Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Reexamination Certificate
1999-06-30
2001-08-28
Kim, Robert H. (Department: 2882)
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
C250S580000
Reexamination Certificate
active
06281507
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to radiography imaging systems and more particularly to a photoconductor structure for direct x-ray detection in a radiography imaging system.
BACKGROUND OF THE INVENTION
Traditionally, medical diagnostic processes record x-ray image patterns on silver halide films. These systems direct an initially uniform pattern of interrogating x-ray radiation through a patient to be studied, intercept the consequently imagewise modulated pattern of x-ray radiation with an x-ray radiation intensifying screen, record the intensified pattern in a silver halide film, and chemically transform the latent radiation pattern into a permanent and visible image called a radiogram.
Radiograms have also been produced by using layers of radiation sensitive materials to directly capture radiographic images as imagewise modulated patterns of electrical charges. Depending upon the intensity of the incident X-ray radiation, electrical charges generated either electrically or optically by the X-ray radiation within a pixelized area are quantized using a regularly arranged array of discrete solid state radiation sensors.
There has been rapid development of large area, flat panel, digital x-ray imaging detectors for digital radiology using active matrix technologies. An active matrix consists of a two-dimensional array of thin film transistors (TFTs) made with amorphous or polycrystalline semiconductor materials. There are two general approaches to making flat-panel x-ray detectors, direct or indirect. The direct method is also referred to as a self-scanned &agr;-Se (amorphous selenium). The indirect method uses phosphor screens or other scintillators to first convert x-rays to visible light, which is then read out with an active matrix array with an additional light sensor at each pixel of the array. The direct method offers the advantages of higher screen resolution provided by electrostatic image formation, elimination of the phosphor screen, and simpler active matrix structure.
The usefulness of photoconductors as x-ray imaging sensors arises from the high sensitivity, i.e., conversion of absorbed x-ray energy to charge, if an appropriate electric field is applied. While a number of photoconductors may be used for x-ray imaging detectors, amorphous selenium is considered particularly well-suited for the task, since it is well-developed technologically, it has been used traditionally as a photoconductor in photocopiers and xeroradiography, it can be made relatively easily and inexpensively in its amorphous form by evaporation in a large area, and it has a uniqueness in its remarkably low dark current. Further, a large intrinsic gain results from its large difference between the hole mobility and electron mobility for ohmic contacts.
While achieving advantages over traditional film radiography, photoconductor use in x-ray imaging has its share of difficulties. Image lag is a problem when utilizing direct x-ray detection. Image lag or a delay in acquiring an image is effected by two sources. A first source is incomplete charge collection i.e., photoconductive lag and a second source is incomplete charge readout i.e., image readout lag. What is desired is a system and method for reducing the photoconductive lag in a cost effective and efficient manner. The present invention addresses such a need.
SUMMARY OF THE INVENTION
The present invention provides system and method aspects for a photoconductive element for direct x-ray detection in a radiography imaging system. The photoconductive element includes a photoconductive material layer for absorbing x-ray radiation transmitted through an object being imaged by the radiography imaging system. Further included is an interdigital contact structure in the photoconductive material layer.
The interdigital contact structure in accordance with the present invention reduces the gap between electrodes, which results in a very short photoconductive lag. Also, a small electrode gap supports an increase in the gain of the detector, since the gain is inversely proportional to the distance between the electrodes and also reduces the bias voltage for a specific electric field. The metallic electrodes not only increase the stopping power of x-ray radiation but emit secondary particles which generate new charge carriers in photoconducting layer. These and other advantages of the aspects of the present invention will be more fully understood in conjunction with the following detailed description and accompanying drawings.
REFERENCES:
patent: 4176275 (1979-11-01), Korn et al.
patent: 4593304 (1986-06-01), Slayman et al.
patent: 4775880 (1988-10-01), Suzuki et al.
patent: 5268569 (1993-12-01), Nelson et al.
patent: 5313066 (1994-05-01), Lee et al.
patent: 5319206 (1994-06-01), Lee et al.
patent: 5381014 (1995-01-01), Jeromin et al.
patent: 5396072 (1995-03-01), Schiebel et al.
patent: 5563421 (1996-10-01), Lee et al.
patent: 5598004 (1997-01-01), Powell et al.
patent: 5821539 (1998-10-01), Jahnke et al.
patent: 34 15 439 (1985-10-01), None
patent: 0 582 397 (1994-02-01), None
patent: WO 98/44568 (1998-10-01), None
Sterling Diagnostic Imaging, Inc., Glasgow, Delaware, “Direct Digital Flat-Panel Radiographic Detector: Principle and 14×17-inch Images”, Lawrence K. Cheung, Phd; Denny L. Lee, PhD; Lothar S. Jeromin, PhD.
Kiknadre Irakli
Kim Robert H.
Siemens Medical Systems Inc.
LandOfFree
Interdigital photoconductor structure for direct X-ray... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Interdigital photoconductor structure for direct X-ray..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Interdigital photoconductor structure for direct X-ray... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2513922