Patent Description:
Differential phase-contrast and dark-field imaging (DPCI and DFI) are promising technologies that will likely enhance the diagnostic quality of X-ray equipment Computer Tomography (CT) and radiography systems. For example, Dark-field X-Ray (DAX) imaging is a new modality with a great potential in the area of diagnosing lung diseases like COPD, pulmonary fibrosis, lung cancer, etc. The basic concept for DAX imaging is to use a Talbot-Lau type interferometer, i.e., to add three gratings G0, G1, and G2 into the X-ray beam. The object can be placed either between the G0 and G1 gratings or between G1 and G2.

<CIT> describes systems and methods for X-ray phase-contrast imaging (PCI). It is described that a quasi-periodic phase grating can be positioned between an object being imaged and a detector, and an analyzer grating can be disposed between the phase grating and the detector. Second-order approximation models for X-ray phase retrieval using paraxial Fresnel-Kirchhoff diffraction theory are also described. It is described that an iterative method can be used to reconstruct a phase-contrast image or a dark-field image.

One of the major challenges in the construction of a DAX system is the analyzer grating G2. It has to cover ideally the entire detector area (for example <NUM> x <NUM>) and has to be highly attenuating (for example ><NUM>%). At the same time, the pitch is still demanding (in the ballpark of <NUM> to <NUM> period). Putting all these requirements together, it is clear that the grating lamellae must be focused to the source.

State of the art grating manufacturing is based on "Lithography, Electroplating and Molding" LIGA technology, which, however, has several limitations and shortcomings like the need to have access to a synchrotron or the need to work with grating tiles since the grating size is limited.

On the other hand, there is the mature technology of foil stacking that is currently established to produce anti-scatter grids. Most recent progress in this area indicates that it might be possible to reach the desired grating periods with this technology.

While the most recent progress in foil stacking might open the way for using this technology for G2, it is not feasible to use it for G0 (because the pitch is even smaller) and G1 (because this is a phase grating). Combining gratings manufactured by LIGA and foil stacking poses the problem of focusing. If gratings are manufactured using the LIGA process, the gratings are inherently flat and focused to infinity, i.e., all lamellae are parallel to each other. Focusing of the gratings is achieved by bending the substrates. However, on the other hand, gratings manufactured by foil stacking are flat and directly focused to a predefined distance. These gratings are very stiff and it is impossible to change the focus after manufacturing. In particular, it is impossible to manufacture a grating with a focus at infinity and bend it later on to the desired distance to the focal spot of the X-ray tube.

It would be advantageous to have improved apparatus, method and system for phase-contrast and/or dark-field imaging.

It should be noted that the following described aspects and examples of the invention apply also to the apparatus for generating X-ray imaging data, the method for generating X-ray imaging data, as well as for the computer program element and a computer readable medium.

According to a first aspect, there is provided an apparatus for generating X-ray imaging data, comprising:.

The X-ray source is configured to produce X-rays. The first grating is positioned between the X-ray source and the second grating. The second grating is positioned between the first grating and the third grating. The third grating is positioned between the second grating and the X-ray detector. At least part of the region between the first grating and the third grating forms an examination region for accommodating an object. Either the first grating or the third grating has a pitch attribute of having a constant grating pitch. Both gratings of an adjacent pair of gratings have a pitch attribute of having a varying grating pitch. Both gratings of an adjacent pair of gratings are bent such that a distance between the two adjacent gratings is constant as a function of fan angle. The X-ray detector is configured to detect at least some of the X-rays transmitted by the three gratings.

In other words, G0, G1 and G2 gratings of a dark-field and/or phase-contrast arrangement are utilized, but with two of the gratings that are adjacent to each other being bent. Thus either G0 and G1 gratings are bent or G1 and G2 gratings are bent. Then either G0 and G1 gratings both have a varying grating pitch (chirped) and G2 has a constant pitch or G1 and G2 gratings have a varying pitch and G0 has a constant grating pitch.

In this way, manufacture of the gratings is simplified, for example through utilization of LIGA.

Furthermore, this completely new arrangement ensures for correct operation of the interferometric design, with the fringe pattern generated by the individual slits of the G0 grating lining up properly at the position of G2, which otherwise would not truly be satisfied.

It is to be noted that the gratings that are bent are each bent on a cylindrical surface having the required radius of curvature.

In an example, the grating that is not bent is a planar grating.

In an example, the adjacent pair of gratings that are bent are the first grating and the second grating.

In other words, the G0 and G1 gratings are bent, and the G2 grating can be planar.

In an example, the first grating and the second grating have the pitch attribute of having a varying grating pitch.

In other words, the G0 and G1 gratings are bent and chirped, and the G2 grating has a constant pitch.

In an example, the second grating and the third grating have the pitch attribute of having a varying grating pitch.

In other words, the G0 and G1 gratings are bent and the G1 and G2 gratings are chirped with G0 having a constant grating pitch.

In an example, the adjacent pair of gratings that are bent are the second grating and the third grating.

In other words, the G1 and G2 gratings are bent, and the G0 grating can be planar.

In other words, the G1 and G2 gratings are bent and the G0 and G1 gratings are chirped and G2 has a constant grating pitch.

In other words, the G1 and G2 gratings are bent and have varying grating pitches, and the G0 grating has a constant grating pitch.

In an example, the imaging data comprises dark field or phase contrast imaging data.

According to a second aspect, there is provided a system for X-ray imaging an object, comprising:.

The processing unit is configured to control the apparatus, and is configured to control the output unit. The X-ray detector is configured to provide the processing unit with data relating to the detection of X-rays. The output unit is configured to output data representative of the object.

In an example, the system is a radiography or a CT system.

According to a third aspect, there is provided a method for generating X-ray imaging data, comprising:.

According to another aspect, there is provided a computer program element controlling apparatus as previously described which, if the computer program element is executed by a processing unit, is adapted to perform the method steps as previously described.

According to another aspect, there is provided a computer readable medium having stored computer element as previously described.

The computer program element, can for example be a software program but can also be a FPGA, a PLD or any other appropriate digital means.

<FIG> shows an example of an apparatus <NUM> for generating X-ray imaging data. The apparatus <NUM> comprises an X-ray source <NUM>, a first grating <NUM>, a second grating <NUM>, a third grating <NUM>, and an X-ray detector <NUM>. The X-ray source <NUM> is configured to produce X-rays. The first grating <NUM> is positioned between the X-ray source <NUM> and the second grating <NUM>. The second grating <NUM> is positioned between the first grating <NUM> and the third grating <NUM>. The third grating <NUM> is positioned between the second grating <NUM> and the X-ray detector <NUM>. At least part of the region between the first grating and the third grating forms an examination region for accommodating an object. Either the first grating or the third grating has a pitch attribute of having a constant grating pitch. Both gratings of an adjacent pair of gratings have a pitch attribute of having a varying grating pitch. Both gratings of an adjacent pair of gratings are bent such that a distance between the two adjacent gratings is constant as a function of fan angle. The X-ray detector is configured to detect at least some of the X-rays transmitted by the three gratings.

In an example, the radii of curvature of the gratings that are bent extends back to the position of the X-ray source.

Also, fan angle relates to an angle of the X-ray beam away from a centerline orientation.

According to an example, the grating that is not bent is a planar grating.

According to an example, the adjacent pair of gratings that are bent are the first grating and the second grating.

According to an example, the first grating and the second grating have the pitch attribute of having a varying grating pitch.

According to an example, the second grating and the third grating have the pitch attribute of having a varying grating pitch.

According to an example, the adjacent pair of gratings that are bent are the second grating and the third grating.

According to an example, the imaging data comprises dark-field and/or phase-contrast imaging data.

<FIG> shows an example of a system <NUM> for X-ray imaging an object. The system comprises an apparatus <NUM> for generating X-ray imaging data as described with respect to <FIG>. The system <NUM> also comprises a processing unit <NUM>, and an output unit <NUM>. The processing unit <NUM> is configured to control the apparatus <NUM>, and is configured to control the output unit <NUM>. The X-ray detector <NUM> of the apparatus <NUM> is configured to provide the processing unit <NUM> with data relating to the detection of X-rays. The output unit <NUM> is configured to output data representative of the object.

According to an example, the apparatus is a radiography or CT apparatus.

According to an example, the system is a radiography or a CT system.

<FIG> shows a method <NUM> for generating X-ray imaging data in its basic steps. The method <NUM> comprises:.

The apparatus, system and method for generating X-ray imaging data are now described in more detail with reference to <FIG>.

<FIG> shows a schematic illustration of a DAX apparatus with three gratings inserted into the optical path. Typically, G0 and G2 are absorber gratings and G1 is a phase grating. The object could however be situated between the G0 and G1 gratings.

<FIG> shows a grating arrangement, with G0 and G1 manufactured by LIGA (focused to the source by bending) and G2 manufactured by foil stacking (focused during manufacturing of a planar grating). The optical axis is indicated by the dashed line, with two exemplary rays at different fan angles shown as solid lines. Note that in this arrangement, the distance from G0 to G1 does not vary with the fan angle, but the distance from G1 to G2 does. This feature of such an arrangement is not however compliant with a standard Talbot-Lau interferometer design, until certain gratings are chirped as discussed in more detail below.

<FIG> shows exemplary rays at a fan angle α. Regarding the design that addresses the issues described above, for the sake of simplicity, it is assumed that G1 is a π/<NUM> phase grating or an absorbing grating. The concept can be easily adapted to a π phase grating by accounting for the frequency doubling of the interference pattern at the location of G2. Now returning to the situation where G1 is a π/<NUM> phase grating or an absorbing grating, the periods of the gratings G0, G1, and G2 can be denoted as p<NUM>, p<NUM>, and p<NUM> respectively, and the distance from G0 to G1 and G1 to G2 denoted as l and d, respectively. Then the following relationship must hold for proper operation of the system: <MAT> and <MAT>.

Note that these relationships are required for proper operation since these relationships ensure that the fringe pattern generated by the individual slits of G0 line up properly at the position of G2. Note that there is usually another relationship related to the design energy of the system, namely <MAT> where λ is the wavelength of the systems design energy. As stated in the background section, it is state of the art to use gratings manufactured by LIGA and all gratings have a fixed period. These gratings are either all flat or all focused by bending. Note that Equations <NUM> and <NUM> hold in both scenarios. However, in the scenario illustrated in <FIG>, according to the situation it does not hold. Consider a ray as illustrated in <FIG>. Note that in this geometry, l and g, the distance from the focal spot to G0, are independent of α whereas d depends on α according to <MAT>.

Then gratings G0 and G1 are fabricated with a chirped period. Given the formulae above, the period of G0 should be <MAT> and the period of G1 should be <MAT>.

Note that the grating structure, and therefore also the period of the gratings manufactured using LIGA, are produced in a lithographic step that easily allows to make such modulation of the period.

Returning to <FIG>, rather than having G0 and G1 bent and chirped and G2 being planar and having a constant grating pitch, G0 and G1 can be bent and G2 can be planar and G0 can have a constant grating pitch, and G1 and G2 can be chirped.

Then, the above equations can be used to determine the required periods p<NUM> and p<NUM> as a function of fan angle α.

Furthermore, rather than having G0 and G1 bent and G2 planar, G0 can be planar and G1 and G2 bent, as shown in <FIG>. Then, taking the case where G0 and G1 are chirped and G2 has a constant pitch, the following applies in order to calculate the necessary varying grating pitches: <MAT> p<NUM> should be constant <MAT> <MAT>.

However, again referring to <FIG>, G0 can have a constant pitch, and G1 and G2 can be chirped. In which case the following applies to calculate the varying grating pitches: <MAT> p<NUM> should be constant <MAT> <MAT>.

This exemplary embodiment of the invention covers both, a computer program that right from the beginning uses the invention and computer program that by means of an update turns an existing program into a program that uses invention.

Claim 1:
An apparatus (<NUM>) for generating X-ray imaging data, comprising:
- an X-ray source (<NUM>);
- a first grating (<NUM>);
- a second grating (<NUM>);
- a third grating (<NUM>); and
- an X-ray detector (<NUM>);
wherein, the X-ray source is configured to produce X-rays;
wherein, the first grating is positioned between the X-ray source and the second grating;
wherein, the second grating is positioned between the first grating and the third grating;
wherein, the third grating is positioned between the second grating and the X-ray detector;
wherein, at least part of the region between the first grating and the third grating forms an examination region for accommodating an object;
wherein, either the first grating or the third grating has a pitch attribute of having a constant grating pitch;
wherein, both gratings of an adjacent pair of gratings have a pitch attribute of having a varying grating pitch;
wherein, both gratings of an adjacent pair of gratings are bent such that a distance between the two adjacent gratings is constant as a function of fan angle; and
wherein, the X-ray detector is configured to detect at least some of the X-rays transmitted by the three gratings.