U.S. patent application number 14/852906 was filed with the patent office on 2015-12-31 for handheld x-ray system for 3d scatter imaging.
The applicant listed for this patent is Aribex, Inc.. Invention is credited to D. Clark Turner.
Application Number | 20150377803 14/852906 |
Document ID | / |
Family ID | 49621598 |
Filed Date | 2015-12-31 |
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United States Patent
Application |
20150377803 |
Kind Code |
A1 |
Turner; D. Clark |
December 31, 2015 |
Handheld X-Ray System for 3D Scatter Imaging
Abstract
Handheld imaging systems and methods for using such systems to
create a 3D image of a desired object using scattered radiation are
described. The handheld imaging apparatus can contain a housing, a
radiation source for irradiating an object with a fan beam or cone
beam, and multiple detector elements for detecting backscattered
radiation from the object, where each detector element has a
different view of the object and collects an image of the object
that is different than the other detector elements. Alternatively,
the handheld imaging apparatus can contain a housing, a radiation
source for irradiating an object with a pencil beam of radiation,
and a detector configured to detect backscattered radiation from
the object, wherein the detector and the radiation source are
oriented off-axis relative to each other. The handheld imaging
apparatus are used to irradiate a desired object to obtain multiple
two dimensional images of the object and then creates a three
dimensional image of the object using the multiple two dimensional
images. Other embodiments are described.
Inventors: |
Turner; D. Clark; (Payson,
UT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Aribex, Inc. |
Orem |
UT |
US |
|
|
Family ID: |
49621598 |
Appl. No.: |
14/852906 |
Filed: |
September 14, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13900299 |
May 22, 2013 |
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14852906 |
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61650354 |
May 22, 2012 |
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Current U.S.
Class: |
378/41 |
Current CPC
Class: |
H05G 1/06 20130101; H05G
1/02 20130101; G01N 23/203 20130101; G01N 23/20008 20130101; G01V
5/0025 20130101 |
International
Class: |
G01N 23/203 20060101
G01N023/203 |
Claims
1. An apparatus for imaging an object, comprising: a radiation
source adapted to irradiate an object with a radiation beam; a
plurality of detector elements adapted to detect scattered
radiation from the object, wherein each of the plurality of
detector elements is arranged to view the object from a different
direction, the plurality of detector elements configured to collect
a plurality of two-dimensional images of the object substantially
simultaneously, each of the plurality of two-dimensional images
taken from a different direction; and a processor configured to
compute a three-dimensional representation of the object from the
plurality of two-dimensional images.
2. The apparatus of claim 1, wherein the apparatus comprises a
collimator for separating each detector element into detector
segments.
3. The apparatus of claim 2, wherein the collimator comprises a
grid that restricts the backscattered radiation impinging on each
detector segment.
4. The apparatus of claim 1, wherein each detector element has an
adjustable orientation angle with respect to the plane of
object.
5. The apparatus of claim 4, wherein the orientation angle is about
0 degrees so that some of the plurality of detector elements are
disposed in a plane substantially parallel to the plane of the
object.
6. The apparatus of claim 1, further comprising a housing enclosing
the radiation source and also enclosing an internal power
source.
7. The apparatus of claim 2, wherein the collimator comprises a
reverse-focusing collimator.
8. The apparatus of claim 2, wherein the collimator comprises a
focusing collimator.
9. The apparatus of claim 2, wherein the collimator comprises a
parallel plate collimator.
10. The apparatus of claim 1, wherein the radiation beam comprises
X-rays.
11. A method of imaging an object, comprising: providing an
apparatus for imaging an object, the apparatus including a
radiation source and a plurality of detector elements, wherein each
detector element is arranged to view of the object from a different
direction; irradiating the object with a radiation beam from the
radiation source to produce scattered radiation from the object;
detecting, by the plurality of detector elements, the scattered
radiation to produce a plurality of two-dimensional images of the
object, the plurality of two-dimensional images taken substantially
simultaneously, each of the plurality of two-dimensional images
taken from a different direction; and computing, by a processor, a
three-dimensional representation of the object from the plurality
of two-dimensional images.
12. The method of claim 11, wherein the apparatus comprises a
collimator for separating each detector element into detector
segments.
13. The method of claim 12, wherein the collimator comprises a
parallel plate collimator, a reverse-focusing collimator, or a
focusing collimator.
14. The method of claim 11, wherein each detector element has an
adjustable orientation angle with respect to the plane of
object.
15. The method of claim 14, wherein the orientation angle is about
0 degrees so that some of the plurality of detector elements are
disposed on a plane substantially parallel to the plane of the
object.
16. The method of claim 14, wherein the apparatus further includes
a housing enclosing the radiation source and also enclosing an
internal power source.
17. The method of claim 11, wherein the radiation beam comprises
X-rays.
18. The method of claim 12, wherein the collimator comprises a grid
that restricts the scattered radiation impinging on each detector
segment.
19. A method for imaging an object, the method comprising:
providing an apparatus for imaging an object, the apparatus
containing a radiation source and multiple, discrete detectors;
using the apparatus to raster-scan a pencil beam of radiation
across an object; detecting scattered radiation from the object in
each of the multiple detectors; generating a plurality of
two-dimensional images from the detected radiation; and using the
two dimensional images to construct a volumetric, three-dimensional
image of the object.
20. The method of claim 19, wherein the radiation beam comprises
X-rays.
21. The method of claim 19, wherein the multiple detectors and the
radiation source are oriented off-axis relative to each other.
22. The method of claim 19, wherein the multiple detectors collect
multiple two-dimensional images at various orientations relative to
the object.
23. The method of claim 19, wherein the beam intensity of the
scattered radiation is different between the multiple
detectors.
24. The method of claim 23, wherein the different beam intensities
are indicative of the absorbing material of the object in the beam
path of the scattered radiation.
25. The method of claim 19, wherein the raster-scanning is
performed with multiple orientations of the apparatus relative to
the object.
26. The apparatus of claim 1, wherein the apparatus is configured
to be handheld.
27. The apparatus of claim 1, wherein the radiation beam is a cone
beam.
28. The method of claim 11, wherein the apparatus is configured to
be handheld, and where the irradiating step comprises holding the
apparatus in a user's hands.
29. The method of claim 11, wherein the radiation beam is a cone
beam.
30. The method of claim 19, wherein the apparatus is configured to
be handheld, and where the step of using the apparatus to
raster-scan a pencil beam comprises holding the apparatus in a
user's hands.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 13/900,299, filed on May 22, 2013, which claims priority to
U.S. Provisional Patent Application 61/650,354, filed May 22, 2012,
the entire disclosures of which are incorporated herein by
reference.
FIELD
[0002] This application relates generally to handheld imaging
systems and methods for using such systems to create an image of a
desired object using scattered radiation. More particularly, this
application relates to handheld x-ray systems and methods for using
such systems to create a three dimensional (3D) image of a desired
object using scattered radiation.
BACKGROUND
[0003] In many industrial, military, security or medical
applications, images of an internal structure of objects are
required. Radiography is one type of technique that can be used for
imaging. Radiography generally comprises either conventional
transmission radiography or backscatter radiography. When access
behind an object to be interrogated is not possible, only
backscatter radiography is possible. One method of backscatter
imaging is Compton Backscatter Imaging (CBI), which is based on
Compton scattering.
[0004] Lateral migration radiography (LMR) is one type of imaging
based on CBI that utilizes both multiple-scatter and single-scatter
photons. LMR uses two pairs of detector with each pair having a
detector that is uncollimated to predominantly image single-scatter
photons and the other detector collimated to image predominantly
multiple-scattered photons. This allows generation of two separate
images, one containing primarily surface features and the other
containing primarily subsurface features.
[0005] Recently, backscatter radiography by selective detection
(RSD), a variant of LMR, has been used. RSD uses a combination of
single-scatter and multiple-scatter photons from a projected area
below a collimation plane to generate an image. As a result, the
image has a combination of first-scatter and multiple-scatter
components, offering an improved subsurface resolution of the
image.
SUMMARY
[0006] This application relates to handheld imaging systems and
methods for using such systems to create a 3D image of a desired
object using scattered radiation. The handheld imaging apparatus
can contain a radiation source for irradiating an object with a fan
beam or cone beam, and multiple detector elements for detecting
backscattered radiation from the object, where each detector
element has a different view of the object and collects an image of
the object that is different than the other detector elements.
Alternatively, the handheld imaging apparatus can contain a
radiation source for irradiating an object with a pencil beam of
radiation, and a detector configured to detect backscattered
radiation from the object, wherein the detector and the radiation
source are oriented off-axis relative to each other. The handheld
imaging apparatus are used to irradiate a desired object to obtain
multiple two dimensional images of the object and then creates a
three dimensional image of the object using the multiple two
dimensional images.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The following description can be better understood in light
of the Figures, in which:
[0008] FIG. 1 illustrates some embodiments of an imaging system
using radiography to detect backscattering;
[0009] FIG. 2a depicts other embodiments of the imaging system and
the images obtained from the system;
[0010] FIG. 2b comprises a three-dimensional image obtained by
using a reconstruction method on the images obtained in FIG.
2a;
[0011] FIG. 3 illustrates some embodiments of simulation details
that can be used in the reconstruction method;
[0012] FIG. 4 illustrates a block diagram backscatter imaging
system in accordance with some embodiments of the invention;
and
[0013] FIGS. 5 and 6 illustrate side views of some embodiments of a
handheld imaging apparatus with a first configuration of detector
elements;
[0014] FIG. 7 illustrates a bottom view of some embodiments of a
handheld imaging apparatus with a first configuration of detector
elements;
[0015] FIG. 8 illustrates a bottom view of some embodiments of a
handheld imaging apparatus with a first configuration of detector
elements along with the images shown by the detector elements;
[0016] FIG. 9 illustrate side views of some embodiments of a
handheld imaging apparatus with a second configuration of detector
elements;
[0017] FIG. 10 illustrates a bottom view of some embodiments of a
handheld imaging apparatus with a second configuration of detector
elements along with the images shown by the detector elements;
[0018] FIG. 11 illustrates a side view of some embodiments of a
handheld imaging apparatus with a third configuration of detector
elements;
[0019] FIGS. 12 and 13 illustrate bottom views of some embodiments
of a handheld imaging apparatus with a third configuration of
detector elements;
[0020] FIGS. 14 and 15 depict side views of other embodiments of a
handheld imaging apparatus; and
[0021] FIG. 16 illustrates various scanning orientations of an
object by the handheld imaging apparatus of in FIGS. 14-15.
[0022] The Figures illustrate specific aspects of the handheld
systems and methods for using the handheld x-ray systems to create
3D images based on backscattered x-rays. Together with the
following description, the Figures demonstrate and explain the
principles of the structures, methods, and principles described
herein. In the drawings, the thickness and size of components may
be exaggerated or otherwise modified for clarity. The same
reference numerals in different drawings represent the same
element, and thus their descriptions will not be repeated.
Furthermore, well-known structures, materials, or operations are
not shown or described in detail to avoid obscuring aspects of the
described devices. Moreover, the Figures may show simplified or
partial views, and the dimensions of elements in the Figures may be
exaggerated or otherwise not in proportion for clarity.
DETAILED DESCRIPTION
[0023] The following description supplies specific details in order
to provide a thorough understanding. Nevertheless, the skilled
artisan will understand that the described imaging system and
associated methods of making and using the system can be
implemented and used without employing these specific details.
Indeed, the imaging system and associated methods can be placed
into practice by modifying the described systems and methods and
can be used in conjunction with any other apparatus and techniques
conventionally used in the industry. For example, while the
description below focuses on using the imaging system for
backscatter x-rays, it could be used for other types of radiations,
such as gamma rays, neutrons, electron beams, or combinations
thereof.
[0024] As the terms on, attached to, or coupled to are used herein,
one object (e.g., a material, a layer, a substrate, etc.) can be
on, attached to, or coupled to another object regardless of whether
the one object is directly on, attached, or coupled to the other
object or there are one or more intervening objects between the one
object and the other object. Also, directions (e.g., above, below,
top, bottom, side, up, down, under, over, upper, lower, horizontal,
vertical, "x," "y," "z," etc.), if provided, are relative and
provided solely by way of example and for ease of illustration and
discussion and not by way of limitation. In addition, where
reference is made to a list of elements (e.g., elements a, b, c),
such reference is intended to include any one of the listed
elements by itself, any combination of less than all of the listed
elements, and/or a combination of all of the listed elements.
[0025] Some embodiments of non-handheld imaging systems and methods
for using such systems to create an image of a desired object using
scattered radiation (including backscattered radiation) are shown
in FIGS. 1-4. FIG. 1 illustrates a schematic representation of a
non-handheld imaging system which can be used for detecting
backscattered radiation. As used herein, scattering radiation
includes any backscattering (with an angle less than about 90
degrees) or forward scattering radiation (with an angle of 91 to
180 degrees) occurring away from the surface of the irradiated
object or material.
[0026] The system 5 contains a source of radiation 10. The
radiation source (or source) 10 can be any source (or sources) of
radiation that penetrates the desired object (or objects),
including an x-ray source, a gamma ray source, a neutron source, an
electron beam source, or combinations thereof. The source 10
irradiates the desired object area (including the object itself)
using the desired type of radiation to a desired depth.
[0027] In some embodiments, the amount of radiation (or intensity)
from the source 10 can be controlled and customized for a specific
object. For example, the radiation source 10 can be controlled to
provide a photon illumination (energy) spectrum with an average
depth in the object to obtain the detail needed to create an image.
In another example, the radiation intensity provided by radiation
source 10 can be sufficiently low so as to not saturate the
detector 12 (described below).
[0028] As shown in FIG. 1, the radiation source 10 transmits
radiation 26 which partially or completely penetrates the surface
of a material 22 that is part of an object or object volume to be
analyzed. The radiation 26 strikes internal portions of the
material 22, such as cracks 20, voids 18, or hidden objects in the
material 22. Those internal portions in the material 22 then
backscatter a portion of the radiation 26 as backscattered
radiation 28. In some configurations, the radiation source 10 is
also capable of independent motion in different directions
including rotation, in-and-out movement of the radiation source 10
from the object region, and angular movement. The radiation source
10 can be adjusted to select or focus on the object that is being
analyzed or scanner by the beam 13 of radiation 26. Alternatively,
the radiation source can be stationary and the object can be
movable.
[0029] The beam 13 from the radiation source 10 can be configured
to be any type of known beam. In some configurations, the beam can
be configured as a pencil beam, fan beam, cone beam, or
combinations thereof. In some instances, a fan beam or cone beam
can be used since they can create a higher intensity backscatter
field and have a larger field of view than a pencil beam, thereby
saving time due to the simultaneous collection from a larger field
of view. The width and/or length of the fan and/or cone beam can be
adjusted to enhance the resolution of the image.
[0030] Where a fan beam is used, it can be configured by utilizing
an aperture. In these embodiments, the beam of radiation can be
passed through the aperture such that the output from the aperture
is a fan beam of radiation. These embodiments can increase the
analysis speed by radiating a line of the object, instead of only a
spot radiated by a pencil beam, and by using the fan beam to create
a higher intensity backscatter field.
[0031] The system 5 also contains a detector 12. The detector 12
can be any detector (or detectors) of radiation that can detect the
radiation scattered from the object. In some embodiments, the
detector can include an x-ray detector, a gamma ray detector, a
neutron detector, an electron beam detector, or combinations
thereof. In other embodiments, the detector 12 can comprise NaI
scintillator crystals, plastic scintillators, photostimuable
phosphor-based image plates, TFT-based flat panel detectors,
amorphous silicon panels, or combinations thereof. For example, for
x-ray radiography on a large area image, a photostimuable
phosphor-based imaging plate and/or an amorphous silicon panel
(ASP) conversion screen bonded to an array of photosensitive
diodes.
[0032] The detector(s) can be separated into multiple detector
segments that each detects radiation along a single path or line of
sight. This separation can be accomplished using any mechanism that
isolates each segment so that it only receives radiation along that
path. For example, in the embodiments depicted in FIG. 1, the
detector 12 comprises a collimator 14 coupled to the detector 12
and so is referred to as a collimated detector 15. The collimator
contains multiple detector segments within each grid of the
collimator. In the embodiments depicted in FIG. 1, the radiation
source 10 and the collimated detector 15 can be disposed on the
same side of the object region to be analyzed. The radiation source
10 can generate photons that are directed toward the object region.
The collimated detector 15 collects photons that are backscattered
from the surfaces of the object and from objects hidden or voids
beneath the surfaces. The collimated detector not only detects the
backscattered radiation, but also assists in generating
three-dimensional images of the object area, including hidden
objects and/or voids.
[0033] The collimator 14 can include any of a variety of cross
sectional areas, including a cylindrical, elliptical
(non-circular), or rectangular. In some embodiments, the collimator
14 and the detector 12 have the shape so that any or all of the
backscattered radiation that travels through the collimator 14 is
detected. The collimator 14 may include any number of collimator
features with various geometries including fins, slats, screens,
and/or plates that may be curvilinear or flat. In some embodiments,
the collimator 14 (and such features) can be formed from any known
radiation absorbing material, such as lead. In other embodiments,
the collimator 14 (and such features) can be formed from radiation
reflective material, such as high density plastic, aluminum, or
combinations thereof. These latter embodiments are helpful when
enhancement, rather than removal, of certain backscatter radiation
is desired. In some configurations, the collimator features can be
oriented substantially perpendicular to the surface of the detector
12. In other configurations, the collimator features can be given
any orientation relative to the detector 12 that provides the
desired line of sight radiation for each segment.
[0034] In some configurations, the separation of the detector using
the collimator can create apertures 16. Backscattered radiation
from the object reaches the detector 12 through the apertures 16 if
the backscatter direction is substantially parallel to the
collimator features or has a narrow enough angle to travel through
the aperture without being absorbed by the collimator feature. The
collimator features can be modified to allow for a wider aperture
to allow in more backscattered radiation or a narrower aperture to
decrease the backscattered radiation from the object.
[0035] In some embodiments, the collimator 14 may be adjustable to
alter the direction of the backscattered radiation which can reach
the detector. In these embodiments, the position and/or orientation
of the collimator features can be modified to change the position
and/or orientation by manual mechanisms or by automatic mechanisms,
such as through computer controlled motor drives.
[0036] The collimator 14 can be coupled to the detector using any
known technique. In some embodiments, the collimator 14 can be
optically coupled to the detector 12 so that radiation passing by
the collimator 14 reaches the detector 12 and is measured, creating
a collimated detector 15. In other embodiments, the collimator 14
can be physically attached to the detector 12.
[0037] The collimated detector 15 can move in different directions
including rotation, in-and-out movement from the object region, and
angular movement. In some configurations, the collimator 14 can
move in different directions relative to the detector, including
rotation, in-and-out movement, and angular movement. These
movements can focus the image by selecting and/or isolating the
desired backscattered radiation. In other words, adjusting the
collimated detector 15 allows the user to select and isolate
particular vectors of backscattered radiation to travel through the
aperture 16 and be detected by the detector 12. Alternatively, the
collimated detector can be stationary and the object movable.
[0038] In some embodiments, the radiation source 10 and the
collimated detector 15 may be attached to a moving structure (such
as plate 24), as shown in FIG. 1. The plate 24 has a movement axis
that is substantially perpendicular to the object. In some
embodiments, this movement axis is a rotational axis and so the
plate 24 is a rotational plate. (Such rotational axis is shown as
axis 35 in FIG. 2a.) The radiation source 10 and collimated
detector 15 may be attached to the plate 24 as known in the art,
such as poles 17 extending from the rotating plate 24. The
radiation source 10 and collimated detector 15 may be located at
any location along the plate 24 and this location can be fixed or
altered as desired. This configuration allows both the collimated
detector 15 to detect backscatter and the source 10 to irradiate
the object from any location along the plate 24.
[0039] In these embodiments, the rotational axis of the plate 24
allows the source 10 and collimated detector 15 to be rotated about
the object region while maintaining a similar distance and
orientation from the object. Independent adjustments can be made to
the source 10 and collimated detector 15 to change the distance and
orientation from the object, if needed. In some configurations, the
plate 24 may comprise a single plate so the source 10 and the
collimated detector 15 remain at about an 180.degree. angle
relative each other. In other configurations, the plate 24 may be
two plates, attached or separate, to allow the radiation source 10
and collimated detector 15 to be rotated independently and oriented
at any desired angle relative to each other. For example, the
radiation source 10 may remain in a fixed position while the
collimated detector 15 can be rotated to create various angles of
orientation relative to the source 10.
[0040] In some embodiments, the system 5 can be contained in a
protective and supportive housing which can be made from any known
flexible and/or known lightweight materials. The housing holds the
various components of the system 5 in place. Lightweight housing
materials facilitate portability of the system, which can be
advantageous in certain applications. Using such materials also
allows the housing to be manufactured in a variety of desired
shapes and allows the system to be relatively lightweight to make
it easy to transport. In some embodiments, the system 5 can be
configured as a compact system so that it is readily transportable
and adopted to work within confined spaces.
[0041] In some embodiments, the system 105 can be used to detect
backscattered radiation, as shown in FIG. 2a. In this Figure, a
radiation source 30 transmits radiation 40 which penetrates the
surface of a material 36 and strikes internal details such as voids
42 and 44, hidden objects, and/or cracks (not shown) in the
material 36. These internal details in the material 36 then
backscatter a portion of the transmitted radiation 41. The
backscatter 41 can pass through a collimator 34 and be detected by
the detector 32.
[0042] In these embodiments, the radiation source 30 can generate
photons that are directed toward an object (including object region
38) and the collimated detector 33 collects photons that are
backscattered from the scanned surface and from the internal
details beneath the scanned surface. The object region 38 can be
shifted by independent adjustments to the radiation source 30 or by
changing the location of the radiation source 30 along a rotating
plate 37. For example, adjustments can be made to the object region
38 by changing the distance from the radiation source 30 to the
object region 38, which will shrink or enlarge amount of the object
region 38 being irradiated. Further, the object region 38 can be
shifted by changing the angle of the radiation source 30 with
respect to the object region 38.
[0043] In these embodiments, the beam from the radiation source 30
may be a pencil beam, a fan beam, or a cone beam. With a cone beam
it is possible to scan the entire object region 38 without the need
to move or modify the radiation source 30. The cone beam may also
be moved to increase or decrease the size of the object region.
When using a pencil beam or fan beam, it can scan a specific part
of the object region 38. The imaging system 105 can use any
scanning design, including raster scanning, to create a desired
object region 38. The object region 38 can be a variety of cross
sectional areas, including cylindrical, elliptical (non-circular),
or rectangular (includes square). As explained in further detail
below, data gathered from multiple orientations of the radiation
source 30 and collimated detector 33 should be of approximately the
same object region 38.
[0044] The configuration of the radiation source 30 and the
collimated detector 33 allow the acquisition of multiple sets of
data or images from the object region 38. Therefore, it is possible
to obtain multiple images of the same object region 38 from
different orientations between the radiation source 30 and the
collimated detector 33. In some embodiments, the orientation
between the source 30 and the collimated detector 33 can range from
about 1.degree. up to about 359.degree. relative to each other. For
example, an image of an object region 38 may be collected when the
radiation source 30 and the collimated detector 33 are initially at
a 180.degree. angle with respect to each other, and thereafter the
radiation source 30 can be rotated in 10.degree. increments around
the object region 38, collecting an image at each location. The
subsequent application of a computer model on these multiple images
will allow a three-dimensional reconstruction of the object region
38.
[0045] As shown in FIG. 2a, multiple images 46, 48, 50, and 52 can
be taken from various configurations of the radiation source 30 and
the collimated detector 33. Although FIG. 2a depicts four images,
any number of images could be used to obtain a three-dimensional
reconstruction. In some embodiments, the number of images can range
from 2 (with appropriate constraints) to any desired number. In
other embodiments, the number of images can range from 3 or 4 to 10
or 15. Of course, the more images that are taken, the better the
resolution of the 3D reconstruction.
[0046] Image 46 can be obtained by data collected from the
configuration of the source 30 and collimated detector 33 depicted
in FIG. 2a. The voids 42 and 44 found in the material 36 can be
depicted in image 46 as two-dimensional objects 42a and 44a. Image
48 can be obtained by rotating the radiation source 30 and/or the
collimated detector 33 by the desired amount and collecting
additional data to depict the voids 42 and 44 as two-dimensional
objects 42b and 44b. To obtain image 48, the radiation source 30
and collimated detector 33 were both rotated 90.degree. about the
object region 38 in the same direction (e.g. remaining at a
180.degree. angle with respect to each other). Image 50 can be
obtained by rotating both the radiation source 30 and collimated
detector 33 another 90.degree. about the object region 38 in the
same direction depicting the voids 42 and 44 as two-dimensional
objects 42c and 44c. In some configurations, the configuration used
to generate image 50 could be the minor image of the configuration
shown in FIG. 2a, having the radiation source 30 located on the
right side of the system and the collimated detector located on the
left side of the system. Image 52 is obtained by again rotating the
radiation source 30 and collimated detector 33 another 90.degree.
about the object region 38 in the same direction depicting the
voids 42 and 44 as two-dimensional objects 42d and 44d.
[0047] Rotation about the object region 38 can be accomplished by
rotating plate 37 around rotational axis 35 that is oriented
substantially perpendicular to the material 36. In these
embodiments, the plate 37 may be a single plate that rotates the
radiation source 30 and collimated detector 33 at the same
rotational distance from each other (i.e. the radiation source 30
and collimated detector 33 remain 180.degree. from each other). In
other embodiments, the plate 37 may be two plates, attached or
separate, that allow the radiation source 30 and collimated
detector 33 to rotate at different rotational distances with
respect to each other. Rotation about the object region can also be
accomplished by keeping the radiation source 30 and collimated
detector 33 stationary and rotating the object region 38.
[0048] FIG. 2b depicts a three-dimensional (3D) structure of the
object region 38 and voids 42 and 44 using the images 46, 48, 50,
and 52. This 3D structure can be obtained using the reconstruction
method described herein. The reconstruction method can be used to
supply a three-dimensional structure of any desired feature of the
material 36, including voids, cracks, corrosion, delaminations, or
other hidden objects.
[0049] The mathematical formulation, which gives rise to a forward
or generative model, for use in reconstruction is as follows. The
formulation only considers photons returning to the detector from a
single backscatter rather than multiple scattering events. The
collimated detector establishes a set of apertures each of which
has an associated line of sight. Incident photons move along the
associated line of sight, which is a three-dimensional space
defined by the location and orientation of the aperture.
[0050] FIG. 3 shows the simulation details for an embodiment of the
reconstruction method. The region of space 61 to be imaged is
called the object region. The position along collimated line 72 a
distance s from the detector segment 63 is referred to as d(s). For
the purposes of this discussion detector segment 63 may be a
portion of detectors, such as detector 12 or 32 discussed above.
Line 68 connects d(s) with source 10. The position along the line
68 a distance t from the radiation source is referred to as e(s,t).
The distance from d(s) to the radiation source 10 is referred to as
f.
[0051] The expression for the number of photons, or signal
intensity, reaching the detector segment 63 from backscatter at
d(s) can include four terms: (A) the number of photons radiated
from the radiation source 10, (B) the loss of intensity traveling
along line 68 from the radiation source 10 as it passes through a
material in the object region to reach d(s), (C) the fraction of
that intensity that is scattered along line 72, and (D) the loss of
intensity as the backscattered photons travel along line 72 to the
detector. The cumulative effects of terms A, B, C, and D are
multiplicative and thus the mathematical expression for the
intensity reaching the detector along a single path i, from a
backscatter at a distance s is:
E i ( s ) = A .times. B .times. C .times. D = E o - .intg. 0 f
.rho. ( e i ( t , s ) ) t .gamma. ( .theta. i ( s ) ) .rho. ( d i (
s ) ) - .intg. s .theta. .rho. ( d i ( q ) ) q , ( 1 )
##EQU00001##
where E.sub.0 is the intensity of the radiation source 10, .rho.(x)
is the material density as a function of the position x in the
object region, .theta..sub.i(s) is the angle formed by the two
lines 68 and 72, and .gamma.(.theta..sub.i(s)) is the differential
scattering cross section as a function of the angle at which the
two lines meet. In order to model the effects of Compton scattering
.gamma.(.theta..sub.i(s)) can be set equal to cos.sup.2(.theta.).
Alternatively, other models of the scattering can be used and
substituted into equation (1).
[0052] The total intensity traveling along path i is the integral
of all the backscatter events along the line 72. This is:
E i - .intg. 0 .infin. E i ( s ) s - E 0 .intg. 0 .infin. .intg. 0
f .rho. ( e i ( t , s ) ) t .gamma. ( .theta. i ( s ) ) .rho. ( d i
( s ) ) .intg. s .theta. .rho. ( d i ( q ) ) q s , ( 2 )
##EQU00002##
where, in practice, the integral along d(s) ends at the effective
boundaries of the object region (i.e. no material or signal becomes
insignificant).
[0053] The basic form of equations 1 and 2, unlike conventional
tomography or tomosynthesis, does not lend itself to an easy
decomposition into linear expressions of .rho., the image density.
Rather there is a nonlinear mixture of terms--a combination of the
multiplicative effect of the backscattering term with the
exponential terms that model the intensity loss and the composition
of backscattering along the line of sight, represented as the
outermost integral in Equation 2.
[0054] For reconstruction the term A=E.sub.0 can be treated as a
constant and absorbed into the detector units. The constant can be
estimated globally or measured separately before imaging. The form
for Equation 2 in terms of the integral along the detector segment
line of sight and the image density therefore becomes:
E i E 0 = .intg. 0 .infin. B i ( .rho. , s ) C i ( s ) .rho. ( d i
( s ) ) D i ( .rho. , s ) s , ( 3 ) ##EQU00003##
where the functions B.sub.i and D.sub.i are nonlinear functions of
.rho..
[0055] By treating the nonlinear interactions as secondary and
using a fixed estimate for .rho., denoted as {circumflex over
(.rho.)}, the equation becomes:
M i = E i E 0 = .intg. 0 .infin. B i ( .rho. , s ) C i ( s ) .rho.
( d i ( s ) ) D i ( .rho. , s ) s = .intg. 0 .infin. w i ( s )
.rho. ( d i ( s ) ) , ( 4 ) ##EQU00004##
where the terms that do not depend explicitly on .rho. into w.sub.i
(s) are combined. The result is a linear operator, and thus, an
expression for the image formulation that is of the same form as a
conventional x-ray formation--and, by analogy, tomographic
reconstruction.
[0056] Considering the discrete form of Equation 4, the
approximation of .rho. on a grid or individual detector segment is
denoted as R.sub.k, the value of p at a grid location is denoted as
X.sub.k, and the number of projection images collected as N. The
discrete reconstruction R.sub.k is designed to optimize the total
difference between the measured detector intensities and those
simulated from applying the imaging model to the discrete
reconstruction, R.sub.k. As shown in equation (4), the function
w.sub.i(s) can be captured as a set of weights W.sub.ij that
measures the relationship between the fixed estimated {circumflex
over (.rho.)}, the solution on the grid R.sub.k where the
backscatter occurs, and the corresponding line integrals from the
radiation source 10 and detector segment 63 to the point. Then the
reconstruction is formulated as:
R = argmax R j = 1 N ( i = 1 M W ij R j - M i ) 2 , ( 5 )
##EQU00005##
where M is the number of grid points (e.g., detector segments) in
the reconstruction, and R represents the entire collection of grid
points in the solution. R represents the object that is to be
reconstructed and M represents the projection data collected. The
weights W.sub.ij can be computed in a manner that is similar to
conventional computer tomography, that is, by using a linear
interpolation (e.g. trilinear in 3D) and using the geometric
relationships between the grid and the line integral to establish
this linear dependence for each pair of points on the detector and
the reconstruction grid.
[0057] The least squares problem in Equation (5) can be solved as
an over-constrained linear system. The linear system in Equation
(5) can be solved in a variety of ways including standard numerical
relaxation (linear system) methods and conventional iterative
methods such as the algebraic reconstruction technique (ART) or
simultaneous algebraic reconstruction technique (SART). If SART is
used, the algorithm formulates the reconstruction problem as
finding an array of unknown variables using algebraic equations
from the projection data. It is an iterative reconstruction
algorithm, which has the advantage of robustness to noise and
incomplete projection data. As the ART and SART algorithms, and
variations thereof, are known to one of skill in the art, they will
not be described further.
[0058] Due to the nature of the formulation and underlying physics,
{circumflex over (.rho.)} can be treated as fixed. Because the
integrals in Equation (4) average (or smooth) the effects of the
material properties between source-detector and position of the
backscatter, and thus, aggregate material properties along the rays
is sufficient to obtain some level of accuracy in the
reconstruction.
[0059] The accuracy results depend on the accuracy of the models of
the intensity loss that takes places as radiation moves to and from
the point of backscatter. Iterative reconstruction can be used,
denoting as a sequence of solutions R.sup.0, R.sup.1, R.sup.2, . .
. , and a sequence of discrete estimates of the solution used to
model intensity loss {circumflex over (R)}.sup.0, {circumflex over
(R)}.sup.1, {circumflex over (R)}.sup.2, . . . . This gives a
sequence of weights in the linear system, W.sub.ij.sup.l. In
implementation, the estimates of {circumflex over (R)}.sup.j simply
lag in the formulation. In this way {circumflex over
(R)}.sup.l=R.sup.l-1 and W.sup.l can be computed from the intensity
loss estimated from the previous solution and they change with each
subsequent iteration. Such schemes can be effective for nonlinear
optimization problem (i.e., let the nonlinear terms lag).
[0060] Some embodiments pertain to a method and apparatus for a
single-sided, non-destructive imaging technique utilizing the
penetrating power of radiation to image subsurface and surface
features. These embodiments can be used for a variety of
applications including non-destructive examination, medical
imaging, military, and security purposes.
[0061] Implementation of the reconstruction algorithms can be
conveniently performed using various means for reconstruction. In
some embodiments, a conventional processing system (such as, for
example, a computer) can provide a means for reconstruction using
computer tomography. In particular, the algorithms can be
implemented in software for execution on one or more general
purpose or specialized processor(s). The software can be compiled
or interpreted to produce machine executable instructions that are
executed by the processor(s). The processor can accept as inputs
any of the following: [0062] a. Orientation/position of the object
relative to the source [0063] b. Orientation/position of the object
relative to the detector [0064] c. Output signal (array of signals)
from the detector
[0065] If desired, the processor can also control the relative
positioning of the object relative to the source and detector.
Thus, the processor can output any of the following: [0066] a.
Rotational control for the object [0067] b. Linear positioning
control for the source [0068] c. Linear positioning control for the
detector
[0069] FIG. 4 illustrates an example of a system for backscatter
imaging. The system 400 can include a computer subsystem 402 (which
can, for example, be a personal computer, tablet computer,
workstation, web server, or the like). In some embodiments, the
computer subsystem 402 may comprise multiple devices that share
computing resources. For example, the computer subsystem 402 may
include computational capacity in the handheld device and the
capacities in a tablet computer, which may be used to display the
rendered images to a user. The computer system can be of
conventional design, including a processor, memory (data storage
and program storage), and input/output. The computer system can
include a display (e.g., for displaying reconstructed images) and
human input devices (e.g., keyboard, mouse, tablet, etc.). The
computer system can interface to a radiation source 404, to and
provide control information 406 to the radiation source. For
example, control information can provide for turning on/off the
radiation output of the source and setting the source output
intensity. The system can include mechanical means (e.g., as
described above) for moving the source, in which case the control
information can also control the position/orientation of the
source.
[0070] The system 400 can also include a detector 408 which can
provide measurements 410 of detected backscattered radiation to the
computer system 402. For example, the measurements can be digital
data provided from the detector. As another example, the
measurements can be analog data, and can be converted (e.g., using
an analog to digital converter) into digital form before
processing. The system can include mechanical means (e.g., as
described above) for moving the detector, in which case control
information 412 can be provided from the computer system to the
detector to control the position/orientation of the detector.
[0071] The computer system 402 can be programmed to implement
reconstruction techniques (e.g., as described above) to combine
data from multiple two-dimensional slices of detected backscattered
radiation 410 to form a three-dimensional reconstructed image. The
three-dimensional reconstructed image can be output for display,
stored in a memory for later use, or transmitted via a
communications link (e.g., the Internet) to another location for
display or storage. In some embodiments, the system 400 can also
include mechanisms for moving the object to be imaged (e.g., as
described above) in which case the computer system 402 can provide
control output 414 for controlling the position/orientation of the
object.
[0072] These imaging systems described above can be used to
detecting flaws and defects in materials and structures, scanners
for detecting target objects and/or foreign object debris inside of
walls and structures, devices for security purposes to identify
objects hidden in walls, containers or on individuals, portal
scanning, law enforcement and other security applications, and
medical imaging.
[0073] Some conventional x-ray systems use a collimated moving
pencil beam of x-rays to irradiate the sample and a large
area-detector to collect the scattered x-rays. For 3-D imaging, the
collimated detectors are used to collect x-rays from a known
scattering angle, and the sample is raster scanned to get the x-y
information. The depth information can be collected at the
intersection of the collimated x-ray beam and collimated detector.
Some of these systems provide only a 2-D image, without any depth
information to show the location of the feature of interest below
the surface. On the other hand, a 3-D imaging method can be used
determine the location of a feature of interest within a larger
volume.
[0074] The x-ray systems and methods described above improve on
some conventional x-ray systems by using a collimated multi-element
detector array and a fan or cone-beam x-ray source to collect a
complete 2-D scatter image. The assembly is then rotated in space
to obtain multiple 2-D images from which a 3-D computed tomography
reconstructed image can be obtained. But still the systems
described above can be bulky and heavy since large components are
used in order to obtain a high image resolution. In fact, such
systems are not handheld because the weight of the systems can
often be about 200 lbs.
[0075] In the embodiments illustrated in FIGS. 5-13 and those
depicted in FIGS. 14-16, the imaging systems are configured so that
they are smaller, lighter, and handheld. In these embodiments, the
handheld systems can still be used to create an image of a desired
object using scattered radiation, including backscattered x-ray
radiation. In the embodiments shown in FIGS. 5-13, the handheld
imaging systems are configured with a cone beam of radiation that
strikes the desired object. The backscattered radiation is then
detected by multiple detector elements that are oriented
differently and that are collimated. Multiple 2-D images can be
collected simultaneously from the multiple detector elements and
then used to create the 3D image.
[0076] Some configurations of these handheld imaging systems are
configured in FIGS. 5-8. As shown in FIG. 5, the system 500 may
include a hand-held x-ray device 540 and a display 580 to show an
image 582 of the desired object 562 (often embedded in a matrix
560) that has been created using the hand-held device 540. The
display 580 may communicate with the hand-held x-ray device 540
through a communication connection 584. The hand-held x-ray device
connection 584 may be wired or wireless, and may be remote or
local. Examples of some wireless transmission mechanisms include
802.11 protocols, wireless application protocols (WAP), Bluetooth
technology, or combinations thereof.
[0077] Any display mechanism can be used as display 580. Examples
of displays that can be used in the system 500 include films,
imaging plates, and digital image displays such as cathode ray
tubes (CRT), or liquid crystal display (LCD) screens. In some
configurations, the display 580 can be integrated into the housing
542 of the x-ray device 540. Such integration, however, will limit
the size of the display since too large a display can detract from
the portability of the handheld device 540. In these integrated
configurations, any small display with sufficient resolution can be
used, including liquid crystal display (LCD) screens. In other
configurations, the display can be located external to the x-ray
device 540. In these configurations, a separate imaging plate (such
as a CMOS or TFT plate) for larger features (such as medical or
veterinary imaging) can be used. The separate imaging plate can be
connected to the remainder of the x-ray device so that it receives
the image to display. In some configurations, the display 580 can
contain multiple displays with each display matched with a detector
element (as described below).
[0078] As shown in FIGS. 5-6, the x-ray device 540 contains a
housing or chassis 542 enclosing all the internal components of the
x-ray device 540. The housing 542 contains a window (or opening)
505 through which x-rays 515 are emitted and strike the desired
object 562 embedded in the matrix 560. The window 505 can be
configured for the desired object 562 so that the desired amount of
x-rays 515 is emitted to strike the object 562. Thus, the window
505 can be configured to be smaller than, larger than, or about the
same size as the desired object 562.
[0079] In the embodiments shown in FIG. 5, the x-ray device 540 may
contain a base 544 with a partial shield 546. The partial shield
546 is located behind the detectors so that the detectors are not
blocked while also partially protecting the user of the x-ray
devices from backscattered radiation.
[0080] As best shown in FIG. 6, the device 540 contains an x-ray
tube 510 which contains an x-ray source (not shown) for producing
the emitted x-rays 515. The x-ray tube 510 contains an aperture 508
through which the x-rays are emitted from the x-ray source and into
the x-ray device 540. In some configurations, the x-rays are
emitted as a fan beam and so the aperture is configured
accordingly. In other configurations, the x-rays are emitted as a
cone beam, as shown in FIG. 6, and the aperture 508 is configured
accordingly. Where a fan beam is used, the device 520 would have to
scan the beam across the desired object so that the full sample
area is illuminated and the user would have to collect the 2D
images at each position of the fan beam and a large number of such
2D images would have to be collected. By using a cone beam, the
user only need to collect one 2D image in each detector.
[0081] The x-ray device 540 also contains a power system 570 to
provide power for the x-ray device 540. The power system 570 can
contain both an internal power supply that is connected to an
internal power source. Details of such a system are described in
U.S. Pat. Nos. 7,496,178 and 7,224,769, the entire disclosures of
which are incorporated herein by reference. In other
configurations, the power source can be located external to the
device.
[0082] The x-ray device 540 also contains any other components for
efficient operation, such as a controller and other electronics
(collectively depicted as electronics 574). Further details of such
components are described in U.S. Pat. Nos. 7,496,178 and 7,224,769,
the entire disclosures of which are incorporated herein by
reference.
[0083] The x-ray device 540 also contains a detector for detecting
or sensing the scattered radiation (i.e., x-rays) 525. Any detector
that is sensitive to x-ray radiation (or the other types of
radiation described herein) can be used in the handheld x-ray
device 540. Examples of such detectors include x-rays receptors,
x-ray film, CCD sensors, CMOS sensors, TFT sensors, imaging plates,
image intensifiers, or combinations thereof.
[0084] In some configurations, the detector used in the x-ray
device 540 comprises the detector elements 548 depicted in FIGS. 5,
6, and 7. In these configurations, the detector is separated into
multiple detector elements 548 that are spaced around the object
562. The detector can be separated into any number of detector
elements, with as few as 2 or as many as thousands or millions of
pixels. In the illustrated embodiments, the detector has been
separated into 6 detector elements 548 that are evenly spaced
around the circumference of the object (i.e., every 60 degrees). In
other embodiments, though, the detector elements 548 need not so be
evenly spaced.
[0085] The individual detector elements 548 can all have
substantially the same size or can have different sizes. In the
illustrated embodiments, all of the detector elements 548 have
substantially the same size. The size of the detector elements 548
can be based on the expected size of the desired object 562 being
imaged.
[0086] The individual detector elements 548 can all have
substantially the same shape or can have a different shape. In the
illustrated embodiments, all of the detector elements have
substantially the same rectangular shape. The shape of the detector
elements used is based on the expected shape of the desired object
562 being imaged. In some embodiments, the detector elements can be
any shape, include rectangular, square, annular, polygonal,
circular, oblong, or any combination thereof.
[0087] In the embodiments shown in FIG. 6, the detector elements
548 can comprise an active detector pixel (i.e., a photodiode) 530
that has been placed on the bottom of a scintillator 535. In these
embodiments, the active detector pixels 530 are sensitive to--and
therefore detect--light. The scintillator 535 can be used to
convert the backscattered x-rays 525 to light which then impinges
on the active detector pixels 530. The active detector pixels 530
then display the light image they receive on the display 580 (or a
portion thereof). Such embodiments can be useful because they can
be cheaper to use than other x-ray detectors.
[0088] The x-ray device 540 also contains a collimator that
separates each detector element into multiple detector segments
that each detect radiation along a single path or line of sight. In
the embodiments depicted in FIGS. 6-7, each detector element 548 is
attached to one end of a collimator structure (or collimator) 512
that contains a series of grid elements 555. The collimator 512 can
include any of a variety of cross sectional areas, including a
cylindrical, elliptical (non-circular), or rectangular and can have
any number of features with various geometries including fins,
slats, screens, and/or plates that may be curvilinear or flat.
[0089] The backscattered radiation 525 from the object 562 reaches
the detector elements 548 through the apertures 528 in the
collimator 512. If the backscatter direction of the x-ray is
substantially parallel to the direction of the collimator 512 or
has a narrow enough angle to travel through the aperture 528 (as
shown in FIG. 6 by beam 526), it will strike the scintillator 535
without being absorbed by the collimator grid elements 555.
Non-substantially parallel x-ray beams (as shown by beam 527) will
be absorbed by the collimator grid elements 555.
[0090] Accordingly, the collimator 512 can be configured with any
size and shape that operates with the detector element 548 to
absorb any off-axis backscattered x-rays while allowing
substantially parallel oriented x-rays to strike the detector
elements 548. The collimator 512 can also have any desired length
or width for the grid elements 555. As well, the collimator 512 can
be modified to allow for a wider aperture to allow in more
backscattered radiation or a narrower aperture to decrease the
backscattered radiation from the object.
[0091] In some configurations, the collimator 512 can be oriented
substantially perpendicular to the surface of the detector elements
548. These configurations are illustrated in FIG. 6 where each
collimator grid element 555 is oriented substantially perpendicular
to the detector elements 548.
[0092] In these configurations, the parallel-plate collimator
restricts the field of view of each detector segment to a single
line of sight to the desired object 562. Thus, each detector
element 548 (i.e., A through F) has a different view of the key, as
shown in FIG. 8. For example, where the object to be imaged is a
key, FIG. 8 illustrates that each different detector element
captures and can display a different image 549 of the key.
[0093] In other configurations, though, the collimator features can
be given a non-parallel orientation. One example of a non-parallel
orientation of the collimator is illustrated in FIG. 9, where the
collimator features are configured so that they have a focusing
orientation so that they focus the backscattered radiation on the
detector elements. With a focusing orientation, the open end of the
collimator 512 (nearer the object 562) has a width larger than the
width at the opposite end of the collimator (where it connects with
the scintillator 535). This focusing orientation can be useful when
each detector element needs a more complete image 551 of the
desired object, as shown in FIG. 10. Such images can be compared to
FIG. 8 where the image of the key 549 on the detector element is
cut off because each detector element 548 is smaller than the
object to be imaged (key). This smaller image results from the
parallel plate collimator because it only allows the detector to
"see" a field of view that is the size of the detector element.
[0094] To obtain a more complete image of the key, other
configurations of the handheld device 540 configures the detector
elements 548 to be larger. But increasing the size of the detector
element is not always possible. So instead, the focusing
orientation of the collimator features can be used to provide a
wider field-of-view for each detector segment. But with the
focusing orientation, the image resolution can be worse than the
parallel plate orientation because the wider aperture opening on
the sample end of the collimator allows a wider incident angle for
the backscattered photons from the sample surface. Whether to use a
parallel plate orientation or a focusing orientation will depend on
the size of the object to be imaged, the size of each detector
element, the need to increase the flux, or the need to maintain the
best possible spatial resolution.
[0095] In other configurations, though, the collimator can have a
reverse-focusing orientation. With a reverse-focusing orientation,
the open end of the collimator has a width smaller than the width
at the opposite end of the collimator. This reverse focusing
orientation can be useful when better spatial resolution is
required.
[0096] In other embodiments, the detector elements 548 can be
disposed on a plane that is substantially parallel to the plane of
the object 562 being analyzed. These embodiments are depicted in
FIG. 11 where the detector elements 548 can be disposed on a plane
substantially parallel to the key 562. This configuration may allow
the detector elements 548 to be positioned closer to the key 562,
which can improve the signal to noise ratio and allow for a shorter
collection time. The image resolution can also be improved in these
embodiments since the divergence of each backscattered x-ray beam
525 is a function of the distance from the collimator 512 to the
key. At long distances, the spatial resolution can be degraded due
to overlapping field of view for each detector pixel 530. This
effect can be minimized by locating the detector elements 548 as
close as possible to the object 562 to be imaged.
[0097] The distance between the device and the desired object is,
in part, a function of the image distance from the end of the
collimator as a ratio of the collimator thickness. Closer distances
give a better surface resolution while locating the device farther
away allows a steeper angle for the detector, which yields better
depth resolution.
[0098] In these embodiments, the collimator grid elements 555 can
be angled to allow each detector element 548 to view substantially
the same field of view of the object, as shown in FIG. 12. By
changing the orientation of the detector elements 548, the
orientation of the collimator 512 has to be changed correspondingly
so that only substantially parallel x-rays 526 are transmitted
through--and off-axis x-rays 527 are absorbed by--the collimator
512.
[0099] In the embodiments shown in FIG. 12, the collimator features
are still oriented substantially parallel to each other. This
configuration provides a substantially 1:1 view of the object. In
other embodiments, though, a reverse-focusing collimator can be
used to achieve geometrical magnification on the detector (with
degraded spatial resolution). In still other embodiments, focusing
collimators can be used to achieve optimum spatial resolution over
a smaller field of view.
[0100] The specific angle of the collimator 512 in these
embodiments is selected based on the distance between the x-ray
device 540 and the object 562 which, in turn, can determine the
angle (relative to the detector element 548) of the backscattered
radiation. The smaller this distance, the smaller the angle of the
backscattered radiation and the smaller the angle of the collimator
(relative to the plane of the detector element). The larger this
distance, the larger the angle of the backscattered radiation and
the larger the angle of the collimator.
[0101] The detector elements 548 can have different configurations.
For examples, the detector elements can have different shapes,
different sizes, and different angles. This allows them to capture
different images of the desired object, which can still be used to
create a 3D image provided the reconstruction algorithm is modified
accordingly. In some embodiments, the detector elements can be
configured so that they individually or collectively lower and
raise, i.e., move along any angle and from a flat position to an
angled position. The collimator can likewise be configured so that
it can change angles as needed.
[0102] The different images collected by the detector elements can
then be used to create a 3D image. The multiple 2D views of the
same location on the sample that are collected can be used by a 3-D
reconstruction algorithm to achieve 3-D images of the object that
is imaged similar to the methods described herein.
[0103] Virtually any object that is small enough can be imaged by
the handheld x-ray devices described herein. Of course, larger
objects can be imaged, by the handheld x-ray device would become
larger and heavier and at some point, would cease to be handheld
even though it is still portable.
[0104] In some embodiments, the object 562 to be imaged (such as
the illustrated key) can be embedded in a matrix 560. The matrix
560 can be made of plastic or other material having a sufficiently
different density from the key so that the backscatter signal is
significantly different from the object 562 than from the matrix
material. In other embodiments, though, the object need not be
embedded in such a matrix. Each detector element 548 can provide a
different view of the object 562, as discussed above. By utilizing
the multiple different images, along with a 3-D reconstruction
algorithm, a 3-D image 582 of the object can be obtained and
displayed on the display 580.
[0105] The 3-D backscatter x-ray imaging with a handheld device 540
provides an advantage relative to some current devices and methods
in that they can be easily transported and used by a single
operator, can be held in place while the image is being collected,
and the 3-D image reconstruction allows the operator to obtain
depth information that is not available in a 2-D image. Similarly,
because the device is hand-held and the 3-D image may be provided
in real time, the device may be adjusted and manipulated to provide
different view of the object being viewed. This flexibility in use
may provide for additional confidence in assessing the nature of
the object. For example if a user is inspecting an airframe for
stress, the ability to explore any anomalies from different
viewpoints may provide for increased safety and decreased downtime
for the aircraft.
[0106] These handheld devices 540 are significantly lighter than
the devices described in FIG. 1-4. This decreased weight is due to
that fact that the handheld devices 540 contain no motor for
rotation, because the handheld devices 540 contain much smaller
detectors, and because they can contain a low-power battery-powered
x-ray module.
[0107] These handheld x-ray devices 540, however, suffer from the
drawback that the use of a collimator can result in high dosages.
Collimating the x-rays in these devices can cause difficulties
because only a small amount of radiation can impinge on the
detector elements. With less radiation striking the detector, the
x-ray dosage has to be increased and the size of the x-ray tube has
to be increased in order to obtain the desired image resolution.
But increased x-ray dosages can lead to safety problems.
[0108] To overcome these drawbacks, the handheld x-ray devices can
be modified with other configurations that do not use collimators.
These embodiments are illustrated in FIGS. 14-16. In these
embodiments, the handheld x-ray device 640 contains a base 660,
housing 642 enclosing the x-ray tube 610, power system 670, and
electronics 674 similar to the embodiments described in FIGS. 5-13.
The handheld x-ray device 640, however, uses a moving pencil beam
605 of x-ray radiation instead of a cone beam. This moving pencil
beam 605 can be created by limiting the aperture of the x-ray tube
610 to a very small size and/or by limiting the window 620 of the
x-ray device 640 to the desired width of the pencil beam. As well,
if needed, a collimator (not shown) can be placed between the x-ray
device 640 and the desired object to limit the size and orientation
of the x-ray beam as shown in FIG. 14. As shown in FIGS. 14-15, the
moving pencil beam 605 is emitted from different locations of the
aperture of the x-ray tube 610 and so can emerge from the handheld
device 640 with multiple orientations that can be used to
raster-scan the desired object 562.
[0109] The x-ray devices 640 in these embodiments also contain
multiple detectors. In the configurations illustrated in FIG. 14,
the x-ray device 640 contains multiple, un-collimated, discrete
detectors 648 that are attached to a support 646 of the device 640.
The detectors 648 can have any shape or size, including those
described herein. The detectors 648 can be also located off-axis
with respect to the x-ray source within the x-ray tube 610. In
other words, the detectors 648 can be located at an angle relative
to the x-ray beam 605. In some configurations, the detectors 648 in
these configurations can be much larger than the multiple detector
elements illustrated in FIGS. 5-13.
[0110] As the pencil beam is raster scanned across the surface of
the sample, the backscatter x-ray intensity is measured on each
detector 648 as a function of the beam position. Since the incident
x-ray beam is illuminating a single volume within the sample,
differences in intensity from detector to detector are indicative
of the absorbing material in the beam path from the scattering
location to the detector. By collecting the scattered intensity
from multiple detector angles, 3D reconstruction techniques can be
used to determine the density of the absorbing material in the beam
paths. That information can be used to reconstruct a full 3D volume
image of the total irradiated sample volume.
[0111] In the embodiments shown in FIG. 14, the multiple detectors
648 comprise multiple concentric circles located outward from the
window 620. Each of the detectors are discrete from each other so
that they detect the samples at different angles. While there are
two detectors illustrated in FIG. 14, the device 640 could contain
any numbers of detectors (i.e., 3, 4, 5, 6, etc.).
[0112] In other embodiments, the handheld x-ray device 640 contains
the multiple, un-collimated, discrete detectors 648 as shown in
FIG. 15. Any number of large detectors can be used, including as
few as 2 (as illustrated) and as many as desired in the final
handheld device given the size and weight restrictions of the
handheld operation. In some configurations, an array of 6 detectors
can be used similar to those shown in FIGS. 5-13 but without the
collimators. These detectors 648 can be oriented so that the
backscattered radiation 625 from the object 562 will impinge on
them.
[0113] In these embodiments, the pencil x-ray beam 605 will be
raster-scanned in 2 dimensions across the desired object 562. This
raster-scanning action will be performed in a first orientation 670
as shown in FIG. 16 to collect a first series of 2D backscatter
images. The number of images will be the same as the number of
detectors used. So if there are 6 detectors, 6 2D backscatter
images will be collected. These six 2D images can be used to can be
used to reconstruct a full 3D volume image of the total irradiated
sample volume.
[0114] Even though with multiple detectors there is no need to move
the device to a 2.sup.nd orientation, in some embodiments this
action can be performed. In these embodiments, the handheld device
640 will then be rotated and the raster-scanning action will be
performed in a second orientation 680 as shown in FIG. 16 to
collect a second series of 2D backscatter images. The handheld
device 640 can then be rotated and the raster-scanning action will
be performed in a third orientation 690 as shown in FIG. 16 to
collect a third series of 2D backscatter image. Additional
rotations and scanning processes can be performed, as needed to
increase the image resolution.
[0115] Since the detector and source are positioned off-axis,
multiple 2-D images can be obtained. Using 3-D computed tomography
algorithms substantially similar to those described above, a 3-D
image can be obtained by the reconstruction of the 3-D volume from
these 2-D projections. This multiple image collection can occur at
various angles, resulting in a 3-D volume reconstruction as
described in detail above.
[0116] In some embodiments, a method of imaging an object
comprises: providing a handheld apparatus for imaging an object
containing a radiation source for irradiating an object with a
raster scan pencil beam of radiation and multiple detectors
configured to detect scattered radiation from the object, wherein
the detectors and the radiation source are oriented off-axis
relative to each other; raster scanning the object with the
handheld apparatus to obtain a series of two dimensional images of
the object; and creating a three dimensional image of the object
using the series of two dimensional images. In this method of
claim, the multiple detectors are configured to collected multiple
2D images at various angles.
[0117] With respect to the use of substantially any plural and/or
singular terms herein, those having skill in the art can translate
from the plural to the singular and/or from the singular to the
plural as is appropriate to the context and/or application. The
various singular/plural permutations may be expressly set forth
herein for sake of clarity.
[0118] In addition to any previously indicated modification,
numerous other variations and alternative arrangements may be
devised by those skilled in the art without departing from the
spirit and scope of this description, and appended claims are
intended to cover such modifications and arrangements. Thus, while
the information has been described above with particularity and
detail in connection with what is presently deemed to be the most
practical and preferred aspects, it will be apparent to those of
ordinary skill in the art that numerous modifications, including,
but not limited to, form, function, manner of operation and use may
be made without departing from the principles and concepts set
forth herein. Also, as used herein, the examples and embodiments,
in all respects, are meant to be illustrative only and should not
be construed to be limiting in any manner.
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