Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Patent
1998-04-06
1999-10-05
Hannaher, Constantine
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
25037002, H01L 2978
Patent
active
059628561
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates in general to medical diagnostic imaging systems, and more particularly to a selenium active matrix universal readout array imager.
BACKGROUND OF THE INVENTION
Despite the development of recent medical imaging modalities, such as computed tomography (CT), ultrasound, nuclear medicine and magnetic resonance imaging (MRI), all of which are digital, X-ray imaging systems remain an important tool for medical diagnosis. Although the majority of X-ray imaging systems in current use are of analog design, digital radiology is an area of considerable recent growth. Digital radiology provides significant advantages over its analog counter-part, such as: easy comparison of radiological images with those obtained from other imaging modalities; the ability to provide image networking within a hospital for remote access and archiving; facilitating computer aided diagnosis by radiologists; and facilitating teleradiology (ie. remote diagnostic service to poorly populated regions from a central facility).
There are currently two commercial approaches to digital radiography--(1) the digitization of a signal from a video camera optically coupled to a an X-ray imaging intensifier, and (2) stimulable phosphor systems. Prior art intensifier systems permit instant readout whereas prior art stimulable phosphor systems require the operator to carry a cassette to a reader. Neither of these systems provide image quality which is acceptable for all applications.
Digital systems based on the use of X-ray image intensifiers suffer from the following disadvantages: the bulky nature of the intensifier often impedes the clinician by limiting access to the patient and prevents the acquisition of important radiographic views; loss of image contrast due to X-ray and light scattering (i.e. veiling glare); and geometric (pin cushion) distortion on the image due principally to the curved input phosphor.
Another prior art X-ray imaging modality which is currently experiencing renewed interest, is the use of amorphous selenium photoconductors as an alternative to phosphors. Xeroradiography, (i.e. the use of amorphous selenium (a-Se) plates which are read out with toner), was a technical and commercial success in the early 1970's. Xeroradiography is no longer commercially competitive. This is believed to be because of the toner readout method, and not because of the underlying properties of a-Se. Commercial as well as scientific interest in a-Se has recently revived. For example, Philips has announced the commercial availability of an a-Se drum scanner for chest radiography based on earlier work at its research laboratories in Aachen. Kodak uses an a-Se plate readout with a phosphor coated toner and laser scanner for the preparation of highly detailed mammography images which are free from significant artifacts. 3M have also published preliminary descriptions of their work on laser discharge readout of a-Se. This work is related to much earlier publications by (1) Korn et al, "A method of electronic readout of electrophotographic and electroradiographic images", Journal of Applied Photographic Engineering, 4, 178-182 (1978); (2) Zermeno et al "Laser readout of electrostatic images", In: Application of Optical Instrumentation to Medicine VII, Edited by J. Gray, et al, SPIE 173, 81-87 (1979); and (3) DeMonts et al, "A new photoconductor imaging system for digital radiography", Medical Physics, 16, 105-109 (1989).
The basis of all existing medical X-ray imaging systems is a phosphor layer or "screen". X-rays absorbed by the screen release light which must reach the surface to create an image. The lateral spread of light is limited only by diffusion and hence is related to the thickness of the screen. Thus, the thicker the screen (which is desirable to increase the quantum absorption efficiency), the more blurry the image will be. This represents a loss of high frequency image information in prior art phosphor systems which is fundamental and largely irreversible. This loss can be alleviated to some ex
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Rowlands John
Zhao Wei
Hannaher Constantine
Israel Andrew
Sunnybrook Hospital
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