X-ray or gamma ray systems or devices – Beam control – Filter
Reexamination Certificate
2001-02-02
2002-07-30
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Beam control
Filter
C378S157000, C378S158000, C378S159000
Reexamination Certificate
active
06426999
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an X-ray apparatus which includes an X-ray source for producing X-rays, an X-ray detector for detecting the X-rays, a filter which is arranged between the X-ray source and the X-ray detector and includes a plurality of tubular filter elements having a longitudinal direction z and a circumference, the X-ray apparatus also including an electrical device for controlling the individual filter elements,
each filter element having an internal volume for receiving a liquid filling having electrically conductive and X-ray absorbing properties, said filter element having an X-ray absorptivity which is dependent on the quantity of X-ray absorbing liquid present in the internal volume,
each filter element being provided with a first electrode for applying a first electric potential to a wall of the filter element and a second electrode for applying a second electric potential to the internal volume of the filter element, and
the X-ray absorptivity of each filter element being adjustable by step-wise control of a level of the X-ray absorbing liquid in the longitudinal direction z of the filter element.
DESCRIPTION OF RELATED ART
An X-ray apparatus of this kind which includes an X-ray filter is known from U.S. Pat. No. 5,666,396 (PHN 15.378). The known X-ray apparatus comprises a filter with a plurality of filter elements having individual absorptivities which are dependent on a level of a liquid filling present in the filter element. The X-ray apparatus is used inter alia for medical diagnosis where a patient to be examined is arranged between the X-ray source and the X-ray detector so as to image internal structures. Thanks to the fact that the patient has structures of different electron density, regions of different density are observed in a resultant X-ray image. The interval in density between regions with the extremes of the density in an X-ray image is defined as the dynamic range. The filter serves to limit a dynamic range for each X-ray image.
In order to limit the dynamic range of the object to be examined, the known X-ray apparatus includes a filter with filter elements provided with a bundle of tubes for receiving a liquid filling which is X-ray absorbing as well as electrically conductive. Each tube is connected to a common supply channel. Each filter element is provided with a first electrode which is arranged in a wall of the filter element in order to apply an electric voltage to the wall of the filter element. A second electrode is in contact with the liquid filling. The electric voltage applied to the first electrode of the filter element influences on the adhesion between the liquid filling having the electrical properties and an inner wall of the filter element; this adhesion determines whether the relevant filter element is filled with the liquid filling. The relative quantity of the liquid filling in individual filter elements is controlled on the basis of the electric voltages applied to individual filter elements. The known apparatus utilizes the phenomenon that a contact angle between an electrically conductive liquid and an electrode which is insulated therefrom is changed by applying a potential difference between the electrically conductive liquid and the electrode. This phenomenon is known as electrowetting. When electrowetting is applied to a tubular filter element which has an electrode arranged in the wall and is filled with an electrically conductive liquid filling, the level of the liquid filling in the filter element can be influenced thanks to the fact that the electrowetting force is directed in the longitudinal direction of the filter element, so that the degree of filling of the filter element can be increased or decreased as desired. In order to enable the potential difference to be realized between the liquid filling and the first electrode in the wall of the filter element, they are electrically insulated from one another by means of an insulation layer provided on the inner wall of the filter element. The known apparatus operates as follows: in the presence of a first value of the electric voltage, the adhesion of the liquid filling to the inner wall is increased and the relevant filter element is filled with the liquid filling from the supply channel. In the presence of a second value of the electric voltage the adhesion is reduced and the liquid filling is discharged from the filter element to the supply channel. Because of the X-ray absorbing properties, filter elements are adjusted to a high X-ray absorptivity by filling with the liquid filling; they are adjusted to a low X-ray absorptivity by keeping the filter elements empty.
It is a drawback of the known device that the filling of each filter element is controlled by application of a sequence of electric voltage pulses to the first electrode of the filter element so that the filter element is electrically charged. The level of the electric charge defines the degree of filling of the filter element. It has been found that the filling level of the filter element becomes poorly reproducible in the course of time. In practice it is often desirable to make the filling reproducible with an a priori known degree of discretization in order to achieve a reliable range of grey values.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an X-ray apparatus which includes a filter provided with the filter elements whose X-ray absorptivity can be step-wise controlled in a reliable and reproducible manner. To this end, the X-ray apparatus according to the invention is characterized in that the first electrode is segmented in the longitudinal direction z of the filter element so as to form at least one sequence of alternating hold electrode segments and barrier electrode segments, the barrier electrode segments having a dimension in the longitudinal direction z of the filter element which is substantially smaller than that of the hold electrode segments, the hold electrode segments constituting a first group and the barrier electrode segments constituting a second group, the electrode segments in each group being electrically interconnected and the first group being electrically insulated from the second group, each group being individually controllable by the electrical device, the electrical device being arranged to apply pulse voltages to the second group and to supply the first group with voltages having a predetermined minimum value which suffices to fill the part of the internal volume which corresponds to the relevant hold electrode.
This step offers the desired effect, because each filter element has a stack of electrode segments in the longitudinal direction, the degree of segmentation being known a priori. Thanks to the fact that the successive electrode segments are electrically insulated from one another, the filter element can be step-wise filled because of the electrical properties of the liquid filling. The absolute value of the electric voltage applied to an individual electrode segment can be chosen to be such that the secondary effects on the reproducibility of the filling, that is, the orientation of the filter element relative to the force of gravity and the aging effects of the cover layer (being the protective layer between the insulation layer and the liquid filling) are compensated. In the filter element of the X-ray apparatus according to the invention a functional distinction is made between two types of electrode, that is, between hold electrodes and barrier electrodes. The function of hold electrodes is to transport the liquid filling in the longitudinal direction of the filter element. The barrier electrodes serve to create potential barriers between the hold electrodes. The activation or deactivation of a number of the potential barriers enables the step-wise filling of the filter element. These two types of electrode constitute the respective sub-groups of the electrode segments, which sub-groups are individually controlled by the electrical device. For efficiency of this method for transporting the liqui
Kim Robert H.
Koninklijke Philips Electronics , N.V.
Vodopia John F.
Wang George
LandOfFree
X-ray apparatus including a filter provided with filter... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with X-ray apparatus including a filter provided with filter..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and X-ray apparatus including a filter provided with filter... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2843578