U.S. patent application number 11/441281 was filed with the patent office on 2007-01-11 for computed tomography system for imaging of human and small animal.
This patent application is currently assigned to The University of North Carolina at Chapel Hill. Invention is credited to Yuan Cheng, Yueh Lee, Weili Lin, Jianping Lu, Jian Zhang, Otto Z. Zhou.
Application Number | 20070009081 11/441281 |
Document ID | / |
Family ID | 39167732 |
Filed Date | 2007-01-11 |
United States Patent
Application |
20070009081 |
Kind Code |
A1 |
Zhou; Otto Z. ; et
al. |
January 11, 2007 |
Computed tomography system for imaging of human and small
animal
Abstract
Computed tomography device comprising an x-ray source and an
x-ray detecting unit. The x-ray source comprises a cathode with a
plurality of individually programmable electron emitting units that
each emit an electron upon an application of an electric field, an
anode target that emits an x-ray upon impact by the emitted
electron, and a collimator. Each electron emitting unit includes an
electron field emitting material. The electron field emitting
material includes a nanostructured material or a plurality of
nanotubes or a plurality of nanowires. Computed tomography methods
are also provided.
Inventors: |
Zhou; Otto Z.; (Chapel Hill,
NC) ; Lu; Jianping; (Chapel Hill, NC) ; Lee;
Yueh; (Durham, NC) ; Lin; Weili; (Chapel Hill,
NC) ; Cheng; Yuan; (Chapel Hill, NC) ; Zhang;
Jian; (Carrboro, NC) |
Correspondence
Address: |
JENKINS, WILSON, TAYLOR & HUNT, P. A.
3100 TOWER BLVD
SUITE 1200
DURHAM
NC
27707
US
|
Assignee: |
The University of North Carolina at
Chapel Hill
|
Family ID: |
39167732 |
Appl. No.: |
11/441281 |
Filed: |
May 25, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10923385 |
Aug 20, 2004 |
7082182 |
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11441281 |
May 25, 2006 |
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10051183 |
Jan 22, 2002 |
6876724 |
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10923385 |
Aug 20, 2004 |
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09679303 |
Oct 6, 2000 |
6553096 |
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10051183 |
Jan 22, 2002 |
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10421931 |
Apr 24, 2003 |
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10923385 |
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Current U.S.
Class: |
378/10 |
Current CPC
Class: |
G01N 2223/612 20130101;
H01J 2201/30469 20130101; H01J 35/065 20130101; G01N 2223/419
20130101; A61B 6/508 20130101; A61B 6/541 20130101; A61B 6/4028
20130101; H01J 2235/068 20130101; B82Y 10/00 20130101; G01N
2223/316 20130101; A61B 6/032 20130101; G01N 23/046 20130101 |
Class at
Publication: |
378/010 |
International
Class: |
A61B 6/00 20060101
A61B006/00; G01N 23/00 20060101 G01N023/00; G21K 1/12 20060101
G21K001/12; H05G 1/60 20060101 H05G001/60 |
Goverment Interests
GOVERNMENT INTEREST
[0002] This subject matter was made with Government support under
Grant No. N00014-98-1-0597 awarded by Office of Naval Research. The
Government has certain rights in the subject matter.
Claims
1. A computed tomography device, comprising: an x-ray source, the
x-ray source comprising a cathode with a plurality of individually
programmable electron emitting units that each emit an electron
beam upon an application of an electric field, an anode target that
emits an x-ray beam upon impact by the emitted electron beam, and a
collimator; and an x-ray detecting unit.
2. The device of claim 1, wherein each electron emitting unit
includes an electron field emitting material.
3. The device of claim 2, wherein the electron field emitting
material includes a nanostructured material.
4. The device of claim 2, wherein the electron field emitting
material includes a plurality of nanotubes or a plurality of
nanowires.
5. The device of claim 4, wherein the nanotubes includes at least
one field emitting material selected from the group consisting of
carbon, boron, and nitrogen.
6. The device of claim 4, wherein the nanowires included at least
one field emitting material selected from the group consisting of
silicon, germanium, carbon, oxygen, oxide, and nitrides.
7. The device of claim 2, wherein the electron field emitting
material includes a plurality of single-wall carbon nanotubes, a
plurality of multi-wall carbon nanotubes or a mixture thereof.
8. The device of claim 1, wherein the x-ray source further
comprises a gate electrode to extract the emitted electron from one
or more of the plurality of individually programmable electron
emitting units when the electrical field is applied between the
gate electrode and the one or more individually programmable
electron emitting units.
9. The device of claim 8, wherein the gate electrode is located
between the cathode and the anode target.
10. The device of claim 8, wherein the electrical field is applied
such that the gate electrode is at a positive potential with
respect to the one or more of the plurality of individually
programmable electron emitting units, and a field strength of the
electrical field is from 0.1 Volt/micron to 100 Volt/micron.
11. The device of claim 1 0, wherein the field strength is from 0.5
Volt/micron to 20 Volt/micron.
12. The device of claim 8, wherein the electrical field applied to
the gate electrode is controlled by a feedback mechanism from the
x-ray detecting unit.
13. The device of claim 1, further comprising a control system for
data collection and reconstruction.
14. The device of claim 1, further comprising a vacuum container
housing the cathode and the anode target.
15. The device of claim 1, wherein at least one of the plurality of
individually programmable electron emitting units has an emission
threshold of less than 3 Volt/micron for a current density of
greater than 0.01 mA/cm.sup.2 and emits 0.1-100 mA total
current.
16. The device of claim 15, wherein the current density is greater
than 0.1 mA/cm.sup.2.
17. The device of claim 1, wherein the plurality of individually
programmable electron emitting units are arranged linearly on an
axis in a plane and each individually programmable electron
emitting unit is focused at one of a plurality of focal spots on
the anode target.
18. The device of claim 17, wherein the collimator generates a fan
beam geometry of x-ray radiation.
19. The device of claim 1, wherein the plurality of individually
programmable electron emitting units are arranged over an area of a
plane and each individually programmable electron emitting unit is
focused at one of a plurality of focal spots on the anode
target.
20. The device of claim 19, wherein the collimator generates a fan
beam geometry of x-ray radiation.
21. The device of claim 1, wherein the device is portable.
22. A method to operate a computed tomography device, the computed
tomography device including an x-ray source, the x-ray source
comprising a cathode with a plurality of individually programmable
electron emitting units that each emit an electron beam upon an
application of an electric field, an anode target that emits an
x-ray beam upon impact by the emitted electron beam, a collimator,
and an x-ray detecting unit, the method comprising: applying the
electric field to at least a first of the plurality of individually
programmable electron emitting units to cause the emission of an
electron beam; focusing the emitted electron beam at one of a
plurality of focal points on the anode target; impacting the anode
target with the emitted electron beam to form an emitted x-ray
radiation beam; collimating the emitted x-ray radiation beam;
passing the collimated x-ray radiation beam through an object;
detecting the x-ray radiation beam -with the x-ray detecting unit;
and processing the detected x-ray radiation image into a
tomographic image.
23. The method of claim 22 further comprising repeating the steps
of applying, focusing, impacting, collimating, passing, detecting,
and processing to produce multiple x-ray radiation images without
rotating the object positioned on the object stage, wherein the
electric field is applied to at least a second individually
programmable electron emitting unit during the repeated step of
applying.
24. The method of claim 22 further comprising repeating the steps
of applying, focusing, impacting, collimating, passing, detecting,
and processing to produce multiple x-ray radiation images without
rotating the object positioned on the object stage, wherein the
emitted electron beam is focused on a second of the plurality of
focal points on the anode target when the step of focusing is
repeated.
25. The method of claim 22, wherein the x-ray source further
includes a gate electrode located between the cathode and the anode
target and the electrical field is applied such that the gate
electrode is at a positive potential with respect to the
individually programmable electron emitting unit and a field
strength of the electrical field is from 0.1 Volt/micron to 100
volt/micron.
26. The method of claim 25, wherein the field strength is from 0.5
Volt/micron to 20 Volt/micron.
27. The method of claim 22, wherein the electron beam emitted from
each electron emitting unit is focused at a different one of the
plurality of focal spots within a line on the anode target.
28. The method of claim 27, wherein the collimator generates a fan
beam geometry of x-ray radiation.
29. The method of claim 22, wherein the step of collimating
produces a fan beam geometry.
30. A computed tomography device for small animal imaging,
comprising: a field emission x-ray source, wherein the x-ray source
can generate a plurality of x-ray beams from a plurality of focal
spots which are arranged in a two-dimensional matrix on a surface
of an x-ray anode, an area multi-pixel digital x-ray detector, and
an object stage placed between the x-ray source and the
detector.
31. The device of claim 30, wherein the x-ray source comprises: a
cathode with a plurality of individually programmable electron
emitting units that each emit an electron beam upon an application
of an electric field, wherein the emitting units are positioned in
a two-dimensional matrix on the cathode; an electron focusing
device; and an anode target that emits an x-ray beam from a focal
spot upon impact by an emitted electron beam.
Description
RELATED APPLICATIONS
[0001] This application is a divisional patent application which
claims the benefit of the filing date of U.S. patent application
Ser. No. 10/923,385, filed Aug. 20, 2004, which is a
continuation-in-part of U.S. patent application Ser. No. 10/051,183
filed Jan. 22, 2002, which is a continuation-in-part of U.S. patent
application Ser. No. 09/679,303 filed Oct. 6, 2000, now U.S. Pat.
No. 6,553,096, and is a continuation of U.S. patent application
Ser. No. 10/421,931 filed Apr. 24, 2003, the disclosure of which is
incorporated herein by reference in its entirety.
TECHNICAL FIELD
[0003] The present subject matter relates generally to field
emission cathodes for x-ray radiation sources. More particularly,
the present subject matter relates to carbon nanotube field
emission cathodes and methods of manufacture and operation of such
cathodes in linear or area x-ray radiation sources with
individually addressable multi-beam x-rays suitable for use in
diagnostic, imaging, and inspection applications.
BACKGROUND ART
[0004] In the description of the background of the present subject
matter that follows reference is made to certain structures and
methods. Such references should not necessarily be construed as an
admission that these structures and methods qualify as prior art
under the applicable statutory provisions. Applicants reserve the
right to demonstrate that any of the referenced subject matter does
not constitute prior art with regard to the present subject
matter.
[0005] Computed tomography (CT) technology is widely used for
medical, industrial and security imaging purposes. The designs of
typical computed tomography machines have gone through major
evolutions. For example, for conventional x-ray imaging, a
three-dimensional (3-D) object is illuminated to form a
two-dimensional (2-D) image. As a result, the spatial resolution in
the illumination direction is lost. This limitation can be overcome
in computed tomography systems by obtaining projection images of
the object in different directions. Typically, the object is
stationary while a single x-ray source rotates around the object
and produces the images at different rotation angles. The
collection of the projected images can then be used to reconstruct
a three-dimensional image of the object.
[0006] Rotation of the x-ray source puts considerable demand on the
system design and can reduce the imaging speed. An electron-beam
computed tomography (EBCT) system can address this problem. In
typical EBCT systems, electrons produced by the cathode are scanned
across the surface of the anode located in the gantry, which
consists of a metal ring or multiple rings. The scanning is
accomplished by electrical and magnetic fields. However, the
machine is expensive and takes significantly larger space than a
regular computed tomography system. Thus, it is highly desirable to
have a small stationary x-ray source computed tomography system
that is potentially more transportable and cost effective.
[0007] In some systems, such as tomography, the x-ray source is
stationary and the object is rotated to collect the projection
images. In the micro-computed tomography systems, the x-ray source
typically produces a fan beam onto the object. In some cases, a
cone beam and two-dimensional detector are used to record the
images. The object is rotated and an image is collected at every
rotation angle. An example of the two-dimensional area detector
consists of a scintillation crystal that converts the x-ray photon
to visible light, and a charge-coupled-detector (CCD) camera
positioned behind the crystal that captures the image. Solid state
and gas detectors are also commonly used.
[0008] From the point of view of image quality, it is preferred to
use a monochromatic x-ray. This is because computed tomography
measures, essentially, the linear absorption coefficient, which
depends on the energy of the incident x-ray photon. However, in
most computed tomography systems, with the exception of a
synchrotron radiation source, continuous-energy x-ray rather than
monochromatic x-ray is used so as to increase the x-ray intensity,
and thus reduce the data collection time. In many computed
tomography systems, the x-ray source is often placed far away from
the object to minimize the non-even spatial distribution of the
x-ray radiation from the single x-ray source and the divergence of
the x-ray beam. As a result, only a small fraction of the produced
x-ray photons are used for imaging.
[0009] It is highly desirable to have an all-stationary computed
tomography system. Such a system will reduce or eliminate the need
to rotate the x-ray source around the patient. Furthermore, novel
x-ray source geometries combined with the precise control of these
x-ray sources can allow the development of imaging techniques and
the refinement of current data acquisition methods.
SUMMARY
[0010] An exemplary embodiment of a computed tomography device
comprises an x-ray source, and an x-ray detecting unit. The x-ray
source comprises a cathode with a plurality of individually
programmable electron emitting units that each emit an electron
upon an application of an electric field, an anode target that
emits an x-ray upon impact by the emitted electron, and a
collimator.
[0011] An exemplary method to operate a computed tomography device,
the computed tomography device including an x-ray source, the x-ray
source comprising a cathode with a plurality of individually
programmable electron emitting units that each emit an electron
upon an application of an electric field, an anode target that
emits an x-ray upon impact by the emitted electron, a collimator,
and an x-ray detecting unit, comprises applying the electric field
to at least a first of the plurality of individually programmable
electron emitting units to cause the emission of an electron,
focusing the emitted electron at one of a plurality of focal points
on the anode target, impacting the anode target with the emitted
electron to form an emitted x-ray radiation, collimating the
emitted x-ray radiation, passing the collimated x-ray radiation
through an object, detecting the x-ray radiation with the x-ray
detecting unit, and recording the detected x-ray radiation. Some of
the objects of the subject matter having been stated hereinabove,
and which are addressed in whole or in part by the present subject
matter, other objects will become evident as the description
proceeds when taken in connection with the accompanying drawings as
best described hereinbelow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Objects and advantages of the present subject matter will
become apparent from the following detailed description of
preferred embodiments thereof in connection with the accompanying
drawings in which like numerals designate like elements and in
which:
[0013] FIG. 1 shows a schematic representation of an exemplary
x-ray radiation source.
[0014] FIG. 2 shows current density as a function of voltage for
carbon nanotube cathodes having a gap distance between 62 .mu.m and
280 .mu.m.
[0015] FIG. 3 shows a schematic representation of an exemplary
embodiment of a collimated monochromatic x-ray radiation
source.
[0016] FIG. 4 shows a schematic representation of an exemplary
embodiment of a linear x-ray radiation source with a fan-beam.
[0017] FIG. 5 shows a schematic representation of an exemplary
embodiment of an arch x-ray radiation source with a cone-beam.
[0018] FIG. 6 shows a schematic representation of an exemplary
embodiment of an area x-ray radiation source with a
pencil-beam.
[0019] FIG. 7 shows a schematic representation of an exemplary
embodiment of a CT system with a linear x-ray radiation source
rotated about a stationary stage.
[0020] FIG. 8 shows a schematic representation of an exemplary
embodiment of a CT system with a circular x-ray radiation source
positioned about a stationary stage.
[0021] FIG. 9 shows a schematic representation of an exemplary
embodiment of an x-ray radiation source that can be operated in a
computed tomography mode and a single projection mode
[0022] FIG. 10 shows a schematic representation of an exemplary
embodiment of a CT system with a ring target, the electron beam
strikes the target by reorienting the electron beam source and/or
by steering the electron beam.
DETAILED DESCRIPTION
[0023] The x-ray systems and x-ray imaging methodologies for
computed tomography disclosed herein are based on our previous
disclosures, including U.S. Pat. No. 6,553,096 to Zhou et al.
entitled "X-RAY GENERATING MECHANISM USING ELECTRON FIELD EMISSION
CATHODE", U.S. Pat. No. 6,876,724 to Zhou et al. entitled
"LARGE-AREA INDIVIDUALLY ADDRESSABLE MULTI-BEAM X-RAY SYSTEM AND
METHOD OF FORMING SAME", and U.S. Pat. No. 6,850,595 to Zhou et al.
entitled "X-RAY GENERATING MECHANISM USING ELECTRON FIELD EMISSION
CATHODE", the entire disclosures of all these applications are
herein incorporated by reference. U.S. Pat. No. 6,553,096 discloses
an x-ray generating device incorporating a nanostructure-containing
material. U.S. Pat. No. 6,876,724 discloses a structure to generate
x-rays having a plurality of stationary and individually
electrically addressable field emissive electron sources with a
substrate composed of a field emissive material, such as carbon
nanotubes, that can be electrically switched at a predetermined
frequency to field emits electrons in a programmable sequence.
[0024] An exemplary embodiment of a computed tomography device
comprises an x-ray source and an x-ray detecting unit. FIG. 1 shows
a schematic representation of an exemplary x-ray radiation source
100. The x-ray source 100 includes a cathode 102 with a plurality
of individually programmable electron emitting units 104 that each
emit an electron 106 upon an application of an electric field (E),
an anode target 108 that emits an x-ray 110 upon impact by the
emitted electron 106, and a collimator 112.
[0025] In exemplary embodiments, the electron emitting unit 104
includes an electron field emitting material. For example, the
electron field emitting material can include a nanostructured
material. In a further example, the electron field emitting
material includes a plurality of nanotubes or a plurality of
nanowires. The nanotubes can include inorganic materials. For
example, the nanowires can include at least one field emitting
material selected from the group consisting of carbon, boron,
nitrogen, sulfur, and tungsten. The nanowires can included at least
one field emitting material selected from the group consisting of
silicon, germanium, carbon, oxygen, indium, cadmium, gallium,
oxide, nitrides, silicides and boride. The nanowires can be
fabricated by a variety of techniques including chemical vapor
deposition, solution synthesis, and laser ablation. The paper by J.
Hu, et al., "Chemistry and Physics in One Dimension: Synthesis and
Properties of Nanowires and Nanotubes", Accounts of Chemical
Research, Vol. 32, pages 435-445, 1999, the entire content of which
is incorporated herein by reference, describes some of these
fabrication methods.
[0026] The cathode 102 can include one or more individually
programmable and/or addressable electron emitting units 104
arranged on a support structure 114. In an exemplary embodiment,
the electron emitting unit 104 is one or more electron emitting
pixels. The electron emitting pixels can be any suitable electron
source. In an exemplary embodiment, the electron emitting pixels
are electron field emission sources, such as electron field
emitting materials including a plurality of single-wall carbon
nanotubes (SWNT), a plurality of multi-wall carbon nanotubes
(MWNT), a plurality of double-wall carbon nanotubes (DWNT), or a
mixture thereof. Examples of suitable electron field emission
sources include the carbon nanotube based electron field emission
sources disclosed in U.S. Pat. No. 6,630,772 to Bower et al.
entitled "DEVICE COMPRISING CARBON NANOTUBE FIELD EMITTER STRUCTURE
AND PROCESS FOR FORMING DEVICE", the entire disclosure of which is
incorporated herein by reference, which discloses a carbon
nanotube-based electron emitter structure, U.S. patent application
Ser. No. 09/351,537 entitled "DEVICE COMPRISING THIN FILM CARBON
NANOTUBE ELECTRON FIELD EMITTER STRUCTURE", the entire disclosure
of which is incorporated herein by reference, which discloses a
carbon-nanotube field emitter structure having a high emitted
current density, U.S. Pat. No. 6,277,318 to Bower et al. entitled
"METHOD FOR FABRICATION OF PATTERNED CARBON NANOTUBE FILMS", the
entire disclosure of which is incorporated herein by reference,
which discloses a method of fabricating adherent, patterned carbon
nanotube films onto a substrate, U.S. Pat. No. 6,553,096 to Zhou et
al. entitled "X-RAY GENERATING MECHANISM USING ELECTRON FIELD
EMISSION CATHODE", the entire disclosure of which is incorporated
herein by reference, which discloses an x-ray generating device
incorporating a nanostructure-containing material, U.S. Pat. No.
6,965,199 to Stoner et al. entitled "COATED ELECTRODE WITH ENHANCED
ELECTRON EMISSION AND IGNITION CHARACTERISTICS", the entire
disclosure of which is incorporated herein by reference, which
discloses an electrode including a first electrode material, an
adhesion-promoting layer and a carbon nanotube-containing material
disposed on at least a portion of the adhesion promoting layer, as
well as associated devices incorporating such an electrode, and
U.S. Pat. No. 6,787,122 to Zhou entitled "METHOD OF MAKING
NANOTUBE-BASED MATERIAL WITH ENHANCED ELECTRON FIELD EMISSION
PROPERTIES", the entire disclosure of which is incorporated herein
by reference, which discloses a technique for introducing a foreign
species into the nanotube-based material in order to improve the
emission properties thereof.
[0027] Preferably the electron emitting pixels can be controlled
individually, e.g., each electron emitting pixel can be individual
electrically addressed and a controller can supply an electronic
field to the electron emitting pixel in any desired manner, such as
individually, as a group or plurality, in a specified sequence or
pattern, or randomly. A suitable method of individual control is
disclosed in U.S. Pat. No. 6,876,724, the entire contents of which
is hereby incorporated by reference. U.S. Pat. No. 6,876,724
discloses individual control by electrically switching the field
emissive electron sources at a predetermined frequency to field
emit electrons in a programmable sequence toward an incidence point
on a target and to thereby generate x-rays corresponding in
frequency and in position to that of the field emissive electron
source. Other suitable methods of control are disclosed in U.S.
Pat. No. 6,553,096 and in U.S. Pat. No. 6,850,595, the entire
content of each is hereby incorporated by reference. Other examples
of individual control are disclosed in Brodie and C. A. Spindt,
"Vacuum Microelectronics," Advances in Electronics and Electron
Physics, vol. 83, p. 1-106 (1992).
[0028] The x-ray source can further comprise a gate electrode. The
exemplary embodiment of an x-ray source 100 shown in FIG. 1
includes a gate electrode 116 located between the cathode 102 and
the anode target 108. The gate electrode 116 can extract the
emitted electron 106 from one or more of the plurality of
individually programmable electron emitting units 104 when the
electrical field is applied between the gate electrode 116 and the
one or more individually programmable electron emitting units 104.
For example, the electrical field can be applied such that the gate
electrode 116 is at a positive potential with respect to the one or
more of the plurality of individually programmable electron
emitting units 104. The field strength of the electrical field can
be from 0.1 Volt/.mu.m (V/.mu.m) to 100 V/.mu.m, preferably from
0.5 V/.mu.m to 20 V/.mu.m. At least one of the plurality of
individually programmable electron emitting units has an emission
threshold of less than 3 V/.mu.m for greater than 0.01 mA/cm.sup.2
current density, preferably greater than 0.1 mA/cm.sup.2 current
density, and emits 0.1-100 mA total current. In an exemplary
embodiment, the emission current is approximately less than or
equal to 100 .mu.A per nanotube at an electrical field of less than
100 V/.mu.m.
[0029] FIG. 2 shows current density (A/cm.sup.2 ) as a function of
voltage for carbon nanotube cathodes having a gap distance between
62 .mu.m and 280 .mu.m. As the gap distance decreases, the current
density also decreases. Table 1 summarizes values of current
density for a given electrical field. The values in FIG. 2 and
Table 1 are merely examples, and values may vary significantly,
depending on the sample preparation and how the measurement is
performed. TABLE-US-00001 TABLE 1 Emission Characteristics for the
Cathode Current Density (mA/cm.sup.2) Electrical Field (V/.mu.m) 1
2 10 2.5 100 4 700 5.3
[0030] The emission current-voltage (1-V) characteristics of the
single-wall carbon nanotube film shown in FIG. 2 and Table 1 were
measured using a hemispherical current collector with a 1
millimeter (mm) diameter (anode) at 5.times.10.sup.-8 Torr base
pressure and different anode-cathode gap distances. As shown in the
FIG. 2 and the inset to FIG. 2, the carbon nanotube film exhibits
the classic Fowler-Nordheim behavior with a threshold field of 2
V/.mu.m for 1 mA/cm.sup.2 current density. The effective emission
area was calculated using a previously described method as
disclosed in W. Zhu, C. Bower, O. Zhou, G. P. Kochanski, and S.
Jin, Appl. Phys. Left., vol. 75, p. 873, (1999), the entire
contents of which are herein incorporated by reference. The
corresponding electric fields for various electron current
densities are listed in Table 1. Emission current density over 1
A/cm.sup.2 was readily achieved.
[0031] The emission material was purified single-wall carbon
nanotube (SWNT) bundles that were produced by the laser ablation
method, as disclosed in O. Zhou, H. Shimoda, B. Gao, S. J. Oh, L.
Fleming, and G. Z. Yue, "Materials Science of Carbon Nanotubes:
Fabrication, Integration, and Properties of Macroscopic Structures
of Carbon Nanotubes", Acc. Chem. Res, vol. 35 p. 1045-1053 (2002),
the entire contents of which are herein incorporated by reference.
The emission material contains approximately 95-wt. % SWNT bundles
with an average SWNT diameter of 1.4 nanometers (nm) and a bundle
diameter of approximately 50 nm. Uniform SWNT film were coated on a
flat metal disc by electrophoretic deposition, substantially
similar to that disclosed in U.S. patent application Ser. No.
09/996,695, the entire contents of which are herein incorporated by
reference. To increase the adhesion between the SWNT coating and
the substrate, an iron inter-layer was first deposited on the
substrate surface by either thermal evaporation or electrochemical
plating before nanotube deposition, substantially similar to that
disclosed in U.S. Pat. No. 6,277,318, the entire contents of which
are herein incorporated by reference. The thickness and packing
density of the nanotube film were controlled by the current,
deposition time and the concentration of the nanotube suspension.
The films were vacuum annealed at 800.degree. C. before use.
[0032] An exemplary embodiment of a computed tomography device also
includes an x-ray detecting unit 118. Any x-ray detecting unit can
be used. For example, the x-ray detecting unit can include an x-ray
scintillation material and a digital imaging acquisition device. A
suitable digital imaging acquisition device includes a
charge-coupled-device (CCD) or a solid state based or gaseous based
imaging device. In addition, the computed tomography device can
have a control system between the x-ray detecting unit and a
controller, a storage device, or a combined controller/storage
device 120 for data collection, storage and reconstruction. The
digital imaging acquisition device digitally records the x-ray
intensity of the x-ray radiation. Depending on the size and
orientation of an object being imaged, e.g, an object located on an
object support stage, each beam of x-ray radiation can pass
through, e.g, transmission x-ray source, or can reflect from, e.g.,
reflection x-ray source, a portion of the object. The x-ray
radiation is then detected by the corresponding x-ray detecting
unit.
[0033] FIG. 3 is a schematic representation of an exemplary
embodiment of a collimated monochromatic x-ray radiation source
300. The collimated monochromatic x-ray radiation source 300
includes an x-ray source 302 and an x-ray detecting unit 304, both
of which can be substantially similar to that described herein with
respect to FIG. 1. In addition, the collimated monochromatic x-ray
radiation source 300 includes a monochromator 306 placed in a path
of the emitted x-ray 308 after the collimator 310. An example of a
suitable monochromator includes a crystal that selects an x-ray
photon with a certain energy. Examples of suitable crystals include
a single crystal of graphite or silicon (Si). The energy of the
outgoing x-ray beam is selected by the diffraction conditions. A
particular diffraction angle is chosen to produce a diffracted beam
with a predetermined energy. By choosing different diffraction
angles, monochromatic x-ray beams with different energies can be
selected.
[0034] An exemplary embodiment of a computed tomography system can
have an x-ray source having any suitable geometry for directing a
desired form of an x-ray beam toward an object of interest, such as
medical applications for a patient or an animal and industrial and
inspection applications such as for a structure or a container. For
example, an x-ray source can be a linear, an arched, and/or an area
x-ray source.
[0035] FIG. 4 is a schematic representation of an exemplary
embodiment of a computed tomography device. The computed tomography
device 400 comprises a linear scanning x-ray source 402, an object
support stage 404, and a detector 406. The linear scanning x-ray
source 402 comprises a cathode 408 and an anode target 410 and a
collimator 412. The cathode 408 includes an array of individually
programmable electron emitting units 414 arranged on a support
structure 416.
[0036] A suitable arrangement of the plurality of individually
programmable electron emitting units 414 includes arrangement
linearly on an axis in a plane. Each individually programmable
electron emitting unit is focused at one of a plurality of focal
spots on the anode target 410.
[0037] The linear scanning x-ray source can have either
transmission geometry or reflection geometry. In an example of a
linear scanning x-ray source with a transmission geometry, the
anode is a metal film which can be either free-standing or
deposited on a low-atomic number material, such as carbon. The
anode is at a higher electrical potential with the cathode. In one
particular example, the anode is electrically grounded. A negative
potential is applied to the cathode. A gate electrode, can be
included in the x-ray source and can be at a positive potential
with respect to the cathode to extract the electrons from the
cathode.
[0038] In one particular example, all of the programmable electron
emitting units are at the same potential. Each programmable
electron emitting unit has a corresponding gate electrode.
Electrons are extracted from a particular programmable electron
emitting unit when the electrical field established between said
unit and the corresponding gate exceeds a critical value (for
example 3V/.mu.m or less).
[0039] In another exemplary embodiment, the distance between the
anode and the cathode is such that the electrical field due to the
anode voltage is sufficient to extract the filed-emitting electrons
from the cathode. In this embodiment, a reverse bias voltage is
applied on the gate electrode to suppress electron emission from
certain emitting units. This reverse bias voltage is scanned across
the gate electrode to suppress a first group of electron filed
emitting units and/or to activate a second group of programmable
electron emitting units.
[0040] Each individually programmable electron emitting unit
comprises a layer of electron field emitting material. Individual
or groups of electron field emitting material in the layer can form
an array or matrix or pattern of electron emitting pixels. In the
exemplary embodiment of FIG. 4, the electron field emitting
material is a layer of carbon nanotubes, but any suitable field
emitting material can be used including nanostructured material and
nanotubes and nanowires as substantially described herein with
respect to FIGS. 1 and 3. For example, a layer of carbon nanotubes,
e.g., single-walled nanotubes, multi-walled nanotubes,
double-walled nanotubes, or mixtures thereof. The field emitters
can also be lithographically formed Spindt-type tips.
[0041] Under an applied potential between the cathode 404 and a
gate electrode 418, electrons 420 are emitted from the each of the
electron emitting units 414. The field emission of electrons from
the array of electron emitting units can be from a single pixel, a
group of pixels, either randomly arranged or in a pattern, or all
the pixels, as determined by the controlled application of the
applied potential. For example, a bias potential applied between
the gate and the cathode extracts electrons. A large, e.g. on the
order of 10 to 200 KV/cm or greater, electrical voltage is further
established between the gate and the anode to accelerate the
emitted electrons to the desired energy level. The emitted
electrons from the electron emitting units are accelerated and
impinge on the anode target 410, for example, each at a
corresponding x-ray emitting pixel. An example of an x-ray emitting
pixel includes a thin layer of metal target material, such as
copper (Cu) and tungsten (W), a heat dissipating target supporting
material. X-ray radiation 422 is emitted from the anode when it is
bombarded by the electrons, e.g., the anode is a target for the
accelerated electrons. The emitted x-ray radiation passes through
the collimator 412 and optionally a monochromator (not shown in
FIG. 4). The collimator 412 enables each x-ray emitting pixel to
generate a particular geometry of x-ray radiation 422, such as an
uniform fan beam geometry. However, any suitable geometry of x-ray
radiation 420 can be formed, including a pencil beam geometry or a
cone beam geometry.
[0042] The computed tomography device 400 has an x-ray detector
406. An exemplary x-ray detector 406 comprises a plurality of x-ray
detecting units 424. Each x-ray detecting unit 424 includes x-ray
scintillation materials and a digital imaging acquisition device,
such as a charge-coupled-device (CCD) or a solid state based or
gaseous based imaging device. The digital imaging acquisition
device digitally records the x-ray intensity of the x-ray radiation
422. Depending on the size and orientation of an object 426 on the
object support stage 404, each beam of x-ray radiation 422 can pass
through, e.g, transmission x-ray source, or can reflect from, e.g.,
reflection x-ray source, a portion of the object 426. The x-ray
radiation 422 is then detected by the corresponding x-ray detecting
unit 424.
[0043] In the exemplary embodiment illustrated in FIG. 4, the x-ray
detector includes a two-dimensional matrix of x-ray detecting
units. The detection scheme depends on the type of x-ray beams
generated by the linear x-ray source. In one embodiment, an x-ray
beam with fan-beam geometry is produced from each focal spot on the
anode. The fan beam illuminates a slice of the object 426. The
illuminated area is defined by the geometry of the collimator used.
The intensity of the x-ray beam from a particular focal spot
passing through the object is measured by a pre-selected set of
x-ray detection units on the x-ray detector. Each focal spot is
associated with a set of x-ray detection units on the x-ray
detector.
[0044] To collect the images of the object, two modes can be used.
In one mode, the electron emitting units are activated one by one
to produce an x-ray beam from the anode that is moving through the
focal spots sequentially. During scanning, the corresponding x-ray
detection unit on the x-ray detector is also switched on to record
the image from a particular x-ray beam, e.g., switched on
sequentially or one-by-one. In another mode, all the electron
emitting units are turned on at the same time. The x-ray detecting
units are also switched on at the same time to collect and/or
record the images of the object.
[0045] In another embodiment, the collimators are designed such
that x-ray radiation with cone-beam geometry is generated from each
focal spot. In this case, the electron emitting units are activated
sequentially or one-by-one. When a particular unit is turned on, a
cone-beam x-ray is generated from the corresponding focal spot on
the anode. The x-ray beam illuminates the entire object 426. The
image of the object formed by this particular x-ray beam is
collected and/or recorded by the entire x-ray detector. The image
is then stored in, for example, a computer. The next electron
emitting unit in the sequence is then switched on to generate
another image of the entire object, from a different projection
angle. The process repeats for all, or a subset of all, the
emitting units in the x-ray source.
[0046] FIG. 5 shows a schematic representation of an exemplary
embodiment of a computed tomography device 500 with a linear
scanning x-ray source 502 arranged as an arch x-ray source. The
x-ray source 502 generates a particular geometry of x-ray radiation
504, such as a cone beam geometry. However, any suitable geometry
of x-ray radiation 504 can be formed by selection of a suitable
collimator, including a pencil beam geometry or a fan beam
geometry. In the exemplary embodiment shown in FIG. 5, the computed
tomography device 500 includes a linear scanning x-ray source 502,
an object rotation stage 506, and a detector 508. The linear
scanning x-ray source 502 includes a series of cathodes 510 and
corresponding anode targets 512 lining the arched-shaped support
structure 514. The x-ray source 502 and x-ray detecting unit 508
can be substantially similar to that described herein with respect
to the x-ray source and x-ray detecting unit of FIGS. 1 and 3.
[0047] The arched-shaped support structure 514 is constructed such
that each focal spot on the anode is at an equal distance from the
center of an object rotation stage, e.g., from a center of rotation
of an object stage or from a central rotation axis of the object
stage. Further, in a preferred case, the two-dimensional detector
has a curved surface so that each detecting unit is also
equidistant to the object.
[0048] The computed tomography device 500 in FIG. 5 has an x-ray
detector 508. As described herein, the x-ray detecting unit can be
of any suitable type and/or any suitable arrangement, based on the
geometric form of the x-ray radiation generated by the x-ray
source. Similar to the geometry described above, the preferred
geometry of the detector surface is a curved one so that each
detecting unit is equidistance to the object. An exemplary x-ray
detector 508 comprises a plurality of x-ray detecting units 516.
Each x-ray detecting unit 516 includes x-ray scintillation
materials and a digital imaging acquisition device, such as a
charge-coupled-device (CCD) or a solid state based or gaseous based
imaging device. The digital imaging acquisition device digitally
records the x-ray intensity of the x-ray radiation 504. Depending
on the size and orientation of an object 518 on the object support
stage 506, each beam of x-ray radiation 504 can pass through, e.g,
transmission x-ray source, or can reflect from, e.g., reflection
x-ray source, a portion of the object 518. The x-ray radiation 504
is then detected by the corresponding x-ray detecting unit 516.
[0049] FIG. 6 shows a schematic representation of an exemplary
embodiment of a computed tomography device 600. The computed
tomography device 600 includes an area scanning x-ray source 602,
an object rotation stage 604, and a detector 606. The linear
scanning x-ray source 602 includes a series of cathodes 608 and
corresponding anode targets 610 lining the planar-shaped support
structure 612. The x-ray source 602 and x-ray detecting unit 606
can be substantially similar to that described herein with respect
to FIGS. 1 and 3. The computed tomography device 600 has an area
linear scanning x-ray source 602 arranged as a planar x-ray source
generating a particular geometry of x-ray radiation 614, such as a
pencil beam geometry. However, any suitable geometry of x-ray
radiation 614 can be formed by selection of a suitable collimator,
including a cone beam geometry or a fan beam geometry. In the
exemplary embodiment shown in FIG. 6, The individually programmable
electron emitting units of the cathode are arranged over an area of
the planar-shaped support structure and each individually
programmable electron emitting unit is focused at one of a
plurality of focal spots on the anode target 610.
[0050] The computed tomography device 600 in FIG. 6 has an x-ray
detector 606. As described herein, the x-ray detecting unit can be
of any suitable type and/or any suitable arrangement, based on the
geometric form of the x-ray radiation generated by the x-ray
source. An exemplary x-ray detector 606 comprises a plurality of
x-ray detecting units 616. Each x-ray detecting unit 616 includes
x-ray scintillation materials and a digital imaging acquisition
device, such as a charge-coupled-device (CCD) or a solid state
based or gaseous based imaging device. The x-ray detecting units
can be suitably arranged, such as in a matrix or an array. The
digital imaging acquisition device digitally records the x-ray
intensity of the x-ray radiation 614. Depending on the size and
orientation of an object 618 on the object support stage 604, each
beam of x-ray radiation 614 can pass through, e.g, transmission
x-ray source, or can reflect from, e.g., reflection x-ray source, a
portion of the object 618. The x-ray radiation 614 is then detected
by the corresponding x-ray detecting unit 616.
[0051] A method to operate a computed tomography device includes
applying an electric field to at least a first of a plurality of
individually programmable electron emitting units. Applying the
electric field causes the emission of an electron. The emitted
electron is focused at one of a plurality of focal points on an
anode target. the emitted electron impacts the anode target to form
an emitted x-ray radiation, which is collimated to a geometry, such
as a cone beam geometry, a pencil beam geometry, or a fan beam
geometry, and passed through an object. The x-ray radiation is then
detected by an x-ray detecting unit and recorded.
[0052] The method can be repeated to produce multiple detected
x-ray radiation images without rotating the object positioned on
the object stage. For example, each of the plurality of
individually programmable electron emitting units of the x-ray
source can be operated in a particular sequence or operated as a
group in a particular pattern to produce an emitted x-ray that
illuminates the object in the computed tomography device from a
different angle, plane, or other orientation. Accordingly, by
repeating the steps of applying, focusing, impacting, collimating,
passing, detecting, and recording with respect to a particular
sequence or grouping of individually programmable electron emitting
units, multiple detected x-ray radiation images can be produced.
For example, during the repetition of the operation of the computed
tomography device, the electric field is applied to at least a
second individually programmable electron emitting unit. Further,
the emitted electrons are focused on a second of the plurality of
focal points on the anode target when the step of focusing is
repeated.
[0053] The step of collimating can produce an x-ray radiation beam
of a particular geometry. For example, the collimator can be
selected such that the emitted x-ray radiation is collimated to
produce a fan beam geometry of x-ray radiation, a pencil beam
geometry of x-ray radiation, or a cone beam geometry of x-ray
radiation. Each of these x-ray radiation beam geometries has an
associated imaging technique, such as a magnified stereo projection
image, a parallel projection image, or projection images from
different viewing angles for reconstruction of three-dimensional
images.
[0054] During the method of operating a computed tomography device,
an electric field is applied between the cathode and a gate
electrode. The gate electrode is at a positive potential with
respect to the individually programmable electron emitting units of
the cathode. An exemplary field strength of the electric field is
from 0.1 V/.mu.m to 100 V/.mu.m, preferably from 0.5 V/.mu.m to 20
V/.mu.m. The application of the electric field accelerates the
emitted electrons to a given energy.
[0055] In another exemplary method, the electric field is
established between the gate electrode and at least two of the
plurality of individual programmable electron emitting unit
sequentially. The electric field is established one individually
programmable electron emitting unit or a group of individually
programmable electron emitting units at a given time, from a first
location on the cathode to a second location on the cathode. The
applied electrical field has a predetermined frequency and pulse
width. The frequency determines how many times per second the
electrical field is switched on. There is a no limitation on the
frequency. For example, the frequency can be in the range of
0.01-10.sup.6 Hz. The pulse width determines the dwell time when
the field is switched on. Again there is no limitation on the dwell
time. For example, it can be in the range of one micro-second to
one minute. At each sequential establishment of the electric field,
a view of the object is illuminated and an x-ray image is
collected. Thus, over the sequential operation, a plurality of
views of the object is collected.
[0056] In another exemplary method of operating a computed
tomography device, an electrical field is established between the
gate electrode and at least two of the plurality of individually
programmable electron emitting units. The electrical field is
established sequentially, one individually programmable electron
emitting unit at a given time or a group of individually
programmable electron emitting units, from a first location on the
cathode to a second location on cathode at a given sweep rate. For
example, the sweep rate can be in the range of 0.01 Hz to 10.sup.6
Hz. The sequential establishment of the electrical field
illuminates the object and produces a plurality of views that are
subsequently collected for later retrieval and/or analysis.
[0057] In one particular embodiment of this subject matter, the
frequency and pulse width of the electrical field applied to the
gate electrode is synchronized with the data collection time of the
x-ray detector. The x-ray radiation is generated only when the
x-ray detector is collecting data. Synchronization of x-ray
generation and data collection can significantly reduce the amount
of unnecessary radiation dosage the object receives during
imaging.
[0058] In yet another embodiment of the subject matter, the
frequency and the pulse width of the electrical field applied to
the gate electrode and thus the frequency and the pulse width of
the x-ray produced are synchronized with either a physiological
signal, an internal signal from the object, or an external signal
source. For example, the frequency and the pulse width of the x-ray
generated can be gated by the cardiac or respiratory signals to
obtain clear images of moving object.
[0059] For a given object orientation, an x-ray radiation having a
cone beam geometry originates from different focal points impinging
on the object from different angles. The corresponding
two-dimensional projection images are different. This is because
the x-ray beams originate from different points in space and have
different projection angles. As a result, by collecting a large
number of images from a wide viewing angle range, internal
structure of the object can be obtained. Thus, in one sweep over
the linear x-ray sources, multiple two-dimensional images are
acquired in short time without rotating the object. This greatly
increases the image acquisition speed.
[0060] To produce a scanning x-ray beam, a pulsed electrical field
between the gate and the cathode is swept through the emitting
pixels at a given speed. The field is set at a value such that each
pixel will emit a certain current for a given duration and in a
given sequence, which is determined by the pulse width of the
sweeping field. During this process, the voltage between the anode
and the gate remains at a constant value. When the electrons
impinge on the anode, x-ray radiation emits from the point of
impact. As the electrical field sweeps through the cathode, the
origin of the x-ray radiation sweeps through the surface of the
anode.
[0061] The pulse-width, frequency and sweep rate of the electrical
field on the gate are synchronized with the electronics that
control the detector such that the images collected are in registry
with the positions of the focal points. For example, a controller
can synchronize the electric field and the detector.
[0062] During operation of an exemplary computed tomography device,
the x-ray radiation from the x-ray source illuminates an object
which is supported on the object support stage. The object support
stage of an exemplary computed tomography device can be either
stationary or can be rotated through a pre-determined set of
angles. One example of a computed tomography system using a single
beam x-ray source and a rotating sample stage is contained in M. D.
Bentley, M. C. Ortiz, E. L. Ritman, and J. C. Romero, "The Use of
Microcomputed Tomography to Study Microvasculature in Small
Rodents," AJP Regulatory Integrative Comp Physiol, 282, R1267-R1279
(2002), the entire content of which is incorporated herein by
reference.
[0063] In another method to operate a computed tomography, the
object is positioned on an object stage and is rotated through a
set of angles. After each rotation of the object, the steps of
applying, focusing, impacting, collimating, passing, detecting, and
recording are repeated to obtain a series of detected x-ray
radiation images. The x-ray radiation images can then be
reconstructed to form a three-dimensional volume of the object. For
example, the detected x-ray radiation images can be reconstructed
using an image reconstruction algorithm to form the
three-dimensional volume of the object. For example, the cone-beam
reconstruction algorithm developed by Feldkamp, et al. in L. A.
Feldkamp, L. C. Davis, and J. W. Kress, "Practical cone-beam
algorithm", J. Opt. Soc. Am., vol.1,612-619 (1984), the entire
content of which is herein incorporated by reference can be
modified for such purpose.
[0064] The exemplary computed tomography system operates in two
different modes. In a first mode, e.g., the computed tomography
mode, the source and detector are rotated about the object,
generating a set of three-dimensional cone beam projections for
reconstruction into an image. In a second mode, a series of
two-dimensional images are acquired from a single projection,
resembling a fluoroscopy unit. As the two-dimensional projection
direction is known, it may be mapped into the three-dimensional
projection from the first mode, allowing localization of
objections. Multiple array source elements may be utilized to
spatially localize objects of interest.
[0065] For example, the object support stage is set to a first
angle and all cathodes of the x-ray source are turned on
simultaneously to generate a linear set of x-ray radiation beams.
Each x-ray detecting unit records an image, such as a projection
image of a slice of the object. All images are combined digitally,
to form a two-dimensional image of the object for the given angle
of the x-ray source. Thus, all slice projections are combined. The
object support stage is then set to a second angle and the process
of acquiring an image repeated. By rotating the stage, a plurality
of two-dimensional images (such as 360 images, one each for 1
degree rotation of the sample) of a sample are obtained. The images
can be combined in real time, or can be electronically stored for
later combination.
[0066] To obtain a set of three-dimensional images of the object,
the object is rotated through a set of angles, such as 30, 60, or
90 degrees. A new set of images are taken after each rotation. Only
a few rotations are needed to obtain the sets of images needed to
reconstruct the three-dimensional volume of the objects. The radial
resolution may also be increased by rotating the object by smaller
angles, such as 5, 10, or 15 degrees.
[0067] The x-ray source and detector are rotated about the object
stage, which is stationary and on which a object is mounted. Image
acquisition may be performed in a continuous manner with the x-ray
source continuously rotating about the object. Finer radial
resolution may be achieved by performing multiple acquisitions at
each rotational angle with or without selectively pulsing each
x-ray source.
[0068] Multiple exemplary embodiments of a computed tomography
device are possible. These exemplary embodiments incorporate some
or all of the features previously discussed herein.
[0069] An exemplary embodiment of a computed tomography device is
shown in FIG. 7. The computed tomography device 700 comprises a
circular x-ray source 702, an object stage 704, and a circular
detector 706. The circular x-ray source includes an array of x-ray
producing elements facing the center of a source circle. The
detectors are in a similar arrangement, e.g., in a detector circle,
positioned adjacent the source circle. By controlling each of the
circular x-ray sources individually, multiple slice projections can
be produced without rotation of the detectors or x-ray source or
with only a slight rotation e.g., 15 degrees or less. The slight
rotation may be incorporated into either the source or the
detectors to provide increased radial resolution. In this
embodiment, near instantaneous single slice imaging can occur
limited only by the switching rate of the x-ray source, which can
be 10.sup.6 Hz or higher, and the time necessary to acquire a
projection, which depends on the sensitivity of the detector and
the x-ray flux produced pulse but can be as short as a
micro-second. In contrast, current medical computed tomography
setups can require at least 250 to 500 msec to acquire a single
slice.
[0070] Another exemplary embodiment of a computed tomography device
is shown in FIG. 8. The computed tomography device 800 comprises an
electron beam source 802, an object stage 804, an area detector
806. The circular x-ray source consists of an array of the x-ray
producing elements facing the center of a circle. The detectors are
in a similar arrangement positioned adjacent the source circle. By
controlling each of the x-ray sources individually, multiple slice
projections may be produced, requiring no rotation of the detectors
or x-ray source. A slight (15 degrees or less) rotation may be
incorporated into either the source or the detectors to provide
increased radial resolution. This setup allows near instantaneous
single slice imaging, limited only by the switching rate of the
x-ray source and the time necessary to acquire a projection. The
current medical CT setups require at least 250 to 500 msec to
acquire a single slice.
[0071] Another exemplary embodiment of a computed tomography device
is shown in FIG. 9. The computed tomography device 900 comprises an
electron beam source 902, an object stage 904, an area detector
906. The system is designed to operate in two different modes.
First, is the computed tomography mode, where the source and
detector are rotated about the object, generating a set of 3-D cone
beam projections for reconstruction. The second mode, the system
acquires a series of 2-D images from a single projection,
resembling a fluoroscopy unit. As the 2-D projection direction is
known, it may be mapped into the 3-D projection that was measured
first, allowing localization of objections. Multiple array source
elements may be utilized to spatially localize objects of
interest.
[0072] Another exemplary embodiment of a computed tomography device
is shown in FIG. 10. The computed tomography device 1000 comprises
an electron beam source 1002, an object stage 1004, an area
detector 1006 and a stationary tungsten ring 1008. The source of
electrons, e.g., a field emission cathode, may be physically
pointed or magnetically steered at the stationary tungsten ring
that surrounds the object stage. Electrons from the electron source
strike the stationary tungsten ring and generate x-ray photons that
are directed back at the object. Multiple projections of the x-ray
may be realized by mechanically moving the electron source such
that the electron beam is directed to different locations of the
stationary x-ray target ring, e.g., the tungsten ring. The object
remains stationary, as does the detector. A high voltage is applied
between the cathode and the target ring to accelerate the electrons
to the desired energy.
[0073] In exemplary embodiments, imaging techniques associated with
computed tomography acquisition can be used. However, additional
imaging techniques are available through the exemplary embodiments
of a computed tomography device described herein. For example,
traditional medical computed tomography techniques have required
that the x-ray computed tomography tube be turned on in a
continuous manner when circling around the patient. However, the
nanotube based x-ray source allows tight switching control of the
x-ray source, enabling more sophisticated imaging patterns. For
example, instead of the traditional circular path of the imaging
x-ray source, a star shaped pattern may be utilized, sequentially
activating sources on opposite sides of the ring. Furthermore, the
ability to provide short bursts of x-rays may also reduce exposure
time to the object; bursts are only needed when the source and
detector are positioned at the next angle--the intermediary
position does not need the x-ray to be on. Any reduction of dose is
of great advantage for the patient. Dose reduction may also be
performed at a loss of spatial resolution; by sampling a smaller
number of angles. Reducing the angular sampling may be useful in
creating a rapid computed tomography screening tool. Rapid,
multi-angle computed tomography fluoroscopy also becomes possible,
incorporating the time resolution of a normal fluoroscopy machine,
with the three-dimensional acquisition capability of the computed
tomography. Tight control of the x-ray source allows prospective
cardiac gating, essential in improving the image quality associated
with cardiac imaging. Furthermore, an addressable x-ray source
allows control of the thickness of the imaging slice at the x-ray
source.
[0074] Example applications for the exemplary computed tomography
devices and methods described herein can include, although not
limited to, the following:
[0075] Clinical imaging: Clinical imaging applications, such as
rapid full body or body part specific imaging, portable imaging
units for specific body parts, such as the head for in-field
diagnosis of trauma, stroke, and so forth, dynamic contrast studies
for perfusion of brain, liver and other organs, gated imaging for
moving body parts (lungs, heart, etc.), low dose imaging techniques
for screening or pediatric purposes, fluoroscopy and diffraction
imaging techniques.
[0076] Small animal imaging: Small animal imaging applications,
such as small animal computed tomography for observing anatomical
structure, rapid screening for identifying animal phenotype,
dynamic studies in small animals (with or without contrast
agents.
[0077] Industrial applications: Industrial applications, such as
non-destructive testing and container inspections, e.g., customs
inspections.
[0078] Although the present subject matter has been described in
connection with preferred embodiments thereof, it will be
appreciated by those skilled in the art that additions, deletions,
modifications, and substitutions not specifically described may be
made without department from the spirit and scope of the subject
matter as defined in the appended claims.
[0079] It will be understood that various details of the subject
matter may be changed without departing from the scope of the
subject matter. Furthermore, the foregoing description is for the
purpose of illustration only, and not for the purpose of
limitation.
* * * * *