Patent Grant
7474735
The present application hereby claims priority under 35 U.S.C. §119 on German patent application number DE 10 2005 052 992.5 filed Nov. 7, 2005, the entire contents of which is hereby incorporated herein by reference.
The invention generally relates to an antiscatter grid for reducing a scattered radiation in an X-ray machine, and/or to an X-ray machine with an antiscatter grid.
In X-ray imaging, scattered radiation frequently causes a reduction in the image quality and the signal-to-noise ratio in the display of an examination object. The scattered radiation is caused, for example, by classical scattering or the so-called Compton effect. An important method for reducing scattered radiation is the use of focused antiscatter grids.
These are generally made from thin absorbing laminas, for example, from lead, with interspaces constructed from a well medium, and are arranged in the beam path of the X-radiation perpendicular to the direction of the latter. The absorber laminas are aligned substantially parallel to the X-radiation or in a fashion focused on to the X-ray focus in such a way that scattered radiation impinging at various angles is filtered out.
Simple antiscatter grids have a maximum line number of approximately 40 lines per centimeter and are usually moved linearly in a fashion perpendicular to the direction of incident radiation at a low speed over a portion of the image area in order not to be visible later on the X-ray image as a striped structure or artifact. There is a need in this case to control and trigger so as to ensure that the movement of the antiscatter grid is coordinated with the emission of the X-radiation and is started in good time before radiation begins.
As an alternative to a movement of the antiscatter grid, the striped structure or the artifact can be corrected by software in the later X-ray image. Using the simple moving antiscatter grid is impossible in the case of rapid, dynamic X-ray imaging methods, because of the rapid image sequence, while using the software correction is very expensive because of the long computing times. Dynamic X-ray imaging methods are understood, for example, as fluoroscopy, angiography, cardioangiography, and various 3-D recording methods.
If simple antiscatter grids with digital X-ray detectors are used, disturbing interference can arise between the regularly arranged absorbing laminas and the pixel structure of the digital X-ray detector, producing so-called Moiré structures. Multiline antiscatter grids that have a high number of, for example, 70 or more lines per centimeter have been developed in order to reduce these Moiré structures. The production of these multiline antiscatter grids is, however, very expensive and complicated, and it is therefore impossible to suppress striped structures or artifacts completely.
In at least one embodiment of the invention, an antiscatter grid and/or an X-ray machine for an antiscatter grid is provided, that creates a particularly effective suppression both of scattered radiation and of interfering striped structures and artifacts, caused by absorbing laminas, on the X-ray image. This can occur, for example, even in the case of dynamic X-ray imaging methods at as low a production cost.
An antiscatter grid, in at least one embodiment, is for reducing a scattered radiation in an X-ray machine. In at least one embodiment, an X-ray machine with an antiscatter grid is disclosed.
Owing to its absorbing laminas that are aligned substantially parallel to the direction of the (primary) X-radiation, the antiscatter grid according to at least one embodiment of the invention reduces scattered radiation, which generally impinges on the antiscatter grid at various angles. Owing to its movement at a frequency of at least 10 Hz, the antiscatter grid according to at least one embodiment of the invention prevents the absorbing laminas from being imaged on to the X-ray image even at the point of reversal of the to and fro movement, and artifacts that are caused by the absorbing laminas could be suppressed.
The to and fro movement is understood here as a movement that is substantially perpendicular to the direction of the X-radiation and substantially perpendicular to the direction in which the absorbing laminas extend. Designated as the travel is the path which is covered by the absorbing laminas when moving to and from between the two points of reversal.
An alignment of the absorbing laminas in a fashion substantially parallel to the direction of the (primary) X-radiation, in this case likewise includes a focused alignment of the absorbing laminas with the X-ray focus of the (primary) X-radiation.
Particularly in the case of dynamic X-ray applications with very short X-ray pulses of, for example, 10 ms at 30 X-ray images per second, the interplay between a relatively high frequency and low maximum travel value ensures transparency of the antiscatter grid for the regular X-radiation, that is to say the X-radiation required for the X-ray imaging of the examination object. Frequencies between 100 Hz and 500 Hz, for example, are particularly suitable for general customary X-ray pulses between 4 ms and 15 ms.
Moreover, the movement to and fro or forward and backward provides a particular suitability of the antiscatter grid for dynamic applications. Thus, there is no need for a complicated and time-intensive triggering of the grid movement at a specific instant as in the case of the known antiscatter grids. Accordingly, an antiscatter grid according to at least one embodiment of the invention can be used to carry out rapidly succeeding X-ray recordings without the occurrence of interfering time delays between the recordings.
The requirements placed on the quality and the number of the absorbing laminas per cm of the antiscatter grid is reduced by the blurring of the imaging of the absorbing laminas by high frequency and short travel. Thus, the antiscatter grid can be fabricated with less complication and therefore also more cost effectively.
The antiscatter grid can be moved to and fro at a minimum frequency value of 150 Hz in an advantageous way with a particularly good suppression of an imaging of the antiscatter grid onto the X-ray image. According to one refinement of at least one embodiment of the invention, the antiscatter grid can, moreover, be moved to and fro with a travel value of substantially one pixel size of the X-ray detector that can be assigned to the antiscatter grid.
If, according to a further refinement of at least one embodiment of the invention, the antiscatter grid has at most 70 absorbing laminas per centimeter, it can be produced with a particularly low degree of complexity and thus cost effectively. Such an antiscatter grid can be used with particular advantage in dynamic applications.
According to a further refinement of at least one embodiment of the invention, the antiscatter grid is moved by means of at least one piezoactuator. Precise movements are possible at high frequency to a particular degree by way of piezoactuators. Moreover, such actuators have small external dimensions and can therefore be accommodated in a space-saving fashion in the housing of the antiscatter grid.
A particularly advantageous possibility of using an inventive antiscatter grid of at least one embodiment occurs in the case of an X-ray machine having a digital flat image detector, in particular in the case of an X-ray machine for carrying out dynamic X-ray imaging methods. Owing to the fast movements of the antiscatter grid at high frequency, it is possible to avoid Moiré structures even without using a multiline grid.
The invention and further advantageous refinements in accordance with the features of the subclaims are explained in more detail below with the aid of schematically illustrated example embodiments in the drawings, without thereby limiting the invention to these example embodiments; in the drawings:
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes” and/or “including”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
In describing example embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner.
Referencing the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, example embodiments of the present patent application are hereafter described.
So that it can be produced with as little complexity as possible in conjunction with a high number of lines, the antiscatter grid advantageously has at most 70 lines, that is to say absorbing laminas 4, per centimeter. The antiscatter grid can also have 60 or even more few, for example 40, lines per centimeter. In this context, the advantage of a relatively low number of line pairs resides in that the height of the absorbing laminas in the direction of the X-radiation can be selected to be low in conjunction with the low number of line pairs, and as a result of this the alignment of the absorbing laminas need be set less exactly parallel to the X-radiation or in a fashion focused on to the X-ray focus, and yet a good recording quality is ensured.
The absorbing laminas 4 are moved to and fro via actuators. According to one refinement of an embodiment of the invention, piezoactuators 6 are used to move the absorbing laminas 4. Since the latter are particularly small, they can be arranged within the housing 3. Moreover, the piezoactuators 6 have the advantage of being particularly energy-saving and thus both of producing a low level of waste heat and of making only slight demands on energy saving. When a voltage is applied to a piezoactuator 6, the latter is deformed and can thus be used for to and fro movements whose frequencies can be set precisely.
In
The raw grid 3 is supported inside the housing 2 on bearings 7 so as to enable a to and fro movement free from friction. Roller, ball, or plain bearings can be used as bearings 7. An air bearing is also possible, for example, as an alternative.
At least one embodiment of the invention may be summarized briefly in the following way: in order to prevent an imaging of an antiscatter grid 1 with particular effectiveness even during dynamic applications, an antiscatter grid 1 for an X-ray detector 11 is provided which exhibits an active pixel matrix and has absorbing laminas 4, aligned substantially parallel to the direction of an X-radiation 17, for reducing a scattered radiation in an X-ray machine 10, it being possible to move the absorbing laminas 4 to and fro in a fashion perpendicular to the direction of the X-radiation 17 at a minimum frequency value of 10 Hz, in particular of 150 Hz, and with a maximum travel value of two pixel sizes of the X-ray detector 11 that can be assigned to the antiscatter grid 1.
Further, elements and/or features of different example embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims.
Example embodiments being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
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| Number | Date | Country | |
|---|---|---|---|
| 20070104321 A1 | May 2007 | US |
