阅读说明：本技术 用于dax成像的全视场散射估计 (Full field of view scatter estimation for DAX imaging ) 是由 S·P·普雷弗尔哈尔 T·克勒 K·J·恩格尔 于 2020-11-25 设计创作，主要内容包括：一种被配置用于相衬成像和/或暗场成像的X射线成像系统(XI)。所述系统包括：X射线源(XS),其能操作用于使X辐射从所述源(XS)的焦斑(SF)发出；以及X射线敏感探测器(D),其能操作用于：如果在所述X射线源与所述探测器(D)之间存在要被成像的对象,则在所述X辐射与所述对象发生相互作用之后探测所述X辐射。控制逻辑单元(CL)能操作用于使所述X射线成像装置在两种模式中的任意一种模式中操作,所述两种模式是对象图像采集模式和散射测量模式。当在散射测量模式中时在所述探测器处能接收到的所述X辐射与当所述系统在对象图像采集模式中时能接收到的X辐射相比包括更高比例的散射辐射。(An X-ray imaging system (XI) configured for phase contrast imaging and/or dark-field imaging. The system comprises: an X-ray source (XS) operable to cause X-radiation to be emitted from a focal Spot (SF) of the source (XS); and an X-ray sensitive detector (D) operable to: detecting the X-radiation after interaction of the X-radiation with the object if there is an object to be imaged between the X-ray source and the detector (D). The control logic unit (CL) is operable to cause the X-ray imaging apparatus to operate in either of two modes, an object image acquisition mode and a scatterometry mode. The X-radiation receivable at the detector when in a scatterometry mode comprises a higher proportion of scattered radiation than X-radiation receivable when the system is in a subject image acquisition mode.)

1. An X-ray imaging system (XI) configured for phase contrast imaging and/or dark-field imaging, comprising:

an X-ray source (XS) operable to cause X-radiation to be emitted from a focal Spot (SF) of the source (XS);

an X-ray sensitive detector (D) operable to: detecting the X-radiation after interaction with the object if there is an object to be imaged between the X-ray source and the detector (D);

a control logic unit (CL) operable to cause the X-ray imaging apparatus to operate in any one of two modes, an object image acquisition mode and a scatterometry mode, wherein the X-radiation receivable at the detector when in scatterometry mode comprises a higher proportion of scattered radiation than X-radiation receivable by the system when in object image acquisition mode; and

a Scatter Corrector (SC) operable to reduce or facilitate reduction or prevention of scatter artefacts in an image of the subject which can be generated from data acquired in an image acquisition mode, based on the measured scatter data.

2. The system of claim 1, comprising a scatterometry promoter (SMF) disposed between the X-ray Source (SX) and the detector (D), at least one or more portions of the scatterometry promoter (SMF) being capable of blocking X-radiation, the control logic unit changing an attitude of the scatterometry promoter when the system is in a scatterometry mode relative to an attitude of the scatterometry promoter when the system is in a subject image acquisition mode such that the at least one or more portions block at least some of the X-radiation.

3. The system of claim 1 or 2, wherein the scatterometry facilitator (SMF) comprises any one or more of: i) an anti-scatter grid (ASG), ii) at least part of an interferometer (G0, G1, G2), iii) an encoding aperture plate.

4. The system of any one of the preceding claims, wherein the direction of the X-radiation can be changed by a source interface (SF), wherein the control logic unit (CL) emits X-radiation in a first direction through the interface (SF) when the system is in an object image acquisition mode, and in a second direction different from the first direction through the interface when the system is in a scatterometry mode.

5. The system of claim 3, wherein the scatterometry facilitator (SMF) comprises at least a portion of the interferometer (G0, G1, G2), the control logic unit (CL) changing the pose of the interferometer or the portion of the interferometer when in scatterometry mode so as to reduce a fringe pattern detectable at the detector.

6. The system of any one of the preceding claims, wherein the X-ray imaging system is a full view imaging system.

7. A method comprising the steps of:

operating (S210) an X-ray imaging apparatus (XI) configured for phase contrast imaging and/or dark-field imaging in any one of two modes, being an object image acquisition mode and a scatterometry mode, wherein the X-radiation receivable at a detector (D) when in scatterometry mode comprises a higher proportion of scattered radiation than X-radiation receivable by the system when in object image acquisition mode; and is

Based on the measured scatter data, scatter artifacts in an image of the subject that can be generated from data acquired in the image acquisition mode are reduced (S220) or facilitated to be reduced or prevented.

8. A computer program element, which, when being executed by at least one Processing Unit (PU), is adapted to cause the Processing Unit (PU) to carry out the method of claim 7.

9. A computer readable medium having stored thereon the program element of claim 8.

Technical Field

The present invention relates to an X-ray imaging system configured for phase contrast imaging and/or dark-field imaging, a method of operating an X-ray imaging apparatus, a computer program element and a computer readable medium.

Background

Dark field ("DAX") imaging has attracted interest, particularly in the medical field. Dark field imaging is one type of X-ray imaging. Contrast in dark field imaging relates to the amount of small angle scattering that X-radiation undergoes.

Experimental Dark-Field imaging with mice has been reported by yaroshenko et al in "plasma analysis Diagnosis with a preliminary Dark-image X-ray Dark-Field Scanner-Contrast Scanner" (radiology, vol. 269, phase 2, 11 months 2013). Phase contrast has also been found to add additional useful insight, particularly when imaging soft tissue.

Dark field imaging has been used excessively, and sometimes dark field images or phase contrast images are destroyed by artifacts.

Disclosure of Invention

Accordingly, alternative systems or methods may be needed to improve dark field imaging or phase contrast imaging.

The object of the present invention is solved by the subject-matter of the independent claims, wherein further embodiments are comprised in the dependent claims. It should be noted that the following described aspects of the invention apply equally to the method of operating an X-ray imaging apparatus, to the computer program element and to the computer readable medium.

According to a first aspect of the present invention, there is provided an X-ray imaging system configured for phase contrast imaging and/or dark-field imaging, comprising:

an X-ray source operable to cause X-radiation to be emitted from a focal spot of the source;

an X-ray sensitive detector operable to: detecting the X-radiation after interaction of the X-radiation with the object, if there is an object to be imaged between the X-ray source and the detector;

a control logic unit operable to cause the X-ray imaging apparatus to operate in either of two modes, an object image acquisition mode and a scatterometry mode, wherein the X-radiation receivable at the detector when in scatterometry mode comprises a higher proportion of scattered radiation than X-radiation receivable by the system when in object image acquisition mode; and

a scatter corrector operable to reduce or facilitate reduction or prevention of scatter artefacts in an image of the subject that can be generated from data acquired in an image acquisition mode based on the measured scatter data.

The system improves the quality of the DAX image and/or the phase contrast image.

In one embodiment, the system comprises a scatterometry promoter arranged between the X-ray source and the detector, at least one or more portions of the scatterometry promoter being capable of blocking X-radiation, the control logic unit changing the attitude of the scatterometry promoter when the system is in a scatterometry mode relative to the attitude of the scatterometry promoter when the system is in a subject image acquisition mode such that the at least one or more portions block at least some of the X-radiation. Preferably, mainly or only, the secondary radiation reaches the detector.

In one embodiment, the scatterometry facilitator comprises any one or more of: i) an anti-scatter grid, ii) at least part of an interferometer, iii) an encoding aperture plate.

In an embodiment the direction of the X-radiation is changeable via a source interface, wherein the control logic unit via the interface emits X-radiation in a first direction when the system is in an object image acquisition mode, and via the interface emits the X-radiation in a second direction different from the first direction when the system is in a scatterometry mode.

In one embodiment, the scatterometry facilitator comprises at least a portion of the interferometer, the control logic unit causing a change in the pose of the interferometer or the portion of the interferometer when in a scatterometry mode, so as to reduce a fringe pattern detectable at the detector.

In one embodiment, the X-ray imaging system is a full view imaging system.

According to a further aspect of the invention, there is provided a method comprising the steps of:

operating an X-ray imaging apparatus configured for phase contrast imaging and/or dark-field imaging in any one of two modes, an object image acquisition mode and a scatterometry mode, wherein the X-radiation receivable at a detector when in scatterometry mode comprises a higher proportion of scattered radiation than X-radiation receivable by the system when in object image acquisition mode; and is

Reducing or facilitating reduction or prevention of scatter artifacts in an image of the subject that can be generated from data acquired in an image acquisition mode based on the measured scatter data.

According to a further aspect of the invention, a computer program element is provided, which, when being executed by at least one processing unit, is adapted to cause the processing unit to carry out the method.

According to a further aspect of the invention, a computer-readable medium is provided, on which the program element is stored.

The proposed system allows for the acquisition and generation of quantitatively corrected DAX images and/or phase contrast ("Φ") images. The system provides sufficiently accurate "large angle" scatter correction. The scatter correction settings that can be implemented by the system are adjusted to suit a given patient and/or patient position, and the signal can be reduced by the order of the square of the patient-to-detector distance.

The applicant has determined that systematic errors due to inaccuracies in the scatter estimation can already be observed in slit scan DAX systems and this may cause further degradation of the full field of view system, with the scatter effect increasing by a factor of about six. For example, it is predicted that in full field-of-view imaging, scatter from lung regions, for example, will significantly degrade the DAX signal. The proposed system is able to cope with large full field of view imaging scenes.

Drawings

Exemplary embodiments of the invention will now be described with reference to the following drawings, which are not to scale, wherein:

FIG. 1 is a schematic X-ray imaging apparatus configured for dark-field imaging and/or phase contrast imaging; and is

Fig. 2 is a flow chart of a method of operating an X-ray imaging apparatus configured for phase contrast imaging and/or dark-field imaging.

Detailed Description

Referring to fig. 1, a schematic block diagram of an image processing arrangement IA comprising a computerized image processing system IPS and an X-ray imaging apparatus XI ("imager") is shown. The X-ray imaging apparatus is configured for dark-field X-ray ("DAX") imaging and/or phase contrast ("Φ") imaging. The imaging device XI comprises an X-ray source XR and an X-radiation sensitive detector D. The imager XI may be configured for 2D radiographic imaging or 3D imaging such as a CT scanner.

The image processing system IPS may run as one or more software modules or routines on one or more data processing units PU (e.g. one or more computers, servers, etc.). The IPS may be arranged outside and remote from the imager XI, or the IPS is integrated into the imager XI, e.g. into a workstation associated with the imager XI or into an operator console. The image processing system IPS may be implemented in a distributed architecture to serve a set of imagers suitably connected in a communication network. Some or all of the components of an IPS may be arranged in hardware (e.g., a suitably programmed FPGA (field programmable gate array)) or as a hardwired IC chip. The image processing system IPS may be partly arranged in software and partly in hardware.

Broadly, the image processing system IPS comprises an image generator IGEN which processes the projection image pi 1 acquired by the imager XI into a dark-field image and/or a phase contrast image. The image processing system IPS comprises a scatter corrector SC to reduce scatter artefacts. The scatter-corrected image provided by the scatter corrector SC in cooperation with the image generator IGEN can then be displayed on the display unit DD, or can be stored in a memory for later review, or can be further processed in other ways. The scatter corrector SC may be integrated into the image generator IGEN to form one functional unit. Alternatively, the image generator IGEN and the scatter corrector SC form separate functional units.

Although the imaging device XI supplies the projected picture pi 1 to the image processing system IPS via a wireless connection or a wired connection as shown in fig. 1, this may not always be the case in all embodiments. For example, the projected image pi may be first stored in a memory (e.g., a picture archiving system (PACS) of a Hospital Information System (HIS) or other system) and retrieved by the IPS at a later stage (e.g., upon user request) and then processed.

Typically, the imaging device XI comprises a DAX/phi imaging facilitator structure IFS. In an embodiment, the DAX/Φ imaging facilitator structure includes interferometers G0, G1, G2. The interferometers G0, G1, G2 include one, two or three gratings. In an embodiment, three gratings are used: two absorber gratings G0, G2 and one phase grating G1, which are described more fully below. In general, a DAX/φ imaging facilitator structure is a device or set of devices that: which allows to convert X-ray beam refraction and/or small angle scattering of the beam into an intensity modulation detectable at the X-ray sensitive detector D, facilitating the interpretation of said modulation into a dark field image signal and/or a phase contrast image signal and, if desired, into an attenuated image signal.

The following will be described primarily with reference to interferometric imaging devices, but this does not exclude other grating-based or non-interferometric imaging DAX/phi-facilitator structures. Other non-interferometric imaging DAX/Φ facilitator structures include coded aperture systems, crystalline or non-grating based structures with periodic or aperiodic substructures.

In general, it is possible to impart a periodic wavefront modulation to the incoming imaging X-ray beam by means of a DAX/Φ imaging facilitator structure IFS and to obtain a dark field or phase contrast by measuring the changes in the wavefront caused by the object OB to be imaged with the X-ray detector D.

In more detail, referring now to the (non-limiting) interferometric embodiment, an imaging region is defined between the X-ray source XR and the detector D, in which an object OB to be imaged (e.g., a subject's chest) resides during imaging. In which imaging area a single, two or three (or more) grating structures of an interferometer are arranged.

By continuing reference to the (non-limiting) interferometric embodiment of the image facilitator structure DAX/Φ -IFS, the periodicity, aspect ratio, etc. of the gratings are such that they cause diffraction of the X-ray beam and/or only achieve sufficient coherence so that small angle scattering can be detected or derived. Absorption gratings and phase gratings may be used. In one embodiment, the grating is formed by photolithography or cutting in a silicon wafer to define a periodic pattern of trenches. The gaps between the grooves of the absorption gratings G0, G1 may be filled with lead or gold to form respective sets of absorption lamellae. In fig. 1, the longitudinal axis of the grating sheet extends perpendicular to the plane of the drawing.

In more detail, in an embodiment, an absorption grating structure G2 is arranged between the detector D and the object OB, while a phase grating is arranged between the object OB and the X-ray detector D. In some embodiments, an additional grating G0 is also disposed at X-ray source XR in the event that the X-ray source is not capable of generating naturally coherent radiation. If the X-ray source produces incoherent radiation (as is often the case), an absorption grating G0 at the X-ray source (also referred to as a source grating) transforms the X-radiation from the X-ray source into an at least partially coherent radiation beam XB. An inverse geometry in which G1 is placed upstream of object OB (i.e., between XR and OB) is also contemplated. In an embodiment, the interferometer is of the Talbot-Lau type. The interferometer must be accurately tuned with the grating lamellae aligned. The distance between G1 and G2 is a suitable Talbot distance. But when properly adjusted, a fringe pattern can be detected at the detector D when exposed to X-radiation, based on which a DAX/Φ image can be generated by the image generator IGEN.

The interferometers G0, G1, G2 are preferably focused. In other words, one, two or all three of the gratings G0, G1, G2 have their lamellae focused on the focal spot FS 1. In some such focused embodiments, the gratings are curved to form respective lateral surfaces of three imaginary concentric cylinders. When properly focused, the central axis of these imaginary cylinders passes through focal spot FS 1. In particular, the absorption gratings G1 and G2 are curved and/or focused. If the DAX/φ facilitator structure is not an interferometer, this may also be focused on focal spot FS 1.

An at least partially coherent radiation beam XB propagates through the imaging region and interacts with the interferometer gratings G1, G2 and the patient OB. After the interaction, radiation is detected in the form of electrical signals at the radiation sensitive pixel elements of the detector D. The data acquisition circuit DAS digitizes the electrical signals into projection (raw) image data pi 1, which is then processed by the IPS in a manner explained in more detail below.

The imaging device XI may be of the full field of view (FoV) type, wherein the detector is of the flat panel type. In a full FoV imaging system, the size of the detector D and the size of the IFS correspond to the desired FoV. Alternatively, the detector D and the imaging facilitator structure IFS may be smaller than the desired FoV, for example in a slit scanning system as shown in FIG. 1. In some of these systems, the detector comprises a discrete series of detector lines. The detector lines are mounted on a scan arm to scan across the desired FoV at different slit positions. In a full field of view (FoV) type imager, the absorber grating G2 is generally coextensive with the detector.

Slit-scan systems as shown in fig. 1 are more cost-effective than full FoV systems, since they require a smaller detector and a smaller grating IFS. The grating IFS is mounted on a scan arm above the detector and equivalently scans across the FoV. In an alternative slit scanning system, although the detector D has the same dimensions as the required FoV, the grating is smaller and the collimation SC is used to scan only part of the FoV (in the "slit") at any one time in terms of collimation. In both full FoV and slit scan systems with non-moving flat panel detectors, there is a simple one-to-one relationship between pixel position and imaginary geometric rays through the imaging region to define the imaging geometry. The rays extend from a focal spot of the X-ray source XR and intersect the detector plane at respective pixel locations. Each of the geometric rays corresponds to a respective different individual one of the pixels. Such a simple relationship does not exist in certain slit scanning systems with smaller detectors, where each geometric ray is seen by many different pixels in different "slits" during scanning. The signals from the different pixels are then processed together by suitable logic for any single geometric ray.

The image generator IGEN outputs the dark-field signal and/or the phase contrast signal as a corresponding array of image values forming a dark-field image and a phase contrast image, respectively. These image values or pixel values represent the contrast of the dark-field signal for the corresponding geometric ray and the phase change experienced by the X-radiation as it travels through the object OB, respectively.

Typically, when X-radiation interacts with a material, it undergoes both attenuation and refraction and thus a phase change. On the other hand, attenuation can be divided into attenuation originating from photoelectric absorption and attenuation originating from scattering. The scattering contribution can in turn be decomposed into compton scattering and rayleigh scattering. For the purposes of current dark-field imaging, small angle scattering is of interest, wherein the qualifier "small angle" means that the scattering angle is so small that scattered photons can still reach the same pixel, as would be the case if no scattering had occurred at all.

Dark field contribution can be modeled as visibility V ═ V₀*e^-∫ε(z)dzWherein ε is the spatial distribution of the diffusion properties of patient OB and integration is performed along the X-ray beam path and V₀Is reference visibility without object interaction(recorded in calibration measurements). Then, a dark field signal recorded in the dark field image is D ═ V/V₀。

Conventional radiography systems are generally unable to resolve the detected signal into a dark field contribution. But these contributions can be converted into intensity fringe patterns that the image generator IGEN can analyze to obtain phase contrast images and/or DAX images by using interferometers G0, G1, G2 as shown in fig. 1 or by using other DAX/Φ imaging facilitator structures IFS. The image generator IGEN acts on a series of projection images obtained in the phase stepping operation. Based on the recorded series of projection images pi 1, the image generator IGEN computationally resolves the fringe pattern detected in the series of projection data pi 1 into three contributions or signals, namely a refraction contribution (also referred to as a phase contrast signal), a dark field signal component and a residual attenuation component. Since these three contrast mechanisms work together, IGEN continues to signal process the detected series of intensities in three signal channels (phase contrast, dark field, and attenuation).

In an imaging system of the above type, the capability for dark-field/phase contrast imaging is achieved as follows: projection data are acquired at the detector D during a series of phase stepping operations (in which the phase of the fringes is typically stepped through a 360 ° range) as a given fixed projection direction. The phase stepping operation is typically achieved by inducing a motion between the X-ray beam and one of the gratings of the image facilitator structure IFS (if an interferometer is used). For example, in one embodiment, the analyzer grating G1 is moved ("scanned") laterally with respect to the optical axis of the X-ray beam. Alternatively, phase stepping can also be achieved by moving the patient OB as in fig. 1, or by moving the X-ray source or the like. This movement causes a change in the fringe pattern which in turn can be recorded in a corresponding series for each step of the movement, thereby resulting in a phase step. The series of measurements for each geometric ray forms an associated phase curve. The phase curves are typically sinusoidally shaped and it has been found that each phase curve encodes a quantity of interest, in particular a dark field signal, as well as attenuation and phase variation.

In more detail, the phase curve for each pixel/each geometrical ray can be analyzed separately, for example by fitting to a sinusoidal signal model to enable image generation. Preferably, at least three fitting parameters are included in the three-channel sinusoidal model. These three fitting parameters represent three contributions, respectively: phase contrast, dark field signal and attenuation. A sinusoidal model is fitted to the phase curves by the image generator IGEN in order to compute the DAX and/or Φ images in particular and the attenuation (also referred to as "transmission") images (but which are of less interest in this context). It may be required to compute a significantly redundant transmission image to correctly account for these three phase contrast effects, otherwise incorrect contributions may be introduced in the DAX and/or phi channels.

An optimization procedure is used to fit the measured series of projections to the model. The flow can be understood from the cost function and the fitting operation can be formulated as an optimization problem. Any suitable optimization scheme is also contemplated, such as gradient descent, conjugate gradients, Newton-Raphson, random gradients, maximum likelihood, other statistical techniques, and so forth. Non-analytical methods, such as neural networks or other machine learning techniques, may also be used.

In general, the optimization problem for the signal model S has the following structure:

argmin_T,D,φF＝‖π-S^T,D,φ(X)‖ (1)

wherein S is^T,D,φ(.) is an at least three-channel modulator function that describes how the three contrast mechanisms combine to modulate and transform the incoming (undisturbed) radiation X into measured data pi, and | is a suitable similarity metric, e.g., p-norm, (squared) euclidean distance, etc. The function F (the objective function (in this case the cost function)) measures how well the signal model S "interprets" or "fits" the measured data pi. The optimization task is how best to select the parameters (T, D, phi) of the model, where the similarity measure | quantifies how well the fit is. Thus, the function F is a cost function or an error function. The task in the optimization is to improve by adjusting the parameters (T, D, phi)A cost function. In this embodiment, the parameters are adjusted in the optimization such that the "cost" returned by the cost function F is reduced. More than three channels may be used in the signal model S, depending on the number of contrast mechanisms that one wishes to consider. In (1), F may be a function of the remainder (term). Each remainder quantifies a corresponding deviation or cost of a given projection image from the prediction of the given projection image under model S.

More particularly, in one embodiment, as a special case of (1), the following analysis signal model F ═ Δ is used for each pixel or each geometric ray²Optimizing:

Δ²(T,D,φ)＝∑_iw_i(M_i-I_iT(1+V_iD cos(φ-α_i)))² (2)

wherein M is_iIs the measured data (taken from π) with undisturbed radiation "X" from blank scan intensity I_iBlank scan variability V_iAnd blank scan phase alpha_iAnd (4) showing. T, D and phi are the three contrast modulators of S () above, i.e. transmission, dark field and differential phase for this image point. w is a_iAre optional statistical weights, which are generally selected to correlate with the measured data M_iIs equal or proportional, and i indicates the phase step. After starting from (1), the task in (2) is to make the data M measured_iA cost of²Minimized in order to find the images D and phi in particular. (2) The right side of (c) can be understood as the weighted sum of the remainder.

The image generation algorithms (1), (2) of the type described above are sometimes referred to as "phase retrieval", but this is not appropriate for the present purpose because the dark-field image is also generated jointly in the fitting operation and the transmission image as described above is actually also generated jointly. The phase retrieval algorithm is described in "Hard-X-ray dark-field imaging using a graphing interferometer" by Pfeiffer et al, published in Nature 7, p. 134-137, 2008. Other phase retrieval algorithms, fourier-based or non-fourier-based algorithms are also contemplated in embodiments.

The DAX/Φ X-ray imaging system XI as proposed herein is configured to reduce or completely eliminate adverse scatter effects on the imaging operation. In particular, the countering effect on high angle scattering (collectively referred to herein as "secondary radiation") is advantageous in the DAX preferably contemplated herein, but scattering management is also advantageous for Φ imaging. Large angle scatter management is advantageous for DAX imaging because in this imaging modality it is desirable to utilize small angle scatter as a contrast mechanism. In depth to the definition of "small angle" scattering given above, "large angle" scattering as used herein is complementary to small angles. In particular, a large angle relates to a scattering angle that is large enough that scattered photons no longer reach the same pixel, unlike the case where no scattering at all or only a small angle of scattering occurs. In this respect, "primary radiation" only includes radiation that is modulated only (or mainly) by absorption, phase contrast and the required small angle scattering. The secondary radiation is mainly modulated by large angle scattering.

Thus, without confounding these two effects (large angle scattering and small angle scattering), it is envisaged herein to reduce the secondary radiation effect on the image that can be obtained by the proposed imaging system IPS. The proposed method is a two-pipe approach in the examples.

In one pipeline, it is envisaged to provide an anti-scatter grid ASG to the imager XI to separate the primary radiation from the secondary radiation. In the second line, the reverse operation is done, i.e. the secondary radiation is separated from the primary radiation to measure the amount of secondary radiation for a given object PAT that is desired to be imaged. This measurement is then used to inform the DAX image generation by the generator IGEN to compensate, remove, reduce, or suppress secondary radiation image artifacts.

Turning now initially to the first pipeline, the ASG includes a set of thin sheets made of a high density material (e.g., lead or other high-Z material). The longitudinal direction of the lamellae extends into the drawing plane of the schematic drawing in fig. 1. They preferably run the full length of one spatial dimension of the detector while multiple slices are chosen to substantially cover the other spatial dimension. In other words, the ASG is coextensive with the detector surface of the detector D. The lamellae are preferably, but not necessarily, in all embodiments focused on the focal spot FS of the X-ray source XS. In other words, the lamella is arranged at a greater inclination further away from the center point of the detector ASG.

When focused or properly adjusted, the ASG lamellae in front of the detector D block unwanted secondary radiation. The best focus posture (i.e. position and orientation) of the ASG is the case when the focal spot FS is located on an imaginary line formed by a set of imaginary planes, which may pass the respective lamella with a given inclination of the respective lamella. The planes intersect in an imaginary line, which is the central axis of the above-mentioned imaginary cylinder with respect to the focused gratings G0, G1, G2. However, even in this focusing arrangement, the ASG effectively blocks only a certain fraction of the secondary radiation.

In order to better take into account substantially all or at least a higher fraction of the secondary radiation effects, a second conduit is provided, which is implemented by a computerized control logic unit CL of the imaging system XI. The control logic causes the imaging system to assume a configuration in which a high fraction or substantially all of the incident patient-specific PAT secondary radiation can be measured by the detector D.

Broadly, the control logic unit CL is configured to allow operating the imaging system in two modes: an (object) image acquisition mode and a scatterometry mode. The imaging system IS may comprise a user interface (not shown) to allow switching between the scatterometry mode and the image acquisition mode. The user request for such switching may be received by a touch screen action on a touch screen display or by a pointing device (e.g. a computer mouse) or any other UI input arrangement preferably provided at an operator console (not shown) of the imaging system IS.

In the image acquisition mode, the DAX/Φ imaging facilitators IFS and ASG are in a focusing arrangement as described above, focused on the focal spot FS1 of the X-ray source. In this arrangement, an object image π 1 (in particular a projection image) is acquired by: the X-ray source is operated such that X-ray beam XB1 is emitted along a primary (average) radiation direction p1 while the depicted components are aligned or focused relative to one another.

The control logic unit CL is configured to switch from this object acquisition mode to a scatterometry mode, wherein a defocus (with respect to the focal spot FS 1) is achieved by effecting a change in the imaging geometry. In this out-of-focus arrangement, the X-ray source is activated again, but preferably at a low dose (lower than the dose in the image acquisition mode), to acquire a second projection data set pi 2 of measurements — measuring a fraction of samples of secondary radiation. A number of embodiments are envisaged as to how such out-of-focus imaging geometries can be achieved, and will be explored more fully below. The control logic unit CL IS switchable to switch the imaging system IS to each of these modes, the switching being done in turn. In this way, the respective measurement data sets pi 1, pi 2 are measured at the detector and the respective measurement data sets pi 1, pi 2 are acquired at the data acquisition circuit DAS and transferred to the image processing section IPS. The acquisition of the two data sets pi 1, pi 2 can be done in any order.

However, it is preferred to first acquire scatterometry data in scatterometry mode π 2 in the first low dose exposure for a given patient. The measured scatter data pi 2 encodes a specific "scatter footprint" for a given patient, which reflects the composition of the individual anatomy of the patient. It is predicted that this scatterometry π 2 need only be done once for a given patient PAT, and can be stored in a database or other memory (e.g., PACS in HIS, etc.) for later reference. The scatter data pi 2 can then be retrieved for subsequent imaging appointments. Alternatively, when imaging a patient, multiple acquisitions of the latest scatter measurement π 2 are required (possibly each imaging requires an acquisition) in order to account for different poses/positions of the patient, which also affects the secondary radiation that can be detected at the detector D.

The image processing system IPS receives the "appropriate" image data pi 1 acquired in the object image acquisition mode to apply any one of the DAX/phi image processing algorithms described above (in particular the phase retrieval algorithm) to extract the DAX or phi information to generate a scatter-corrected DAX image and/or phi image, respectively, of the patient. Scatter correction is effected by interfacing the image generator IGEN with a scatter corrector component SC of the image processing system IPS. The scatter corrector component SC processes the scatterometry data pi 2 in cooperation with the image generator. Many different embodiments are envisaged for this purpose, which will be described below.

The measurement result pi 2 can either be used directly as a scatter estimate or first be processed by low-pass filtering or other pre-processing. The measurement result pi 2 (possibly preprocessed) can serve as a calibration input for scatter correction for scatter-based simulation calculations. A monte carlo method may be used in the simulation.

In an embodiment the scatter corrector component SC and the image generator together act on both datasets pi 2, pi 1.

In particular, the scatter corrector CS may apply a corrected pre-phase search or post-phase search based on the scatter measurement result pi 2. For example, the corrector SC may subtract the scatter data pi 2 from the image data pi 1, and the image generator IGEN then processes the difference | pi 1-pi 2| in a phase retrieval algorithm. Alternatively, the image generator IGEN first generates the DAX/Φ imagery I on the basis of pi 1_DAXOr I_ΦThen from I_DAXOr I_ΦSubtract pi 2 or otherwise combine pi 1 and pi 2 to obtain a scatter-corrected image. In general, the scatter corrector component SC uses the scatterometry data pi 2 to correct the DAX and/or Φ images for artifacts resulting from secondary radiation.

In other embodiments, the scatter corrector component SC feeds the scatterometry data pi 2 to the image generator IGEN, and the image generator IGEN processes the two data sets together to obtain a scatter-corrected output DAX and/or Φ imagery. In this and similar embodiments, the retrieval algorithm implemented by the image generator IGEN may be modified to include additional channels or fitting variables contributing to high angle scatter in the optimization procedure for functions (1) or (2) when fitting the model to data pi 2 and pi 1. In this modified optimization scheme, large angle scatter measured by data π 2 can be considered in a customized manner for a given patient. The measured scatter data π 2 can be used in other scatter correction schemes, analysis or machine learning based scatter correction schemes, all of which are contemplated herein.

With continued reference to fig. 1, different embodiments for implementing a scatterometry mode will now be explained in more detail.

In a first embodiment, the out-of-focus configuration of the focal spot FS1 with respect to the X-ray source is obtained by changing the position of the focal spot itself with respect to the ASG as shown in fig. 1 from one focal spot position FS1 to another focal spot position FS 2. The focal spot switching can be controlled by the control logic unit CL through a suitable actuator AC. The actuator AC may be controlled by the control logic unit CL via the X-ray source XR interface SI.

In these embodiments, beam XB1 propagates along the normal direction p1 when in image acquisition mode. In this configuration, the propagation direction p1 follows a focusing arrangement. In the out-of-focus arrangement caused by moving focal spot FS1 to another position FS2, there is a new X-ray beam XB2 propagating along a different direction p2, which new X-ray beam XB2 is now in an out-of-focus state relative to the DAX/Φ imaging facilitator structure IFS and/or ASG.

By moving the X-ray focal spot FS1 out of the focus of the ASG, the scatter fraction can now be measured. In this out-of-focus imaging geometry, now non-scattered radiation is dominant, which is blocked by the ASG, since the ASG is now misaligned with respect to radiation XB2 emanating from the new focal spot FS 2. The only (or at least a high fraction of) radiation that remains to reach the detector D is secondary radiation, which is now not blocked by the ASG. In other words, the radiation detected now consists mainly of X-ray scatter not blocked by the ASG. This radiation will thus provide an accurate estimate of the amount of non-suppressed scatter if measured with the patient in place.

Many different embodiments are envisaged for the focal spot variation. For example, the anode and/or cathode may shift or otherwise cause the actuator AC to change the attitude of the anode and/or cathode such that the X-ray beam is directed in different directions. Alternatively, the actuator AC comprises an electronic focal spot selector, such as an electrostatic deflection device. The electrostatic deflection device AC changes the direction of the electron beam inside the tube such that the focal spot and thus the direction of the X-ray beam is moved.

Instead of or in addition to changing the focal spot position in the X-ray source, other embodiments are envisaged in which the out-of-focus configuration leaving the ASG is used for the scatterometry mode. In these embodiments, there is a scatterometry facilitator SMF integrated into the imaging system XI. In an embodiment, scatterometry facilitator SMF is a hardware structure that can be disposed between X-ray source XS and detector D to facilitate scatterometry measurements. By imposing a translation or rotation on the SMF, the control logic unit CL perturbs or changes the pose of the scatterometry facilitator SMF to put the imaging system into a scatterometry mode. The envisaged scatterometry facilitator SMF is able to provide different functions: in one function, the SMF facilitates scatterometry measurements when the system IS in a scatterometry mode. In an embodiment, when the system is in an image acquisition mode, the scatterometry facilitator SMF may be switched into its configuration serving another imaging support function. In an alternative embodiment, the SMF IS dedicated and not serving other imaging functions and IS completely exited by the control logic unit CL when the system IS in image acquisition mode.

In some embodiments where the scatterometry facilitator SMF has dual or multiple functions, it is assumed that it is in a focused arrangement relative to the focal spot when the system is in an image acquisition mode. But for use in a scatterometry mode, scatterometry facilitator SMF is moved out of focus with respect to focal spot FS 1.

The actuator AC may be used to move the scatterometry facilitator SMF out of focus. In general, the setting of the actuators for moving the scatterometry facilitator SMF out of focus can be done in a number of different ways. The scatterometry facilitator SMF may be held in a frame or other fixture that is movably (translatably or rotatably or both) mounted. An actuator AC (e.g., a gear or screw mechanism) powered by a power source may be used to engage the frame to push or pull or rotate the frame and in turn push or pull or rotate the SMF to achieve the out-of-focus configuration. Hydraulic or piezoelectric actuators AC are also envisaged in the embodiments. The actuator AC is responsive to control signals issued by the control logic unit CL through a suitable device interface. The control logic unit CL may in turn answer the request signal issued by the user interface UI.

In some embodiments, the scatterometry promoter SMF is part of the DAX/Φ imaging promoter discussed above. For example, in an embodiment, the scatterometry facilitator SMF is one or both of the two absorption gratings G0, G2 of an interferometer, assuming that the DAX/Φ imaging facilitator includes such an interferometer. In this embodiment, the posture of G0 or G2 is changed by the actuator AC. For example, either grating is rotated or shifted. Preferably, in an embodiment, the G2 grating is rotated by 90 ° around an optical axis (an axis through the focal spot FS1 of the X-ray source XS) through the center of said grating G2. The focal spot is not required to be variable. An amount of rotation other than 90 is also contemplated. The source grating G0 may also be rotated 90 ° (or any other angular amount) in either direction, in addition to or instead of the rotary analyzer grating G2, G2.

It has been observed that even if one or both of the gratings G0, G2 are moved in the above described embodiments, some remaining primary radiation will still reach the detector. In this case, it may be necessary to ensure that there are no remaining stripe patterns in the data. To ensure this requirement, either G0 or G2 can be moved or rotated. In an exemplary embodiment, the movement of G0 or G2 to reduce the fringe pattern may be accomplished in a feedback loop arrangement including a control logic unit CL, an actuator AC and a detector D. The control logic unit CL senses the fringe pattern via the detector D. The control logic unit CL instructs the actuator AC with instructions to move G0 or G2 in order to reduce the intensity of the fringe pattern detected at the detector D, with the aim of removing the fringe pattern or at least reducing the intensity of the fringe pattern based on a suitably defined negligible threshold. In this embodiment, the control logic unit CL may comprise a machine learning component configured to implement an reinforcement learning algorithm. In this embodiment, the control logic unit operates the actuator to change the attitude of G0 or G2. The action is driven by optimizing a reward function R, which measuresThe intensity of the detected fringe pattern is measured. Readjustment of the attitude of G0 or G2 is performed under exposure conditions that prefer low X-radiation. The goal of the machine learning algorithm is to make the fringe pattern measured by the reward function disappear. Visibility or related quantities may be used to formulate a reward function, e.g., R ═ I_max-I_min)/(I_max+I_min) Wherein, I_minAnd I_maxAre the corresponding maximum and minimum intensities.

While the DAX/Φ imaging facilitator is assumed to be an interferometer in the above embodiments, this need not be the case in all embodiments, and the scatterometry modes described above can be equally practiced in non-interferometric DAX/Φ imaging settings. For example, the DAX/Φ imaging facilitator may be an encoded aperture plate or other plate, and this is moved by the control logic unit CL and the actuator AC.

In another embodiment, the scatterometry facilitator SMF comprises the ASG itself. The actuator AC is controlled by the control logic unit to change the attitude of the AGS. For example, the ASG may be rotated by an angle such that the longitudinal axis of its lamella now points in different directions and no longer extends into the drawing plane as schematically shown in fig. 1. In particular, a rotation of 90 ° in either direction is envisaged, wherein the rotation axis passes through a central point of the ASG and a (possibly single) stationary focal spot FS1 of the X-ray source. Instead of or in addition to rotation, the ASG may be tilted by an angle, which may be measured with respect to an optical axis passing through a center point of the ASG and focal spot FS 1. The ASG may be so moved instead of or in addition to moving G0 or G2 to reduce the stripe pattern as discussed in previous embodiments.

For DAX/Φ imaging, in particular the mutual alignment of the gratings G1, G2, G0 and ASG is crucial for a good quality of the object image acquisition. Proper alignment and focusing of these components can be cumbersome, time consuming, and not always easily achievable. In this context, it may not be desirable to have the control logic unit CL interfere with any of these components, since fine refocusing or rescaling work may need to be done anew when switching back to the image acquisition mode.

In order to solve this problem, it is proposed in an alternative to the described components that the facilitator SMF is arranged as a separate dedicated component which can be arranged in the beam between the patient and the detector or between the source XS and the patient, as required. That is, rather than using existing hardware as a scatterometry facilitator in a DAX/Φ imaging setup, it is proposed to introduce a dedicated additional component, shown as component B, into the beam when operating in a scatterometry mode. This component B is arranged to partially block X-radiation and can be manufactured similarly to the manufacturing method of a grating or ASG or the like of a radiation blocking sheet or plate having holes. Part of the radiation block B may be removed completely by the actuator, e.g. by sliding the beam out within the object acquisition mode and back into the beam when the image system is operating in the scatterometry mode.

In general, the control logic unit CL may be implemented by one or more computing units PU. The control logic unit may be fully integrated into the imaging system or may be arranged as one or more microcontrollers, but may also be remotely arranged at one or more computing systems PU that are remote. The control logic unit CL may interact with the imaging system but is connected wirelessly or by wire to the components of the imaging system. The control logic unit CL may be arranged in software or in hardware or partly in software and hardware. The control logic unit may be implemented as one or more microcontrollers and integrated into the imaging system IS.

Each of the scatterometry embodiments described above can be used alone or in combination or in any subcombination.

It has been observed that the scatter management principles described herein produce very good contrast in DAX images. It is believed to be due, at least in part, to the fact that the proposed scatter reduction mechanism only provides the correct amount of tolerance required for DAX imaging. A too efficient scatter removal may actually hinder the DAX imaging target, since a strict removal of all scatter would risk that all DAX effects are removed, resulting in a low DAX contrast. The proposed scatter management scheme described herein achieves the correct balance. Due to the switching between these two modes, two separate and/or dedicated measurement procedures are defined. In each procedure, the entire detector-sensitive surface of the detector is disposable for the respective measurement in the embodiment. Operating in such dedicated/standalone mode may also facilitate achieving proper scatter correction, particularly suitable for the purposes of DAX imaging as primarily contemplated herein.

Referring now to the flowchart of FIG. 2, there is illustrated the steps of a computer-implemented method for DAX/Φ with scatter management. It should be understood, however, that the method steps described below constitute the particular architecture shown in fig. 1 herein, but are not necessarily tied to the particular architecture shown in fig. 1.

At step S210, the X-ray imaging apparatus XI is operated in two modes in sequence, first in one mode and then in the other mode. These two modes are referred to herein as an image acquisition mode and a scatterometry mode. The X-radiation that can be received at the detector of the imaging system when in the scatterometry mode comprises a higher proportion of scatter than the scatter radiation that can be received at the detector of the imaging system when in the object acquisition mode. Step S210 results in two measurement data sets pi 1 and pi 2, where pi 2 encodes a higher proportion of scattered radiation. In particular, only or mainly scattered radiation is measured in this second data set pi 2, whereas the first data set pi 1 encodes primary radiation, which has no or a lower fraction of secondary radiation.

In step S220, a scatter-corrected image is generated using scatterometry data n 2 obtained in the image acquisition mode and data n 1 obtained in the image acquisition mode. This can be done, for example, by simply: the scatterometry data is removed or subtracted from the image measurement data to obtain difference image data, and then a phase retrieval operation is performed based on the difference data to obtain a scatter-corrected DAX or Φ image. Alternatively, a phase search is first performed based on the data π 1 obtained in the image acquisition mode to obtain a preliminary DAX or φ image. And then post-processing the preliminary DAX or phi image based on the scatterometry data pi 2 to obtain a scatter-corrected DAX or phi image. Alternatively, the two data sets are jointly processed in a phase retrieval to obtain a scatter-corrected DAX or Φ image. Other scatter correction methods based on scatterometry data π 2 are also contemplated herein.

The measured scatterometry data π 2 may be used directly or the scatterometry data π 2 may first be preprocessed (e.g., by filtering or otherwise). In an embodiment, scattering simulation is used based on the measured data π 2.

In optional step S230, the scatter corrected image is displayed on a display device or otherwise provided so that the scatter corrected image is available.

One or more features disclosed herein may be configured or implemented as/with circuitry encoded within a computer-readable medium and/or combinations thereof. The circuits may include discrete circuits and/or integrated circuits, Application Specific Integrated Circuits (ASICs), systems on a chip (SOCs) and combinations thereof, machines, computer systems, processors and memory, computer programs.

In a further exemplary embodiment of the present invention, a computer program or a computer program element is provided, which is characterized in that it is adapted to run the method steps of the method according to one of the preceding embodiments on a suitable system.

Thus, the computer program element may be stored in a computer unit, which may also be part of an embodiment of the present invention. The computing unit may be adapted to perform or cause the performance of the steps of the above-described method. Furthermore, the computing unit may be adapted to operate the components of the apparatus described above. The computing unit can be adapted to operate automatically and/or to run commands of a user. The computer program may be loaded into a working memory of a data processor. Accordingly, a data processor may be equipped to perform the methods of the present invention.

This exemplary embodiment of the invention covers both a computer program that uses the invention from the outset and a computer program that is updated by means of an existing program to a program that uses the invention.

Further, the computer program element may be able to provide all necessary steps to complete the flow of an exemplary embodiment of the method as described above.

According to a further exemplary embodiment of the present invention, a computer-readable medium, for example a CD-ROM, is proposed, wherein the computer-readable medium has a computer program element stored thereon, which computer program element is described by the preceding sections.

A computer program may be stored and/or distributed on a suitable medium, particularly but not necessarily a non-transitory medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the internet or other wired or wireless telecommunication systems.

However, the computer program may also be present on a network, such as the world wide web, and may be downloaded into the working memory of a data processor from such a network. According to a further exemplary embodiment of the present invention, a medium for making a computer program element available for downloading is provided, the computer program element being arranged to perform the method according to one of the previously described embodiments of the present invention.

It has to be noted that embodiments of the invention are described with reference to different subject matters. In particular, some embodiments are described with reference to method type claims whereas other embodiments are described with reference to apparatus type claims. However, unless otherwise indicated, a person skilled in the art will gather from the above and the following description that, in addition to any combination of features belonging to one type of subject-matter, also any combination between features relating to different subject-matters is considered to be disclosed with this application. However, all features can be combined to provide a synergistic effect more than a simple addition of features.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the word "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. Although some measures are recited in mutually different dependent claims, this does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims shall not be construed as limiting the scope.