U.S. patent application number 10/922186 was filed with the patent office on 2005-01-27 for method and system for high-speed, 3d imaging of optically-invisible radiation and detector and array of such detectors for use therein.
This patent application is currently assigned to The Regents of the University of Michigan. Invention is credited to Kearfott, Kimberlee J., McGregor, Douglas S..
Application Number | 20050017181 10/922186 |
Document ID | / |
Family ID | 33312820 |
Filed Date | 2005-01-27 |
United States Patent
Application |
20050017181 |
Kind Code |
A1 |
Kearfott, Kimberlee J. ; et
al. |
January 27, 2005 |
Method and system for high-speed, 3D imaging of optically-invisible
radiation and detector and array of such detectors for use
therein
Abstract
A high-speed, three-dimensional, gamma-ray imaging method and
system as well as a detector and array of such detectors for use
therein are provided which characterize radioactivity distributions
in nuclear and radioactive waste and materials facilities by
superimposing radiation images on a view of the environment using
see-through display screens or shields to provide a stereoscopic
view of the radiation. The method and system provide real-time
visual feedback about the locations and relative strengths of
radioactive sources. The method and system dynamically provide
continuous updates to the displayed image illustrating changes,
such as source movement. A pair of spaced gamma-ray cameras of a
detector subsystem function like "gamma eyes". A pair of CCD
cameras may be coupled to the detector subsystem to obtain
information about the physical architecture of the environment. A
motion tracking subsystem is used to generate information on the
user's position and head orientation to determine what a user
"sees". The invention exploits the human brain's ability to
naturally reconstruct a 3D, stereoscopic image from 2D images
generated by two "imagers" separated by a known angle(s) without
the need for 3D mathematical image reconstruction. The method and
system are not only tools for minimizing human exposure to
radiation thus assisting in ALARA (As Low As Reasonably Achievable)
planning, but also are helpful for identifying contamination in,
for example, laboratory or industrial settings. Other
optically-invisible radiation such as infrared radiation caused by
smoldering fires may also be imaged. Detectors are manufactured or
configured in curvilinear geometries (such as hemispheres, spheres,
circles, arcs, or other arrangements) to enable sampling of the
ionizing radiation field for determination of positional activity
(absolute or relative amounts of ionizing radiation) or
spectroscopy (energy distributions of photons). More than one
detector system may be used to obtain three-dimensional
information. The detector systems are specifically suitable for
direct visualization of radiation fields.
Inventors: |
Kearfott, Kimberlee J.; (Ann
Arbor, MI) ; McGregor, Douglas S.; (Ann Arbor,
MI) |
Correspondence
Address: |
BROOKS KUSHMAN P.C.
1000 TOWN CENTER
TWENTY-SECOND FLOOR
SOUTHFIELD
MI
48075
US
|
Assignee: |
The Regents of the University of
Michigan
Ann Arbor
MI
|
Family ID: |
33312820 |
Appl. No.: |
10/922186 |
Filed: |
August 19, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10922186 |
Aug 19, 2004 |
|
|
|
09549464 |
Apr 14, 2000 |
|
|
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6815687 |
|
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60129837 |
Apr 16, 1999 |
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Current U.S.
Class: |
250/361R ;
257/E27.14 |
Current CPC
Class: |
H01L 27/14658
20130101 |
Class at
Publication: |
250/361.00R |
International
Class: |
G01T 001/20 |
Claims
What is claimed is:
1. A method for high-speed, 3D imaging of optically-invisible
radiation, the method comprising: detecting optically-invisible
radiation within an environment to obtain signals; processing the
signals to obtain stereoscopic data; and displaying the
stereoscopic data in the form of optically-visible radiation images
superimposed on a view of the environment so that a user can obtain
a 3D view of the radiation by utilizing natural human stereo
imaging processes.
2. The method as claimed in claim 1 wherein the environment is a
virtual environment.
3. The method as claimed in claim 1 wherein the environment is an
optically-visible environment.
4. The method as claimed in claim 1 wherein the radiation is
ionizing radiation.
5. The method as claimed in claim 4 further comprising energizing
material so that the material emits or deflects the ionizing
radiation.
6. The method as claimed in claim 1 wherein the radiation is
infrared radiation.
7. A system for high-speed, 3D imaging of optically-invisible
radiation, the system comprising: a detector subsystem for
detecting optically-invisible radiation within an environment to
obtain signals; a signal processor for processing the signals to
obtain stereoscopic data; and a display subsystem for displaying
the stereoscopic data in the form of optically-visible radiation
images superimposed on a view of the environment so that a user can
obtain a 3D view of the radiation by utilizing natural human stereo
imaging processes.
8. The system as claimed in claim 7 wherein the environment is a
virtual environment.
9. The system as claimed in claim 7 wherein the environment is an
optically-visible environment.
10. The system as claimed in claim 7 wherein the radiation is
ionizing radiation.
11. The system as claimed in claim 10 further comprising means for
energizing material so that the material emits or deflects the
ionizing radiation.
12. The system as claimed in claim 7 wherein the radiation is
infrared radiation.
13. The system as claimed in claim 7 wherein the detector subsystem
includes a set of field or area detectors.
14. The system as claimed in claim 7 wherein the detector subsystem
includes a set of point detectors.
15. The system as claimed in claim 7 wherein the detector subsystem
includes a set of passive detectors.
16. The system as claimed in claim 7 wherein the detector subsystem
includes a set of active detectors.
17. The system as claimed in claim 13 wherein the radiation is
gamma-ray radiation and wherein the set of field detectors includes
a pair of gamma-ray or other positional radiation detectors.
18. The system as claimed in claim 17 wherein the gamma-ray cameras
are scanning gamma-ray cameras and wherein each of the gamma-ray
cameras is capable of scanning the environment through a plurality
of angles and wherein the signals are processed to locate a source
within the environment.
19. The system as claimed in claim 7 wherein the radiation is
ionizing radiation and wherein the detector subsystem includes a
scintillator and a collimator for directing the ionizing radiation
into the scintillator.
20. The system as claimed in claim 19 wherein the scintillator is
curved.
21. The system as claimed in claim 7 wherein the detector subsystem
includes a compound eye detector.
22. The system as claimed in claim 21 wherein the compound eye
detector includes a plurality of individual detectors.
23. The system as claimed in claim 22 wherein the plurality of
individual detectors are movable independently or as a group.
24. The system as claimed in claim 21 wherein the compound eye
detector includes a single detector movable in three
dimensions.
25. The system as claimed in claim 14 wherein the signal processor
processes the signals to obtain a 3D map of radiation-emitting
sources.
26. The system as claimed in claim 7 wherein the detector subsystem
has stereoscopic capabilities.
27. The system as claimed in claim 7 wherein the detector subsystem
is portable.
28. The system as claimed in claim 7 wherein the display subsystem
includes a see-through display subsystem and wherein the system
further includes a tracking system for tracking the display
subsystem.
29. The system as claimed in claim 28 wherein the display subsystem
is head-mountable.
30. The system as claimed in claim 7 wherein the system provides
real-time visual feedback about location and relative strength of
at least one radiation-emitting source.
31. An ionizing radiation detector comprising: an ionization
substrate for converting ionizing radiation into a signal; a
converter coupled to the substrate for converting the signal into a
corresponding electrical signal; and a positioner for moving the
substrate in three dimensions to image over a surface of a
sphere.
32. The detector as claimed in claim 31 wherein the substrate is a
scintillator for converting ionizating radiation into photons of
light.
33. The detector as claimed in claim 32 wherein the signal is an
optical signal and the converter is a photodetector.
34. The detector as claimed in claim 32 wherein the signal is an
optical signal and the converter is a multiplier phototube.
35. An array of detectors wherein each of the detectors is a
detector as claimed in claim 31 and wherein the detectors are
arranged in a curvilinear geometry.
36. The array as claimed in claim 35 wherein the detectors are
arranged so that the array forms a substantially hemispherical
device.
37. The array as claimed in claim 35 wherein the substrates of the
detectors are formed from separate materials.
38. An ionizing radiation detector comprising: an ionization
substrate formed from a single material and having a curved first
surface and a second surface opposing the first surface for
converting ionizing radiation at the curved first surface into a
signal; and a radiation shield disposed at the second surface to
substantially block ionizing radiation at the second surface.
39. The detector as claimed in claim 38 wherein the radiation
shield is a fanned collimator.
40. The detector as claimed in claim 38 wherein the ionization
substrate is a curved scintillator for converting ionizating
radiation into photons of light.
41. The detector as claimed in claim 38 wherein the ionization
substrate is a semiconductor substrate.
42. The detector as claimed in claim 38 wherein the detector forms
a substantially hemispherical device.
43. The detector as claimed in claim 38 wherein the second surface
is curved and is substantially parallel to the curved first
surface.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. provisional
patent application Ser. No. 60/129,837, filed on Apr. 16, 1999,
entitled "Augmented Reality Radiation Display System and In Situ
Spectrometry Method For Determining the Depth Distribution of
Radionuclides". This application is related to co-pending U.S.
patent application entitled "High-Resolution Ionization Detector
and Array of Such Detectors" filed May 8, 1998 and having U.S. Ser.
No. 09/075,351.
TECHNICAL FIELD
[0002] This invention relates to methods and systems for
high-speed, 3D imaging of optically-invisible radiation and
detectors and arrays of such detectors for use therein.
BACKGROUND ART
[0003] One of the fundamental problems involving work with
radioactive materials is that radiation is invisible to the human
eye and thus poses an invisible hazard. The hazard is compounded
when one considers that these materials can be present in an
environment when not expected such as with radioactive
contamination or leaking radioactive waste storage tanks. To make
the concern even more valid, these sources of radiation can be
moving, as can be the case with airborne contamination. Thus, it is
clear that there is a need for a way to localize radioactive
sources, preferably in real-time.
[0004] Much work has been done on ways to image various forms of
radiation to provide the user with a "picture" of the radiation
present in an environment. Currently available gamma-ray cameras
are capable of providing two-dimensional information about the
location and spectroscopy of a radioactive source similar to taking
a snapshot with a standard camera. However, these cameras are not
independently capable of providing information to locate the source
in three dimensions. There have been cameras built that are capable
of obtaining real-time information, which is useful for viewing
changing sources. However, based on current designs, the
performance of some tasks in radiation environments precludes
simultaneous monitoring of the radiation field by the individual
worker, possibly resulting in increased radiation exposures. 3D
detection systems are available for medical and other environments,
but these involve different geometries and source distributions
than those considered here. Also, these methods rely on complex
mathematical reconstruction making them cumbersome and
time-consuming.
[0005] A new problem arises if one considers the complex
environments that these sources can exist in since even when
radiation images are blended with light images three-dimensionality
is lost, real-time manipulation of the images becomes complex, and
difficulties arise with time-varying source distributions. Only
three-dimensional source location truly allows for accurate
position determinations of radioactive materials. Furthermore,
real-time simultaneous display of the physical and radiation
environments is essential for observing moving or redistributing
radiation sources.
[0006] Augmented Reality
[0007] Both virtual reality (VR) and augmented reality (AR) provide
real-time interactivity which requires 3D registration. VR and AR
require a motion tracker to determine the user's position in the
virtual environment (VE), a computer to coordinate the user's
relative location, and a display. VR and AR are currently being
used in various fields including research and development, design
and testing, navigation and targeting, training, and visualization
(Azuma, 1997). There exists a wide variety of hardware and software
capable of displaying VEs. Virtual Reality Modeling Language (VRML)
2.0 is the current industry standard for programming with many
large software packages, such as AutoCAD and 3D Studio Max
(Autodesk, Inc.), exporting to this file format. The display of VR
is achieved by a head-mounted device (HMD), head-coupled display
(HCD), or a Cave Automatic Virtual Environment (CAVE). AR display
is limited to HMDs with modifications that allow the user to see
the real world through the display.
[0008] With an VE application, there are always certain limitations
that current researchers are trying to overcome. Those who program
for VR or AR applications must achieve a high level of realism
while not slowing down the computer system to intolerable speeds.
Designers of VR and AR hardware must always consider problems
arising from concerns of simplicity, spatial resolution, and
safety. For AR, one must also be concerned with using reasonable
separation for data collection and display so as to simulate the
user's interpupillary distance. Focus also presents a current field
of AR research since the human eye, when observing real objects,
must match virtual object focus at the same distance as the
physical objects. Finally, current research is being conducted into
how to increase the field of view of HMDs and HCDs to most
accurately match that of the user (Azuma, 1997).
[0009] Semiconductor Technology
[0010] Semiconductor devices typically operated by measuring the
number of electrons and holes excited by ionizing radiation (gamma
rays or charged particles) within the detector. The number of
excited charge carriers is remarkably linear with respect to the
absorbed energy from an ionizing event. The excited charge carriers
are drifted across the semiconductor detector by an externally
applied electric field, which, in turn, produces an image charge or
induced charge on the output circuit. Electrons are drifted toward
the device anode and holes are drifted toward the device cathode.
For a planar detector, the Shockley-Ramo (Shockley, 1938; Ramo,
1939) theorem describes the relationship between the induced charge
(Q*) and the displacement distance of the free electrons and holes:
1 Q * = Q 0 | x e | + | x h | W D ( 1 )
[0011] where Q.sub.0 is the initial magnitude of free charge
liberated, .DELTA.x refers to the distance traveled by the
electrons or holes from their point of origin toward their
respective electrode, W.sub.D is the width of the planar detector,
and e and h subscripts refer to electrons and holes, respectively.
If the charge carriers are removed completely from the device, in
which case they reach their respective electrodes, then the
solution to Equation (1) is simply Q*=Q.sub.0. The importance of
this result is that gamma-ray spectroscopy can be performed by
simply measuring the total induced charge measured from electrons
and holes drifted to the detector electrodes. In the presence of
charge carrier trapping (caused by imperfections in the
semiconductor), charge carriers often do not reach their respective
electrodes, and the induced charge observed becomes very dependent
on the location of the gamma-ray interaction (Day, Dearnaley and
Palms, 1967; Knoll and McGregor, 1993). The Hecht relationship
(Hecht, 1932) describes the expected induced charge for a planar
detector with charge trapping: 2 Q * = Q 0 { ( 1 - exp [ x i - W D
e W D ] ) + h ( 1 - exp [ - x i h W D ] ) } ( 2 )
[0012] where x.sub.i represents the interaction location in the
detector as measured from the cathode. The electron or hole carrier
extraction factor (Knoll and McGregor, 1993) is described by: 3 e ,
h = v e , h e , h * W D ( 3 )
[0013] where .nu. is the charge carrier mobility and .tau.* is the
carrier mean free drift time before a trapping event occurs. As can
be observed from Equations (2) and (3), the induced charge becomes
a function of the interaction location within the detector. High
.rho. values (above 50) for both electrons and holes are desirable
for high resolution gamma-ray spectroscopy. Unfortunately, the
value of .rho..sub.h for most compound semiconductors is generally
much lower than the value of .rho..sub.e Largely differing values
of .rho. for electrons and holes are not conducive to high
resolution gamma-ray energy spectroscopy when using simple planar
semiconductor detector designs (Day, Dearnaley and Palms, 1967;
Knoll and McGregor, 1993).
[0014] Recent results with novel geometrically weighted Frisch grid
CdZnTe detectors demonstrate dramatic improvements in gamma-ray
resolution (McGregor et al., 1999; McGregor and Rojeski, 1999). The
devices no longer require signals from hole transport, hence the
higher carrier extraction factor values of the electrons can be
manipulated while ignoring the difficulties imposed by hole
trapping. The device uses the geometric weighting effect, the small
pixel effect and the Frisch grid effect to produce high gamma-ray
energy resolution. The design is simple and easy to construct. The
device performs as a gamma-ray spectrometer without the need for
pulse shape rejection or correction, and it requires only one
signal output to any commercially available charge sensitive
preamplifier. The device operates very well with conventional NIM
electronic systems. Presently, room temperature (23.degree. C.)
energy resolutions of 2.68% FWHM at 662 keV and 2.45% FWHM at 1.332
MeV have been measured with 1 cubic cm CdZnTe devices.
[0015] FIG. 5 shows the basic features of a geometrically weighted
semiconductor Frisch grid radiation detector. The device dimensions
are designated as follows: cathode width=W.sub.c, anode
width=W.sub.a, width at the pervious region center=W.sub.p,
interaction region height=L.sub.i, pervious region height=L.sub.p,
measurement region height=L.sub.m, overall detector height=H and
the detector length=D. The major physical effects for the device
are briefly discussed in the following sections.
[0016] For simplicity, one assumes that gamma-ray interactions
occur uniformly throughout the detector volume. For a trapezoidal
prism, the fraction of gamma-ray interactions occurring in the
interaction region is approximated by: 4 F i ( W c + W p ) ( 2 L i
+ L p ) 2 ( W a + W c ) ( L i + L p + L m ) . ( 4 )
[0017] For the following examples, a restraint of W.sub.a=2 mm is
imposed in all cases. With W.sub.c=10 mm, D=10 mm, H=10 mm,
.theta.=43.5.degree. and with the Frisch grid=1 mm wide centered
2.0 mm back from the anode, the fraction of events occurring in the
interaction region can be shown to be 85.3%. The overall result is
high gamma-ray sensitivity in the interaction region and high
rejection for gamma-ray interactions occurring in the measurement
region while retaining good screening with the Frisch grid.
[0018] The gamma-ray interaction probability distribution function
is highest near the cathode and lowest near the anode for a
trapezoidal prism semiconductor Frisch grid detector. For uniform
irradiation, the normalized total gamma-ray probability
distribution function for a trapezoidal device is: 5 P N ( x ) dx =
2 x tan ( 2 ) + W a H 2 tan ( 2 ) + HW a dx , 0 x H , ( 5 )
[0019] where x refers to the distance from the anode toward the
cathode and .theta. refers to the acute angle at the anode (see
FIG. 5). Returning to the previous example, consider the number of
gamma-ray interactions that occur within 1 mm of the cathode.
Integrating Equation (2) from x=9 mm to x=10 mm yields a normalized
interaction probability of 16%, whereas integrating from x=0 mm to
x=1 mm yields a normalized gamma-ray interaction probability of
3.9%. Hence, over four times as many events occur within 1 mm of
the cathode than within 1 mm of the anode, which serves to
demonstrate that the accumulated gamma-ray pulse height spectrum
will be formed primarily from electron dominated induced charge
pulses. The probability of electron-dominated induced charge motion
is much higher than hole-dominated induced charge motion for simple
geometric reasons.
[0020] The signal formation from a basic planar type semiconductor
detector has a linear dependence between the carrier travel
distance and the induced charge (Day, Dearnaley and Palms, 1967;
Knoll and McGregor, 1993). Such a relationship is not true when the
contacts of a device are not the same size (Shockley, 1938;
Barrett, Eskin and Barber, 1995). The "small pixel" effect is a
unique weighting potential and induced charge dependence observed
with devices having different sized electrodes (Barrett, Eskin and
Barber, 1995).
[0021] In the case that a detector has a small anode and a large
cathode, the weighting potential changes much more abruptly near
the anode than the region near the cathode. As a result, more
charge is induced as charge carriers move in the vicinity of the
small anode than charge carriers moving in the vicinity near the
cathode. From the natural effect of geometrical weighting, more
charge carrier pairs are produced near the cathode over that of the
anode. As a result, more electrons will be drifted to the region
near the small anode than the number of holes "born" at the small
anode. The result is that the induced charge influenced by the
electron carriers becomes even greater when the small pixel effect
is coupled to the geometrically weighted effect. The combined
effects of geometrical weighting and the small pixel effect cause
the formation of a "pseudo-peak", a peak that is gamma-ray energy
dependent, but forms as a direct consequence of the geometrical
shape of the device and the device electrodes.
[0022] Device performance is best with the Frisch grid turned on
due to the hole charge motion screening (McGregor et al., 1999;
McGregor and Rojeski, 1999; McGregor et al. 1998). The Frisch grid
acts as the reference plane by which charge carriers induce charge
on the anode. Only after electrons pass into the measurement region
(see FIG. 5) do they begin to form an induced charge signal on the
preamplifier. Since holes are moving in the opposite direction
(toward the cathode), the difficulties imposed by hole trapping are
significantly negated.
[0023] Charge carriers excited in the "interaction region" are
drifted into a "measurement region". The measured induced charge
begins to accumulate only when the free carriers enter into the
measurement region, hence the device is designed such that carrier
transport comes mainly from electrons moving into the interaction
region.
[0024] Research has been undertaken in France to use AR for the
teleoperation of robots in nuclear environments in order to develop
safer and more efficient procedures for maintenance and dismantling
(Viala and Letelleir, 1997). Telerobotics using AR is also being
explored by research groups in the United States whose goal is to
develop a semi-autonomous robot using a VE of the nuclear power
plant being used (Rocheleau and Crane, 1991). The most pertinent
research project whose purpose is to perform a radiological
analysis by VR simulation for predicting radiation doses for
robotic equipment working at the Hanford Site (Knight et al. 1997).
The outcome of this research was to provide a static representation
of radiation. Mapping vasculature at an angiographic level of
detail is described by Bullitt et al. and Chen and Metz. However,
3D digital angiography involves relatively simple, string-like
geometries which lend themselves to easy visualization using its
method, and it also benefits from a fixed user position relative to
the structures of interest.
[0025] U.S. Pat. No. 5,418,364 to Hale discloses an optically
multiplexed dual line of sight system. Dual lines of sight pass
through dual independent thermal references and produce two
separate video signals, which can be viewed separately or
simultaneously.
[0026] U.S. Pat. No. 4,931,653 to Hamm discloses an ionizing
radiation detector system. The system determines the
three-dimensional spatial distribution of all secondary electrons
produced. A 3-D image is reconstructed by combining the digital
images produced by video cameras. The system analyzes the
electromagnetic spectrum from visible through gamma-ray
radiation.
[0027] U.S. Pat. No. 4,957,369 to Antonsson discloses an apparatus
for measuring three-dimensional surface geometries. A pair of diode
detectors, mounted on the focal length of the cameras, reconstruct
the full three-dimensional geometry of the surface examined using
infrared radiation.
[0028] The following U.S. patents provide general background
information: 3,932,861; 4,118,733; 4,868,652; and 5,534,694.
DISCLOSURE OF INVENTION
[0029] An object of the present invention is to provide a method
and system for high-speed, 3D imaging of optically-invisible
radiation and detector and array of such detectors for use therein
wherein 3D radiation images are superimposed on a view of the
environment.
[0030] In carrying out the above object and other objects of the
present invention, a method is provided for high-speed, 3D imaging
of optically-invisible radiation. The method includes detecting
optically-invisible radiation within an environment to obtain
signals and processing the signals to obtain stereoscopic data. The
method also includes displaying the stereoscopic data in the form
of optically-visible radiation images superimposed on a view of the
environment so that a user can obtain a 3D view of the radiation by
utilizing natural human stereo imaging processes.
[0031] The environment may be a virtual environment (i.e. generated
using a computer or other means) or it may be an optically-visible
(i.e. physical or real) environment.
[0032] The radiation may be ionizing radiation or may be infrared
radiation. Ionizing radiation works to stimulate detectors; such
radiation includes charged particles, electromagnetic waves and
neutrons-sensitive coatings (like .sup.9B, .sup.6Li).
[0033] In further carrying out the above object and other objects
of the present invention, a system is provided for high-speed, 3D
imaging of optically-invisible radiation. The system includes a
detector subsystem for detecting optically-invisible radiation
within an environment to obtain signals and a signal processor for
processing the signals to obtain stereoscopic data. The system also
includes a display subsystem for displaying the stereoscopic data
in the form of optically-visible radiation images superimposed on a
view of the environment so that a user can obtain a 3D view of the
radiation by utilizing natural human stereo imaging processes.
[0034] The detector subsystem may include a set of field detectors,
a set of point detectors, a set of passive detectors, and/or a set
of active detectors.
[0035] The radiation may be gamma-ray radiation wherein the set of
field detectors includes a pair of gamma-ray cameras. The gamma-ray
cameras may be scanning gamma-ray cameras wherein each of the
gamma-ray cameras is capable of scanning the environment through a
plurality of angles and wherein the signals are processed to locate
a source within the environment.
[0036] The radiation may be ionizing radiation wherein the detector
subsystem includes a scintillator and a collimator for directing
the ionizing radiation into the scintillator or any other radiation
detector which may be curved.
[0037] The detector subsystem may include a compound eye detector
including a plurality of individual detectors. The plurality of
individual detectors may be movable independently or as a group.
The compound eye detector may include a single detector movable in
three dimensions.
[0038] The signal processor may process the signals to obtain a 3D
map of radiation-emitting sources.
[0039] The detector subsystem may have stereoscopic capabilities
and may be portable.
[0040] The display subsystem may include a see-through display
subsystem such as a screen which may be portable or head-mountable.
The system may then include a tracking subsystem for tracking the
display subsystem.
[0041] The system typically provides real-time visual feedback
about the location and relative strength of at least one
radiation-emitting source.
[0042] Still further in carrying out the above objects and other
objects of the present invention, an ionizing radiation detector is
provided. The detector includes an ionization substrate for
converting ionizing radiation into a signal, a converter coupled to
the substrate for converting the signal into a corresponding
electrical signal, and a positioner for moving the substrate in
three dimensions to image over a surface of a sphere.
[0043] The substrate may be a scintillator for converting
ionizating radiation into photons of light. The signal is an
optical signal and the converter may be a photodetector or a
multiplier phototube.
[0044] Yet still further in carrying out the above objects and
other objects of the present invention, an array of detectors is
provided wherein each of the detectors is a detector as noted
above. The detectors are arranged in a curvilinear geometry. For
example, the detectors may be arranged so that the array forms a
substantially hemispherical device.
[0045] Preferably, the substrates of the detectors are formed from
separate materials.
[0046] Still further in carrying out the above objects and other
objects of the present invention, an ionizing radiation detector is
provided. The detector includes an ionization substrate formed from
a single material. The substrate may have a curved first surface
and a second surface opposing the first surface for converting
ionizing radiation at the curved first surface into a signal. The
detector also includes a radiation shield disposed at the second
surface to substantially block ionizing radiation at the second
surface.
[0047] The radiation shield may be a fanned collimator. The
ionization substrate may be a curved scintillator for converting
ionizating radiation into photons of light.
[0048] The ionization substrate may be a semiconductor
substrate.
[0049] The detector may form a substantially hemispherical
device.
[0050] Preferably, the second surface is curved and is
substantially parallel to the curved first surface.
[0051] The method and system of the present invention have several
unique benefits for potential users. In general, the invention has
its strongest applications in dose minimization since it allows the
user to see the radiation in the environment she is working in. For
example, there are many instances when one desires to locate
radioactive contamination in an environment. These environments can
be quite complex thus requiring more sophisticated images than the
standard 2D images. Contamination searches are presently conducted
by a radiation worker with a survey meter who spends a great deal
of time inspecting the environment by hand. The invention would
allow the user to obtain rapid 3D radiation maps in real-time.
Should the source by moving or changing, this would be able to be
monitored. Thus, the clean up of the contamination would be
significantly faster, reducing the worker's exposure to the
radiation. This application would be extremely useful to any
industrial or laboratory setting which uses gamma-ray
radiation.
[0052] Another example involves the survey of waste drums or casks
such as those stored at Hanford National Laboratory (HNL), a
facility run by the Department of Energy. Such containers require
constant monitoring to determine if they are leaking. This
monitoring could be quickly and easily achieved by the invention
which would minimize worker time and possible exposures to
unnecessary amounts of radiation.
[0053] These casks at HNL and similar casks and waste drums would
provide another interesting problem that the invention could solve.
It is frequently the case that little is known about the isotropic
concentration of materials within the containers. For example, the
HNL casks are a sludge of various radioisotopes, but little is
known about where within the cask each isotope is located. It is
also possible that there could be various types of solid waste
within a waste drum, but its position and orientation within the
drum is not known. Using its spectroscopic features, the method and
system of the invention can select an energy region of interest and
image just materials emitting that particular energy, thus
determining the position within the drum or cask of materials of
the isotope in question.
[0054] The above objects and other objects, features, and
advantages of the present invention are readily apparent from the
following detailed description of the best mode for carrying out
the invention when taken in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0055] FIG. 1 is a block diagram schematic view of a system
constructed in accordance with the present invention wherein a 3D
gamma-ray detection subsystem is coupled to an augmented reality
radiation display subsystem;
[0056] FIG. 2 is a schematic view of a scanning gamma camera
subsystem; the cameras illustrated are able to scan the environment
through various angles; triangulation of the source is achieved by
matching the points of highest intensity and the distance of the
source is then determined by calculating the parallax between the
converging lines of sight of various angles with simple geometric
considerations;
[0057] FIG. 3 is a schematic view of a fanned (or radial)
collimator and a curved scintillator;
[0058] FIGS. 4a and 4b are schematic views of a compound eye
detector; FIG. 4a represents the single detector version of this
radiation camera which is capable of rotating in three dimensions
to image over the surface of a sphere, thus creating an active
compound eye; FIG. 4b is a cross section of a collection of
multiple detectors similar to the view of FIG. 4a which create a
passive compound eye; and
[0059] FIG. 5 is a view of a geometrically weighted semiconductor
Frisch grid radiation spectrometer which may be used in the method
and system of the invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0060] The method and system of the present invention solves the
broad problem of detecting physical things, such as ionizing and
non-ionizing radiation, that are not able to be easily and directly
perceived by human vision and presenting the radiation using
methods of supplementing optical input data with other information
such as by augmented reality (AR) and using some visualization
method for displaying these data as shown in FIG. 1. This invention
may combine the principles of computerized tomography (in
particular, limited angle emission tomography, simplified by the
lack of significant attenuation of transmitted photons in air) or
other alternatives such as the techniques of computer vision to
produce data to be viewed in 3D using AR.
[0061] The computer of FIG. 1 may be programmed to perform
tomographic algorithms which are able to reconstruct 3D images
rapidly, and are accompanied by an additional algorithm or hardware
device to derive stereoscopic data from the resulting 3D maps.
These data or other forms of data from detectors are then fed to
human eyes to allow for 3D stereoscopic visualization of the
optically invisible substance, source, or field. An alternative to
using computerized tomography is the use of computer vision or
other specialized computational algorithms to produce stereoscopic
data sets from simple pairs (or more) of 2D views as optionally
noted in FIG. 1.
[0062] Special designs of a detection subsystem, examples of which
are noted below, eliminate the requirement of having either a
computerized tomographic method or computer vision algorithm. With
special attention paid to the selection of the detectors themselves
(optimized efficiencies), the devices could operate in real-time.
This may be more difficult for some types of the "invisible to the
eyes" radiation or other substances. This problem is circumvented
by the use of a specialized, rapid computer vision algorithms, or
alternative detection subsystem designs with direct display to the
eyes, or data obtained from 3-D reconstruction. A different
approach would be to move the detection subsystems in such a
fashion that all signals originating from one plane of interest are
blurred. Motion could be changed to then "focus" on other planes,
and the results or set of results processed in order to derive
appropriately stereoscopic data sets for input to a display
subsystem.
[0063] AR or other methods applied to this overall problem require
special care in the display of the data, so that: 1) the objects
being added to the physical, optically-opaque reality are easily
visualized; 2) the physical (optically-opaque) reality can be seen
into to reveal the data of interest; and 3) the physical reality
can be viewed through the previously optically-invisible data being
displayed. Such displays most likely will be of stationary or
moving dots, groups of dots, spheres, groups of spheres, or other
objects possibly with a cloud-like appearance as well as
three-dimensional surface(s) and wire-frame, computer-generated
objects. The best approach, however, is yet to be determined and
may need to be adjusted for the needs and capabilities of
individual users. Optically invisible substances, sources, or
fields with signals emanating from behind optically opaque objects
could appear to be (appropriately) located behind these physical
objects (e.g. allowing one to "see through" walls). In some cases,
the signal could be attenuated in magnitude as a result of passage
through the physical barriers (unless point detectors are placed in
those locations). Because the physical barriers would still be
apparent to the user, the user will learn to use these clues to
mentally adjust for any signal attenuation. Some training of the
user in visualizations using the methods may be needed with the
system for optimal performance. More complex feature identification
techniques, possibly including distance-to-object sensors, could be
used to further enhance performance of the overall system.
[0064] Variations on each of the portions of the system for
stereoscopic display (AR or other methods) of "invisible" data
follow. The example of ionizing radiation (x-rays and gamma-rays)
will be primarily used for illustrative purposes in the discussion
which follows.
[0065] Detectors of the System
[0066] A key component for the system is the detector subsystem
which, as indicated, can include either a point detector (a
detector which obtains data from a single point such as a
voltmeter) or a field detector (a detector that is capable of
obtaining data from a variety of points simultaneously such as an
optical camera). Table 1 illustrates examples of the types of
detectors that could be used with the overall approach,
corresponding to different types of optically-invisible substances
for which visualization is desired. This list is by no means
exhaustive, and does not contain all possible point and field
detectors.
1TABLE 1 Example set of point and field detectors. Most point
detectors listed below are passive, or detectors that would require
a network of point detectors at various locations. * denotes point
detectors that are active, or systems that would not require a
network of detectors but would actively detect these quantities
remotely. Field Point Gamma-ray cameras Alpha particle detectors
X-ray cameras Beta particle detectors
Infrared/temperature-sensitive Smoke detectors cameras Neutron
radiographs Chemical sensors Positron emission tomographs
Laser-scanning spectrographs* Single photon emission Thermometers
tomographs Flow velocity and Gauss meters (magnetic field)
acceleration meters Laser/radar/ledar range finders Laser
transmission for smoke detection* Neutron detectors (i.e. non-
radiographs)
[0067] Additional care must be taken in the selection of the
detector subsystem to ensure that appropriate stereoscopic data
result. For example, the primary detector subsystem used for the
ionizing radiation visualization could be a pair of gamma-ray
cameras adapted to provide stereoscopic data. For optimal
performance, these cameras would require not only planar imaging
capability from different angles, but focusing or production by
other means of the image information needed for stereoscopic
vision.
[0068] Gamma-ray cameras are not able to "focus" gamma-rays which
is a primary requirement for stereo vision. Thus, compensation for
this is required to achieve the best possible result. A variety of
camera designs are possible to achieve this. One approach would be
through source location by computed parallax obtained by two gamma
cameras which would swing through a series of angles to pin-point
the location of the radiation (see FIG. 2). This method would
require a computer algorithm to determine the parallax angle or
angles where the maximum amount of radiation is detected for each
camera and then perform the necessary geometric calculations to
determine the source position. Other computational approaches may
be possible.
[0069] Referring now to FIGS. 3, 4a and 4b, ionizing radiation
detectors may be manufactured or configured in a curved geometry to
allow the simultaneous detection of ionizing radiation from
multiple angles in a "lens-like" fashion. Combinations of multiple
detector systems could be combined to obtain three-dimensional
information about ionizing radiation source distributions. Curved
detector configurations can be accomplished through employment of a
curved scintillator or semiconductor or other detector combined
with an appropriately shaped collimation system.
[0070] Alternatively, multiple detector units can be configured in
a semicircle or as a hemisphere in a convex arrangement relative to
the environment being examined. Such an arrangement would allow a
shifting in the positions of the detectors to "focus" on an area or
improve sampling for better data (image) quality. One way of
accomplishing this is to place individual detectors at the ends of
"arms" which may be moved within given angles to adjust the number
of detectors looking in a given direction as illustrated in FIG.
4b.
[0071] A second radiation camera possibility exists if one uses
techniques similar to the above using a fanned (or radial)
collimator. If such a collimator is used to direct the gamma rays
into a curved scintillator, then it would be possible to derive the
distance to the source by examining the output signal at various
regions of the detector to determine, by a series of mathematical
weights, the location and distance to the source (see FIG. 3).
Again, other computational methods of doing this may be possible.
This design functions, effectively, as a focused radiation eye
(although it is technically not an "x-ray lens" since the x-rays
are not bent). Similar results could possibly be achieved by using
a lens or similar material to focus the light created by the
scintillator (in any configuration), or other signals created from
detectors which are capable of being focused, before it reaches the
eye or display device.
[0072] Another design example is based upon how the eye of an
insect works. The principle behind such a detector is that there
are multiple individual detectors with feedback to a processor, as
shown in FIG. 4a. As in the case of the insect, such as a fly which
has multiple "lenses" making up each one of its eyes, the output of
each detector (or "lens") is considered by the human (insect's)
brain to derive 3D and stereoscopic information. If the detector
contains an image, for example a radioactive source, its image is
compared with images from all other detectors with source
information. The processor (analogous to the insect's brain) then
interpolates between each of the detectors to determine both the
location and the distance to the source. For this invention, the
processor could be electronic, physical, or optical, or inherent in
the detection system itself. The output data from such a processor
would be those data which the human brain could then interpret
appropriately. A design having multiple detectors viewing "lines"
at different angles in the environment has several advantages. Such
a design could enable the use of radiation detectors with superior
energy resolution (for determining different types or energies of
radiation, which could be displayed differently for ease of
visualization) which otherwise would be difficult to apply to this
situation (or any situation requiring broad area radiation
detectors, for that matter) because of limitation in the size which
such detectors can be manufactured. The individual detectors can be
moved independently or as a group to adjust the angle and field of
view of the eye, or, alternatively, to change its effective
focus.
[0073] Further, a series of point detectors could be used to obtain
data to be displayed in AR or other techniques using similar means
of visualization to the above. In this case, the point detectors,
fixed in space, would be used to obtain a 3D map of the substances,
sources or fields in the environment. The computer could use a
mapping algorithm, possibly associated with a computer simulation
model, to reconstruct and interpolate the data into one smooth 3D
map. This map could then be processed to obtain the necessary
stereoscopic data.
[0074] The ideal detector would be a detector that would have a
wide field-of-view in order to obtain the most information from the
environment in one image as possible. It would be sensitive to low
levels of the substance, source, or field, yet still be able to
provide resolved data for high levels. The detector should ideally
function in real-time thus placing significant constraints on both
the detector efficiency as well as the computer processing
algorithms used to generate the stereoscopic data. It should be
able to function remotely so that should the strength of the
substance, source, or field be too strong, this would not pose an
unnecessary hazard to the user. In order to be able to display
different energies or types of optically invisible signals, the
detector would need spectroscopic capabilities. Finally, the
detector should be as portable as possible to allow for the most
flexibility of use in a wide variety of environments.
[0075] Visualization and Data Display
[0076] Once the stereoscopic data have been obtained and the
computer processing has been performed, the stereoscopic data have
to be output to the display. This requires a visualization process
to display the data so that the user receives the most possible
information from the graphical representation of the optically
invisible data. Thus, from the generated image, the user would
perceive information about both the detected substance, source, or
field strength, type, energy, or quantity and its location.
However, this display must not interfere with the user's view of
the real world. The real world provides a context for the location
of the sources relative to other objects in the real environment.
So the visualization process must not only accurately and
efficiently represent the data, but it must do so such that
augmentation of the normal human perception does not interfere with
the data the user's senses collect naturally. This includes the
natural human stereo imaging processes such as parallel line
convergence, binocular disparity, shading and texture cues, and
image motion parallax.
[0077] Part of the process imaging the data includes determining
how to best display the stereoscopic data and present other,
related information such as intensity/concentration of
substances/sources/fields, types of sources/fields, distances to
maximum field/source strength, and warning signals for significant
hazards which might be detected. For example, the visualization
scheme needs to be able to provide the user with a broad variety of
tools and different display methods to display the data optimally.
Additional information could be determined through processing of
the collected data and using the computer to identify significant
features and substance, source, or field strengths or weaknesses.
These data could be displayed as numerical or graphical information
along with the stereoscopic data superimposed upon reality.
Auditory information could be added as supplementary input to the
user.
[0078] The selected method of stereoscopic data display will
influence the observer's performance in interpreting the data,
detecting local and temporal variations, sensing small or subtle
signals, and possible other desirable tasks. One must thus
determine what the best means to display gamma-ray radiation would
be. This could include, but is not limited to, using the following
moving or stationary virtual objects for visualization: moving
dots; dot clouds; spheres in different sizes and colors; sphere
clouds; optical "sparks" for each count detected; expanding
bubbles; hazy clouds; shaded voxels with different shades
representing different source strengths; variable opacities with
more opaque regions corresponding to regions of more radiation;
blinking lights indicating the region of a detected count;
displaying the entire room in various colors including time-variant
patterns to indicate the source strengths and their locations;
floating numbers to represent the number of detected counts in a
region; or 3D surface contour plots indicating a 3D radiation
map.
[0079] Referring again to FIG. 1, in another embodiment of the
present invention, a pair of CCD cameras are coupled to the
gamma-ray cameras for obtaining information about physical
architecture of an environment such as a room. In this embodiment,
software rapidly renders a realistic, navigable, interactive
graphical representation, or Virtual Environment (VE), which is
displayed using a fully immersive CAVE system. The 3D radiation
dose rate information is used to simulate radiation in the VE,
resulting in a Virtual Radiation Environment (VRE). Rehearsal of
procedures could be performed in the VRE, with accurate estimations
of virtual doses using the continuous tracking of an individual's
location in the VRE. The invention thereby provides tools for
actively managing worker doses and is also helpful for both
accident management (dose reconstruction) and robotic operations in
high dose-rate environments.
[0080] For simulation of radiation environments using Virtual
Reality (VR), rapid rendering of a simulation of the physical
environment is required for combination with the 3D radiation
source distribution information. In order to accomplish this, the
two charge coupled device (CCD) cameras are mounted, at angles, on
a motorized table with the gamma-ray cameras. Software based upon
known quantitative stereoscopic imaging techniques is utilized to
obtain 3D information about the environment. The detection system
is capable of surveying the environment to obtain information both
about physical objects in the room as well as the location of any
sources of radiation. Information is collected by a computer which
will then output the physical architecture of the room, which is
processed using software, in order to rapidly create a VE. The VE
is viewed in a CAVE (cave automatic visual environment) where the
user will be able to visualize the radiation, if desired, and its
location relative to the physical objects in the room. Information
about the CAVE user's position as a function of time is combined
with the information about the radiation dose distributions to make
estimates of "virtual radiation dose". The Virtual Radiation
Environment (VRE) has application to high radiation environments,
with the data collection system mounted on a robot.
[0081] Another embodiment of the method and system of the present
invention includes specific radionuclide detection using a CdZnTe
detector or any other type of detector. The system of the invention
allows more rapid, real-time assessment of the locations of
gamma-emitting materials which could be used in nuclear weapons
thus allowing for CTBT verification without requiring
after-the-fact detonation. The radiation imaging system also has
significant application in assisting in the 3D location of
contamination for procedures in very high radiation fields in which
robotic labor is to be employed, as previously described.
[0082] The detector subsystem in three dimensions locates gamma-ray
emission from materials that could be used in nuclear weapons. The
detector subsystem includes two NaI(T1) or other detectors in Anger
cameras to be used to locate the radioactive source and two CdZnTe
or other type of detectors which will be used to spectroscopically
identify the radionuclide. The data will then be conveyed to the
user via the display subsystem so the user will be able to "see"
the radiation, thus identifying its locations in real-time.
[0083] The dual Anger camera subsystem is sensitive to low doses of
radiation and has a wide field of view. The subsystem creates basic
radiation images taken from slightly different angles. The cameras,
each offset by a given angle, scan the environment and obtain
sufficient information to construct a 3D profile of the radiation
source distribution. The initial NaI(T1) or detector search device
is used to locate with acceptable efficiency and confidence a
region that demonstrates statistically higher levels of radiation.
Although the system allows for crude energy resolution of
gamma-rays, the performance falls short of the necessary energy
resolution required to confidently identify gamma-ray-emitting
isotopes. Hence, the NaI(T1) cameras serve to quickly locate
regions of radiation and produce a low resolution gamma-ray
spectrum of the region under investigation. To positively identify
the presence of special nuclear materials and related by-products
from nuclear weapons tests, a portable, high energy resolution
device should accompany each NaI(T1) detector. Other area detectors
besides Anger cameras could be used. Other selections of radiation
detector materials are also possible.
[0084] A series of CdZnTe or other semiconductors, scintillators,
or other radiation detectors like the one illustrated in FIG. 5 are
dynamically linked to the Anger camera or other area detection or
positionally sensitive detection system. These detectors typically
are mounted on collimated rods such that the direction and
field-of-view of the array may be easily adjusted to view different
volumes of different sizes in the environment. Once radiation is
detected by the Anger cameras, the CdZnTe system alters its
direction and size of field-of-view to obtain spectroscopic
information from the source located by the 3D Anger camera imaging
system for radionuclide identification. The resulting data is
processed utilizing software. Prior art image reconstruction
algorithms for obtaining 2D and/or 3D maps make the system
real-time. The combination of dual Anger cameras, CdZnTe detectors,
visualization hardware, and necessary software result in an
Augmented Reality Radiation Display System (ARRDS).
[0085] Once the collection of 2D and 3D information is achieved,
the positional information about the source is used as input data
for code written in VRML or any other software or hardware
implementation, which generate the display of the radiation in AR.
Radiation incident on the camera system appears in 3D to the user.
Colors, textures, and intensities may be utilized to display the
information to the user. To further minimize the potential for
damage or interference in high radiation fields, only those
components whose presence in the environment is required is exposed
to radiation. These include the camera system, the motion tracker,
and the HMD or other device to achieve the same end result. Further
damage can be minimized by only having the motion tracker and HMD
in the environment while the user is viewing the VR image and not
during the image acquiring and reconstruction processes.
[0086] Relatively large volume CdZnTe trapezoid Frisch grid
gamma-ray spectrometers may be coupled to the NaI(T1) search
devices. The compound scintillation/semiconductor detector operates
and accumulates data in real-time, is portable, and operates at
room temperature.
[0087] Geometrically-weighted, semiconductor Frisch grid detectors
function as room-temperature-operated, portable gamma-ray
spectrometers. Arranging many trapezoid detectors into an array can
increase gamma-ray counting efficiency. Simply circuitry with
modern miniaturized electronics allow for the realization of such a
device, including compensation for slight signal differences
between individual detectors. Obviously, other detectors are
possible such as coplanar and/or drift detectors, detectors in a
variety of geometries, etc.
[0088] While the best mode for carrying out the invention has been
described in detail, those familiar with the art to which this
invention relates will recognize various alternative designs and
embodiments for practicing the invention as defined by the
following claims.
* * * * *