U.S. patent number RE37,474 [Application Number 08/916,985] was granted by the patent office on 2001-12-18 for adjustable dual-detector image data acquisition system.
This patent grant is currently assigned to ADAC Laboratories. Invention is credited to Horace H. Hines, Paul Hug, Mark L. Lamp.
United States Patent |
RE37,474 |
Hug , et al. |
December 18, 2001 |
Adjustable dual-detector image data acquisition system
Abstract
An improved image acquisition system allows the angular
displacement between two detectors to be adjusted between
90.degree. and 180.degree. to reduce the imaging time for both
360.degree. and 180.degree. scans. A patient table is displaced
vertically and horizontally from a lateral axis to allow the body
of a patient to be positioned next to the detectors and to improve
resolution.
Inventors: |
Hug; Paul (Saratoga, CA),
Hines; Horace H. (San Jose, CA), Lamp; Mark L. (San
Jose, CA) |
Assignee: |
ADAC Laboratories (Milpitas,
CA)
|
Family
ID: |
26851272 |
Appl.
No.: |
08/916,985 |
Filed: |
August 21, 1997 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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704759 |
May 23, 1991 |
6184530 |
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Reissue of: |
154239 |
Nov 18, 1993 |
05444252 |
Aug 22, 1995 |
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Current U.S.
Class: |
250/363.08;
250/363.05 |
Current CPC
Class: |
A61B
6/037 (20130101); G01T 1/166 (20130101) |
Current International
Class: |
A61B
6/03 (20060101); G01T 1/166 (20060101); G01T
1/00 (20060101); G01T 001/164 (); G01T
001/166 () |
Field of
Search: |
;250/363.08,363.04,363.05 ;378/15 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2070464 |
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Jun 1992 |
|
CA |
|
314543A1 |
|
Nov 1981 |
|
DE |
|
0332937A1 |
|
Mar 1989 |
|
EP |
|
465952A2 |
|
Jun 1991 |
|
EP |
|
1175032 |
|
Mar 1967 |
|
FR |
|
1572809 |
|
Dec 1975 |
|
GB |
|
2120060A |
|
Apr 1983 |
|
GB |
|
61207978 |
|
Mar 1985 |
|
JP |
|
61-83984 |
|
Apr 1986 |
|
JP |
|
62-5193 |
|
Jan 1987 |
|
JP |
|
62-145181 |
|
Jun 1987 |
|
JP |
|
64-9390 |
|
Jan 1989 |
|
JP |
|
4256885 |
|
Feb 1991 |
|
JP |
|
1540365 |
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Sep 1977 |
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NL |
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WO9207512 |
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Oct 1991 |
|
WO |
|
Other References
US. Statutory Invention Registration, H12, "Nuclear Medicine
Imaging System," Gerald W. Bennett, et al., Published Jan. 7, 1986.
.
Stefan P. Mueller et al., "Collimator Selection for SPECT Brain
Imaging: The Advantage of High Resolution," The Journal of Nuclear
Medicine, vol. 27, No. 11, Nov. 1986, pp. 1729-1738. .
Robert L. Eisner, "Principles of Instrumentation in SPECT," Journal
of Nuclear Medicine Technology, vol. 13, No. 1, Mar. 1995, pp.
23-31. .
John W. Keyes, Jr., M.D., "Computed Tomography in Nuclear
Medicine," Lieberman, D.E., Computer Methods, C.V. Mosby Co., St.
Louis, 1977, pp. 130-138. .
Lim et al., "Performance Analysis of Three Camera Configurations
for Single Photon Emission Computer Tomography," IEEE Transactions
on Nuclear Science, Feb. 1980, pp. 559-568. .
Stoddart et al., "A New Development in Single Gamma Transaxial
Tomography Union Carbide Focused Collimator Scanner," IEEE
Transactions on Nuclear Science, 1979, pp. 2710-2712. .
Gottschalk et al., "SPECT Resolution and Uniformity Improvements by
Noncircular Orbit," The Journal of Nuclear Medicine, vol. 24, No.
9, 1983, pp. 822-828..
|
Primary Examiner: Epps; Georgia
Assistant Examiner: Hanig; Richard
Attorney, Agent or Firm: Becker; Jordan M.
Parent Case Text
This application is a continuation-in-part of Ser. No. 07/704,759,
filed May 23, 1991 .Iadd.U.S. Pat. No. 6,184,530.Iaddend..
Claims
What is claimed is: .[.
1. An imaging system for acquiring imaging data generated by an
object positioned about a lateral axis to form a SPECT image, said
system comprising:
first and second gamma ray detectors;
a first pair of rings, oriented substantially perpendicular to and
approximately centered on the lateral axis;
means for coupling said first detector to said first pair of rings,
with the first detector pointed toward the lateral axis and
disposed between said rings;
an arc shaped groove in each of said first pair of rings being
substantially parallel to a circumference of the rings;
means for coupling said second detector to said arc shaped groove;
and
means for moving said second detector along said arc shaped groove
to vary the angular displacement, relative to the lateral axis,
between said first and second detectors to predetermined
magnitude..]. .[.
2. An imaging system for acquiring imaging data generated by an
object positioned about a lateral axis, said system comprising:
first and second detectors each having a collimator surface
oriented perpendicularly to the direction said detectors are
pointing;
a first ring oriented substantially perpendicular to and
approximately centered on the lateral axis;
a first cantilever support coupled to said ring having said first
detector mounted thereon;
an arc shaped groove on said ring said groove being substantially
parallel to the circumference of said ring;
a second cantilever support having said second detector mounted
thereon;
one or more guide rollers rotatably attached to said second
cantilever support and engaged to said groove;
a shaft rotatably attached to said second cantilever support;
a gear fixedly attached to said shaft and engaged to said ring;
a motor controllingly coupled to said shaft, whereby the operation
of said motor by moving said second cantilever support along said
groove varies the orientation, relative to the lateral axis and in
said plane, of the collimator surfaces of said first and second
detectors between a first position where said collimator surfaces
are parallel and a second position where said collimator surfaces
are perpendicular..]. .[.
3. The system of claim 2 further comprising:
a radial motion mechanism coupling said first cantilever support to
said first ring said radial motion mechanism comprising
a first base plate attached to said first ring;
a first slotted guide bar fixedly attached to said first base
plate;
one or more guide rollers rotatably attached to said first
cantilever support and engaged to said first slotted guide bar;
a swivel nut attached to said first cantilever support through a
bracket;
a first lead screw rotatably coupled to said swivel nut, said first
lead screw rotatably mounted in a plurality of bearing blocks, said
bearing blocks fixedly attached to said first base plate;
a trailer gear fixedly attached to said first lead screw;
a coupling gear fixedly attached to said first lead screw;
a lead drive gear controllingly coupled to said trailer gear
through a coupling chain;
a drive motor controlling by coupled to said lead drive gear;
whereby through the action of said drive motor said first detector
may be moved toward and away from the lateral axes..]. .[.
4. The system of claim 3 further comprising:
a second ring substantially parallel to said first ring with said
detectors lying between said rings;
a third cantilever support coupling said first detector to said
second ring;
a second radial motion mechanism coupling said third cantilever
support to said second ring, said second radial motion mechanism
comprising
a second base plate fixedly attached to said second ring;
a second slotted guide bar fixedly attached to said second base
plate;
one or more guide rollers rotatably attached to said third
cantilever support and engaged to said second slotted guide
bar;
a swivel nut fixedly attached to said first cantilever support;
a second lead screw rotatably coupled to said swivel nut, said
second lead screw rotatably mounted in a plurality of bearing
blocks, said bearing blocks fixedly attached to said second base
plate;
a coupling gear fixedly attached to said second lead screw;
a coupling chain coupling said coupling gear of said first radial
motion mechanism and said coupling gear of said second radial
motion mechanism;
whereby said first radial motion mechanism and said second radial
motion mechanism may be operated in tandem to move said first
detector toward and away from the lateral axis..]. .[.
5. The system of claim 2 further comprising
a radial motion mechanism coupling said second cantilever support
to said first ring said radial motion mechanism comprising
a first base plate attached to said first ring;
a first slotted guide bar fixedly attached to said first base
plate;
one or more guide rollers rotatably attached to said second
cantilever support and engaged to said first slotted guide bar;
a swivel nut attached to said first cantilever support through a
bracket;
a first lead screw rotatably coupled to said swivel nut, said first
lead screw rotatably mounted in a plurality of bearing blocks, said
bearing blocks fixedly attached to said first base plate;
a trailer gear fixedly attached to said first lead screw;
a coupling gear fixedly attached to said first lead screw;
a lead drive gear controllingly coupled to said trailer gear
through a coupling chain;
a drive motor controlling by coupled to said lead drive gear;
whereby through the action of said drive motor said second detector
may be moved toward and away from the lateral axis..]. .[.
6. The system of claim 5 further comprising:
a second ring substantially parallel to said first ring with said
detectors lying between said rings;
a third cantilever support coupling said second detector to said
second ring;
a second radial motion mechanism coupling said third cantilever
support to said second ring said radial motion mechanism
comprising
a second base plate fixedly attached to said second ring;
a second slotted guide bar fixedly attached to said second base
plate;
one or more guide rollers rotatably attached to said third
cantilever support and engaged to said second slotted guide
bar;
a swivel nut fixedly attached to said first cantilever support;
a second lead screw rotatably coupled to said swivel nut, said
second lead screw rotatably mounted in a plurality of bearing
blocks, said bearing blocks fixedly attached to said second base
plate;
a coupling gear fixedly attached to said second lead screw;
a coupling chain coupling said coupling gear of said first radial
motion mechanism and said coupling gear of said second radial
motion mechanism;
whereby said first radial motion mechanism and said second radial
motion mechanism may be operated in tandem to move said second
detector toward and away from the lateral axis..]. .[.
7. An imaging system for acquiring imaging data generated by an
object positioned about a lateral axis to form a SPECT image, said
system comprising:
a main gantry body having left and right upright cylindrical walls
each having an inner surface and an outer surface, said walls
including a plurality of guide rollers rotatably attached to the
inner surface of the walls at spaced apart radial positions;
first and second gamma ray detectors;
a first pair of rings located between said walls and oriented
substantially perpendicular to and approximately centered on the
lateral axis, each of said first pair of rings including a main
cylindrical body having an inner face and an outer face, an outer
radial flange integral with and perpendicular to an upper portion
of said outer face and disposed towards and adjacent said gantry
walls, and an L-shaped inner flange having a first member defining
an upper radial support surface, said first member being integral
with and perpendicular to a middle portion of said inner face, said
L-shaped flange having a second member integral with and
perpendicular to said first member and having one end proximate
said lateral axis and having an integral upper lip extending above
said radial support surface at the opposite end of the second
member, wherein said outer flange defines a radial abutment
undersurface for engaging said rollers attached to said walls of
the main gantry body, and wherein said second member of said
L-shaped inner flange and said inner face of said main cylindrical
body define an inner radial groove therebetween;
a second pair of rings located between said walls and oriented
substantially perpendicular to and approximately centered on the
lateral axis, each of said second pair of rings having an inner
face, an outer face, a side wall face, and a radial groove formed
in the side wall face between the inner and outer face, wherein
each of said rings includes a plurality of guide rollers rotatably
mounted within the groove and extending slightly beyond said
groove, said rollers radially spaced apart from each other around
an inner surface of the groove for positioning each of said second
rings upon said upper radial support surface of said first member
of said L-shaped inner flange of each of said first pair of rings
so that said second pair of rings is disposed between said first
pair of rings and is rotatable along said radial support surface
and is prevented from falling off of said surface by said upper lip
of the second member of the L-shaped flange;
means for coupling said first and second detectors to said first
and second pairs of rings respectively, with the first and second
detectors pointed toward the lateral axis and disposed between said
rings, said coupling means including means for moving the first and
second detectors respectively toward and away from the lateral
axis; and
means for independently rotating said first and second detectors
along a circular path approximately centered at said lateral
axis..]. .[.
8. An imaging system as claimed in claim 7 wherein said independent
by rotating means includes a motor operatively coupled to first and
second drive shafts, a pair of first and second drive gears fixedly
attached to said first and second shafts, at least one pair of
first and second idler gears operatively coupling said first and
second drive gears to said first and second pairs of rings, and a
braking means coupled to said second drive shaft;
wherein when said braking means is disengaged, the operation of the
motor rotates said first and second shafts to thereby rotate said
drive gears, said idler gears, and said rings and said detectors
coupled thereto in a circular path approximately centered on the
lateral axis, and wherein when said braking means is engaged,
operation of said motor rotates only said first shaft so that
rotation occurs only for said first gears and said first pair of
rings to thereby adjust the angular displacement, relative to the
lateral axis, between said first and second detectors to a
predetermined magnitude..]. .[.
9. An imaging system as claimed in claim 7 further comprising a
plurality of adjustment blocks movably mounted to said gantry body
walls and spaced radially apart from each other, each of said
blocks having a guide roller rotatably fixed to the block and
adapted to be positioned within the inner radial groove of said
first pair of rings, wherein said adjustment blocks may be moved
axially within said gantry walls substantially parallel to said
lateral axis to thereby vary a lateral displacement of said first
pair of rings from said gantry walls..]..Iadd.
10. A medical imaging system for acquiring image data of an object,
said system comprising:
a first pair of rotatable members rotatable about and substantially
centered on a lateral axis;
a second pair of rotatable members rotatable about and
substantially centered on a lateral axis;
a first radiation detector coupled to and disposed between the
first pair of rotatable members; and
a second radiation detector coupled to and disposed between the
second pair of rotatable members, the second pair of rotatable
members movable with respect to the first pair of rotatable members
so as to allow the angular displacement between the first and
second detectors about the lateral axis to be
varied..Iaddend..Iadd.
11. A medical imaging system according to claim 10, wherein the
first and second detectors are gamma radiation
detectors..Iaddend..Iadd.
12. A medical imaging system according to claim 10, wherein the
first pair of rotatable members comprises a pair of ring-shaped
members including a first ring-shaped member and a second
ring-shaped member, and wherein the second pair of rotatable
members comprises a pair of ring-shaped members including a third
ring-shaped member and a fourth ring-shaped
member..Iaddend..Iadd.
13. A medical imaging system according to claim 10, wherein the
second pair of rotatable members is disposed between the first pair
of rotatable members..Iaddend..Iadd.
14. An imaging system according to claim 10, wherein the angular
displacement can be substantially any angle in a range from less
than 90 degrees to approximately 180 degrees..Iaddend..Iadd.
15. An imaging system according to claim 10, wherein each of the
first and second radiation detectors includes a substantially
planar surface, and wherein the imaging system further comprises
first and second extended collimators mounted to the first and
second radiation detectors, respectively, each of the first and
second extended collimators having a collimator surface extending
substantially beyond the planar surface of the corresponding
detector..Iaddend..Iadd.
16. An imaging system according to claim 15, wherein each of the
first and second detectors comprises a beveled edge for reducing
mechanical interference between the first and second detectors when
the first and second detectors are oriented substantially
perpendicular to each other..Iaddend..Iadd.
17. An imaging system according to claim 10, further
comprising:
means for rotating the first and second radiation detectors through
a circular path centered substantially about the lateral axis to a
plurality of angular positions to acquire the image data; and
means for varying the relative position of the object with respect
to the first and second radiation detectors, vertically and
horizontally with respect to the lateral axis, to substantially
minimize the distance between the object and the first and second
gamma ray detectors at each of the plurality of angular
positions..Iaddend..Iadd.
18. A medical imaging system for acquiring tomographic image data
of an object, said system comprising:
a first pair of ring members rotatable about and substantially
centered on a lateral axis;
a second pair of ring members rotatable about and substantially
centered on a lateral axis and disposed between the first pair of
ring members;
a first gamma ray detector coupled to and disposed between the
first pair of ring members; and
a second gamma ray detector coupled to and disposed between the
second pair of ring members, the second pair of ring members
rotatable with respect to the first pair of ring members so as to
allow the angular displacement between the first and second gamma
ray detectors about the lateral axis to be
varied..Iaddend..Iadd.
19. An imaging system according to claim 18, wherein the angular
displacement can be substantially any angle in a range from less
than 90 degrees to approximately 180 degrees..Iaddend..Iadd.
20. An imaging system according to claim 18, wherein each of the
first and second gamma ray detectors includes a substantially
planar surface, and wherein the medical imaging system further
comprises first and second extended collimators mounted to the
first and second gamma ray detectors, respectively, each of the
first and second extended collimators having a collimator surface
extending substantially beyond the planar surface of the
corresponding detector..Iaddend..Iadd.
21. A medical imaging system according to claim 18, wherein each of
the first and second gamma ray detectors comprises a beveled edge
for reducing mechanical interference between the first and second
gamma ray detectors when the first and second gamma ray detectors
are oriented substantially perpendicular to each
other..Iaddend..Iadd.
22. An imaging system according to claim 18, further
comprising:
means for rotating the first and second gamma ray detectors through
a circular path centered substantially about the lateral axis to a
plurality of angular positions to acquire the image data; and
means for varying the relative position of the object with respect
to the first and second gamma ray detectors, vertically and
horizontally with respect to the lateral axis, to substantially
minimize the distance between the object and the first and second
gamma ray detectors at each of the plurality of angular
positions..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to imaging systems and more
particularly to imaging systems for use in nuclear medicine.
2. Description of the Relevant Art
Gamma ray cameras are used in nuclear medicine to generate high
quality images for brain, SPECT (Single Photon Emission Computer
Tomograph), and total body bone studies. These cameras are most
frequently used for cardiac and total body bone studies.
It is very important that the gamma ray camera be designed for high
patient throughput for both economic and therapeutic reasons. The
cost for diagnosing each patient is reduced if more patients can be
diagnosed per unit time. For very sick patients or patients in
intensive care it is important to minimize the time required to
acquire image data. Patient throughput is increased if imaging time
is reduced. Other factors, such as patient set-up time also affect
patient throughput.
Modern gamma ray cameras utilize detectors, such as Anger cameras,
having a wide field of view so that it is possible to image the
full width of the body of a patient at each angular stop without
the requirement of rectilinear scanning. These detectors use thick
lead collimators to focus images and are thus very heavy. The
collimators must be positioned as close to the patient as possible
to acquire image data required to generate high resolution images.
The image data acquired by the detectors is processed by a computer
to generate an image. Techniques for processing image data are
well-know in the art and described in "Principles of
Instrumentation in SPECT" by Rober Eisner, Journal of Nuclear
Medicine, Vol. 13, #1, March 1985, pp. 23-31; Computed Tomography
in Nuclear Medicine" by John Keyes, (chapter in) Computer Methods,
C. V. Mosley, St. Louis, 1977, pp. 130-138; and "Single Photon
Emission Computed Tomography," by Bernard Oppenheim and Robert
Appledown, (chapter in) Effective Use of Computers in Nuclear
Medicine, Michael Gelfand and Stephen Thomas, McGraw-Hill Book Co.,
New York 1988, pp. 31-74.
Recent technological innovations have produced dual-head systems,
with two detectors having their detector image direction arrows
oriented at a fixed angle of 180.degree., and triple-head systems,
with three detectors having their image direction arrows oriented
at fixed angles of 120.degree., SPECT gamma ray cameras capable of
rapid, high quality SPECT imaging. FIGS. 1A and 1B are schematic
diagrams depicting the fixed orientation of the detector image
direction arrows 2 of the detectors 4 in a dual-head and
triple-head system.
When the detectors rotate about the patient, a lateral axis is
defined as the mechanical axis of rotation aligned with the
computer matrix for reconstructing the SPECT images.
The single, dual, and triple head cameras each have certain
features which are advantageous for a particular type of
application. To determine which system is best for a particular
application factors such as 1) the ability of the camera to perform
required imaging tasks; 2) the quality of the images generated; and
3) patient throughput should be considered.
The acquisition of data for a total body scan requires movement of
the detector along the length of the patient's body. The dual-head
system is very efficient because image data for anterior/posterior
images can be acquired simultaneously. The time required to
complete a scan can be reduced from 45 to 60 minutes, for a
single-head camera, to 30 minutes. The triple-head system is no
more efficient than the single-head system because the detectors
cannot be aligned to acquire simultaneous anterior/posterior or
left/right lateral data.
To generate high-quality SPECT for brain, bone, or liver studies
views taken along a complete 360.degree. circle (360.degree. scan)
around the body of the patient are required. Typically, about 64 to
128 angular stops are required to acquire the image data. The
above-described dual-head camera reduces the imaging time to 1/2
the imaging time of a single-head system because data is acquired
from two stops simultaneously. The triple-head camera reduces the
imaging time to about 1/3 the imaging time of a single-head system
because data is acquired from three stops simultaneously.
For cardiac SPECT studies, the analysis of complex imaging
considerations has led to the use of at least 32 stops over a
180.degree. arc about the patient's body (180.degree. scan). For a
180.degree. scan the imaging time of a single-head and dual-head
system are the same because only one detector of the dual-head
system is within the 180.degree. arc at any given time. A
triple-head system reduces the image time to about 2/3 the time of
a single-head system for a 180.degree. scan because two detectors
are within the 180.degree. arc about 1/3 of the time.
In view of the above it is apparent that the mechanical system for
orienting the detectors must be designed to provide a mechanism for
accurately orienting the detectors at various angular stops
relative to the patient and to position the collimator as close to
the patient as possible. Additionally, the system must be stable so
that the heavy detectors are held still at each stop to facilitate
the acquisition of accurate imaging data. Other attributes that are
required of the mechanical system are ease of patient positioning,
size of footprint, and overall size.
Further, as described above, the existing systems each have
advantages for particular applications but generally lack the
flexibility for optimal performance over a range of applications.
Additionally, although cardiac SPECT imaging accounts for about 33%
of the use of gamma ray cameras, none of the systems significantly
reduce the imaging time for the 180.degree. scan used in forming
cardiac SPECT images.
SUMMARY OF THE INVENTION
The present invention is a unique system for reducing the imaging
time required to generate a 180.degree. SPECT image.
According to one aspect of the invention, the angular displacement
between two detectors may adjusted to any angle between about
90.degree. and 180.degree. and the detectors can be rotated to any
desired angular position along a circular path centered on a
lateral axis. Thus, the system can be optimally configured for
total body scans and 360.degree. SPECT (relative angular
displacement of 180.degree.) and 180.degree. SPECT (relative
angular displacement of 90.degree.) to provide a very flexible
system.
According to a further aspect of the invention, each detector can
be independently rotated along different circular paths centered on
the lateral axis.
According to another aspect of the invention, both detectors are
coupled to a single pair of rings. Each of the rings has an arc
shaped groove which is substantially parallel to the circumference
of the ring and aligned with the arc-shaped groove in the other
ring. The second detector is coupled to the groove via guide
rollers mounted to a support arm attached to the second detector
which allows the second detector to move along the groove so as to
vary the lateral displacement, relative to the lateral axis,
between the first and second detectors to a selected magnitude
having a value of between 90.degree. and 180.degree..
According to another aspect of the invention, each detector is
separately coupled to a first and second pair of rings
respectively. Each of the first pair of rings has a radial support
flange that is integral with and perpendicular to the inner surface
of each of the first pair of rings. The second pair of rings is
positioned on the radial support flange of each of the first pair
of rings so that the second pair of rings is displaced laterally
away from the first pair of rings and is disposed between the first
pair of rings. The second pair of rings may be rotated independent
of the first pair of rings to adjust the angular displacement
between the detectors to a predetermined magnitude.
According to another aspect of the invention, each detector may be
independently moved toward or away from the lateral axis.
Other features and advantages of the invention will be apparent in
view of the appended figures and following detailed
description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B are schematic views depicting the fixed orientation
of the detectors for existing dual-head and triple head imaging
systems;
FIGS. 1C-1E are schematic views showing 3 of the multiple angular
stops required for a 360.degree. scan with the angular displacement
of the detectors at 180.degree.;
FIGS. 2A-2C are schematic views showing 3 of the multiple angular
stops required for a 180.degree. scan with the angular displacement
of the detectors at 90.degree.;
FIG. 3 is a perspective view of a preferred embodiment of the
invention;
FIG. 4 is a view taken along A--A of FIG. 3;
FIG. 5 is a view taken along B--B of FIG. 3;
FIG. 6 is a view taken along C--C of FIG. 3;
FIG. 7 is a top view of the embodiment depicted in FIG. 3;
FIGS. 7A-7C are a schematic views of an alternative rotational
drive mechanism;
FIG. 8 is a schematic view of two detectors oriented at
90.degree.;
FIG. 9 is a schematic view of two detectors oriented at
120.degree.;
FIG. 10 is a schematic view of two detectors having extended
collimators and oriented at 90.degree.;
FIG. 10A is a schematic view of two detectors having their centers
displaced from the lateral axis;
FIG. 11 is a schematic view of two detectors oriented at 90.degree.
with a reduced lateral detector;
FIG. 12 is a schematic view depicting a patient table that can be
horizontally and vertically displaced relative to the lateral
axis;
FIGS. 13A and 13B are cut away views of mechanisms for displacing
the table from the lateral axis; and
FIG. 14 is a schematic view of a positional feedback mechanism.
FIGS. 15A and 15B are schematic views of an alternative means for
varying the angular displacement between the detectors.
FIG. 16 is a perspective view of an alternative means for varying
the angular displacement between the detectors.
FIG. 17 is a schematic view of an alternative embodiment of the
invention showing the positional relationship between the two pairs
of ring gears.
FIG. 18 is a view taken along line D--D of FIG. 17.
FIG. 19 is a perspective view of the rotational drive assembly for
the alternative embodiment of FIG. 17.
FIG. 20 is a schematic elevational view of the rotational drive
assembly of FIG. 19.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIGS. 1C-1E depict the required angular stops for two detectors 4
displaced by 180.degree. to accomplish a 360.degree. scan. In the
180.degree. configuration the size of the detectors does not limit
their radial motion and the detectors 4 can be positioned to touch
the body 10 of the patient at each stop. However, the detectors
cannot be moved in circular path while maintaining close proximity
to the body of the patient 10 because the body 10 of the patient is
not circular.
FIGS. 2A-2C depict a preferred embodiment of the invention. The
detectors 4 have their image direction arrows oriented at
90.degree. to reduce the imaging time of a 180.degree. scan to 1/2
the imaging time of a single-head system because data is acquired
from two stops simultaneously.
FIG. 3 is a perspective view of a preferred embodiment of the
invention that allows the adjustment of the relative angular
displacement of the detectors to have any magnitude from less than
90.degree. up to 180.degree.. Further, each detector may be
independently moved toward or away from the lateral axis 48.
In FIG. 3, a gantry 30, having left and right upright sections 30L
and 30R, supports first and second detector I drive gear rings 32
and 34 and first and second detector II drive gear rings 36 and 38.
A detector I radial motion mechanism 40 connects detector I to the
interior surface of the second detector I drive gear ring 34 and a
detector II radial motion mechanism 42 connects detector II, via a
first detector II support arm 44, to the exterior surface of the
first detector II drive gear ring 36.
A left drive gear 45L and idler gear 46L controllably engages the
first detector drive gear ring 36 to move detector II in a circular
path about a lateral axis 48.
FIG. 4 is perspective view of the detector I radial motion
mechanism 40 taken along A--A of FIG. 3. In FIG. 4, base plates 60
and 62 having slotted guide bars 64 and 66 fixedly mounted thereon,
are attached to the interior surface of the second detector I ring
gear 34. Lead screws 68 and 70 are rotatably mounted in bearing
blocks 72, 74, 76, and 78 which are fixedly attached to the base
plates 60 and 62. Arm supports are engaged with the grooves of the
guide bars 64 and 66 by guide rollers 84 and 86. Swivel nuts (only
one 90 is shown) couple the lead screws to the arm supports 80 and
82 via brackets (only one 94 is shown). A detector support arm 88
is fixedly mounted to the arm supports 80 and 82.
A drive motor has a lead drive gear 98 coupled to a trailer gear
100 mounted on the second lead screw 70 by a drive chain 102. First
and second lead screw coupling gears 104 and 106 are coupled by a
coupling chain 108.
FIG. 5 is an end view, taken along B--B of FIG. 3, of the rotary
drive mechanisms for detectors I and II. In FIG. 5, a first rotary
drive motor 120 has a lead drive pulley 122 coupled to a
transmission shaft drive pulley 124 by a first drive belt 126. A
first transmission shaft 128 is coupled to the second detector I
ring gear 34 by a right drive gear 130R and idler gear 131R. The
first transmission shaft extends through the gantry 30 parallel to
the lateral axis 48 and is also coupled to the first detector I
ring gear 32 by left drive and idler gears 130L and 131L (not
shown). The drive and idler gears 130 and 131 for driving the
detector I ring gears 32 and 34 are located on the interior sides
of the upright sections 30L and 30R of the gantry 30.
Similarly, a second rotary drive motor 132 has a lead drive pulley
134 coupled to a transmission shaft drive pulley 136 by a second
drive belt 138. A second transmission shaft 140 is coupled to the
second detector II ring gear 38 by a right drive gear 45R and idle
gear 46R (depicted in phantom). The second transmission shaft
extends through the gantry 30 parallel to the lateral axis 48 and
is also coupled to the second detector II ring gear 36 by drive and
idler gears. The drive and idler gears 45 and 46 for driving the
detector II ring gears 36 and 38 are located on the exterior sides
of the upright sections 30L and 30R of the gantry 30.
FIG. 6 is a cross-sectional view, taken along C--C of FIG. 3,
depicting the drive and detector support mechanisms. The detector
ring gears 32, 34, 36, and 38 have support grooves which are
engaged with gear support bearings 150, 152, 154, 156, 158, 160,
162, and 164 mounted on the upright sections 30L and 30R of the
gantry 30. Detector I and the detector I radial drive mechanism are
mounted on the interior surfaces of the first and second detector I
ring gears 32 and 34. The radial drive mechanism for detector II is
mounted on the exterior surface of the detector II ring gears 36
and 38. The detector II support arms 44R and L are coupled to the
exterior surfaces of the detector II ring gears and extend through
the annular space created by the ring gears and supports detector
II.
FIG. 7 is a top view of the embodiment depicted in FIG. 3 and
further depicts the details of the rotary drive mechanism. The
first transmission shaft 128 transmits the rotary motion of the
first rotary drive motor 122 to both the first and second detector
I ring gears 32 and 34 and the second transmission shaft 140
transmits the rotatory motion of the second rotary drive motor 132
to the first and second detector II ring gears 36 and 38.
The operation of the embodiment depicted in FIGS. 3-7 will now be
described. Detectors I and II may be independently rotated about
the lateral axis 48 by activating either the first or second rotary
drive motors 132 or 122. If the first rotary motor is activated
rotary motion is transmitted to the first detector ring gears 32
and 34 which in turn impart rotary motion to detector I through the
support arms 88.
Additionally, each detector may be independently moved radially
toward or away from the lateral axis 48 by activating the radial
drive motor 96 in the radial drive mechanism for the detector.
FIGS. 7A and 7B depict an alternative rotary drive mechanism
utilizing a single rotary drive motor 122 coupled to the first and
second transmission shafts 128 and 140. In FIG. 7A a lead drive
gear 166 is directly coupled to the shaft drive gears 167 and 168
to rotate both transmission shafts 128 and 140 in the same
direction.
The rotational motion of shaft drive gear 166 is transmitted to the
first transmission shaft 128 when a first electromagnetic clutch
169 is engaged and rotation of the first transmission shaft 128 is
stopped when a first electromagnetic brake 170 is engaged.
Similarly, the rotational motion of shaft drive gear 166 is
transmitted to the second transmission shaft 140 when a second
electromagnetic clutch 171 is engaged and rotation of the second
transmission shaft 140 is stopped when a second electromagnetic
brake 172 is engaged.
FIG. 7B is a view, taken along 7B--7B of FIG. 7A, depicting the
rotation of the lead gear 166 and shaft drive gears 167 and
168.
In operation, both detectors I and II are rotated when both
clutches 169 and 170 are engaged and both brakes 170 and 172 are
disengaged. Detector I is moved independently if the first clutch
169 is engaged and the first brake 170 is disengaged and detector
II is moved independently if the second clutch 171 is engaged and
the second brake 172 is disengaged. The brakes are used for safety
reasons and to counteract the system imbalance.
FIG. 7C is a schematic view of an alternative drive system that
uses a single drive motor 122 and drive shaft 128. Drive gears 48
are fixed on the end of the shaft 128 and engaged with the first
and second detector II ring gears 36 and 38. First and second shaft
gears 175 and 176 couple the rotational motion of the shaft 128 to
the first and second detector I ring gears 32 and 34 when
electromagnetic clutches 177 and 178 are engaged and the motion of
the first and second detector I ring gears 32 and 34 is stopped
when the electromagnetic brakes 179 and 180 are engaged.
In operation, both detectors rotate together when both clutches 177
and 178 are engaged and the brakes 179 and 180 are released and the
rotational drive motor 122 is activated. Detector II is
independently rotated to adjust the angular displacement relative
to detector I when the brakes 179 and 180 are engaged and the
clutches 177 and 178 are released.
As described above, high patient throughput requires that detectors
having a wide field of view be utilized. However, when the detector
image direction arrows 2 are oriented at 90.degree., to efficiently
perform a 180.degree. scan, the physical size of the detectors 4
limits their radial motion. Referring to FIG. 8, the detector edges
will touch when the radius Rmin is reached. Thus the detectors 4
are not able to touch the body 10 of the patient which is necessary
to achieve high resolution. Also, each detector 4 has a lateral
shielding section 182 to prevent external gamma rays from reaching
the scintillation medium.
In one embodiment of the invention the detector image direction
arrows 2 are oriented at 120.degree. when a 180.degree. scan is to
be performed. As depicted in FIG. 9, this orientation allows
greater radial motion to allow the detectors 4 to be positioned
closer to the body 10 of the patient than in the 90.degree.
configuration. However, the imaging time is reduced to only about
2/3 of the imaging time of a single-head system because both
detectors 4 are within the 180.degree. arc only a fraction of the
time.
In another embodiment, depicted in FIG. 10, extended collimators
184 are utilized to decrease Rmin and to place the collimator 184
closer to the body 10 of the patient.
In FIG. 10A, a configuration where the centers of the detectors 4
are displaced from the lateral axis 48 so that the image arrows 2
do not point toward the lateral axis is depicted. SPECT algorithms
for correcting for such displacements are known in the art.
Alternatively, as depicted in FIG. 11, detector II is oriented
laterally to the body 10 of the patient and has a narrower
cross-section and field of view. The smaller cross-section of
detector II facilitates closer positioning of the collimator to the
body of the patient.
In another embodiment of the invention, depicted in FIG. 12, a
table 200 holding the patient is displaced vertically and
horizontally from the lateral axis 48 so that the body 10 of the
patient touches the detectors 4.
FIGS. 13A and B depict mechanisms for imparting horizontal motion
and vertical motion of the table 200 relative to the lateral axis
48. In FIG. 13A, a view taken perpendicular to the lateral axis 48,
a horizontal drive motor 202 imparts rotary motion to an axle 204,
supported by bearings 205, through bevel gear 206. Horizontal
motion of the table 200 is effected by movement along gear racks
208, oriented parallel to the lateral axis 48, through rotational
motion imparted to gears 210 engaged to gear racks 208 by axle
204.
In FIG. 13b, a view taken perpendicular to the lateral axis 48, a
vertical drive motor 212 imparts rotational motion to a lead screw
214 through a drive mechanism 216. The threads of the lead screw
214 are engaged to threads of a telescope tube 219 to impart
vertical motion to the telescope tube and table 200 when the
vertical drive motor 212 is activated.
FIG. 14 depicts a positional feedback device for indicating the
positions of the detectors. In FIG. 14, a sensor gear 250 engages a
ring gear 32 and has a sprocket 252 coupled to a chain 254. The
chain engages sprockets 256 and 258 coupled to a potentiometer 260
and an encoder 262.
In operation, the potentiometer 260 is used for coarsely indicating
position and the encoder 262 for finely indicating position. For
example, the sprockets can be sized so that for each revolution of
the ring gear 32 the potentiometer 260 makes 10 turns varying the
resistance from 0 to 1,000 ohms. If power is lost the potentiometer
260 will not loose its position or reading.
Similar devices are utilized to indicate the radial position of the
detectors and the vertical and horizontal displacement of the table
200.
FIGS. 15A and 15B depict an alternative mechanism for adjusting the
angular displacement between the detectors between 90.degree. and
180.degree.. FIG. 15A depicts the detectors positioned 180.degree.
apart. FIG. 15B depicts the detectors positioned 90.degree. apart.
Detector I 300 is fixedly attached to ring gear 302 through
cantilever support arm 304. Detector II 306 is attached to ring
gear 302 through cantilever support arm 308. The angular
displacement between the detectors is varied by moving detector II
306 in a circular path along the ring gear 302.
FIG. 16 shows the coupling of detector II 306 to ring gear 302 in
greater detail. Guide rollers 310 and 312 are rotatably mounted to
baseplate 314. These guide rollers engage a groove 316 along an arc
parallel to the circumference of the ring gear 302 and on the ring
gear's interior surface. Transmission shaft 318 is rotatably
mounted to baseplate 314 and is driven by motor 320. This
transmission shaft is fixedly attached to angular displacement gear
322 which is engaged to ring gear 302. A brake 324 is coupled to
ring gear 302. In an alternative embodiment the brake 324 is
coupled to ring gear 302 through a shaft which drives the ring gear
through a drive gear.
The operation of the embodiment depicted in FIGS. 15A, 15B and 16
will now be described. Rotating ring gear 302 with brake 324
disengaged causes both detectors I and II 300 and 306 to move in a
circular path around the lateral axis 326. Rotating angular
displacement gear 322 through the action of motor 320 with brake
324 engaged causes detector II 306 to move in a circular path
around the lateral axis 326 while detector I 300 remains fixed thus
varying the angular displacement between detectors I and II 300 and
302.
FIG. 15 depicts part of the radial motion mechanism provided in one
embodiment for detector II 306. Base plate 314 having slotted guide
bar 328 fixedly mounted thereon, is attached to the interior
surface of the ring gear 302. Lead screw 330 is rotatably mounted
in bearing blocks 332 and 334 which are fixedly attached to the
base plate 314. Detector cantilever support 308 is engaged with the
grooves 336 and 338 of the guide bar 328 by guide rollers (not
shown). Swivel nut 340 couples the lead screw 330 to the cantilever
support 308 via bracket 342. A drive motor 344 has a lead drive
gear 346 coupled to a trailer gear 348 mounted on the lead screw by
a drive chain 350. Through the operation of this radial motion
mechanism, detector II 306 may be moved toward and away from the
lateral axis. In one embodiment, a similar radial motion mechanism
is provided for detector I 300.
In another embodiment there is a second ring gear parallel to the
first ring gear. Both detectors then lie between said rings. One or
both detectors are further supported by cantilever supports
attached to the second ring gear. In a further embodiment one or
both of these cantilever supports are attached to the second ring
gear through radial motion mechanisms similar to those described
above. Where two radial motion mechanisms support one detector, the
coupling gears of the mechanisms are coupled with a coupling chain
to allow tandem operation.
FIGS. 17 and 18 depict an alternative mechanism for adjusting the
relative angular displacement of the detectors between 90.degree.
and 180.degree.. In FIG. 17, Detector I 400 is fixedly attached to
a pair of slave gear rings 404 (only one of which is shown) through
cantilever support arm 402. Detector II 410 is attached to a pair
of master gear rings 414 (only one of which is shown) through
cantilever support arm 403. The angular displacement between
Detector I 400 and Detector II 410, which is 180 degrees in FIGS.
17 and 18, is varied by independently rotating slave gear rings 404
in relation to master gear rings 414 via the operation of drive
assembly 500 (See FIG. 19) as will be described in more detail
hereinafter.
FIG. 18 shows the coupling of one of the slave gear rings 404 to a
respective master gear ring 414 proximate gantry wall 418L in
greater detail. It is to be understood that the coupling of the
other slave gear ring 404 to its respective master gear ring 414
proximate gantry wall 418R is accomplished in a similar manner to
the coupling of the gear rings proximate wall 418L, the former
merely being a mirror image of the latter. Master gear ring 414 is
located between the gantry walls 418L and 418R and is oriented
substantially perpendicular to and approximately centered on the
lateral axis 326. Master gear ring 414 includes a main cylindrical
body 420 which has an inner face 422 and an outer face 421. Outer
radial flange 424 is integral with and perpendicular to the upper
region of the outer face 421 and is located adjacent gantry wall
418L. The outer flange 424 defines a radial abutment undersurface
423 for engaging guide rollers 431, which are rotatably fixed
within and radially spaced-apart around the entire inner peripheral
surface of gantry wall 418L. In the preferred embodiment of the
invention, there are ten guide rollers 431 secured to gantry wall
418L which are positioned to engage and rotate along abutment
surface 423. This helps to securely position the master gear ring
414 adjacent the gantry wall 418L (and 418R).
Master gear ring 414 also includes an L-shaped inner flange 426
having first and second members 427, 428. First member 427 is
integral with and perpendicular to a middle portion of the inner
face 422 and defines an upper radial support surface 429 for
engaging guide rollers 433 rotatably fixed to slave gear ring 404,
as will be described in more detail hereinafter. The second member
428 of the L-shaped flange 426 is integral with and perpendicular
to first member 427 and is disposed towards the lateral axis.
Second member 428 has an integral upper lip 430 which extends above
radial support surface 429 and prevents slave gear ring 404 from
falling off of support surface 429. The second member 428 of the
L-shaped inner flange and the lower portion of the inner face 422
of the cylindrical body 420 define between them an inner radial
groove 425.
Slave gear ring 404, which is positioned about radial support
surface 429, has radially spaced apart guide rollers 433 rotatably
attached to an inner radial groove 406 formed in side wall 405 of
the slave gear ring. The preferred embodiment of the invention is
provided with twelve guide rollers 433 equidistantly positioned
along the entire inner periphery of radial groove 406 which are
secured in place by upper lip 430 and which are free to rotate
along radial support surface 429 as will be described in more
detail hereinafter. FIG. 18 also shows one of several adjustment
blocks 440 that is used to vary the lateral displacement 450
between master gear ring 414 and gantry wall 418L. Each adjustment
block 440 includes a guide roller 432 which is rotatably attached
at the distal end 445 of adjustment block 440 and is positioned
within inner radial groove 425 formed in master gear ring 414. In
the preferred embodiment of the invention, there are six adjustment
blocks 440 and six corresponding guide rollers 432 radially spaced
apart along the entire circumference of the inner surface of gantry
wall 418L. Guide rollers 432 are used to secure the gear rings 414,
404 proximate the gantry wall while also being free to rotate
within inner radial groove 425 in master gear ring 414. Adjustment
block 440 also includes a pair of guide slots (not shown) at its
proximal end 447 which are used to change the axial position of
adjustment block 440 within gantry wall 418L to thus allow for
variations in the lateral displacement of master gear ring 414
relative to the gantry wall 418L.
FIGS. 19 and 20 depict the embodiment of the drive assembly 500
that is used to rotate master gear rings 414 and slave gear rings
404. Drive assembly 500 includes single motor 460 that is
operatively coupled to drive shafts 462 and 470. A pair of drive
gears 464 is rigidly attached to drive shaft 462 at opposite ends
of the shaft and is in engaging contact with a pair of idler gears
466. Each one of the idler gears 466 engages a respective one of
the slave gear rings 404. A pair of drive gears 472 are similarly
rigidly attached to drive shaft 470 at opposite ends of the shaft
and are in engaging contact with idler gears 474. Each one of the
idler gears 474 engages a respective one of the master gear rings
414. A 90 degree gear drive 480 is also coupled to each drive shaft
462 and 470 and is used to help reduce back-driving of the
respective drive gears 464 and 472. Drive assembly 500 also
includes brake 468 coupled to clutch 469 which function together to
inhibit rotation of drive shaft 470 and thus allow slave gear rings
404 to rotate independently of master gear rings 414 as will now be
described with reference to FIGS. 17, 18, and 19.
With brake 468 disengaged and clutch 469 engaged, the operation of
motor 460 results in the rotation of both of the drive shafts 462,
470 which causes all of the drive gears 464, 472 attached to the
shafts to rotate simultaneously. This forces idler gears 466, 474
to rotate which in turn rotates slave gear rings 404 and master
gear rings 414 in tandem. As best seen in FIG. 18, each slave gear
ring 404 rotates around radial support surface 429 of each
respective master gear ring 414 through the rotation of guide
rollers 433, which effectively act like bearings. Each master gear
ring 414 likewise rotates about guide rollers 431 and 432, in
tandem with the rotation of slave gear ring 404. Such an operation
allows Detector I 400 and Detector II 410 to rotate together with a
fixed angular displacement between them.
When brake 468 is engaged and clutch 469 is disengaged, brake 468
engages drive shaft 470 to prevent its movement. Operation of motor
460 thereby causes only the rotation of drive shaft 462 and gears
464, 466 attached thereto, while gears 472 and 474 remain in a
fixed position. As a result, slave gear rings 404 rotate
independently of master gear rings 414. As each slave gear ring 404
rotates, guide rollers 433 attached thereto are forced to rotate
about radial support surface 429 on each respective master gear
ring 414 which allows slave gear ring 404 to rotate relative to its
respective master gear ring 414. This causes detector I 400 to move
in a circular path around the lateral axis 326 while detector II
410 remains fixed thus varying the relative angular displacement of
detectors I and II, 400 and 410.
An improved method for imaging that utilizes the movable table 200
will now be described. The table is moved up and down or left and
right using microprocessor control and the positional feedback
device enables the microprocessor to calculate the position of the
table.
First, the motion limits of the detectors and table are defined.
The operator moves the detectors to have the desired relative
angular displacement (e.g., 90.degree.). The table holding the
patient is positioned parallel to the lateral axis. The operator
then moves the detectors into the desired position relative to the
patient (e.g. anterior and lateral). The operator then moves the
table so that the body of the patient touches the lateral detector
and the microprocessor stores the x-location. The operator then
moves the table so that the body of the patient touches the
anterior detector and the microprocessor stores the y-location. The
microprocessor then calculates the required table motion based on
the size of the detectors, the number of angular stops required,
and x and y locations determined above.
Once the motion limits are defined image data is acquired. The
table is moved to a location to allow motion of the detectors and
the detectors are moved to the first angular stop. The table is
then moved to the starting position for the first angular stop and
data is acquired. The positions of the detectors are stored. The
procedure is repeated until data is acquired for all the required
angular stops. The stored location data is utilized to generate an
image from the acquired data.
The invention has now been described with reference to the
preferred embodiments. Alternatives and substitutions will now be
apparent to persons of ordinary skill in the art. For example, if
detectors I and II were to be maintained at a fixed angle, e.g.,
120.degree. or 90.degree., then both detectors and their radial
drive mechanisms could be attached to the detector I ring gears 32
and 34. Accordingly, it is not intended to limit the invention
except as provided by the appended claims.
* * * * *