CN101011257B - Focus-detector device for generating projection or tomographic phase-contrast images - Google Patents

Abstract

The present invention relates to a focus-detector arrangement (F, D) of an X-ray apparatus for generating projective or tomographic phase contrast recordings of an observed region of a subject. In at least one embodiment, the arrangement includes a radiation source (2) which emits a coherent or quasi-coherent X-radiation and irradiates the subject (7, P), a phase grating (G1) which is arranged behind the subject (7, P) in the beam path of the radiation source and generates an interference pattern of the X-radiation in a predetermined energy range, and an analysis-detector system (G2, D) which detects at least the interference pattern generated by the phase grating (G1) in respect of its phase shift with position resolution. Further, the beam path of the X-radiation used diverges in at least one plane between the focus (F) and the detector (D).

Description

Focus-detector device for generating projection or tomographic phase-contrast images

technical field

The invention relates to a focus-detector arrangement of an X-ray device for generating projection or tomographic phase-contrast images of an observation region (=FOV, field of view) of an examination object, with the ability to emit coherent or quasi-coherent X-rays and perform fluoroscopy A radiation source of the object, a phase grating arranged in the radiation path of the radiation source behind the inspection object, which phase grating produces an X-ray coherent pattern in a predetermined energy range, and an analysis detector system for position-resolved analysis of at least the phase The coherent pattern produced by the grating is detected to detect the phase shift of the phase grating.

Background technique

In general, for x-ray imaging, two effects that occur when x-rays pass through matter are mostly observed, namely the absorption of specific x-ray components and the phase shift of the emitted x-rays.

For a refractive index given by equation (1) for X-rays,

n=1-δ-iβ(1)

The absorption depends on the size of the imaginary number attenuation β, which forms a certain relationship with the mass absorption coefficient through equation (2),

μ/ρ=4πβ/λ(2)

where λ is the wavelength, μ is the linear absorption coefficient, and ρ is the mass density.

The phase shift is derived from the real part of the refractive index 1-δ. The phase shift Δ of the X-ray wave in matter compared to vacuum is given by equation (3),

Δ=2πδT/λ(3)

where T is the material thickness and δ is the real attenuation of the refractive index.

In X-ray radiology an object is examined with X-ray radiation and the intensity of the X-rays after passing through the object is recorded. Projection images showing the absorption caused by the object can be generated by means of this measurement. In X-ray tomography, a plurality of projection images is used to calculate a three-dimensional data set representing the spatial distribution of the absorption coefficient μ.

For phase contrast radiology and phase contrast tomography, the phase shift caused by the object has to be analyzed. Similar to absorption imaging, a three-dimensional data set representing the spatial distribution of the real part 1-δ of the refractive index can be calculated.

Since the phase of a wave cannot be measured directly, the phase shift is first converted into a measurable intensity by interfering with the wave under examination with a reference wave. Practical implementations of such measurements for both projection and tomographic images are shown, for example, in European patent application EP1447046A1 and in German patent applications 102006017290.6, 102006015358.8, 102006017291.4, 102006015356.1 and 102006015355.3 which enjoy the same priority.

The method presented in this document utilizes a phase grating arranged behind the examination object in the radiation path, which operates as a diffraction grating and splits the x-rays into radiation of the +1 and −1 order. In the wave field behind the phase grating, the diffracted rays interfere with each other forming an x-ray standing wave field. The object under examination induces a local phase shift which distorts the wavefront and thus changes the local amplitude, phase and offset of the standing wave field. The effect of local phase shifts across the object under examination can therefore be calculated using measurements that provide information about the standing wave field, such as the phase, amplitude and median of the stationary wave. In order to scan the wavefield with the required resolution, the analyzer grating is moved stepwise over the wavefield while simultaneously monitoring the intensity pixel by pixel with the corresponding detector.

In the above-mentioned European patent application EP1447046A1 parallel X-rays are used to scan the examination object. For surface observation, it is possible to proceed from the fact that any desired magnification effects can be achieved by using a diverging beam geometry and correspondingly positioning the examination object on the beam path. But if one considers the refraction effect of the rays at the object under examination, it seems that the phase shift can no longer be measured, since a "disordered" pattern of deflected rays would certainly occur which would not lead to a usable image reconstruction. For this reason, X-ray phase contrast measurements with phase gratings in magnification geometry have not yet been possible.

Contents of the invention

The technical problem underlying the present invention is therefore to find a focus-detector arrangement for X-ray phase-contrast radiology and X-ray phase-contrast tomography which can produce magnified to strongly magnified projections of the spatial distribution of the refractive index of the object under examination and CT scans.

In principle, the following points should also be observed for X-ray phase contrast measurements with phase gratings and coherent or quasi-coherent X-rays:

X-ray photon emission from laboratory X-ray sources (X-ray tubes, secondary targets, plasma sources, radioactive sources, parametric X-ray sources, channel radiation) as well as first to third generation conventional synchrotron radiation sources is based on stochastic processes. Therefore the emitted X-rays themselves have no spatial coherence. But if the observation angle is sufficiently small at which the source appears to the observer or object, the grating or the detector, the rays of the X-ray source are indistinguishable from phase contrast radiography and phase contrast tomography or any interference experiment. The same is true for spatially coherent rays. As a measure of the spatial coherence of an enlarged X-ray source, the so-called spatial/transverse coherence length L _c can be given:

${\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\frac{\mathrm{<span\; class="notranslate">\; a</span>}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}$

Here λ is the wavelength, s is the lateral radiation source size, and a is the distance between the radiation source and the observer. The exact value is secondary; what matters is that the coherence length L is large compared to the size of the spatial region over which the rays should interfere with each other.

Within the scope of this patent application, coherent radiation is to be understood as radiation which, given the geometry and the desired distance between the X-ray gratings, produces a coherent pattern. Of course the spatial coherence and thus the spatial coherence length are always determined by the 3 parameters wavelength, radiation source size and observation distance. For the sake of compactness, the case is simplified to concepts such as "coherent X-rays", "source of coherent X-rays" or "point source for generating coherent X-rays". The basis for this simplification is on the one hand the penetration through the desired examination object in the application discussed here and on the other hand the limitation of the wavelength (or energy E) of the x-rays in the spectrum provided by the laboratory x-ray source. The distance a between the radiation source and the observation point is subject to certain restrictions in laboratory configurations for non-destructive material testing or medical diagnosis. The radiation source s is thus mostly reserved as the last degree of freedom, even though the relationship between the radiation source size and the X-ray power is also strictly limited here.

More powerful radiation sources and thus larger focal spot sizes can be employed in the focus-detector arrangement presented here if a source grating of suitable size is used. The narrow slits of the source grating are responsible for maintaining the required spatial coherence of all rays emerging from the same slit. Photons from the same slit can interfere with each other, that is, the phases overlap correctly. In contrast, it is impossible for photons from different slits of the source grating to overlap correctly in phase. However, when properly tuning the source grating period _g0 and the coherent pattern period _g2 as well as the distance l between the source grating G0 and the phase grating _G1 and the _distance d between the phase grating _G1 and the coherent pattern _G2 , it is possible to obtain according to

g ₀ /g ₂ =l/d(5)

The wave maxima and wave minima of the standing wave field overlap correctly at least in terms of intensity in a first approximation of . In the simplified representation of this patent application, the concept of "quasi-coherent ray" or "quasi-coherent ray source" is used.

The monochromaticity of X-rays or X-ray sources is accompanied by temporal or longitudinal coherence of the rays. Characteristic lines of X-rays have sufficient monochromaticity or temporal coherence length for the applications discussed here. The selection of the resonant energy by the height of the bars connected to the preceding monochromator or via a phase grating can also filter out a sufficiently narrow spectral range from the bremsstrahlung spectrum or the synchronous spectrum, thus satisfying the requirement for the temporal coherence length in the setup shown requirements.

Contrary to the professional knowledge that the magnified structure of the focus-detector arrangement cannot be used for phase-contrast measurements, the inventors have found that contrary to all assumptions satisfactory imaging results can be achieved.

Based on this knowledge, the inventors propose a focus-detector arrangement of an x-ray system for generating projection or tomographic phase-contrast images of an observation region (=FOV, field of view) of an examination object, which arrangement has at least the following characteristics:

A radiation source that emits coherent or quasi-coherent X-rays and transmits the object under examination,

a phase grating arranged in the radiation path of the radiation source behind the examination object, which phase grating produces a coherent pattern of X-rays in a predetermined energy range, and

analysis-detector system for position-resolved detection of a coherent pattern produced by a phase grating to detect a phase shift of the phase grating, wherein

The radiation path of the used X-rays diverges in at least one plane between the focal point and the detector, ie corresponds to a fan beam.

In a further embodiment, the focus detector arrangement can also be designed such that the radiation paths of the x-rays used diverge in two planes between the focus and the detector and thus correspond to a cone of radiation.

In order to form a compact structure, it is particularly preferred that the radiation beams used spread out at least 5°, preferably at least 10°, in at least one plane. In applications in the field of medical computed tomography, fan angles of more than 45° are even used.

Depending on the divergence of the beam geometry used, the observed region of the examination object seen in projection in the direction of the optical axis of the radiation path can be smaller than the use region of a phase grating arranged downstream in the radiation path, which In turn, the usage range is smaller than the usage range of the analysis-detector system arranged downstream in the radiation path. Of course, the gradually increasing size is also meaningful when viewed in the opposite direction from the focal point.

In a particularly preferred embodiment, it is proposed that the distance from the radiation source to the analysis-detector system is at least twice as large as the distance from the radiation source to the examination object. Thus, for the first time, an effectively magnified phase-contrast recording can be performed using the phase grating and the analyzer-detector system, wherein only the phase shift is displayed in this image. This magnification factor can be magnified by a factor of 10 or even a factor of 1000, if required, by a corresponding selection of the distance between the x-ray source and the examination object and the distance between the x-ray source and the analysis-detector system.

In the focus-detector arrangement of the invention it is proposed to maintain the following geometrical relationship for the periods of the phase grating and the analyzer grating:

${\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="g"\; filenames="H07107968720070209E000032.png,H07107968720070209E000041.png"\; state="\{\{state\}\}">g</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="r"\; filenames="H07107968720070209E000021.png,H07107968720070209E000022.png"\; state="\{\{state\}\}">r</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; g</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

where _dm is the distance between the gratings, _r1 is the distance between the radiation source and the phase grating, _g2 is the period of the analyzer grating, and _g1 is the period of the phase grating.

Using the relational expression r ₂ =r ₁ +d _m can also rewrite the equation (6) as

${\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="g"\; filenames="H07107968720070209E000032.png,H07107968720070209E000041.png"\; state="\{\{state\}\}">g</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="g"\; filenames="H07107968720070209E000021.png,H07107968720070209E000022.png"\; state="\{\{state\}\}">g</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; .</span>$

It is also proposed to position the analysis-detector system in such a way that the analyzer grating when the analysis-detector system consists of a detector with an analyzer grating, or when the analysis-detector system consists of a detector without an analyzer grating The distance between the incident surface of the detector and the phase grating is such that the standing wave field is maximized. For the so-called Talbot distance, the following equation holds in a first approximation:

${\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="g"\; filenames="H07107968720070209E000021.png,H07107968720070209E000022.png"\; state="\{\{state\}\}">g</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

in:

d _m = the distance between the phase grating and the analyzer grating, the so-called Talbot distance;

m=the order of Talbot interference; m=1,2,3,...;

g ₁ = period of the phase grating;

λ = wavelength of the X-rays used.

Equation (7) describes the exact distance for parallel rays. Equation (7) is only valid to a first approximation when using cone rays, since the coherence pattern becomes larger with increasing distance from the phase grating, as described by equation (6). This equation is equivalent to the effect that the grating period g ₁ of the phase grating becomes larger as the distance increases.

According to the invention, two different variants of the relative arrangement of the phase grating and analysis-detector system can be adjusted in this embodiment of the focus-detector arrangement. If the phase grating is closer in the radiation direction to the analyzer-detector system than to the examination object, the grating period of the amplitude grating in the analyzer-detector system is smaller than the grating period of the phase grating, typically by approximately half.

In another focus-detector arrangement, the phase grating is closer to the examination object in the radiation direction than to the detector, and the analyzer grating is operated with a greater grating period. Analyzer gratings can even be operated with a larger grating period than the phase grating.

The above two variants can be implemented with an analysis-detector system that replaces the analyzer grating with a detector, the individual detector elements of which are in turn formed in the form of stripes whose direction corresponds to the grating lines of the phase grating, The fringes must have a period at most equal to 1/3 of the corresponding period of the analyzer grating in order to be able to determine the phase shift of the x-rays in the detector element with one measurement.

In order to generate coherent x-rays, the inventors propose that, in a first alternative, the radiation source has a focal point configured as a microfocus with respect to the geometry of the focal point detector arrangement.

According to another alternative, the radiation source can also have a diverging focus if an x-ray grating, a so-called source grating, is additionally arranged in the radiation direction to generate the necessary coherence. Although this imposes a limit on the achievable resolution, the performance can be increased so that, for example, the required irradiation time can be reduced.

Although the preferred embodiments of the invention are given in the above variants, all other known X-ray sources producing coherent X-ray light, such as free electron lasers, 4th generation synchrotrons, are also within the scope of the invention, provided that is the divergent radiation geometry.

According to the knowledge of the inventors, it is also proposed to use the focus-detector arrangement according to the invention in combination with an X-ray system for producing projected phase-contrast images or with an X-ray computed tomography system for producing tomographic phase-contrast images , each of these systems can enlarge and display the inspection object. Most often such systems are used in conjunction with the analysis of small samples, but can also be used for detailed imaging in medical computed tomography equipment or when examining small animals.

Description of drawings

：检测器元件E_x上的相移；

：检测器元件之间的相对相移；λ：所使用的X射线的波长。The invention is described in detail below with the aid of a preferred exemplary embodiment in the drawing, in which only the features necessary for understanding the invention are shown. The following reference numbers are used here: 1: computed tomography system; 2: first X-ray tube; 3: first detector; 4: second X-ray tube; 5: second detector; 6: holder housing; 7: patient; 8: patient couch; 9: system axis; 10: control and computing unit; 11: memory; d: distance between phase grating G ₁ and analyzer grating G ₂ ; D: detector; d _m : Talbot distance; E _i , E _j : detector elements; F: focal point; G ₀ : source grating; G ₁ : phase grating; G ₂ : analyzer grating; g ₁ , g ₂ : grating period I(E _x (x _G )): measured intensity on the detector element _Ex at a grating displacement of x _G ; I: measured intensity of the photon flux; M: coherent pattern; P: sample; Prg _n : program; QD : the distance between the radiation source and the analyzer-detector system; QP: the distance between the radiation source and the sample; r ₁ : the radial distance from the focus to the phase grating; r ₂ : the distance from the focus to the analyzer-detector system Radial distance; S _i : X-ray; x _G : displacement of analyzer grating;

: the phase shift on the detector element _Ex ;

: relative phase shift between detector elements; λ: wavelength of X-rays used.

Specifically show:

Figure 1 : a longitudinal section showing a schematic of a focus-detector arrangement with a phase grating, an analyzer grating and a detector for displaying interference phenomena;

Figure 2: shows the intensity variation on selected detector elements in relation to the relative position of the analyzer grating to the coherent pattern;

Figure 3: shows a schematic cross-sectional view of a focus-detector combination with a strong amplification effect and a phase grating arranged in the vicinity of the analyzer-detector system according to the invention;

Figure 4: shows a schematic sectional view of a focus-detector combination with a strong magnification effect and a phase grating arranged in the vicinity of the object under examination according to the invention;

Figure 5: shows a schematic sectional view of a focus-detector combination with a strong amplification effect and using an analyzer-detector system without an analyzer grating according to the invention;

Figure 6: shows a schematic cross-sectional view of a focus-detector combination with a strong amplification effect and a phase grating arranged near the analyzer-detector system and employing a source grating on the radiation source according to the invention;

Figure 7: shows a schematic sectional view of a focus-detector combination according to the invention with a strong magnification effect and a phase grating arranged in the vicinity of the object under examination and using a source grating on the radiation source;

FIG. 8 : shows a schematic diagram of a computed tomography system with a focus-detector combination according to the invention, with a magnification effect and a phase grating, and with a source grating at the radiation source.

In order to better understand the basic principle of the phase contrast measurement is described below with Fig. 1 and Fig. 2 .

Detailed ways

FIG. 1 shows a quasi-coherent beam from a radiation source or a separate coherent beam from a source grating, which passes through an examination object or sample P, wherein a phase shift occurs when passing through the examination object P. FIG. When passing through the grating _G1 , a coherence pattern, shown by gray shading, is produced, which with the aid of the grating _G2 produces radiation that differs for the individual detector elements at the downstream detector D and its detector elements _Ei , _Ej Intensity, where a coherent pattern or X-ray standing wave field is formed at the so-called Talbot distance.

和检测器元件之间的相对相移

If, for example, the detector element _Ei is considered in terms of the relative position _xG of the analyzer grating _G2 and the intensity I( _Ei ( _xG )) is a function of this relative position _xG , then the sine of the intensity on the detector element _Ei is obtained The deformation process is shown in Figure 2. If the radiation intensity I measured for each detector element _Ei or _Ej is related to the displacement _xG , the function I can be used for the different detector elements that ultimately form the focal point and the spatial X-rays between the corresponding detector elements (E _i (x _G )) or the function I(E _j (x _G )) to approximate. From this function the phase shift can be determined for each detector element

and the relative phase shift between the detector elements

Thus, for each ray in space, the phase shift for each detector pixel or ray under consideration is determined by at least 3 measurements with respectively offset analyzer gratings, from which it can be directly calculated in the case of projection x-ray recordings The pixel values of the projection image, on the other hand, in the case of a CT examination, can produce a projection whose pixel value is equal to the phase shift, so that it can be calculated from this by means of per se known reconstruction methods which volume element in the examination object corresponds to the measured phase Which part to move. From this, cross-sectional images or volume data are calculated, which reflect the effect of the object under examination with respect to the phase shift of the x-rays. Since small differences in composition or small differences in thickness have a strong effect on the phase shift, it is possible to reproduce solid data with rich details and high contrast for substances that are relatively close in themselves, especially organ tissues.

The phase shift of the X-rays passing through the object under examination is detected by means of a multiple shifted analyzer grating and the measurement of the radiation intensity on the detector element located behind the analyzer grating, so that each X-ray is shifted separately by the analyzer grating Part of the grating period must perform at least 3 measurements as a condition.

In principle, it is also possible to use not such an analyzer grating but a sufficiently high-resolution detector, in which case no loss of intensity in the bars of the analyzer grating due to absorption occurs, And the phase shift between individual rays/pixels can be determined with a single measurement.

To measure phase contrast it is necessary to use coherent or at least quasi-coherent radiation. The radiation can be generated, for example, through a point-like focal point, or as a field of individual coherent rays through a source grating located behind a planar focal point or through a corresponding grating-type structure for compensating the burning spot (Brennfleck) on the anode of such a grating produce.

The line orientation of the grating should be selected such that the grating lines of the existing grating and, if applicable, the stripe structure of the detector elements are parallel to one another. Furthermore, it is preferred, but not necessary, that the grating lines are aligned parallel or perpendicular to the system axis of the focus-detector system shown here.

3 shows a schematic illustration of a focus-detector combination according to the invention with a focus F which emits a diverging beam of rays S _i in the direction of a sample or examination object P. FIG. After passing through the examination object P, the beam of rays falls expanded onto the first phase grating _G1 , in which a coherent pattern is produced, which is passed through the downstream connected detector D comprising the analyzer grating _G2 and the subsequent detector D analysis-detector system to analyze. The analysis is carried out by means of an analysis-detector system of the type shown here, which has an analyzer grating and a subsequent detector comprising a plurality of detector elements, as shown in FIGS. 1 and 2. describe. In order to improve the effect of the analyzer grating G2, a highly absorbing material is also shown in the grating gaps of this grating G2. It is pointed out, however, that analyzer gratings without such filling material in the grating interstices are also within the scope of the invention.

Also shown at the bottom of the figure are important radial distances between the main elements of the focus-detector combination, such as the radial distance r between the focus and the phase grating _G and the distance _r between the focus and the analysis-detector system. Radial distance r ₂ . The distance QP between the focal point or radiation source and the sample and the distance QD between the radiation source or focal point and the analysis-detector system are likewise plotted to describe the magnification behavior of the divergent radiation. The magnification factor V is given by the ratio of the distance QD between the radiation source or focal point and the analysis-detector system and the distance QP between the radiation source or focal point and the sample, where

$\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; =</span>\frac{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; QD</span>}}}{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; QP</span>}}}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

The ratio of the projected size of the scanned area (=FOV=field of view) in the object under examination to the area of use of the subsequent phase grating _G1 and to the area of the subsequent analyzer-detector system used is the same as in scanning according to the invention Corresponds to the above geometric conditions when examining the object.

FIG. 4 shows a variant of the focus detector system, also according to the invention, in which the distance between the phase grating and the subsequent analysis detector system is significantly increased. The inventors have realized that the Talbot distance can be increased by choosing a larger Talbot order m and/or by enlarging the phase grating period _gi . Enlarging _g also results in an increase in the period of the analyzer grating. Firstly, however, the period of the standing wave field to be scanned and thus the period of the analyzer grating is increased by enlarging the geometry. This reduces the aspect ratio and thus simplifies the production of the grating. If an analyzer-detector system is to be implemented without an analyzer grating, it is preferably possible to select a slightly lower requirement for the positional resolution of the detector by means of the geometry described above.

A variant of such a focus-detector system with a phase grating _G1 that interferes with a downstream analysis-detector system is shown in FIG. 5, in which the detectors are divided into individual detector elements, and these detector elements, which determine the positional resolution of the detector, are in turn divided into stripe shapes corresponding to the grating lines of the phase grating to measure the phase shift of each detector element. Here too, the distance between phase grating G ₁ and subsequent detector D is chosen to be equal to Talbot distance d _m .

Figures 6 and 7 show variants of the focus-detector system in which a source grating is also connected between the focus F and the examination object P, so that quasi-coherent X-rays can also be generated for an enlarged focus, whereby Can work with significantly higher power/intensity.

It is thus also possible to use such a focus detector system in combination with projection x-ray systems for medical applications or computer tomography systems.

The ratio of the distances between the gratings in FIGS. 6 and 7 is the same as in FIGS. 3 and 4 .

FIG. 8 shows an example of a medical application—a computed tomography system 1 with one or optionally two focus detector systems according to the invention. The stand housing 6 is shown, in which the first X-ray tube 2 and the detector system 3 opposite it are arranged, in which a phase grating as shown in the above-mentioned figures is also integrated. Optionally, a further focus-detector system with a second x-ray tube 4 and a second detector system 5 can also be provided. For scanning along the system axis 9 , the patient 7 to be examined can be moved through the opening of the support by means of the movable patient couch 8 . The control and evaluation of the computed tomography system is carried out by means of a control and computing unit 10 in which a memory containing the programs Prg ₁ -Prg _n is provided. In this control and computing unit 10 it is also possible to analyze the image and carry out the reconstruction.

It should be pointed out that not only phase contrast measurements but also absorption measurements can be carried out with the focus-detector system presented here in this document. Phase information and absorption information are obtained as each pixel is analyzed.

It is to be understood that the above-mentioned features of the present invention can be used not only in the respectively stated combination but also in other combinations or alone without departing from the scope of the present invention.

Claims (12)

1. A focus-detector arrangement (F, D) of a CT system (1) for generating projection or tomographic phase-contrast images of an observation region of an examination object, the arrangement having: 1.1. A radiation source (2) for emitting coherent or quasi-coherent X-rays and transmitting them through the examination object (7, P), 1.2. a phase grating (G ₁ ) arranged in the radiation path of the radiation source behind the examination object (7, P), which phase grating generates an X-ray coherence pattern in a predetermined energy range, and 1.3. Analysis-detector system (G ₂ , D) for position-resolved detection of the coherent pattern produced by the phase grating (G ₁ ) to detect the phase shift of the phase grating, said analysis-detector system (G ₂ , D) has an analyzer grating (G ₂ ), characterized in that, 1.4. The radiation path of the X-rays used diverges in at least one plane between the focal point (F) and the detector (D), and 1.5. Maintain geometric relationship

where d is the distance between the phase grating (G ₁ ) and the analyzer grating (G ₂ ), r ₁ is the distance between the radiation source and the phase grating, g ₂ is the period of the analyzer grating (G ₂ ), g ₁ is the grating period of the phase grating (G ₁ ). 2. Focus-detector arrangement according to claim 1, characterized in that the radiation paths of the used X-rays diverge in two planes between the focus (F) and the detector (D). 3. Focus-detector arrangement according to claim 1, characterized in that the observed region of the examination object seen in projection in the direction of the optical axis of the radiation path is smaller than a phase grating arranged behind in the radiation path ( G ₁ ), which in turn _has a smaller use range than the analysis-detector system (G ₂ , D) arranged downstream in the radiation path. 4. Focus-detector arrangement according to claim 1, characterized in that the distance from the radiation source (2) to the analysis-detector system ( _G2 , D)

at least the distance from the source of radiation (2) to the object of examination (7, P)

twice as much. 5. Focus-detector arrangement according to any one of claims 1 to 4, characterized in that the distance from the radiation source (2) to the detector of the analysis-detector system (G ₂ , D)

at least the distance from the source of radiation (2) to the object of examination (7, P) 10 times. 6. The focus-detector arrangement according to any one of claims 1 to 4, characterized in that the phase grating (G ₁ ) is in the direction of radiation at a distance from the analysis-detector system (G ₂ , D) ratio Closer to the inspection object (7, P). 7. Focus-detector arrangement according to any one of claims 1 to 4, characterized in that the phase grating (G ₁ ) is farther in the radiation direction from the examination object (7, P) than the distance analysis-detection The device system (G ₂ , D) is closer. 8. Focus-detector arrangement according to any one of claims 1 to 4, characterized in that the analysis-detector system (G ₂ , D) has an analyzer grating (G ₂ ) Next said detector (D) comprising a plurality of detector elements ( _Ex ). 9. The focus-detector arrangement according to claim 8, characterized in that the distance (d _m ) between the phase grating (G ₁ ) and the analyzer grating (G ₂ ) satisfies the following geometric relationship: ${\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>\frac{{\mathrm{<span\; class="notranslate">\; g</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}$ in: d _m = distance between phase grating (G ₁ ) and analyzer grating (G ₂ ); m=1,2,3,...; g ₁ = grating period of the phase grating (G ₁ ); λ = wavelength of the X-rays used. 10. Focus-detector device according to any one of claims 1 to 4, characterized in that the radiation source has a focal point configured as a micro focus with respect to the geometry of the focus-detector device, wherein: $\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\frac{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; g</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}$ where s is the size of the focal spot, λ is the wavelength of the ray used, _r1 is the radial distance from the focal point to the phase grating, and _g1 is the grating period of the phase grating. 11. Focus-detector arrangement according to any one of claims 1 to 4, characterized in that the radiation source has the focus (F) and a source grating (G ₀ ) arranged in the radiation direction. 12. An X-ray computed tomography system for producing tomographic phase-contrast images that can display an examination object in a magnified manner, characterized in that it has a focal point detector according to any one of claims 1 to 11 device.

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