X-ray or gamma ray systems or devices – Electronic circuit – With display or signaling
Reexamination Certificate
1999-02-18
2001-03-06
Porta, David P. (Department: 2876)
X-ray or gamma ray systems or devices
Electronic circuit
With display or signaling
C378S098800
Reexamination Certificate
active
06198801
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an X-ray examination apparatus which is provided with an X-ray detector which includes an image sensor arranged to derive an image signal and a measurement signal from the X-ray image, and also provided with an exposure control for adjusting the X-ray examination apparatus on the basis of the measurement signal.
2. Description of Related Art
An X-ray examination apparatus of this kind is known from German Offenlegungsschrift DE 44 06 677.
The known X-ray examination apparatus includes an X-ray detector with a conversion screen and an image sensor. The conversion screen derives an optical image from the X-ray image and the image sensor derives the image signal from the optical image. The image sensor of the known X-ray examination apparatus is provided with shift registers for reading out electrical charges from the image sensor. The shift registers, moreover, are sensitive to light of the optical image and convert a part of the light of the optical image into electrical charges which constitute the measurement component.
The shift registers are arranged at the edge of the image sensor. Consequently, it is a drawback of the known X-ray examination apparatus that the measurement component can be derived only from a part of the edge of the optical image. Because brightness values of the edge of the optical image usually are not representative of brightness values in the remainder of the optical image, the measurement signal is not very well suitable for accurate adjustment of the X-ray examination apparatus in order to form an image signal whereby details in the optical image can be suitably visualized.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an X-ray examination apparatus which can be adjusted more accurately than the known 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 is arranged in such a manner that the measurement signal relates predominantly to relevant image information in the X-ray image.
The X-ray examination apparatus according to the invention is adjusted on the basis of relevant image information in the X-ray image. Consequently, the X-ray examination apparatus can be readily adjusted in such a manner that relevant image information is suitably visualized. The X-ray examination apparatus can be accurately adjusted notably because it is not necessary to take into account differences between brightness values relating to relevant image information and brightness values wherefrom the measurement signal is derived. Relevant image information concerns image information in a portion of the x-ray image that is required to be accurately reproduced. Such relevant information may be selected by the operator (e.g. the radiologist) in view of the part of the patient's body to be radiologically examined.
From the European patent application EP 0 629 105 it is known to adjust an X-ray examination apparatus on the basis of relevant image information, but the X-ray examination apparatus disclosed therein utilizes a separate auxiliary light detection system for deriving a measurement signal, using an own photodetector, in addition to a television camera for supplying the image signal. It is a further advantage of the X-ray examination apparatus according to the invention that the accurate adjustment can be achieved without utilizing such a complex and expensive auxiliary light detection system. The adjustment of the X-ray examination apparatus concerns, for example the adjustment of an X-ray source or the X-ray detector. The adjustment of the X-ray source concerns notably the energy and the intensity of the X-rays emitted by the X-ray source and the duration of the irradiation.
These and other aspects of the invention will be described in detail hereinafter on the basis of the embodiments as defined in the dependent Claims.
The X-ray detector is preferably provided with a conversion unit for deriving an optical image from the X-ray image. The image sensor is preferably provided with an image pick-up section for deriving electrical charges from the optical image. The image pick-up section is arranged to receive light from substantially the entire optical image. The image pick-up section notably receives light from a part of the optical image which contains relevant image information. The electrical charges in the image pick-up section represent brightness values in the optical image. For the measurement component a part is selected of the electrical charges which relate notably to relevant image information. It is thus achieved that the measurement signal relates to relevant image information in the optical image so that the X-ray examination apparatus can be accurately adjusted. In the case of such an adjustment it is achieved that signal levels of the image signal lie in a range such that the relevant image information can be clearly visualized by means of the image signal. The image signal is notably suitable for reproducing an image of high diagnostic quality, that is to say an image in which small details of low contrast, such as a small tumor in an early stage of pathology, are suitably visible.
Because brightness values of the optical image correspond to brightness values of the X-ray image, the optical image contains image information which corresponds to image information of the X-ray image.
The adjustment of the X-ray detector concerns, for example the adjustment of the image pick-up apparatus. The adjustment of the image pick-up apparatus concerns notably the control of a variable amplifier which is used to derive the image signal from electrical charges and the adjustment of a diaphragm for controlling the amount of light received by the image sensor from the optical image.
When the image sensor is adjusted on the basis of the mean brightness of the optical image, it is achieved that the image sensor is sensitive mainly to the range of brightness values occurring in the optical image. It is notably when the image sensor is a charged coupled (CCD) image sensor that the sensitivity of the CCD sensor can be adjusted by adjustment of the integration time on the basis of the measurement of the mean brightness of the optical image by the photosensor or on the basis of the substrate current. The measurement component is preferably available separately from the image component in order to derive the measurement signal therefrom. Consequently, first the measurement component can be read from the image memory, followed by the formation of the measurement signal which is subsequently used for accurate adjustment of the X-ray examination apparatus so that subsequently the X-ray image is formed and the image signal can be derived from the X-ray image. Using this accurate adjustment, the image component is formed and the image signal is derived therefrom. The measurement component is preferably much smaller than the image component, so that the formation of the measurement signal requires substantially less time than the formation of the image signal. Thus, a correspondingly small portion of the x-ray image is used to derive the measurement signal that is employed to adjust the x-ray examination apparatus. Consequently, accurate adjustment of the X-ray examination apparatus requires a short time only, so that image signals can be derived from successive X-ray images in rapid succession and image information contained in a rapid succession of X-ray images can be suitably visualized.
For example, the image sensor is provided with an image memory for the storage of electrical charges from the image pick-up component. In such an image sensor the electrical charges are read out from the image pick-up component by way of transfer to the image memory. Subsequently, the measurement signal is derived from the electrical charge of the measurement component in the image memory.
It has been found that the transport of the electrical charges of the measurement component to the subs
Hobden Pamela R.
Porta David P.
U.S. Philips Corporation
Vodopia John F.
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