CN107748341B - High-contrast low-dose phase contrast CT imaging device - Google Patents

Abstract

The invention discloses a high-contrast low-dose phase contrast CT imaging device, which comprises: the imaging device comprises a base, a rotary table, an imaging platform and a sample table which is axially embedded in the center of the circle inside the rotary table; an X-ray light source, a source grating, a beam splitting grating, an opening for the upper part of the sample table to stretch out and draw back, an analysis grating and a detector are sequentially arranged on the imaging platform along the direction of the light path; the source grating, the beam splitting grating and the analysis grating are arc-shaped, and the circle centers of the source grating, the beam splitting grating and the analysis grating are all positioned at the X-ray light source. The high-contrast low-dose phase contrast CT imaging device can realize larger penetration depth by utilizing the high-energy X-ray source, thereby being applied to high-contrast low-dose imaging of thick samples (tens of centimeters) and even human bodies. The imaging device can realize the rotation of the sample stage and the rotation of the imaging system, is stable and reliable, and can provide the precision requirement required by the imaging technology.

Description

High contrast and low dose phase contrast CT imaging device

Technical Field

The invention relates to the technical field of X-ray imaging, and in particular to a high-contrast and low-dose phase-contrast CT imaging device.

Background Art

Traditional X-ray imaging technology is based on the different X-ray absorption properties of substances. For substances composed of heavy elements such as metals, traditional X-ray imaging technology can obtain good image contrast. However, for substances composed of light elements such as carbon, oxygen, nitrogen, and oxygen, such as human soft tissues such as breasts, blood vessels, fat, and cartilage in medical imaging, their absorption of X-rays is very weak. The images of these tissues obtained under traditional X-ray imaging technology are blurry and indistinguishable.

X-ray phase contrast imaging technology detects the phase change (i.e. phase shift) of X-rays passing through matter to perform imaging. In the hard X-ray band (10-100keV), for light elements such as carbon, hydrogen, nitrogen, and oxygen, their coherent scattering cross section (i.e. phase shift cross section) is more than 1,000 times their respective absorption cross sections. Therefore, in theory, for materials composed of light elements, hard X-ray phase contrast imaging technology can provide image contrast and measurement sensitivity thousands of times higher than traditional absorption contrast imaging.

However, the imaging energy of this technology is mainly around 30keV, and the penetration depth in the human body model is only 5 cm. Therefore, it is only suitable for imaging studies of thin samples (such as mice). Moreover, because the photon flux emitted by the X-ray machine is low, a long exposure time (about 26 hours) is required to reduce noise and increase image quality. In addition, in the phase contrast CT machine built based on the current theoretical framework, when the frame rotates, the three gratings need to rotate around the sample together, and at the same time, the three gratings need to be strictly aligned. However, during the rotation process, gravity, mechanical manufacturing errors, mechanical assembly errors, mechanical vibrations, thermal expansion and other factors will seriously affect the alignment of the three gratings. Therefore, their system has very stringent requirements for mechanical stability. At present, most of the domestic and foreign can only build a simple desktop platform with a rotating sample table and a stationary imaging system. There is no CT device with a rotating imaging system put into use.

Summary of the invention

The technical problem to be solved by the present invention is to provide a high-contrast, low-dose phase-contrast CT imaging device in view of the deficiencies in the above-mentioned prior art.

In order to solve the above technical problems, the technical solution adopted by the present invention is: a high-contrast low-dose phase contrast CT imaging device, comprising: a base, a rotating table arranged above the base, an imaging platform arranged on the rotating table, and a sample table axially embedded in the center of the inner circle of the rotating table;

The imaging platform is provided with an X-ray light source, a source grating, a beam splitting grating, an opening for the upper part of the sample stage to extend and pass through, an analysis grating and a detector in sequence along the optical path direction;

A micro-displacement stepping mechanism is provided at the lower end of the beam splitting grating, and the micro-displacement stepping mechanism includes a flexible hinge mechanism and a piezoelectric ceramic driving mechanism;

The lower ends of the source grating and the beam splitting grating are both provided with posture adjustment mechanisms;

The source grating, beam splitting grating and analysis grating are all in arc shape, and the centers of the circles are all located at the X-ray light source.

Preferably, the source grating is also provided with an aperture mechanism for adjusting the incident range of X-rays. Preferably, a heat insulation device is provided between the X-ray light source and the source grating.

Preferably, the sample stage comprises a lifting mechanism, a plane adjustment mechanism and a rotating mechanism.

Preferably, the posture adjustment mechanism includes an X, Y, Z three-axis translation adjustment mechanism and a three-axis adjustment mechanism rotating around the X, Y, Z axes.

Preferably, the base and the rotating table are connected via a radial shaft system and a thrust shaft system.

Preferably, a slip ring for transmitting electrical signals and data signals is connected to the lower end of the rotating platform, and a slip ring reading bracket fixedly connected to the base is arranged below the slip ring.

Preferably, a torque motor is arranged in the center of the rotating table.

Preferably, the bottom of the base is provided with leveling feet.

Preferably, the data acquisition process of the high-contrast, low-dose phase-contrast CT imaging device during detection work includes the following steps:

Step 1: Collecting data detected by the detector when the beam splitting grating is respectively at a preset first acquisition position, a second acquisition position, a third acquisition position and a fourth acquisition position when there is no sample, and using the four sets of data collected as the background intensity of the above four acquisition positions respectively;

Step 2: Collect data from each slice of the sample, which specifically includes:

Step 2-1: Fixing the beam splitting grating to the first acquisition position;

Step 2-2: Control the rotating stage to rotate at a speed of 0.5 cycles/second, control the detector to collect data at a rate of 2.5 ms per frame, and stop collecting data after the rotating stage rotates one circle;

Step 2-3: driving the beam splitting grating to move to the second acquisition position by the micro-displacement stepping mechanism, and repeating step 2-2;

Step 2-4: driving the beam splitting grating to move to the third acquisition position by the micro-displacement stepping mechanism, and repeating step 2-2;

Step 2-5: driving the beam splitting grating to move to the fourth acquisition position through the micro-displacement stepping mechanism, repeating step 2-2, and completing data acquisition of one slice of the sample;

Step 3: Control the sample stage to move a set distance in the axial direction, and repeat step 2 to collect data of the next slice of the sample;

Step 4: Data separation and reconstruction: The four groups of data obtained when the beam splitting grating is at the four acquisition positions in each slice of the sample acquired in the above steps are respectively combined into one set of data to complete the data acquisition.

The beneficial effects of the present invention are as follows: the high-contrast, low-dose phase-contrast CT imaging device of the present invention can utilize a high-energy X-ray source to achieve a greater penetration depth, and thus can be applied to high-contrast, low-dose imaging of thick samples (tens of centimeters) or even the human body. The present invention can greatly reduce the radiation dose received by the sample. In addition, the imaging device of the present invention can realize both the rotation of the sample stage and the rotation of the imaging system, and is stable and reliable, and can provide the accuracy requirements required by the imaging technology. The system of the present invention has high stability, is easy to install and manufacture, and is easy to operate. It can well meet user needs and has broad market prospects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic structural diagram of a high-contrast, low-dose phase-contrast CT imaging device according to the present invention;

FIG2 is a cross-sectional view of a high-contrast, low-dose phase-contrast CT imaging device according to the present invention;

FIG3 is a schematic structural diagram of a sample stage of a high-contrast, low-dose phase contrast CT imaging device according to the present invention;

FIG4 is a schematic structural diagram of a source grating of a high-contrast, low-dose phase contrast CT imaging device according to the present invention;

FIG. 5 is a schematic structural diagram of a beam splitting grating of a high-contrast, low-dose phase contrast CT imaging device according to the present invention.

Description of reference numerals:

1—base; 2—rotating table; 3—imaging platform; 4—sample stage; 5—radial axis system; 6—thrust axis system; 7—slip ring; 8—slip ring reading bracket; 9—torque motor; 10—leveling foot; 30—X-ray light source; 31—source grating; 32—beam splitting grating; 33—opening; 34—analyzer grating; 35—detector; 36—micro-displacement stepping mechanism; 37—posture adjustment mechanism; 38—thermal insulation device; 40—lifting mechanism; 41—plane adjustment mechanism; 42—rotation mechanism; 310—aperture mechanism; 370—three-axis translation adjustment mechanism; 371—three-axis adjustment mechanism 371.

DETAILED DESCRIPTION

The present invention is further described in detail below in conjunction with embodiments so that those skilled in the art can implement the invention with reference to the description.

It should be understood that terms such as “having”, “including” and “comprising” used herein do not exclude the existence or addition of one or more other elements or combinations thereof.

As shown in FIGS. 1-5 , a high-contrast, low-dose phase contrast CT imaging device of the present embodiment comprises: a base 1, a rotating table 2 arranged above the base 1, an imaging platform 3 arranged on the rotating table 2, and a sample table 4 axially embedded at the inner center of the rotating table 2; an X-ray light source 30, a source grating 31, a beam splitting grating 32, an opening 33 for the upper part of the sample table 4 to extend and pass through, an analyzing grating 34, and a detector 35 are sequentially arranged on the imaging platform 3 along the optical path direction; the base 1 and the rotating table 2 are connected by a radial shaft system 5 and a thrust shaft system 6. A torque motor 9 is arranged in the center of the rotating table 2; the sample stage 4 includes a lifting mechanism 40, a plane adjustment mechanism 41 and a rotating mechanism 42, the lifting mechanism 40 realizes the axial lifting of the sample stage 4, the rotating mechanism 42 realizes the rotation adjustment of the sample stage 4 around the axial direction, and the plane adjustment mechanism 41 is used to adjust the displacement of the rotating mechanism 42 in the horizontal direction. By adjusting the horizontal position of the sample on the rotating mechanism 42, the scanning range of the X-ray light source 30 can be adjusted; the material of the imaging platform 3 is granite; the bottom of the base 1 is provided with a leveling foot 10.

The source grating 31 , the beam splitting grating 32 and the analyzer grating 34 are all in arc shape, and the centers thereof are all located at the X-ray light source 30 .

The lower ends of the source grating 31 and the beam splitting grating 32 are both provided with a posture adjustment mechanism 37. The posture adjustment mechanism 37 includes an X, Y, Z three-axis translation adjustment mechanism 370 and a three-axis adjustment mechanism 371 rotating around the X, Y, and Z axes. The three-axis translation adjustment mechanism 370 realizes movement adjustment in the three directions of X, Y, and Z, and the three-axis adjustment mechanism 371 realizes rotation adjustment around the three axes of X, Y, and Z, so that the posture adjustment mechanism 37 is used to realize adjustment in the up, down, left, right, front, and back directions and three rotation directions. A locking mechanism is also provided on the adjustment mechanism.

An aperture mechanism 310 for adjusting the X-ray incident range is also provided on the source grating 31 , and a heat insulation device 38 is provided between the X-ray light source 30 and the source grating 31 .

A micro-displacement stepping mechanism 36 is disposed at the lower end of the beam splitting grating 32 . The micro-displacement stepping mechanism 36 includes a flexible hinge mechanism and a piezoelectric ceramic driving mechanism.

The lower end of the rotating table 2 is also connected to a slip ring 7 for transmitting electrical signals and data signals, and the slip ring 7 is connected to the electrical signal and data signal transmission line on the upper end of the rotating table 2. A slip ring reading bracket 8 fixed to the base 1 is provided below the slip ring 7. The slip ring reading bracket 8 is used to transmit the electrical signal and data signal of the slip ring 7 to an external controller.

When the high-contrast, low-dose phase-contrast CT imaging device performs sample detection, the sample is irradiated with X-rays and data is collected to obtain a CT image.

The X-ray source is a light source that emits a cone beam of rays. The source grating 31 is located 100 mm from the focus of the X-ray source. Since the imaging system has a geometric magnification factor, the area of the source grating 31 does not need to be too large, as long as its projection on the detector 35 is larger than the receiving area of the detector 35. From a process point of view, a grating with a smaller area is easier to process and manufacture, can better ensure its uniformity, and has low cost. The source grating 31 includes an aperture mechanism 31 for adjusting the X-ray incident range, so that in the subsequent imaging process, the detector 35 can only receive photons in the area with moiré fringes, so that the aperture completely blocks the photons directed to the area without moiré fringes, which can improve the accuracy of the image collected by the detector 35 and increase the service life of the detector 35.

The beam splitter grating 32 is set at 400mm from the focus of the X-ray source, the analysis grating 34 is set at 1600mm from the focus of the X-ray source, the sample stage 4 is located at the center of the rotating stage 2 and is set behind the beam splitter grating 32, and the detector 35 is set behind the analysis grating 34.

To ensure the accuracy of the imaging system, the radial runout of the turntable spindle does not exceed 10 microns, the axial runout error does not exceed 37 microns, and the turntable positioning accuracy does not exceed 0.1rad.

During imaging, the source grating 31 first divides the millimeter-level X-ray source into a series of line light sources. For each line light source, its spatial coherence length at the beam splitting grating 32 is greater than the period of the beam splitting grating 32. In this way, the beam splitting grating 32 forms a self-image at the position of the analysis grating 34 under the illumination of coherent light through the Taibao effect.

Then, through the Lau effect, the self-imaging fringes generated by the beam splitting grating 32 under the illumination of each linear light source will be staggered by one period, and thus incoherently superimposed together, and the intensity of the self-imaging fringes will be greatly enhanced.

Then, the self-imaging fringes of the beam splitting grating 32 and the analyzing grating 34 will form moiré fringes. If there is a small angle between the self-imaging fringes of the beam splitting grating 32 and the fringes of the analyzing grating 34, or there is a small difference between the period of the self-imaging fringes of the beam splitting grating 32 and the period of the analyzing grating 34, then the moiré fringes with a very large period can be detected by the X-ray detector 35 behind the analyzing grating 34.

Then, the X-rays will be refracted when passing through the sample. The deflection of the light will cause the shape of the moiré fringe to be distorted, which is reflected in the actual experiment as the change of pixel light intensity. By measuring the change of each pixel intensity, the refraction image of the sample can be obtained.

The data acquisition process (i.e., imaging process) of the high-contrast, low-dose phase contrast CT imaging device includes the following steps:

Step 1: Collect data detected by the detector 35 when the beam splitting grating 32 is respectively at the first acquisition position, the second acquisition position, the third acquisition position and the fourth acquisition position when there is no sample, and use the four sets of data collected as the background intensity of the above four acquisition positions respectively;

Step 2: Collect data from each slice of the sample, which specifically includes:

Step 2-1: Fix the beam splitting grating 32 to the first collection position;

Step 2-2: Control the rotating stage 2 to rotate at a speed of 0.5 cycles/second, control the detector 35 to collect data at a rate of 2.5 ms per frame, and stop collecting data after the rotating stage 2 rotates one circle;

Step 2-3: drive the beam splitting grating 32 to move to the second acquisition position through the micro-displacement stepping mechanism 36, and repeat step 2-2;

Step 2-4: drive the beam splitting grating 32 to move to the third acquisition position through the micro-displacement stepping mechanism 36, and repeat step 2-2;

Step 2-5: driving the beam splitting grating 32 to move to the fourth acquisition position through the micro-displacement stepping mechanism 36, and repeating step 2-2 to complete the data acquisition of one slice of the sample;

Step 3: Control the sample stage 4 to move a set distance in the axial direction, and repeat step 2 to collect data of the next fan-beam tomography of the sample;

Step 4: Data separation and reconstruction: The four sets of data obtained when the beam splitting grating 32 is in the four acquisition positions in each slice of the sample acquired in the above steps are respectively combined into one set of data to complete the data acquisition. Subsequently, data separation and CT reconstruction are performed. The same method as the traditional PS solution is used for data separation and CT reconstruction.

Among them, the four collection positions are arranged along the arc extension line of the arc-shaped beam splitting grating 32, that is, the four collection positions and the beam splitting grating 32 are on the same circumference. Therefore, when collecting data, the beam splitting grating 32 needs to move in an arc, which is driven by a piezoelectric ceramic driving mechanism to push the beam splitting grating 32 to move, and the flexible hinge mechanism is used to limit the displacement, limiting the movement path of the beam splitting grating 32 to an arc, thereby realizing the arc movement of the beam splitting grating 32 through the micro-displacement stepping mechanism 36.

In another embodiment, the imaging system may not rotate, and the imaging of the object may be achieved by rotating the sample stage 4 .

Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to specific details.

Claims (2)

1. A high contrast, low dose phase contrast CT imaging apparatus, comprising: the device comprises a base, a rotary table arranged above the base, an imaging platform arranged on the rotary table, and a sample table axially embedded in the center of the rotary table;

An X-ray light source, a source grating, a beam splitting grating, an opening for the upper part of the sample table to stretch out and draw back, an analysis grating and a detector are sequentially arranged on the imaging platform along the direction of the light path;

The lower end of the beam splitting grating is provided with a micro-displacement stepping mechanism, and the micro-displacement stepping mechanism comprises a flexible hinge mechanism and a piezoelectric ceramic pushing mechanism;

the lower ends of the source grating and the beam splitting grating are respectively provided with an attitude adjusting mechanism;

The source grating, the beam splitting grating and the analysis grating are arc-shaped, and the circle centers of the source grating, the beam splitting grating and the analysis grating are all positioned at the X-ray light source;

the sample stage comprises a lifting mechanism, a plane adjusting mechanism and a rotating mechanism;

the data acquisition process of the high-contrast low-dose phase contrast CT imaging device during detection operation comprises the following steps:

step 1: when no sample is collected, the data detected by the detector when the beam splitting grating is respectively positioned at a preset first collecting position, a preset second collecting position, a preset third collecting position and a preset fourth collecting position are respectively collected, and the collected four groups of data are respectively used as the background intensities of the four collecting positions;

Step 2: data acquisition of each fault of the sample is performed, which specifically comprises:

Step 2-1: fixing the beam splitting grating to the first acquisition position;

step 2-2: the rotating table is controlled to rotate at a rotating speed of 0.5 cycle/second, the detector is controlled to collect data at a rate of 2.5ms per frame, and the collection is stopped after the rotating table rotates for one cycle;

step 2-3: driving the beam splitting grating to move to the second acquisition position through the micro-displacement stepping mechanism, and repeating the step 2-2;

step 2-4: driving the beam splitting grating to move to the third acquisition position through the micro-displacement stepping mechanism, and repeating the step 2-2;

Step 2-5: driving the beam splitting grating to move to the fourth acquisition position through the micro-displacement stepping mechanism, repeating the step 2-2, and completing data acquisition of one fault of the sample;

Step 3: controlling the sample table to move along the axial direction by a set distance, and repeating the step 2 to acquire data of the next fault of the sample;

step 4: data separation and reconstruction: the 4 groups of data acquired by the step when the beam splitting grating is positioned at four acquisition positions in each fault of the sample are respectively combined into one group of data, so that data acquisition is completed;

The 4 acquisition positions are arranged along the arc extension line of the arc-shaped beam splitting grating, namely the 4 acquisition positions and the beam splitting grating are positioned on the same circumference;

the source grating is also provided with a diaphragm mechanism for adjusting the incidence range of X rays;

A heat insulation device is arranged between the X-ray light source and the source grating;

the gesture adjusting mechanism comprises an X, Y and Z three-axis translation adjusting mechanism and a three-axis adjusting mechanism rotating around three axes of X, Y and Z;

the base is connected with the rotary table through a radial shafting and a thrust shafting;

the lower end of the rotary table is also connected with a slip ring for transmitting electric signals and data signals, and a slip ring reading bracket fixedly connected to the base is arranged below the slip ring;

the center of the rotary table is provided with a torque motor.

2. The high-contrast low-dose phase contrast CT imaging apparatus of claim 1, wherein the base bottom is provided with leveling feet.