X-ray or gamma ray systems or devices – Electronic circuit – With display or signaling
Reexamination Certificate
1999-07-23
2001-05-01
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Electronic circuit
With display or signaling
C378S098300, C378S098800
Reexamination Certificate
active
06226351
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an X-ray examination apparatus which includes an X-ray detector for deriving an optical image from an X-ray image, and an image pick-up apparatus for deriving an image signal from the optical image, which image pick-up apparatus includes an image sensor provided with plurality of sensor elements.
2. Description of Related Art
An X-ray examination apparatus of this kind is known from European patent application EP 0 655 860.
The known X-ray examination apparatus includes an image pick-up apparatus with an adjustable spatial resolution. The image pick-up apparatus of such an X-ray examination apparatus is provided with a semiconductor CCD image sensor in which sensor elements are defined by way of gate electrodes. Incident light is absorbed in the semiconductor material of the individual sensor elements so that electric charges, electrons or holes, are released in the sensor elements. Said electric charges are collected in the sensor elements after which they are transported to a read-out register and the image signal is derived from the electric charges in the read-out register by means of a read-out amplifier.
The CCD image sensor in the known X-ray examination apparatus is notably provided with groups of collecting gate electrodes which are isolated from one another by isolating gate electrodes. The collecting gate electrodes receive an electric voltage whose polarity opposes that of the charge of electric charges collected in the relevant sensor elements. The isolating gate electrodes receive an electric voltage having the same polarity as the electric charges being collected. The spatial resolution of the known image pick-up apparatus is determined by adjusting the gate electrodes to the collecting state or the isolating state. The spatial resolution of the known image pick-up apparatus is thus adjustable. However, when an image containing a large number of pixels, for example 1000×1000 pixels, is to be picked up by means of an equally large number of sensor elements, an intricate operation is required to change the spatial resolution of the known image pick-up apparatus, because a very large number of gate voltages must be adapted. It is notably difficult to pick up an image of large dimensions with a high spatial resolution by means of the known X-ray examination apparatus.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an X-ray examination apparatus which includes an X-ray detector or image pick-up apparatus whose spatial resolution can be readily changed.
This object is achieved by means of an X-ray examination apparatus according to the invention which is characterized in that
an active surface area of individual sensor elements differs for individual optical spectral components of the optical image, and that
the image pick-up apparatus is provided with an adjusting system for selecting such an optical spectral component in order to derive the image signal therefrom by means of the image sensor.
The spatial resolution of the image pick-up apparatus is not high in the case of a large active surface area of individual sensor elements. The smaller the active surface area, the higher the spatial resolution will be. The spatial resolution of the image pick-up apparatus differs for the individual optical spectral components. This enables adjustment of the spatial resolution of the image pick-up apparatus by selecting such an optical spectral component and deriving the image signal therefrom.
The optical spectral components of the optical image are components of the optical image having different optical frequency ranges. Such different optical frequency ranges may have optical frequencies in common or not. The essential aspect is that the different optical spectral components of the optical image are components of different colors of the optical image and that the spatial resolution of the image pick-up apparatus deviates for the different colors of the optical image. Such optical spectral components can be selected by means of optical elements such as optical spectral absorption filters, optical grids or optical interference filters.
When the active surface of the individual image sensors is large, the spatial resolution is low but the sensitivity of the image sensors to the optical image is very high. A high sensitivity means that the image pick-up apparatus delivers an image signal having a high signal level even when the intensity of the incident light is low. Selection of a suitable optical frequency component of the optical image enables the image pick-up apparatus to be switched, if desired, between a state of high spatial resolution or a state of high light sensitivity. In the case of X-ray fluoroscopy, during which a patient to be examined is irradiated for a prolonged period of time but with a low X-ray intensity, it is notably advantageous to adjust the image pick-up apparatus to the state of high sensitivity. During an X-ray exposure, where a high X-ray intensity is applied during a brief period of time, preferably the state of high spatial resolution is adjusted. The fact that in that case the sensitivity of the image pick-up apparatus is somewhat lower is not objectionable, because the high X-ray intensity ensures that, even in the case of a low sensitivity, the brightness of the optical image is sufficiently high to derive an image signal having a high signal-to-noise ratio from the optical image. It is thus ensured that even very small details in the X-ray image can be suitably visualized in the case of an X-ray exposure.
Preferably, the sensor elements are provided with an optical spectral filter section having a transmission profile which varies in a lateral direction. The lateral direction is an arbitrary direction in the plane of the sensor elements on which the light is incident. The transmission profile is the transmittance for incident light as a function of the optical frequency of the incident light. The transmission profile of the optical spectral filter section varies in the lateral direction in the surface of individual sensor elements on which the light of the optical image is incident. Thus, the position in the lateral direction determines which optical spectral component is transmitted by the optical spectral filter section of the sensor elements. This means that individual parts of a sensor element are sensitive to different optical spectral components of light of the optical image. These individual parts may overlap or not. It is notably possible to realize such a lateral variation of the transmission profile that one spectral component can reach only half the surface of individual sensor elements whereas another spectral component can reach the entire surface of individual sensor elements. The optical spectral filter section associates different optical spectral sensitivities for individual optical spectral components with different spatial sensitivities. Picking up different optical spectral components individually by means of the relevant separate parts of the sensor elements enables the image signal to be derived from separate optical spectral components of the optical image.
The image pick-up apparatus preferably includes an adjustable optical spectral filter unit for isolating an optical spectral component from the optical image. In different settings of the adjustable optical spectral filter unit different optical spectral components of the optical image are admitted to the image sensor. Preferably, the optical spectral filter unit is adjustable by displacement in space of the optical spectral filter unit. The position of the optical spectral filter unit then determines which optical spectral component of the optical image can reach the image sensor. When the spectral filter unit is arranged in front of the image sensor in the image carrying light beam, essentially only the optical spectral component for which the filter has a high transmittance will be admitted to the image sensor. When the spectral filter unit is not arranged i
Dillen Bartholomeus G. M. H.
Snoeren Rudolph M.
Van Den Meijdenberg Willibrordus H. F. M.
Ho Allen C.
Kim Robert H.
U.S. Philips Corporation
Vodopia John F.
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