The present invention generally relates to a device and method for phase stepping a grating for differential phase contrast and/or dark field x-ray imaging, a switchable grating and a phase contrast imaging procedure.
Phase contrast imaging, such as dark-field x-ray imaging (DAX) and differential phase contrast imaging (DCPI), provide high sensitivity to phase-gradients and scattering structures in the object and are a promising addition to diagnostic or analytical (x-ray) imaging, for instance for medical diagnoses, material analysis and security scanning.
Phase contrast imaging (this term is used throughout this document to cover both DAX and DCPI) is an imaging technique that only recently found practical use in medical imaging. Phase contrast imaging has already been long known for visual optics, but for x-ray imaging it was restricted to highly brilliant synchrotron x-ray sources that are not suitable for medical imaging due to their size and very limited energy band width and angular divergence. However, a grating-based solution was developed to generate dark field x-ray images using x-ray tubes commonly used in medical imaging. See for instance: Pfeiffer et. al., “Hard-X-ray dark-field imaging using a grating interferometer”, Nature Materials, Vol. 7, February 2008, page 134-137].
Such grating-based phase contrast imaging may be performed using a phase contrast set-up 10 as is schematically depicted in
The obtained dark field image data represents scatter information of the x-ray beam 13 through the subject 50. This scatter data is obtained simultaneously with x-ray transmission image data, which provides attenuation measurement data, particularly of a difference between high and low absorption areas, and with phase contrast image data, which provides increased soft-tissue contrast, which makes it particularly suitable for imaging ‘soft’ materials with many surface area transitions and/or micro-structures (e.g. lungs, fibrous materials and the like).
The obtained differential phase contrast image represents refractive index information of the x-ray beam 43 through the subject 50. This may be advantageously used, on its own or in combination with the simultaneously obtained transmission image, to enhance image contrast by using detailed differing refractive index changes within structures that are otherwise uniform.
The described phase contrast set-up is very suitable for this purpose, but the presently claimed invention would work with any phase contrast set-up suitable for medical, analytical or security imaging based on gratings.
To be able to take multiple acquisitions at different positions over the period of the grating (pitch) in phase contrast imaging a process called phase stepping is often employed. In this, preferably, the phase grating G1 (but this could also be any one of the other two gratings) is “stepped”, in other words: the grating is slightly shifted in a direction perpendicular to the x-ray beam 13. Phase stepping is a necessity in most of currently existing differential phase contrast setups making use of Talbot-Lau interferometry. The stepping is typically implemented by an actuator that activates any of the three gratings of a Talbot-Lau interferometer with respect to the two others in synchrony with the readout of the X-ray detector sensing the changes in intensity at various locations within the field-of-view induced by the stepping.
The activation leads to a positional shift of the grating. After the shifting of the grating the X-ray detector is read out. Therefore, the operator acquires a readout prior to the shifting and after the shifting.
An example of a phase stepping device is described in US 2015/0294749 A1. The interferometric dynamic grating is actuated by a microelectromechanical system (MEMS) to change its periodicity. A movable part of the dynamic grating is anchored by springs on two lateral sides of the grating in the direction of movement of the grating. Comb drive means on the sides of the grating allow for modification of the grating in the desired direction. The comb drive means may be piezo-electrically or electrostatically driven.
Known disadvantages of known phase stepping devices include possible delays which are required before the X-ray readout of each phase step can be triggered in view of a possible time it takes the actuator to settle at the new position. Furthermore, positional inaccuracies, back-lash, etc. may occur.
Further, the use of such ultra-precision actuators requires time-consuming installation and extensive calibration steps and is easily disturbed by outside influences, e.g. mechanical disturbances or thermal influences. Also, the actuators and their controls take up valuable space in or near the examination area of the imaging device. And further, if an imaging system is to be used in normal, attenuation-based imaging then the gratings and support devices need to be moved outside of the beam field of view.
Therefore it would be advantageous to obtain a new phase stepping device for phase contrast imaging that overcomes the above-mentioned drawbacks.
The presently claimed invention provides a solution to the above-mentioned problems and more.
Embodiments according to the present invention are directed towards a phase stepping device for differential phase contrast and/or dark field x-ray imaging comprising a switchable grating. The switchable grating comprises a reservoir containing a substantially x-ray transparent medium comprising particles that substantially attenuate x-ray radiation; a first ultrasound generator, arranged at and acoustically connected to a first side of the reservoir, configured to generate a first soundwave such that a first standing wave is formed within the medium causing the x-ray absorbing particles to organize along pressure nodes of the standing wave; and a second ultrasound generator and acoustically connected to the reservoir configured to generate a second soundwave such that a second standing wave is formed within the medium causing the x-ray absorbing particles to organize along pressure nodes of the standing wave. The switchable grating is configured to shift a position of the pressure nodes between at least two positions by generating the first standing wave by the first ultrasound generator and the second standing wave by the second ultrasound generator in a predetermined sequence. Using both ultrasound generators allows to shift the pressure nodes, and therewith the organized particles, to another position. As such the position of the formed x-ray absorbing structures may be shifted in a predetermined sequence between at least two (preferably three and more preferably four) positions and the switchable grating may therefore be used for phase stepping. An advantage thereof is that no mechanical actuation means need to be implemented and/or the switchable grating does not need to be moved itself, thereby avoiding errors in repositioning.
In the context of the presently claimed invention when the term ‘shifting the position of the pressure nodes’ is mentioned it is meant that the row or grid of pressure nodes is shifted laterally as a whole.
In an embodiment the predetermined sequence is a sequence in which the first ultrasound generator and the second ultrasound generator are switched on and off alternatingly such that only one is switched on at the time or a sequence wherein the first ultrasound generator is switched on while the second ultrasound generator is alternatingly switched on and off. In the first option the grating position is determined by one ultrasound generator at the time, each producing a (different) standing wave with a different pressure node position. This is possible if the ultrasound generators are positioned differently or are operating at different settings (e.g. frequency or phase). In the second option the second ultrasound generator causes the standing wave caused by the first ultrasound to change such that the pressure node position is changed.
In an embodiment the second ultrasound generator is arranged along a second side of the reservoir opposite to the first side. When the second ultrasound generator is also switched on it generates a second soundwave in the opposite direction of the first soundwave causing the position of the pressure nodes of the resulting soundwave to change with respect to the original node position in the original soundwave. This is a very precise and easily controllable embodiment that results in well-defined and exactly positioned pressure nodes along which the x-ray absorbing particles organize.
In an embodiment the reservoir comprises a first sub-reservoir and a second sub-reservoir stacked on the first sub-reservoir and shifted laterally with respect to the first sub-reservoir. The first ultrasound generator is arranged at and acoustically connected to a first side of the first sub-reservoir and the second ultrasound generator is arranged at and acoustically connected to a first side of the second sub-reservoir. As such each ultrasound generator may form a soundwave in each sub-reservoir. As the sub-reservoirs are shifted with respect to each other the pressure nodes of the standing wave of each sub-reservoir are shifted with respect to each other. As such the x-ray absorbing walls formed by organized particles may be formed alternatively in the first sub-reservoir and the second sub-reservoir, causing them to shift position each time one ultrasound generator is switched on and the other off, which makes this arrangement very suitable for phase stepping.
In an embodiment the reservoir comprises at least one further sub-reservoir, stacked on and shifted laterally with respect to the previous sub-reservoir, wherein a further ultrasound generator is arranged at and acoustically connected to a first side of the further sub-reservoir. Stacking one or more laterally shifted sub-reservoir allows for phase stepping between multiple (sub)-positions.
In an embodiment a further ultrasound generator is arranged at and acoustically connected to a second side, opposite of the first side, of at least one, but preferably all, of the sub-reservoirs. This allows phase stepping within one-sub-reservoir as well, thereby further extending the amount of possible stepping positions.
In an embodiment the first ultrasound generator and the second ultrasound generator are phase locked, preferably by means of phase locked loop electronic circuits. This ensures formation of a stable standing wave.
In an embodiment the phase stepping device further includes an acoustic diode arranged to prevent a soundwave of an ultrasound generator to reach the opposite side of the reservoir. This prevents distortions in the standing wave that may influence the stability or positioning of the organized particles.
Preferably the acoustic diode comprises a compartment containing a first bubbly liquid and a compartment containing a second bubbly liquid placed in series between the ultrasound generator and the reservoir. This is a preferred implementation of an acoustic diode that provides sufficient dampening of reflections.
The invention further is directed towards a switchable grating as used in the claimed phase stepping device described previously.
The invention is further directed towards a method of phase stepping a grating using the phase stepping device and switchable grating as claimed and described previously.
The invention is further directed towards a phase contrast imaging procedure including the phase stepping method as claimed and described previously.
Still further aspects and embodiments of the present invention will be appreciated by those of ordinary skill in the art upon reading and understanding the following detailed description. Numerous additional advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of preferred embodiments.
The present invention is illustrated by drawings of which:
The invention may take form in various components and arrangements of components, and in various process operations and arrangements of process operations. The drawings are only for the purpose of illustrating preferred embodiments and are not to be construed as limiting the invention. To better visualize certain features may be omitted or dimensions may be not be according to scale.
The insight underlying the presently claimed invention is that phase stepping may be performed with a so-called ultrasound switchable grating, as are for instance known from US2007/0183584A1. Herein a temporary grating structure is formed in a medium by means of ultrasound standing waves that allow the alignment of attenuating particles (e.g. Au) along one direction into three dimensional walls or slabs along formed pressure nodes perpendicular to the ultrasound wave direction. The advantage of this is that a grating may be formed on demand in desired dimensions without the need to introduce and position the grating structure into a beam path of an x-ray imager. Also this provides an alternative for currently highly expensive manufacturing costs to produce gratings suitable for phase contrast imaging. Adapting and using such a grating in a novel and inventive way, as will be elaborated on extensively in the following, results in phase stepping enforced by changing the phase shift between opposing traveling ultrasound waves forming a standing wave. The difference in phase determines the location of the pressure nodes. As such this known switchable grating technology is modified electronically to the effect of changing the effective phase, i.e. phase stepping.
The presently claimed invention is described with a focus on the analyzer grating G2 as being the switchable grating 20. However, the switchable grating 20 as claimed may also be used for the source grating G0 or the phase grating G1 or for two or all three of the gratings G0, G1, G2.
The presently claimed invention is described with a focus on the phase contrast arrangement as shown in
The detector 14 employed in the phase contrast arrangement according to the presently claimed invention may have a pitch sufficiently small, hence a spatial resolution sufficiently large, for detecting, i.e. adequately resolving the interference pattern generated by the phase grating G1. For that purpose such detection unit may comprise a high resolution x-ray detector 14 known per se having a resolution of 50 micrometers or more, or an x-ray detector 14 of the type as described in US 2014/0177795 A1. Alternatively, the detection unit may comprise an x-ray detector 14 having less high resolution, however, in conjunction with an analyzer grating G2, i.e. an absorption grating arranged in the optical path between the phase grating G1 and said x-ray detector 14.
In case no analyzer grating G2 is used, then also G0 may optionally be removed.
The interferometer employed in the phase contrast arrangement according to the present invention may be implemented by various geometries. The interferometer may comprise (i) (optionally, depending on the x-ray source) a source grating G0 with pitch p0, (ii) a phase grating G1 with pitch p1 and installed between the source grating G0 and the detector 14, and (iii) (optionally, depending on the implementation of the detection unit 14) an analyzer grating G2 with pitch p2 and installed between the phase grating G1 and the detector. Introducing s as the distance between the source grating G0 and the analyzer grating G2 (if any), l as the distance between the source grating G0 and the phase grating G1 and d as the distance between the phase grating G1 and the analyzer grating G2 (if any), the various geometries are defined on the basis of said quantities. As a first option, the interferometer may be implemented in the so-called “conventional geometry” in which l>d and p0>p1>p2. In the conventional geometry, the object to be imaged is typically arranged between the source grating G0 and the analyzer grating G1. As a second option, the interferometer may be implemented in the so-called “inverse geometry” in which l<d and p0<p1<p2. In the inverse geometry, the object to be imaged is typically arranged between the phase grating G1 and the x-ray detection unit 14 (i.e. between the phase grating G1 and, if present, the analyzer grating G2). As a third option, the interferometer may be implemented in the so-called “symmetric geometry” in which d=1 and p0=p1=p2 (presuming a π-shifting phase grating G1). For more information (incorporated herein by reference) see Tilman Donath et al, “Inverse geometry for grating based x-ray phase contrast imaging”, JOURNAL OF APPLIED PHYSICS 106, 054703, 2009.”
The reservoir 22 is at least acoustically, connected to an ultrasound generator 21.
Preferably, the distance between the two sides of the reservoir 22 are better integer multiples of half the wavelength of the induced standing wave (λ/2). Waves will still form in other cases, but if this condition is met, the standing waves are much stronger because it then operates as a resonance cavity with larger pressure amplitudes, which results in increased focusing of particles 24 in the pressure nodes.
The reservoir 22 has a minimum thickness to allow the particles 24 to arrange to the full height to form grating structures. The height is comparable with the length of regular, non-switchable gratings used in phase contrast imaging, preferably between 100 and 300 micron, more preferably between 150 and 250 micron and most preferably about 200 micron. Preferably the standing soundwave forces the particles 24 to organize in structures substantially extending from the bottom to the top reservoir to the top. However it may be possible that there remains a non-used volume above the grating structures in the reservoir 22. The thickness of the reservoir 22 should increase or decrease if the used particles 24 absorb less or more respectively than a common grating.
The reservoir 22 should be constructed of a material that has negligible x-ray absorption. Glass is a particularly suitable material. Also most plastics would be suitable, provided that the walls are sufficiently thin. The thickness of the reservoir walls should be such that there is a balance between reducing x-ray absorption and structural integrity.
Upon exposing the suspension 23, 24 to a strong ultrasound signal 21′ generated by the ultrasound generator 21, standing waves are generated causing the particles 24 to align along pressure nodes of the standing wave, as is schematically shown in
During ultrasound excitation the walls or slabs remain in place, forming an equivalent grating with an absorbing pitch of 30 μm that is suitable for use as an analyzer grating G2. For a sufficiently absorbing cross-section, the ultrasound transducer(s) must be such that a standing wave is generated across the full volume of the suspension exposed to the x-ray beam.
The ultrasound generator 21 comprises an ultrasound transducer that is used to stablish a standing wave 21′ across the water (or other) filled container. The ultrasound transducer may be a single transducer or consist of a plurality of smaller transducers each tuned to generate a standing wave.
In an example the particles 24 are gold particles. The medium 23 is water and the cross-section of the reservoir 22 is 0.2 mm.
An interesting additional useful property of ultrasound generated grating structures is the flexibility of their formation and modification by means of proper beam forming techniques. For example, the modification of the speed of sound of the suspension, e.g. by dilution would cause the speed of sound to change and with it the periodicity of the structures formed. The same effect can be achieved by change in the ultrasound frequency. The addition of higher harmonics with the correct phase and amplitude by means of Fourier synthesis might be used to manipulate and improve the profile of the resulting attenuating walls (steeper profile).
As an example, in
In the above described ultrasound-induced switchable grating the frequency of the standing wave and the speed of sound of the medium determine the pitch of the resulting absorbing walls or slabs. It is an insight underlying the presently claimed invention that in a similar way, the phase stepping can be implemented.
Although phase stepping can be done at any of the three gratings, it makes most sense to consider phase stepping the analyzer grid G2. At a given frequency and medium, the position of the walls across the reservoir 22 depends on the standing wave. Phase stepping may be accomplished by modifying the phase of the resulting ultrasound standing wave. The use of two ultrasound generators 21-1, 21-2 each comprising radio frequency (RF) transducers on opposite sides of the reservoir 22 may be used to modify the phase of the resulting standing wave. That is, when both ultrasound generators 21-1, 21-2 are switched on, opposing ultrasound travelling waves result in a standing wave where a position of the pressure nodes in the medium will depend on the phase difference of both RF transducers. Both RF transducers operate at the same frequency and are phase locked to the desired difference in phase. See
An added advantage of the present invention is that there is a large degree of freedom in the amount of shift that may be induced. Shifts may be in a positive or negative direction and set to any desired stepping distance if physically possible. It is for instance also possible to increment the phase shift in small increments to a desired stepping distance. It is therefore possible to relocate the walls of absorbing particles on demand at different positons, effectively allowing for phase stepping without mechanical parts or moving the grating itself.
The difference in phase may be realized very precisely by electronics means. For instance, Phase Locked Loop (PLL) circuits force both transducers to sync to the same frequency while allowing to precisely tune the phase difference.
In the embodiment of the switchable grating 20 as shown in
There are also other known ways of preventing ultrasound reflections, such as use of a so-called acoustic diodes 30 that allow unidirectional wave propagation. Such acoustic diodes 30 prevent the wave to reach the transducer at the other side by blocking its propagation. Such an acoustic diode was disclosed in C. Vanhille and C. Campos-Pozuelo in “Ultrasounds in bubbly liquids: Unidirectional propagation and switch”, Physics Procedia 63 (2015), pages 163-166. This particular acoustic diode 30 makes used of sound propagation properties of sound in bubbly liquids.
The basic principle is shown in
In
In
An alternative embodiment of the phase stepping device 20 as claimed is shown in
The sub-reservoirs 22-1, 22-2, 22-3, 22-4 may individually be separated by an x-ray transparent wall to prevent mobility of particles 24 between sub-reservoirs to ensure homogeneous operation and x-ray absorption for each sub-reservoir 22-1, 22-2, 22-3, 22-4. Optionally these separating walls are acoustically dampened to prevent x-ray absorbing structures from being formed in neighboring sub-reservoirs.
Each sub-reservoir is acoustically connected to a separate ultrasound generator 21-1, 21-3, 21-5, 21-7 on a first side of the sub-reservoir. Each ultrasound generator 21-1, 21-3, 21-5, 21-7 may independently induce a standing wave in the sub-reservoir 22-1, 22-2, 22-3, 22-4 it is connected to and, preferably, not substantially in neighboring sub-reservoirs 22-1, 22-2, 22-3, 22-4. As such, in each sub-reservoir a standing wave with a different pressure nodes position may be induced, causing the x-ray absorbing particles 24-1, 24-2, 24-3, 24-4 to organize in walls that have a different position in each sub-reservoir 22-1, 22-2, 22-3, 22-4 in case one or more of the ultrasound generators 21-1, 21-3, 21-5, 21-7 are switched on.
In a preferred embodiment each ultrasound generator 21-1, 21-3, 21-5, 21-7 operates at the same settings and therefore generates the same soundwave and standing wave as the other ultrasound generators. In that case, the lateral shift distance d of the sub-reservoirs also results in the same shift in formed pressure node positions, when switched on.
Alternatively each ultrasound generator 21-1, 21-3, 21-5, 21-7 may operate at different settings to induce different soundwaves and standing waves to allow for more variation in pressure node positions and therefore stepping distances. However, this will entail more complex positioning and calibration.
In the example shown in
As is exemplary shown in
Preferably each sub-reservoir 22-1, 22-2, 22-3, 22-4 is equipped with means for flushing particles from the field of view (indicated by the thick dotted lines in
Each sub-reservoir 22-122-2, 22-3, 22-4 and connected ultrasound generator 21-1, 21-2, 21-3, 21-4, 21-5, 21-6, 21-7, 21-8 may also have an acoustic diode as described previously associated with them.
In a further embodiment of the phase stepping device 20 an additional pair of ultrasound generators 21-9, 21-10 are placed on adjacent walls of the reservoir 22, as is schematically depicted in
This allows to selectively extend phase stepping to the possibility of rotating the direction of the phase resolution by 90° (which requires rotating the other two gratings in the interferometer with the same amount, either mechanically or by the same electronics method). In this embodiment, only a pair of (opposing) transducers are active at any given time. In a further embodiment, all four transducers are switched on to implement inclinations of the structures by small angles. Depending on the used frequency and phase of each pair of ultrasound generators 21-1/21-2, 21-9/21-10 x-ray absorbent pillars are formed at pressure nodes caused by the two overlapping, orthogonal standing waves.
Acoustic diodes 30 may also be added to the second pair of ultrasound generators 21-9, 21-10 to avoid or reduce reflections of propagating ultrasound waves that may influence the formation and location of the x-ray absorbent grating structures 24.
In this example the orthogonally placed ultrasound generators (21-9, 21-10) were shown for the embodiment of two oppositely placed ultrasound generators (21-9, 21-10), but it would also be possible to adapt this to an embodiment based on stacked ultrasound generators, as depicted and described in relation to
Use of ultrasound generators 21-1, 21-2 as described in all embodiments (or even two orthogonal pairs 21-1/21-2, 21-9/21-10) as described previously results in fast, precise and fully electronic phase stepping.
Imagers equipped with a phase contrast grating arrangement and phase stepping device 20 may be used for regular transmission imaging as well. As mentioned previously, a transmission image is obtained simultaneously with the differential phase contrast and dark field signal, but the signal is incomplete due to attenuation of the gratings G0, G1, G2. For instance, when an analyzer grating G2 is present, then about 50% of the radiation reaching the analyzer grating G2 is attenuated just before it reaches the detector 14. This is particularly problematic when the imager is used for medical transmission x-ray imaging, since 50% of the dose that already passed the object is not used for the actual imaging, thereby unnecessarily exposing the object to too much harmful ionizing radiation.
To avoid this, the grating(s) G0, G1, G2 must be removed from the system, but this will cause extensive repositioning and calibration when the grating arrangement is used again for a later imaging procedure. With the known switchable grating, in the off-state the particles 24 are in suspension or they may have precipitated to the bottom of the reservoir. Since the x-ray absorbing particles still remain in the path of the x-ray beam 13, even in the off-state, they have a non-negligible x-ray absorption for radiation that already passed the object and to avoid this the known switchable grating must still be removed from the path of the radiation beam 13.
To obtain a true transmission image without attenuation by the x-ray absorbing particles 24 in the reservoir 22, they should be removed from the path of the x-ray beam when the transducer is switched off. It is therefore preferable to ensure that they are displaced out of the field-of-view of the x-ray beam 13. This may be achieved in many ways, for instance, by flushing the medium to a further reservoir, by sweeping the particles 24 towards a side of the reservoir (e.g. using a membrane-like structure) or by generating a propagating ultrasound wave from the ultrasound generator 21 that sweep the particles to a side of the reservoir outside the field-of-view of the x-ray beam.
In a method for phase contrast imaging using a device and method according to the presently claimed invention, first, the first ultrasound generator 21-1 is switched on (101) and a soundwave propagates into a reservoir filled with a medium 23 and x-ray absorbing particles, causing a standing wave and organization of the particles into x-ray absorbing wall-like structures at pressure nodes at a first node pattern in the medium, thereby forming a grating structure. Said grating structure is part of a phase contrast interferometer in a phase contrast x-ray imaging device.
Next an imaging procedure is started by introducing an object 50 (in case the object 50 was not yet present) in an examination region of the x-ray beam of the imaging device, switching on the x-ray beam and detecting (102) phase contrast imaging information of the object.
After a predetermined time a second ultrasound generator 21-2 opposite the first ultrasound generator 21-1 as described previously, modifies (103) the standing wave, causing the wall structures to shift to a next node pattern in which the nodes are shifted laterally compared to the previous node position. Further phase contrast information of the object is then detected (104).
After a predetermined time the ultrasound generator is switched off or removed (105) such that the standing wave transitions back to its form and the pressure nodes shift back to their initial positions. After which again phase contrast imaging information is obtained (102) of the object.
This sequence is repeated until the whole object 50, or at least the section of interest of the object 50, is imaged.
In an alternative embodiment the method for phase contrast imaging using a device and method according to the presently claimed invention, in a first step, the first ultrasound generator 21-1 is switched on (101) and a soundwave propagates into a first sub-reservoir 22-1 filled with a medium 23 and x-ray absorbing particles, causing a standing wave and organization of the particles into x-ray absorbing wall-like structures 24-1 at pressure nodes in the medium in the first sub-reservoir, thereby forming a grating structure. Said grating structure is part of a phase contrast interferometer in a phase contrast x-ray imaging device.
Next an imaging procedure is started by introducing an object 50 (in case the object 50 was not yet present) in an examination region of the x-ray beam of the imaging device, switching on the x-ray beam and detecting (102) phase contrast imaging information of the object.
After a predetermined time the first ultrasound generator 21-1 is switched off, thereby removing the x-ray absorbing wall structures 24-1 and simultaneously the second ultrasound generator 21-2, in this embodiment stacked above and shifted laterally with respect to first ultrasound generator 21-1 as described previously, is switched on (103), causing a standing wave in a second sub-reservoir 22-2, which is stacked above and shifted laterally compared to the first sub-reservoir 22-1, causing the wall structures 24-1 to form in the second sub-reservoir 22-2. These wall structures 24-2 are shifted laterally compared to the originally formed wall structures 24-1 in the first sub-reservoir 22-1, as seen from above in the direction of the incoming x-ray beam 13. Further phase contrast information of the object is then detected (104).
After a predetermined time the second ultrasound generator 21-2 is switched off and the first ultrasound generator (21-3) is switched (101) on again to form x-ray absorbing walls 24-1 in the original position, after which again phase contrast imaging information is obtained (102) of the object.
This sequence is repeated until the whole object 50, or at least the section of interest of the object 50, is imaged.
Preferably the x-ray absorbing particles 24-1, 24-2 are flushed from the sub-reservoir 22-1, 22-2 when the connected ultrasound generator 21-1, 21-2 is not switched on.
The latter embodiment of the method may easily be expanded to accommodate a sequence of switching on and off ultrasound generators 21-1, 21-2, 21-3, 21-4 associated with more than two stacked and laterally shifted sub-reservoirs 22-1, 22-2, 22-3, 22-4.
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.
The presently claimed invention is suitable for any kind of x-ray phase contrast imaging, such as 2D x-ray imaging, x-ray tomosynthesis or computed tomography.
The presently claimed invention allows for useful application in a clinical environment such as a hospital. More specifically, the present invention is very suitable for application in imaging modalities such as mammography, diagnostic radiology, interventional radiology and computed tomography (CT) for the medical examination of patients.
In addition, the presently claimed invention allows for useful application in a medical or non-medical (such as an industrial) environment. More specifically, the present invention is very suitable for application in medical scanning, non-destructive testing (e.g. analysis as to composition, structure and/or qualities of biological as well non-biological samples) as well as security scanning (e.g. scanning of luggage on airports).
The terms ‘object’ or ‘subject’ should each in light of the present invention be understood as an inanimate object, e.g. a material for structural or other testing or objects for security checks, or a human or animal subject for, for instance, a medical diagnosis imaging scan.
The terms ‘first’, ‘second’, ‘further’, etc. indicate options and are not limited to a particular sequence or order unless specified. The term ‘second’ may occur without the presence of a ‘first’.
The term substantially means at least >50%, preferably >75%, more preferably >85%, even more preferably >90% and most preferably >95%.
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 indefinite article “a” or “an” does not exclude a plurality. A single unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.
Number | Date | Country | Kind |
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18215305.6 | Dec 2018 | EP | regional |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2019/086137 | 12/19/2019 | WO | 00 |