Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Reexamination Certificate
1999-01-20
2001-10-30
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
C250S370080, C250S580000
Reexamination Certificate
active
06310351
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to apparatus and methods for detecting images and more specifically relates to apparatus and methods for digital detection of X-ray images.
BACKGROUND OF THE INVENTION
There are described in the patent literature numerous systems and methods for the recording of X-ray images. Conventional X-ray imaging systems use an X-ray sensitive phosphor screen and a photosensitive film to form visible analog representations of modulated X-ray patterns. The phosphor screen absorbs X-ray radiation and is stimulated to emit visible light. The visible light exposes photosensitive film to form a latent image of the X-ray pattern. The film is then chemically processed to transform the latent image into a visible analog representation of the X-ray pattern.
Recently, there have been proposed systems and methods for detection of X-ray images in which the X-ray image is directly recorded as readable electrical signals, thus obviating the need for film in the imaging process.
For example, U.S. Pat. No. 4,961,209 to Rowlands et al describes a method for employing a transparent sensor electrode positioned over a photoconductive layer and a pulsed laser which scans the photoconductive layer through the transparent sensor electrode.
U.S. Pat. No. 5,268,569 to Nelson et al. describes an imaging system having a photoconductive material which is capable of bearing a latent photostatic image, a plurality of elongate parallel strips adjacent the photoconductive material, and a pixel source of scanning radiation.
U.S. Pat. No. 5,652,430 to Lee describes a radiation detection panel for X-ray imaging systems which is made up of a matrix assembly of radiation detection sensors arrayed in rows and columns to record still or moving images.
Examples of commercially available systems in which X-ray images are directly recorded as readable electrical signals include the Direct Radiography line of detector arrays offered by Sterling Diagnostic Imaging (formerly DuPont) of Delaware, USA; the Pixium line of flat panel X-ray detectors for radiography offered by Trixell of Moirans, France; the Digital Imaging Center offered by Swissray Medical AG of Switzerland; and the Canon Digital Radiography System offered by the Canon Medical Division of Canon U.S.A.
In addition, digital mammographic X-ray systems are commercially available. For example, the Opdima system offered by Siemens Medical Systems, Inc. of New Jersey, USA.
SUMMARY OF THE INVENTION
There is thus provided in accordance with a preferred embodiment of the present invention a radiation detection module including an ionizing radiation sensitive multi-layer structure having a charge accepting outer surface and comprising a conductive layer, the ionizing radiation sensitive multi-layer structure being operative such that imagewise ionizing radiation impinging on the ionizing radiation sensitive multi-layer structure causes a charge distribution, representing the imagewise ionizing radiation, to be formed in the conductive layer, and readout electronics coupled to the conductive layer to detect the charge distribution formed in the conductive layer.
Further in accordance with a preferred embodiment of the present invention the ionizing radiation sensitive multi-layer structure includes a layered stack having layers in the following order: a dielectric layer; the conductive layer; and an ionizing radiation sensitive layer; wherein the charge accepting outer surface is an outer surface of the ionizing radiation sensitive layer.
Still further in accordance with a preferred embodiment of the present invention the ionizing radiation sensitive multi-layer structure includes a layered stack having the following order: a first dielectric layer; the conductive layer; an ionizing radiation sensitive layer; and a second dielectric layer; wherein the charge accepting outer surface is an outer surface of the second dielectric layer.
Moreover in accordance with a preferred embodiment of the present invention the second dielectric layer serves as an optical filter tailoring a radiation spectrum of non-ionizing radiation penetrating into the ionizing radiation sensitive layer.
Further in accordance with a preferred embodiment of the present invention the ionizing radiation sensitive layer is either amorphous selenium or alternatively a selenium alloy.
Additionally in accordance with a preferred embodiment of the present invention, the ionizing radiation sensitive layer is a material selected from the group of lead oxide, thallium bromide, cadmium telluride, cadmium zinc telluride, cadmium sulfide, and mercury iodide.
In yet further accordance with the present invention, the ionizing radiation sensitive multi-layer structure includes a layered stack having the following order: a scintillation layer; a dielectric layer; the conductive layer; and a photoelectric conversion layer, with the charge accepting outer surface being an outer surface of the photoelectric conversion layer and with the conductive layer and the dielectric layer being generally transparent to optical radiation.
Still further in accordance with a preferred embodiment of the present invention, the ionizing radiation sensitive multi-layer structure includes a layered stack having the following order: a scintillation layer; a first dielectric layer; the conductive layer; a photoelectric conversion layer; and a second dielectric layer with the charge accepting outer surface being an outer surface of the second dielectric layer and with the conductive layer and the first dielectric layer being generally transparent to optical radiation.
Moreover, in accordance with a preferred embodiment of the present invention, the second dielectric layer is an optical filter tailoring a radiation spectrum of non-ionizig radiation penetrating into the photoelectric conversion layer.
Additionally, in accordance with a preferred embodiment of the present invention, the photoelectric conversion layer is amorphous selenium, a selenium alloy or amorphous silicon. Alternately, in accordance with a preferred embodiment of the present invention, the photoelectric conversion layer is an organic photoconductor.
Still further in accordance with a preferred embodiment of the present invention, the scintillation layer is cesium iodide or a doped version thereof.
Preferably, the radiation detection module includes a charge injector which scans the outer charge accepting surface of ionizing radiation sensitive multi-layer structure providing injection of charges thereinto, thereby generating in the readout electronics measurable currents which represent the charge distribution formed in the conductive layer.
Yet further in accordance with a preferred embodiment of the present invention, an electrostatic barrier, associated with the charge injector, spatially tailors the charge injection.
Further in accordance with a preferred embodiment of the present invention, the charge injector includes an embedded electrode; an exposed screen electrode in proximity to the embedded electrode, the embedded electrode and the exposed screen electrode being separated at a region of proximity by a thin dielectric layer; a generator that provides an AC voltage between the embedded electrode and the screen electrode causing air discharge at said region of proximity, thus generating positive and negative charges; and a voltage source which provides a DC bias voltage, in the range of several hundreds of volts to several thousands of volts, to the screen electrode, providing the acceleration force for charge injection.
Still in further accordance with a preferred embodiment of the present invention, the DC bias voltage can be selected such that the DC component associated with the Fourier spectrum of spatial frequencies of an image to be detected is factored out.
Moreover, in accordance with a preferred embodiment of the present invention, the measurable currents have an induction component and an injection component.
Additionally in accordance with a preferred embodiment of the present invention, the radiation detectio
Edge Medical Devices, Inc.
Hannaher Constantine
Israel Andrew
Pillsbury & Winthrop LLP
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