Note: Descriptions are shown in the official language in which they were submitted.
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PERSONNEL SCREENING SYSTEM
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application relies on United States Provisional Patent Application
Number
61/313,772, filed on March 14, 2010, for priority, which is herein
incorporated by reference in its
entirety.
The present application also relies on United States Provisional Patent
Application
Number 61/423,585, filed on December 15, 2010, for priority, which is herein
incorporated by
reference in its entirety.
In addition, the present application relies on United States Provisional
Patent Application
Number 61/423,582, filed on December 15, 2010, for priority, which is herein
incorporated by
reference in its entirety.
In addition, the present application relies on United States Provisional
Patent Application
Number 61/423,586, filed on December 15, 2010, for priority, which is herein
incorporated by
reference in its entirety.
Further, the present application is a continuation-in-part of United States
Patent
Application Number 12/887,510, entitled "Security System for Screening People"
and assigned
to the applicant of the present invention, which is a continuation of United
States Patent Number
7,826,589, of the same title and also assigned to the applicant of the present
invention, both of
which are herein incorporated by reference in their entirety.
Further, the present application is a continuation-in-part of United States
Patent
Application Number 12/849,987, entitled "Personnel Screening System with
Enhanced Privacy"
and assigned to the applicant of the present invention, which is a
continuation of United States
Patent Number 7,796,733, of the same title and also assigned to the applicant
of the present
invention, both of which are herein incorporated by reference in their
entirety.
FIELD OF THE INVENTION
The present specification relates generally to security systems for screening
threats
contained on persons, and specifically, to a personnel screening system that
comprises modular
components for improved portability, and more specifically, to compact and
portable detector
towers.
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BACKGROUND OF THE INVENTION
Radiation based systems for screening people and in use today at transit
points, such as
airports, courthouses, etc., are generally portal systems that are bulky and
not conducive for
portable applications. Unfortunately, such prior art screening systems are not
compact enough
(example, have heavy back-end cables and wires for connecting the
photomultiplier tubes to a
centralized analog-to-digital conversion and power station) and are often
difficult and time-
consuming to use and/or transport.
Also, security systems are presently limited in their ability to detect
contraband, weapons,
explosives, and other dangerous objects concealed under clothing. Metal
detectors and chemical
sniffers are commonly used for the detection of large metal objects and
certain types of
explosives, however, a wide range of dangerous objects exist that cannot be
detected using these
devices. Plastic and ceramic weapons increase the types of non-metallic
objects that security
personnel are required to detect. Manual searching of subjects is slow, is
inconvenient, and
would not be well tolerated by the general public, especially as a standard
procedure in high
traffic centers, such as at airports.
Known prior art X-ray systems for detecting objects concealed on persons have
limitations in their design and method that prohibit them from achieving low
radiation doses,
which is a health requirement, or prevent the generation of high image
quality, which are
prerequisites for commercial acceptance. An inspection system that operates at
a low level of
radiation exposure is limited in its precision by the small amount of
radiation that can be directed
towards a person being searched. X-ray absorption and scattering further
reduces the amount of
X-rays available to form an image of the person and any concealed objects. In
prior art systems
this low number of detected X-rays has resulted in unacceptably poor image
quality.
This problem is even more significant if an X-ray inspection system is being
used in open
venues such as stadiums, shopping malls, open-air exhibitions and fairs, etc.
At such venues,
people can be located both proximate to and/or at a distance from the machine.
If a person being
scanned is not very close to the X-ray machine, the resultant image may not be
clear enough
since the amount of radiation reaching the person is very low. This limits the
range of scanning
of the system to a few feet from the front of the machine. If, however, a
person being scanned is
too close to the X-ray machine, the amount of radiation impinging on the
person may not be safe.
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Therefore, there is a need for a compact radiographic detector/source
screening system
that has improved detection efficiency, is light yet sufficiently rugged and
can be easily
unassembled for transportation and then is simple to reassemble at a site.
There is also a need for
the radiographic screening system that provides good resolution as well as
large range of view
and fast scanning speed, while keeping the radiation exposure within safe
limits. That is, the
system should not only be safe for people at close distances, but also provide
a good resolution
and penetration at standoff distances.
SUMMARY OF THE INVENTION
In one embodiment, the present specification discloses an inspection system
for detecting
objects being carried by a person, wherein said person is moving along a plane
defined by a Z
axis and a Y axis, the inspection system comprising: a) a first detection
system configured to
detect radiation scattered from said person as the person moves along the Y
axis of the plane,
wherein said first detection system comprises a first planar surface
positioned opposite to the
plane, and configured to generate electronic signals responsive to the
detected radiation; b) a
second detection system configured to detect radiation scattered from said
person as the person
moves along the Y axis of the plane, wherein said second detection system
comprises a second
planar surface positioned opposite to the plane, and configured to generate
electronic signals
responsive to the detected radiation; c) an X-ray source positioned between
said first detection
system and said second detection system, wherein said X-ray source is
configured to generate a
beam spot pattern along the Z axis of the plane and wherein said X-ray source
does not generate
beams that move along the Y axis of the plane; and d) a processing system for
analyzing the
electronic signals generated by the first detection system and the second
detection system and for
generating an image on a display.
Optionally, the X-ray source is coupled with a beam chopper and wherein said
beam
chopper operates to produce a scanning pencil beam of X-rays along the Z axis.
The beam
chopper does not produce a scanning pencil beam of X-rays along the Y axis. In
one
embodiment, the beam chopper comprises a chopper wheel having three slits and
wherein each
slit positioned 120 degrees apart from an adjacent slit. The slits are aligned
with at least two
parallel collimator slits and wherein X-rays emitted from the X-ray source
conically illuminate
the collimator slits to generate at least two parallel scanning beams
interleaved in time. In
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another embodiment, the beam chopper comprises a hollow cylinder having at
least one helical
aperture. The scanning pencil beam has a linear scan velocity and wherein said
linear scan
velocity is varied or kept constant by modifying a pitch and roll of at least
one of said helical
apertures. The scanning pencil beam has a spot size and wherein said spot size
is varied or kept
constant by modifying an aperture width of at least one of said helical
apertures.
Optionally, the first detection system is contained within a first enclosure,
wherein said
first enclosure has a first width extending from one end of said first
enclosure to an opposing end
of said first enclosure and wherein the planar surface extends along the
entire first width. The
second detection system is contained within a second enclosure, wherein said
second enclosure
has a first width extending from one end of said second enclosure to an
opposing end of said
second enclosure and wherein the planar surface extends along the entire first
width. The first
enclosure is physically separate from, and independent of, said second
enclosure. The X-ray
source is contained within a third enclosure and wherein the third enclosure
is physically
separate from, and independent of, the first and second enclosures.
Optionally, each of the first, second, and third enclosures weigh less than 88
pounds. The
third enclosure may be detachably connected to the first enclosure and the
second enclosure.
Each of the first, second, and third enclosures may be detachably connected to
a frame. The
beam chopper comprises a disk chopper that is configured to be rotated by a
motor. The speed
of the chopper wheel is dynamically controlled by a controller to optimize a
scan velocity of an
X-ray beam. The first enclosure comprises a) a first side defined by a planar
surface having an
exterior surface facing the person and an interior surface, wherein the first
side is configured to
receive the radiation scattered from the person; b) a second side in an acute
angular relationship
with said first side, wherein said second side is defined by a planar surface
having an interior
surface adapted to receive radiation passing through the first side and
wherein said second side is
configured to only receive radiation after it passes through said first side;
c) a first substrate
positioned on the interior surface of the first side, wherein the first
substrate further comprises an
active area for receiving and converting said radiation into light; d) a
second substrate positioned
on the interior surface of the second side, wherein the second substrate
further comprises an
active area for receiving and converting said radiation into light; and e) at
least one photodetector
having a light responsive area and a non-light responsive area, wherein the
light responsive area
is positioned to receive the light emitted from the first substrate and the
second substrate.
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Optionally, the radiation comprises X-ray photons and wherein said first
substrate detects
30-60% of the X-ray photons impinging on said first side. The second substrate
detects 10-30%
of the X-ray photons impinging on said first side. The inspection system
further comprises a
conveyor for enabling a standing or sitting person to move along the plane.
The generated image
comprises 480 rows, 160 columns, and 8 bits per pixel. The X-ray source
generates a beam spot
pattern along the Z axis of the plane by pivoting from a first point to a
second point and wherein
said pivoting is centered around a predefined point of rotation. The X-ray
source and a beam
chopper are coupled to a surface configured to tilt vertically in relation to
a guide member and in
response to a motor.
In another embodiment, the present specification discloses a method for
detecting
threatening objects concealed on body of person by using an inspection system
comprising at
least one radiation source to produce a scanning pencil beam of X-rays,
wherein said scanning
pencil beam has a path, and a detector arrangement comprising at least a first
detector enclosure
having a first surface and a second detector enclosure having a second
surface, the method
comprising the steps of. a) having the person move past the at least one
radiation source in a
plane perpendicular to the beam path of the scanning pencil beam and parallel
to said first
surface and second surface; b) generating an X-ray beam within an radiation
source enclosure,
wherein the radiation source comprises an X-ray source coupled with a beam
chopper and
wherein the scanning pencil beam is collimated by at least one slit in the
radiation source
enclosure to generate a vertical beam spot pattern and not a horizontal beam
spot pattern; c)
detecting radiation scattered by the person in at least one of the first
detector enclosure or second
detector enclosure; and d) processing the detected radiation to generate a two
dimensional image,
wherein said image displays any concealed explosive material being carried by
the person.
Optionally, the beam chopper comprises a chopper assembly having a hollow
cylinder
with helical slits extending along a length of the cylinder, a carbon fiber
cylinder covering the
hollow cylinder, and a polyethylene epoxy cylinder covering the carbon fiber
cylinder. The
chopper assembly is rotated by a magnetic bearing assembly comprising a
magnetic rotor and a
magnetic bearing stator and wherein the magnetic bearing assembly provides
magnetic levitation
for the chopper assembly at least during power-up and power-down states of the
beam chopper.
Optionally, the X-ray source is coupled to a vertical elevating mechanism
wherein said
elevating mechanism is coupled to a weight configured to counterbalance the X-
ray source. The
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X-ray source is coupled to a vertical elevating mechanism wherein said
elevating mechanism is
coupled to at least one lifting belt. The X-ray source is coupled to a
vertical elevating
mechanism wherein said elevating mechanism is coupled to a gear reducer and
motor and is not
coupled to a counterbalancing weight.
In another embodiment, the present specification discloses a method for
manufacturing
an inspection system, comprising: a) receiving at least one container, wherein
said at least one
container comprises a first detection system configured to detect radiation
scattered from a
person as the person moves along a path, wherein the first detection system is
contained within a
first enclosure; a second detection system configured to detect radiation
scattered from the
person as the person moves along the path, wherein the second detection system
is contained
within a second enclosure; an X-ray source positioned between said first
detection system and
said second detection system, wherein said X-ray source is configured to
generate a vertical
beam spot pattern and wherein the X-ray source is contained within a third
enclosure having an
angled left side and an angled right side; b) attaching said first enclosure
to the angled left side of
the third enclosure; and c) attaching said second enclosure to the angled
right side of third
enclosure. Stated differently, the X-ray source is configured to generate a
vertical beam spot
pattern and does not generate beams that move horizontally or configured such
that the source is
constrained to generating a beam spot that moves up and down (vertically) but
does not move
side to side (horizontally).
Optionally, the first, second, and third enclosures are each physically
separate from, and
independent of, each other. Each of the first, second, and third enclosures
weigh less than 88
pounds. Each of the first, second, and third enclosures are detachably
connected to a frame.
As further discussed below, the system can be configured with two systems
opposing
each other and defining a pathway for a person to walk through and an
inspection volume. In
one embodiment, the detection system and X-ray system enclosures are
configured with hinged
doors which open into the inspection volume and which do not open behind the
systems, thereby
decreasing the required footprint of the systems.
BRIEF DESCRIPTION OF THE DRAWINGS
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These and other features and advantages of the present invention will be
appreciated, as
they become better understood by reference to the following detailed
description when
considered in connection with the accompanying drawings, wherein:
FIG. 1 illustrates an exemplary X-ray backscatter system configuration,
including a
detection system and towers, for the screening system of the present
invention;
FIG. 2A shows multiple views of the detector towers in accordance with an
embodiment
of the present invention;
FIG. 2B shows an exploded view of the photomultiplier tubes, mounting plate
and signal
processing card;
FIG. 2C shows an exploded view of the structures that cover the assembly of
the
photomultiplier tubes, mounting plate and signal processing card within the
detector tower;
FIG. 2D shows a photomultiplier tube assembly in accordance with an embodiment
of the
present invention;
FIG. 2E shows a signal processing board in accordance with an embodiment of
the
present invention;
FIG. 2F shows the wiring connections of four photomultiplier tubes with the
signal
processing board;
FIG. 2G shows Table 1 comprising a first set of bill-of-materials with
reference to
corresponding item numbers marked in the views of FIGS. 2A through 2F;
FIG. 2H shows Table 2 comprising a second set of bill -of-materials with
reference to
corresponding item numbers marked in the views of FIGS. 2A through 2F;
FIG. 3A is an unassembled and packaged illustration of an exemplary modular X-
ray
backscatter system configuration, including detection system and towers, for
the personnel
screening system of the present invention;
FIG. 3B is an assembled illustration of the exemplary modular X-ray
backscatter system
configuration shown in FIG. 3A;
FIG. 4 illustrates a detector tower pulled apart from the radiation housing
for ease of
service access to the modular components of the screening system of the
present invention;
FIG. 5A illustrates a top view of an exemplary chopper wheel used in the
screening
system of the present invention;
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FIG. 5B illustrates an exemplary disk chopper assembly, with integrated
electromagnetic
motor and bearings;
FIG. 5C illustrates an X-ray source coupled to a disk chopper, according to
one
embodiment of the present invention;
FIG. 6A illustrates an X-ray source being used in conjunction with a chopper
wheel in an
exemplary threat detection system, further showing a tilt "CAM" mechanism
coupled to a
source;
FIG. 6B shows a diagram of the metal frame title CAM mechanism 600 in an
expanded
view, further showing the drive wheel up against a CAM arm, such that it
enables vertical
motion of the source;
FIG. 6C illustrates another view of the module illustrated in FIG. 6A, further
showing a
rotating platform to rotate the source and corresponding power supply;
FIG. 7A is a mechanical illustration of an exemplary design of one embodiment
of an
exemplary beam forming apparatus;
FIG. 7B illustrates an exemplary beam forming apparatus with an X-ray source;
FIG. 7C is a mathematical expression of the trajectory of the beam using the
spin-roll
chopper of the present invention with a single source, in accordance with one
embodiment;
FIG. 8 illustrates another embodiment of the screening system of the present
invention, in
use;
FIG. 9A is an image obtained from using a segmentation algorithm in accordance
with
one embodiment of the present invention;
FIG. 9B is an image obtained from using a segmentation algorithm in accordance
with
one embodiment of the present invention;
FIG. 9C is a close view of the segmented object from the image shown in FIG.
9b using a
segmentation algorithm in accordance with one embodiment of the present
invention;
FIG. l0A is an image obtained from using a segmentation algorithm in
accordance with
one embodiment of the present invention;
FIG. 10B is an image obtained from using a segmentation algorithm in
accordance with
one embodiment of the present invention;
FIG. 11 is a side view diagram illustrating vertical scanning using a single
radiation
source;
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FIG. 12 shows the top view of an exemplary screening arrangement used in the
present
invention;
FIG. 13 illustrates an exemplary source arrangement, having dual wheels and a
flying
aperture for range selection;
FIG. 14 illustrates an exemplary chopper wheel that can be used in the dual
wheel system
described with respect to FIG. 13;
FIG. 15 is another top view of the vertical scanning system described with
respect to FIG.
11, further illustrating a flying aperture in accordance with one embodiment
of the present
invention;
FIG. 16 illustrates an exemplary arrangement for a dual-view, quad-range
system,
according to one embodiment of the present invention;
FIG. 17A illustrates the response of two detectors to a radiation beam
traversing over an
object;
FIG. 17B is another illustration of the response of two detectors to a
radiation beam
traversing over an object; and
FIG. 17C is yet another illustration of the response of two detectors to a
radiation beam
traversing over an object.
DETAILED DESCRIPTION OF THE INVENTION
The present specification is directed towards personnel screening systems
comprising
modular components, including detector and source units. The modular
components of the
present invention allow for compact, light and yet sufficiently rugged overall
structure that can
be disassembled for ease of transportation and is also simple to reassemble at
a required site for
inspection. The novel modular architecture of the screening system of the
present invention also
allows for the modular components to be fabricated separately and be quickly
snapped on for
assembly. Similarly, the modular components can be easily disassembled for
ease of service
access to the selective components and/or for packaging for subsequent
transportation.
The present specification is also an improved method for screening individuals
at security
locations without exposing individuals to high radiation and retaining the
efficiency of the
screening process. The disclosed system allows for maximum threat detection
performance and
image clarity irrespective of the distance of the individuals from the
screening system.
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In one embodiment, a radiographic image is formed using any available
radiation
imaging technique for "body imaging" such as, but not limited to X-ray
scattering, infrared
imaging, millimeter wave imaging, RF imaging, radar imaging, holographic
imaging, CT
imaging, and MRI. Any "body imaging" system that has the potential for
displaying body detail
may be employed. In one embodiment, any photodetectable radiation or any
radiation source
with a light beam may be employed in the present invention.
In one embodiment, the system of present invention requires a subject under
inspection to
assume only one position and uses a single source with a single group of
detectors, circuits and
processor to generate two separately processed scanning beams and associated
images.
In one embodiment, the system of present invention is a walk-through
inspection system
that uses a single source with a single group of detectors, circuits and
processor to generate two
separately processed scanning beams and associated images.
In another embodiment, the system operates in a dual-source mode but uses a
single
group of detectors, circuits and processor.
The system allows for detection of threats by efficient imaging of explosive
materials
such as dynamite, C-4, as well as ceramics, graphite fibers, plastic
containers, plastic weapons,
glass vials, syringes, packaged narcotics, bundled paper currency, and even
wooden objects.
In X-ray backscatter systems for detecting concealed objects, a pencil beam of
X-rays
traverses over the surface of the body of a person being examined. X-rays that
are scattered or
reflected from the subject's body are detected by a detector such as, for
example, a scintillator
and photomultiplier tube combination. The resultant signal produced by the X-
ray detector is
then used to produce a body image, such as a silhouette, of the subject and
any concealed objects
carried by the subject.
In one embodiment, the X-ray backscatter imaging system of the present
invention is
designed such that it is optimized for near-real time imaging of people or
objects with an
interrogating radiation beam, while they are in motion. The system is also
capable of
automatically detecting threats by processing detection algorithms on the
image data in near real -
time.
The present invention is directed towards multiple embodiments. The following
disclosure is provided in order to enable a person having ordinary skill in
the art to practice the
invention. Language used in this specification should not be interpreted as a
general disavowal
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of any one specific embodiment or used to limit the claims beyond the meaning
of the terms used
therein. The general principles defined herein may be applied to other
embodiments and
applications without departing from the spirit and scope of the invention.
Also, the terminology
and phraseology used is for the purpose of describing exemplary embodiments
and should not be
considered limiting. Thus, the present invention is to be accorded the widest
scope encompassing
numerous alternatives, modifications and equivalents consistent with the
principles and features
disclosed. For purpose of clarity, details relating to technical material that
is known in the
technical fields related to the invention have not been described in detail so
as not to
unnecessarily obscure the present invention.
FIG. 1 illustrates an exemplary X-ray backscatter system configuration for the
novel
modular screening system 100 of the present invention. Referring to FIG. 1, an
X-ray source
160 is enclosed in a modular housing 165 and is employed to generate a narrow
pencil beam 102
of X-rays directed towards the subject under inspection 103.
In one embodiment, pencil beam 102 is formed with the integration of an X-ray
tube and
a beam chopping mechanism 167. The pencil beam 102 is rastered either
horizontally or
vertically across the subject. This rastering is the result of the beam
chopping mechanism by
only allowing a minimal exit aperture for the x-ray beam to project. If a
chopper wheel is
employed, as described below, the exit aperture is 1 mm in diameter resulting
in a X-ray beam
that has diverged to about 7 mm. In one embodiment, subject 103 is a human. As
the target
(person being scanned) 103 poses in front of or walks by the screening system
100, the resultant
pencil beam 102 hits the target, whereby at least a portion of the X-rays are
backscattered.
Exemplary embodiments of beam chopping mechanism 167 are described in greater
detail
below.
It should be understood to those of ordinary skill in the art that any number
of ionizing
radiation sources may be used, including but not limited to gamma radiation,
electromagnetic
radiation, and ultraviolet radiation. Preferably the X-ray energies employed
are between 30kV
and 100kV.
In one embodiment, sensors 104a and 104b are employed to detect the presence
of a
person as he or she poses in front of or walks through the screening system.
At least a portion of the scattered X-rays 105 impinges upon detector
arrangement 106. In
one embodiment, detector arrangement 106 in the screening system of the
present invention
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comprises first and second detector enclosures 110 and 120 for enabling
detection. In one
embodiment, first and second detector enclosures 110 and 120 are embodied in
the form of
modular detector towers, which comprise at least one scintillator screen. In
another embodiment,
first and second detector enclosures 110 and 120 are modular detector towers
that comprise at
least two detector screens. In alternate embodiments, the detector enclosures
may comprise any
number of arrangements including, but, not limited to a plurality of detector
screens. United
States Patent Application No. 12/262,631, entitled "Multiple Screen Detection
System" and
assigned to the applicant of the present invention, is herein incorporated by
reference. In
addition, United States Provisional Patent Application No. 61/313,733,
entitled "Multiple Screen
Detection Systems" and filed on March 14, 2010, is herein incorporated by
reference in its
entirety.
As shown in FIG. 1, detector towers 110 and 120 each comprise first side area
141,
second side area 142, and third side area 143 that are connected to each other
at an angle to form
a triangular cross-section. The first side area 141 comprises screen 147 and
faces subject 103
under inspection. The second side area 142 comprises a second screen 148 in
the interior of the
towers. In one embodiment, screens 147, 148 are relatively thick CaWO4
scintillator screens that
have a relatively short decay time of 10 microseconds that allows for the
rapid scanning of the
radiation beam with minimal image degradation. The CaWO4 screen, in one
embodiment, is
capable of detecting approximately 70% of the backscattered or transmitted
radiation, and thus,
produces approximately 250 usable light photons per 30 keV X-ray.
Additionally, the use of a
thicker screen enables the detection of more of the radiation incident upon
the detector at the
expense of lower light output. In one embodiment, the areal density of the
screen is 80
milligrams per square centimeter.
In one embodiment, to fasten the detector towers to the base, large diameter
shoulder
bolts are pre-fastened to the base, such that the detector towers can be
"twisted" and locked onto
the base. Once the radiation source and housing is attached to the base, the
detector towers
cannot be moved and twisted off. Radiation housing area 165 comprises first
angled side 170
and second angled side 171 such that they easily abut and coincide with the
sides 142 of the
detector towers 110 and 120, when the detector towers and the radiation source
housing are
integrated or assembled together. A front-end side strip 172 facing the
subject 103 comprises an
opening 173 through which X-ray beam 102 passes before striking subject 103.
Limited opening
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173 aids in the reduction of electromagnetic interference and radiation noise.
The side strip 172
also acts as a separator for the two detector towers such that the two
detector towers are
assembled symmetrically around incident X-ray pencil beam 102 to detect
backscattered X-rays
105 and provide an electronic signal characteristic of the X-ray reflectance.
In one embodiment, the detector towers 110 and 120 are spaced apart by the
strip 172
such that the chopper wheel or other beam collimation means is in the middle
of the two towers.
The two towers 110, 120 are separated by a distance `d', that in one
embodiment ranges from 1/2
to 2 times the diameter of the chopper wheel. The distance `d' defines the
field of view for the X-
ray source and is optimized for a sufficient field of view while preventing
overexposure of the
detectors.
According to one embodiment of the present invention, detector towers 110, 120
and
radiation housing 165 are of composite walls or any other similar non-
conductive material
evident to those of ordinary skill in the art that provides an optimization of
a sturdy yet light
overall structure. Specifically, housing the back-end electronics, wires and
cables associated with
the photomultipliers and radiation source within composite walls creates a
Faraday cage, thus
substantially reducing electromagnetic interference.
In an embodiment of the present invention, detector towers 110, 120 also
comprise
lighting means, such as LEDs, on the periphery or any one of the edges of the
front area 141 for
illumination depicting that the screening system is on and/or screening is in
progress. Each of the
towers 110, 120 comprises photomultiplier tubes 150 that are placed in the
interior of the towers
proximate to third side area 143. The back-end electronics of the
photomultiplier tubes 150 is
housed in the substantially semi-circular housing 151.
FIGS. 2a through 2f show structural details of the detector towers in
accordance with one
specific embodiment of the present invention. FIGS. 2g and 2h show the bill-of-
materials with
reference to corresponding item numbers marked in the views of FIGS. 2a
through 2f.
Specifically, FIG. 2a shows perspective views of identical detector towers 210
and 220 along
with their respective front views 205, top view 215 and side view 216. In one
embodiment, the
towers have a height `h' of 67 inches, lateral width `w' of 30 inches and
maximum thickness `t'
of 16 inches.
Referring now to exploded views of the detector towers in FIGS. 2b and 2c,
simultaneously, the mounting plate 225 is shown as "broken-away" and separate
from the four
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photomultiplier tube assemblies 230 that are mounted on the plate 225 when
assembled. In
accordance with an embodiment of the present invention, back-end electronics
of the
photomultiplier tubes 230 comprises a signal processing board 235 co-located
on the mounting
plate 225 in proximity to the photomultiplier tubes. FIG. 2d provides a more
detailed view of the
photomultiplier assembly 230 while FIG. 2e shows a detailed view of the signal
processing
board 235 that in this embodiment is a four-channel card corresponding to the
four
photomultiplier tubes.
At least one analog to digital conversion card and a power supply module is
mounted on
the signal processing board 235. The power supply module applies an operating
voltage to the
photomultiplier tubes while the analog to digital conversion card converts
pulse current output
from the photomultiplier tubes into digital signals for further processing.
Conventionally,
massive cables are employed to connect the photomultiplier tubes with a
central analog-to-digital
converter and power station located at a distance from the photomultiplier
tubes. By having
power supply as well as analog-to-digital converter closer to the
photomultiplier tubes, smaller
wires are needed thereby also reducing signal transient noise and improving
the overall signal-to-
noise ratio (SNR). Similarly, FIG. 2f shows wiring connections of the four
photomultiplier tubes
230 with the signal processing board 235.
Referring again to FIGS. 2b and 2c, simultaneously, a seal 226 allows the
assembly
comprising mounting plate 225, photomultipliers 230 and signal processing
board 235 to fit
tightly into the corresponding tower premise 227. An inter-connectable set of
structures cover,
both protect and allow easy access when needed to the photomultiplier tubes
located on the
mounting plate assembly. These set of structures comprise a corner cover 240
with a connector
corner cover 241; a closure cover 245 with a corresponding connector 246; two
trim side plates
250 and top and bottom handle frames 255.
Referring back to FIG. 1, in one embodiment, the inspection system 100 has
modular
components that can be disassembled for mobility and ease of transportation
and reassembled
again at the site of interest. Thus, the teardrop -shaped detector towers 110,
120 and the radiation
source housing 165 with associated electronics and cables are manufactured as
separate modules
or cabinets that can be integrated quickly to form the system 100. The novel
teardrop modular
architecture enables a compact and light overall system 100.
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FIG. 3a shows a disassembled view 300a of the screening system of the present
invention
such that its modular components, such as detector towers 310, 320 along with
radiation source
housing 365, are unassembled and packaged for ease of transportation. For
example, the
triangular cross-section of detector towers 310, 320 enables these to be
packaged abutting each
other in a way that requires minimal space for transportation. FIG. 3b shows
an assembled view
300b of the screening system that has been constructed from the transportable
package 300a of
FIG. 3a. The modular components or cabinets of the screening system of the
present invention
are designed such that they have simple and intuitive points of connection,
such as being able to
be fastened to each other, via snap buttons, for quick assembly. In one
embodiment, it takes less
than 30 minutes to assemble/deploy the screening system from its
transportable, packaged
condition. In one embodiment, it takes approximately 15 to 30 minutes to
assemble/deploy the
screening system from its transportable, packaged condition. In one
embodiment, the
assembly/deployment time is dependent upon whether the unit must be heated or
cooled to bring
the unit to safe operating temperatures.
Persons of ordinary skill in the art should appreciate that the modular
components design
of the screening system of the present invention also facilitates ease of
service access for repair
and maintenance. For example, FIG. 4 shows an assembled/deployed view 400 of
the screening
system of the present invention with detector tower 410 being pulled away from
the radiation
housing 465 for service access to the housing 465 and/or for selective repair
and maintenance of
the tower 410.
In one embodiment of the present invention, in order to obtain 2D images of
scattered
radiation, detector systems make use of a dual-axis scanning beam. Referring
back to FIG. 1,
during operation, as the subject 103 walks-by or stands in front of the
detector towers 110, 120 a
part of the pencil beam 102 of X-rays that strikes the subject 103 are back-
scattered, as rays 105
due to Compton scattering and impinge on the first screen 147 at the front
side area 141 of the
detector towers. While a portion of the scattered X-rays are detected by the
first screen 147,
some portion of theses get transmitted through the first screen 147 without
being detected and
impinge on the second screen 148 (at side 142) in the interior of the detector
towers. In one
embodiment approximately 40% of the X-ray photons impinging the first screen
147 are detected
by it while approximately 24% of the remaining X-ray photons are detected by
the second screen
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148. It should be noted that these percentages may change, depending upon the
energy of the x-
rays and the thickness of the scintillator screen.
The photomultiplier tubes 150 generate electronic signals in response to
detected rays
that are initially converted into light. The light emitted by scintillation at
screens 147, 148 is
bounced around the triangular enclosures/towers 110, 120 until captured with
the photomultiplier
tubes 150.
The electronic signals produced by the two detector towers 110, 120 are
directed to a
processor. The processor analyzes the received signals and generates an image
on a display
means. The intensity at each point in the displayed image corresponds to the
relative intensity of
the detected scattered X-rays as the beam is rastered across the subject. In
one embodiment, X-
ray source 160 communicates synchronization signals to the processor. The
processor analyzes
the detected signals and compares them to the synchronization signals to
determine the display
image. In one embodiment, display means is a monitor and is employed to
display graphical
images signaled by the processor. Display means can be any display or monitor
as commonly
known in the art, including a cathode ray tube monitor, an LCD monitor or an
LED monitor. In
one embodiment, the digitized scatter image displayed by display means
preferably consists of
480 rows by 160 columns with 8 bits per pixel.
In one embodiment of the present invention, and as shown in greater detail in
FIG. 8,
however, a single axis scanning beam through which a target will walk is
employed. The
walking motion of the target provides the second axis of motion. Thus, at any
one given instant
where the subject under inspection 103 or target moves through the vertically
moving pencil X-
ray beam 102, the precise location of the beam is known via the motor that
controls the chopper
wheel (described in greater detail below). At each instant, the detector
arrangement 106 provides
the measured response of backscattered x-rays, the strength of which is
represented in the
resultant image. Because the system knows exactly where the pencil beam is
located at every
instant that the backscattered rays are detected, the image can be "stitched"
together, to form the
comprehensive image of the target.
Thus, in one embodiment, a fixed vertical scan beam constitutes one axis of
motion and
the intended subject provides the second axis of motion by walking or being
conveyed through
the vertical scanning beam. This configuration is advantageous because the
single axis beam
requires a very small rectangular opening at the detector panel. In current
backscatter detection
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systems utilizing a dual axis scanning beam, the mechanical assembly requires
a significant
opening between the detectors to allow the scanning beam to exit. A
significant opening is
required because for a dual axis scanning beam system when the target is
stationary (where a
spinning chopper wheel provides one axis of motion and the vertical motion of
this spinning
chopper wheel provides the second axis of motion), the pencil beam of x-rays
is projected in the
horizontal direction. Thus, to cover a target the size of a person, the
opening must be wider to
allow the beam to cover entire person. In addition, a conventional large sized
opening allows a
large portion of backscatter radiation to escape undetected.
As described above, in one embodiment of the present invention, the second
axis of
motion is provided by the moving target. Thus, the beam can be oriented for
vertical motion to
allow for a smaller opening and optimum detector positioning. Referring back
to FIG. 1, and as
described above, the single axis scanning system of the present invention
incorporates a small
rectangular opening 172 between detector regions 110 and 120 for the X-rays to
emanate
therefrom. Further, the small opening 172 makes it possible to position
additional and/or larger
detector panels in the direct backscatter path, thereby enhancing image
quality.
As described above, pencil beam 102 is rastered either horizontally or
vertically across
the subject, by employing a beam chopping mechanism by only allowing a minimal
exit aperture
for the x-ray beam to project. In one embodiment, the beam chopping mechanism
is a chopper
wheel having three slits positioned at 120 degrees apart and aligned with two
parallel collimator
slits such that each chopper slit will leave one of the parallel collimator
slits while another is just
entering the opposite parallel slit. This creates two parallel scanning beams
that are interleaved
in time and can be processed separately even with a single common detector
array, circuitry and
processing, all using a single source which conically illuminates the two
parallel slits.
FIG. 5A illustrates a top view of an exemplary chopper wheel 500 which can be
used for
obtaining a dual view (using two parallel, interleaved scanning beams) using a
single source. The
chopper wheel 500 has three slits, 501a, 501b and 501c, placed at an angular
distance of 120
degrees from each other. There are also two parallel collimator slits 502a and
502b. Arrow 503
depicts the direction of motion of the chopper wheel, which in this embodiment
is clockwise.
This arrangement creates two "staggered" parallel scanning beams which, as
mentioned earlier,
are interleaved in time and can thus be processed separately using common
detectors, circuitry
and processing components.
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In one embodiment, the disk chopper assembly is dynamically controlled for
rotation
using an electromagnetic motor drive. FIG. 5B illustrates an exemplary disk
chopper assembly,
with integrated electromagnetic motor and bearings. Referring to FIG. 513, the
disk chopper 501
is coupled to the radiation source 502, which, in one embodiment, comprises an
X-ray tube. The
electromagnetic motor 503 is integrated with the X-ray tube 502 and the
chopper 501. The motor
assembly further comprises three compression bearings 504, and a V-groove 505
for belt drive
backup. FIG. 5C illustrates the X-ray tube (source) 501 coupled to the disk
chopper 502, minus
the motor assembly.
In one embodiment, the X-ray inspection system further comprises a reference
detector
that compensates and monitors each emitted beam and further functions as a
radiation monitor
for monitoring emitted radiation within the inspection region. The reference
detector is, in one
embodiment, positioned within the beam path before the beam chopping
apparatus, such as the
beam chopper disk. The reference detector is may also be positioned after the
beam chopping
apparatus, such as the beam chopper disk, at the beginning of the formed
scanned line. In such a
case, the radiation detector may acceptably block the first 2 degrees of the
beam.
FIG. 6A illustrates an X-ray source being used in conjunction with a chopper
wheel, as
described in FIGS. 5A, 513, and 5C, in an exemplary threat detection system.
The source and
chopper wheel are couple to a tilt "CAM" mechanism such that it enables
substantially equal
spacing between scan lines throughout the vertical motion of the x-ray beam.
Referring to FIG.
6A, the module comprises a tilt CAM mechanism 602 coupled with an x-ray source
assembly
610 all housed on frame 620. The tilt CAM mechanism 602 further comprises CAM
guide 604.
In addition, also housed on frame 620 is a motor for driving CAM mechanism and
the belts used
to lift the source. In one embodiment, a handle is attached to the source
assembly 610 for
enabling fitting in and removing the source assembly from the metal CAM guide
frame 604. In
various embodiments, all parts of the source assembly are securely attached by
using predefined
sizes of nuts, screws and clamps. In addition, lift belt 606 is provided to
further enable lifting
and counterbalancing of the source.
FIG. 6B shows a diagram of the tilt CAM mechanism 602 in an expanded view,
further
showing drive wheel 640 abutted up against CAM arm 642 such that it enables
vertical motion of
the source.
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In another embodiment, a counterweight is employed to counterbalance the
source and
reduce stress on the lifting motor. In another embodiment, two lift belts may
be employed to
balance the source, eliminating the counterbalance and resulting in a much
lighter source. In
another embodiment, a gear reducer (15:1 reduction) and higher torque motor
may be employed
to eliminate the use of a counterbalance, as the source now seems 15 times
lighter to the motor.
However, the motor, in this case, would have to turn 15 times faster to
achieve the same
radiation pattern.
Referring back to FIG. 6A, the source assembly 610 comprises an X-ray source
612 and a
disk wheel chopping mechanism 614 made of a suitable material such as metal or
plastic for
guiding the X-rays 616 generated by the X-ray source in a desired direction.
In one embodiment,
source assembly 610 also comprises a high voltage power supply enabling the
operation of the
source assembly. In an embodiment, the X-ray source 612, along with beam
chopping
mechanism 614, generates a narrow pencil beam of X-rays which are directed
towards a subject
under inspection through source rotation or beam traversal to create a scan
line. In one
embodiment, the disk wheel chopping mechanism 614 is optionally coupled with a
cooling plate,
which dissipates heat generated by the rotating chopper wheel. FIG. 6C
illustrates another view
of the module illustrated in FIG. 6A, further showing a rotating platform 650
to rotate the source
and corresponding power supply.
It should be understood by persons having ordinary skill in the art that
radiation sources
are typically very heavy. In order to accommodate for the weight of the X-ray
source, a chopper
wheel configuration, as employed above, has to be rather large, and thus
contributes to the
overall weight of the system. Therefore, in another embodiment, the screening
system of the
present invention is equipped with a spin-roll chopper that is designed to
present a helical profile
aperture shutter for X-ray beam scanners and that is lightweight and easy to
deploy. In addition,
the use of the spin-roll chopper obviates the need for source rotation, rather
the beam traverses
from -45 to +45 degrees.
In one embodiment, the spin-roll chopper allows for variability in both
velocity and beam
spot size by modifying the physical characteristics or geometry of the beam
chopper apparatus.
In addition, the spin-roll chopper provides a vertically moving beam spot with
constant size and
velocity to allow for equal illumination of the target and creates a wider
field of view during
operation.
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FIG. 7A illustrates an exemplary design for one embodiment of the spin-roll
chopper, as
used in various embodiments of the present invention. Beam chopper 702 is, in
one
embodiment, fabricated in the form of a hollow cylinder having helical chopper
slits 704. The
cylindrical shape enables the beam chopper 702 to rotate about the Z-axis and
along with the
helical apertures 704, create a spin-roll motion.
Thus, an X-ray beam scanner employing the spin-roll chopper of the present
invention
effectuates beam chopping by rotating the hollow cylinder 702 machined with at
least two helical
slits 704, which enables X-ray beam scanning with both constant and variable
linear scan beam
velocity and scan beam spot size. The spin-roll chopper enables both constant
and variable
linear scan beam velocity by manipulating the geometry of the helical
apertures. In one
embodiment, the velocity is varied or kept constant by manipulating the pitch
and roll of the
helical apertures along the length of the spin-roll chopper. Thus, it is
possible to have a constant
speed or to slow the scan down towards areas where more resolution is desired.
The spin-roll chopper also enables variable and constant beam spot size by
manipulating
the geometry of the helical apertures, thus varying the resultant beam power.
In one
embodiment, it is possible to manipulate the actual width of the aperture to
alter the beam spot
size. In one embodiment, the width of the helical aperture varies along the
length of the spin-roll
chopper cylinder to compensate for the varying distance of the aperture from
the center of the
source and allow for uniform beam spot projection along the scan line. Thus,
in one
embodiment, the farther the aperture is away from the source, the narrower the
width of the
helical aperture to create a smaller beam spot size. In one embodiment, the
closer the aperture is
to the source, the wider the helical aperture to create a larger beam spot
size.
When employed in a body scanning system, it is possible to vary the pitch and
roll and
width of the helical apertures such that more beam scanning power is directed
towards areas of
the body (hair, feet, etc) that require more detail and resolution and less
power is directed
towards areas of the body (midsection, etc.) that are more sensitive to
radiation.
Helical slits 704 also ensure that the projection of the X-ray beam is not
limited by the
dual collimation of the two slits. As described in greater detail below, dual
collimation refers to
the concept whereby the X-ray beam will pass through two helical slits at any
given point in
time. The resultant X-ray beam trajectory 730 is also shown in FIG. 7A and
described in greater
detail with respect to FIG. 7C below.
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In an embodiment of the present invention a plurality of viewing angles
ranging from
sixty degrees to ninety degrees can be obtained through the helical slits in
the spin-roll chopper.
In one embodiment, the scan angle is a function of the distance between the
spin-roll chopper
and both the source and the target. In addition, the overall height and
diameter of the spin-roll
chopper affects the viewing angle. The closer the spin-roll is placed to the
source, the smaller
the spin-roll chopper will need to be and similarly, the farther the spin-roll
chopper is placed
from the source, the larger the spin-roll chopper would need to be.
FIG. 7B illustrates a beam chopping mechanism using the spin-roll chopper
described
with respect to FIG. 7A. Referring to FIG. 7B, the cylindrical spin-roll
chopper 752 is placed in
front of a radiation source 754, which, in one embodiment, comprises an X-ray
tube. In one
embodiment, rotation of the chopper 752 is facilitated by including a suitable
motor 758, such as
an electromagnetic motor. In another embodiment, as described in greater
detail below, magnetic
bearings are employed to facilitate rotational movement of the spin-roll
chopper of the present
invention. The speed or RPM of rotation of the spin-roll chopper system is
dynamically
controlled to optimize the scan velocity. In one embodiment, the spin-roll
chopper system is
capable of achieving speeds up to 80K RPM.
In one embodiment, a radiation shield is provided on radiation source 754 such
that only
a fan beam of radiation is produced from the source. The fan beam of radiation
emits X-rays and
then passes through the spin-roll chopper, which acts as an active shutter.
Thus, there is only a
small opening when the spin-roll chopper, and therefore helical apertures are
rotating, which
provides the moving flying spot beam.
FIG. 7B also shows a disk chopper wheel 760 superimposed upon the source along
with
the spin-roll chopper. It can be seen from FIG. 7B that chopper wheel 760 is
substantially larger
than spin-roll chopper 752.
In accordance with an embodiment of the present invention, at certain
distances from the
center of the beam, the helical slit (of the spin roll chopper) is kept wider
than others. FIG. 7C
shows a mathematical expression of the trajectory 770 of the beam using a
single source, in
accordance with one embodiment. In order to get the dimensions of the helical
cuts in the spin-
roll cylinder, one dimension of this trajectory was removed. More
specifically, the slit is
narrower at the top 775 because there is a greater distance for the beam to
travel. Note that when
an X-ray beam travels through any opening, the beam is collimated. The farther
the beam
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travels, the wider the resultant "spot" (fan beam) is at the end of the beam.
By making the slit
narrower at the top 775, this greater distance and beam widening is accounted
for. In addition,
the slit is made wider where the distance to the object is shorter, such as at
point 780. Also,
persons of ordinary skill in the art should appreciate that by controlling the
size of the slit one
can control the density of the beam that is projected straight through.
United States Provisional Patent Application Number 61/313,772 entitled "Walk-
Through People Screening System" and filed on March 14, 2010, and its
corresponding children
applications are incorporated herein by reference in their entirety.
The system of the present invention is designed such that the distance of the
beam
chopping mechanism from the target is directly correlated with a minimum scan
height. This
allows for longer distance from source to the target, thereby extending the
depth of field with
respect to dose rate to the target. Therefore, for a given depth of imaging, a
smaller radiation
dose is required with the system of the present invention as compared to other
systems known in
the art.
An exemplary practical application of the screening system of the present
invention is
illustrated in FIG. 8. Referring to FIG. 8, first scanning side 810 and second
scanning side 820
are used to create an inspection area through which the individual to be
scanned walks. The first
scanning side 810 comprises two detector panel towers 811 and 812. In one
embodiment, X-ray
enclosure 813 is also located proximate to first scanning side 810. Second
scanning side 820 is
positioned across the walkway from first scanning side 810, thus forming
inspection area or
volume 840. Second scanning side 820 comprises two detector panel towers 821
and 822. A
second X-ray enclosure is located proximate to the second scanning side 820.
As subject 830
walks through the system both first scanning side 810 and second scanning side
820 scan the
subject to obtain an image of both a front left and a back right view of the
person. In one
embodiment, first scanning side 810 and second scanning side 820 scan the
subject sequentially,
with a minimal time delay between scans. Therefore, subject 830 does not need
to turn or stop
for scanning; a complete image is produced simply as the person walks through
the inspection
area 840. In one embodiment, a person being scanned is conveyed or moved, such
as by a
moving walkway, through the detection area. The generated image can be
reviewed at the
operator station 850. Since scanning sides comprising a source and detector
array are used for
imaging, the image produced by each scanning side can also be viewed
individually. Thus,
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referring back to FIG. 8, the operator's screen 860 also separately presents
front and rear views
852 and 854, respectively, in addition to overall picture 856. Further, in
this kind of walk-
through arrangement, several persons can be rapidly screened by simply asking
them to walk
through the inspection area in a queue. In the exemplary application, the
operator's screen 860
also shows queued front and rear images, 852 and 854, from three persons.
It should be appreciated that the inspection system is capable of imaging both
metal and
non-metal objects (including explosives and non-metal weapons) on a person
(including within
or under clothing) without the removal of clothing and is capable of
processing generated images
to only show a body outline and highlight threatening or illegal objects,
including both organic
and inorganic materials, while hiding private body features, thereby creating
a privacy image.
The inspection system is configurable such that only the privacy image will be
available to the
operator. Alternatively, the system may be configurable such that the privacy
image is the default
image but the raw image, generated prior to processing to only show a body
outline and
threatening or illegal objects, is still available to the operator.
Additionally, the system a) comprises an internal safety monitoring circuit to
continually
monitor safety of system and radiation levels during each scan, b) provides an
ionizing radiation
dose no greater than 5 micro-rem per scan to any person under inspection, c)
scans one side of
person in 8 seconds or less, d) shall have a length no greater than 125cm
(length dimension faces
person under scan), e) shall have width no greater than 100cm, f) shall have
height no greater
than 205cm, g) shall have an optional wall to aid in privacy of the subject
being screened and
prevent interference from the background, which will enhance the detection
capabilities of the
system by making inorganic objects on the side edge of the body more visible
in the image and
permit full coverage of the body in 2 scans as opposed to 4 scans when the
wall is not used, h)
shall have an optional communications monitor to facilitate communications
between a remote
inspector and a local operator and to communicate an image outline of the real
body instead of
the stick man or a simplified, i.e. "stick man", image with search locations
highlighted therein
where the image is "calibrated" to adjust for varying body heights of persons
relative to the body
height of the stick man, i) shall be able to scan a six foot person standing
10 inches away,
measured from the detector wall to the person's nose, j) shall be capable of
communicating to a
workstation deployed remote from the scanning system, k) shall be possible to
initiate a scan
from the remote workstation, 1) can be configured to a predefined number of
scans per person
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which shall complete before incrementing to the next person, m) shall permit
extra scans to be
taken, as an option available to an operator, before incrementing to the next
person, n) shall be
configurable to force an operator to pass or clear each scan independently,
even if multiple scans
are required of the same person, o) shall communicate scan results (pass or
fail) to a remote
operator via visual light indications, which can be remotely viewed by the
remote operator, on
the local system, i.e. a red light for "fail" and a green light for "pass", p)
shall be able to report
what operator was logged into the system during which time period and how many
persons were
scanned by the operator during such period, how many total persons were
scanned during each
hour of the day, and the number of scans and number of persons scanned in any
predefined time
period (such as hour, day, or month), q) shall have the option of a training
simulator with an
image library of at least 100 training images. U.S. Patent No. 7,110,493 is
hereby incorporated
by reference.
Image processing software of the detection system of present invention makes
use of
appropriate algorithms to reconstruct images such as combining separate front
and rear images to
create a complete image, as well as for image analysis to determine threats.
In one embodiment,
a segmentation algorithm is used to distinguish threat objects. An example of
use of the
segmentation algorithm is illustrated in FIGS. 9a through 9c. Referring to
FIG. 9a, image 901
shows a person free of threats carried on the body (benign subject). In FIG.
9b, image 902 shows
a person carrying a backpack 903. In order to determine whether the backpack
poses a threat, the
software uses segmentation algorithm to segment out the backpack 903 from the
image 902, and
generate a separate image 904 as shown in FIG. 9c. The object size and the
pixel intensity of the
segmented object are then used to identify threats.
The segmentation algorithm is also used to distinguish dark objects on a white
background. This feature helps to accurately identify threats comprising
absorbing materials,
such as metal knives and guns, and ceramic knives. An example of use of this
feature of the
segmentation algorithm is illustrated in FIGS. I Oa and I Ob. Referring to
FIG. I Oa, three potential
threat objects 1001, 1002 and 1003 are detected on the individual 1004 being
screened. In FIG.
10b, two threat objects 1005, 1006 are detected on the individual 1007 being
screened. In both
FIGS. lOa and 10b, the same algorithm is used for imaging, with the same
parameter settings.
From these images, it would be apparent to a person skilled in the art that
the image analysis
algorithm used by the detection system of the present invention is
significantly insensitive to the
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level of the background. This is because the background is computed from the
original image
itself, and any potential threats are highlighted. As should be evident to one
of ordinary skill in
the art, as shown in FIGS. l0a and 10b, the individual's body fills only a
partial area of the
image. The balance of the image is considered background X-ray scattered
signal.
Computational methods as simple as averaging or localized smoothing (averaging
over localized
areas) provide an accurate measure of the background signal level.
Further, the image analysis algorithm of the present invention also
facilitates rapid
screening, as it typically takes less than one second to generate an image.
United States Patent Application Number 12/887,510, entitled "Security System
for
Screening People" and United States Patent Number 7,826,589, of the same
title, both assigned
to the applicant of the present invention, are herein incorporated by
reference in their entirety.
United States Patent Application Number 12/849,987, entitled "Personnel
Screening
System with Enhanced Privacy" and United States Patent Number 7,796,733, of
the same title,
both assigned to the applicant of the present invention, are herein
incorporated by reference in
their entirety.
As mentioned earlier, with respect to FIG. 1, the design of the present
invention allows
for more detector panels to exist in the direct backscatter path, thereby
contributing to image
quality. The image quality is increased further in another embodiment, by
using an approach that
increases the area of the detection field and the number of detectors that can
be employed. This
novel approach is described with reference to FIGS. 11 and 12. FIG. 11
illustrates a side view
showing vertical scanning with a single source 1101. In this configuration,
the height 1102 of a
subject 1103 that can be scanned using the single source 1101 is limited by
the view width 1104
or the illumination span of the source.
To overcome this limitation, the present invention, in one embodiment, employs
a novel
configuration illustrated in FIG. 12, which shows a top view of an exemplary
scanning
arrangement. Referring to FIG. 12, the single axis scanning source assembly
1201 is pivoted
from point 1202a to 1202b, with a center of rotation 1203 at the front panel
of the system. As can
be seen from FIG. 12, 1204a is the view width available for the subject 1206,
when the source
1201 is fixed, whereas 1204b is the view width available when the source is
pivoting. Thus, the
view width for a given source expands when it is pivoted. In this case, a
larger number of
detectors 1205 can be added to the system, thereby providing for an increased
detection area.
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Further, a fixed rectangular opening is provided at the front panel, which
also serves as an
aperture keeping the focal spot very small in at least one axis. Further, with
an optionally
pivoting source as shown in FIG. 12, the same system can be employed to
perform scans of
targets when the person is in motion (and the source is not pivoting) or when
the person is
stationary (and the source is pivoting). With a stationary target, the image
quality is nominally
better than when a target is in motion because distortions are caused by
differential velocity in
the part of the moving subject (e.g., legs and arms). Thus under certain
operational situations,
the same system could perform a more detailed scan (with the target
stationary) if an anomalous
object is found on the first scan (when the target is in motion). The choice
of system depends
upon scanning requirements and is a trade-off between threat detection and
high through-put.
As described above, in one embodiment, the detection system of the present
invention is
implemented as a walk-through detection system. The novel design of the system
enables
utilization of low-level radiation doses for detection of weapons and
dangerous materials,
regardless of whether they consist of metal, high-Z or low-Z materials. The
radiation dose is in
range of less than 20 microrem, preferably less than 10 microrem, more
preferably less than 5
microrem and even more preferably less than 1 microrem. This portal
configuration can
accommodate a high throughput of people as compared to conventional systems
because each
person being screened simply walks through the portal. Further, the person
being screened does
not need to stop and turn his or her body as directed by a scanner system
operator. In addition, in
using such a portal configuration through which the target walks, with its
relatively confined
area, is easier to combine with other walk-through devices, including metal
detectors, drug and
explosives sniffers, and video cameras.
Besides being employed for screening of passengers at airports and railway
stations, at
open and crowded venues such as stadiums and shopping malls, applications of
the system of
present invention may be extended to inspecting the contents of vehicles and
containers at transit
points such as ports, border crossings and customs checkpoints etc. In one
embodiment, the
detection system is implemented as a `drive-through' system, through which a
cargo vehicle to
be scanned can be driven, thereby providing a second axis of motion. The
detection system of the
present invention may also be used for medical purposes.
In cases where there is a short distance between the target and the source, a
large scan
angle is required for close-up scans. This requirement of a large scan angle
competes with
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chopper wheel size and spatial resolution. In order to attain a balance
between conflicting
requirements, the system of present invention, in one embodiment, employs a
dual wheel
approach using a flying aperture for range selection. This is illustrated in a
top -down view of the
scanning system in FIG. 13. Referring to FIG. 13, the illustrated embodiment
uses two chopper
wheels 1301 and 1302. The chopper wheels 1301 and 1302 have slits 1303 and
1304,
respectively, which provide a fixed aperture for the radiation beam. A flying
aperture 1305 is
also provided close to the source 1306 which is used to select view or range
of scan just prior to
the subject entering the scan area. In one embodiment, the range selection is
aided by use of
sensor and/or camera. The range selection feature of the present invention
allows several optical
geometries to be used for various target ranges.
In one embodiment, each chopper wheel used in the dual wheel arrangement
described
above has inner and outer slits with different slit sizes, scan angles and
filtration. FIG. 14
illustrates an exemplary chopper wheel 1400 that can be used in the dual wheel
system.
Referring to FIG. 14, the wheel 1400 has inner slits 1401 and outer slits 1402
which can be used
to obtain a fixed aperture with two views and two different scan angles.
FIG. 15 illustrates another top down view of the vertical scanning system with
flying
aperture 1502 placed next to the source 1501. The system has a near view
chopper 1503 with
slits 1505 and a far view chopper 1504 with slits 1506. The outer slits of the
near view chopper
1503 are used for closest view, largest scan angle, highest filtration and its
inner slits are used for
near-mid view with medium scan angle and filtration. The outer slits of the
far view chopper
1504 are used for far-mid view, small scan angle, low filtration and its inner
slits are used for
farthest range with smallest scan angle and no filtration. The use of two
chopper wheels for scan
angle and range selection also offers the opportunity to adjust dose levels
based on target
distances.
In another embodiment, the system is implemented as a dual source, two-sided 4-
view
backscatter walk-through system, which also works on the principle of
employing a single axis-
scanning beam with the motion of object/subjects through the beam providing
the second axis.
FIG. 16 illustrates an exemplary arrangement for the dual view, quad-range
system. Referring to
FIG. 16, two sources 1601 and 1602 are used. Two choppers are used with each
source for near
and far views, in an arrangement similar to that discussed above with
reference to FIGS. 13 and
15. In the arrangement of FIG. 16 however, the near chopper 1603 is shared
between the two
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sources. Two far choppers 1604 and 1605 are used for sources 1601 and 1602
respectively. In
one embodiment, all the chopper wheels 1603, 1604 and 1605 have three slits
each. Further, the
chopper wheels 1604 and 1605 are synchronized in geometry as well as movement.
A "Vertical
Scan Aperture" or VSA 1606 is provided in the scanning system, which is
connected between
detector panels thereby offering better spatial resolution in one axis. In one
embodiment, the
VSA 1606 comprises multiple slits and helps maintain high resolution in the X-
axis.
In this embodiment, a single VSA 1606 is used for the beams 1607 and 1608
emanating
from both the sources 1601 and 1602, respectively. The dual source arrangement
described
above provides near views or ranges at larger angles. This keeps far targets
closer to the center of
the detector and hence provides better imaging for quad-range views.
In one embodiment, the detection system of the present invention utilizes the
concept of
`vector imaging' for obtaining additional information in images. In current
imaging methods, the
signals from detectors are all electrically summed together. However, in the
vector imaging
method of the present invention, the signals generated on multiple detector
panels are separated.
This allows additional `vector' information that is otherwise masked, to be
obtained. This
concept is illustrated in FIGS. 17a through 17c.
Referring to FIGS. 17a through 17c, a series of pictures illustrates the
response of two
detectors to a radiation beam traversing over an object.
In general, when the X-ray beam approaches a contour or edge of a material,
the scatter
will be blocked in the direction of the thicker object and a reduced signal
will occur on the
detector opposite to the edge. As the spot traverses upon the thicker
material, more scatter exits
through the recent edge toward the thinner side and the corresponding detector
receives more
signal. This is the method for determining contours in current imaging
systems, with dark
regions followed by bright regions in the image. Having separate signals,
however, would offer
additional information as the spot moves across the edge.
Referring now to FIG. 17a, initially, the signal 1705 received on Dl 1701a
begins to
decrease as the spot 1703a approaches the edge of the object 1704a. At this
time, the signal 1706
received at D2 1702a remains normal. Referring to FIG. 17b, as the spot 1703b
moves over the
edge of the object 1704b, the signal 1705 corresponding to the detector Dl
1701b begins to
increase back to `normal' while the signal 1706 for D2 1702b increases above
normal until the
spot 1703b has moved some distance past the edge of the object 1704b and
returns to normal.
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During the transition as shown in FIG. 17c, the signal 2006 from detector D2
1702c grows while
the signal 1705 from D 1 1701 c is still coming back from a reduced state.
At this time, a loss of information occurs if a combined signal (D1+D2) is
used, as is
apparent from the curve 1707 representing the combined signal. This is because
when the signals
for D 1 1705 and D2 1706 are equal at points A 1711 and B 1712, the combined
signal D 1+D2
1707 also follows the same path. However, the difference signal (D 1-D2), as
represented by
curve 1708 touches a near zero value at point A 1711 and a positive (or +
vector) value at point
B 1712. Similarly, the difference signal for an opposite edge contour would
create a negative
vector value. This additional information obtained from the difference signal
curve 1708 can be
used to enhance contours and edges in the images displayed.
The above examples are merely illustrative of the many applications of the
system of
present invention. Although only a few embodiments of the present invention
have been
described herein, it should be understood that the present invention might be
embodied in many
other specific forms without departing from the spirit or scope of the
invention. Therefore, the
present examples and embodiments are to be considered as illustrative and not
restrictive.
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