Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1999-04-23
2002-09-10
Pyo, Kevin (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S227110, C250S239000, C348S218100, C348S359000
Reexamination Certificate
active
06448544
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to optical detectors and, more particularly, to imaging sensors.
2. Related Art
Systems utilizing high energy radiation, such as x-radiation and gamma radiation, to examine the internal structure of a solid object are well known. Such systems typically irradiate an object under examination with high energy x-radiation or gamma radiation and utilize detection apparatus to measure the intensity of the radiation that is transmitted through the object.
Conventional detection systems, particularly those used for medical applications, use a film to record an image of x-rays that are passed through a human body. Such a film typically includes a screen of fluorescent material that fluoresces to produce visible light radiation in response to incident high energy x-rays. The light radiation from the screen passes to a photosensitive film that reacts to the emitted visible light to physically record an image. Such films are used to provide a radiograph of the irradiated region of the body, the radiograph having a spatial resolution of up to 15 line pairs per millimeter.
Although x-ray film produces a radiograph having a relatively high spatial resolution, the intensity resolution is relatively low. The intensity resolution, or dynamic range, of film is typically less than 50. In addition, the film necessarily requires a substantial amount of time to develop, and the film requires a relatively high level of exposure of x-rays to produce a satisfactory radiograph. Also, the film image is not in a form that readily lends itself to computer storage or analysis.
Accordingly, detection systems have been developed for more rapidly recording the intensity of x-rays or other high energy radiation that are transmitted through a target object. Such systems typically employ a scintillation plate to covert incident x-rays to corresponding visible light radiation. A photodetector is typically used to generate an electrical signal corresponding to the intensity of the visible light produced. The electrical signal from the photodetector may be readily converted to a digital representation suitable for use with a computer and stored in a memory device or electronically displayed, for example, on a cathode ray tube.
Conventional electronic radiation detection devices have been used to produce electronic radiographic images much more quickly than can be achieved with film. Such systems also typically have a somewhat larger dynamic range than x-ray film systems. However, the radiographic images produced with such prior art electronic radiation detectors have not had the high spatial resolution that is characteristic of radiographic images produced on film. Furthermore, such conventional detectors produce significant electronic noise resulting in a dynamic range (intensity resolution) that is insufficient for most imaging tasks. Therefore, electronic imaging systems have not heretofore been suitable for producing high resolution radiographic images.
SUMMARY OF THE INVENTION
The present application is directed to different inventive aspects of a low noise, high spatial resolution, high dynamic range (high intensity resolution) image detection system. The following aspects of the present invention may be utilized in different detection systems and such detection systems may be suitable for different applications. For example, the disclosed aspects of the present invention may be utilized in medical imaging applications such as x-ray mammography systems, scientific imaging systems such as x-ray crystallography and astronomy, industrial quality-control systems, etc.
One aspect of the present invention includes a sensor array in an image sensor that minimizes damage and performance degradation due to shock, vibration and thermal stresses. In one embodiment, a sensor array for implementation in an image sensor is disclosed. The sensor array includes a mounting frame and a plurality of sensor modules removably mounted in the mounting frame. Each sensor module includes a high demagnification fiberoptic taper having an input surface and an output surface. The sensor module also includes a photodetector array optically coupled to the fiberoptic taper output surface to receive light photons transferred through the fiberoptic taper. The photodetector array is rigidly attached to the fiberoptic taper such that movement of the fiberoptic taper does not interfere with photodetector array operation. The sensor module also includes a flange constructed and arranged to individually mount the fiberoptic taper to the mounting frame, the flange flexibly attached to the fiberoptic taper and rigidly attached to the mounting frame. The fiberoptic tapers of the sensor modules are mounted in a non-contact arrangement in the mounting frame. In one embodiment, the photodetector array is a CCD photodetector array. Alternatively, the photodetector array may be a CID or CMOS photodetector array. In addition, each flange mechanically supports a fiberoptic taper such that the orientation of the fiberoptic taper may be individually adjusted.
Significantly, this aspect of the present invention provides the benefits associated with a modular design such as functional compactness and individual replacement and adjustment while minimizing the space consumed by the composite sensor array.
Another aspect of the invention includes a sensor array including a plurality of sensor modules each including a high demagnification taper and a photodetector array. In one disclosed embodiment, a sensor array for implementation in an image sensor is disclosed. The sensor array includes a mounting frame and a plurality of sensor modules mounted in the mounting frame. Each sensor module includes a high demagnification fiberoptic taper having a demagnification ratio of at least 3:1 and an input surface and an output surface. A photodetector array optically coupled to the fiberoptic taper output surface to receive light photons transferred through the fiberoptic taper is also included.
In one embodiment, the fiberoptic tapers have a demagnification ratio of greater than 2.4:1. In another embodiment, between 3.5:1 and 4.5:1.; in a further embodiment, greater than 4:1; in a still further embodiment, greater than 3.1:1. The use of fewer high demagnification fiberoptic tapers provides for fewer sensor modules resulting in an image detection system which is less complex, less costly and easier to maintain, than conventional systems.
Another aspect of the present invention includes a technique for eliminating direct physical contact between neighboring fiberoptic tapers in an array of fiberoptic tapers while simultaneously minimizing the loss of data due to misalignment of such fiberoptic tapers. In one embodiment, a sensor array for implementation in an image sensor having a composite resolution is disclosed. The sensor array includes a mounting frame and a plurality of sensor modules. The sensor modules are individually mounted in the mounting frame such that the sensor modules are secured in a fixed relative position that provides a predetermined gap between neighboring fiberoptic input surfaces that is less or equal to the resolution of sensor module. In one embodiment, the gap is the minimum of the CCD pixel size or the distance associated with an modulation transfer function (MTF) of the sensor array of approximately 5%. In another embodiment, the resolution of each sensor module is substantially equal to a resolution of the photodetector array in the sensor module. In this embodiment, the gap may be a predetermined percentage of the photodetector array resolution, such as approximately 50%. In an implementation where, for example the size of individual elements of the photodetector array is 50 microns, the gap is approximately 25 microns.
Advantageously, this arrangement enables the input surfaces of the fiberoptic tapers to be mechanically aligned with each other so as to capture the entire image with minimal or no data loss overcoming problems typically associated wit
Ingersoll Charles
Phillips Walter
Stanton Martin J.
Stuart Alex
Brandeis University
Nutter & McClennen & Fish LLP
Pyo Kevin
LandOfFree
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