CN201191275Y - X ray grating contrast image-forming system - Google Patents

Abstract

The utility model provides an X-ray grating phase contrast imaging system, which is used to detect objects. The X-ray grating phase contrast imaging system comprises an X-ray transmitting apparatus, a first absorption grating, a second absorption grating, a detection unit and a data processing unit, wherein the X-ray transmitting apparatus is used to transmit X-ray for a object to be detected, the first absorption grating and the second absorption grating are parallelly sequentially located in the direction of the X-ray, the X-ray which is refracted by the object to be detected forms an X-ray signal with variable strength through the first absorption grating and/ or the second absorption grating, the X-ray signal comprises the refraction angle information of the refracted X-ray, the detection unit is used to receive the X-ray signal with variable strength, and transforms the X-ray signal into an electrical signal, the data processing unit is used to receive electrical signals from the detection unit, extract the refraction angle information from the electrical signal, and reconstruct an sectional image of the distribution of the refractive index in the object by the pre-defined algorithm according to the refraction angle information. The X-ray grating phase contrast imaging system can get rid of the dependence to the coherence of a diographic source, is not limited by the Tablot distance, and can use the grating having a period above ten micron dimensions to realize the phase contrast imaging of near decimeter dimension viewing field.

Description

A kind of X ray optical grating contrast imaging system

Technical field

The utility model relates to the pattern imaging field, in particular to the field of object being carried out the CT imaging with X ray.

Background technology

Traditional x-ray imaging and CT technology thereof are 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 is formed is obvious, then the effect of x-ray imaging is particularly remarkable.But with the material that light element (for example hydrogen, charcoal, nitrogen and oxygen) constitutes, 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, for example stamp contrast preparation and also be difficult to obtain distinct image to biological tissue with other auxiliary means.Middle 1990s, because the development of third generation Synchrotron Radiation, HARD X-RAY PHASE-CONTRAST imaging (phase-contrastimaging is called for short phase contrast imaging) technology is arisen at the historic moment.The phase contrast imaging technology is exactly to observe the electron density variation of interior of articles by the phase shift information of catching 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 during the decade, by radiogenic high brightness of synchrotron radiation and good coherence, the phase contrast imaging technology has developed at least 4 kinds formation method: interferometric method, roughly the same imaging shaft, diffraction enhanced imaging and optical grating contrast imaging etc., various existing imaging techniques such as these technology and traditional X-ray radial imaging and CT technology thereof, MRI technology, ultrasonic technique are compared has special advantages, 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 on general X-ray production apparatus, realize phase contrast imaging, 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, class be coaxial to be subjected to certain restriction in actual use.Because interferometric method, roughly the same imaging shaft obtains 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 generally all very little (about several square centimeters) of the detector of micron resolution, and this has just determined that the visual field of whole imaging system is also smaller, thereby can not do the imaging inspection of large sample.Though the diffraction enhanced imaging method can use the so not high detector of general X-ray production apparatus and resolution to realize the imaging that the object edge of high-contrast (density resolution) strengthens, but the monochrome effect of monochromating crystal makes the visual field 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.

The hard X ray optical grating contrast formation method that the people such as David C of Switzerland PSI (Paul Scherrer Institut.) realized on the light path with 2 phase gratings and 1 analyzing crystal formation on the ESRF based on optical grating diffraction Tabot effect first in 2002.The Momose A of Japan equals also to have launched after 2003 the research based on the optical grating contrast formation method of phase grating and absorption grating on Spring-8, propose the technology with two gratings extraction single order phase informations.The Weitkamp T of Switzerland PSI and Pfeiffer F equal the 2003 phase contrast imaging technology that realized equally based on 2 gratings on SLS and ESRF on the basis of DavidC work.Yet said method all is based on and carries out on the synchrotron radiation radiographic source, and the visual field is all very little, greatly limited the application of phase contrast imaging.

People such as Pfeiffer F have obtained 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, obtained big small field of view, from then on opened up practicable road for the practical application of phase contrast imaging technology near 64mm * 64mm; But the imaging time of the optical grating contrast imaging system that they built long (time shutter is 40 seconds) can't carry out experiment made on the living; This cover system is not realized phase contrast CT imaging in addition.Yet this method has used source grating (source grating) Talbot 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 a partial coherence, produces the Talbot effect with the phase grating effect.In itself, the incoherent light that this formation method utilizes the source grating that general X-ray production apparatus is sent produces partial coherence, utilizes the Talbot effect of optical grating diffraction to realize phase contrast imaging.

Therefore, the essence of 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 (density resolution just) 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 use the grating of 3 difference in functionalitys to realize, 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, big 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 utility model proposes a kind of phase contrast CT imaging system that adopts the phase contrast imaging technology, it uses two absorption gratings just can obtain single order differential phase shift information down at polychrome, the relevant radiographic source (general X-ray production apparatus) of non-space.

The utility model provides a kind of X ray optical grating contrast imaging system, is used for object is detected, and this system comprises: the X ray emitter is used for to object to be detected emission X ray; First and second absorption gratings, the two is positioned on the X ray direction abreast successively, the X ray of object to be detected refraction is via the X ray signal of this first and/or second absorption grating formation Strength Changes, and wherein this X ray signal comprises the refraction angle information that is refracted X ray; Detecting unit is used to receive the X ray of described Strength Changes, and is electric signal with the X ray conversion of signals; And data processing unit is used for receiving described electric signal from described detecting unit, extracts refraction angle information in this electric signal, and utilizes pre-defined algorithm to come the faultage image of the index distribution of reconstruction of objects inside according to described refraction angle information.

The utility model biggest advantage 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 ten micron dimensions to realize the phase contrast imaging 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 (for example 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, big 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 CT imaging system of the present utility model and the natural compatibility of traditional CT imaging system only need be set up two raster translation rotary systems and can be realized on common CT imaging system.The utility model 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 shows the synoptic diagram of optical grating contrast CT imaging system of the present utility model;

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

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

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

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

Fig. 6 a and Fig. 6 b show the dual mode of CT pattern respectively;

The light intensity curve that Fig. 7 shows certain picture element in inner certain pixel of plastic pattern and the background compares;

Fig. 8 a-8d shows three examples of refraction angle image respectively;

Fig. 9 illustrates the Moire fringe synoptic diagram;

Figure 10 shows the synoptic diagram that adds the collimating apparatus of seam more than in the radiographic source front; And

Figure 11 shows testee and is placed on synoptic diagram between two absorption gratings.

Embodiment

See accompanying drawing 1, optical grating contrast CT imaging system of the present utility model mainly comprises following ingredient: X ray emitter (being expressed as radiographic source in the drawings) is used for to object to be detected emission X ray; First and second absorption gratings (being expressed as grating A and grating B in the drawings respectively), the two is positioned on the X ray direction abreast successively, the X ray of object to be detected refraction is via the X ray signal of this first and/or second absorption grating formation Strength Changes, and wherein this X ray signal comprises the refraction angle information that is refracted X ray; Detecting unit (being expressed as detector in the drawings) is used to receive the X ray of described Strength Changes, and is electric signal with the X ray conversion of signals; And the data processing unit (not shown), be used for receiving described electric signal from described detecting unit, extract refraction angle information in this electric signal, and utilize pre-defined algorithm to come the faultage image of the index distribution of reconstruction of objects inside according to described refraction angle information.

For clearer description the utility model, utilize three blocks of gratings to come the technical scheme of inspected object to compare explanation in 2006 people such as the technical solution of the utility model and Pfeiffer F, with more outstanding characteristics of the present utility model.

People such as Pfeiffer F in the technical schemes that 2006 propose, can utilize three blocks of gratings and use general X-ray production apparatus to realize that the basic reason of optical grating contrast formation method is that the source grating is subdivided into the wide line radiographic source of a plurality of 25-50 microns with incoherent radiographic source, they send the X ray with partial coherence, these X ray and 4 microns cycle phase grating generation optical grating diffraction effects, make phase grating on the Talbot distance, produce 2 microns cycles from imaging.This is adopted the phase information extractive technique of phase place stepping (Phase stepping) technology or More's interferometry (Moireinterferometry) from the absorption grating in imaging and last 1 micron cycle of piece, thereby calculate refraction angle testee, relevant with single order refractive index information.The spatial coherence condition that makes X ray and grating A produce optical grating diffraction is:

${\mathrm{<figure-callout\; id="0"\; label="p"\; filenames="Y20072019034100221.png,Y20072019034100261.png"\; state="\{\{state\}\}">p</figure-callout>}}_0<\frac{1}{p_1}\mathrm{\&lambda;}---\left(1\right)$

P wherein ₁Be the cycle of grating A, l is that radiographic source is the X ray wavelength to grating A distance and λ.Suppose the grating period p ₁Be 4 microns, radiographic source is 2 meters to grating A's apart from l, uses 12.4keV, then requires radiogenic focal spot size to be at least

This is just by the radiogenic width requirement of the line of source grating subdivision.

Based on the phase contrast imaging technology of 3 gratings, phase contrast imaging technology of the present utility model is used noncoherent radiographic source direct irradiation, and does not need the source grating above being different from.That is to say that phase contrast imaging technology of the present utility model does not need radiogenic coherence (comprising temporal coherence and spatial coherence), do not need equally 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.The condition that makes X ray and grating A not produce diffraction according to formula (1) is

${\mathrm{<figure-callout\; id="0"\; label="p"\; filenames="Y20072019034100221.png,Y20072019034100261.png"\; state="\{\{state\}\}">p</figure-callout>}}_0>>\frac{1}{p_1}\mathrm{\&lambda;}---\left(3\right)$

From equation (3), as can be seen, be p when the grating Ade cycle ₁Big more, then the value on equation right side is more little, so the utility model 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.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 big more just good more, it is limited by the accuracy requirement of the phase place stepping technique of two absorption gratings.Fig. 2 is respectively 20 microns and 22 microns the cycle of two absorption gratings, the source is to 2 meters of grating A distances, distance is 0.2 meter the time between two gratings, under the radiographic source illuminate condition of different focal spot sizes, and pairing simulation light intensity curve when two gratings use the phase place stepping technique.Horizontal ordinate is step size (0.5 micron/step), and ordinate is a light intensity value.Be noted that the result according to formula (4) estimation, focal spot size is that the X ray that 1 micron radiographic source sends is concerned with, but compare for convenience and 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 big more, light intensity curve is just level and smooth more, becomes straight line when focal spot size equals 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.

According to the principle of phase place stepping technique, the critical value that can extrapolate this ray source focus size is p _{0, critical}:

${\mathrm{<figure-callout\; id="0"\; label="p"\; filenames="Y20072019034100221.png,Y20072019034100261.png"\; state="\{\{state\}\}">p</figure-callout>}}_{0,\mathrm{critical}}=\frac{l}{d}{p}_2---\left(5\right)$

According to shown in Figure 2 because change, still can obtain the image of phase contrast effect according to this point when focal spot size still has light intensity during greater than this critical value, but the contrast effect when focal spot size less than p _{0, critical}Situation to get well.According to The above results, can draw, at p _{0, critical}In the scope, focal spot size is more little, and light intensity curve is steep more, and the contrast of the phase contrast image that extracts so is also high more.Under the preferable case, ray source focus size p ₀Requirement is no more than p _{0, critical}Half.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, so big radiographic source is subdivided into the little focal line radiographic source of a series of equivalences, in order to improve the figure image contrast, the radiogenic focal spot size size of each little focal line p _{0, i}Also require to be no more than p _{0, critical}Half.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 understood by those skilled in the art that under the situation that adopts many seam collimating apparatuss, described apart from l be actually grating A with should the distances of stitching between the collimating apparatuss 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 form the light source with expectation focus size before radiographic source, therefore will no longer describe in detail here.

Discussed above radiogenic requirement, discuss between the grating below and the relation between grating and the ray emission device, it will be appreciated that, here said x-ray apparatus can only comprise the radiographic source that focal spot size meets the demands, and can also comprise radiographic source and many seam collimating apparatuss of focal spot size greater than predetermined value.

Because the X ray line of general X-ray production apparatus is a cone-beam, the cycle request of two absorption gratings that phase contrast imaging therefore of the present utility model system is adopted also becomes the geometric proportion relation:

$\frac{p_1}{p_2}=\frac{l}{l+d}---\left(6\right)$

Therefore, compare with original optical grating contrast imaging technique, in the phase contrast imaging of the present utility model system between two gratings apart from d, irrelevant with the wavelength X of X ray, therefore, can decide by formula (5) (6) according to the actual conditions demand with the Talbot range-independence.

Below in conjunction with the utility model and aforesaid equation the employed technical scheme of the utility model is discussed specifically.

Because radiographic source can be the bigger 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 utility model is preferably disposed under the 5-40kVp condition that (concrete numerical value highly is determined by the gold of absorption grating, the height that is to say gold is high more, and the operating voltage that permission is used is then high more).At least tens microns of focal spot sizes of general X-ray production apparatus or more than the hundreds of micron, the X ray that it sends is polychrome and is non-spatial coherence.

Preferably, native system is fit to use on little focus source, and radiogenic focal spot size is preferably between the 50-1000 micron.If but used little focus device (focus is less than 50 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, and 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 1000 microns x-ray apparatus, soft edge can increase so, thereby is unfavorable for the enhancing of figure image contrast.For this situation, can place many seam collimating apparatuss (the width size of every seam is between the 50-200 micron) as shown in figure 10 in the radiographic source front, so big radiographic source is subdivided into the little focal spot size line radiographic source of a series of equivalences, though the spatial resolution of image is still determined by the ray source focus size, but the high image overlay of the contrast that each line radiographic source produces together, still can obtain a phase contrast image that contrast is quite high.

According to the utility model preferred implementation, the grating department branch comprises two absorption gratings, i.e. grating A among Fig. 1 and grating B are used to extract the single order phase information of X ray.The making of absorption grating has two kinds usually: 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 to depict grating on heavy metal material.Grating A and grating B plane all are parallel to detector plane (XY direction).The area size of grating has determined the visual field size of whole phase contrast imaging system.Illustrate, if the substrate of grating is 4 silicon chips, then the visual field of system is in the scope of diameter 10cm.

According to cycle of two absorption gratings of the native system of the utility model preferred implementation between the 2-30 micron.Described grating uses heavy metal as absorbing material, is example with gold (Au), and the height of gold is by the energy decision of the X ray that uses, between the 10-100 micron.For example, concerning the X ray of 20keV, gold is tall and big to stop 90% X ray in 16 microns, can obtain the reasonable phase contrast image of contrast like this.Wherein, the cycle of grating A is p ₁, the cycle of grating B is p ₂, dutycycle (duty cycle) is generally 1.The distance of two gratings is d, as shown in Figure 1.

Described explorer portion is discussed below.

What detector system write down is the X ray Strength Changes.Native system can use high-resolution X ray CCD camera or flat panel detector.Native system is compared with other phase contrast imaging method, less demanding to the spatial resolution (pixel size) of detector: do not require the high resolving power of tens microns even several microns, can only use the resolution of tens microns or hundreds of micron dimension.Certainly, if the spatial resolution of detector is high more, then the information of final phase contrast image is clear more.Because the advantage of phase contrast imaging is to improve the density resolution of image (contrast resolution), thus to the dynamic range of detector have than higher requirement (＞12bits).

The technology of extracting refraction angle information (or single order phase information of X ray) from the signal that receives is discussed below.

As everyone knows, X ray has " wave-particle duality " (wave-particle duality), that is to say the existing corpuscular property of X ray, and undulatory property is arranged again.With undulatory property, X ray possesses transmission, reflection, refraction, polarization, relevant and optical properties such as incoherent scattering, diffraction equally.When X ray passes jobbie, the amplitude of X ray because object to it absorption and weaken; Simultaneously, X ray and material atom coherent scattering make X ray produce phase shift (phase shift), and the wave front that shows as X ray on the macroscopic view produces distortion.That is to say that refraction effect has taken place 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 (7)

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

$p=\frac{2\mathrm{\&pi;\&delta;}}{\mathrm{\&lambda;}},$ $\mathrm{\&mu;}=\frac{4\mathrm{\&pi;\&beta;}}{\mathrm{\&lambda;}}---\left(8\right)$

Wherein λ is the wavelength of X ray, and δ is called as phase factor, and β is called as absorption factor.δ is generally 10 concerning X ray ^-5About, thus n less than 1, thereby small refraction only takes place in X ray on the material interphase, (being about the microradian magnitude) represented at available refraction angle.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

$\mathrm{\&Delta;\&theta;}\&ap;\frac{\mathrm{\&lambda;}}{2\mathrm{\&pi;}}\frac{\&PartialD;\mathrm{\&Phi;}\left(y\right)}{\&PartialD;y}---\left(9\right)$

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

$\mathrm{\&Phi;}\left(y\right)=\underset{M}{\&Integral;}p(x,y)\mathrm{dx}=\frac{2\mathrm{\&pi;}}{\mathrm{\&lambda;}}\underset{M}{\&Integral;}\mathrm{\&delta;}(x,y)\mathrm{dx}---\left(10\right)$

Convolution (9) and (10) have

$\mathrm{\&Delta;\&theta;}=\underset{M}{\&Integral;}\frac{\&PartialD;\mathrm{\&delta;}(x,y)}{\&PartialD;y}\mathrm{dx}=-\underset{M}{\&Integral;}\frac{\&PartialD;n(x,y)}{\&PartialD;y}\mathrm{dx}---\left(11\right)$

Formula (11) 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 (11).

Therefore, how measuring refraction angle Δ θ is the core of two optical grating contrast imaging techniques of the present utility model.According to the approximation in geometric optics theory, 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 during just as gate, thereby the power that causes the light distribution of detector changes.As shown in Figure 5, observe from the two dimensional surface vertical view of two optical grating contrast imaging systems.Illustrate, do not having under the situation of object, X ray 1 is blocked promptly by grating A and is absorbed by Au, and X ray 2 is not blocked by two gratings and arrives detector smoothly.When after putting object on the 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 detector detected changes the situation that X ray is reflected by object that reflected.Can calculate refraction angle information by phase place stepping (Phase stepping) technology and More's interferometry (Moireinterferometry).

The radiographic source that is noted that two optical grating contrast CT imaging systems of the present utility model is the polychrome radiographic source, so the information that native system obtained all is average energy

Refraction angle information under the meaning

The single order phase information

And refractive index information

For helping to understand better the utility model, above-mentioned phase place stepping technique and More's interferometry are discussed below.

1) phase place stepping (Phase stepping) technology

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

Wherein A represents amplitude, and B is relevant with the grating cycle,

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 difference better, two grating relative translations a semiperiod).Can find that from Fig. 7 after X ray was by the object refraction, its light intensity curve had taken place to move with respect to the light intensity curve of background.Light intensity curve can be described with sine function, and the mobile Δ f correspondence of light intensity curve the phase change 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 (14)

Association type (13) and (14) have

So just can obtain refraction angle information.

Illustrate, experiment condition is: X ray bulb focal spot size is 400 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 bulb is provided with 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 is gathered a data for projection.Testee is the plastic pattern (shown in Fig. 8 a) of 1 centimetre of diameter.For eliminate The noise as far as possible, every projected image is gathered 400 images altogether and is superposeed.The refraction angle image that calculates according to formula (15) is shown in Fig. 8 b at last.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.

2) More's interferometry (Moire interferometry)

Grating A is parallel with grating B, and both are rotating a minute angle ε relatively.After these two blocks of gratings are arrived in x-ray bombardment, the Moire fringe that on detector, can observe, its cycle is

$w:w=\frac{p_2}{\mathrm{\&epsiv;}}---\left(16\right)$

As shown in Figure 9.As seen, ε is more little, and w is big more.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 (17) is obtained:

$\mathrm{\&Delta;\&theta;}=\frac{\mathrm{\&epsiv;\&lambda;\&Delta;f}}{2\mathrm{\&pi;d}}---\left(17\right)$

Comprehensive above-mentioned two kinds of information extraction technologies all can obtain refraction angle information.

2.CT reconstruction algorithm

Source grating detector three is motionless, rotating object; Perhaps object is motionless, and source grating 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 (Phase stepping) technology or More's interferometry (Moire interferometry) method to calculate the refraction angle information Δ θ of current projection angle _φ:

${\mathrm{\&Delta;\&theta;}}_{\mathrm{\&phi;}}=\underset{M}{\&Integral;}\&dtri;\mathrm{\&delta;}(x,y,z)\mathrm{dl}---\left(18\right)$

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

$U=\underset{M}{\&Integral;}\mathrm{\&mu;}(x,y,z)\mathrm{dl}---\left(19\right)$

Wherein U represents

I and I ₀Be respectively output intensity and incident intensity.We find that formula (18) is very similar with formula (19).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 utility model, 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, need to use Hilbert (Hilbert) wave filter that single order differential data for projection is carried out filtering because of adopting CT reconstruction algorithm at single order differential data for projection, 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 under the less situation of radiographic source subtended angle, can use the collimated beam CT reconstruction formula of single order differential data for projection to come approximate reconstruction refractive index n (or phase factor δ) faultage image:

$\mathrm{\&delta;}(x,y)=\frac{1}{2\mathrm{\&pi;}}{\&Integral;}_0^{\mathrm{\&pi;}}\mathrm{d\&phi;}{\&Integral;}_{-\&infin;}^{\&infin;}\{{\mathrm{\&Theta;}}_P^{\&prime;}(\mathrm{\&rho;},\mathrm{\&phi;})\&CenterDot;[-\mathrm{jsign}\left(\mathrm{\&rho;}\right)\left]\right\}{e}^{j2\mathrm{\&pi;\&rho;}(x\cos \mathrm{\&phi;}+y\sin \mathrm{\&phi;})}\mathrm{d\&rho;}---\left(20\right)$

Wherein $\mathrm{sign}\left(\mathrm{\&rho;}\right)=\left\{\begin{array}{cc}1,& \mathrm{\&rho;}>0\\ -1,& \mathrm{\&rho;}<0\end{array}\right..$ Formula (20) is to describe in the frequency domain polar coordinate system.-jsign (ρ) promptly is Hilbert (Hilbert) filter function.Θ _P' (ρ β) is refraction angle Δ θ _φRepresentation on the frequency domain polar coordinates.

Certainly also can directly adopt the fan beam CT reconstruction formula of single order differential data for projection 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, (φ s) is refraction angle Δ θ to 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 data for projection, and its reconstruction formula is explained with the FDK type:

Wherein,

$Y^{\&prime;}=-\frac{D\stackrel{\&RightArrow;}{r}\&CenterDot;{\hat{y}}^{\&prime;}}{R+\stackrel{\&RightArrow;}{r}\&CenterDot;{\hat{x}}^{\&prime;}}$

$Z^{\&prime;}=-\frac{D\stackrel{\&RightArrow;}{r}\&CenterDot;\hat{z}}{R+\stackrel{\&RightArrow;}{r}\&CenterDot;{\hat{x}}^{\&prime;}}$

${\stackrel{\&OverBar;}{\mathrm{\&Theta;}}}_{\mathrm{\&phi;}}(Y^{\&prime;},Z)={\&Integral;}_{-\&infin;}^{\&infin;}\mathrm{dY}\frac{1}{Y^{\&prime;}-Y}\&times;{\mathrm{\&Theta;}}_{\mathrm{\&phi;}}(Y,Z)\frac{D^2\sqrt{R^2+Z^2}}{D^2(1+Z^2/R^2)+Y^2}$

Θ _φ(Y, Z) expression refraction angle,

Be the specified point of space vector, Be of the projection of x-ray spread direction on the x-y plane,

It is the neutralization of x-y plane Vertical direction, R is a 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 reconstruction formula such as fan-beam or cone-beam reconstruct

(or phase factor

) faultage image.

Need to prove that in the two optical grating contrast CT imaging systems of the present utility model, 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.

Above-mentioned processing procedure can realize by multi-purpose computer or special purpose computer, wherein can handle the data for projection that obtains, comprise that original data processing and demonstration, refraction angle information extraction, birefringence angular projection data reconstruct subject image and drawing three-dimensional stereo-picture or the like, and show by display.Computing machine can be high performance single PC, also can be a workstation or a group of planes.Display can be that the CRT traditional monitor also can be a LCD.

According to the utility model, the CT scan mode can be divided into two kinds, and promptly source and detector are motionless, object self rotation; Perhaps object is motionless, and source and detector rotate around object.Be the function that realizes detecting automatically, X ray optical grating contrast imaging system of the present utility model further comprises mechanical control unit, and this Machinery Control System comprises: the object table whirligig is used for object to be detected is rotated.At this moment, only have detected object to rotate, and X ray emitter-grating-detecting unit maintenance is motionless.Perhaps, Machinery Control System comprises X ray emitter-grating-detecting unit whirligig, is used for only making emitter-grating-detecting unit to rotate, and this moment, object kept motionless, this is inconvenient to rotate at object to be detected, and is especially convenient when for example object to be detected is too huge.

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.

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

Claims (17)

1. an X ray optical grating contrast imaging system is used for object is detected, and is characterised in that this system comprises:

The X ray emitter is used for to object to be detected emission X ray;

First and second absorption gratings, the two is positioned on the X ray direction abreast successively, the X ray of object to be detected refraction is via the X ray signal of this first and/or second absorption grating formation Strength Changes, and wherein this X ray signal comprises the refraction angle information that is refracted X ray;

Detecting unit is used to receive the X ray of described Strength Changes, and is electric signal with the X ray conversion of signals; And

Data processing unit is used for receiving described electric signal from described detecting unit, extracts refraction angle information in this electric signal, and utilizes pre-defined algorithm to come the faultage image of the index distribution of reconstruction of objects inside according to described refraction angle information.

2. system as claimed in claim 1 is characterised in that wherein the focal spot size of described X ray emitter satisfies equation $p_0>>\frac{l}{p_1}\mathrm{\&lambda;},$ Wherein λ is the wavelength of X ray, p ₀Be the focal spot size of X ray emitter, p ₂Be the cycle of described first absorption grating, l is the distance of described first absorption grating and described X ray emitter.

3. system as claimed in claim 2, be characterised in that wherein described X ray emitter comprises x-ray source, preferably, the focal spot size of this x-ray source is not more than half of critical focus size of described X ray emitter, the critical focus size p of wherein said X ray emitter _{0, critical}For $p_{0,\mathrm{critical}}=\frac{l}{d}{p}_2,$ P wherein ₂Be the cycle of described second absorption grating, d is the distance between described first absorption grating and described second absorption grating.

4. system as claimed in claim 3 wherein is characterised in that, the distance between described first and second absorption gratings satisfies equation $\frac{p_1}{p_2}=\frac{l}{l+d}.$

5. system as claimed in claim 4 wherein is characterised in that, the focal spot size size of described X ray emitter is the 50-1000 micron.

6. system as claimed in claim 4 wherein is characterised in that, the cycle of described first absorption grating and second absorption grating is between 2 microns-30 microns.

7. system as claimed in claim 2, wherein be characterised in that, described X ray emitter comprises x-ray source and 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 emitter, and the critical focus of described X ray emitter is of a size of $p_{0,\mathrm{critical}}=\frac{l}{d}{p}_2,$ Described many seam collimating apparatuss are placed between described X ray emitter and described first absorption grating, and preferably, and the width of every seam of described many seam collimating apparatuss are not more than half of critical focus size of described X ray emitter.

8. system as claimed in claim 7 wherein is characterised in that, the size of described many each seams of seam collimating apparatus is the 50-200 micron.

9. system as claimed in claim 2 wherein is characterised in that, described first and second absorption gratings adopt heavy metal as absorbing material, and the thickness of described absorbing material is 10 microns-100 microns.

10. system as claimed in claim 9 wherein is characterised in that, described heavy metal is a gold.

11., be characterised in that wherein described object to be detected is between described X ray emitter and described first and second absorption gratings as each system among the claim 1-10.

12., be characterised in that wherein described first absorption grating and second absorption grating lay respectively at the both sides of object to be detected as each system among the claim 1-10.

13. system as claimed in claim 1 wherein is characterised in that, the dynamic range of described detecting unit is greater than 12.

14. system as claimed in claim 1 wherein is characterised in that, extracts described refraction angle information and comprises use phase place step-by-step method and More's interferometry.

15. system as claimed in claim 1 wherein is characterised in that, the faultage image of the index distribution of reconstruction of objects inside is realized by the CT restructing algorithm, comprises collimated beam, the single order differential data for projection reconstruction algorithm of fan-beam and cone-beam form.

16. the system as claim 15 wherein is characterised in that, described CT restructing algorithm comprises parallel mode and vertical mode.

17. system as claimed in claim 1 wherein is characterised in that, described system further comprises mechanical control unit, and this Machinery Control System comprises: the object table whirligig is used for object to be detected is rotated; And/or X ray emitter-grating-detecting unit whirligig, be used for only making emitter-grating-detecting unit to rotate.

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