METHOD AND X-RAY APPARATUS FOR INTERFEROMETRIC 2D X-RAY IMAGING

Abstract

A method and an x-ray apparatus for interferometric 2D x-ray imaging, use a Talbot-Lau interferometer having at least one phase grating and an analysis grating for producing 2D images of an object to be examined using a phase stepping method. A stepwise readout of a detector is carried out continuously at a multiplicity of the phase positions of an interference pattern. Time sequences of readout interval data records which overlap in time are extracted from the readout data records, and at least one result image data record is calculated from an absorption image and/or a phase-contrast image and/or a dark-field image from each readout interval data record.

Claims

1. A method for interferometric 2D x-ray imaging with a Talbot-Lau interferometer, which comprises the steps of: using the Talbot-Lau interferometer having at least one phase grating and an analysis grating for producing 2D images of an object to be examined using a phase stepping method; producing an interference pattern with a period at intervals by the phase grating in accordance with a Lau condition, the interference pattern being read in temporal succession as readout data with an aid of the analysis grating and a pixelated detector disposed downstream in a beam direction at at least three phase positions within at least one period of the interference pattern; producing a readout data record from the readout data for each readout time and phase position and a readout interval data record is produced within a time interval; carrying out a stepwise readout of the pixelated detector continuously at a multiplicity of the phase positions of the interference pattern; extracting time sequences of readout interval data records which overlap in time from readout data records; and calculating at least one result image data record from at least one of an absorption image, a phase-contrast image or a dark-field image from each of the readout interval data records.

2. The method according to claim 1, which further comprises producing a new readout interval data record successively with each n-th production of a new readout data record with n>=1 from the new readout data record and at least two of the readout data records lying in a past and a new result image data record is produced therefrom.

3. The method according to claim 1, wherein an image sequence of result image data records is produced and, output, each of the result image data records is formed from a same number of the readout data records which on average shift in time.

4. The method according to claim 1, which further comprises using the readout data records with a different weighting when producing result image data records.

5. The method according to claim 4, wherein the readout data records) which are further away in time from a reference time are weighted less strongly than the readout data records which are closer to the reference time when weighting the readout data records, with the reference time changing for each of the result image data records.

6. The method according to claim 1, wherein for purposes of producing a final result image data record in each case, a plurality of intermediate image data records are initially produced from at least three of the readout data records lying in the past in each case and the intermediate image records are combined with weighting to form the final result image data record.

7. The method according to claim 6, which further comprises weighting the intermediate image data records which are further away in time from a further reference time less strongly than the intermediate image data records lying closer to the further reference time when weighting the intermediate image data records.

8. The method according to claim 7, which further comprises using m=k*n readout data records for producing the final result image data record).

9. The method according to claim 8, which further comprises calculating k said intermediate image data records from in each case n said readout data records adjacent in time with m said readout data records and the final result image data record is combined from the k intermediate image data records.

10. The method according to claim 1, wherein there is a sawtooth-shaped relative movement with multiple forward steps and one backward step during the stepwise readout of detector data in the phase-stepping method.

11. The method according to claim 1, wherein there is a cyclical relative movement with multiple forward steps and multiple backward steps during the stepwise readout of detector data in the phase-stepping method.

12. The method according to claim 1, wherein there is a relative movement of one of the x-ray gratings or of the object to be examined or of at least one focal spot in an emitter during the stepwise readout of detector data.

13. The method according to claim 10, wherein the stepwise readout takes place during a standstill of a relative movement.

14. The method according to claim 10, wherein the step readout takes place during part of a cyclical relative movement.

15. The method according to claim 8, which further comprises calculating k said intermediate image data records from in each case n said readout data records adjacent in time with m said readout data records and the final result image data record is combined from the k intermediate image data records, with m=12, n=3 and k=4.

16. An x-ray apparatus for an interferometric x-ray examination of an object to be examined, the x-ray apparatus comprising: an interferometric emitter-detector configuration having a beam path in which the object to be examined may be disposed, said interferometric emitter-detector configuration having a detector, an analysis grating and at least one phase grating disposed in the beam path, and by means of said phase grating a self-image of said phase grating is produced as an interference pattern at at least one distance, the interference pattern being read out with an aid of said analysis grating disposed upstream of said detector in a phase-stepping mode; and a computer system having at least one program memory in which program code is stored, the program code being run during an operation of the x-ray apparatus, the program code executing the method according to claim 1 during the operation and is also stored.

17. The x-ray apparatus according to claim 16, wherein said interferometric emitter-detector configuration has an emitter; and further comprising a source grating disposed downstream of said emitter.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0041] FIG. 1 is a schematic illustration of an x-ray system according to the invention;

[0042] FIG. 2 is a graph showing a symbolized illustration of the timing of a conventional phase-stepping method on a basis of radiation intensity curve at a detector element;

[0043] FIG. 3 is a graph showing a symbolized illustration of the timing of the first method according to the invention on the basis of the radiation intensity curve at a detector element with a frame rate equal to the phase stepping;

[0044] FIG. 4 is a graph showing a symbolized illustration according to FIG. 3, but with a frame rate which is half of that of the phase stepping;

[0045] FIG. 5 is a graph showing an illustration of an exemplary weighting function for a continuous readout interval data records; and

[0046] FIG. 6 is a flowchart showing the procedure of an exemplary method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0047] Below, the invention is described in more detail with the aid of the figures, with only the features required for understanding the invention being depicted. Here, the following reference signs are used: 1: emitter-detector arrangement; 2: phase-stepping apparatus; 3: control element; 4: control and computation unit; I-V: method steps; A(t.sub.i): readout data record of the detector at the time t.sub.i; AI(t.sub.i, t.sub.i+7): readout interval data record of the detector during the time interval t.sub.i to t.sub.i+7; A(t.sub.i): readout data of the detector elements at the time t.sub.i; D: x-ray detector; d: detector elements; F: focus; G.sub.0: source grating; G.sub.1: phase grating; G.sub.2: analysis grating; I.sub.p: radiation intensity at a detector element; M: interference pattern; m: measurement value; n: measurement value; O: object to be examined; S: x-ray beam; and t.sub.i: measurement time.

[0048] Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown a schematic illustration of an exemplary x-ray apparatus according to the invention, containing an emitter-detector arrangement which has a Talbot-Lau grating arrangement.

[0049] The emitter-detector apparatus 1 according to the invention contains a focus F as an emitter and a detector D which is pixelated into a multiplicity of detector elements, with a beam path forming therebetween. Directly behind the focus F in this beam path there is a source grating G.sub.0 embodied as an absorption grating, the source grating producing quasi-coherent x-ray radiation in the form of a multiplicity of inherently coherent x-rays S. This is followed by a phase grating G.sub.1 which produces an interference pattern M which produces a self-image of the phase grating at predetermined distances. With the aid of the subsequent analysis grating G.sub.2, an interference pattern M may be read out pixel-by-pixel at the detector elements E in a phase-stepping mode with the aid of the phase-stepping apparatus 2, which displaces the analysis grating G.sub.2 step-by-step during the measurement, and the following detector D.

[0050] The phase-stepping apparatus 2 is controlled by a control segment 3. This control segment 3 may also constitute part of the control and computational unit 4 which, otherwise, operates the control of the x-ray system and, where necessary, also carries out image reconstructions on the basis of measured projections. Overall, computer programs Prg.sub.1-Prg.sub.n are stored in a memory of the control and computational unit 4, the computer programs being carried out during operation, for the purposes of carrying out at least the method steps according to the invention and also the mode of operation, known per se, of an interferometric x-ray apparatus.

[0051] The grating arrangement shown here, in which only the analysis grating G.sub.2 is moved for the phase stepping, merely represents one example of an embodiment variant. The present invention may also be carried out in combination with phase-stepping methods in which one of the other x-ray gratings is used for the phase stepping. Alternatively, the focus or the focal spot on an anode of an x-ray tube may be moved in place of the grating, or an entire focal spot pattern on an anode of an x-ray tube may be displaced.

[0052] FIG. 2 shows a schematic illustration of the intensity curve of an exemplary detector element E of the detector D in the case of a step-by-step readout of the radiation intensity Ip during a phase-stepping method downstream of an analysis grating G.sub.2, which is displaced in a relative manner, of the apparatus from FIG. 1. The ordinate plots the measured radiation intensity Ip of a detector element or of the pixel formed thereby, while the abscissa forms the time axis t. Since the relative movement advances in time, each time position t.sub.i also represents a corresponding phase position p.sub.i in the interference pattern M. The measurement points from two conventional measurement data records of the phase-contrast measurement are denoted by m, m+1, . . . and n, n+1,

[0053] However, according to the invention, the measurements and calculations resulting therefrom are carried out using result image data records, as depicted in an exemplary manner in FIG. 3. Like FIG. 2, it shows the intensity curve Ip of a detector element or of a pixel resulting therefrom over the time t, with individual measurement points a(t.sub.i) being denoted by the “+” sign. In summary, the sum of the read measurement values a(t.sub.i) of all detector elements of a detector at the time t.sub.i forms a readout data record A(t.sub.i). At least three readout data records A(t.sub.i) are required at at least three phase positions p.sub.i within a time interval for the purposes of calculating a result image data record E(t). In the shown example, such readout interval data records AI(j) are formed over the time intervals t.sub.1-t.sub.8, t.sub.2-t.sub.9, etc. from the available readout data records A(t.sub.i) at the relevant measurement times and are depicted in a symbolized manner along the abscissa or time axis. Thus, readout interval data records with intervals progressing in time are formed here by virtue of an oldest readout data record being removed and a newest, preferably just measured, readout data record being added to the interval in each case, this being carried out successively from the readout interval data record to readout interval data record. If result image data records are calculated from these readout interval data records in each case, this results in a frame rate which corresponds to the readout rate of the readout data records.

[0054] FIG. 4 shows an illustration corresponding to FIG. 3, with, however, the difference from readout interval data record AI(j) to readout interval data record AI(j+1), etc. respectively being two measurement cycles or two readout data records. Accordingly, a frame rate which is only half as large emerges here.

[0055] As already explained above, the produced and used readout data records may be used in a weighted manner when forming the calculation of the result image data record, with a reduction in the weighting with increasing temporal distance from the most current readout data record being preferred. FIG. 5 depicts such weighting curves g(AI(j)) in a manner fitting for the embodiment of the method according to FIG. 4 situated thereabove. Accordingly, each time interval obtains a dedicated weighting curve, with the weighting curve behaving relatively the same within the time intervals.

[0056] Finally, FIG. 6 shows a flowchart for the procedure of an exemplary method according to the invention, without special weighting of the readout data. Here, the successive measurement of the readout data a(t.sub.i) is shown in step I. Reference is once again made here to the fact that, on account of the temporally advancing relative displacement of at least one of the x-ray gratings or of the focus with the change in time t.sub.h this is also accompanied by a shift of the interference pattern to advancing phase points p.sub.i.

[0057] In the second step II, eight readout data records A(1) to A(8) at eight successive times (1) to (8) are respectively taken from the data pool of available readout data and, in step III, these are combined to a corresponding readout interval data record AI(t=1-8). A result image data record E(1) is calculated from this readout interval data record AI(t=1-8) in step IV, the result image data record containing at least one image data record containing the absorption I.sub.A(1), the phase-contrast I.sub.PK(1) or the dark-field information I.sub.DF(1). Accordingly, the corresponding image data records I.sub.A(1), I.sub.PK(1) and/or I.sub.DF(1) are output and/or stored in step V. Subsequently, there is a return to step II and steps II to V are carried out for a further time interval, in this case (2) to (9), wherein further readout data relating to at least one new time were ascertained previously, while carrying out steps II to V. If this procedure is carried out continuously, it facilitates a video representation of at least one of the result image data records in respect of the absorption, phase-contrast and/or dark-field with an image data rate corresponding at most to the readout rate of the detector.

[0058] Overall, the invention therefore proposes a method and x-ray device for interferometric 2D x-ray imaging, using a Talbot-Lau interferometer containing at least one phase grating and an analysis grating for producing 2D images of an object to be examined using a phase stepping method. The stepwise readout of the detector is carried out continuously at a multiplicity of the phase positions of the interference pattern, time sequences of readout interval data records which overlap in time are extracted from the readout data records, and at least one result image data record is calculated from an absorption image and/or a phase-contrast image and/or a dark-field image from each readout interval data record. Optional complementary features are described in detail above.

[0059] Even though the invention was illustrated more closely and described in detail by the preferred exemplary embodiment, the invention is not restricted by the disclosed examples and other variations may be derived herefrom by a person skilled in the art without departing from the scope of protection of the invention. In particular, the invention is not restricted to the feature combinations specified below, but other combinations and partial combinations which a person skilled in the art can obviously carry out may also be formed from the disclosed features.