X-ray or gamma ray systems or devices – Beam control – Filter
Reexamination Certificate
1999-12-22
2001-08-14
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Beam control
Filter
C378S156000, C378S157000
Reexamination Certificate
active
06275568
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an X-ray examination apparatus for forming X-ray images of an object, which apparatus includes
an X-ray source for generating an X-ray beam,
an X-ray filter which is provided with filter elements which are arranged to contain an adjustable quantity of X-ray absorbing liquid in order to adjust an intensity profile on an object, and with a supply duct for connecting the filter elements to a reservoir for the X-ray absorbing liquid,
an X-ray detector for receiving a part of the X-ray beam, having traversed the object, in order to detect an X-ray image.
The invention also relates to an X-ray filter for use in an X-ray examination apparatus of this kind.
An X-ray examination apparatus of the kind set forth is known from international patent application WO 96/13040. The X-ray filter in the known X-ray examination apparatus is used to limit the dynamic range of an X-ray image of an object which is formed on the X-ray detector, for example a human or animal body to be examined. The filter elements of the X-ray filter are constructed as capillary tubes, one end of which communicates with the X-ray absorbing liquid present in the reservoir. The X-ray absorbing liquid contains, for example aqueous solutions of salts of, for example lead, cesium or tungsten. The quantity of X-ray absorbing liquid can be adjusted by way of electrowetting. To this end, the tubes are provided with an electrical conductor which serves as an electrode. Furthermore, an electrically insulating coating layer is provided on the electrode. In the context of the present application the term “electrowetting” is to be understood to mean an adjustable adhesion of the X-ray absorbing liquid to the electrically insulating coating layer, which adhesion is dependent inter alia on the value of an electric voltage applied across the electrically conductive layer and the X-ray absorbing liquid. As a result, the filling of each of the capillary tubes can be adjusted by variation of the electric voltage value so that an X-ray absorption profile of the X-ray filter is adjusted within a short period of time, for example 0.4 seconds.
In order to form an image of the desired organs in the object, the X-ray detector is arranged opposite the X-ray source on a first axis with a part of the object to be imaged, and the X-ray filter is situated on this first axis between the X-ray source and the object, an entrance face of the X-ray filter then being oriented transversely of the first axis.
The arrangement is functional if the first axis is directed vertically during operation. It is a drawback of the known X-ray examination apparatus that, when the first axis is directed horizontally, the adjustment of the quantity of X-ray absorbing liquid in the capillary tubes is susceptible to an uneven hydrostatic pressure distribution in the supply duct.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an X-ray examination apparatus in which the susceptibility of the adjustment of the quantity of X-ray absorbing liquid in the capillary tubes to the uneven hydrostatic pressure distribution is reduced. To this end, an X-ray examination apparatus according to the invention is characterized in that the supply duct includes sub-ducts, and that each of the sub-ducts connects at least one of the filter elements to the reservoir. When the X-ray filter is arranged in the X-ray examination apparatus in such a manner that, a longitudinal axis of the sub-channels is directed horizontally during operation, the uneven hydrostatic pressure distribution, which is due to the fact that the capillary ducts are situated above one another in this condition, is counteracted by the taking up of the hydrostatic pressure by partitions between the sub-ducts. Attractive embodiments of the X-ray examination apparatus are defined in the dependent claims.
A special embodiment of the invention is characterized in that the sub-ducts are arranged so as to extend parallel to one another. Orienting all sub-ducts so that they extend substantially in parallel minimizes the uneven pressure distribution in the sub-ducts when the sub-ducts are directed horizontally.
A further embodiment of the invention is characterized in that the X-ray examination apparatus is provided with adjusting means for keeping the X-ray source, the X-ray filter and the detector oriented along a first axis and for adjusting an orientation of the first axis relative to a horizontal plane, the X-ray examination apparatus also including means for rotating the X-ray filter about the first axis. As a result of the addition of such adjusting means, a projection image of the object can be formed at different angles. Rotation of the X-ray filter about the first axis enables the sub-ducts to be oriented in such a manner that the gravitational force component along the sub-ducts amounts to substantially zero and the uneven pressure distribution in a sub-duct is minimum. The rotation of the X-ray filter can be realized by arranging a rotatable X-ray filter in a collimator, or by mounting the collimator so as to be rotatable about the first axis in the X-ray examination apparatus.
A further embodiment of the X-ray examination apparatus according to the invention is characterized in that the X-ray examination apparatus is provided with means for generating a signal which represents an angle of inclination between a longitudinal axis of the sub-ducts and a horizontal plane. As a result of these steps, an operator or an automatic control system can orient the longitudinal axis of the sub-ducts in dependence on the signal upon a change of orientation of the first axis.
A further embodiment according to the invention is characterized in that the means for generating the signal representing the angle of inclination include a roll-independent inclinometer. Such an inclinometer is insensitive to a rolling motion about the axis with to respect to which the inclination relative to the horizontal plane is determined. Such an inclinometer can be used for an arbitrary orientation of the first axis.
Another embodiment according to the invention is characterized in that the means for rotating the X-ray filter include an electrically controllable drive and that the X-ray examination apparatus is provided with control means which are arranged to generate control signals for the electrically controllable drive in order to orient the sub-ducts horizontally in dependence on the signal representing the angle of inclination.
A further embodiment according to the invention is characterized in that the X-ray filter contains the reservoir which is arranged outside the X-ray beam to be generated, the reservoir containing chambers and each chamber being connected to at least one of the sub-ducts. In order to avoid the necessity of long supply and discharge ducts between the reservoir and the sub-ducts, the reservoir can be mounted in the X-ray filter. In order to counteract an uneven hydrostatic pressure distribution in the sub-ducts, the reservoir is subdivided into chambers, each chamber being connected to at least one sub-duct. The number of sub-ducts connected to a chamber of the reservoir amounts to, for example, three in practice.
A further embodiment of the X-ray examination apparatus according to the invention is characterized in that the X-ray examination apparatus is provided with means for generating a control signal whereby the adjustable quantity of X-ray absorbing liquid in the filter elements is adjusted.
A further embodiment of the X-ray examination apparatus according to the invention is characterized in that the X-ray examination apparatus is provided with means for generating a compensation signal which is dependent on the orientation of the X-ray filter, and with means for correcting the control signal by way of the compensation signal.
It is thus possible in practice to compensate hydrostatic pressure differences which are due to several capillary tubes being situated above one another. A maximum magnitude of such a compensation voltage can be determined
Giesbers Jacobus B.
Prins Menno W. J.
Vissenberg Michel C. J. M.
Vugts Coenraad A. A. M.
Weekamp Johannus W.
Kim Robert H.
Thomas Courtney
U.S. Philips Corporation
Vodopia John F.
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