X-ray or gamma ray systems or devices – Electronic circuit – With display or signaling
Reexamination Certificate
1998-12-09
2001-04-10
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Electronic circuit
With display or signaling
C378S098800, C250S370090, C382S294000
Reexamination Certificate
active
06215848
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of deriving an assembled image from successive X-ray images. The invention also relates to an X-ray examination apparatus which is suitable for deriving an assembled image from successive X-ray images.
2. Description of Related Art
A method and an X-ray examination apparatus of this kind are known from European patent application EP 0 655 861.
According to the known method the successive X-ray images are picked up by means of an image intensifier pick-up chain which includes an X-ray image intensifier and a television camera. A series of successive X-ray images of the relevant parts of the patient is formed on an entrance screen of the X-ray image intensifier by irradiating separate parts of an object, for example a patient to be radiologically examined, by means of an X-ray beam; these X-ray images are converted into successive optical images which appear on the exit window of the X-ray image intensifier and electronic video signals are derived from the successive optical images by means of the television camera. An image processing unit forms an image signal representing the assembled image from the electronic video signals. The assembled image reproduces the individual parts of the patient together in a single image.
Because the known method utilizes an X-ray image intensifier, merely a comparatively narrow strip at the center of the successive individual X-ray images can be used. The use of the X-ray image intensifier introduces distortions in the optical image; these distortions are pronounced notably at the edge of the optical image. One cause of the distortions is the cushion distortion in the X-ray image which is due to the curvature of the entrance screen. Despite the fact that only narrow strips at the center of respective X-ray images, where the distortion is lowest, are used, according to the known method extensive operations must be performed so as to produce an assembled image which does not contain an excessive amount of distortion. Because only narrow strips of the successive X-ray images can be used, the known method requires a comparatively large number of X-ray images so as to form an assembled image of an elongate part of the patient. Notably peripheral angiography, being the imaging of blood vessels in an arm or a leg of a patient, requires the formation of a large number of X-ray images which may even reach a few dozen. Consequently, the patient to be examined is exposed to a rather high X-ray dose.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method for deriving an assembled image from successive X-ray images which requires substantially fewer X-ray images, in comparison with the known method, so as to produce an assembled image of high diagnostic quality. It is a further object of the invention to provide a method which, in comparison with the known method, requires substantially fewer operations so as to produce an assembled image of high diagnostic quality.
This object is achieved by means of a method according to the invention which is characterised in that the X-ray images are picked up by means of an X-ray detector having a predominantly flat X-ray sensitive surface.
The X-ray-sensitive surface of the X-ray detector is flat to such a degree that the X-ray images are formed on the X-ray-sensitive surface substantially without geometric image distortions. Any image distortion occurring nevertheless will be so small that it does not affect the diagnostic quality of the individual X-ray images. This means that hardly any or even no corrections will be required for suitably visible reproduction of small details upon display of the image information of the X-ray images, and that the anatomic details in the image will not be distorted or only hardly so. Therefore, the image information contained in the X-ray images is suitable for diagnostic purposes.
Using the method according to the invention, even in the case of an elongate scene such as the limbs of a patient very few successive X-ray images will be required so as to form an assembled image which reproduces substantially the entire scene without essential distortions. Because only a few X-ray images are required according to the invention, the patient to be examined is exposed to an X-ray dose which is much smaller than that required according to the known method.
These and other aspects of the invention will be elaborated on the basis of the embodiments as defined in the dependent Claims.
An image sensor matrix constitutes a suitable X-ray detector for the method according to the invention. Such an image sensor matrix includes, for example X-ray sensitive sensor elements which are arranged in a matrix. Individual sensor elements are coupled to a read-out line by means of a switching element. Individual switching elements are coupled to a control line. Incident X-rays are converted into electric charges in the sensor elements. The sensor elements are made of, for example a material which converts X-rays into electric charges, for example amorphous hydrated silicon (&agr;-Si:H) or an X-ray sensitive photoconductor such as selenium (Se) or lead oxide (PbO). Alternatively, the sensor elements can be constructed as infrared sensitive, ultraviolet sensitive or light sensitive elements, such as photodiodes or phototransistors; in that case the image sensor matrix also includes a conversion layer for converting incident X-rays into radiation whereto the sensor elements are sensitive. The conversion layer is, for example a doped cesium iodide (CsI) layer. An image sensor matrix of this kind predominantly has a flat X-ray sensitive surface so that hardly any geometrical distortions occur during the picking up of an X-ray image. The image sensor matrix derives sub-image signals from individual X-ray images. Such a sub-image signal is derived from the electric charges read out from the sensor elements via the read-out lines. In order to read out the sensor elements, the switching elements are controlled by way of signals which are supplied via the control lines. Such sub-image signals are processed in an image processing unit so as to form an image signal for the assembled image.
Another embodiment of the X-ray detector preferably includes a conversion screen provided with an essentially flat layer of scintillation material, for example doped cesium iodide (CsI). The X-ray images are formed substantially without distortion on the conversion screen. The conversion screen converts an X-ray image into a radiation image of infrared or ultraviolet radiation or visible light. Sub-image signals are derived from individual radiation images by means of one or more image sensors. The image processing unit processes such sub-image signals so as to form an image signal for the assembled image.
Furthermore, the image information of the successive X-ray images can be combined so as to form a single assembled image. This assembled image reproduces, by way of a single image, a scene which is so large that the scene cannot be reproduced (or only with great difficulty) in an X-ray image in one step. For example, this scene is extremely elongate, for example the legs of the patient. Reproducing the entire scene in a single image offers the radiologist an effective survey of said scene, for example the vascular system in the legs of the patient. Sub-image signals derived from the individual X-ray images are preferably merged so as to form such an image signal representing the assembled image. Because hardly any distortions occur during the formation of the individual X-ray images, hardly any corrections will be required for the individual sub-image signals. For merging it may be necessary to take into account overlap between successive X-ray images.
Furthermore, it is advantageous to form subtraction images from successive X-ray images. Brightness values of individual difference images represent differences between corresponding brightness values of successive X-ray images. The object to be examined is notably a patien
Linders Petrus W. J.
Van Eeuwijk Alexander H. W.
Dunn Drew A.
Kim Robert H.
U.S. Philips Corporation
Vodopia John F.
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