WO2005109969A2

WO2005109969A2 - Compact x-ray source and panel

Info

Publication number: WO2005109969A2
Application number: PCT/US2005/015794
Authority: WO
Inventors: Stephen E. Sampayan
Original assignee: The Regents Of The University Of California
Priority date: 2004-05-05
Filing date: 2005-05-05
Publication date: 2005-11-17
Also published as: WO2005109969A3

Abstract

A compact, self-contained x-ray source, and a compact x-ray source panel having a plurality of such x-ray sources arranged in a preferably broad-area pixelized array. Each x-ray source includes an electron source (42) for producing an electron beam, an x-ray conversion target, and a multilayer insulator (44) separating the electron source and the x-ray conversion target (46) from each other. The multi-layer insulator preferably has a cylindrical configuration with a plurality of alternating insulator and conductor layers surrounding an acceleration channel leading from the electron source to the x-ray conversion target. A power source is connected to each x-ray source of the array to produce an accelerating gradient between the electron source and x-ray conversion target in any one or more of the x-ray sources independent of other x-ray sources in the array, so as to accelerate an electron bA compact, self-contained x-ray source, and a compact x-ray source panel having a plurality of such x-ray sources arranged in the preferably broad-area pixelized array. Each x-ray source includes an electron source for producing an electron beam, an x-ray conversion target, and a multilayer insulator separating the electron source and the x-ray conversion target from each other. The multi-layer insulator preferably has a cylindrical configuration with a plurality of alternating insulator and conductor layers surrounding an acceleration channel leading from the electron source to the x-ray conversion target. A power source is connected to each x-ray source of the array to produce an accelerating gradient between the electron source and x-ray conversion target in any one or more of the x-ray sources independent of other x-ray sources in the array, so as to accelerate an electron beam towards the x-ray conversion target. The multilayer insulator enables relatively short separation distances between the electron source and the x-ray conversion target so that thin panel is possible for compactness. This id due to the ability of the plurality of alternating insulator and conductor layers of the multilayer insulators to resist surface flashover when sufficiently high acceleration energies necessary for x-ray generation are supplied by the power source to the x-ray sources.

Description

IL-11361 S -104,033 Customer No. 024981

COMPACT X-RAY SOURCE AND PANEL

BY

Stephen E. Sampayan (USA) 1456 Titleist Way Manteca, CA

COMPACT X-RAY SOURCE AND PANEL

[0001] The United States Government has rights in this invention pursuant to

Contract No. W-7405-ENG-48 between the United States Department of Energy

and the University of California for the operation of Lawrence Livermore

National Laboratory.

I. FIELD OF THE INVENTION

[0002] The present invention relates to x-ray generating systems, and more

particularly to a compact x-ray source having a substantially minimized drift

distance, and a thin broad-area x-ray source panel comprising a plurality array of

such compact x-ray sources.

II. BACKGROUND OF THE INVENTION

[0003] Broad beam x-ray sources, such as shown in Figure 1 at reference

character 10, are commonly known, and typically utilize a scanning technique of

a highly collimated electron beam to develop a line or raster scanned pattern. In

particular, these broad beam X-ray sources include a hot filament cathode 11 to

produce electrons, and a positively-charged anode 16, i.e. an x-ray conversion

target such as tungsten, spaced from the cathode to draw and accelerate the

electrons to a specified energy. Between the anode and cathode are focusing and

auxiliary electrodes 12 to focus the electrons into an electron beam 14, and deflection plates 13, e.g. electrostatic or magnetic deflection plates, to scan the

electron beam 14 across the X-ray conversion target 16 as indicated by arrow 15

and generate x-rays from the various scanned locations/ points of the target. The

x-rays generated in this manner can be directed at a subject 17, e.g. a patient or

object, and detected with a suitable detector 18 for imaging the subject. One

example of such an x-ray imaging system using electron beam scanning is shown

in U.S. Pat. No. 6,628,745. Other methods may use mechanical means to move

the x-ray source relative to a detector and object so as to also generate x-rays

from spatially-differentiated locations. In any case, such methods are often used,

for example, in CT scans of luggage, cargo containers and the like for security

and commercial inspection purposes, as well as for use in medical diagnostic

applications.

[0004] The problem, however, with the scanning technique utilized in current

broad-beam x-ray sources is the large and bulky size typically associated with

such systems due to the geometry of the scanning arrangement. Scanning over a

large area x-ray conversion target requires that the electron beam undergo a drift

(i.e. separation distance between cathode and anode) comparable to the longest

dimension of the area to be scanned in order to reach the outer extremities of the

target. Due to this geometric limitation, the dimensions of the vacuum envelope

of the x-ray source (spanning between the hot filament to target) consumes a

significant portion of the overall system size, making the system large, cumbersome, and usually very expensive. And because the expense of such

large-scale/ dimensioned systems is so significant, a designer cannot easily

anticipate the wide variety of objects a user would seek to image, resulting in a

"one-size fits all" mentality in the design and acquisition of such systems, with

the net result being a narrowed use of the technology only by larger institutions.

[0005] What is needed therefore is a small, compact, and relatively inexpensive x-

ray source that can be used in a broad range of settings and for imaging a wide

variety of target subjects/ shapes. Furthermore, what is needed is a compact x-

ray source panel having a simple basic construction which enables complex

panel shapes to be realized for adaptably conforming to a subject to be imaged.

Such an x-ray source and imaging system would be particularly useful in

providing rapid diagnosis, such as for emergency medical response, to determine

what emergency procedure should be implemented.

IV. SUMMARY OF THE INVENTION

[0006] The present invention is generally directed to a compact x-ray source

having an electron source, an x-ray conversion target, and a multilayer insulator

separating the electron source a short distance away from the x-ray conversion

target to establish a short drift distance/ spacing therebetween. Short separation

distances between a cathode and anode can produce surface flashovers in

insulators when high voltage energies are applied therebetween, especially at the high voltages necessary for x-ray production, e.g. 150 kV. The multilayer

insulator used in the present invention is of a type similar to that disclosed in

U.S. Patent No. 6,331,194, designed to inhibit such surface flashover between the

closely spaced electrodes and thereby enable large differences in potential to be

applied therebetweeen (typically over 100 kV/cm). In this manner, the use of the

multilayer insulator enables the substantial reduction of the scale size of a unit x-

ray source into an extremely compact structure which may be 10 to 100 times less

the volume of existing technology, with an attendant reduction in cost.

Similarly, a plurality of such unit x-ray sources arranged as a broad-area array of

an x-ray source panel can also realize substantial reduction in size in that the

panel depth is substantially smaller/ thinner than it is tall or wide.

[0007] One aspect of the present invention includes a compact x-ray source panel

comprising: an array of x-ray sources, each x-ray source comprising: an electron

source; an x-ray conversion target capable of generating x-rays when incidenced

by electrons; and a multilayer insulator having a plurality of alternating insulator

and conductor layers separating the electron source from the x-ray conversion

target; and a power source operably connected to each x-ray source of the array

to produce an accelerating gradient between the electron source and the x-ray

conversion target in any one or more of the x-ray sources, for accelerating

electrons to toward a corresponding x-ray conversion target. [0008] Another aspect of the present invention includes a compact x-ray source

comprising: an electron source; an x-ray conversion target; a multilayer insulator

comprising a plurality of alternating insulator and conductor layers which

separate the electron source from the x-ray conversion target; and a power source

operably connected to the electron source and the x-ray conversion target to

produce an accelerating gradient therebetween, for accelerating electrons toward

the x-ray conversion target.

[0009] And another aspect of the present invention includes a compact x-ray

source panel comprising: a broad-area array of independently controllable x-ray

source pixels, each x-ray source pixel comprising: an electron source for

producing electrons; an x-ray conversion target capable of generating x-rays

when incidenced by electrons; and a cylindrical multilayer insulator having a

plurality of alternating insulator and conductor ring-shaped layers separating the

electron source from the x-ray conversion target, and an evacuated acceleration

channel communicating therebeween; and a power source operably connected to

each x-ray source pixel of the broad-area array to produce an accelerating

gradient in the acceleration channel of any one or more of the x-ray source pixels,

for accelerating electrons through the acceleration channel towards a

corresponding x-ray conversion target, wherein the plurality of alternating

insulator and conductive layers of the multilayer insulators enable a high

resistance to surface flashover in the energy range necessary to produce a sufficiently high accelerating gradient for generating x-rays and with the electron

source and x-ray conversion target in close proximity to each other.

[0010] And another aspect of the present invention includes an x-ray imaging

system comprising: a compact x-ray source panel comprising an array of x-ray

sources, each x-ray source comprising: an electron source; an x-ray conversion

target capable of generating x-rays when incidenced by electrons; and a

multilayer insulator having a plurality of alternating insulator and conductor

layers separating the electron source from the x-ray conversion target; a power

source operably connected to each x-ray source of the array to produce an

accelerating gradient between the electron source and the x-ray conversion target

in any one or more of the x-ray sources, for accelerating electrons to toward a

corresponding x-ray conversion target; a detector capable of detecting x-rays

generated by said compact x-ray source panel; and a controller operably

connected to receive signals from the detector and control the compact x-ray

source panel based upon said signals.

V. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings, which are incorporated into and form a part

of the disclosure, are as follows:

[0012] Figure 1 is a schematic view of a conventional example of x-ray generation

and detection known in the art. [0013] Figure 2 is a schematic side view of an exemplary embodiment of a unit

compact x-ray source of the present invention.

[0014] Figure 3 is a schematic side view of an exemplary planar embodiment of

the broad-area x-ray source panel of the present invention used for scanning an

object.

[0015] Figure 4 is an exploded perspective view of a first exemplary planar

embodiment of the broad-area x-ray source panel of the present invention.

[0016] Figure 5 is an exploded perspective view of a second exemplary planar

embodiment of the broad-area x-ray source panel of the present invention.

[0017] Figure 6 is a schematic side view of an exemplary curviplanar

embodiment of the broad-area x-ray source panel of the present invention.

VI. DETAILED DESCRIPTION

[0018] Turning now to the drawings, Figure 2 shows a preferred embodiment of

a single unit x-ray source of the present invention, generally indicated at

reference character 20. The x-ray source 20 is shown having an electron source

21 for producing electrons, an x-ray conversion target 22 capable of generating

an x-ray beam when incidenced by electrons, an insulator 23 separating the

electron source 21 and the x-ray conversion target 22, and a power supply 26

electrically connected to the electron source 21 (cathode) and x-ray conversion

target 22 (anode) to produce a voltage potential, i.e. an acceleration gradient, in the drift space 24 therebetween which accelerates electrons toward the x-ray

conversion target 22. The electron source 21 is preferably a heated filament

which sputters electrons when hot. In the alternative, various types of electron

sources which are individually controllable may be utilized, such as for example,

thin film ferroelectric emitters, pulsed hybrid diamond field emitters (see for

example U.S. Pat. No. 5,723,954 incorporated by reference herein), diamond

emitters with an added grid structure, or nanofilament field emitters (see for

example U.S. Pat. No. 6,045,678 incorporated by reference herein), etc. And

tungsten or gold is preferably used for the x-ray conversion target. The electron

source is preferably separated from the x-ray conversion target at a distance of

about 2-3 centimeters.

[0019] The insulator 23 is preferably of a type disclosed in U.S. Pat. No. 6,331,194,

incorporated by reference herein, having multiple layers of alternating insulator

and conductor layers, e.g. 25 and 26. In particular, the layers are serially

arranged in stacked succession to span the drift distance (i.e. separation gap)

between the electron source and the conversion target, and preferably formed

using the fabrication methods also disclosed in U.S. Pat. No. 6,331,194.

Preferably the layers have a thickness less than about 1mm, with a combined

thickness of less than about 2-3 cm. Furthermore, the multilayer insulator 23

preferably has a cylindrical configuration with an acceleration channel 24 leading

from the electron source 21 to the x-ray conversion target 22, and the alternating layers having a ring-shaped configuration with a preferably circular cross-

section. Furthermore, because the energies required for x-ray production are

necessarily higher, a supplemental acceleration voltage would be applied across

the multilayer insulator structure. To this end, each x-ray source at least one

intermediate electrode may be provided and positioned between the electron

source and the x-ray conversion target for controlling an electron beam from the

electron source.

[0020] Figures 3 and 4 show a preferred planar embodiment of a compact broad-

area x-ray source panel of the present invention, generally indicated at reference

character 30, and comprising a plurality of the unit compact x-ray sources 31

arranged to form a planar broad-area array. In particular, Figure 3 shows a

schematic side view of the compact x-ray source panel 30, and Figure 4 shows an

exploded perspective view illustrating the component layers forming the panel

30. The component layers include an electron source component layer 41 having

a plurality of unit electron sources 42, a multilayer insulator component layer 43

having a plurality of unit multilayer insulators 44, and an x-ray conversion target

component layer 45 having a plurality of unit x-ray conversion targets 46. Each

unit x-ray source includes a corresponding component in each of the component

layers (one-to-one correspondence), with each independent of other electron

sources, insulators, and x-ray conversion targets. Together, the broad-area

component layers form a thin and compact broad-area panel having a panel depth 37 which is substantially smaller/ thinner than it is tall or wide. A power

source (not shown) is electrically connected to each unit x-ray source to activate

and produce an acceleration gradient in any one or more of the x-ray sources.

[0021] With this arrangement, the plurality of unit x-ray sources 31 may be

activated and controlled, such as with controller 38, independent of other unit x-

ray sources in the array. For example, each of the unit x-ray sources 32-34 are

shown in Figure 3 independently activated to produce respective x-ray cone

beams, represented by rays 32' and 32" for unit x-ray source 32, by rays 33' and

33" for unit x-ray source 33; and by rays 34' and 34" for unit x-ray source 34. In

this manner, spatially differentiated x-ray cone beams are generated and directed

at a subject, such as block 35, and detected at detector 36. It is appreciated that

the unit x-ray sources in the array may be suitably spaced to achieve a desired

operational resolution. In a preferred embodiment, for example, the plurality of

unit x-ray sources may be so closely spaced to produce a pixelized array

comprising a plurality of virtually contiguous x-ray source pixels spanning

across the array.

[0022] Furthermore, the controller 38 shown in Figure 3 may be utilized as part

of a feedback control system to actively control individual source pixels and

selectively generate x-rays to target particular areas of a target subject as

necessitated by the application. The controller 38 is shown connected to the

detector 36 and the broad-area x-ray source panel 30. The active control may be based on feedback criteria, such as signal to noise ratios at the detector. As such,

the compact x-ray source panel of the present invention can be made highly

adaptive to specifically target a wide variety of material densities within the

object. It is appreciated that active control is enabled in part by the use of

individually controllable electron sources, such as the thin film ferroelectric

emitters, pulsed hybrid diamond field emitters, diamond emitters with an added

grid structure, or nanofilament field emitters, etc. previously discussed.

[0023] Figure 5 shows an alternative preferred embodiment of the present

invention, with an electron source component layer 51 having a plurality of unit

electron sources 52, a multilayer insulator component layer 53 having a plurality

of unit multilayer insulators 54 corresponding in number to the unit electron

sources, and a single, monolithic x-ray conversion target 55 which spans across

and serves as the target for all electron source/ multilayer insulator pairs. In this

case, electron beams are independently generated, accelerated, and incidenced

on various sections of the bulk x-ray conversion target to produce spatially-

differentiated x-ray beams.

[0024] Figure 6 shows a curviplanar embodiment of the broad area x-ray source

panel of the present invention, generally indicated at reference character 60. It is

appreciated that "curviplanar" describes a two-dimensional plane contoured in a

curved manner to occupy volumetric space. For example, the curviplanar

configuration of panel 60 may be representative of, for example, a cross-section of a hemispheric configuration or trough-like configuration. Similar to the panel

30 in Figure 3, the panel 60 includes a plurality of unit x-ray sources 61, such as

for example unit x-ray sources 62, 63 and 64, which are located at different

positions of the curviplanar panel. In particular the various positions of the

plurality of unit x-ray sources 61 produce different orientations of the unit x-ray

sources such that the x-ray cone beams are directed at different angles toward a

target subject 65 for detection by detector 66. See for example x-ray cone beams

represented by 62' and 62"; 63' and 63"; and 64' and 64". It is appreciated that

the curviplanar configuration may in the alternative also be constructed into a

complex shape (not shown) to allow adaptation to a principal object type having

an irregular or otherwise arbitrary shape. For example, the curviplanar panel

may be particularly sized and configured to receive a patient's entire head, while

leaving only the face uncovered.

[0025] While the present invention is preferably utilized as a compact x-ray

source and panel, it is appreciated that the reduction in scale advantages is not

limited only for x-ray generation. The technique of the present invention

described above can also be applied using neutrons and positive ions. The ion

source can be made, for example, from a surface flashover ion source, or by

having a gas discharge behind the accelerating structure and using individual

grids to control each pulse to produce the same effect. And for neutron production, the x-ray conversion target discussed above would be replaced with

a deuteriated (i.e. H²) of tritiated (H³) target.

[0026] While particular operational sequences, materials, temperatures,

parameters, and particular embodiments have been described and or illustrated,

such are not intended to be limiting. Modifications and changes may become

apparent to those skilled in the art, and it is intended that the invention be

limited only by the scope of the appended claims.

Claims

I Claim:

1. A compact x-ray source panel comprising: an array of x-ray sources, each x-ray source comprising: an electron source; an x-ray conversion target capable of generating x-rays when incidenced by electrons; and a multilayer insulator having a plurality of alternating insulator and conductor layers separating the electron source from the x-ray conversion target; and a power source operably connected to each x-ray source of the array to produce an accelerating gradient between the electron source and the x-ray conversion target in any one or more of the x-ray sources, for accelerating electrons to toward a corresponding x-ray conversion target.

2. The compact x-ray source panel of claim 1, wherein the x-ray sources are each controllable independent of other x-ray sources.

3. The compact x-ray source panel of claim 1, wherein the multilayer insulator has a cylindrical shape with ring- shaped insulator and conductor layers and an acceleration channel leading from the electron source to the x-ray conversion target.

4. The compact x-ray source panel of claim 1, wherein the insulator layers and conductor layers are each less than 1 mm thick.

5. The compact x-ray source panel of claim 1, wherein the electron source is chosen from the group consisting of: hot filament, field emitter, diamond emitter, hybrid diamond, and nanofilament emitter.

6. The compact x-ray source panel of claim 1, wherein the separation distance between the electron source and the x-ray conversion target is from about two to three centimeters.

7. The compact x-ray source panel of claim 1, wherein each x-ray source further comprises at least one intermediate electrode positioned between the electron source and the x- ray conversion target for controlling an electron beam from the electron source.

8. The compact x-ray source panel of claim 1, wherein the array is a broad-area array of x-ray sources.

9. The compact x-ray source panel of claim 8, wherein the broad-area array has a planar configuration.

10. The compact x-ray source panel of claim 8, wherein the broad-area array has a curviplanar configuration

11. The compact x-ray source panel of claim 10, wherein the broad-area array has a hemispherical configuration.

12. The compact x-ray source panel of claim 10, wherein the broad-area array has a trough-shaped configuration.

13. The compact x-ray source panel of claim 8, wherein the broad-area array is pixelized to comprise a plurality of closely-spaced x-ray source pixels.

14. A compact x-ray source comprising: an electron source; an x-ray conversion target; a multilayer insulator comprising a plurality of alternating insulator and conductor layers which separate the electron source from the x-ray conversion target; and a power source operably connected to the electron source and the x-ray conversion target to produce an accelerating gradient therebetween, for accelerating electrons toward the x-ray conversion target.

15. The compact x-ray source of claim 14, wherein the multilayer insulator has a cylindrical shape with ring- shaped insulator and conductor layers and an acceleration channel leading from the electron source to the x-ray conversion target.

16. The compact x-ray source of claim 14, wherein the insulator layers and conductor layers are each less than 1 mm thick.

17. The compact x-ray source of claim 14, wherein the electron source is chosen from the group consisting of: hot filament, field emitter, diamond emitter, hybrid diamond, and nanofilament emitter.

18. The compact x-ray source of claim 14, wherein the separation distance between the electron source and the x-ray conversion target is from about two to three centimeters.

19. The compact x-ray source of claim 14, further comprising at least one intermediate electrode positioned between the electron source and the x-ray conversion target for controlling an electron beam from the electron source.

20. A compact x-ray source panel comprising: a broad-area array of independently controllable x-ray source pixels, each x-ray source pixel comprising: an electron source for producing electrons; an x-ray conversion target capable of generating x- rays when incidenced by electrons; and a cylindrical multilayer insulator having a plurality of alternating insulator and conductor ring-shaped layers separating the electron source from the x-ray conversion target, and an acceleration channel communicating therebeween; and a power source operably connected to each x-ray source pixel of the broad-area array to produce an accelerating gradient in the acceleration channel of any one or more of the x-ray source pixels, for accelerating electrons through the acceleration channel towards a corresponding x-ray conversion target, wherein the plurality of alternating insulator and conductive layers of the multilayer insulators enable a high resistance to surface flashover in the energy range necessary to produce a sufficiently high accelerating gradient for generating x-rays and with the electron source and x-ray conversion target in close proximity to each other.

21. An x-ray imaging system comprising: a compact x-ray source panel comprising an array of x-ray sources, each x-ray source comprising: an electron source; an x-ray conversion target capable of generating x-rays when incidenced by electrons; and a multilayer insulator having a plurality of alternating insulator and conductor layers separating the electron source from the x-ray conversion target; a power source operably connected to each x-ray source of the array to produce an accelerating gradient between the electron source and the x-ray conversion target in any one or more of the x-ray sources, for accelerating electrons to toward a corresponding x-ray conversion target; a detector capable of detecting x-rays generated by said compact x- ray source panel; and a controller operably connected to receive signals from the detector

and control the compact x-ray source panel based upon said signals.