruction by the patient, and manually operable brake
mechanisms.
[0090] It should be noted that other types of translation apparatus
could be used for providing vertical movement of vertical carriage
translation element 128. One conventional method for vertical
movement control uses a system of pulleys and counterweights to
provide lifting force, with motorized assistance. Such an
arrangement, however, can be disadvantageous because it can add
considerable weight to the column 120 and supporting structure. In
spite of its weight-related drawbacks, use of a pulley mechanism
can be advantageous for allowing a retractable or telescoping
column 120 arrangement, for example, to simplify transport of
imaging apparatus 100 between rooms.
Gimbaled Arrangement for Scanner
[0091] Forked support arm 130 can support scanner 110 in a gimbaled
arrangement. Source 22 and detector 24 are shown on gantry 36 for
reference in FIG. 6A and covered in the alternate view of FIG. 6E.
Vertical carriage translation element 128 is configured to ride
within a track 112 (FIG. 6A) within support column 120.
[0092] For certain exemplary embodiments, some level of manual
operability can be provided, such as for power loss situations. In
one embodiment, forked support arm 130 can be lifted upwards in
position by one or more persons, for example, raising vertical
carriage translation element 128 even when brakes 142 are set.
Shifting support arm 130 upwards does not release the brakes 142,
but simply sets the brakes 142 to hold element 128 position at new
levels.
[0093] According to an alternate embodiment of the application,
vertical carriage translation element 128 can be a motor that moves
vertically along supporting threaded shaft 132; alternately,
vertical carriage translation element 128 can be driven using a
chain, pulley, or other intermediate mechanism that has
considerable counterweights for manually raising and lowering
vertical carriage translation element 128 and its connected forked
support arm 130 and components within support column 120.
Additional supporting components include a more complex braking
system, such as a pneumatic braking system for providing a force
opposing gravity in order to prevent sudden movement of forked
support arm 130 as a precaution against damage or injury. Vertical
carriage translation element 128 can be automated or may be a
manually operated positioning device that uses one or more springs
or counterweight devices to allow ease of manual movement of forked
support arm 130 into position.
[0094] Next, considering the .alpha.-axis movement of forked
support arm 130, in one embodiment a rotational actuator 136 can be
energizable to allow rotation of shaft 132 (FIG. 6A). This
rotational actuation can be concurrent with z-axis translation as
well as with rotation with respect to the .gamma.-axis.
[0095] Forked support arm 130 allows movement relative to the
.gamma.-axis according to the position and angle of forked support
arm 130. In the example of FIG. 6A, the .gamma.-axis is oriented
vertically, substantially in parallel with the z-axis. FIG. 6E
shows the .gamma.-axis oriented horizontally. A pivoting mount 140
with a rotational actuator 146, provided by forked support arm 130,
allows rotation along the .gamma.-axis. The gimbaled combination of
.alpha.-axis and .gamma.-axis rotation can allow the imaging
apparatus to be set up for imaging in a number of possible
positions, with the patient standing, seated, or prone.
[0096] An exemplary positioning capability of the imaging apparatus
100 is shown n FIGS. 7A-7C. FIG. 7A shows movement of forked
support arm 130 on support column 120 to provide z-axis (vertical)
translation of scanner 110. FIG. 7B shows rotation of forked
support arm 130 about the horizontal .alpha.-axis. FIG. 7C shows
rotation about the .gamma.-axis as defined by the C-arm arrangement
of forked support arm 130.
Sequence and Controls for Positioning Support Arm 130
[0097] According to an embodiment of the present invention, an
initial set of operator commands automatically configure CBCT
imaging apparatus 100 to one of a well-defined set of default
positions for imaging, such as those described subsequently. The
patient waits until this initial setup is completed. Then, the
patient is positioned at CBCT imaging apparatus 100 and any needed
adjustments in height (z--axis) or rotation about the .alpha. or
.gamma. axes can be made by the technician. This type of
fine-tuning adjustment is at slow speeds for increased patient
comfort and because only incremental changes to position are needed
in most cases.
[0098] FIG. 7D and the enlarged view of FIG. 7E show user control
stations 156, 158 that are provided on arm 130 (with scanner 110
removed for improved visibility) for operator adjustment of z-axis
translation and .alpha.-and .gamma.-axis rotation as described in
FIGS. 7A-7C. Both control stations 156 and 158 are essentially the
same, duplicated to allow easier access for the operator for
different extremity imaging arrangements. By way of example, FIG.
7E shows an enlarged view of control station 158. An enablement
switch 159 is pressed to activate a control 160 and an associated
indicator illuminates when control 160 is active or enabled. As a
patient safety feature to protect from inadvertent patient contact
with the controls in some imaging configurations, one or both
control stations 156, 158 are disabled. One or both control
stations 156, 158 can also be disabled following a time-out period
after switch 159 has been pressed. An emergency stop control 162
can stop all motion of the imaging apparatus including downward
motion of support arm 130.
[0099] Still referring to FIG. 7E, control 160 can activate any of
the appropriate actuators for z-axis translation, .alpha.-axis
rotation and/or .gamma.-axis rotation. Exemplary responses of the
system can be based on operator action, as follows: [0100] (i)
z-axis vertical movement is effected by pressing control 160 in a
vertical upward or downward direction. The control logic adjusts
for the angular position of the support arm 130, so that pressing
the control upward provides z-axis movement regardless of support
arm 130 orientation. [0101] (ii) .alpha.-axis rotation is effected
by rotating control 160. Circular motion of control 60 in an either
clockwise (CW) or counterclockwise (CCW) direction causes
corresponding rotation about the .alpha. axis. [0102] (iii)
.gamma.-axis rotation is effected by horizontal left-to-right or
right-to-left movement of control 60. As with z-axis movement,
control logic adjusts for the angular position of the support arm
130, so that left-right or right-left movement is relative to the
operator regardless of support arm 130 orientation.
[0103] It should be noted that CBCT imaging apparatus 100 as shown
in FIG. 6E provides three degrees of freedom (DOF) for scanner 110
positioning. In addition to the z-axis translation and rotation
about .alpha.-and .gamma.-axes previously described, casters 122
allow rotation of scanner 110 position with respect to the z-axis
as well as translation along the floor.
Configurations for Imaging Various Extremities
[0104] Given the basic structure described with reference to FIGS.
6A-7D, the positioning versatility of scanner 110 for various
purposes can be appreciated. Subsequent FIGS. 8--14 show, by way of
example, how this arrangement serves different configurations for
extremity imaging.
[0105] FIG. 8 shows an exemplary scanner 110 positioning for a knee
exam, where subject 20 is a standing patient. An optional patient
support bar 150 can be attached to support column 120. In one
embodiment, support bar 150 is mounted to vertical carriage
translation element 128. Accordingly, as the vertical carriage
translation element 128 moves, a corresponding position of the
support bar 150 can be moved. According to an alternate embodiment
of the application, the support bar 150 can be mounted to the
scanner 110, such as to the cover of scanner 110 or to the forked
support arm 130. In contrast, embodiments of support bar 150 can be
motionless during imaging or during a scan by the scanner 110. For
this embodiment, vertical adjustment along the z-axis sets the knee
of the patient at the center of the scanner 110. Forked support arm
130 is arranged so that the plane that contains both the
.alpha.-axis and the .gamma.-axis is substantially horizontal.
Patient access is through an opening, circumferential gap or
opening 38 in scanner 110. A door 160 is pivoted into place across
gap 38 to enclose an inner portion of circumferential gap or
opening 38. Door 160 fits between the legs of the patient once the
knee of the patient is positioned.
[0106] Certain exemplary embodiments of optional patient support
bar 150 can be mounted to movable portions of the CBCT apparatus
100, preferably to have a prescribed spatial relationship to an
imaging volume. For such embodiments, a presence detector 151 can
be configured to detect when the support bar 150 is mounted to the
CBCT system 100. When detected, a controller or the like, for
example, in the control panel 124, can calculate scanner 110,
and/or forked support arm 130 movements to prevent collisions
therebetween with the affixed support bar 150. Thus, when attached
support bar 150 can limit motion of the scanner 110. Exemplary
presence detectors 151 can include but are not limited to magnetic
detectors, optical detectors, electro-mechanical detectors or the
like. As shown in FIG. 9, a pair of optional or removable support
arms 150 can be affixed to the vertical carriage translation
element 128 and have their attachment reported by a pair of
presence detectors 151.
[0107] For FIG. 8 and selected subsequent embodiments, door 160,
once pivoted into its closed position, can effectively extend the
imaging path by protecting and/or providing the curved detector
transport 34 path as shown in FIG. 4. With this arrangement, when
door 160 is closed to protect the transport path, the knee can be
examined under weight-bearing or non-weight-bearing conditions. By
enclosing the portion of detector transport 34 path that crosses
opening 38, door 160 enables the extremity to be positioned
suitably for 3D imaging and to be maintained in position between
the source and detector as these imaging components orbit the
extremity in the CBCT image capture sequence.
[0108] FIG. 9 shows scanner 110 positioning for a foot or ankle
exam wherein subject 20 is a standing patient. With this
configuration, scanner 110 is lowered to more effectively scan the
area of interest. The plane that contains both the .alpha.-axis and
the .gamma.-axis is approximately 10 degrees offset from
horizontal, rotated about the .gamma. axis. A step 116 is provided
across circumferential gap or opening 38 for patient access.
[0109] FIG. 10 shows scanner 110 positioning for a knee exam with
the patient seated. For this configuration, forked support arm 130
is elevated with respect to the z-axis. Rotation about the
.alpha.-axis orients the .gamma.-axis so that it is vertical or
nearly vertical. Circumferential gap or opening 38 is positioned to
allow easy patient access for imaging the right knee. It should be
noted that 180 degree rotation about the .gamma.-axis would
position circumferential gap or opening 38 on the other side of
scanner 110 and allow imaging of the other (left) knee.
[0110] FIG. 11 shows scanner 110 positioning for a foot or ankle
exam with the patient seated. For this configuration, forked
support arm 130 is elevated with respect to the z-axis. Some slight
rotation about the .alpha.-axis may be useful. Rotation about the
.gamma.-axis orients scanner 110 at a suitable angle for imaging.
Circumferential gap or opening 38 is positioned for comfortable
patient access.
[0111] FIG. 12 shows scanner 110 positioning for a toe exam with
the patient seated. For this configuration, forked support arm 130
is elevated with respect to the z-axis. Rotation about the
.gamma.-axis positions circumferential gap 38 at the top of the
unit for patient access.
[0112] FIG. 13 shows scanner 110 positioning for a hand exam, with
the patient seated. For this configuration, forked support arm 130
is elevated with respect to the z-axis. Rotation about the
.gamma.-axis positions circumferential gap 38 suitably for patient
access. Rotation about the cc-axis may be provided to orient
scanner 110 for patient comfort.
[0113] FIG. 14 shows scanner 110 positioning for an elbow exam,
with the patient seated. For this configuration, forked support arm
130 is again elevated with respect to the z-axis. Rotation about
the .gamma.-axis positions circumferential gap 38 suitably for
patient access. Further rotation about the .alpha.-axis may be
provided for patient comfort.
[0114] In one embodiment of CBCT imaging apparatus 100, the
operator can first enter an instruction at the control console or
control panel 124 that specifies the exam type (e.g., for the
configurations shown in FIGS. 8-14). The system then automatically
adapts the chosen configuration, prior to positioning the patient.
Once the patient is in place, manually controlled adjustments to
z-axis and .alpha.-and .gamma.-axes rotations can be made, as
described previously.
Scanner Configuration and Operation
[0115] As previously described with reference to FIGS. 1-4, scanner
110 is configured to provide suitable travel paths for radiation
source 22 and detector 24 about the extremity that is to be imaged,
such as those shown in FIGS. 8-14. Scanner 110 operation in such
various exemplary configurations can present a number of
requirements that can be at least somewhat in conflict, including
the following: [0116] (i) Imaging over a large range of angles,
preferably over an arc exceeding 180 degrees plus the fan angle of
the radiation source. [0117] (ii) Ease of patient access and
extremity positioning for a wide range of limbs. [0118] (iii)
Capability to allow both weight-bearing and non-weight-bearing
postures that allow imaging with minimized strain on the patient.
[0119] (iii) Enclosure to prevent inadvertent patient contact with
moving parts. [0120] (iv) Fixed registration of source to detector
throughout the scan cycle.
[0121] The top view of FIG. 15A shows a configuration of components
of scanner 110 that orbit subject 20 according to an embodiment of
the application. One or more sources 22 and detector 24 are mounted
in a cantilevered C-shaped gantry 36 that is part of a transport
assembly 170 that can be controllably revolved (e.g., rotatable
over an arc about central axis .beta.). Source 22 and detector 24
are thus fixed relative to each other throughout their movement
cycle. An actuator 172 is mounted to a frame 174 of assembly 170
and provides a moving hinge for gantry pivoting. Actuator 172 is
energizable to move gantry 36 and frame 174 with clockwise (CW) or
counterclockwise (CCW) rotation as needed for the scan sequence.
Housing 184 can reduce or keeps out dust and debris and/or better
protect the operator and patient from contact with moving
parts.
[0122] The perspective view of FIG. 15B shows frame 174 and gantry
36 of transport assembly 170 in added detail. Actuator 172
cooperates with a belt 178 to pivot frame 174 for moving source 22
and detector 24 about axis .beta.. The perspective view of FIG. 15C
shows frame 174 with added counterweights 182 for improved balance
of the cantilevered arrangement.
[0123] Because a portion of the scan arc that is detector path 28
(FIG. 2) passes through the circumferential gap or opening 38 that
allows patient access, this portion of the scan path should be
isolated from the patient. FIGS. 16A, 16B, and 16C show, in
successive positions for closing over gap or opening 38, a slidable
door 176 that is stored in a retracted position within a housing
180 for providing a covering over the detector path 28 once the
patient is in proper position. In one embodiment, door 176 can be
substantially a hollow structure that, when closed, allows passage
of the detector 24 around the patient's extremity. Referring to
FIG. 15B, the portion of frame 174 of gantry 36 that supports
detector 24 can pass through the hollow inner chamber provided by
door 176 during the imaging scan. At the conclusion of the imaging
sequence, frame 174 of gantry 36 rotates back into its home
position and door 176 is retracted to its original position for
patient access or egress within housing 180. In one embodiment, the
door 176 is manually opened and closed by the operator. In one
embodiment, interlocks are provided so that movement of scanning
transport components (rotation of cantilevered frame 174) is only
possible while full closure of the door 176 is sensed.
[0124] FIG. 16B also shows top and bottom surfaces 190 and 192,
respectively, of housing 180. An outer circumferential surface 194
extends between and connects top and bottom surfaces 190 and 192.
An inner circumferential surface 196 is configured to connect the
top and bottom surfaces 190 and 192 to form a central opening 198
extending from the first surface to the second surface, where the
central opening 198 surrounds the .beta.axis.
[0125] As shown with respect to FIGS. 2 and 4, in one embodiment
radiation source 22 and detector 24 each can orbit the subject
along an arc with radii R2 and R1, respectively. According to an
alternate embodiment, within source transport 32, a source actuator
could be used, cooperating with a separate, complementary detector
actuator that is part of detector transport 34. Thus, two
independent actuator devices, one in each transport assembly, can
be separately controlled and coordinated by an external logic
controller to move source 22 and detector 24 along their respective
arcs, in unison, about subject 20.
[0126] In the context of the present disclosure, a surface is
considered to be "substantially" flat if it has a radius of
curvature that exceeds about 10 feet.
[0127] The perspective view of FIG. 10 shows the extremity CBCT
imaging apparatus 100 configured for knee imaging with a seated
patient. From FIG. 10, it can be seen that the patient needs room
outside of the scan volume for comfortable placement of the leg
that is not being imaged. For this purpose, housing 78 is shaped to
provide additional clearance.
[0128] As is readily visible from FIGS. 8-14 and 16A-16D, imaging
scanner 110 has a housing 78. According to one embodiment of the
application, housing 78 is substantially cylindrical; however, a
cylindrical surface shape for housing 78 is not required. By
substantially cylindrical is meant that, to at least a first
approximation, the housing 78 surface shape closely approximates a
cylinder, with some divergence from strict geometric definition of
a cylinder and with a peripherally gap and some additional features
for attachment and component interface that are not in themselves
cylindrical.
[0129] FIGS. 17A-17D show a number of features that are of interest
for an understanding of how scanner 110 is configured and operated
(e.g., scans). FIG. 17A shows how peripheral gap 38 is formed by
housing 78, according to an embodiment of the application. Scan
volume 228, outlined with a dashed line, is defined by the source
and detector paths 26 and 28, as described previously, and
typically includes at least a portion of the .beta. axis. An inner
central volume 230 can be defined by surface S2 of housing 78 and
can typically enclose scan volume 228. Inner central volume 230 can
also be defined by door 176 when closed, as shown in FIG. 17C.
Peripheral gap 38 is contiguous with inner central volume 230 when
door 176 is in open position (e.g., fully or partially opened).
[0130] FIG. 17A shows source transport 32 and detector transport 34
at one extreme end of the scan path, which may be at either the
beginning or the end of the scan. FIG. 17B shows source transport
32 and detector transport 34 at the other extreme end of the scan
path. It should be noted that source 22 is offset along source
transport 32. With this asymmetry, the extent of travel of source
22 relative to surface S3 of housing 78 differs from its extent of
travel relative to surface S4. At the extreme travel position shown
in FIG. 17B, source 22 is more than twice the distance from surface
S4 as source 22 is from surface S3 at the other extreme travel
position shown in FIG. 17A. In one embodiment, the inventors use
this difference to gain additional clearance for patient
positioning with the patient seated.
[0131] FIG. 17C shows the configuration of housing 78. In the
context of the present disclosure, top surface 190 is considered to
be aligned with the top of, at least partially above, or above scan
volume 228; bottom surface 192 is aligned with the bottom of, at
least partially below, or below scan volume 228. In one embodiment,
the top surface 190 or the bottom surface 192 can intersect a
portion of the scan volume 228. As shown in FIG. 17C, scan volume
228 can be cylindrical or circularly cylindrical. However,
exemplary embodiments of the application are intended to be used
with other known 2D scan areas and/or 3D scan volumes. The cover of
housing 78 can be metal, fiberglass, plastic, or other suitable
material. According to an embodiment, at least portions of top and
bottom surfaces 190 and 192 are substantially flat.
[0132] As shown in FIGS. 17A-17C, the scanner 110 has a number of
surfaces that define its shape and the shape of peripheral gap or
opening 38: [0133] (i) an outer connecting surface S1 extends
between a portion of top surface 190 and a portion of bottom
surface 192 to at least partially encompass the source and
detector; at least a portion of the outer connecting surface
extends outside the path the source travels while scanning;
embodiments of the outer connecting surface S1 shown in FIGS.
17A-17C provide an arcuate surface that is generally circular at a
radius R5 about center .beta. and that extends, between edges E1
and E2 of the housing; [0134] (ii) an inner connecting surface S2
extends between a portion of the first surface and a portion of the
second surface to define an inner central volume 230 that includes
a portion of scan volume 228; in the embodiment shown in FIG. 17D,
inner connecting surface S2 is approximately at a radius R4 from
the .beta. axis. At least portions of inner connecting surface S2
can be cylindrical. [0135] (iii) other connecting surfaces can
optionally include a surface S3 that corresponds to a first
endpoint of the travel path for source transport 32 (FIGS. 17A-17B)
and is adjacent to curved surface S1 along an edge E1, wherein
surface S3 extends inward toward curved inner surface S2; and a
surface S4 that corresponds to a second endpoint at the extreme
opposite end of the travel path from the first endpoint for source
transport 32 and is adjacent to curved surface S1 along an edge E2
wherein surface S4 extends inward toward curved inner surface S2.
According to an embodiment, surfaces S3 and S4 are substantially
flat and the angle between surfaces S3 and S4 is greater than about
90 degrees. In general, other additional surface segments (e.g.,
short linear or curved surface segments) may extend between or
comprise any of surfaces S1-S4.
[0136] Inner and outer connecting surfaces S1, S2, and, optionally,
other surfaces, define peripheral gap or opening 38 that is
contiguous with the inner central volume 230 and extends outward to
intersect the outer connecting surface S1 to form gap 38 as an
angular recess extending from beyond or toward where the outer
connecting surface S1 would, if extended, cross the opening 38. As
shown in FIG. 17D ,a central angle of a first arc A1 that is
defined with a center located within the scan volume and between
edges of the peripheral gap 38 determined at a first radial
distance R4 outside the scan volume is less than a central angle of
a second arc A2 that is defined with the first arc center and
between the edges of the peripheral gap 38 at a second radial
distance R3 outside the scan volume, where the second radial
distance R3 is greater than the first radial distance R4. In one
embodiment, as shown in FIG. 17D, a first distance that is defined
between edges of the peripheral gap 38 determined at a first radial
distance R4 outside the scan volume is less than a second distance
between the edges of the peripheral gap 38 at a second radial
distance R3 outside the scan volume, where the second radial
distance R3 is greater than the first radial distance R4. According
to one embodiment, arcs A1 and A2 are centered about the .beta.
axis, as shown in FIG. 17D and edges of gap 38 are defined, in
part, by surfaces S3 and S4 of housing 78.
[0137] The needed room for patient anatomy, such as that described
with reference to FIG. 10, can be provided when the central angle
for arc A2 is large enough to accommodate the extremity that is to
be imaged. According to one embodiment, the central angle for arc
A2 between edges of gap 38 exceeds the central angle for arc A1 by
at least about 5 degrees; more advantageously, the central angle
for arc A2 exceeds the central angle for arc A1 by at least about
10 or 15 degrees.
[0138] The perspective views of FIGS. 8-14 show various
configurations of extremity CBCT imaging apparatus 100 for imaging
limbs of a patient. For each of these configurations, the limb or
other extremity of the patient must be positioned at the center of
scanner 110 and space must be provided for the paired extremity. As
described herein, peripheral gap or opening 38 is provided to allow
access space for the patient and room for other parts of the
patient anatomy. Door 176 is withdrawn into the housing 78 until
the patient is positioned; then, door 176 is pivoted into place in
order to provide a suitable transport path for the imaging
receiver, detector 24, isolated from the patient being imaged.
[0139] FIG. 16A shows scanner 110 with door 176 in open position,
not obstructing opening 38, that is, keeping opening 38 clear,
allowing patient access for extremity placement within opening 38.
FIG. 16C is a top view that shows scanner 110 with door 176 in
closed position, held by a latch 92. Door 176 thus extends into the
opening 38, enclosing a portion of opening 38 for imaging of the
patient's extremity. A sensor 82 provides an interlock signal that
indicates at least whether door 176 is in closed position or in
some other position. Movement of internal scanner 110 components
such as c-shaped gantry 36 is prevented unless the door 176 is
latched shut. A release 90 unlatches door 176 from its latched
position. As shown in FIGS. 16C and 16D, handle 76 can be
positioned outside of opening 38, such as along surface S1 as
shown, for opening or closing door 176. Placement of handle 76, or
other type of door closure device, outside of opening 38 is
advantageous for patient comfort when closing or opening door 176.
As shown in the exemplary embodiment of FIGS. 16C and 16D, handle
76 is operatively coupled with door 176 so that movement of handle
76 in a prescribed direction, such as along the circumference of
scanner 110 housing 78 (e.g., a corresponding direction, or in the
clockwise direction shown), causes door 176 corresponding movement
(e.g., in the same direction). In one embodiment, clockwise
movement of handle 76 causes clockwise movement of door 176,
extends door 176 into the opening, and closes door 176;
counterclockwise movement of handle 76 causes counterclockwise
movement of door 176 and opens door 176, so that it does not
obstruct the opening or moves to a position that is clear of the
opening.
[0140] According to one embodiment, the door 176 is manually
pivoted, closed, and opened by the operator. This allows the
operator to more carefully support the patient and the extremity
that is to be imaged. According to an alternate embodiment, an
actuator is provided to close or open the door automatically.
[0141] FIG. 18 shows partial paths of scanner components within
housing 78 for separate actuation of the source 22 and detector 24
for orbit about the scan volume 228 that is centered about the
.beta. axis. A radiation source actuator 294 translates radiation
source 22 along source path 26. Independent of the radiation source
22 movement, a detector actuator 290 translates detector 24 along
detector path 28. The combined and coordinated movements of
radiation source actuator 294 and detector actuator 290 cooperate
to provide the scan action needed for acquiring the volume image
data from scan volume 228.
[0142] FIG. 19 shows a schematic top view of the scanning
components of FIG. 18 as they orbit the scan volume 228 about the
.beta. axis. Scanning begins with components at position 300 and
progresses to position 302, position 304, and position 306. In the
example shown, coordinated rotation of actuators 290 and 294 causes
orbital movement of source 22 and detector 24 about scan volume
228. Source 22 orbits along a radius R2. Detector 24 orbits along a
shorter radius R1.
[0143] Separate actuation for the source 22 and detector 24
components allows one or the other to be separately moved, which
can be convenient for patient positioning or for storage or
transport of the imaging apparatus.
[0144] Radiation-absorbent shielding is provided within housing 78
and about the enclosed components in order to help absorb stray and
scattered radiation. As shown in FIG. 20 (with top surface 190
removed for visibility of internal components), shielding 250 is
added to either or both the inner or outer surfaces of housing 78,
including top and bottom surfaces 190, 192 as well as side surfaces
that extend between top and bottom surfaces. Shielding 250 is
typically lead or some other radiation-absorbent material and may
be provided in sheet form, fitted against and coupled to housing
78. In gantry 36, detector 24 is coupled to a shielded back plate
252 to absorb radiation that might pass through and around detector
24. Shielding 250 can also be provided on surfaces of door 176,
including along closure portion 188.
[0145] In the perspective view of gantry 36 given in FIG. 21, it
can be seen that shielding 250 is also provided along straight and
curved surfaces that extend between source 22 and detector 24. In
addition, a backing plate 252 provides a shielding function,
blocking x-rays from source 22. In position behind detector 24,
backing plate 252 also serves as a counterweight to help balance
gantry 36 as it rotates through its scan cycle. The use of backing
plate 252 as counterweight helps to move the center of gravity of
gantry 36 toward its center of rotation. In one embodiment, the
backing plate can move a center of gravity of the scanner 110
(e.g., source, C-ring, detector) to the beta axis.
[0146] It should be noted that, in order to provide a clear path
between source 22 and detector 24 at all positions of these
components during exposure, shielding cannot be provided on
surfaces of housing that surround and define opening 38. Thus, some
additional radiation-absorbent shielding for the patient and
technician may be helpful for some exam types.
[0147] Certain exemplary system and/or method embodiments according
to the application can provide a tomosynthesis imaging capability.
In one embodiment, the scanner 110 can also support tomosynthesis,
which can provide an image with less rotation than a CT scan.
Generally, the source 22 and the detector 24 travel about 40 degree
path while aiming the scan volume. However, embodiments according
to the application can provide a tomosynthesis imaging capability
over a range of 30-80 degrees relative to a scan volume or patient
extremity. In one embodiment, the scanner 110 or system 100 provide
the tomosynthesis imaging capability or mode in addition to the
CBCT imaging capability or mode.
[0148] FIG. 22 is a diagram that shows an exemplary embodiment for
tomosynthesis imaging conducted by a CBCT imaging apparatus. As
shown in FIG. 22, a shoulder of a patient is placed in the scan
volume 228 of the scanner 110. In FIG. 22, the patient's body is
radially aligned with the peripheral gap 38. In one embodiment, the
peripheral gap 38 is one feature of the scanner 110 that allows the
tomosynthesis imaging capability to be implemented.
[0149] FIG. 23 is a diagram that shows another exemplary embodiment
for tomosynthesis imaging conducted by a CBCT imaging apparatus. As
shown in FIG. 23, a shoulder of a patient is placed in the scan
volume 228 of the scanner 110 and the patient's body is aligned
parallel to a longitudinal axis of the scan volume 228 (e.g. the
.beta. axis) again in the peripheral gap 38. In one embodiment, the
system 100 can be configured to provide at least one of coronal
tomography imaging, transverse tomography imaging and sagittal
tomography imaging.
[0150] In one embodiment, the door 176 of the scanner 110 can cover
a detector path through the peripheral gap 38. The door 176 can be
in an open position in the tomosynthesis imaging mode. In an
alternative embodiment, the scanner 110 can include a removable
door, to cover the detector path that is removed in the
tomosynthesis imaging mode.
[0151] In one embodiment, the tomosynthesis imaging conducted by a
CBCT imaging apparatus can use independent source and detector
actuators. For example, the independent source actuator 294 and
detector actuator 290 can translate the source 22 and detector 24
using less space in the scanner 110, which can allow for additional
movement in the scanner 110 or a larger peripheral gap. In another
embodiment of the tomosynthesis imaging provided by the CBCT
imaging apparatus 100, a subset of CBCT projection data can be
collected during an imaging scan (or selected from the entire set
of CBCT projection data) and used to generated 3D tomography images
to reduce metal artifacts.
[0152] Consistent with at least one embodiment, exemplary
methods/apparatus can use a computer program with stored
instructions that perform on image data that is accessed from an
electronic memory. As can be appreciated by those skilled in the
image processing arts, a computer program of an embodiment herein
can be utilized by a suitable, general-purpose computer system,
such as a personal computer or workstation. However, many other
types of computer systems can be used to execute the computer
program of described exemplary embodiments, including an
arrangement of networked processors, for example.
[0153] The computer program for performing methods of certain
exemplary embodiments described herein may be stored in a computer
readable storage medium. This medium may comprise, for example;
magnetic storage media such as a magnetic disk such as a hard drive
or removable device or magnetic tape; optical storage media such as
an optical disc, optical tape, or machine readable optical
encoding; solid state electronic storage devices such as random
access memory (RAM), or read only memory (ROM); or any other
physical device or medium employed to store a computer program.
Computer programs for performing exemplary methods of described
embodiments may also be stored on computer readable storage medium
that is connected to the image processor by way of the internet or
other network or communication medium. Those skilled in the art
will further readily recognize that the equivalent of such a
computer program product may also be constructed in hardware.
[0154] It should be noted that the term "memory", equivalent to
"computer-accessible memory" in the context of the present
disclosure, can refer to any type of temporary or more enduring
data storage workspace used for storing and operating upon image
data and accessible to a computer system, including a database, for
example. The memory could be non-volatile, using, for example, a
long-term storage medium such as magnetic or optical storage.
Alternately, the memory could be of a more volatile nature, using
an electronic circuit, such as random-access memory (RAM) that is
used as a temporary buffer or workspace by a microprocessor or
other control logic processor device. Display data, for example, is
typically stored in a temporary storage buffer that can be directly
associated with a display device and is periodically refreshed as
needed in order to provide displayed data. This temporary storage
buffer can also be considered to be a memory, as the term is used
in the present disclosure. Memory is also used as the data
workspace for executing and storing intermediate and final results
of calculations and other processing. Computer-accessible memory
can be volatile, non-volatile, or a hybrid combination of volatile
and non-volatile types.
[0155] It will be understood that computer program products for
exemplary embodiments herein may make use of various image
manipulation algorithms and processes that are well known. It will
be further understood that exemplary computer program product
embodiments herein may embody algorithms and processes not
specifically shown or described herein that are useful for
implementation. Such algorithms and processes may include
conventional utilities that are within the ordinary skill of the
image processing arts. Additional aspects of such algorithms and
systems, and hardware and/or software for producing and otherwise
processing the images or co-operating with the computer program
product of the application, are not specifically shown or described
herein and may be selected from such algorithms, systems, hardware,
components and elements known in the art.
[0156] It should be noted that while the present description and
examples are primarily directed to radiographic medical imaging of
a human or other subject, embodiments of apparatus and methods of
the present application can also be applied to other radiographic
imaging applications. This includes applications such as
non-destructive testing (NDT), for which radiographic images may be
obtained and provided with different processing treatments in order
to accentuate different features of the imaged subject.
[0157] Although sometimes described herein with respect to CBCT
digital radiography systems, embodiments of the application are not
intended to be so limited. For example, other DR imaging system
such as dental DR imaging systems, mobile DR imaging systems or
room-based DR imaging systems can utilize method and apparatus
embodiments according to the application. As described herein, an
exemplary flat panel DR detector/imager is capable of both single
shot (radiographic) and continuous (fluoroscopic) image
acquisition. Further, a fan beam CT DR imaging system can be
used.
[0158] Exemplary DR detectors can be classified into the "direct
conversion type" one for directly converting the radiation to an
electronic signal and the "indirect conversion type" one for
converting the radiation to fluorescence to convert the
fluorescence to an electronic signal. An indirect conversion type
radiographic detector generally includes a scintillator for
receiving the radiation to generate fluorescence with the strength
in accordance with the amount of the radiation.
[0159] Exemplary embodiments according to the application can
include various features described herein (individually or in
combination). Priority is claimed from commonly assigned, copending
U.S. provisional patent application Ser. No. 61/710,832, filed Oct.
8, 2012, entitled "Extremity Scanner and Methods For Using The
Same", in the name of John Yorkston et al., the disclosure of which
is incorporated by reference.
[0160] While the invention has been illustrated with respect to one
or more implementations, alterations and/or modifications can be
made to the illustrated examples without departing from the spirit
and scope of the appended claims. In addition, while a particular
feature of the invention can have been disclosed with respect to
one of several implementations, such feature can be combined with
one or more other features of the other implementations as can be
desired and advantageous for any given or particular function. The
term "at least one of" is used to mean one or more of the listed
items can be selected. The term "about" indicates that the value
listed can be somewhat altered, as long as the alteration does not
result in nonconformance of the process or structure to the
illustrated embodiment. Finally, "exemplary" indicates the
description is used as an example, rather than implying that it is
an ideal. Other embodiments of the invention will be apparent to
those skilled in the art from consideration of the specification
and practice of the invention disclosed herein. It is intended that
the specification and examples be considered as exemplary only,
with a true scope and spirit of the invention being indicated by
the following claims.
* * * * *