X-ray or gamma ray systems or devices – Electronic circuit – With display or signaling
Reexamination Certificate
2000-05-19
2001-08-28
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Electronic circuit
With display or signaling
C378S098200, C378S098800
Reexamination Certificate
active
06282261
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to x-ray image intensifiers allowing x-ray imaging using low intensity x-rays. In particular, the invention relates to an image intensifier having a shortened form factor.
X-ray images are produced by projecting x-rays from an x-ray source, through an object to be imaged, to an x-ray detector. In x-ray fluoroscopy, x-rays are projected semi-continuously to a phosphor panel that emits light when struck by the x-rays.
In order to reduce the x-ray dose needed to produce such an image, modern fluoroscopy machines may use an image intensifier. A conventional image intensifier tube provides a front phosphor surface receiving x-rays and converting them to light. The light exits from the rear side of the phosphor surface and strikes a photo cathode, which converts the light to electrons that are discharged into an evacuated chamber behind the photo cathode.
High voltage plates, increasing the energy of individual electrons and/or their number, amplify the electrons. Focusing electrodes, micro channel plates, or other means may be used to preserve the spatial relationship of the electrons until the time they hit a target phosphor material to produce an optical image. This latter image is substantially brighter than that formed by the front phosphor surface. An electronic camera such as those using a charge-coupled device (CCD) may record the optical image to convert the optical image to electrical signals.
A drawback to image intensifiers is that they are relatively bulky structures often having a length several times the width of the entrance aperture defined by the front phosphor surface. X-ray machines using image intensifiers guide physicians in invasive procedures, such as catheterizations. A bulky image intensifier may interfere with the required repositioning of the x-ray machine during such procedures.
It is difficult to make the image intensifier shorter for a given entrance aperture. If the path over which the electrons are focused is reduced, the spatial distortion of the electrons increases requiring more complex focusing fields and structures. At some point the distortion compromises accurate guidance of medical instruments.
Micro channel plates can be used to amplify the electron stream without focusing it to a smaller area, eliminating the distortion of the electron focusing process. The large area image produced by such a micro channel system, however, must then be optically reduced by the lens system of the electronic camera. Short focal length optical reduction introduces distortion similar to those produced by short length electron focusing.
BRIEF SUMMARY OF THE INVENTION
The present invention provides an extremely short form image intensifier with low image distortion. This is accomplished by the use of multiple cameras, each of which receive only a portion of the image generated by the image intensifier. The multiple cameras allow longer focal length lenses to be used reducing distortion of the images and possibly increasing resolution. Minor image distortion is corrected through an electronic image correction circuit prior to assembling the multiple images of the multiple cameras into a single image. Each camera may have its own correction factors.
Multiple correction factors may also allow the use of multiple lenses each having a different correction factor. As the lenses are switched into position or refocused, the appropriate correction factor may be provided to the image correction circuitry. A similar approach may be used to correct for changing image distortion caused, for example, by changing orientations of the image intensifier with respect to the earth's magnetic field.
Specifically, then, the present invention provides an imaging x-ray detector having an image intensifier, at least two digital cameras and an image correction circuit. The image intensifier includes a front target ejecting electrons into an internal volume of the image intensifier upon receipt of x-rays. An electron amplifier receives the ejected electrons to amplify the same and to direct them against a rear target receiving the amplified electrons to produce an optical image.
The digital cameras are directed toward the rear target to produce digital signals representing different portions of the optical image projected at a camera image plane. An image correction circuit receives the digital signals and corrects for spatial distortion underlying different portions of the optical image captured in the digital signals and provides corrected images to a combining circuit receiving the corrected digital signals and combining them to produce a spatially continuous representation of the optical image.
Thus it is one object of the invention to use multiple digital cameras to provide low distortion, large entrance aperture image intensifiers. The image correction circuit allows the multiple images to be seamlessly blended together.
The different portions of the optical image recorded by the cameras may include overlapping portions and the combining circuit may apply weighting values to the digital signals representing overlapping portions prior to combining the digital signals.
Thus it is another object of the invention to accommodate a degree of overlap in the camera field of views without unduly emphasizing the overlapped regions as would occur with a simple addition.
The rear target may be rectangular and the invention may provide four digital cameras directed toward different quadrants of the optical image on the rear target.
Thus it is another object of the invention to provide for a rectangular image intensifier in distinction to the normal circular image intensifier systems without excessive image distortion. The use of multiple cameras allows for the square image to be more readily generated with simple optical structures.
The front target may receive x-rays across a width and the camera plane may be removed from the target by an amount no greater than the width. The front target may be rectangular and the width may be a measure of the diagonal of the rectangle of the front target or the front target may be circular and the width may be a measure of the diameter of the front target.
Thus it is another object of the invention to provide an extremely short form factor image intensifier that is no deeper than it is wide.
In an alternative embodiment, the imaging x-ray detector may include as few as one camera and the image correction circuit may store multiple correction parameters and receive a mode signal to apply a selected one of different correction parameters to the digital signal from the camera dependent on the mode signal for correcting for spatial distortion of underlying optical images captured in the digital signals.
Thus it is another object of one aspect of the invention to provide for different spatial distortion corrections associated with different modes of operation of the detector.
The invention may include an orientation sensor for detecting an orientation of the imaging x-ray detector to produce the mode signal. Alternatively, the invention may provide a lens support positioning at least one lens between the rear target and the imaging array according to the mode signal to project the optical image onto the imaging array at different magnifications associated with the mode signals.
Thus it is another object of the invention to provide an image intensifier tube offering improved imaging flexibility in terms of orientation and magnification without compromising on image distortion.
The foregoing and other objects and advantages of the invention will appear from the following description. In this description, reference is made to the accompanying drawings, which form a part hereof, and in which there is shown by way of illustration, a preferred embodiment of the invention. Such embodiment and its particular objects and advantages do not defined the scope of the invention, however, and reference must be made therefore to the claims for interpreting the scope of the invention.
REFERENCES:
patent: 4367490 (198
Bisek Joseph P.
Ergun David L.
Mazess Richard B.
Ho Allen C.
Kim Robert H.
Lunar Corporation
Quarles & Brady LLP
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