X-ray or gamma ray systems or devices – Beam control – Filter
Reexamination Certificate
1999-05-21
2001-01-30
Church, Craig E. (Department: 2876)
X-ray or gamma ray systems or devices
Beam control
Filter
C378S158000
Reexamination Certificate
active
06181774
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an X-ray examination apparatus, comprising an X-ray source, an X-ray detector and an X-ray filter which is arranged between the X-ray source and the X-ray detector and includes a plurality of filter elements whose X-ray absorptivity can be adjusted by adjustment of a quantity of X-ray absorbing liquid within individual filter elements.
2. Description of Related Art
An X-ray examination apparatus of this kind is known from U.S. Pat. No. 5,625,665.
The X-ray examination apparatus forms an X-ray image of an object to be examined, for example a patient to be radiologically examined. The X-ray source irradiates the object by means of an X-ray beam and an X-ray image is formed on the X-ray detector due to local differences in the X-ray absorption within the object. The X-ray filter ensures that the range of brightness values of the X-ray image remains limited. The X-ray filter is adjusted in such a manner that on the one hand parts of the X-ray beam which are only hardly attenuated by the object are slightly attenuated by the X-ray filter and that on the other hand parts of the X-ray beam which are significantly attenuated by the object are transmitted by the filter substantially without attenuation. Because the brightness values of the X-ray image lie within a limited range, the X-ray image can be readily further processed so as to reproduce small details of low contrast clearly.
The X-ray filter of the known X-ray examination apparatus includes a bundle with a very large number of capillary tubes, each of which communicates with the X-ray absorbing liquid by way of one end. The adhesion of the X-ray absorbing liquid to the inner wall of such a capillary tube is dependent on the electric voltage applied to the relevant capillary tube. Specifically, the contact angle enclosed by the X-ray absorbing liquid relative to the inner wall of such a capillary tube is dependent on the electric voltage difference between the inner wall and the X-ray absorbing liquid. When the contact angle is larger than 90°, the X-ray absorbing liquid hardly penetrates such a capillary tube and when the contact angle is smaller than 90°, such a capillary tube is filled with a quantity of X-ray absorbing liquid which is dependent on the magnitude of the electric potential difference. The capillary effect of the capillary tubes in respect of the X-ray absorbing liquid can thus be electrically controlled. The quantity of X-ray absorbing liquid in each of the capillary tubes is controlled on the basis of the electric voltages applied to the capillary tubes.
The manufacture of the X-ray filter of the known X-ray examination apparatus is intricate and hence expensive, because it is very difficult to bundle a very large number of capillary tubes in a regular pattern.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an X-ray examination apparatus which includes an X-ray filter that can be more readily manufactured.
This object is achieved by means of an X-ray examination apparatus according to the invention which is characterized in that
the X-ray filter includes a stack of deformable foils,
individual filter elements are formed by spaces between individual deformable foils,
neighboring foils are locally attached to one another, the stack of deformable foils is arranged between rigid plates,
the rigid plates are mechanically coupled to the stack of deformable foils,
the stack of foils is expanded transversely of the surface of the foils, and
a buffer member is provided between the stack of foils and at least one of the rigid plates, said buffer member being contractable parallel to the surface of the foils. Because the stack of foils is expanded transversely to the surface of the foils, for example by stretching the stack of foils transversely to the surface of the foils, spaces are created between neighboring foils between the locations where the foils are attached to one another. As the stack of foils is stretched further, larger spaces are created between the foils until a given maximum size of these spaces is reached. When the stack of foils is stretched very far, the spaces become smaller again. The spaces are preferably formed as capillary tubes which act as filter elements. The X-ray absorptivity of the capillary tubes, being the filter elements, is adjusted by adjustment of the quantity of X-ray absorbing liquid within said capillary tubes. The stack of foils can be readily stretched, because the stack of foils is arranged between the rigid plates so that the force for stretching the stack of foils can be exerted on the rigid plates. The mechanical coupling ensures that the force exerted on the rigid plates causes a force to act on the stack of foils, transversely to the surface of the foils, so that the foils are pulled apart at the areas where they are not attached to one another. The rigid plates need not be fully inflexible, but should be significantly less readily deformable than the foils. It is thus achieved that the force exerted transversely to the surface of the foils mainly expands the stack of foils, without the rigid plates being deformed or their deformation being at least substantially less. The mechanical coupling is provided by the buffer member. For example, the stack of foils and at least one of the rigid plates are connected to the buffer member to either sides of the buffer member. In response to the force exerted on the buffer member, transversely to the surface of the foils, by the rigid plates, the buffer member is contracted in the direction substantially parallel to the surface of the foils. It is thus achieved that the neighboring foils practically throughout the stack of foils are pulled apart equally far between the spaces where they are attached to one another. Thus, capillary tubes having essentially the same crosssection can be formed between the foils throughout the stack of foils. It is thus achieved that the spatial resolution of the X-ray filter is substantially uniform across the entire surface. Artefacts and/or disturbances in the X-ray image due to the X-ray filter are thus avoided. Preferably, use is made of two buffer members; in that case individual buffer members are provided between the stack of foils and each of the rigid plates so as to achieve a particularly high degree of uniformity of the spatial resolution. The X-ray examination apparatus according to the invention then enables the formation of X-ray images of high diagnostic quality, i.e. small details of low contrast can nevertheless be suitably reproduced in the X-ray image.
The foils are preferably thin foils of a synthetic material. When use is made of flexible foils, the stacked foils can be readily deformed in the direction transversely of the plane of the foils, so that spaces which constitute the filter elements are locally formed between neighboring foils. Preferably, thin foils are used because they hardly absorb any X-rays and hence do not disturb the X-ray image. Flexible, thin, stacked foils can be readily handled; they are notably less vulnerable than preformed thin plates. The foils are preferably thin; for example, foils having a thickness of approximately 5 &mgr;m are used. Furthermore, the foils preferably transmit X-rays as well as possible, so that the background absorption of X-rays by the X-ray filter remains low. Moreover, it is advantageous to utilize foils of high mechanical strength which are suitably capable of withstanding X-rays. It has been found that polypropylene sulphone (PPS) is a suitable material for the foils; polyethyleneterephtalate (PETP), polyethylene and polyesters are also suitable foil materials.
The stacked foils are preferably expanded by clamping them transversely to the plane of the foils. As a result, neighboring foils locally move apart at areas where they are not attached to one another. The expanded, stacked foils can be maintained in the expanded condition by keeping them mechanically tensioned. The stacked foils can also be kept expanded by drastically redu
Giesbers Jacobus B.
Jans Theodorus J. A. M.
Prins Menno W. J.
Weekamp Johannes W.
Welters Wilhelmus J. J.
Church Craig E.
Renfrew Dwight H.
U.S. Philips Corporation
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