CN113281358B - Multi-energy X-ray cone-beam CT imaging system and method - Google Patents
Multi-energy X-ray cone-beam CT imaging system and method Download PDFInfo
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Abstract
The invention discloses a multi-energy X-ray cone-beam CT imaging system and a multi-energy X-ray cone-beam CT imaging method. The system comprises a ray source, an energy spectrum modulator, a detector and a mechanical/electrical control and data transmission/processing unit, wherein the ray source has a zoom point function and a rapid kilovolt switching function, and the ray source performs periodic high-energy and low-energy spectrum rapid switching through the rapid kilovolt switching function in the CT scanning rotation process; the energy spectrum modulator is arranged between the ray source and an object to be imaged so as to change the intensity distribution and the energy spectrum shape distribution of the X-rays; the detector is used for detecting an X-ray transmission value of an energy spectrum emitted by the ray source after passing through the energy spectrum modulator and an object to be imaged; the mechanical/electrical control and data transmission/processing unit is used for controlling the ray source, the energy spectrum modulator and the detector, classifying the acquired X-ray transmission values into different categories according to the position of the zoom point, and performing data processing on the X-ray transmission values based on the different categories. The CT image obtained by the invention has high quality.
Description
Technical Field
The invention relates to the technical field of CT radiation imaging, in particular to a multi-energy X-ray cone-beam CT imaging system and a multi-energy X-ray cone-beam CT imaging method.
Background
The CT apparatus can observe the internal structure of an object to be imaged by using the attenuation characteristics of X-rays, and plays an important role in the field of medical diagnosis. However, the conventional CT apparatus cannot accurately distinguish different materials with similar attenuation, which brings difficulty to the identification and diagnosis of CT images. Therefore, in 1973, Godfrey Hounsfield proposed that two spectra could be scanned separately to effectively distinguish different materials, and the research of dual-energy CT was gradually developed.
In the field of dual-energy or multi-energy CT, the current mainstream CT systems mainly use dual-source dual-probe, fast kv switching, and dual-layer detector technologies. These techniques are superior and inferior, and play an important role in clinical practice. Meanwhile, in the last 20 years, with the rise of large-area flat panel detectors, cone-beam CT imaging is an important academic hotspot of theory and application research of imaging frontier due to the advantages of high integration level, high spatial resolution, convenience, flexibility and the like, and becomes a new important subject development direction of X-ray imaging. Cone beam CT imaging has a wide application prospect in many fields such as industry, agriculture and medicine, has played an indispensable important role in the fields such as human oral (dental) examination, image-guided interventional therapy and radiotherapy, and the theory and application research related to multi-functional cone beam CT are also in depth.
Ray scattering is the fundamental physical challenge which affects the quality of CT images and exists since birth, and can cause problems of image artifacts, inaccurate CT values and the like. For cone beam CT imaging, radiation scatter exists and is significant in practical applications. Flat panel detectors cannot place high performance backscatter gratings because the pixels are small (otherwise the detector ray utilization is too low and the dose loss is too large). One of the most central issues in improving cone-beam CT imaging performance is to remove or reduce ray scatter. Current methods of scattering treatment can be divided into two broad categories: a pretreatment method and a post-treatment method. The preprocessing method is to reduce the scattering transmittance by preventing scattering from reaching the detector, so as to suppress scattering signals; the post-processing method is based on an estimation of the scatter contribution in the projection data, removing the scatter signal in the acquired data.
Among the numerous post-processing methods, the source modulation scatter correction method is taken as an example. The method is characterized in that a modulator (a semitransparent attenuation grid) is inserted between an X-ray source and a measured object to attenuate a high-frequency signal of projection data, a transmission signal and a scattering signal are strongly separated in a frequency domain according to the low-frequency characteristic of scattering distribution, and then accurate scattering estimation is obtained by utilizing filtering and demodulation technologies. In a fast kilovolt switching cone beam CT multi-energy imaging system, due to the existence of scattering, the energy resolution is poor, and the addition of source modulation and variable focus has important significance for improving the scattering correction and the energy resolution.
Disclosure of Invention
The present invention is directed to solving at least one of the problems of the prior art. Therefore, an object of the present invention is to provide a multi-energy X-ray cone-beam CT imaging system, which can obtain high quality CT images.
A multi-energy X-ray cone-beam CT imaging system according to an embodiment of the first aspect of the invention comprises:
the source of rays, the source of rays is used for transmission imaging, the source of rays has a zoom point function, the source of rays has a fast kilovolt switching function, and the source of rays performs periodic high-low energy spectrum fast switching through the fast kilovolt switching function during CT scanning rotation;
the energy spectrum modulator is arranged between the ray source and an object to be imaged, and is a non-uniform filter plate formed by periodically arranging a plurality of different sub-modules and used for changing the intensity distribution and the energy spectrum shape distribution of X rays;
the detector is used for detecting an X-ray transmission value of an energy spectrum emitted by the ray source after passing through the energy spectrum modulator and the object to be imaged;
the mechanical/electrical control and data transmission/processing unit is used for controlling the ray source, the energy spectrum modulator and the detector, classifying the acquired X-ray transmission values into different categories by combining a zoom point function, and performing data processing on the X-ray transmission values based on the different categories; the data processing includes, but is not limited to, dividing the obtained X-ray transmission value into X-ray transmission data of a plurality of energy regions, and combining a zoom point function to realize scattering correction and improve the capability of material decomposition.
According to the multi-energy X-ray cone-beam CT imaging system disclosed by the embodiment of the first aspect of the invention, the radiation source is introduced with a quick kilovolt switching function to realize multi-energy CT imaging, and meanwhile, the non-uniform filter plate is used as an energy spectrum modulator to be combined with a zoom point function of the radiation source to realize scattering correction, so that the multi-energy CT imaging and the scattering correction are combined.
Compared with the multi-energy imaging system in the prior art, the ray source of the multi-energy X-ray cone-beam CT imaging system in the embodiment of the first aspect of the invention introduces the function of fast kilovolt switching, and the influence of the penumbra area of the plurality of sub-modules of the energy spectrum modulator on the detector on the spectral region division is well avoided. The ray source in the prior art emits a single energy spectrum, and if a detector pixel is positioned in a penumbra area, the multi-energy spectrum area has poor degree of differentiation and poor material decomposition effect, which can affect the image quality. The introduction of the rapid kilovolt switching technology enables the ray source to emit dual-energy spectrums, and even if the detector pixels are located in a penumbra area, the distinguishing degree of the dual-energy spectrums is enough to ensure the image quality of the dual-energy CT, so that the image quality of the CT is greatly improved.
In summary, the multi-energy X-ray cone-beam CT imaging system according to the embodiment of the first aspect of the present invention can flexibly control the dual-energy spectrum imaging capability, thereby not only avoiding the problem of small energy spectrum discrimination of part of data in the original energy spectrum imaging system based on the energy spectrum modulator and the zoom point technology, but also solving the problem of scattering correction faced by fast kv switching application and cone-beam CT, and expanding the energy spectrum data from simple dual-energy imaging to multi-energy spectrum imaging such as three-energy imaging, four-energy imaging, and the like.
According to an embodiment of the first aspect of the present invention, the mechanical/electrical control and data transmission/processing unit obtains, by combining with a zoom point function of the radiation source, the multiple-energy X-ray transmission values passing through different sub-units of the energy spectrum modulator at the same pixel of the detector, which are approximated by processing the X-ray transmission values acquired at different positions of the focal point of the radiation source through translation or interpolation.
According to an embodiment of the first aspect of the present invention, the fast kilovolt switching function is to simultaneously fast switch the tube voltage, the tube current and the exposure time as required.
According to an embodiment of the first aspect of the invention, in the spectral modulator different ones of the sub-modules have different attenuations for X-rays.
According to an embodiment of the first aspect of the present invention, the spectrum modulator is manufactured by an integral forming process, or manufactured by a splicing process, or manufactured by an overlapping process.
The invention also provides a multi-energy X-ray cone-beam CT imaging method.
The multi-energy X-ray cone-beam CT imaging method according to the second aspect of the present invention is applied to the multi-energy X-ray cone-beam CT imaging system according to any one of the embodiments of the first aspect of the present invention, and includes the following steps:
s1: setting a CT acquisition mode, wherein the CT acquisition mode is a quick kilovolt switching mode with a variable focus;
s2: acquiring the X-ray transmission value;
s3: solving the estimated scattering intensity according to the set CT acquisition mode;
s4: deducting the estimated scattering intensity from the acquired X-ray transmission value to obtain a main beam X-ray transmission value;
s5: and carrying out data processing by using the main beam X-ray transmission value, and then carrying out material decomposition and reconstruction to obtain a final CT image.
According to the multi-energy X-ray cone-beam CT imaging method disclosed by the embodiment of the second aspect of the invention, the finally obtained CT image is high in quality.
According to an embodiment of the second aspect of the invention, the estimated scattering intensity is obtained by solving:
pre-establishing a mapping relation between the X-ray transmission value and the estimated scattering intensity and between equivalent thickness integrals of the two base materials; the estimated scattering intensity is obtained by a look-up table or an iterative solution.
According to a further embodiment of the second aspect of the present invention, the mapping relationship is obtained based on:
based on the CT projection theory, the X-ray transmission value detected by the detector after the high-energy and low-energy spectrums pass through the spectrum modulator and the object to be imaged is related to the scattering intensity value, and the functional relationship between the equivalent thickness integrals of the two base materials can be expressed as follows:
wherein the content of the first and second substances,
expressed as the X-ray transmission value detected by the detector;i＝P 0 ，P 1 respectively representing the position of the focal point in the case of a zoom point; according to the spectral CT substance decomposition theory, L 1 And L 2 For the equivalent thickness integral of the two selected materials,
under the condition of i ═ P 0 ，P 1 Scattering intensity at the focal position;
since the scattering intensity distribution is relatively low-frequency, the scattering distribution at different focus positions is strongly correlated in the case of a zoom point, and therefore, with two focus positions P 0 ，P 1 For example, the scattering intensity distribution correlation function is expressed by equation (2):
in the actual calculation, consider that
Thereby pre-establishing the mapping relationship:
according to a still further embodiment of the second aspect of the present invention, the specific process of the estimated scattering intensity using the table lookup method is: obtaining multiple groups by simulation or actual measurement
And can establish
About { I Sc ，L 1 ，L 2 Is calculated from the table, thereby solving for the estimated scattering intensity I Sc 。
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a schematic diagram of a multi-energy X-ray cone-beam CT imaging system in accordance with an embodiment of a first aspect of the present invention.
Fig. 2a is a schematic view of a flying focus of a multi-energy X-ray cone-beam CT imaging system according to an embodiment of the first aspect of the present invention.
Fig. 2b is a schematic diagram of a state of a distributed light source of the multi-energy X-ray cone-beam CT imaging system according to the embodiment of the first aspect of the present invention.
Fig. 2c is a schematic diagram of another state of the distributed light source of the multi-energy X-ray cone-beam CT imaging system according to the embodiment of the first aspect of the present invention.
Fig. 3 is a functional diagram of a radiation source of a multi-energy X-ray cone-beam CT imaging system with a zoom point according to an embodiment of the first aspect of the present invention.
Fig. 4 is a schematic diagram of an energy spectrum modulator of a multi-energy X-ray cone-beam CT imaging system according to an embodiment of the first aspect of the present invention.
Fig. 5a to 5c are schematic diagrams of energy spectrums corresponding to different rotation angles on a detector of a multi-energy X-ray cone-beam CT imaging system according to an embodiment of the first aspect of the present invention.
Fig. 6 is a flowchart illustrating a multi-energy X-ray cone-beam CT imaging method according to a second embodiment of the present invention.
Reference numerals are as follows:
Mechanical/electrical control and data transmission/processing unit 5
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.
A multi-energy X-ray cone-beam CT imaging system 1000 according to an embodiment of the first aspect of the present invention is described below with reference to fig. 1 to 5 c.
As shown in fig. 1 to 5c, the multi-energy X-ray cone-beam CT imaging system 1000 according to the first aspect of the present invention comprises a radiation source 1, an energy spectrum modulator 2, a detector 4 and a mechanical/electrical control and data transmission/processing unit 5. The radiation source 1 generates rays for transmission imaging, the radiation source 1 has a zoom point function, the radiation source 1 has a rapid kilovolt switching function, and the radiation source 1 performs periodic high-low energy spectrum rapid switching through the rapid kilovolt switching function in the CT scanning rotation process; the energy spectrum modulator 2 is arranged between the ray source 1 and an object 3 to be imaged, and the energy spectrum modulator 2 is a non-uniform filter plate formed by periodically arranging a plurality of different sub-modules and used for changing the intensity distribution and the energy spectrum shape distribution of X rays so as to realize energy spectrum modulation; the detector 4 is used for detecting the X-ray transmission value of the energy spectrum emitted by the ray source after passing through the energy spectrum modulator 2 and the object to be imaged 3; the mechanical/electrical control and data transmission/processing unit 5 is used for controlling the radiation source 1, the energy spectrum modulator 2 and the detector 4, classifying the acquired X-ray transmission values into different categories in combination with a zoom point function, and performing data processing on the X-ray transmission values based on the different categories, wherein the data processing includes but is not limited to X-ray transmission data which is divided into a plurality of energy regions by using the acquired X-ray transmission values, and the scatter correction is realized in combination with the zoom point function, so that the material decomposition capability is improved.
Specifically, the radiation source 1 generates radiation for transmission imaging, including but not limited to X-ray tubes, carbon nanotubes, isotope sources, and accelerators.
The ray source 1 has a fast kilovolt switching function, and the ray source 1 performs periodic high-low energy spectrum fast switching through the fast kilovolt switching function in the CT scanning rotation process. Here, the kilovolt switching function may be understood as that two high and low energy spectrums (such as 70/120kvp, 80/140kvp) are periodically switched during the CT rotation scanning process, and specifically, the high and low energy spectrums may be periodically switched by simultaneously and periodically switching parameters such as tube voltage, tube current and exposure time. By introducing a fast kilovolt switching functionality to the radiation source 1, the radiation source 1 itself emits a dual energy spectrum (i.e. a high and low energy spectrum).
Because the quick kilovolt switching has the characteristic of flexibly adjusting the double energy spectrums, the double energy spectrum difference which is better than that of a system only using an energy spectrum modulator in the prior art can be obtained, and the situation that partial data energy difference possibly exists when multiple energy spectrums are generated only using the energy spectrum modulator is well avoided. That is to say, in the prior art, the radiation source is usually a single energy spectrum, the radiation source itself is not an ideal point source, and since the energy spectrum modulator itself is composed of multiple sub-modules, the radiation of the radiation source may pass through the module intersection region when passing through the sub-modules of the energy spectrum modulator, or the detector pixel may be in the intersection region where passing through the radiation of two sub-modules, that is, the penumbra effect, which may cause that when the radiation source is a single energy spectrum, originally different energy spectrums may be obtained when passing through different sub-modules of the energy spectrum modulator, but the energy spectrum difference of the penumbra region may become smaller. The ray source 1 of the invention introduces the function of fast kilovolt switching, so that the dual energy spectrums have larger difference, even if the influence of the energy spectrum modulator 2 on the discrimination of the energy spectrums is small due to the penumbra effect, the larger difference of the dual energy spectrums can be ensured, and the imaging quality of the dual energy cone beam CT is ensured.
The radiation source 1 has a zoom point function. That is, when the radiation source 1 has a zoom point function (as shown in fig. 3), a slight movement of the position of the radiation source 1 during the CT rotational scanning can be achieved.
As shown in fig. 2a to fig. 2c, the zoom point function means that the focal position of the radiation source 1 can vary in X, Z two dimensions, and this function can be implemented by the radiation source 1 flying focal point technology (as shown in fig. 2a), or other technologies capable of rapidly changing the position of the radiation source 1, such as other distributed light sources (as shown in fig. 2b and fig. 2 c). If the flying focus technology of the radiation source 1 (as shown in fig. 2a) is adopted, assuming that the initial position of the radiation source 1 is at the central point of fig. 2a, the focus can be rapidly switched to move to the upper and lower points in the Z direction, or to the left and right points in the X direction, or to the four corners in the oblique direction by the electric control operation. If a distributed light source is used (as shown in fig. 2b and 2 c), it is assumed that the initial exposure position of the radiation source 1 is at the central point of fig. 2a, and the radiation source 1 is not working at the rest points; through the fast switching exposure function of the distributed ray source 1, as shown in fig. 2c, the ray source 1 at the right side point is controlled to be exposed, the rest ray sources 1 do not work, and one ray source 1 at the rest yellow points can be controlled to work, and the rest ray sources 1 do not work, so that the fast switching of the position of the ray source 1 in the x and z directions is realized.
The energy spectrum modulator 2 is arranged between the ray source 1 and an object 3 to be imaged, and the energy spectrum modulator 2 is a non-uniform filter plate formed by periodically arranging a plurality of different sub-modules and used for modulating energy spectrum; therefore, the scattering correction can be simply and well realized, the cost of the energy spectrum modulator 2 is relatively low, and the fixation between the ray source 1 and the object 3 to be imaged is simple and convenient.
The detector 4 is used for detecting the X-ray transmission value after the energy spectrum emitted by the radiation source passes through the energy spectrum modulator 2 and the object 3 to be imaged, and includes, but is not limited to, a flat panel detector 4 with high spatial resolution.
The mechanical/electrical control and data transmission/processing unit 5 can comprise an electromechanical control module, a data acquisition module, a data processing and display module and the like, the electromechanical control module can control the ray source 1, the energy spectrum modulator 2 and the detector 4, the data acquisition module can acquire X-ray transmission values, the acquired X-ray transmission values are classified into different categories by combining the zoom point function of the ray source 1, the data processing module can perform data processing on the X-ray transmission values based on the different categories to finally obtain a CT image, and the display module can visually display the CT image.
In the multi-energy X-ray cone-beam CT imaging system 1000 according to the first aspect of the present invention, the radiation source 1 and the detector 4 rotate around the object 3 to be imaged, and fast kilovolt switching is performed at the radiation source 1 during rotation, so that the tube voltage and the tube current can be flexibly controlled during rotation, and thus two energy spectrums can be better acquired, because the energy spectrums change after passing through the energy spectrum modulator 2, different modules of the energy spectrum modulator 2 may have higher requirements on the energy spectrums, and flexible switching of multiple energy spectrums can better meet the requirements.
The ray source 1 has a zoom point function, the focal position of the ray source 1 can be changed in the X or Z direction, the X-rays emitted by the ray source 1 before and after the change pass through different subunits of the energy spectrum modulator 2 and fall on adjacent pixels of the detector 4, and the deviation of the X-rays before and after the change in the object 3 to be imaged or the inconsistency degree of the ray paths is small. Finally, the X-ray transmission values are acquired on the detector 4.
In a specific implementation, the position or energy spectrum of the radiation source 1 is changed (the position of the radiation source 1 is changed in two dimensions, the positions are respectively defined as 1,2 and 3; the energy spectrum of the radiation source 1 can be changed on a plurality of energy spectrums, for example, two energy spectrums, namely the energy spectrum 1 and the energy spectrum 2, can be changed once every angle or a plurality of angles) because the radiation source 1 and the detector 4 are always rotated. Taking an angle as an example, the position variation rule of the radiation source 1 can be partially circulated in the form of arbitrary alternation of three positions, namely position 1, position 2, position 3, position 2, position 1, etc., and the corresponding image is shown in fig. 5 a. Or the image may be partially looped in the form of position 1, position 2, position 1 or two positions, position 1, position 3, position 1, etc., and the corresponding image is shown in fig. 5 b. The parts cycle in position 1, the corresponding image is shown in fig. 5 c; the energy spectrum change rule of the radiation source 1 can be a form cycle of two energy spectrums such as an energy spectrum 1, an energy spectrum 2, an energy spectrum 1, an energy spectrum 2 and the like, and can also be an arbitrary staggered appearance of the energy spectrum 1, the energy spectrum 2 and the energy spectrum 1. The position and energy spectrum changes can be carried out cyclically or randomly and alternately, similarly to the case of spacing once every few angles or uneven spacing.
Therefore, under the system structure, better dual-energy spectrum difference can be obtained, meanwhile, the insertion of the energy spectrum modulator 2 enables the implementation of scattering correction to be simpler, the cost of the non-uniform filter plate of the energy spectrum modulator 2 is relatively lower, and a simple and low-cost energy spectrum modulation module is added on the basis of the quick kilovolt switching technology, so that scattering artifacts which may affect the image quality in dual-energy imaging can be better inhibited or eliminated.
According to the multi-energy X-ray cone-beam CT imaging system 1000 of the embodiment of the first aspect of the present invention, the radiation source 1 introduces a fast kv switching function to realize multi-energy CT imaging, and at the same time, the non-uniform filter is used as the energy spectrum modulator 2 to realize scattering correction, so that the multi-energy CT imaging and the scattering correction are combined. In combination with the zoom point function of the radiation source 1, a better scatter correction can be achieved.
Compared with the multi-energy imaging system in the prior art, the ray source 1 of the multi-energy X-ray cone-beam CT imaging system 1000 according to the embodiment of the first aspect of the present invention introduces the fast kilovolt switching function, so that the influence of the penumbra regions existing on the detector 4 by the plurality of sub-modules of the energy spectrum modulator 2 on the spectral region division is well avoided. The ray source 1 in the prior art emits a single energy spectrum, and if the pixels of the detector 4 are positioned in a penumbra area, the multi-energy spectrum has poor discrimination and poor material decomposition effect, which affects the image quality. And the introduction of the rapid kilovolt switching technology enables the ray source 1 to emit dual-energy spectrums, and even if the pixels of the detector 4 are positioned in a penumbra area, the distinguishing degree of the dual-energy spectrums is enough to ensure the image quality of the dual-energy CT, thereby greatly improving the image quality of the CT.
In summary, the multi-energy X-ray cone-beam CT imaging system 1000 according to the first aspect of the present invention can flexibly control the dual-energy spectrum imaging capability, not only avoid the problem of small discrimination of partial data energy spectrum in the original energy spectrum imaging system based on the energy spectrum modulator 2 and the zoom point technology, but also solve the problem of scattering correction faced by fast kv switching application and cone-beam CT, and further expand the energy spectrum data from simple dual-energy imaging to multi-energy spectrum imaging such as three-energy and four-energy imaging.
According to an embodiment of the first aspect of the present invention, the mechanical/electrical control and data transmission/processing unit 5 combines the zoom point function of the radiation source 1, and processes the X-ray projection values collected at different positions of the focal point of the radiation source 1 by translation or interpolation to obtain approximate multi-energy X-ray projection values of the same pixel of the detector 4 passing through different sub-units of the energy spectrum modulator 2, so as to obtain a high-quality CT image. Here, the multi-energy X-ray transmission value may be understood as a plurality of X-ray transmission values when the focal positions of the corresponding radiation sources 1 at the same pixel of the detector 4 are different.
According to an embodiment of the first aspect of the present invention, the fast kilovolt switching function is to rapidly switch the tube voltage, the tube current and the exposure time simultaneously as required. Therefore, the high-low energy spectrum can be flexibly adjusted.
According to an embodiment of the first aspect of the invention, in the spectral modulator 2, different sub-modules have different attenuation for X-rays in order to achieve better spectral scatter correction.
According to an embodiment of the first aspect of the present invention, the energy spectrum modulator 2 is manufactured by an integral forming process, for example, a metal plate is retained or hollowed out with different thicknesses, so as to obtain different modules; or, the spectrum modulator 2 is manufactured by splicing, for example, small modules made of different materials or with different thicknesses are spliced; or, the energy spectrum modulator 2 is manufactured by overlapping, for example, the energy spectrum modulator 2 is formed by overlapping not less than two one-dimensional grids having a partial attenuation function to the X-ray, the not less than two one-dimensional grids are made of different materials or have different thicknesses, the overlapped grids are formed by the same units periodically arranged in space, each unit includes four or more than four sub-units, different sub-units have different attenuations to the X-ray, and the overlapping mode includes vertical overlapping or oblique angle overlapping or parallel overlapping.
The invention also provides a multi-energy X-ray cone-beam CT imaging method.
As shown in fig. 6, the multi-energy X-ray cone-beam CT imaging method according to the embodiment of the second aspect of the present invention is applied to the multi-energy X-ray cone-beam CT imaging system 1000 according to any one of the embodiments of the first aspect of the present invention, and includes the following steps:
s1: a CT acquisition mode is set, which is a fast kilovolt switching mode with variable focus. Specifically, parameters for kilovolt switching and position information of the focus changing point are set.
S2: x-ray transmission values are collected. Here, the X-ray transmission value is the X-ray transmission value detected by the detector 4 after the high-low energy spectrum of the radiation source 1 is attenuated by the spectrum modulator 2 and the object 3 to be imaged.
S3: the estimated scatter intensity is solved according to the set CT acquisition mode.
Specifically, the estimated scattering intensity is obtained by solving the following: pre-establishing a mapping relation between an X-ray transmission value and an estimated scattering intensity and between equivalent thickness integrals of two base materials; the estimated scattering intensity is obtained by a look-up table or an iterative solution.
The mapping relation between the equivalent thickness integrals of the two base materials is based on the following steps:
based on the CT projection theory, the X-ray transmission value detected by the detector 4 after the high-low energy spectrum passes through the energy spectrum modulator 2 and the object 3 to be imaged is expressed by formula (3):
in formula (3), { S k (E) K is low, high represents high and low energy spectrum respectively,
representing an X-ray transmission value; i ═ P 0 ，P 1 Respectively representing the position of the focus in the case of a zoom point,
and
respectively the attenuation coefficient and the equivalent thickness corresponding to the spectral modulator 2,
and
attenuation coefficients, L, corresponding to the two selected base materials 1 And L 2 For the equivalent thickness integral of the two selected materials,
to in the energy spectrum S k (E) (ii) scattering intensity of;
it should be noted that the two selected base materials are understood that according to the theory of the spectral CT material decomposition algorithm, the attenuation coefficient of any one material can be expressed as a linear combination of the attenuation coefficients of the two selected base materials, and water/bone or water/iodine is usually selected as the two base materials.
Since the scattering intensity distribution is relatively low-frequency, the correlation of the scattering distribution is strong at different focus positions in the case of a zoom point, and therefore, two focus positions P are used 0 ，P 1 For example, the scattering intensity distribution correlation function is expressed by equation (2):
in practical situations, the relationship of the scattering intensity distribution can be calibrated and tested according to different systems, and the multi-energy X-ray cone-beam CT imaging system 1000 of the present invention can calibrate the relationship of the scattering intensity distribution by using the following formula (4):
at two focal positions P 0 ，P 1 For example, based on the relatively low frequency of the scattering intensity distribution, equation (3) may be changed to equation (5):
it can be considered that according to the formula (4),
and
the strong correlation exists between the two, and the expression (6) is adopted:
in actual calculations, it can be approximately considered
Can become:
in the formula (7), Isc is the estimated scattering intensity;
according to the formula (7), a functional relation formula (1) of the mapping relation is established in advance:
the specific process of the estimated scattering intensity by using a table look-up method is as follows: calibration spectrum S k (E) (ii) a Pixel-by-pixel focus at P 0 ，P 1 Under the circumstances
Calibrating, and solving by using lookup table or Newton iteration method
And can establish
About { I Sc ，L 1 ，L 2 A look-up table of, and thus solved for, the estimated scattering intensity I Sc ；
The specific process of obtaining the estimated scattering intensity by adopting an iterative solution method is as follows: by subtracting the two formulae in formula (7), the scattering term I is eliminated Sc And obtaining:
solving by equation (8) to obtain { L 1 ，L 2 Is then utilized to solve for { L } 1 ，L 2 Substituting formula (7) to solve for the estimated scattering intensity I Sc 。
It should be noted that, before the mapping relationship is established in advance, the energy spectrum correction, for example, the water correction, is performed on the formula (7) to obtain the change of the scattering intensity distribution after the energy spectrum correction, and then the estimated scattering intensity I is obtained by the iterative solution method Sc . Meanwhile, considering that the zoom point can change once at intervals of a plurality of angles or have uneven intervals, and the scattering intensity distribution is relatively low frequency, the scattering intensity obtained by solving under the current zoom angle can be adopted to approximate the scattering distribution under other angles.
S4: subtracting the estimated scattering intensity from the acquired X-ray transmission values to obtain main beam attenuation values, namely:
s5: and (3) carrying out data processing by using the main beam X-ray transmission value, and then carrying out material decomposition and reconstruction, wherein the reconstruction can adopt an analysis or iteration method to obtain a final CT image.
In summary, the multi-energy X-ray cone-beam CT imaging method according to the embodiment of the second aspect of the present invention sets the CT acquisition mode, which is a fast kv switching mode with variable focus; collecting X-ray transmission values; solving the estimated scattering intensity according to the set CT acquisition mode; deducting the estimated scattering intensity from the acquired X-ray transmission value to obtain a main beam X-ray transmission value; and (3) carrying out data processing by using the main beam X-ray transmission value, and then carrying out material decomposition and reconstruction to obtain a final CT image with high quality.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an illustrative embodiment," "an example," "a specific example," or "some examples" or the like mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
While embodiments of the invention have been shown and described, it will be understood by those of ordinary skill in the art that: various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.
Claims (8)
1. A multi-energy X-ray cone-beam CT imaging system, comprising:
the source of rays, the source of rays is used for transmission imaging, the source of rays has a zoom point function, the source of rays has a fast kilovolt switching function, and the source of rays performs periodic high-low energy spectrum fast switching through the fast kilovolt switching function during CT scanning rotation;
the energy spectrum modulator is arranged between the ray source and an object to be imaged, and is a non-uniform filter plate formed by periodically arranging a plurality of different sub-modules and used for changing the intensity distribution and the energy spectrum shape distribution of X rays;
the detector is used for detecting the X-ray transmission value of the ray emitted by the ray source after passing through the energy spectrum modulator and the object to be imaged;
the mechanical/electrical control and data transmission/processing unit is used for controlling the ray source, the energy spectrum modulator and the detector, classifying the acquired X-ray transmission values into different categories by combining a zoom point function, and performing data processing on the X-ray transmission values based on the different categories; the data processing comprises but is not limited to X-ray transmission data which is divided into a plurality of energy areas by using the obtained X-ray transmission value, and the scattering correction is realized by combining the function of a zoom point, so that the material decomposition capability is improved;
the rapid kilovolt switching function is to rapidly switch the tube voltage, the tube current and the exposure time simultaneously as required.
2. The multi-energy X-ray cone-beam CT imaging system according to claim 1, wherein said mechanical/electrical control and data transmission/processing unit combines with said source zoom point function to process said X-ray transmission values collected at different positions of the focal point of said source by translation or interpolation to obtain approximate multi-energy X-ray transmission values passing through different subunits of said spectral modulator at the same pixel of the detector.
3. The multi-energy X-ray cone-beam CT imaging system of claim 1 wherein different ones of the sub-modules in the spectral modulator have different attenuations of X-rays.
4. The multi-energy X-ray cone-beam CT imaging system of claim 1 wherein the spectral modulator is fabricated by integral forming, or by tiling, or by overlapping.
5. A multi-energy X-ray cone-beam CT imaging method applied to the multi-energy X-ray cone-beam CT imaging system of any one of claims 1 to 4, comprising the steps of:
s1: setting a CT acquisition mode, wherein the CT acquisition mode is a quick kilovolt switching mode with a variable focus;
s2: acquiring the X-ray transmission value;
s3: solving the estimated scattering intensity according to the set CT acquisition mode;
s4: deducting the estimated scattering intensity from the acquired X-ray transmission value to obtain a main beam X-ray transmission value;
s5: and carrying out material decomposition and reconstruction after carrying out data processing by using the main beam X-ray transmission value to obtain a final CT image.
6. The method of claim 5, wherein the estimated scatter intensity is obtained by solving:
pre-establishing a mapping relation between the X-ray transmission value and the estimated scattering intensity and between equivalent thickness integrals of the two base materials; the estimated scattering intensity is obtained by a look-up table or an iterative solution.
7. The method of claim 6, wherein the mapping is based on:
based on the CT projection theory, the X-ray transmission value detected by the detector after the high-energy and low-energy spectrums pass through the spectrum modulator and the object to be imaged is related to the scattering intensity value, and the functional relationship between the equivalent thickness integrals of the two base materials can be expressed as follows:
wherein the content of the first and second substances,
expressed as the X-ray transmission value detected by the detector; i ═ P 0 ,P 1 Respectively representing the position of the focal point in the case of a zoom point; according to the spectral CT material decomposition theory, L 1 And L 2 For the equivalent thickness integral of the two selected materials,
under the condition of i ═ P 0 ,P 1 Scattering intensity at the focal position;
since the scattering intensity distribution is relatively low frequency, the scattering distribution at different focal positions is strongly correlated in the case of a zoom point, and therefore, two are usedA focal point position P 0 ,P 1 For example, the scattering intensity distribution correlation function is expressed by equation (2):
in the actual calculation, consider that
Thereby pre-establishing the mapping relationship:
8. the multi-energy X-ray cone-beam CT imaging method according to claim 7, wherein said estimated scattering intensity is obtained by using said lookup table by the following specific procedure: obtaining multiple sets by simulation or actual measurement
And can establish
About { I Sc ,L 1 ,L 2 Is calculated from the table, thereby solving for the estimated scattering intensity I Sc 。
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