X-ray or gamma ray systems or devices – Electronic circuit – With display or signaling
Reexamination Certificate
1998-12-09
2001-09-18
Porta, David P. (Department: 2882)
X-ray or gamma ray systems or devices
Electronic circuit
With display or signaling
C378S098800, C378S205000
Reexamination Certificate
active
06292534
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an X-ray examination apparatus.
An X-ray examination apparatus of this kind is known from European patent Application 08/926 867.
The known X-ray examination apparatus is used to pick up successive X-ray images by means of an image intensifier pick-up chain which includes an X-ray image intensifier and a television camera. The X-ray image intensifier includes an entrance screen provided with an X-ray sensitive conversion layer. The X-ray image intensifier has a substantially circular X-ray sensitive surface. Consequently, it is not very well possible to make the X-ray sensitive surface so large that a substantial part of the patient to be examined, for example the limbs, can be imaged in a single X-ray image. In the known Xray examination apparatus separate parts of an object, for example a patient to be radiologically examined, are irradiated by means of an X-ray beam and a series of successive X-ray images of the relevant parts of the patient is formed on the entrance screen of the Xray image intensifier; these X-ray images are converted into successive optical images on the exit window of the X-ray image intensifier and the television camera derives electronic video signals from the successive optical images. An image processing unit forms an image signal which represents the assembled image from the electronic video signals. The assembled image shows the separate parts of the patient together in a single image.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an X-ray examination apparatus which enables an X-ray image to be formed of a substantial part of an object to be examined while utilizing a lower X-ray dose in comparison with the known X-ray examination apparatus.
This object is achieved by means of an X-ray examination apparatus according to the invention which is characterized in that the X-ray detector has an essentially elongate X-ray sensitive surface, or the read-out circuit is arranged to read-out a selected part of the X-ray detector. Preferably, the X-ray detector or the selected part that is read-out has a width to length ratio less that ⅝ or even less than ½ or ⅔. Such values of the width to length ratio appear to correspond accurately to the shape of a patent's leg so that the X-ray detector according to the invention is advantageously employed in peripheral angiographic X-ray examinations.
The X-ray examination apparatus includes an X-ray source for irradiating an object, for example a patient to be examined, by means of an X-ray beam. An X-ray image is formed on the X-ray sensitive surface due to local differences in the X-ray absorption within the patient. Such an elongate X-ray detector enables an X-ray image to be made of a substantial part of the patient to be examined, without it being necessary to displace the X-ray source and the X-ray detector together and relative to the patient so as to form individual sub-images. Because only a single X-ray exposure is required, the X-ray dose required is much lower than in the known X-ray examination apparatus. Moreover, the construction of the X-ray examination apparatus according to the invention is less complex than that of the known X-ray examination apparatus. It is notably no longer necessary to perform a complex image processing operation so as to merge sub-images into a high-quality diagnostic image in which substantially the entire region to be examined is reproduced in such a manner that small details of low contrast are still suitably visible; for example, substantially the entire vascular system of a leg of the patient is reproduced in the X-ray image.
It has been found in practice that in many radiological examinations the relevant part of the X-ray image used has an essentially elongate shape. Consequently, the X-ray examination apparatus according to the invention offers the advantage that the shape of the X-ray sensitive surface corresponds better to the relevant part of the X-ray image than in a conventional X-ray examination apparatus. An X-ray image of a part of the patient to be examined can thus be formed by means of a single X-ray exposure while utilizing essentially the entire X-ray detector nevertheless. The surface of the X-ray detector need not be much larger than the surface of the part of the patient to be examined.
It is also possible to realize an X-ray detector having a desired X-ray sensitive surface by combination of individual X-ray detector modules. Such X-ray detector modules are preferably manufactured so as to have standard dimensions.
An X-ray detector having a substantially elongate X-ray sensitive surface is, for example an image sensor matrix. Such an image sensor matrix includes, for example X-ray-sensitive sensor elements which are arranged in a matrix. Individual sensor elements are connected to a read-out line by means of a switching element. Individual switching elements are connected 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). An X-ray detector of this kind is known from European patent applications EP 0 444 720 and EP 0 440 282. The sensor elements can alternatively be constructed as infrared-sensitive, ultraviolet-sensitive or photosensitive elements, such as photodiodes or phototransistors; the image sensor matrix is then also provided with a conversion layer for converting incident X-rays into radiation whereto the sensor elements are sensitive.
The X-ray detector having a substantially elongate surface may also be an X-ray detector which is provided with an essentially flat conversion screen for deriving optical images from the X-ray images, and with an image pick-up system with one or more image sensors for deriving image signals from the optical images.
The conversion screen is provided with an essentially flat layer of scintillation material, such as 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. The image processing unit can operate with a fixed setting because the image sensors occupy a known position relative to the conversion screen and the settings of the individual image sensors, such as an internal amplification, do not change during the picking up of the image. An X-ray detector of this kind is known per se from European patent application EP 0 583 844.
These and other aspects of the invention will be described on the basis of the embodiments defined in the dependent Claims.
When the X-ray detector is integrated in the patient table, it is achieved that the X-ray examination apparatus according to the invention occupies less space than the known apparatus. The X-ray detector accommodated in the patient table is also suitably protected, so that it cannot be easily damaged. Furthermore, it is not necessary to clean or sterilize the X-ray detector when it is accommodated in the patient table. Moreover, the X-ray detector can be suspended independently of the X-ray source, so that there are hardly any restrictions as regards the accessibility of the examination space in which the patient is arranged during the formation of the X-ray images. Notably when the X-ray detector extends over a large part of the length of the patient table and the X-ray source is movable independently of the X-ray detector, digital tomosynthesis can be performed during which the X-ray detector forms an image of a longitudinal cross-section of the patient to be examined. Such a tomosynthesis techni
Linders Petrus W. J.
Meulenbrugge Hendrik J.
Porta David P.
U.S. Philips Corporation
Vodopia John F.
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