CN1965760A - synchrotron radiation X-ray phase contrasting computed tomography and experimental method thereof - Google Patents

Abstract

The invention relates to a computer tomography imaging technique, especially a synchronous radiation X-ray phase contrast CT imager and test method, wherein it is formed by monochromator crystal, sample table, analysis crystal, ionize room, and image detector; the sample table is formed by three rotations and two translations; the method comprises that S1 , finding the image conditions of phase contrasts in different image modes; S2, obtaining phase contrast CT test data; S3, rebuilding the test data.

Description

Synchrotron Radiation X-ray Phase Contrast CT Imaging Device and Experimental Method

technical field

The invention relates to the technical field of computer tomography, in particular to a synchrotron radiation X-ray phase contrast CT imaging device and an experimental method.

Background technique

Since Roentgen discovered X-rays in 1895, X-ray fluoroscopy imaging based on absorption contrast has become an important detection method in the fields of medical diagnosis and material research because it can obtain the internal structure information of samples non-destructively. . Especially after the invention of X-ray CT (computed tomography) by A.M.Cormack and G.N.Hounsfield and others in the middle and late 20th century, CT has become an essential means of medical diagnosis. But whether it is X-ray fluoroscopic imaging or traditional CT, the imaging contrast is based on the difference in the absorption of X-rays by the sample. For biological soft tissues with light elements as the main components, since the absorption of light element materials on hard X-rays is very small, and the absorption difference between different light element materials is even smaller, only low-contrast absorption can be obtained. picture. Therefore, conventional CT based on absorption difference, even if the spatial resolution is improved, still cannot generate contrast to the internal fine structure of biological soft tissue, and cannot see the internal structural details of biological soft tissue (such as early tumors, microvessels, etc.). This greatly limits the application of X-ray absorption imaging methods in the study of biological soft tissues.

In recent years, with the emergence of X-ray phase contrast imaging technology, people have a further understanding of the imaging mechanism of X-rays. Phase contrast imaging is an imaging technique that records the phase change after X-rays pass through an object. In the hard X-ray band (λ≤0.2nm), the phase term δ of light elements is 3 to 4 orders of magnitude larger than the absorption term β. Therefore, phase contrast imaging has higher sensitivity and resolution than traditional X-ray absorption imaging, and is more conducive to the study of the internal structure information of substances in the range of light elements, and it is possible to reveal the internal structure details of biological samples and some It plays a certain role in the early diagnosis of diseases, which is of great significance to related research in biology and medicine.

Although both theory and experiments have shown that X-ray phase contrast imaging can achieve high contrast and resolution, it is still a two-dimensional imaging, which is the superimposition of the projection images of the sample at various levels perpendicular to the beam direction, and the sample cannot be obtained yet. three-dimensional structure. Therefore, it is an urgent problem to be solved to apply phase contrast imaging technology with high contrast and resolution to three-dimensional imaging, and to carry out synchrotron radiation X-ray phase contrast CT imaging method and application research.

Figure 1 is a schematic diagram of the optical paths of two imaging modes widely used in phase contrast imaging.

The synchrotron radiation X-ray phase contrast imaging device generally consists of a monochromator crystal, a sample stage, an analysis crystal, an ionization chamber and a detector.

The monochromator crystal is a monochromatic X-ray device that monochromatizes the incident "white light" X-ray and obtains a very narrow bandwidth. The monochromator crystal is generally made of silicon or germanium single crystal. By adjusting the diffraction surface and the incident The angle (Bragg angle) of the "white light" X-rays allows the selection of the wavelength (energy) of the emitted X-rays. The analytical crystal is generally the same type of crystal as the monochromator crystal. In the diffraction-enhanced phase-contrast imaging mode, the analytical crystal is a high-precision angular filter; while in the coaxial phase-contrast imaging mode, the analytical crystal is a deflector for monochromatic X-rays. In the device of the present invention, both the monochromator crystal and the analysis crystal are fixed on the corresponding rotating shaft, and the turntable of the rotating shaft is realized by a stepping motor through a corresponding reduction transmission device. The rotational angle resolution of the rotating shaft is much smaller than the full width at half maximum (FWHM) of the twin crystal rocking curve, so as to meet the requirement of imaging at different parts of the rocking curve. Be that the X-ray of 10KeV is example with energy, the FWHM of the twin crystal rocking curve of Si (111) crystal is about 8 arc seconds, and in the device of the present invention, the rotation precision of monochromator crystal and analytical crystal rotating shaft can reach 0.05 arc seconds is enough to meet the needs of imaging at different parts of the rocking curve.

The main function of the ionization chamber is to monitor and analyze the intensity of X-rays emitted by the crystal in real time. The photocurrent generated by the X-rays measured in the ionization chamber can be displayed by the micro-electrometer. The specific role of the ionization chamber is reflected in two aspects: 1) When the sample is not placed, when the analytical crystal is rotated, the intensity of the X-rays emitted from the analytical crystal recorded by the ionization chamber can be used to determine the rocking curve of the twin crystal, and determine that the diffraction surface of the analytical crystal is relative to The relative angular position of the crystal diffraction surface of the monochromator to meet the requirements of different phase contrast imaging modes. 2) When the sample is placed for the experiment, the intensity change of the X-ray emitted from the analysis crystal recorded by the ionization chamber can determine the exposure time and the influence of the X-ray intensity drop during the experiment, and provide information for subsequent image data processing and normalization. in accordance with.

Imaging detectors are generally two-dimensional surface detectors, which are required to facilitate image digitization and have a certain spatial resolution. Imaging detectors facilitate image digitization for easy synchronization or subsequent processing of images. At the same time, in order to meet the requirements of imaging resolution, the detector must have sufficient spatial resolution.

Contents of the invention

The object of the present invention is to provide a synchrotron radiation X-ray phase contrast CT imaging device and an experimental method.

In synchrotron radiation phase-contrast CT imaging experiments, since the light source is fixed, subsequent experimental devices must be adjusted according to the position and direction of the light source. Therefore, the phase-contrast CT experiment can only be completed by rotating the experimental sample.

A monochromator crystal, a sample turntable, an analysis crystal, an ionization chamber and an imaging detector constitute the X-ray phase contrast CT experimental device of the present invention.

In the above-mentioned X-ray phase contrast imaging CT experimental device, the combination of computer can realize the complete automation of monochromator crystal, analysis crystal and sample stage turntable, ionization chamber data readout and recording, imaging shooting and recording, etc. .

In the diffraction-enhanced phase contrast CT imaging experiment, the sample turret is placed between the monochromator crystal and the analysis crystal, and the angle between the analysis crystal and the monochromator crystal is determined according to the double crystal rocking curve measured in the ionization chamber. Fixed and adjusted analytical crystal and monochromator crystal, sample turret (turntable 1) after a specific angle for each turntable, using imaging detector to obtain a diffraction enhanced projection image of the sample, the range of sample turret can be 180°, 360° ° or other arbitrary angles, and finally obtain the corresponding number of diffraction-enhanced two-dimensional projection images (number of two-dimensional projection images = sample turret degree/turntable step size). According to the relevant theory of diffraction-enhanced imaging and the corresponding CT algorithm, the obtained two-dimensional projection image is processed to obtain the diffraction-enhanced phase contrast CT tomographic image of the sample.

In the coaxial phase contrast CT imaging experiment, the sample stage is placed behind two crystals, which form a double-crystal monochromator, and the detector is placed on a linear slide that can automatically slide along the direction of the X-ray optical path. According to the Bragg angle of crystal diffraction, the X-ray wavelength irradiated on the sample can be selected; according to the double crystal rocking curve measured in the ionization chamber, the diffraction planes of the two crystals can be adjusted to be parallel. According to the coaxial phase contrast imaging theory, the coaxial phase contrast two-dimensional projection image can be obtained on the imaging detector by selecting an appropriate sample-detector distance. Rotate the sample according to a specific step length and collect two-dimensional projection images at each angular position. After the sample rotates the entire predetermined turntable range, complete projection image data can be collected. According to the relevant theory of coaxial phase contrast imaging and corresponding CT algorithm, the obtained two-dimensional projection image is processed to obtain the coaxial phase contrast CT tomographic image of the sample.

In the device of the present invention, after determining the exposure time under different imaging conditions, input the total angle of the turntable (sample scanning range) and the step length of the turntable for the sample in the program, and determine the path where the data is stored on the computer , the entire data collection process can run automatically until the end of the data collection process. The movement process of the program is: collect the two-dimensional projection image and save it to disk → rotate the sample by one step → collect the two-dimensional projection image again and save it on disk → continue to rotate the sample by one step, and so on, until the sample rotates to complete the entire scanning range. Fig. 3 is a schematic diagram of the working process of the phase contrast CT imaging experiment of the present invention.

Based on the device of the present invention, the synchrotron radiation X-ray phase contrast CT imaging experiment mode mainly includes:

There are four main working modes of diffraction-enhanced phase-contrast CT imaging experiments:

1) The sample rotation axis is parallel to the monochromator crystal rotation axis and the analysis crystal rotation axis. This mode can be realized by adjusting the turntable 2,

2) The rotation axis of the sample is perpendicular to the rotation axis of the monochromator crystal and the analysis crystal. This mode is realized by rotating the turntable 2 by 90° on the basis of the previous mode.

3) Monochromator crystal and analysis crystal tuning mode, monochromator crystal and analysis crystal diffraction planes are completely parallel,

4) There is a very small angle between the monochromator crystal and the analysis crystal in the detuning mode of the monochromator crystal and the diffraction plane of the analysis crystal;

The main working modes of the coaxial phase contrast CT imaging experiment are as follows:

1) This mode needs to pre-determine the optimal distance between the sample and the detector, and then conduct CT imaging experiments under the condition that the sample-detector distance remains unchanged.

2) Select several different sample-detector distances, collect CT imaging experiment data at different distances, and then use the obtained several sets of data to obtain the optimal phase contrast in data processing.

Under different phase contrast CT imaging experiment working modes, the phase contrast CT imaging experiment process described in the present invention. The specific steps are:

Step S1, determination of phase contrast imaging conditions in different imaging modes:

(1) In the diffraction-enhanced phase contrast CT imaging experiment, according to the relationship between the required imaging conditions of the sample and the corresponding positions on the twin crystal rocking curve, determine the angle between the monochromator crystal and the analysis crystal,

(2) In the coaxial phase contrast CT imaging experiment, determine the appropriate distance between the sample and the detector according to different samples to obtain the best imaging effect or obtain the required information,

(3) Determine the corresponding imaging exposure time under different conditions according to different parameters such as X-ray light intensity and detectors;

Step S2, the acquisition of phase contrast CT imaging experiment data, under the imaging conditions determined in step S1, after the sample turntable (1) rotates a specific angle, use the imaging detector to obtain a phase contrast projection image of the sample , the range of the sample turntable can be 180°, 360° or other arbitrary angles, and finally obtain a corresponding number of phase contrast two-dimensional projection images. In the device, after determining the exposure time under different imaging conditions, the Input the total angle and rotation step of the sample to be rotated in the program, and after determining the data storage path on the computer, the entire data collection process can run automatically until the end of the data collection process;

Step S3, the reconstruction of the experimental data of phase contrast imaging, based on the relevant theory of diffraction-enhanced phase contrast imaging or coaxial phase contrast imaging, the phase contrast of the sample can be reconstructed by processing the obtained two-dimensional projection image CT tomogram.

Description of drawings

Figure 1 is a schematic diagram of the optical paths of two imaging modes widely used in phase contrast imaging.

Fig. 2 is a schematic diagram of the sample turntable in the present invention.

Fig. 3 is a flowchart of the synchrotron radiation X-ray phase contrast CT imaging method of the present invention.

Detailed ways

Figure 1 is a schematic diagram of the optical paths of two imaging modes widely used in phase contrast imaging. Among them, Fig. 1(a) is the optical path diagram of the coaxial phase contrast CT imaging experiment, and Fig. 1(b) is the optical path diagram of the diffraction-enhanced phase contrast CT imaging experiment.

In synchrotron radiation phase-contrast imaging experiments, since the light source is fixed, subsequent experimental devices must be adjusted according to the position and direction of the light source. Therefore, in phase-contrast CT imaging CT experiments, the acquisition of projection data can only be achieved through the rotation of the experimental sample. Not the rotation of the light source to do it.

In the synchrotron radiation X-ray phase contrast CT imaging device of the present invention, the device includes a monochromator crystal, a sample turntable, an analysis crystal, an ionization chamber, and an imaging detector. In diffraction-enhanced phase contrast CT imaging, a single Chromochromator crystal, sample turret, analysis crystal, ionization chamber and imaging detector are sequentially arranged on the optical path; in coaxial phase contrast CT imaging, monochromator crystal, analysis crystal, sample turret, ionization chamber and imaging detector are sequentially arranged Arranged on the optical path; the role of the ionization chamber is as a monitoring device for X-ray intensity, and the X-ray intensity measured by the ionization chamber is displayed in real time by a micro-electrometer in the form of photocurrent.

Fig. 2 is a schematic diagram of the sample turntable in the present invention. Turntable 1, turntable 2, and turntable 3 correspond to ω1, ω2, and ω3 respectively, and translation 1 and translation 2 correspond to P1 and P2 in the figure respectively.

The sample turntable of the present invention is made up of three turntables and two translations, among the three turntables, the effect of turntable 1 (ω1) is to rotate and fix the sample on turntable 1, and is the main turntable in the CT experiment process; turntable 2 (ω1) ) is used to adjust the orientation of the sample relative to the X-ray emitted from the monochromator crystal to meet the needs of different imaging conditions, because the turntable 1 is fixed on the turntable 2, so when the turntable 2 turns, the sample fixed on the turntable 1 is relative to the The orientation of the incident X-ray will change with the turntable 2 (for example, the rotation axis of the sample can be changed from a horizontal turntable to a vertical turntable through the turntable 2); turntable 3 (ω3) is used to adjust the orientation of the sample stage relative to the incident X-ray to ensure that the X-ray For the normal incidence of the sample, when the turntable 3 turns, the turntable 2 fixed on the turntable 3 rotates with it, and the turntable 1 fixed on the turntable 2 rotates with it at the same time to realize the normal incidence of X-rays on the sample. The movement P1 is used to adjust the height position of the sample stage relative to the X-ray, and the translation P2 is used to realize the adjustment of the horizontal position of the sample stage relative to the X-ray.

In addition, in order to avoid the impact of strong scattering of synchrotron radiation X-rays incident on the metal parts, the central part of the turntable 2 where the X-rays pass through is designed as a sufficiently large X-ray channel; the rotation axis of the sample turntable (turntable 1) must be It has high enough concentric stability to meet the requirements of CT imaging resolution.

Fig. 3 is the process flow of the synchrotron radiation X-ray phase contrast imaging CT method, and its specific steps are as follows:

Step S1, determination of phase contrast imaging conditions in different imaging modes:

(1) In the diffraction-enhanced phase contrast CT imaging experiment, according to the relationship between the required imaging conditions of the sample and the corresponding positions on the twin crystal rocking curve, determine the angle between the monochromator crystal and the analysis crystal,

(2) In the coaxial phase contrast CT imaging experiment, determine the appropriate distance between the sample and the detector according to different samples to obtain the best imaging effect or obtain the required information,

(3) Determine the corresponding imaging exposure time under different conditions according to different parameters such as X-ray light intensity and detectors;

Step S2, the acquisition of phase contrast CT imaging experiment data, under the imaging conditions determined in step S1, after the sample turntable (1) rotates a specific angle, use the imaging detector to obtain a phase contrast projection image of the sample , the range of the sample turntable can be 180°, 360° or other arbitrary angles, and finally obtain a corresponding number of phase contrast two-dimensional projection images. In the device, after determining the exposure time under different imaging conditions, the Input the total angle and rotation step of the sample to be rotated in the program, and after determining the data storage path on the computer, the entire data collection process can run automatically until the end of the data collection process;

Step S3, the reconstruction of the experimental data of phase contrast imaging, based on the relevant theory of diffraction-enhanced phase contrast imaging or coaxial phase contrast imaging, the phase contrast of the sample can be reconstructed by processing the obtained two-dimensional projection image CT tomogram.

Claims (5)

1. synchrotron radiation X-ray phase contrast CT image-forming device, described device is made up of monochromator crystal, sample rotary table, analyzing crystal, ionization chamber and imaging detector, strengthen in the phase contrast CT image-forming experiment at diffraction, monochromator crystal, sample rotary table, analyzing crystal, ionization chamber and imaging detector sequence arrangement are on light path; In coaxial phase contrast CT image-forming experiment, monochromator crystal, analyzing crystal, sample rotary table, ionization chamber and imaging detector are sequentially arranged on the light path; The effect of ionization chamber is the monitoring equipment as X ray intensity, and the X ray light intensity that ionization chamber records shows by microelectrometer in real time with the form of photoelectric current.

2. synchrotron radiation X-ray phase contrast CT image-forming device according to claim 1, it is characterized in that, sample rotary table is made up of three turntables and two translations, in three turntables, the effect of turntable (1) is to realize being fixed on the rotation that turntable (1) is gone up sample, is the main turntable in the CT imaging experiment process; Turntable (2) be used for adjusting sample with respect to from the orientation of the X ray of monochromator crystal outgoing to satisfy the needs of different image-forming conditions, because turntable (1) is fixed on the turntable (2), so when turntable (2) rotates, the sample that is fixed on the turntable (1) will change with turntable (2) with respect to the orientation of incident X-rays; Turntable (3) is used for adjusting the orientation of the relative incident X-rays of sample platform to guarantee the normal incidence of X ray to sample, when turntable (3) rotates, be fixed in turntable (2) on the turntable (3) with commentaries on classics, be fixed on turntable (1) on the turntable (2) simultaneously with changeing to realize the normal incidence of X ray to sample, in two translations, translation P1 is in order to realize the adjusting of sample platform with respect to the X ray height and position, and translation P2 is in order to realize the adjusting of sample platform with respect to the X ray horizontal level.

3. synchrotron radiation X-ray phase contrast CT image-forming device according to claim 1 and 2 is characterized in that, by automatic control, can satisfy diffraction and strengthen phase contrast CT image-forming and the experiment needs of coaxial phase contrast CT image-forming under different condition; Simultaneously, this device can be realized whole automatizatioies of whole data collection process in conjunction with computer.

4. the method for a synchrotron radiation X-ray phase contrast CT image-forming, its concrete steps are as follows:

Step S1, the phase contrast image-forming condition is definite under the different imaging patterns:

(1) strengthen in the phase contrast CT image-forming experiment at diffraction, the relation of the relevant position on required per sample image-forming condition and the twin crystal rocking curve is determined the angle between monochromator crystal and analyzing crystal,

(2) in the experiment of coaxial phase contrast CT image-forming, the distance of determining suitable sample and detector according to different samples to be obtaining best imaging effect or to obtain required information,

(3) determine respective imaging time of exposure under the different condition according to the different parameters of X ray light intensity, detector etc.;

Step S2, the phase contrast CT image-forming experimental data acquisition, under the determined image-forming condition of step S1, after the moving specific angle of sample rotary table (1) revolution, utilize imaging detector to obtain the phase contrast projection image of a sample, the scope of sample rotary table can be 180 °, 360 ° or other are arbitrarily angled, the final phase contrast two-dimensional projection picture that obtains corresponding number, in described device, after determining the time of exposure under the good different image-forming conditions, the input total angle that need rotate of sample and rotate step-length in program, determined path that data deposit on computers after, the whole data collection process can be moved automatically until data acquisition and finish;

Step S3, the reconstruction of phase contrast imaging experiment data, the correlation theory that strengthens phase place contrast imaging or coaxial phase contrast imaging with diffraction is handled the phase contrast CT layer image that can rebuild sample as the algorithm basis to the two-dimensional projection's picture that is obtained.

5. synchrotron radiation X-ray phase contrast CT image-forming method according to claim 4 is characterized in that, can realize multiple phase contrast CT image-forming pattern experiment

The main pattern that diffraction strengthens the phase contrast CT image-forming experiment has following four kinds:

1) the sample shaft parallel is in rotating shaft of monochromator crystal and analyzing crystal rotating shaft, and this kind pattern is passed through to adjust turntable 2 and realized,

2) the sample rotating shaft is perpendicular to monochromator crystal and analyzing crystal rotating shaft, and this kind pattern can be by being achieved turntable 2 half-twists on a last pattern basis,

3) monochromator crystal and analyzing crystal tuning mode, the monochromator crystal is parallel fully with the analyzing crystal diffraction surfaces,

4) there are a very little angle in monochromator crystal and analyzing crystal off resonance pattern, the diffraction surfaces of monochromator crystal and analyzing crystal;

The groundwork pattern of coaxial phase contrast CT image-forming experiment has following two kinds:

1) carry out coaxial phase contrast imaging CT experiment at optimum sample-detector distance place, this kind pattern need pre-determine the optimum distance between sample and the detector, carries out the CT imaging experiment then under the constant condition of sample-detector distance,

2) choose several different sample-detector distance, carry out the data acquisition of CT imaging experiment at the different distance place respectively, utilize several sets of data that obtained in date processing, to obtain the optimum angle contrast then.

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