Radiant energy – Source with recording detector
Reexamination Certificate
1999-04-01
2001-10-23
Sugarman, Scott J. (Department: 2878)
Radiant energy
Source with recording detector
C250S484400, C250S483100
Reexamination Certificate
active
06307212
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to high resolution imaging, and more specifically to high resolution imaging of objects using sources of ionizing radiation.
2. Description of the Background Art
A variety of methods exist for imaging objects using UV, x-ray, and other ionizing radiation sources. These methods have used photographic films, phosphor screens in conjunction with CCD cameras, and thermoluminescent or optically stimulable luminescent phosphor powders in conjunction with a scanning laser readout system. In these techniques, the dimensions of the photosensitive grains in the film or phosphor and scattering effects limit the obtainable resolution. Grain sizes in typical phosphors are on the order of tens of microns, and crushing the phosphor to sub micron dimensions often results in a loss of phosphor activity. Grain sizes in photographic films range from 0.15 &mgr;m
2
for very slow speed (low sensitivity) film to 2.6 &mgr;m
2
for very high speed (high sensitivity) film. For film, the resolution is from 10 to 100 times the grain size because of the chemistry involved in the developing process. Problems with photographic films include the necessity for chemical developing, nonlinear response, limited dynamic range and single use. The resolution for direct imaging using a CCD camera is determined by the individual pixel size of the CCD array and the magnification factor used for collecting the image. Modern CCD cameras have pixel dimensions of approximately 8 &mgr;m×8 &mgr;m.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to provide improved spatial resolution when imaging objects using high energy sources such as uv, x-ray, and &ggr;-ray photon sources, and ionizing radiation particles.
It is another object of the present invention to provide a media for image storage and a method to readout images without the need for photographic development.
It is yet another object of the present invention to provide a reusable media, with a linear response and good dynamic range, for the storage and readout of images made by exposing objects to high energy photon and particle sources.
These and additional objects of the invention are accomplished by exposing optically transparent, optically stimulable luminescent glasses including luminescent centers and trapping centers, to a projection formed by directing ionizing radiation at an object (Throughout this specification and the claims that follows, the terms “projection” encompasses forms created by radiation transmitted through an object, forms created by radiation transmitted around an object, and/or forms created by radiation scattered from an object. Typically, projections imaged according to this invention are formed by the interpositioning of an object between the source of ionizing radiation and the optically stimulable luminescent glass, which will hereinafter be referred to as a backside projection). These optically stimulable luminescent glasses are fully described in U.S. Pat. No. 5,811,822, issued Sep. 22, 1998 and entitled “OPTICALLY TRANSPARENT, OPTICALLY STIMULABLE GLASS COMPOSITES FOR RADIATION DOSIMETRY” (the entireties of which are incorporated by reference herein for all purposes). In these glasses, the trapping centers are capable of storing charges for extended periods of time. The trapped charges may be electrons or holes that were generated upon exposure to ionizing radiation. The trapped charges may be optically stimulated to recombine by the application of light at optical frequencies, resulting in the emission of light energy at higher optical frequencies. This optical stimulation is direct, i.e., it does not involve conversion of the optical excitation energy to thermal energy that heats the glass sufficiently to detrap the electron. This direct optical stimulation may, however, include optical absorption with the release of a phonon that participates in phonon-assisted detrapping of an electron. This direct optical stimulation process is known as optically-stimulated luminescence (OSL). In several embodiments, the glass (e.g., fused quartz, fused silica, alumina glass, or borate glass) matrix includes Cu (typically Cu
1+
) as an activator (sometimes referred to as a “dopant” in the glass). In other embodiments, the glass matrix includes an activator/co-activator pair of samarium and another rare earth element. In other alternative embodiments, the glass (e.g., silica, alumina, or borate glass) matrix is doped with ZnS and copper, lead, manganese, or cerium. In yet another embodiment, a glass (e.g., silica, alumina, or borate glass) matrix is doped with Cu or Ce ions in the absence of a metal sulfide component, or even in the absence of any sulfide component. A glass is considered essentially free of a component if the glass lacks an amount of that component sufficient to significantly alter the optical stimulability or radiation sensitiveness of the glass.
The OSL glasses described above may also scintillate when exposed to ionizing radiation. This scintillation advantageously permits the present invention to also provide real time images produced by exposure of the glass to ionizing radiation. Of course, the specific OSL glass used may be selected to maximize scintillation or optically-stimulated luminescence The resulting image may be either real-time, using the prompt luminescence component of the phosphor luminescence, or it may be stored in the media, using the charge trapping and storage capability of the glass.
REFERENCES:
patent: 5585640 (1996-12-01), Huston et al.
patent: 5811822 (1998-09-01), Huston et al.
Huston Alan L.
Justus Brian L.
Hanig Richard
J.Karasek John
L.Ressing Amy
Sugarman Scott J.
The United States of America as represented by the Secretary of
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