WO2020206657A1

WO2020206657A1 - Multi-energy ct imaging system, and application for same

Info

Publication number: WO2020206657A1
Application number: PCT/CN2019/082286
Authority: WO
Inventors: 高河伟; 张丽; 邢宇翔; 陈志强; 吴承鹏; 刘以农
Original assignee: 清华大学
Priority date: 2019-04-11
Filing date: 2019-04-11
Publication date: 2020-10-15

Abstract

A multi-energy CT imaging system and an application for the same. The multi-energy CT imaging system comprises: a radiation ray source having a flying focal spot function and generating a radiation ray used for transmission imaging; an energy spectrum filter comprising multiple filter modules, used for modulating an energy spectrum of an incident radiation ray, and generating an energy spectrum-modulated emergent radiation ray according to respective relative positions of each filter module with respect to a focus point of the radiation ray source, the emergent radiation ray irradiating an object under test; and a detector module used to receive a radiation ray signal having passed through the object under test. The invention uses the radiation ray source having the flying focal spot function, and combines an energy spectrum modulation method and static spatial energy spectrum filtering, thereby enabling fast switching between different radiation ray energy spectra, and achieving multi-energy CT imaging. In addition, the invention acquires non-sparse multi-energy CT data by improving an inter-layer sampling rate and/or an intra-layer sampling rate of a CT scanner, and performs accurate material decomposition of basis materials accordingly, thereby providing promising application prospects in the field of multi-energy CT imaging.

Description

Multi-energy CT imaging system and its application

Technical field

The present disclosure belongs to the field of radiation imaging, and relates to a multi-energy CT imaging system and its application, in particular to a multi-energy CT imaging system and its application based on flying focus and energy spectrum filtering.

Background technique

In the past 20 years, with the rise of large-area flat-panel detectors, cone-beam computed tomography (CT, Computed Tomography) imaging has become a cutting-edge imaging theory and application research due to its high integration, high spatial resolution, convenience and flexibility. The important academic hotspot of X-ray imaging has become a new important subject development direction of X-ray imaging. Cone-beam CT imaging has broad application prospects in many fields such as industry, agriculture, and medicine. It has already played an indispensable and important role in human oral (dental) examination, image-guided interventional therapy, and radiotherapy. Related imaging Theoretical and applied research has also continued to deepen.

Ray scattering is a basic physical challenge that affects the quality of CT images since the birth of CT, which can cause image artifacts and inaccurate CT values. For cone beam CT imaging, ray scattering exists and is very serious in practical applications. Flat-panel detectors cannot be placed with high-performance de-scattering gratings due to their small pixels. Placing the scatter gratings will cause the detector's ray utilization rate to be too low and the dose loss too large.

One of the core issues to improve the imaging performance of cone beam CT is to remove or reduce ray scattering. The methods for removing scattering can be roughly divided into two categories. One is hardware-based direct scattering measurement, such as using scattering occlusion blocks/scattering occlusion bars, and the other is algorithm-based scattering estimation, such as physics-based analysis/Monte Carlo calculations, projection domain convolution filtering, and artifact estimation based on prior images. Generally speaking, the direct measurement type scattering correction method has high accuracy, but it has additional requirements on the hardware, and often requires a second scan, which may increase the dose; while the algorithm estimation method has no additional requirements on the hardware, and does not require a second scan, but The correction effect may be worse, or the computational complexity may increase significantly.

In the dynamic energy spectrum filter multi-energy imaging system, its imaging quality mainly has two limiting factors: (1) Complicated mechanical and electrical control is required to realize the movement of the energy spectrum filter; (2) There is a problem of sparse data and the base material Material decomposition is difficult.

Summary of the invention

(1) Technical problems to be solved

The present disclosure provides a multi-energy CT imaging system and its application to at least partially solve the technical problems mentioned above.

(2) Technical solution

According to one aspect of the present disclosure, a multi-energy CT imaging system is provided, including: a ray source with a flying focus function to generate rays for transmission imaging; an energy spectrum filter for modulating the energy spectrum of incident rays , Including a plurality of filter modules, according to the relative position of each filter module and the focal point of the ray source to generate energy spectrum modulated emitted rays, the emitted rays irradiate the object to be measured; and a detector module for receiving the object to be measured Ray signal.

In some embodiments of the present disclosure, the focal point of a ray source with a flying focus function can move back and forth along the interlayer direction of the detector during CT imaging, or move back and forth along the intralayer direction of the detector, or along The detector moves back and forth in any combination of the two directions between the layers and the layers.

In some embodiments of the present disclosure, the energy spectrum filter is a device relatively fixed to the ray source, and the filter module is made of a material that can change the ray energy spectrum and its spatial distribution. The type, thickness, and distribution of the material determine the energy The energy spectrum distribution of the emitted rays after spectrum modulation.

In some embodiments of the present disclosure, the focus of the flying focus ray source moves back and forth, which occurs during the data collection process of all projection angles of CT imaging, so that the focus positions of data collection at adjacent projection angles are different; or, The focus of the flying focus ray source moves back and forth during the data collection process of the CT imaging part of the projection angle, so that only the focus position of the data collection under the partial projection angle changes.

In some embodiments of the present disclosure, the multiple filter modules of the energy spectrum filter are semi-transparent module units that attenuate part of the rays, and the multiple filter modules are periodically distributed.

In some embodiments of the present disclosure, the multiple filter modules include two or more filter grids or filter bars of different thicknesses or materials.

In some embodiments of the present disclosure, in the multi-energy CT imaging system, the ray source with the flying focus function includes one of the following devices: X-ray tubes, carbon nanotubes, or accelerators.

In some embodiments of the present disclosure, the rays used for transmission imaging are X-rays or gamma rays.

In some embodiments of the present disclosure, the multi-energy CT imaging system further includes: a mechanical/electrical control module for mechanical and/or electrical control of the movement of the focus position of the ray source; a data transmission unit for controlling the detector The ray signal received by the module performs data transmission; and a data processing unit is used for data processing.

According to another aspect of the present disclosure, an application of a multi-energy CT imaging system in the field of multi-energy CT imaging is provided.

(3) Beneficial effects

It can be seen from the above technical solutions that the multi-energy CT imaging system and its application provided by the present disclosure have the following beneficial effects:

Using a ray source with flying focus function, combined with an energy spectrum modulation method and a static spatial energy spectrum filter, it can quickly switch to generate different ray energy spectra to realize multi-energy CT imaging, and at the same time, it can improve the CT detector layer (Z direction) Sampling rate and/or intra-layer (X-direction) sampling rate to obtain non-sparse multi-energy CT data, which can then carry out more accurate decomposition of base materials and adopt faster and more convenient analytical reconstruction methods. It has Good application prospects.

Description of the drawings

Fig. 1 is a simplified schematic diagram of a planar structure of a multi-energy CT imaging system according to an embodiment of the present disclosure.

Fig. 2 is a schematic diagram of a three-dimensional structure of a multi-energy CT imaging system according to an embodiment of the present disclosure.

Fig. 3 is a schematic diagram of the function of a ray source flying focus in a multi-energy CT imaging system according to an embodiment of the disclosure.

4 is a schematic diagram of the energy spectrum filter of the multi-energy CT imaging system according to an embodiment of the present disclosure modulating the energy spectrum of the incident rays, and generating rays of different energy spectra according to the relative position of the focus of the ray source, wherein, (a) is a schematic diagram of incident rays containing multiple energy spectra, (c) is a schematic diagram of energy spectrum distribution corresponding to incident rays; (b) is a schematic diagram of emitted rays modulated by an energy spectrum filter, (d) is a The schematic diagram of the energy spectrum distribution corresponding to the ray; (e) is the schematic diagram of the material distribution of the energy spectrum filter.

detailed description

Source modulation scattering correction has been developed in the past 10 years. Its basic principle is to place a high-frequency translucent attenuation grid between the X-ray source and the scanned object, and pass a series of physical assumptions (mainly scattered photon distribution). The low-frequency characteristics) and mathematical derivation to achieve fast scatter correction requiring only one CT scan measurement. In recent years, source modulation scatter correction has been further developed, especially in scatter estimation algorithms. The main difficulty of source modulation scattering correction is that the modulator will introduce ray hardening and energy spectrum inconsistency, which may limit the performance of scattering correction in practical applications.

Currently, research on ray source filtering is very active, such as dynamic bow tie filters and dynamic spatial energy spectrum filters. Dynamic spatial energy spectrum filtering can realize cone-beam CT multi-energy imaging, but it needs more complicated mechanical and electrical control to realize the movement of energy spectrum filter, there is a problem of sparse data, and it is difficult to decompose the base material. The latest research results in source modulation extend the source modulation method to cone-beam CT dual-energy imaging, but it also has the problem of sparse data and requires iterative reconstruction methods.

The ray source flying focus technology has been successfully applied to high-end medical diagnostic CT machines. It increases the sampling rate between layers (Z direction) or intralayer (X direction) of the CT detector by changing the position where the electron beam bombards the tungsten target during the generation of the X-ray source, that is, the focus position of the X-ray source.

The present disclosure innovatively uses the ray source flying focus technology, combines the energy spectrum modulation scattering correction theory, and the static spatial energy spectrum filtering method to establish a brand-new multi-energy CT imaging system to realize non-sparse multi-energy CT data and single energy Multi-energy CT imaging system with ray source and static energy spectrum filtering.

In order to make the objectives, technical solutions, and advantages of the present disclosure clearer, the following further describes the present disclosure in detail with reference to specific embodiments and drawings. In the present disclosure, "A/B" means A and/or B. For example, a data transmission/processing unit includes a data transmission unit or a data processing unit, or the unit has both data transmission and processing functions.

In the first exemplary embodiment of the present disclosure, a multi-energy CT imaging system is provided.

Fig. 1 is a simplified schematic diagram of a planar structure of a multi-energy CT imaging system according to an embodiment of the present disclosure. Fig. 2 is a schematic diagram of a three-dimensional structure of a multi-energy CT imaging system according to an embodiment of the present disclosure.

1 and 2, the multi-energy CT imaging system of the present disclosure includes: a ray source with a flying focus function to generate rays for transmission imaging; an energy spectrum filter for performing the energy spectrum of incident rays Modulation, including multiple filter modules, according to the relative position of each filter module and the focal point of the ray source to generate energy spectrum modulated emitted rays, which irradiate the object to be measured; and a detector module for receiving the object to be measured Ray signal.

In this embodiment, the multi-energy CT imaging system further includes: a mechanical/electrical control module, which is used to mechanically and/or electrically control the movement of the focal position of the radiation source.

In some embodiments, the multi-energy CT imaging system further includes: a data transmission unit for data transmission of the radiation signal received by the detector module. Furthermore, it also includes: a data processing unit for data processing. Of course, the data transmission unit and the data processing unit may be integrated in the same module, or may be separate units.

Referring to FIG. 2, the multi-energy CT imaging system in this embodiment includes: a ray source, an energy spectrum filter, a detector module, a mechanical/electrical control and a data transmission/processing unit.

In this embodiment, the ray source is a ray source with a flying focus function, which can be one of X-ray tubes, carbon nanotubes and accelerators, which can generate rays for transmission imaging; the rays are X-rays or Gamma rays. Horse ray; the focus of the ray source can move along the interlayer (Z direction shown in Figure 3) and/or within the layer (X direction shown in Figure 3) or two directions successively to change the initial position of the ray emitted by the ray source . The ray source can rotate 360 degrees around the object to be measured, as shown by the circular dashed line in the figure, so as to scan all angles of the object to be measured.

Fig. 3 is a schematic diagram of the function of a ray source flying focus in a multi-energy CT imaging system according to an embodiment of the present disclosure.

Please refer to Figure 3, assuming that the focus of the ray source is initially at the center point, the focus can be quickly switched to the upper and lower points in the Z direction, or the left and right points in the X direction, or the four points in the diagonal direction through electrical control operations. Place. In this way, the fly-focus function of the ray source is used to make the focal point of the ray source move as required, so as to realize the regulation of the initial position of the ray emitted by the ray source.

Of course, in actual use, it is not necessary to use the flying focus function for sampling at every angle. The frequency of the flying focus can be determined according to actual needs. For example, the sparse flying focus adopting mode is used, that is, a flying focus sampling is done every few angles.

In some embodiments of the present disclosure, the plurality of filter modules of the energy spectrum filter are semi-transparent module units that attenuate part of the rays, and the plurality of filter modules are arranged in a periodic distribution form, for example, the plurality of filter modules are arranged in a high frequency period. Sexual grid-like.

In some embodiments of the present disclosure, the energy spectrum filter is a device relatively fixed to the ray source, and the filter module is made of a material that can change the ray energy spectrum and its spatial distribution, and the type, thickness and distribution of the material are determined The energy spectrum distribution of the emitted rays after energy spectrum modulation.

In this embodiment, the energy spectrum filter is a device relatively fixed to the ray source, and a plurality of filter modules are made of materials that can absorb part of the rays, and are processed into translucent module units, arranged in a high-frequency periodic grid. The incident ray energy spectrum is modulated, and rays of different energy spectrum are generated according to the relative position of the filter module and the focus of the ray source. The ray energy spectrum or energy spectrum distribution represents the quantity distribution formed by rays of different energy.

4 is a schematic diagram of the energy spectrum filter of the multi-energy CT imaging system according to an embodiment of the present disclosure modulating the energy spectrum of the incident rays, and generating rays of different energy spectra according to the relative position of the focus of the ray source, wherein, (a) is a schematic diagram of incident rays containing multiple energy spectra, (c) is a schematic diagram of the energy spectrum distribution corresponding to the incident rays, the ordinate is normalized; (b) is the outgoing ray modulated by an energy spectrum filter In the schematic diagram, (d) is the schematic diagram of the energy spectrum distribution corresponding to the emitted rays, and the ordinate is normalized; (e) is the schematic diagram of the material distribution of the energy spectrum filter.

Please refer to Figure 4. In this embodiment, it is assumed that three different energy spectra need to be generated through an energy spectrum filter, and the corresponding energy spectrum filter is composed of three different types of materials with different thicknesses, which are respectively material 1, material 2. And material 3 are arranged at intervals in order to form a high-frequency periodic grid, as shown in Figure 4 (e), which can modulate the energy spectrum of incident rays. The incident rays are shown in Figure 4 (a). Parallel lines at the same starting position indicate rays of the same energy. Figure 4(a) illustrates incident rays of multiple energies, such as three energies. The energy spectrum distribution diagrams of these three energies are shown in Figure 4(c) ) Means; after the incident rays containing multiple energies are modulated by energy spectrum filters arranged in a high-frequency periodic grid, the outgoing rays are generated according to the relative position of the focus of the ray source. The outgoing rays are shown in Figure 4 ( As shown in b), compared with the incident ray shown in Fig. 4(a), each energy value and the distribution of each energy value have changed. The energy spectrum distribution diagram of the outgoing ray is shown in Fig. 4(d) , So as to achieve energy spectrum modulation, and then change the energy spectrum of rays passing through the object.

Of course, in the actual embodiment, the material type, thickness, and arrangement manner of the corresponding energy spectrum filter can be designed according to system design requirements, and it is not limited to the material type, thickness and arrangement manner in this embodiment.

Based on the multi-energy CT imaging system of the present disclosure, combined with the patent application "Multi-energy CT-based material decomposition method" filed by the applicant on the same day, CT imaging without artifacts can be realized. Based on the multi-energy CT system, it can quickly switch to generate different ray energy spectra, realize multi-energy CT imaging, and at the same time, it can increase the sampling rate between the CT detector layers (Z direction) and/or the intra-layer (X direction) sampling rate to obtain non- Sparse multi-energy CT data, and then more accurate decomposition of the base material; by adding the scattering intensity under the corresponding energy spectrum to the energy spectrum projection value under multi-energy, the relationship between the scattering intensity under different energy is calibrated , The scattering distribution correlation function is obtained. At this time, the weighted coefficient projection value and the scattering intensity distribution of the two base materials can be calculated through the pre-established mapping model. According to the actual measured projection value, based on the pre-established two-way mapping relationship, Then the projection value can be decomposed to M base materials, and the projection data and scattering intensity of the M base materials corresponding to the unknown object structure can be found. Since the scattering intensity and the projection data of the M base materials are separated, Elimination of artifacts, image reconstruction only based on the projection data of a variety of base materials, images without artifacts can be obtained, with a very good effect of eliminating artifacts, has a good application in the field of multi-energy CT imaging prospect.

In summary, the present disclosure provides a multi-energy CT imaging system and its application. By using a ray source with flying focus function, combined with a source modulation method and static spatial energy spectrum filtering, it can quickly switch to generate different ray energy spectra. , To achieve multi-energy CT imaging, and at the same time to obtain non-sparse multi-energy CT data by increasing the inter-layer (Z-direction) sampling rate and/or the intra-layer (X-direction) sampling rate of the CT detector, thereby enabling more accurate base materials Material decomposition and the use of faster and more convenient analytical reconstruction methods have good application prospects in the field of multi-energy CT imaging. Based on this multi-energy CT imaging system, CT imaging without artifacts can be realized.

It should be noted that various structural schematic diagrams introduced according to the embodiments of the present disclosure are shown in the accompanying drawings. The figures are not drawn to scale, in which some details are enlarged for clarity of presentation, and some details may be omitted. Furthermore, the word "comprising" or "including" does not exclude the presence of elements or steps not listed in the claims. The word "a" or "an" preceding an element does not exclude the presence of multiple such elements.

The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present disclosure in further detail. It should be understood that the above are only specific embodiments of the present disclosure and are not intended to limit the present disclosure. Any modification, equivalent replacement, improvement, etc., made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.

Claims

A multi-energy CT imaging system, characterized in that it comprises:

A ray source with flying focus function to generate rays for transmission imaging;

The energy spectrum filter is used to modulate the energy spectrum of the incident ray. It contains multiple filter modules to generate energy spectrum modulated emission rays according to the relative position of each filter module and the focus of the ray source, which irradiates the object to be measured On; and

The detector module is used to receive the ray signal passing through the object to be measured.
The multi-energy CT imaging system according to claim 1, wherein the focal point of the ray source with flying focus function can move back and forth along the interlayer direction of the detector during the CT imaging process, or along the detection It moves back and forth in the direction of the detector layer, or moves back and forth along any combination of the two directions between the layers of the detector.
The multi-energy CT imaging system according to claim 1, wherein the energy spectrum filter is a device relatively fixed to the ray source, and the filter module is made of a material capable of changing the ray energy spectrum and its spatial distribution. The type, thickness and distribution of the material determine the energy spectrum distribution of the emitted rays after the energy spectrum modulation.
The multi-energy CT imaging system according to claim 2, wherein:

The movement of the focal point of the flying focus ray source back and forth occurs during the data collection process of all the projection angles of CT imaging, so that the focal positions of the data collection at adjacent projection angles are different; or,

The back and forth movement of the focal point of the ray source of the flying focus occurs during the data collection process of the CT imaging partial projection angle, so that only the focal position during data collection under the partial projection angle changes.
The multi-energy CT imaging system of claim 3, wherein the plurality of filter modules of the energy spectrum filter are semi-transparent module units that attenuate part of the rays, and the plurality of filter modules are periodically distributed.
The multi-energy CT imaging system according to claim 5, wherein the multiple filter modules comprise two or more filter grids or filter bars of different thicknesses or materials.
The multi-energy CT imaging system according to claim 1, wherein the radiation source with a flying focus function comprises one of the following devices: X-ray tubes, carbon nanotubes or accelerators.
The multi-energy CT imaging system of claim 1, wherein the radiation used for transmission imaging is X-ray or gamma-ray.
The multi-energy CT imaging system of claim 1, further comprising:

The mechanical/electrical control module is used for mechanical and/or electrical control of the movement of the focus position of the ray source; the data transmission unit is used for data transmission of the ray signal received by the detector module; and the data processing unit is used for data deal with.
The application of the multi-energy CT imaging system according to any one of claims 1 to 9 in the field of multi-energy CT imaging.