CN101532969B - System and method for phase-contrast imaging by use of X-ray gratings - Google Patents

System and method for phase-contrast imaging by use of X-ray gratings Download PDF

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CN101532969B
CN101532969B CN 200810166472 CN200810166472A CN101532969B CN 101532969 B CN101532969 B CN 101532969B CN 200810166472 CN200810166472 CN 200810166472 CN 200810166472 A CN200810166472 A CN 200810166472A CN 101532969 B CN101532969 B CN 101532969B
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ray
absorption grating
object
described
detected
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CN 200810166472
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CN101532969A (en
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康克军
黄志峰
张丽
陈志强
李元景
刘以农
赵自然
刑宇翔
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同方威视技术股份有限公司
清华大学
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    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B6/00Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
    • A61B6/48Diagnostic techniques
    • A61B6/484Diagnostic techniques involving phase contrast X-ray imaging

Abstract

The application relates to a system and a method for the phase-contrast imaging by use of X-ray gratings. The system comprises an X-ray device, a first absorption grating, a second absorption grating, a detection unit, a data processing unit and an imaging unit, wherein the X-ray device transmits an X-ray bundle to a detected object; the first and second absorption gratings are positioned in the direction of the X-ray bundle; the X-ray refracted by the detected object forms an X-ray signal with variable intensity through the first absorption grating and/or the second absorption grating; the detection unit receives and converts the X-ray with variable intensity into an electrical signal; the data processing unit processes and extracts refraction-angle information in the electrical signal, and utilizes the refraction-angle information to figure out pixel information; and the imaging unit constructs images of the object. In addition, the system and the method can also realize CT imaging by using a rotating structure to rotate the object so as to obtain refraction angles in a plurality of projection directions and the corresponding images, and use CT reconstruction algorithm to figure out refraction-index fault images of the detected object. According to the invention, the phase-contrast imaging of approximate decimeter-magnitude viewing fields under incoherent conditions can be realized by use of common X-ray machines or multi-seam collimator such as source gratings, as well as two absorption gratings.

Description

X ray grating contrast image-forming system and method

Technical field

The present invention relates to the perspective imaging field, be specifically related to X ray object be carried out photographing imaging and CT imaging.

Background technology

Traditional x-ray imaging technology is to utilize material to come non-destructive ground to check the inner structure of object to the attenuation characteristic of X ray.If the density variation that the each several part structure of interior of articles forms is obvious, then the effect of traditional x-ray imaging technology is particularly remarkable.But with the material that light element (for example hydrogen, charcoal, nitrogen and oxygen) consists of, they are weakly absorbing materials to X ray, so almost can't see the concrete structure of their inside with traditional x-ray imaging technology.Even with other auxiliary means, for example stamp contrast preparation to biological tissue and also be difficult to obtain clearly image.

Middle 1990s, because the development of third generation Synchrotron Radiation, HARD X-RAY PHASE-CONTRAST imaging (phase-contrast imaging is called for short phase contrast imaging) technology is arisen at the historic moment.The phase contrast imaging technology is observed the electron density variation of interior of articles exactly by the phase shift information that catches X ray, thereby discloses the inner structure of object.The phase contrast imaging technology makes the spatial resolution of x-ray imaging be advanced to micron dimension even nanometer scale by the millimeter magnitude, and with the light element material of the detectable material scope of x-ray imaging by absorption a little less than the high heavy element material that absorbs of X ray is expanded to.

So far, by the radiogenic high brightness of synchrotron radiation and good coherence, the phase contrast imaging technology has developed at least 4 kinds formation method: interferometric method, quasi-coaxial imaging, diffraction enhanced imaging and optical grating contrast imaging etc.These technology are compared with various existing imaging techniques such as traditional X-ray radial imaging technology, MRI technology, ultrasonic techniques has unique advantage, and therefore, the phase contrast imaging technology has become one of technology of forefront in the x-ray imaging field.Yet the phase contrast imaging technology requires the harshness of x-ray source and self imaging characteristics, has greatly limited its clinical practice medically.

At first, from the x-ray source aspect, the involving great expense of Synchrotron Radiation, bulky, visual field little (ten millimeters magnitudes) limited its range of application.It is microfocus X-ray source that another one is selected, and the X ray that it sends has partial coherence, can realize phase contrast imaging.But microfocus X-ray source brightness is very low, so detector needs the time shutter quite to grow (tens seconds even a few minutes), and this also is that clinical practice institute is flagrant.If can realize phase contrast imaging at general X-ray production apparatus, will be the thing that actual value and meaning are arranged very much so.

Secondly, from the own characteristic of phase contrast imaging method, interferometric method, quasi-coaxial are subject to certain restrictions in actual use.Because interferometric method, quasi-coaxial imaging are obtained phase information by interference or the Fresnel diffraction phenomena of observing relevant X ray, all need to have the very x-ray source of high spatial coherence and the detector that resolution reaches micron dimension.But these two kinds of devices are all very expensive, and the area of the detector of micron resolution generally all very little (about several square centimeters), and this visual field that has just determined whole imaging system is also smaller, thereby can not do the imaging inspection of large sample.Although the diffraction enhanced imaging method can realize the imaging that the object edge of high-contrast (density resolution) strengthens with general X-ray production apparatus and the so not high detector of resolution, but the monochrome effect of monochromating crystal is so that the visual field is flat little in the light path, and monochromatic light brightness reduces.Therefore, these phase contrast imaging methods have certain limitation in clinical medicine is used.

In 2002, the man-years such as David C of Switzerland PSI (Paul Scherrer institute) have realized the hard X ray optical grating contrast formation method based on optical grating diffraction Tabot effect first on the upper light path with 2 phase gratings and 1 analyzing crystal formation of ESRF (European Synchrotron Radiation Facility, European Synchrotron Radiation).2003, the people such as Momose A of Japan also launched the research based on the optical grating contrast formation method of phase grating and absorption grating on Spring-8, proposed to extract with two gratings the technology of single order phase information.In 2003, the people such as the Weitkamp T of Switzerland PSI and Pfeiffer F realized the phase contrast imaging technology based on 2 gratings equally on SLS (Swiss Light Source, Switzerland's light source) and ESRF on the basis of David C work.Yet said method all is based on the synchrotron radiation radiographic source and carries out, and the visual field is all very little, has greatly limited the application of phase contrast imaging.

In 2006, the people such as Pfeiffer F have obtained important breakthrough in 2006, they use three blocks of different gratings of function to realize optical grating contrast formation method based on general X-ray production apparatus, overcome the little shortcoming in diffraction enhanced imaging method visual field, obtain the large small field of view near 64mm * 64mm, from then on opened up practicable road for the practical application of phase contrast imaging technology.But the imaging time of the grating contrast image-forming system that they build long (time shutter is 40 seconds) can't carry out experiment made on the living.This method has used source grating (sourcegrating) the X-ray production apparatus radiographic source to be divided into a series of width are between 25 microns to 50 microns, mutual incoherent line radiographic source.The radiogenic X ray that sends of single line is partial coherence, produces the Talbot effect with the phase grating effect.In itself, the incoherent light generating portion coherence that this formation method utilizes the source grating that general X-ray production apparatus is sent, the Talbot effect of recycling optical grating diffraction realizes phase contrast imaging.

Therefore, the essence of existing existing all phase contrast imaging method (comprising the optical grating contrast formation method) is to utilize the interference of X ray of relevant or partial coherence or the low contrast resolution (namely density resolution) that diffraction phenomena comes the enhanced rad image.Because the X ray that general X-ray production apparatus sends is that polychrome, non-space are relevant, according to the Talbot effect principle, for existing optical grating contrast imaging technique, must realize with the grating of 3 difference in functionalitys, and, distance between phase grating and the absorption grating (being called as the Talbot distance) must be chosen appropriate, could satisfy the imaging requirements of Talbot effect under the polychrome condition.In order to be implemented in the optical grating diffraction of hard X ray, very high requirement has been proposed for the making of grating: the precision in micron dimension cycle, large depth-to-width ratio.These unfavorable factors will greatly limit the optical grating contrast imaging technique in medical science and industrial practical application.

Summary of the invention

The present invention proposes a kind of phase contrast imaging system that adopts non-coherent approaches to realize, it uses two absorption gratings in polychrome, the relevant lower single order differential phase shift information that obtains after X-ray passes object of radiographic source (general X-ray production apparatus) of non-space, thereby rebuilds thus the image of object.

According to an aspect of the present invention, a kind of X ray grating contrast image-forming system is provided, being used for that object is carried out imaging detects, this system comprises: the X ray emitter, be used for to the object to be detected emitting x-ray, wherein in large focal spot light source situation, can add and stitch collimating apparatus (being the source grating) more one and produce one group little focal line light source with to the object to be detected emitting x-ray; The first and second absorption gratings, the two is positioned on the X ray direction successively, forms the X ray signal of Strength Changes via this first and second absorption grating through the X ray of object to be detected refraction; Detecting unit receives the X ray of described Strength Changes, and the X ray signal is converted to electric signal; And data processing unit, process described electric signal, extract the refraction of X-ray angle information in the electric signal, and utilize described refraction angle information to obtain the Pixel Information of object; Image-generating unit utilizes described Pixel Information to rebuild the X ray projected image of object.

According to a second aspect of the invention, provide a kind of X ray that utilizes that object is carried out the method that imaging detects, the method comprises: to the object to be detected emitting x-ray, wherein can add more than one seam collimating apparatus (being the source grating) and produce one group little focal line light source with to the object to be detected emitting x-ray in large focal spot light source situation; Make the X ray signal that forms Strength Changes through the X ray of object refraction via the first and second absorption gratings; Receive the X ray of described Strength Changes, and the X ray signal that receives is converted to electric signal; And from the electric signal of described reception, extract X-ray beam through the refraction angle information of object, and utilize predetermined algorithm to draw the Pixel Information of object.

According to a third aspect of the invention we, a kind of X ray optical grating contrast CT imaging system is provided, it also comprises a rotational structure except comprising that the described system of first aspect forms, be used for so that detected object is rotated with respect to x-ray source and grating, detecting unit etc.Described CT imaging system can by the detected object of rotation, obtain refraction angle information and corresponding planar pixel information under each projection angle, and then utilize pre-defined algorithm to come the faultage image of the index distribution of reconstruction of objects inside under the CT pattern.

The advantage of maximum of the present invention is the dependence of being completely free of the radiographic source coherence, does not have the restriction of Tablot distance, and can use the grating in above cycle of micron dimension to realize phase contrast imaging under the incoherent condition of nearly decimetre magnitude visual field.Compare with the traditional X-ray radial imaging, native system can carry out the imaging of high-contrast to weakly absorbing material (soft tissues such as mammary gland, blood vessel and muscle, fibrous material, insect etc.).Compare with existing phase contrast imaging, need not to consider coherence's condition of light source, also reduced simultaneously the manufacture difficulty requirement of micron dimension cycle, large depth-to-width ratio grating, and can be generalized at an easy rate use high-energy (〉 40keV) X-ray carries out phase contrast imaging.And phase contrast imaging system of the present invention and the natural compatibility of traditional X-ray radiation imaging system only need to be set up two raster translation rotary systems at the traditional X-ray radial imaging and can be realized.The present invention will further reduce the threshold of phase contrast imaging practical application, and developing brand-new thinking and approach are used in the fields such as medical science, biology, industrial materials of moving towards for phase contrast imaging, have great practical significance and using value.

Description of drawings

Fig. 1 illustrates the synoptic diagram of grating contrast image-forming system of the present invention;

Fig. 2 is illustrated under the radiographic source illuminate condition of different focal spot sizes, corresponding simulation light intensity curve when two gratings use the phase place stepping technique;

Fig. 3 illustrates the wave front situation of change behind X-ray and the object interaction;

Fig. 4 illustrates the synoptic diagram that X ray is reflected by object;

Fig. 5 illustrates " optical gate " effect to X ray of two absorption gratings;

Fig. 6 a and Fig. 6 b illustrate respectively the dual mode according to CT pattern of the present invention;

Fig. 7 be illustrated in when utilizing the raster phase stepping technique certain point on the detection faces through after the testee refraction with without the refraction situation under the comparison of light intensity curve of the X ray that detects;

Fig. 8 a-8d illustrates respectively three examples using the refraction angle reconstructed image;

Fig. 9 illustrates the synoptic diagram that uses More's striped that interferometric method is surveyed among the present invention;

Figure 10 illustrates according to an embodiment of the invention synoptic diagram, wherein adds the collimating apparatus (being the source grating) of seam more than in the radiographic source front; And

Figure 11 illustrates according to another embodiment of the present invention synoptic diagram, and wherein testee is placed between two absorption gratings.

Embodiment

Conceive a kind of X ray grating contrast image-forming system of design according to the present invention, shown in accompanying drawing 1, it mainly comprises following part:

X ray emitter (representing with radiographic source among Fig. 1), it is used for to object to be detected (figure represents with object) emitting x-ray, wherein can add to stitch collimating apparatus (being the source grating) more one and produce one group little focal line light source with to the object to be detected emitting x-ray in large focal spot light source situation; (be expressed as respectively in the drawings grating A and grating B, its cycle is respectively p to the first and second absorption gratings 1, p 2), it is positioned on the transmit direction of X-ray beam abreast successively; Detecting unit represents with detector among the figure, is used for receiving described X ray, by signal switch technology (for example, digitized photography technology (DR)) the X ray signal is converted to electric signal; And data processing unit (also not shown among the figure), be used for calculating X ray through the light intensity change information behind the object to be detected from described electric signal, and utilize described light intensity changing value to calculate the refraction angle information of X ray, and utilize the refraction angle information calculations to go out the Pixel Information of described object to be detected; The image-generating unit (not shown) is rebuild the image of object and is demonstrated according to described refraction angle information (Pixel Information).

As described later, in the CT of X ray grating contrast image-forming system use pattern, can obtain the refraction angle information on a plurality of projecting planes, old complaint utilizes predetermined C T composition algorithm to come the faultage image of the index distribution of reconstruction of objects inside according to described refraction angle information.

Now further specify with regard to each ingredient and concrete operations.

The X ray emitter

Be different from the 3 optical grating contrast imaging techniques of mentioning in the background technology of front, phase contrast imaging of the present invention can use noncoherent radiographic source direct irradiation.That is to say that phase contrast imaging technology of the present invention does not rely on radiogenic coherence (comprising temporal coherence and spatial coherence), also do not need to consider optical grating diffraction or Talbot effect, also can obtain phase contrast image.When not needing to consider the coherence of X ray, imaging system can be described with the approximation in geometric optics theory.According to the optical diffraction principle, the condition that X ray and grating A do not produce diffraction is:

p 0 > > l p 1 λ - - - ( 1 )

Can find out, be p when the cycle of grating A 1Larger, then the value on equation right side is less, so the present invention adopts the phase contrast image that also can be met requirement than the grating of large period.The cycle of supposing grating A is 20 microns, and radiographic source is to 2 meters of grating distances, then

And at least tens microns of focal spot sizes of general X-ray production apparatus or more than the hundreds of micron, so general X-ray production apparatus satisfies the requirement of system of the present invention.The grating in 20 microns cycles requires the grating in 2 or 4 microns cycles to compare with existing optical grating contrast imaging technique, and manufacture difficulty will reduce greatly.

Yet, be not that the ray source focus size is larger just better yet, it is limited by the accuracy requirement of the phase place stepping technique of two absorption gratings.Shown in Figure 2, be to be respectively 20 microns and 22 microns in for example cycle of two absorption gratings, the source is to 2 meters of grating A distances, between two gratings during 0.2 meter of distance, under the radiographic source illuminate condition of different focal spot sizes, when using the phase place stepping technique, put on two gratings corresponding simulation light intensity curve.Wherein horizontal ordinate is step size (0.5 micron/step), and ordinate is light intensity value.Be noted that the result according to formula (2) estimation, focal spot size is that the X ray that 1 micron radiographic source sends is concerned with, but for convenient and compare than the radiographic source of large focal spot, too the acquisition under approximation in geometric optics.Find that from Fig. 2 focal spot size is larger, light intensity curve is just more level and smooth, until focal spot size becomes straight line when equaling 220 microns.That is to say that the phase place stepping technique no longer works.When focal spot size during greater than 220 microns, light intensity curve presents other variation tendency.The critical value that can extrapolate the ray source focus size is p 0, critical:

p 0 , critical = l d p 2 - - - ( 3 )

According to shown in Figure 2 because change when focal spot size still has light intensity during greater than this critical value, still can obtain according to this point the image of phase contrast effect, but the contrast effect when focal spot size less than p 0, criticalSituation to get well.According to the above results, can draw, at p 0, criticalIn the scope, focal spot size is less, and light intensity curve is steeper, and the contrast of the phase contrast image that extracts so is also higher.Under the preferable case, ray source focus size p 0Requirement is no more than p 0, criticalHalf.Certainly, if ray source focus size p 0Greater than this critical value, also can adopt other modes to solve this problem.Wherein a kind of method is greater than p in focal spot size 0Radiographic source before place many seam collimating apparatuss (being the source grating) (for example, shown in Figure 10), its period p s=Mp 0, critical, M=1,2,3 ....So large radiographic source is subdivided into the little focal line radiographic source of a series of equivalences, in order to improve image contrast, the radiogenic focal spot size size of each little focal line p 0, iAlso require to be no more than p 0, criticalHalf.Certainly, the ray source focus size also can be greater than p 0, critical, the contrast of phase contrast image is decided by at that time light intensity curve like this.Nature, it will be appreciated by those skilled in the art that, in the situation that adopts many seam collimating apparatuss (being the source grating), described apart from l be actually grating A with should the distances of stitching between the collimating apparatuss (being the source grating) more, rather than and actual radiographic source between distance.It is conventionally known to one of skill in the art placing the method that many seam collimating apparatuss (being the source grating) form the light source with expectation focus size before radiographic source, therefore will no longer describe in detail here.

Because radiographic source can be the larger x-ray source of focal spot size, therefore common commercial X-ray production apparatus can meet the demands.Be different from the traditional X-ray radial imaging, the operating voltage of phase contrast imaging technical requirement x-ray apparatus of the present invention is preferably disposed under the 5-40kVp condition that (concrete numerical value is by the highly decision of gold of absorption grating, the height that is to say gold is higher, and the operating voltage that permission is used is then higher).

Preferably, native system is fit to use little focus source, and its focal spot size is preferably between the 10-1000 micron.If but used little focus device (focus is less than 10 microns), then because radiogenic spatial coherence increases, absorption grating will produce the Talbot effect.The principle of the optical grating contrast method of this situation and Pfeiffer F is consistent.Like this, an other absorption grating only is placed on the location point of Talbot distance just can have reasonable imaging effect.If the use focus is greater than 100 microns x-ray apparatus, soft edge can increase so, thereby is unfavorable for the enhancing of image contrast.For this situation, can place in the radiographic source front many seam collimating apparatuss (being the source grating) (the width size of every seam is between the 10-200 micron), as shown in figure 10, its period p s=Mp 0, critical, M=1,2,3 ....So large radiographic source is subdivided into the little focal spot size line radiographic source of a series of equivalences, although the spatial resolution of image is still determined by the ray source focus size, but the high image of contrast that each line radiographic source produces is superimposed, and still can obtain a phase contrast image that contrast is quite high.

The grating part

The X-ray beam of general X-ray production apparatus emission can be fan-beam, cone-beam or collimated beam.Cone-beam preferably among the present invention, so the cycle of two absorption gratings adopting of the phase contrast imaging of the present invention system geometric proportion relation of also preferably will hoping for success, that is:

p 1 p 2 = l l + d - - - ( 4 )

Wherein, l is the distance that radiographic source arrives first grating A, and d is the distance between two absorption grating A and the B.

Therefore, compare with original optical grating contrast imaging technique, phase contrast imaging of the present invention take a picture and the CT system between two gratings apart from d, irrelevant with the wavelength X of the X ray of launching, therefore with the Talbot range-independence, can be decided by formula (3) and (4) according to the actual conditions demand.

And for example shown in Figure 1, grating department divides and comprises two absorption gratings, grating A and grating B, and it is combined with the single order phase place change information that passes the X ray of object for extraction.Particularly, for absorption grating, general using MEMS technology powers in silicon chip substrate and plates heavy metal material (for example Au) lines as the grating lightproof part; Also can use at heavy metal material in addition and depict grating.Grating A and grating B plane all are parallel to detector plane (XY direction).The size of grating has determined the visual field size of whole phase contrast imaging system.Illustrate, if the substrate of grating is 4 inch silicon chips, then the visual field of system is in the scope of diameter 10cm.

Preferably, the cycle of two absorption gratings is between the 0.1-30 micron.Described grating uses heavy metal as absorbing material, and take gold (Au) as example, the height of gold is determined by the energy of the X ray that uses, between the 10-100 micron.For example, concerning the X ray of 20keV, the height of gold can stop 90% X ray greater than 16 microns, can obtain so the reasonable phase contrast image of contrast.Wherein, the cycle of grating A is p 1, the cycle of grating B is p 2, dutycycle (dutycycle) is generally 1, also can be other dutycycle.As shown in Figure 1, the distance between two gratings is d.

Detecting unit

Detecting unit comprises detector, thus represent described detecting unit with detector among Fig. 1, for detection of with the record X ray wave front on Strength Changes.Preferably, described detector can be matrix detector, and wherein each surveyed unit can detect the Strength Changes that is mapped to the X ray on this unit.(X ray) detector in the native system, compare with other phase contrast imaging method, less demanding to the spatial resolution (pixel size) of detector: needn't require the high resolving power of tens microns even several microns, but can only use the resolution of tens microns or hundreds of micron dimension.Certainly, if the spatial resolution of detector is higher, then the information of final phase contrast image is more clear.Because the advantage of phase contrast imaging is to improve the density resolution of image (contrast resolution), so digitized photography technology DR has higher requirement (〉 12bits to the dynamic range of detector).Each surveys unit can detect the light intensity variation (as shown in Figure 7) that is mapped to the X ray on it.Wherein, light intensity can change electric signal into.

Extract X-ray beam through the refraction angle information of object

Now with way of example, the single order phase information of utilizing digitized photography technology (DR) for example to extract X ray from the signal that receives is described, and and then obtains refraction angle information.

As everyone knows, X ray has " wave-particle duality ".With undulatory property, X ray possesses transmission, reflection, refraction, polarization, the relevant and fluctuation properties such as incoherent scattering, diffraction.When X ray passed jobbie, the amplitude of X ray weakened its absorption because of object; Simultaneously, X ray and material atom coherent scattering make X ray produce phase shift (phaseshift), and the wave front that shows as X ray on the macroscopic view produces distortion.That is to say that refraction effect has occured X ray, as shown in Figure 3 when passing object.On macroscopic view, the interaction between X ray and the material can be described with the complex index of refraction n of material to X ray:

n=1-δ-iβ??(5)

Wherein δ is relevant with the phase shift cross section p of material, and β is relevant with the linear absorption coefficient μ of material, the following expression of the relation between them

p = 2 πδ λ , μ = 4 πβ λ - - - ( 6 )

Wherein λ is the wavelength of X ray, and δ is called as phase factor, and β is called as absorption factor.Concerning X ray, δ is generally 10 -5About, thus n less than 1, thereby small refraction only occurs in X ray on the material interphase, available refraction angle Δ θ represents (being about the microradian magnitude).Suppose that on the two Dimensional XY plane X ray is propagated along the Cartesian coordinates X-direction, as shown in Figure 4, the refraction angle that the propagation of the X ray that is reflected by object departs from original direction is approximately

Δθ ≈ λ 2 π ∂ Φ ( y ) ∂ y - - - ( 7 )

Wherein Φ (y) expression X ray is along the total phase shift on the travel path M.The phase shift of the X ray of process interior of articles geometric point is p (x, y) dx, then can try to achieve total phase shift along the travel path integration and be

Φ ( y ) = ∫ M p ( x , y ) dx = 2 π λ ∫ M δ ( x , y ) dx - - - ( 8 )

Convolution (7) and (8) draw

Δθ = ∫ M ∂ δ ( x , y ) ∂ y dx = - ∫ M ∂ n ( x , y ) ∂ y dx - - - ( 9 )

Formula (9) shows that refraction angle Δ θ is the integration along travel path of interior of articles refractive index single order differential.As long as we can measure the refraction angle Δ θ of refraction X ray, just can and solve the distribution of interior of articles refractive index n in conjunction with phase contrast CT method for reconstructing according to formula (9).

Therefore, how measuring refraction angle Δ θ is the core of two optical grating contrast imaging techniques of the present invention.Theoretical according to approximation in geometric optics, the effect of two absorption gratings quite " optical gate " is the same.In the time of two absorption grating relative motions, the grating pair X ray closes when opening just as gate the time, thereby causes that the light intensity in the detection unit of detecting unit changes.For example referring to shown in Figure 5, observe from the 2 d plane picture of two grating contrast image-forming systems.Illustrate, do not having in the situation of object, X ray 1 is blocked namely by grating A and is absorbed by Au, and X ray 2 is not blocked by two gratings and the smooth detection unit that arrives.After putting object in light path, the refraction angle after X ray 1 is reflected by object is Δ θ 1, the refraction angle after X ray 2 is reflected by object is Δ θ 2At this moment situation changes, and X ray 1 blocks the arrival detector because of what two gratings were avoided in refraction smoothly, thereby 2 of X ray are blocked by Au by grating B and absorb.So, the light intensity that detects of detector changes the situation that X ray is reflected by object that reflected.

Particularly, for example utilize digitized photography technology (DR) can draw refraction angle information by phase place stepping technique or More's interferometry.

It should be noted that the radiographic source that the optical grating contrast imaging that the present invention relates to is used is the polychrome radiographic source, so the information that obtains of native system all is refraction angle information (the Δ θ under average energy (λ) meaning λ), the single order phase information ( ) and refractive index information (n λ).

For helping to understand better the present invention, the below discusses respectively above-mentioned phase place stepping (Phasestepping) technology and More's interferometry (Moire interferometry).

The phase place stepping technique

For system shown in Figure 5, two gratings (A, B) relative motion: for example, grating A maintains static, grating B along directions X in the grating period p 2Translation N in the distance range (N〉1) step (also can maintain static by grating B, grating A is along the directions X stepping).Every one step of translation of grating B, image of system acquisition; After collection N opens image in the translation distance scope, can obtain each pixel (each point on the test surface of detector) in the distribution situation of grating light intensity curve in the cycle.The shape that this light intensity changes function is similar to sine function:

Wherein A represents amplitude, B and grating Periodic correlation, The expression phase place.Illustrate, the light intensity curve of getting certain pixel of certain inner pixel of plastic pattern (seeing accompanying drawing 8a) and background parts compares, and sees Fig. 7 (for showing better difference, two grating relative translations a semiperiod).Can find that from Fig. 7 after X ray was reflected by object, its light intensity curve with respect to the light intensity curve of background movement had occured.Light intensity curve can be described with sine function, and the mobile Δ f correspondence of light intensity curve the phase place variation of sine function so Obviously, as two grating relative motion one-period p 2, sine function phase place then Change 2 π, so have

And Δ f causes owing to X ray is refracted, and the relation at it and refraction angle is:

Δf=dΔθ(12)

Association type (11) and (12) have

Thus, obtain the phase place variation of refraction angle and X ray Between relation, and Also can be by comparing and calculating.

Illustrate at following experiment condition: the focal spot size of x-ray source is 170 microns, and grating A and grating B cycle are respectively 20 and 22 microns, and source and grating A are 1916.4mm apart from l, and two gratings are 191.6mm apart from d, 127 microns of detector resolutions.The X ray emitter is set to high pressure 27kVp, electric current 9.6mA.1 micron of the step-length of two grating relative motions, altogether 22 steps of stepping, per step gathers a data for projection.Testee is the plastic pattern (shown in Fig. 8 a) of 1 centimetre of diameter.For eliminate the impact of noise as far as possible, every projected image gathers altogether 400 images and superposes.The refraction angle image that calculates according to formula (13) at last is shown in Fig. 8 b.Find from Fig. 8 b, showed the edge clear of three hole ground structures of plastic pattern inside.Fig. 8 c and 8d have shown the rear solid end of the mouselet of measuring and the refraction angle image of tail under same system condition.

More's interferometry

So that grating A and grating B are substantially parallel, but both relatively rotate a minute angle ε.Principle according to the More interferes after these two blocks of gratings are arrived in x-ray bombardment, can observe Moire fringe on detector, fringe period is

w = p 2 ϵ - - - ( 14 )

As shown in Figure 9.As seen, ε is less, and w is larger.When X ray after object refraction, its corresponding Moire fringe also will produce corresponding deformation, establishing its side-play amount is Δ f, but then refraction angle through type (15) is obtained:

Δθ = ϵλΔf 2 πd - - - ( 15 )

Also can calculate refraction angle information thus.

Comprehensively above-mentioned, can obtain required refraction angle information by two kinds of information extraction technologies.

Image shows

Refraction of X-ray angle (Δ θ) information of utilizing preceding method to obtain can be passed through certain algorithm, and for example linear mapping method, the algorithm of tabling look-up wait the Pixel Information that draws on this aspect.For example, can utilize the formula of linear mapping method calculating pixel value to realize:

Z = ( Δθ ) j - ( Δθ ) min ( Δθ ) max - ( Δθ ) min × 255 - - - ( 16 )

Wherein, z is the pixel number in the 0-255 scope.Like this, the refraction angle Δ θ that occurs through the every bit on the object of X ray just can be converted into the Pixel Information of this point.The Pixel Information about the object every bit that utilization obtains can draw the image pixel value of object and shows at display.

The CT image reconstruction

Source Optical grate detector three is motionless, rotating object; Perhaps object is motionless, and source Optical grate detector three rotates around object simultaneously, all can realize the phase contrast CT imaging to object.

To each projection angle φ, all adopt phase place stepping technique or More's interferometry to calculate the refraction angle information Δ θ of current projection angle φ:

Δ θ φ = ∫ M ▿ δ ( x , y , z ) dl - - - ( 17 )

Wherein l represents the x-ray spread path.

And the data for projection expression formula based on linear attenuation coefficient of traditional CT technology is

U = ∫ M μ ( x , y , z ) dl - - - ( 18 )

Wherein U represents I and I 0Be respectively output intensity and incident intensity.We find that formula (17) is very similar with formula (18).Therefore can use for reference the traditional CT reconstruction algorithm and rebuild the refractive index n of object (or phase factor δ) distribution.

As shown in Figure 6, two optical grating contrast CT imaging systems of the present invention, according to object rotary middle spindle and grating parallel direction (Z direction among Fig. 1) mutual relationship, the CT pattern can be divided into 2 kinds of modes: the mode (parallel mode is shown in Fig. 6 a) that object rotary middle spindle and grating parallel direction are parallel to each other; Object rotary middle spindle and the mutually perpendicular mode of grating parallel direction (vertical mode is shown in Fig. 6 b).The phase contrast CT reconstruction formula of this dual mode is different.

1) parallel mode

In parallel model, refraction angle information Δ θ ψCan regard a vector in XOY plane as, its direction vector is all the time perpendicular to projecting direction.Therefore, Δ θ φDirection vector can change along with the change of projecting direction, therefore just can not directly use the decay reconstruction algorithm (μ does not change with projecting direction) of CT of tradition to calculate refractive index n (or the phase factor δ) faultage image of object.And because adopting the CT reconstruction algorithm for single order differential projection data, need to use Hilbert (Hilbert) wave filter that single order differential projection data are carried out filtering, and then back projection, reconstruct refractive index n (or phase factor δ) faultage image.

If the distance between radiographic source and the object is distant, and in the less situation of radiographic source subtended angle, can come approximate reconstruction refractive index n (or phase factor δ) faultage image with the collimated beam CT reconstruction formula of single order differential projection data:

δ ( x , y ) = 1 2 π ∫ 0 π dφ ∫ - ∞ ∞ { Θ l ′ ′ ( ρ , φ ) · [ - jsign ( ρ ) ] } e j 2 πρ ( x cos φ + y sin φ ) dρ - - - ( 19 )

Wherein sign ( &rho; ) = 1 , &rho; > 0 - 1 , &rho; < 0 . Formula (19) is to describe in Frequency Domain Polar system.-jsign (ρ) namely is Hilbert (Hilbert) filter function. Refraction angle Δ θ φRepresentation on Frequency Domain Polar.

Certainly also can directly adopt the fan beam CT reconstruction formula of single order differential projection data to rebuild refractive index n (or phase factor δ) faultage image, its reconstruction formula is described as at the real number field polar coordinates

Wherein, Θ (φ, s) is refraction angle Δ θ φAt the real number field polar coordinate representation.R is the distance of source and object, and D is the distance of source and detector, and s is the distance at the pixel range finder center on the detector, and U is back projection's weight factor:

What in fact radiographic source emitted is cone-beam X-ray, therefore can directly adopt cone-beam CT reconstruction formula refractive index n (or the phase factor δ) faultage image of single order differential projection data, and its reconstruction formula is explained with the FDK type:

Wherein,

Y &prime; = - D r &RightArrow; &CenterDot; y ^ &prime; R + r &RightArrow; &CenterDot; x ^ &prime;

Z &prime; = - D r &RightArrow; &CenterDot; z ^ R + r &RightArrow; &CenterDot; x ^ &prime;

&Theta; &OverBar; &phi; ( Y &prime; , Z ) = &Integral; - &infin; &infin; dY 1 Y &prime; - Y &times; &Theta; &phi; ( Y , Z ) D 2 R 2 + Z 2 D 2 ( 1 + Z 2 / R 2 ) + Y 2

Θ φ(Y, Z) represents the refraction angle, The specified point of space vector, Be the x-ray spread direction in the projection on x-y plane, It is the neutralization of x-y plane Vertical direction, R is distance between radiographic source and object, and D is the distance between radiographic source and detector, and Y represents the horizontal ordinate of detector cells, and Z represents the ordinate of detector cells.

2) vertical mode

In parallel model, refraction angle information Δ θ ψCan regard one as perpendicular to the vector (Z direction) in XOY plane, it does not change and changes along with projecting direction, therefore can directly adopt the collimated beam of traditional CT the inside, and the reconstruction formula such as fan-beam or cone-beam reconstruct (or phase factor ) faultage image.

Need to prove that in two optical grating contrast imaging photographics of the present invention and the CT system thereof, object to be detected also can be placed between two absorption gratings, as shown in figure 11, principle equally also can obtain phase contrast image as mentioned above.

According to the present invention, the CT scan mode can be divided into two kinds, and namely source and detector are motionless, object self rotation; Perhaps object is motionless, and source and detector rotate around object.Be the function that realizes automatically detecting, X ray grating contrast image-forming system of the present invention further comprises mechanically actuated system, be subjected to the control of the control module of imaging system of the present invention, this mechanically actuated system comprises: whirligig is used for only making object to be detected that relatively rotation occurs.At this moment, perhaps only have detected object to rotate, and X ray emitter-grating-detecting unit maintenance is motionless; Perhaps, X ray emitter-grating-detecting unit whirligig, and the object maintenance is motionless.Be inconvenient to rotate at object to be detected, when for example object to be detected was too huge, this was especially easily.Certainly, described thing platform whirligig and X ray emitter-grating-detecting unit whirligig can be present in this Machinery Control System simultaneously, perhaps can only adopt wherein a kind of device.

Multiple concrete grammar about processes pixel has been arranged in the prior art, and such as stretching and the pixel of outstanding certain part etc., the present invention can use for reference use herein.Above-mentioned processing procedure can realize by computing machine, wherein can process the data for projection that obtains, comprise that original data processing and demonstration, refraction angle information extraction, birefringence angular projection data reconstruction go out subject image and drawing three-dimensional stereo-picture etc., and show by display.Namely, related data processing unit and the display unit of the application can be by computer realization.Computing machine can be high performance single PC, also can be workstation or a group of planes.Display can be that the CRT traditional monitor also can be liquid crystal display.In addition, detecting unit and data are processed and display unit can be integrated on the equipment.

In sum, utilize X ray phase contrast imaging provided by the invention system, can realize two kinds of imaging patterns, i.e. photographing imaging pattern and CT imaging pattern, it can realize respectively planar imaging and three-dimensional imaging for detected object.

Embodiment 1

Under the photographing imaging pattern, detected object is relatively fixing, then adopt phase place stepping technique or More's interferometry, gather X ray through the refraction angle information behind the object, and utilize the refraction angle information of each point that object is carried out the radioscopy imaging, thereby obtain the plane picture of this object.

If the detector that wherein uses is X-ray film or PI plate or DR detector device, the fluoroscopy images of the object in the time of can obtaining the specific relative position of two gratings.Single fluoroscopy images has shown the enhancing effect of similar single order differential on the border of each structure of interior of articles.If the DR detector device can use the refraction angle image (phase contrast image) that adopts phase place stepping technique or More's interferometry to calculate object.

Embodiment 2

Under the CT imaging pattern, object to be detected should be able to rotate with respect to other parts of system such as grating, radiographic source.So, for object to be detected arranges a kind of wheelwork, be used for rotating detected object, or a kind of rotational structure is set, and radiographic source, grating etc. relatively rotate so that detected object is motionless.Described wheelwork or rotational structure do not illustrate in the drawings, and it can have multiple implementation according to existing common practise.And such wheelwork or structure are connected with the control section of imaging system, adapt so that rotation is moved with system's (stepping and other).According to phase contrast CT image-forming principle, this CT imaging that utilizes system of the present invention to carry out object can obtain each projecting direction of object is carried out the X ray planar imaging, the CT reconstruction process of then all directions plane projection data that obtain being correlated with, thereby obtain the faultage image of the refractive index of object to be detected, or stereo-picture.

Although described the present invention in detail, it will be appreciated by those skilled in the art that for present given disclosure, within not breaking away from the spiritual scope of concept of the present invention as described herein, can make distortion.And do not mean that scope of the present invention is confined to shown and described specific embodiment therefore.

Claims (20)

1. an X ray grating contrast image-forming system is used for object is carried out perspective imaging, and this system comprises:
The X ray emitter is used for launching noncoherent X-ray beam to object to be detected;
The first absorption grating and the second absorption grating are positioned on the transmit direction of X-ray beam, are used for obtaining X-ray beam through the refraction angle information of object to be detected by relatively motion;
Detecting unit is positioned at the back of object to be detected and described the first absorption grating, the second absorption grating, is used for receiving the X ray through described object to be detected refraction, and is converted into discernible electric signal; And
Data processing unit, for the treatment of described electric signal and from wherein calculating X-ray beam in the refraction angle of each planimetric position of described object to be detected information, and the Pixel Information that calculates object to be detected;
Image-generating unit is for the image of rebuilding object to be detected.
2. system as claimed in claim 1, wherein, noncoherent X-ray beam of described X ray emitter emission, its energy range at several KeV between the hundreds of KeV.
3. system as claimed in claim 2, wherein, this X ray emitter comprises x-ray source.
4. system as claimed in claim 3, wherein, the focal spot size of described x-ray source is not more than half of critical focus size of described x-ray source, the critical focus size p of wherein said x-ray source 0, criticalFor Wherein l is the distance between the x-ray source of described the first absorption grating and described X ray emitter, p 2Be the cycle of described the second absorption grating, d is the distance between described the first absorption grating and described the second absorption grating.
5. system as claimed in claim 1, wherein, the X-ray beam of described X ray emitter emission taper.
6. system as claimed in claim 1, the distance between wherein said the first absorption grating and the second absorption grating (A, B) satisfies equation P wherein 1, p 2Be respectively the cycle of the first absorption grating, the second absorption grating, l is the distance between described X ray emitter and the first absorption grating, and d is the distance between the first absorption grating and the second absorption grating.
7. system as claimed in claim 4, wherein the focal spot size of x-ray source size is the 10-1000 micron.
8. system as claimed in claim 6, the period p of wherein said the first absorption grating and the second absorption grating 1, p 2Between 0.1 micron-30 microns.
9. system as claimed in claim 3, wherein
Described x-ray source comprises many seam collimating apparatuss, and the focal spot size of wherein said x-ray source is greater than half of the critical focus size of described x-ray source, and the critical focus of described x-ray source is of a size of Wherein, l is the distance between the first absorption grating and the many seam collimating apparatuss, and d is the distance between the first absorption grating and the second absorption grating, p 2Be the cycle of the second absorption grating,
The period p of described many seam collimating apparatuss s=Mp 0, critical, M=1,2,3 ..., be placed between described x-ray source and described the first absorption grating, and the width of every seam of wherein said many seam collimating apparatuss is not more than half of critical focus size of described x-ray source.
10. such as the system of claim 1 or 8, wherein said the first absorption grating and the second absorption grating adopt heavy metal as absorbing material, and the thickness of described absorbing material is 10 microns-100 microns.
11. system as claimed in claim 1, wherein said detecting unit comprises the detection unit of matrix structure, and each is surveyed unit for detection of the Strength Changes of X ray and is converted into discernible electric signal.
12. system as claimed in claim 1, described data processing unit changes by the light intensity that described electric signal is calculated X ray, and the value of utilizing described light intensity to change calculates X ray through the refraction angle of object to be detected.
13. such as the system of claim 12, wherein said data processing unit calculates the Pixel Information for described object to be detected imaging by described refraction angle information.
14. system as claimed in claim 1, wherein said object to be detected is between described X ray emitter and described the first absorption grating and the second absorption grating.
15. system as claimed in claim 1, wherein said the first absorption grating and the second absorption grating lay respectively at the both sides of object to be detected.
16. system as claimed in claim 1 has a minute angle ε, so that produce Moire fringe in the detection faces of detecting unit between wherein said the first absorption grating and the second absorption grating; Can obtain thus the Moire fringe variable quantity when object to be detected being set and object to be detected is not set, measured in detection faces; This Moire fringe variable quantity according to predetermined about the relational expression between described Moire fringe variable quantity and the refraction angle, the refraction angle information when drawing X ray through object to be detected.
17. the system such as claims 14 or 15, wherein said the first absorption grating is connected with a stepping moving device with the second absorption grating, so that one of first absorption grating, the second absorption grating are motionless, and another absorption grating is being parallel to stepwise operation on the direction of grating planar.
18. one kind is utilized X ray that object to be detected is carried out the method for phase contrast imaging, the method comprises the steps:
Launch noncoherent X-ray beam to object to be detected;
Make the X-ray beam through refraction pass the first absorption grating and the second absorption grating (A, B), thereby form the X ray signal of Strength Changes in detection faces;
Receive the X ray signal of described Strength Changes, the X ray signal is converted to discernible electric signal; And
From described discernible electric signal, the light intensity of Calculation of X-Ray changes, and utilizes described light intensity change calculations to go out the refraction angle information of X ray;
Utilize the refraction angle information that obtains, calculate the image of object to be detected;
The cycle of wherein said the first absorption grating and the second absorption grating is 0.1 micron.
19. an X ray optical grating contrast CT formation method is used for object to be detected is carried out the CT imaging, the method comprises:
Launch noncoherent X-ray beam to object to be detected;
Make the X-ray beam through refraction pass the first absorption grating and the second absorption grating (A, B), thereby form the X ray signal of Strength Changes in detection faces;
Receive the X ray signal of described Strength Changes, the X ray signal is converted to discernible electric signal;
From described discernible electric signal, the light intensity of Calculation of X-Ray changes, and utilizes described light intensity change calculations to go out the refraction angle information of X ray;
Utilize the refraction angle information that obtains, calculate the plane picture of object to be detected;
Rotate object to be detected, repeat above-mentioned steps, thereby and a plurality of plane pictures that obtain are processed the CT image that obtains this object to be detected;
Wherein said the first absorption grating and the second absorption grating extract described X ray through the refraction angle information behind the object to be detected in imaging process, used the phase place step-by-step method;
Described phase place step-by-step method comprises that one of the first absorption grating, second absorption grating are motionless, and another absorption grating stepwise operation on perpendicular to the direction of grating gap;
In described stepwise operation process, measure the light intensity curve of X ray on detection faces, and the light intensity curve of the background X ray of obtained light intensity curve when not placing object to be detected is compared, thereby obtain the amount of movement of light intensity curve, draw refraction angle information according to the predetermined relational expression about between light intensity curve amount of movement and the refraction angle.
20. an X ray optical grating contrast CT formation method is used for object to be detected is carried out the CT imaging, the method comprises:
Launch noncoherent X-ray beam to object to be detected;
Make the X-ray beam through refraction pass the first absorption grating and the second absorption grating (A, B), thereby form the X ray signal of Strength Changes in detection faces;
Receive the X ray signal of described Strength Changes, the X ray signal is converted to discernible electric signal;
From described discernible electric signal, the light intensity of Calculation of X-Ray changes, and utilizes described light intensity change calculations to go out the refraction angle information of X ray;
Utilize the refraction angle information that obtains, calculate the plane picture of object to be detected;
Rotate object to be detected, repeat above-mentioned steps, thereby and a plurality of plane pictures that obtain are processed the CT image that obtains this object to be detected;
Be in the situation of large focal spot light source at radiographic source wherein, add the collimating apparatus of seam more than, produce one group little focal line light source to launch X ray to object to be detected.
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