U.S. patent application number 15/978924 was filed with the patent office on 2018-10-11 for method for fabricating pixelated scintillators.
The applicant listed for this patent is Varian Medical Systems, Inc.. Invention is credited to Richard Mead, Daniel Shedlock, Josh Star-Lack.
Application Number | 20180292547 15/978924 |
Document ID | / |
Family ID | 58407023 |
Filed Date | 2018-10-11 |
United States Patent
Application |
20180292547 |
Kind Code |
A1 |
Shedlock; Daniel ; et
al. |
October 11, 2018 |
METHOD FOR FABRICATING PIXELATED SCINTILLATORS
Abstract
In a method of making pixelated scintillators, an amorphous
scintillator material in a molten state is pressed into a plurality
of cavities defined by a plurality of walls of a mesh array. The
molten scintillator material in the plurality of cavities is cooled
to form a pixelated scintillator array. An x-ray imager including a
pixelated scintillator is also described.
Inventors: |
Shedlock; Daniel;
(Knoxville, TN) ; Star-Lack; Josh; (Palo Alto,
CA) ; Mead; Richard; (Los Altos Hills, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Varian Medical Systems, Inc. |
Palo Alto |
CA |
US |
|
|
Family ID: |
58407023 |
Appl. No.: |
15/978924 |
Filed: |
May 14, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14870044 |
Sep 30, 2015 |
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15978924 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C03B 2215/414 20130101;
C03C 4/087 20130101; G01T 1/2018 20130101; G01T 1/20 20130101; C03B
2215/07 20130101; C03B 11/08 20130101; B29C 39/26 20130101; C03B
37/025 20130101; B29C 39/38 20130101; B29K 2025/00 20130101; B29K
2105/162 20130101; C03B 2215/79 20130101; C03B 19/02 20130101; C03B
2215/06 20130101; C03B 2215/16 20130101; G01T 1/2002 20130101; B29C
39/026 20130101; B29C 65/48 20130101; G01T 1/202 20130101; C03B
2215/20 20130101; C03B 37/02 20130101 |
International
Class: |
G01T 1/20 20060101
G01T001/20; B29C 39/26 20060101 B29C039/26; C03B 19/02 20060101
C03B019/02; G01T 1/202 20060101 G01T001/202; B29C 39/02 20060101
B29C039/02; B29C 65/48 20060101 B29C065/48; B29C 39/38 20060101
B29C039/38 |
Claims
1. A method of making pixelated scintillators, comprising:
providing a mesh array including a plurality of walls defining a
plurality of cavities; providing an amorphous scintillator material
in a molten state; introducing the amorphous scintillator material
in the molten state into the plurality of cavities of the mesh
array; and cooling the amorphous scintillator material in the mesh
array to form a pixelated scintillator array.
2. The method of claim 1, wherein the introducing step comprises
pouring the amorphous scintillator material in the molten state
over the mesh array to allow it to flow into the plurality of
cavities.
3. The method of claim 1, wherein the introducing step comprises
placing the amorphous scintillator material in the molten state
over the mesh array and pressing it into the plurality of
cavities.
4. The method of claim 1, wherein the mesh array is constructed
from a material having a thermal expansion coefficient
substantially same as or smaller than a thermal expansion
coefficient of the scintillator material.
5. The method of claim 4, wherein the mesh array is constructed
from a material having a melting temperature higher than a melting
temperature of the scintillator material.
6. The method of claim 5, wherein the mesh array is constructed
from a material comprising a metal or metal alloy selected from the
group consisting of cupronickel, Hastalloy C, Inconel, iridium,
iron, Monel, molybdenum, steel, steel-carbon alloy, tantalum,
thorium, titanium, tungsten, vanadium, and zirconium.
7. The method of claim 5, wherein the mesh array is constructed
from a material comprising a ceramic selected from the group
consisting of HfB.sub.2, HfC, NfN, ZrB.sub.2, ZrC, ZrN, TiB.sub.2,
TiC, TiN, TaB.sub.2, TaC, TaN, and SiC.
8. The method of claim 5, wherein the mesh array is constructed
from a material selected from the group consisting of graphite,
silicon carbide, and boron nitride.
9. The method of claim 1, wherein the plurality of walls of the
mesh array are coated with a reflective layer.
10. The method of claim 9, wherein the reflective layer has a color
substantially matches a color of light emitted by the scintillator
material.
11-19. (canceled)
20. A method of fabricating pixelated scintillators, comprising:
forming a plurality of scintillator pixels from an amorphous
scintillator material in a molten state; applying a reflective
layer on each of the plurality of scintillator pixels formed; and
assembling the plurality of scintillator pixels applied with the
reflective layer to form a pixelated scintillator array.
21. The method of claim 20, wherein the plurality of scintillator
pixels are assembled by inserting them into a mesh array including
a plurality of walls defining a plurality of cavities configured to
receive the plurality of scintillator pixels.
22. The method of claim 21, further comprising fixing the plurality
of scintillator pixels in the mesh array using an adhesive in the
plurality of cavities.
23. The method of claim 20, wherein the plurality of scintillator
pixels are assembled by binding them to each other using an
adhesive.
24. The method of claim 20, wherein each of the plurality of
scintillator pixels has a first end portion and a second end
portion, and the plurality of scintillator pixels are assembled
through attachments to the first end portions of the plurality of
scintillator pixels.
25. The method of claim 20, wherein the plurality of scintillator
pixels are formed from the amorphous scintillator material by a
drawing technique.
26. The method of claim 20, further comprising fire polishing the
plurality of the scintillator pixels formed.
27. The method of claim 20, wherein each of the plurality of
scintillator pixels has a shape of a cylinder, a rectangular prism,
or a square prism.
28-30. (canceled)
31. The method of claim 20, wherein the reflective layer has a
color substantially matches a color of light emitted by the
scintillator material.
32. (canceled)
33. The method of claim 20, wherein the plurality of scintillator
pixels are assembled in plural rows and plural columns.
34. The method of claim 33, wherein scintillator pixels in adjacent
rows and/or columns are arranged staggered.
35-52. (canceled)
53-58. (canceled)
Description
TECHNICAL FIELD
[0001] Embodiments of this disclosure relate generally to x-ray
imaging apparatuses and methods. In particular, various embodiments
of methods of fabricating pixelated scintillators and image
detectors containing pixelated scintillators are described.
BACKGROUND
[0002] X-ray image detectors are widely used in medical imaging,
security inspection, scientific research, and other industries. An
x-ray image detector may include a scintillator layer and a
detector array. The scintillator layer absorbs incident x-ray
radiation indicative of the structure of a subject imaged and
converts the absorbed radiation into light photons. The detector
array may collect light photons generated and convert them into
measurable electrical signals, which may be amplified, digitized,
or further processed by various electrical circuitry and algorithms
known in the art. The detector array may include addressable
photosensitive elements such as photodiodes and switching
transistors such as TFT or CMOS transistors.
[0003] To improve the spatial resolution of images, light photons
generated in the scintillator layer should ideally be recorded by
the detector elements located vertically beneath the scintillators
that generate the light photons. Crosstalk between pixels should be
kept to a minimum. To accomplish that, pixelated scintillators,
which can limit lateral spread of light photons, are used.
Conventionally, a pixelated scintillator is formed by a "slice and
dice" approach. A block of a scintillator crystal is cut into
slices that may or may not be polished. The slices are applied with
a layer of reflective septa or coating and reassembled against each
other, now separated by the reflective septa. The assembly is then
rotated 90 degrees and the block is again sliced, coated, and
reassembled. The final pixelated array then has square or
rectangular "pixels" surrounded by reflective septa on all four
sides.
[0004] The conventional approach of preparing pixelated
scintillators is labor intensive and the cost for large area
pixelated scintillators is prohibitive. There is a need for
innovative and more efficient methods for fabricating pixelated
scintillators.
SUMMARY
[0005] Certain embodiments of a method of making pixelated
scintillators are set forth below. It should be understood that
these embodiments are presented merely to provide the reader with a
brief summary of certain forms the invention might take and that
these embodiments are not intended to limit the scope of the
invention. Indeed, the invention may encompass a variety of
embodiments or aspects that may not be set forth below.
[0006] In an exemplary embodiment of a method for fabricating
pixelated scintillator array, a molten scintillator material may be
poured into the hollow cavities of a mesh array with reflective
walls. Alternatively, a molten scintillator material may be pressed
into the hollow cavities of a mesh array with reflective walls. The
assembly may be then cooled and annealed, leaving a rigid pixelated
scintillator array in place. The scintillator material may be an
amorphous material such as a scintillating glass with a thermal
expansion coefficient similar to the thermal expansion coefficient
of the mesh material. The pixel pitches may range from about 0.05
mm to about 40 mm depending upon applications.
[0007] Exemplary scintillator materials include borate and silicate
glasses doped with rare earths such as cerium and terbium to
optimize the wavelength of the emitted light to the detector array.
For example terbium doped scintillator are typically in the green
spectrum, around 550 nm, near the optimal level for amorphous
silicon (a-Si) detector arrays. Other scintillator materials
include scintillating nanospheres that are embedded in the glass.
The nanospheres may have diameters significantly smaller than the
wavelength of the emitted light. Further scintillator materials
include plastic scintillators with various dopant materials such as
poly vinyl toluene (PVT). In general, any scintillator materials
that melt below the melting temperature of the mesh grid can be
used.
[0008] The mesh may be made from a material with a melting
temperature higher than the melting temperature of the scintillator
material. The mesh walls can be constructed from metals or metal
alloys, ceramics, or other suitable materials, and may be coated
with a reflective layer.
[0009] Exemplary metals or metal alloys suitable for making the
mesh include and are not limited to Cupronickel, Hastalloy C,
Inconel, Iridium, Iron, Monel, Molybdenum, Steel, Steel and Carbon
alloys, Tantalum, Thorium, Titanium, Tungsten, Vanadium, Zirconium.
The metals or metal alloys may be coated with a diffuse or
Lambertian reflective paint such as TiO.sub.2. They may also be
coated with an efficient specular reflector such as silver, gold or
aluminum depending on the melting temperature of the glass.
[0010] Exemplary ceramics suitable for making the mesh include and
are not limited to HfB.sub.2, HfC, NfN, ZrB.sub.2, ZrC, ZrN,
TiB.sub.2, TiC, TiN, TaB.sub.2, TaC, TaN, SiC. It is desired that
the ceramic be white or have a color matching the wavelength(s) of
the emitted light from the scintillator. Alternatively, the ceramic
may be coated with a paint such as TiO.sub.2 or a metal. Other
exemplary materials suitable for making the mesh include graphite,
silicon carbide, or boron nitride.
[0011] In an alternative embodiment of a method for fabricating
pixelated scintillators, scintillator "pixels" or pieces may be
drawn using a standard glass draw technique. The drawn pixels may
optionally be fire polished. The pixels can then be assembled into
an array with reflective walls. One way of achieving this is to
insert the drawn pixels into a mesh array with cavities. In this
case, the melting temperature of the mesh array does not have to be
very high and in addition to the metals listed above for a mesh
array, it is possible to use other metals with high reflectivity
such as aluminum. It may be desired that the scintillator pixels be
drawn into cylinders to maximize the area of the air-glass
interface, thus maximizing the differences in index of refraction
between the glass and its surroundings to enhance the probability
for total internal reflection. The pixels may also be hexagon or
triangular in applications where a high fill factor is desired. A
potting material or glue may be melted in to hold the pixels in
place. It is desirable that the glue, adhesive or other bonding
adhesives have optical properties that maximize internal
reflection. This can be accomplished with either a reflective
surface, index of refraction or both.
[0012] Other aspects and embodiments of the disclosure are
described in the section of Detailed Description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] These and various other features and advantages will become
better understood upon reading of the following detailed
description in conjunction with the accompanying drawings and the
appended claims provided below, where:
[0014] FIG. 1A is a perspective view of an exemplary mesh array
according to embodiments of the disclosure;
[0015] FIG. 1B is a top view of the mesh array shown in FIG. 1A
according to embodiments of the disclosure;
[0016] FIGS. 2A, 2B, and 2C are top views of exemplary mesh arrays
according to alternative embodiments of the disclosure;
[0017] FIG. 3 is a top view of an exemplary pixilated scintillator
array according to embodiments of the disclosure;
[0018] FIG. 4 schematically shows an exemplary x-ray image detector
according to embodiments of the disclosure;
[0019] FIG. 5 schematically shows an exemplary pixelated
scintillator layer and a method of making the same according to
embodiments of the disclosure; and
[0020] FIG. 6 schematically shows an alternative pixelated
scintillator layer and a method of making the same according to
embodiments of the disclosure.
DETAILED DESCRIPTION
[0021] Various embodiments of methods of making pixelated
scintillators and image detectors comprising a pixelated
scintillator layer are described. It is to be understood that the
disclosure is not limited to the particular embodiments described
as such may, of course, vary. An aspect described in conjunction
with a particular embodiment is not necessarily limited to that
embodiment and can be practiced in any other embodiments.
[0022] Embodiments of the disclosure may be described with
reference to the figures. It should be noted that some figures are
not necessarily drawn to scale. The figures are only intended to
facilitate the description of specific embodiments, and are not
intended as an exhaustive description or as a limitation on the
scope of the disclosure. Further, in the following description,
specific details such as examples of specific materials,
dimensions, processes, etc. may be set forth in order to provide a
thorough understanding of the disclosure. It will be apparent,
however, to one of ordinary skill in the art that some of these
specific details may not be employed to practice embodiments of the
disclosure. In other instances, well known components or process
steps may not be described in detail in order to avoid
unnecessarily obscuring the embodiments of the disclosure.
[0023] All technical and scientific terms used herein have the
meaning as commonly understood by one of ordinary skill in the art
unless specifically defined otherwise. As used in the description
and appended claims, the singular forms of "a," "an," and "the"
include plural references unless the context clearly dictates
otherwise. The term "or" refers to a nonexclusive "or" unless the
context clearly dictates otherwise.
[0024] As used herein, the term "scintillator pixel," "pixelated
scintillator array," or "pixelated scintillator layer" refers to
embodiments where a scintillator piece is physically or optically
isolated from adjoining scintillator pieces.
Methods of Fabricating Pixelated Scintillators
[0025] The disclosure provides a method of making pixelated
scintillators. According to some embodiments of the method, a mesh
array including a plurality of walls defining a plurality of
cavities is provided. The walls of the mesh array may be coated
with a reflective layer. An amorphous scintillator material in a
molten state is provided and introduced into the plurality of
cavities. The molten scintillator material may be poured over the
mesh array to allow the molten scintillator material to flow into
the plurality of cavities. Alternatively, the molten scintillator
material may be placed over the mesh array and pressed into the
plurality of cavities. The assembly may be cooled or annealed to
form a pixelated scintillator array.
[0026] FIGS. 1A and 1B schematically show a mesh array 100 that can
be used in the method according to some embodiments of the
disclosure. The mesh array 100 may include a plurality of walls 102
defining a plurality of cavities 104. As shown, the plurality of
cavities 104 may be arranged in rows and columns, each having a
cross-section in the shape of a square or rectangle. It should be
noted that the mesh array 100 shown in FIGS. 1A and 1B is provided
for illustration purpose. Any other mesh arrays generally in the
form of a grid can be used in the method of this disclosure. For
example, the cross section of the cavities may be in the shape of a
circle (FIG. 2A), diamond (FIG. 2B), hexagon (FIG. 2C), or any
other regular or irregular shape. The cavities may be arranged in
rows and columns as shown in FIGS. 1A and 1B. The cavities in
adjacent rows and/or columns may also be arranged staggered, as
shown FIGS. 2B and 2C, to improve sampling density. In FIGS. 2A, 2B
and 2C, the u and v axes are the horizontal and vertical axes on
the detector.
[0027] Referring to FIG. 1A, the spacing (S) between adjacent walls
102 may determine the size or surface area of the cavities 104,
which in turn may determine the size of a pixel of the pixelated
scintillator array formed. The thickness (T) of the walls 102 may
determine the gap between adjacent cavities, which in turn may
determine the pixel pitch of the pixelated scintillator array
formed. The depth (D) of the walls may determine the thickness of
the pixelated scintillator array formed. In some embodiments, two
or more pixelated scintillator arrays formed may be further
assembled to form a pixelated scintillator layer with a larger area
as will be described in greater detail below in conjunction with
description of other embodiments of the disclosure.
[0028] In exemplary embodiments, the mesh array 100 may be provided
such that the pixelated scintillator array formed may have a pixel
size ranging from about 0.05 mm to about 40 mm. In exemplary
embodiments, the mesh array 100 may be provided such that the
pixelated scintillator array formed may have a pixel pitch ranging
from about 0.05 mm to about 40 mm. In exemplary embodiments, the
mesh array 100 may be provided such that the pixelated scintillator
array formed may have an aspect ratio (array thickness to pixel
pitch) from about 1:1 to about 50:1. It should be noted that the
above specific details are provided for a thorough understanding of
the disclosure. It will be apparent to one of ordinary skill in the
art that some of these specific details may not be required to
practice embodiments of the disclosure.
[0029] The mesh array may be constructed from a material that has a
melting temperature higher than the melting temperature of the
scintillator material used. In some embodiments, the mesh array may
be constructed from a material having a thermal expansion
coefficient substantially similar to or smaller than the thermal
expansion coefficient of the scintillator material used.
[0030] The mesh array 100 may be constructed from a metal or metal
alloy. Suitable metals or metal alloys that can be used to
construct the mesh array include and are not limited to
Cupronickel, Hastalloy C, Inconel, Iridium, Iron, Monel,
Molybdenum, Steel, Steel and Carbon alloy, Tantalum, Thorium,
Titanium, Tungsten, Vanadium, Zirconium, and so on.
[0031] In alternative embodiments, the mesh array 100 may be
constructed from ceramics. Suitable ceramics that can be used to
construct the mesh array include and are not limited to HfB.sub.2,
HfC, NfN, ZrB.sub.2, ZrC, ZrN, TiB.sub.2, TiC, TiN, TaB.sub.2, TaC,
TaN, SiC, and so on.
[0032] Other materials suitable for constructing the mesh array
include graphite, silicon carbide, or boron nitride.
[0033] The mesh array 100 can be manufactured using precision
electrical discharge machining (EDM), stereolithography, or other
suitable techniques known in the art.
[0034] The mesh array 100, or at least the surfaces of the walls
102 defining the cavities 104 of the mesh array 100, may be applied
with a reflective coating. The reflective coating may be applied to
the wall surfaces using deposition, sputtering, spray, plating, or
any other suitable techniques known in the art.
[0035] The color of diffuse reflector coatings may be white or a
color matching the wavelength(s) of the emitted light from the
scintillator. Exemplary reflective coating includes TiO.sub.2.
Other reflective coatings include specular reflectors such as
silver, gold, or aluminum depending on the melting temperature of
the scintillator materials used. Wrappings such as aluminized
Mylar.RTM. and ESR Vikuiti.RTM. may also be bonded as reflector
materials to scintillators.
[0036] The scintillator material used in the method of this
disclosure may be an amorphous scintillator material. Any suitable
amorphous scintillator materials that melt at a temperature below
the melting temperature of the mesh array can be used.
[0037] Exemplary scintillator materials include and are not limited
to borate glasses incorporated with terbium oxides and silicate
glasses incorporated with terbium oxides. Other elements or
compounds that can be incorporated in the borate or silicate
glasses include gadolinium oxides, cerium oxides, or europium
oxides, etc. By way of example, the scintillating borate or
silicate glasses may include 1-20 percent of terbium oxides, 1-15
percent gadolinium oxides, and certain percent of other oxides.
Other suitable ingredients such as stabilizers and flux etc. may
also be included in the scintillator glasses. U.S. Pat Nos.
5,108,959, 5,120,970, 5,122,671, and 5,391,320 disclose various
silicate and borate scintillator glasses, the disclosures of all of
which are incorporated herein by reference in their entirety.
[0038] Other exemplary scintillator materials include scintillating
nanoparticles embedded in an amorphous base material. The
nanoparticles are preferably nanospheres having diameters smaller
than the wavelength of the emitted light to reduce scatter centers
and re-absorption. Plastic scintillator materials such as poly
vinyl toluene (PVT) embedded with various scintillating dopants can
also be used. In general, dopants in the amorphous base material
control the emission spectra and decay time. Plastic scintillator
materials are commercially available e.g. from Saint-Gobain of
Hiram, Ohio, United States.
[0039] According to embodiments of the disclosure, solid amorphous
scintillator materials may be heated e.g. in a furnace at elevated
temperatures to provide a molten glass or an amorphous scintillator
material in a molten state. The hot liquid glass can be poured over
a mesh array shown in FIGS. 1A-2C, to allow the hot liquid glass to
flow into the cavities. The assembly can be then annealed or cooled
over a period of time at certain temperatures to relieve thermal
stress, forming a pixelated scintillator array.
[0040] According to alternative embodiments of the disclosure,
solid amorphous scintillator materials may be heated e.g. in a
furnace at elevated temperatures to provide a molten glass or an
amorphous scintillator material in a molten state. The molten
glass, which may be in the form of a soft glass blob, is placed
over a mesh array shown in FIGS. 1A-2C. The soft glass blob can be
pressed e.g. using a plunger, to allow the molten glass to be
distributed or filled into the cavities of the mesh array. The
assembly can be then annealed or cooled over a period of time at
certain temperatures to relieve thermal stress, forming a pixelated
scintillator array.
Alternative Methods of Fabricating Pixelated Scintillators
[0041] The disclosure further provides an alternative method of
making pixelated scintillators. According to the alternative
embodiment, a scintillator material in a molten state is provided.
A plurality of scintillator pixels are formed by drawing from the
molten scintillator material. If desired, the scintillator pixels
may be fire polished. A reflective layer may be applied on each of
the plurality of scintillator pixels formed. The plurality of
scintillator pixels applied with a reflective layer can be
assembled to form a pixelated scintillator array.
[0042] The plurality of scintillator pixels may be assembled by
inserting the drawn pixels into a mesh array. The mesh array may
include a plurality of walls defining a plurality of cavities
configured to receive the plurality of scintillator pixels. The
plurality of scintillator pixels may be fixed in the mesh array
using an adhesive. For example, a potting material or glue can be
melted in the plurality of cavities to hold the scintillator pixels
in place. It is desirable that the glue is transparent.
[0043] The mesh array used in the alternative method described
herein may be the same as or similar to the mesh array shown in
FIGS. 1A-2C described above. For example, the cavities may be
aligned in rows and columns, each having a cross-section in the
shape of a square, rectangle, circle, diamond, hexagon, or any
other regular or irregular shape. The cavities in adjacent rows
and/or columns may also be arranged staggered to improve sampling
density. The materials for constructing the mesh array described
above can be used for the mesh array used in the alternative method
described herein. For example, the mesh array may be constructed
from a material that has a melting temperature higher than the
melting temperature of the scintillator material used. The mesh
array may be constructed from a material having a thermal expansion
coefficient substantially similar to or smaller than the thermal
expansion coefficient of the scintillator material used.
[0044] In some embodiments, the mesh array used in the alternative
method described herein can be constructed from a material
different from the material for constructing the mesh array used in
the method described above. Because the scintillator pixels are
formed by drawing from the molten scintillator material and then
inserted into the mesh array in the alternative method, as opposed
to by pouring or pressing the hot molten material into the cavities
of the mesh array, it is not required that materials for
constructing the mesh array have a melting temperature higher than
the melting temperature of the scintillator material. As such,
materials other than, or in addition to, metals or metal alloys,
ceramics, or other materials described above, can be used. For
example, metal aluminum, which has high reflectivity, may be used
in the alternative method of making pixelated scintillator
arrays.
[0045] In alternative embodiments, the scintillator pixels coated
with a reflective layer may be assembled by binding them to each
other using an adhesive, or held in place through attachments to
the top or bottom portions of individual scintillator pixels
drawn.
[0046] The scintillator material used in the alternative method may
be the same as the material used in the method described above. For
example, amorphous scintillator materials such as borate or
silicate glasses incorporated with terbium oxides may be used.
Other suitable scintillator materials include scintillating
nanoparticles embedded in an amorphous base material, and plastic
scintillator materials such as poly vinyl toluene (PVT) embedded
with various scintillating dopant materials.
[0047] The scintillator pixels may be drawn or formed using a
standard glass drawing technique. Various glass drawing techniques
are known in the art and therefore their detailed description is
omitted herein in order to focus on description of embodiments of
this disclosure. In general, an amorphous scintillator material may
be heated in a furnace at elevated temperatures to provide a molten
glass or an amorphous scintillator material in a molten state. The
molten glass may then pass through a bushing plate including one or
more fine orifices. The molten glass passes through the fine
orifices and come out as fine filaments or scintillator pixels. The
orifices in the bushing plate may have a size and shape designed to
allow formation of scintillator pixels with a desired size and
shape. A reflective coating may be applied to the drawn pixels by
spray, deposition or other suitable means. Optionally, the drawn
scintillator pixels may be fire polished and then applied with a
reflective coating. It should be noted that any other glass drawing
apparatuses and techniques may be used to make the scintillator
pixels. For example, scintillator pixels may be pulled or drawn
from softened molten glass or preform.
[0048] The scintillator pixels may be drawn in various kinds of
forms or shapes. For example, the scintillator pixels may have a
cross-sectional shape of a circle, square, rectangle, hexagon, and
other regular or irregular shape. In some embodiments, the
scintillator pixels may be drawn into the form of cylinders to
maximize the area of interface between the scintillator pixels and
their surroundings such as air or the mesh array, thus maximizing
the differences in index of refraction, to enhance the probability
for total internal reflection. The scintillator pixels can be drawn
to various lengths and cross-sectional sizes for different
applications. For example, it is possible to draw scintillator
cylinders to a diameter of 6 microns in some cases. Scintillator
pixels with small sizes may reduce the light output to an unusual
value when the aspect ratio (height to pitch) becomes too large. In
general, the aspect ratio may range from about 1:1 to about 50:1,
or from about 33:1 to about 7.7:1.
Pixelated Scintillators and X-ray Imagers Including Same
[0049] In another aspect, the disclosure provides a pixelated
scintillator array. The pixelated scintillator array includes a
mesh array having a plurality of walls defining a plurality of
cavities, and a plurality of scintillator pixels in the plurality
of cavities. The scintillator pixels are formed of an amorphous
scintillator material. FIG. 3 shows an exemplary pixelated
scintillator array 300 according to embodiments of this disclosure.
The pixelated scintillator array 300 includes a mesh array 100
having a plurality of walls 102 defining a plurality of cavities
104, and plurality of scintillator pixels 302 (grayed) received in
the plurality of cavities 104. The pixelated scintillator array 300
shown in FIG. 3 may be used alone or as a scintillator block in a
scintillator layer of an image detector.
[0050] The cavities 104 of the mesh array 100 may be arranged in
rows and columns, each having a cross-section in the shape of a
square, rectangle, circle, diamond, hexagon, or any other regular
or irregular shape. The cavities 104 may be aligned in rows and
columns. The cavities 104 in adjacent rows and/or columns may also
be arranged staggered to improve sampling density. The mesh array
100 may be constructed from a material that has a thermal expansion
coefficient similar to or smaller than the thermal expansion
coefficient of the scintillator material. The mesh array 100 may be
constructed from a material having a melting temperature higher
than the melting temperature of the amorphous scintillator
material. Alternatively, the mesh array 100 may be constructed from
a material having a melting temperature that is the same as or
smaller than the melting temperature of the amorphous scintillator
material. The mesh array 100 may be constructed from a metal or
metal alloy, a ceramic, graphite, silicon carbide, or boron
nitride, etc. The mesh array, or at least the inside surfaces of
the walls defining the cavities, may be coated with a reflective
coating.
[0051] The scintillator pixels 302 may be formed of an amorphous
scintillator material such as silicate or borate glasses
incorporated with terbium oxides, scintillating nanoparticles
embedded in an amorphous base material, and plastic scintillator
materials such as poly vinyl toluene (PVT) embedded with various
dopant materials.
[0052] In a further aspect, the disclosure provides an x-ray image
detector. FIG. 4 schematically shows an exemplary x-ray image
detector 400 according to embodiments of the disclosure. The x-ray
image detector 400 includes a pixelated scintillator layer 402 and
a detector array 404. The pixelated scintillator layer 402
generates light photons from x-ray radiation. The pixelated
scintillator layer 402 may include one or more scintillator arrays
described above.
[0053] The detector array 404 converts light photons generated in
the pixelated scintillator layer 402 to electrical signals. Various
detector arrays are known and therefore their detailed description
is omitted here in order to focus on description of embodiments of
this disclosure. In general, a detector array may include a large
number e.g. hundreds of thousands or millions of detector elements.
The large number of detector elements may be arranged in a
plurality of rows and a plurality of columns forming an active
detector area. Each detector element may include an addressable
photosensitive element such as a photodiode and a switching
transistor such as a TFT or CMOS transistor.
[0054] The image detector 400 may also include a driver control 406
and a readout control 408. The driver control 406 provides control
signals for addressing the signal data generated by the detector
array 404. The readout control 408 provides control signals for
reading out the signal data. In the exemplary embodiment shown in
FIG. 4, the detector array 404 and the readout control assembly 408
are mounted on opposing sides of a base plate 410 to minimize the
lateral size of the image detector 400. The driver control assembly
406 may also be placed beneath the detector array 404, or the
readout control assembly 408 may be placed at a side of the
detector array 404. A housing 401 encloses the pixelated
scintillator layer 402, the detector array 404, the driver control
assembly 406, and the readout control assembly 408. The image
detector 400 may further include other electronics for amplifying,
digitizing, and processing the electrical signals as known in the
art. U.S. Pat. Nos. 5,970,115, 7,291,842, 7,816,651 and 8,552,386
disclose various embodiments of x-ray imaging apparatuses, systems,
and electronic components thereof, the disclosures of all of which
are incorporated herein by reference in their entirety.
Alternative Embodiments
[0055] An x-ray imager may be used with an x-ray source that
generates x-rays of cone-beam or fan-beam. X-rays of cone-beam or
fan-beam may have a centerline passing through the x-ray source.
The peripheral portions of the x-rays of cone-beam or fan-beam form
angles with respect to the centerline.
[0056] In conventional x-ray imaging systems using pixelated
scintillator layers, all of the scintillator pixels are vertically
aligned in parallel with the centerline of x-rays. In such a
system, although the central portion of x-rays may pass through
single scintillator pixels when propagating in the scintillator
layer, the peripheral portions of x-rays may cross through multiple
pixels. As a result, the resolution of the imaging system is
degraded. This issue becomes severer when the thickness of the
scintillator layer increases in imaging systems for use with x-rays
having e.g. MV energy levels.
[0057] According to embodiments of the disclosure, a pixelated
scintillator layer may include two or more pixelated scintillator
blocks or arrays. A first pixelated scintillator array may include
a plurality of scintillator pixels arranged substantially in
parallel in a first direction. A second pixelated scintillator
array may include a plurality of scintillator pixels arranged
substantially in parallel in a second direction different from the
first direction. The first and second pixelated scintillator arrays
may be arranged such that the first and second directions focus at
an x-ray source or form a non-zero angle at the x-ray source.
[0058] FIG. 5 is a cross-sectional side view of an exemplary
pixelated scintillator layer 500 and shows a method of making the
same according to embodiments of the disclosure. As shown, a first
pixelated scintillator array 502 comprising a plurality of
scintillator pixels 504 is provided. The first pixelated
scintillator array 502 has a top surface 506 and a bottom surface
508. As provided, the top and bottom surfaces 506, 508 may be
substantially parallel. The plurality of scintillator pixels 504
are aligned substantially in parallel to each other and
substantially perpendicular to the top and bottom surfaces 506,
508. Between the adjoining scintillator pixels 504 is a reflective
layer or septa 510.
[0059] The plurality of scintillator pixels 504 may be formed from
either an amorphous scintillator material or a crystalline
scintillator material. A pixelated scintillator array comprising an
amorphous scintillator material can be made using a method
described above under "Method of Fabricating Pixelated
Scintillators" or using a glass drawing technique described above
under "Alternative Method of Fabricating Pixelated Scintillators"
of this disclosure. A pixelated scintillator array comprising a
crystalline scintillator material can be made using a "slice and
dice" technique known in the art.
[0060] The first pixelated scintillator array 502 may be cut along
a plane near the bottom surface 508 as indicated by the dashed line
512, forming a second pixelated scintillator array 514. The second
pixelated scintillator array 514 formed is thus has a new bottom
surface 516 non-parallel to the top surface 506. The plurality of
scintillator pixels 504, while still substantially perpendicular to
the top surface 506, become non-perpendicular to the newly formed
bottom surface 516. When the second pixelated scintillator array
514 is placed with the bottom surface 516 on a horizontal plane, an
angle (.theta.) is formed between the vertical axis and the pixel
aligning direction. The degree of the angle (.theta.) depends on
the angle of the cutting plane 512 with respect to the bottom
surface 508 of the first pixelated scintillator array 502.
[0061] The side of the formed second pixelated scintillator array
514 may be further cut along the plane indicated by dash line 518
so that when a first pixelated scintillator array 502 and a second
pixelated scintillator array 514 are assembled in forming a
pixelated scintillator layer 500, the second scintillator array 514
may be disposed in close proximity with the first scintillator
array 502, leaving no substantial gap between the sides of two
adjoining scintillator arrays, and still allowing the scintillator
pixels of the second scintillator array 514 to lean toward the
x-ray source.
[0062] A plurality of first scintillator arrays 502 may be cut,
with varying cutting angles, forming a plurality of second
scintillator arrays 514 having varying degrees of angles between
the newly formed bottom surface and top surface. The plurality of
second pixelated scintillator arrays 514 may be assembled with a
first scintillator array 502, forming a pixelated scintillator
layer 500, as shown in FIG. 5. As assembled, the aligning
directions of scintillator pixels 504 in each of the scintillator
array 502, 514 may be focused on an x-ray source (pixel-wise
focusing at the source). When in use, x-rays of cone-beam or
fan-beam produced by the x-ray source may pass single scintillator
pixels when propagating in the scintillator layer 500, without
crossing through neighboring scintillator pixels. This can
advantageously increase spatial resolution of the imaging
system.
[0063] FIG. 6 is a cross-sectional side view of an alternative
pixelated scintillator layer 600 and a method of making the same
according to alternative embodiments of the disclosure. The
pixelated scintillator layer 600 shown in FIG. 6 is similar to the
pixelated scintillator layer 500 shown in FIG. 5 in some aspects.
For example, the first pixelated scintillator array 602 has a top
surface 606 and a bottom surface 608 substantially parallel to each
other. The plurality of scintillator pixels 604 of the first
pixelated scintillator array 602 are aligned substantially in
parallel to each other and substantially perpendicular to both the
top and bottom surfaces 606, 608. Between adjoining scintillator
pixels 604 is a reflective layer or septa 610. The plurality of
scintillator pixels 604 may be formed from either an amorphous
scintillator material or a crystalline scintillator material.
[0064] In comparison with FIG. 5, the second pixelated scintillator
array 614 in FIG. 6 has a different shape or configuration. As
shown in FIG. 6, the top and bottom surfaces 606, 617 of the second
pixelated scintillator array 614 are parallel to each other.
However, the pixels 604 of the second pixelated scintillator array
614, while still substantially in parallel to each other, are
non-perpendicular to both the top and bottom surfaces 616, 617.
[0065] Still referring to FIG. 6, the first pixelated scintillator
array 602 may be cut along both a plane near the bottom surface 508
as indicated by the dashed line 612 and a plane near the top
surface 606 as indicated by the dashed line 613. The second
pixelated scintillator array 614 formed is thus has a new bottom
surface 616 and a new top surface 617. The newly cut top and bottom
surfaces 616, 617 may still be parallel to each other. However, the
aligning direction of the scintillator pixels 604 becomes
non-perpendicular to both the top and bottom surfaces 616, 617.
When the second pixelated scintillator array 614 is placed with the
bottom surface 616 on a horizontal plane, an angle (.theta.) is
formed between the vertical axis and the pixel aligning direction.
The degree of the angle (.theta.) depends on the angle of the
cutting plane with respect to the bottom surface 608 of the first
pixelated scintillator array 602.
[0066] Still referring to FIG. 6, one or both sides of the second
pixelated scintillator array 614 may be further cut along planes
indicated by dash lines 618, 619 so that when a first pixelated
scintillator array 602 and a second pixelated scintillator array
614 are assembled in forming a pixelated scintillator layer 600,
the second scintillator array 614 may be disposed in close
proximity with the first scintillator array 602, leaving no
substantial gap between the sides of two adjoining scintillator
arrays, and still allowing the aligning direction of the
scintillator pixels 604 of the second scintillator array 614 to
lean toward the x-ray source.
[0067] A plurality of first scintillator arrays 602 may be cut,
with varying cutting angles, forming a plurality of second
scintillator arrays 614 having varying degrees of angles between
the newly formed bottom surface and the pixel aligning direction.
The plurality of second pixelated scintillator arrays 614 may be
assembled with the first scintillator array 602, forming a
pixelated scintillator layer 600, as shown in FIG. 6. As assembled,
the aligning directions of scintillator pixels 604 in each of the
scintillator arrays 602, 614 may be focused on an x-ray source.
When in use, x-rays of cone-beam or fan-beam produced by the x-ray
source may pass single scintillator pixels when propagating in the
scintillator layer 600, without crossing through neighboring
scintillator pixels. This can advantageously increase spatial
resolution of the imaging system.
[0068] Methods of making pixelated scintillators, pixelated
scintillator arrays, and image detectors including pixelated
scintillators have been described. Those skilled in the art will
appreciate that various other modifications may be made within the
spirit and scope of the invention. All these or other variations
and modifications are contemplated by the inventors and within the
scope of the invention.
* * * * *