A dual-energy filter and dual-energy CT

Abstract

The present invention discloses a dual-energy filter and a dual-energy CT, comprising a first ray filter layer and a second ray filter layer, wherein the first ray filter layer and the second ray filter layer are used to output the wide-spectrum rays emitted by the radiation source into two rays with different average energies for reception by the detector, and the two rays with different average energies are irradiated to different areas of the receiving surface of the detector. By arranging two ray filter layers between the radiation source and the detector, the wide-spectrum rays emitted by the radiation source pass through the first ray filter layer and the second ray filter layer to form two rays with different average energies, and the two rays with different average energies reach different areas of the detector, and the detector receives the two rays at different positions, and the detector realizes dual-energy detection at the same time. Based on the above scheme, scanning and collection of X-rays with two different average energies are realized without making significant modifications to the existing CT technical scheme.

Description

Technical Field

[0001] The invention relates to the technical field of ray imaging, and in particular to a dual-energy filter and a dual-energy CT. Background Art

[0002] CT (Computed Tomography) dual-energy imaging is an imaging technology that uses two types of energy X-ray beams to scan the object being scanned.

[0003] Currently, dual-energy CT imaging design has a variety of solutions, such as dual-source dual-detector solution, double-layer detector solution, fast kVp switching solution, dual-circle sequence scanning solution, etc.

[0004] The dual-source dual-detector and dual-layer detector solutions are different from general CT solutions. They require the addition of radiation sources and / or detectors, and significantly upgrade and modify the imaging system structure or core components, with high design and cost requirements. The fast kVp switching solution requires high-voltage components with fast kVp switching capabilities and gem detectors with fast response capabilities, with high design and cost requirements. The dual-circle sequence scanning solution does not require changes to the existing CT structure or core components. After completing the scan of one or more beds at one kVp, the kVp is switched and repeated scanning is performed, but the dual-energy image obtained has poor matching in the time domain. Summary of the invention

[0005] In view of this, it is necessary to provide a dual-energy filter and a dual-energy CT to solve the technical problem in the prior art of how to obtain a dual-energy image with better matching without increasing radiation sources and detectors.

[0006] In order to achieve the above technical objectives, the technical solution of the present invention provides a dual-energy filter, including a first ray filtering layer and a second ray filtering layer, wherein the first ray filtering layer and the second ray filtering layer are used to output the wide-spectrum rays emitted by the radiation source as two rays with different average energies for reception by a detector, and the two rays with different average energies are irradiated on different areas of the receiving surface of the detector.

[0007] In one embodiment, the first ray filter layer and the second ray filter layer are arc structures with the same inner diameter and different materials, and the first ray filter layer and the second ray filter layer are arranged along the axial direction of the arc.

[0008] In one embodiment, the arc lengths of the first ray filtering layer and the second ray filtering layer are equal, a side of the second ray filtering layer close to the radiation source is flush with a side of the first ray filtering layer close to the radiation source, and both ends of the second ray filtering layer are flush with the first ray filtering layer.

[0009] In one embodiment, a support layer is further included, and the support layer is connected to the first ray filtering layer and the second ray filtering layer.

[0010] In one embodiment, the support layer is disposed on a side of the second ray filtering layer away from the radiation source, and the side of the support layer away from the radiation source is flush with a side of the first ray filtering layer away from the radiation source.

[0011] In one embodiment, the radial thickness of the first ray filtering layer is equal at all locations along the circumference, and the radial thickness of the second ray filtering layer is equal at all locations along the circumference.

[0012] In one embodiment, a thickness of the second ray filtering layer in the radial direction is smaller than a thickness of the first ray filtering layer in the radial direction.

[0013] In one embodiment, the atomic number of the material in the second ray filtering layer is higher than the atomic number of the material in the first ray filtering layer.

[0014] In one embodiment, it further includes a shielding layer for shielding radiation, wherein the shielding layer is disposed between the first ray filtering layer and the second ray filtering layer.

[0015] In one embodiment, the number of the first ray filter layers is two, and the two first ray filter layers are respectively disposed on both sides of the second ray filter layer and are arranged in parallel with the second ray filter layer.

[0016] The present invention also relates to a dual-energy CT, comprising a radiation source, a detector and the above-mentioned dual-energy filter, wherein the dual-energy filter is arranged between the radiation source and the detector, the dual-energy filter is arranged between the radiation source and the detector, and the axes of the first ray filter layer and the second ray filter layer pass through the focus of the radiation source.

[0017] Compared with the prior art, the beneficial effects of the present invention include: by setting two ray filter layers between the radiation source and the detector, the wide-spectrum rays emitted by the radiation source pass through the first ray filter layer and the second ray filter layer to form two rays with different average energies, the two rays with different average energies reach different areas of the detector, the detector receives the two rays at different positions, and the detector realizes dual-energy detection at the same time. Based on the above scheme, without making significant modifications to the existing CT technical scheme, scanning and acquisition of X-rays with two different average energies is realized. Then, by modifying the spiral scanning pitch (normalized pitch in spiral scanning) value or entering the bed, dual-energy scanning of the same position of the support bed is realized, and a dual-energy image of the same area is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a three-dimensional schematic diagram of a dual-energy filter, a radiation source and a detector provided by an embodiment of the present invention when in operation;

[0019] Figure 2 is a three-dimensional schematic diagram of a dual-energy filter provided by an embodiment of the present invention;

[0020] Figure 3 is the emission spectrum of the rays after being filtered by the dual-energy filter provided by an embodiment of the present invention;

[0021] Figure 4 is the emission spectrum of the rays after being filtered by the first ray filter layer and the second ray filter layer of different thicknesses provided in one embodiment of the present invention;

[0022] Figure 5 is a scanning trajectory of the first scanning area and the second scanning area when the detector provided by an embodiment of the present invention is working;

[0023] Figure 6 is a scanning trajectory of the first scanning area and the second scanning area in another working state of the detector provided by an embodiment of the present invention;

[0024] Figure 7 is a three-dimensional schematic diagram of a dual-energy filter provided by another embodiment of the present invention;

[0025] Figure 8 It is a schematic diagram of the maximum deviation of the depth of X-rays penetrating the filter layer at various angles when the focus of the radiation source and the center of the filter layer do not coincide with each other, provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0026] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0027] like Figure 1 and Figure 2 As shown, the present invention provides a dual-energy filter, including a first ray filter layer 3 and a second ray filter layer 4, the first ray filter layer 3 and the second ray filter layer 4 are used to output the wide-spectrum rays emitted by the radiation source 1 into two rays with different average energies for reception by the detector 2, and the two rays with different average energies are irradiated on different areas of the receiving surface of the detector 2.

[0028] The wide-spectrum rays emitted by the radiation source 1 pass through the first ray filter layer 3 and the second ray filter layer 4 to form two rays with different average energies. The two rays with different average energies reach different areas of the detector 2. The detector 2 receives the two rays at different positions, and the detector 2 realizes dual-energy detection at the same time. Based on the above scheme, without making significant changes to the existing CT technical scheme, the scanning and collection of X-rays with two different average energies is realized. Then, by means of bed entry, dual-energy scanning of the same position of the carrier bed is realized, and a dual-energy image of the same area is obtained.

[0029] It can be understood that the radiation emitted by the radiation source 1 can be X-rays.

[0030] In one embodiment, the first ray filter layer 3 and the second ray filter layer 4 are arc structures with equal inner diameters and different materials. The first ray filter layer 3 and the second ray filter layer 4 are arranged along the axial direction of the arc, that is, along the Z direction, and the first ray filter layer 3 and the second ray filter layer 4 take the focus of the radiation source 1 as the center of the circle. The Z direction is the bed entry direction, the horizontal direction perpendicular to the Z direction is the X direction, and the vertical direction perpendicular to the Z direction is the Y direction.

[0031] In one embodiment, the atomic number of the material in the second ray filter layer 4 is higher than the atomic number of the material in the first ray filter layer 3. Through the above arrangement, the first ray filter layer 3 and the second ray filter layer 4 form two filter layers of different materials, which can achieve two different attenuation filters for X-rays.

[0032] In one embodiment, the first ray filter layer 3 and the second ray filter layer 4 are made of different materials.

[0033] When the rays pass through the first ray filter layer 3 and the second ray filter layer 4 made of different materials, the different materials attenuate the rays differently, thereby obtaining two rays with different average energies.

[0034] It can be understood that the material constituting the first ray filter layer 3 can be one or more of lithium, beryllium, sodium, magnesium, aluminum, potassium, calcium, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, rubidium, strontium, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, cesium, barium and lanthanum.

[0035] It is understandable that the material constituting the second ray filter layer 4 can be one or more of titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, rubidium, strontium, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, cesium, barium and lanthanum.

[0036] In one embodiment, the radial thickness of the first ray filter layer 3 is equal at all locations along the circumference, and the radial thickness of the second ray filter layer 4 is equal at all locations along the circumference. Since the filtering thickness has a significant effect on X-ray attenuation, the present application sets the radial thickness of the first ray filter layer 3 to be equal at all locations along the circumference, and sets the radial thickness of the second ray filter layer 4 to be equal at all locations along the circumference, so as to ensure that the filtering thickness of X-rays in all directions is the same, so that the X-ray spectra formed after the X-rays in all directions pass through the filtering layer in the radial direction of the filtering layer are consistent.

[0037] In one embodiment, the radial thickness of the second ray filter layer 4 is smaller than the radial thickness of the first ray filter layer 3. Since the atomic number of the material in the second ray filter layer 4 is greater than the atomic number of the material in the first ray filter layer 3, the radial thickness of the second ray filter layer 4 is designed to be smaller than the radial thickness of the first ray filter layer 3, which can reduce the interception of rays by the second ray filter layer 4 and avoid the second ray filter layer 4 with a higher atomic number completely blocking the passage of rays.

[0038] In one embodiment, the arc lengths of the first ray filter layer 3 and the second ray filter layer 4 are equal, a side of the second ray filter layer 4 close to the radiation source 1 is flush with a side of the first ray filter layer 3 close to the radiation source 1 , and both ends of the second ray filter layer 4 and the first ray filter layer 3 are flush.

[0039] It can be understood that the first ray filter layer 3 and the second ray filter layer 4 can be arranged in parallel. The parallel arrangement means that the first ray filter layer 3 and the second ray filter layer 4 are fitted on the basis of the first ray filter layer 3 and the second ray filter layer 4 being arranged axially along the arc; wherein the second ray filter layer 4 is flush with both ends of the first ray filter layer 3 means that the two ends of the second ray filter layer 4 are flush with the two ends of the first ray filter layer 3 respectively.

[0040] In one embodiment, the number of the first ray filter layers 3 is two, and the two first ray filter layers 3 are respectively arranged on both sides of the second ray filter layer 4 and are arranged in parallel with the second ray filter layer 4. By arranging two first ray filter layers 3 with relatively low atomic numbers on both sides of the second ray filter layer 4 with relatively high atomic numbers, a single bed non-helical continuous scanning protocol can be used, and its use method is similar to the double-circle sequence scanning. The first circle uses the second ray filter layer 4 and the first ray filter layer 3 on one side for scanning; the second circle switches to the second ray filter layer 4 and the first ray filter layer 3 on the other side for scanning. The dual-energy image time domain matching degree of this scanning scheme is equivalent to that of the double-circle sequence scanning scheme.

[0041] In one embodiment, the dual-energy filter further includes a support layer 5, and the support layer 5 is connected to the first ray filter layer 3 and the second ray filter layer 4. By providing the support layer 5, the first ray filter layer 3 and the second ray filter layer 4 can be fixed by the support layer 5, so as to form a filter with good engineering reliability.

[0042] In one embodiment, the support layer 5 is arranged on the side of the second ray filter layer 4 away from the radiation source 1 and along the circumference of the second ray filter layer 4, and the side of the support layer 5 away from the radiation source 1 is flush with the side of the first ray filter layer 3 away from the radiation source 1. Since the thickness of the second ray filter layer 4 is thinner than that of the first ray filter layer 3, the support layer 5 is installed on the side of the second ray filter layer 4 away from the radiation source 1, and the spare gap is fully utilized, making the device more compact; since the inner circles of the first ray filter layer 3 and the second ray filter layer 4 are flush and arranged side by side, when the support layer 5 is attached to the outer side of the second ray filter layer 4 and arranged side by side with the first ray filter layer 3, the positioning and fixing of the first ray filter layer 3 and the second ray filter layer 4 are achieved.

[0043] In one embodiment, the interior of the support layer 5 is hollow, and the material of the support layer 5 is PMMA (polymethyl methacrylate, also known as acrylic or organic glass). Setting the support layer 5 as a hollow PMMA can reduce the deadweight of the support layer 5 and reduce the blocking of the support layer 5 to radiation.

[0044] In one embodiment, the dual energy filter further includes a shielding layer 6 for shielding radiation, and the shielding layer 6 is disposed between the first radiation filter layer 3 and the second radiation filter layer 4. The shielding layer 6 is disposed to separate the X-ray scattering of two different frequencies in the first radiation filter layer 3 and the second radiation filter layer 4.

[0045] In one embodiment, the shielding layer 6 is made of tungsten or a material with a higher atomic number, and an alloy material with a mass percentage higher than 90%, and a thickness of 100 um or more.

[0046] In one embodiment, shielding layers 6 are provided on both sides of the first ray filter layer 3. When the second imaging filter layer 4 is provided on both sides of the first ray filter layer 3, the shielding layers 6 on both sides of the first ray filter layer 3 can prevent the rays scattered by the second ray filter layer 4 from entering the first ray filter layer 3.

[0047] The specific working principle of the present invention is as follows: when scanning imaging is performed through the dual-energy filter of the present application, the radiation source 1 emits rays toward the first ray filter layer 3 and the second ray filter layer 4. When the rays pass through the first ray filter layer 3 and the second ray filter layer 4, the first ray filter layer 3 and the second ray filter layer 4 perform two different attenuation filtrations on the rays to obtain emission spectra with different average energies. The two rays of different energies pass through the object to be detected and act on the detector 2. The detector 2 receives the rays that pass through the object to be detected and converts the rays into visible light, which is converted into electrical signals by photoelectric conversion, and then converted into digital signals by an analog / digital converter, which are input into a computer for processing to obtain a reconstructed image of the object to be detected.

[0048] Since different substances have different specific absorption coefficients for rays of different energies, when the proportion of a substance is unknown, two rays of different energies can be used to image the object, and the composition ratio of the substance can be obtained by a method similar to solving a linear equation.

[0049] like Figure 3 and Figure 4 As shown, at 140 kVp, when the first ray filter layer 3 is 4 mm thick Al and the second ray filter layer 4 is 0.6 mm thick Cu, the emission spectrum based on Monte Carlo simulation is as follows Figure 3 As shown. In the figure, the curves are respectively the emission spectrum of the ray passing through 4mm thick Al, the emission spectrum of the ray passing through 0.6mm thick Cu, and the subtraction spectrum of the emission spectrum of the ray passing through Cu and the emission spectrum of the ray passing through Al. The vertical axis value is the energy distribution of the number of photons measured per square millimeter per second at an X-ray source current of 1mA and a detector distance of 1m. In actual use, the emission spectrum and subtraction spectrum of Cu will be used for image reconstruction respectively to obtain a higher energy separation. The average energy of the emission spectrum of Al is 75.8keV, and the average energy of the emission spectrum of Cu is 47.0keV. The dose ratio between the two is 1.68:1, and the ratio of the number of photons is 1.04:1, which can be used for dual-energy imaging applications. Different dual-filtration combinations can be designed according to the actual voltage and scanning scenarios to meet the needs of various usage scenarios, and they can be switched during use.

[0050] The present invention also provides a dual-energy CT, comprising a radiation source 1, a detector 2 and the above-mentioned dual-energy filter, wherein the dual-energy filter is arranged between the radiation source 1 and the detector 2, and the axes of the first ray filter layer 3 and the second ray filter layer 4 pass through the focus of the radiation source 1.

[0051] In one embodiment, the dual-energy CT further includes a carrier bed (not shown in the prior art drawings), the radiation source 1 and the detector 2 are arranged on both sides of the carrier bed, the first ray filter layer 3 and the second ray filter layer 4 are arranged between the radiation source 1 and the carrier bed, and the axes of the first ray filter layer 3 and the second ray filter layer 4 are parallel to the moving direction of the carrier bed.

[0052] This design does not use butterfly filter design, mainly because dual-energy CT has high requirements for the accuracy of X-ray spectrum, so the emission spectrum after the ray filter layer is relatively pure. Figure 4 As shown, they are the emission spectra of rays passing through 0.3mm thick Cu, 0.6mm thick Cu, 2mm thick Al and 4mm thick Al, respectively. It can be seen from the emission spectra that the energy spectra obtained after the rays pass through the filter layers of different thicknesses are quite different. In the butterfly filter design, due to the uneven thickness of the ray filter layer in the butterfly filter setting, the thickness of the ray filter layer passed by X-rays with different divergence angles is different, and the thickness difference at different positions can reach more than 2 times. When X-rays pass through different thicknesses of the same material, the shape of the X-ray spectrum will change, which will cause the ray spectrum to shift, forming different spectral shapes corresponding to different divergence angles, further reducing the energy separation of dual-energy imaging, and will cause the system to measure the attenuation coefficient of different positions of the same material. There is a shift and distortion, affecting the accuracy of the dual-energy reconstruction image contrast. In this application, the ray filter layer uses an arc design, and X-rays with different divergence angles all pass through the filter of the same thickness, and the emitted ray spectrum is consistent, the purity of the dual spectrum is higher, and the dual-energy imaging image contrast will also reduce the distortion level.

[0053] In addition, when the filter layer of the arc design has assembly deviation, that is, the focus and the center of the filter layer do not coincide, it will cause different penetration depths of X-rays at different angles. Assuming that the inner diameter of the filter layer arc is R (the distance from the focus to the inner surface of the filter layer when there is no assembly deviation), considering the existence of the focus FOD and the effective ray fan angle, R is generally greater than 100mm, and the thickness of the filter layer is r. On the XY plane perpendicular to the bed entry direction, the offset distance between the focus and the arc center is dr, then the maximum depth of X-ray penetration into the filter layer at any angle range is The minimum depth is r. Taking the filter layer thickness r as an example, the R parameter range is 100-150mm, and the dr parameter range is 0-2mm. Through actual measurement, the maximum deviation of the depth of X-ray penetration of the filter layer at various angles (the difference from r) is as follows: Figure 8 As shown in the figure. Within the above parameter range, the maximum deviation of the penetration depth is below 0.8um. ​​This penetration depth deviation has a negligible effect on the X-ray spectrum of the filter layer.

[0054] In dual-energy scanning with dual filtration, the scanning protocol needs to be modified in accordance with the scanning scene to achieve the acquisition of dual-energy images. In a normal spiral scan with a pitch (normalized pitch in spiral scanning) value of 1, the movement of the carrier bed and the rotation of the detector 2 and the radiation source 1 are performed simultaneously. The image obtained by the current scan is generally spiral, such as Figure 5 As shown, the first scanning area 2a and the second scanning area 2b of the detector 2 scan a part of the area of ​​the carrier bed respectively, and a single energy zone cannot traverse all areas of the carrier bed. Now, by modifying the pitch value of the spiral scan, the image obtained by rotating the detector 2 and the radiation source 1 for one circle coincides with the image of the starting position; when there is no shielding layer, the spiral pitch value is 0.5 (if the shielding layer 6 is used, the moving speed of the carrier bed can be slightly reduced or the number of revolutions of the detector 2 and the radiation source 1 can be increased according to the thickness of the shielding layer 6), as shown in FIG. Figure 6 As shown, the two energy detection areas of the detector 2 can both traverse the support bed. At this time, the CT system is equivalent to using a detector 2 with half the length in the bed direction for spiral scanning. After the X-ray passes through the first ray filter layer 3 and the second ray filter layer 4, two first X-rays 7a and second X-rays 7b with different energies are formed. The time interval of the same bed under the scanning of the first X-ray 7a and the second X-ray 7b of the two energies, that is, the time of the detector 2 from the first scanning area 2a to the second scanning area 2b, is the scanning time of a bed. Since the spiral scanning speed is very fast, the scanning time of a clinical CT bed can be as short as 0.25s, so the time interval of the images corresponding to the two X-ray energies collected under this scheme is 0.25s, and even the motion artifacts caused by breathing can be reduced. In the double-circle sequence scanning scheme, after completing a high-energy scan, a low-energy scan is performed. In this scanning scenario, the time interval of the dual-energy images of n beds is at least n×0.25s (excluding the kVp switching time and the bed exit time, the latter is longer). In comparison, the design scheme of the present invention has a higher degree of time domain matching, which can significantly reduce the impact of problems such as motion artifacts.

[0055] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A dual-energy filter, characterized in that: The invention comprises a first ray filter layer (3) and a second ray filter layer (4), wherein the first ray filter layer (3) and the second ray filter layer (4) are used to output wide-spectrum rays emitted by a radiation source (1) into two rays with different average energies for reception by a detector (2), and the two rays with different average energies are irradiated on different areas of a receiving surface of the detector (2), the first ray filter layer (3) and the second ray filter layer (4) are arc structures with equal inner diameters and different materials, the first ray filter layer (3) and the second ray filter layer (4) are arranged along the axial direction of the arc, the first ray filter layer (3) and the second ray filter layer (4) take the focus of the radiation source (1) as the center of the circle, the radial thickness of the first ray filter layer (3) is equal at all locations along the circumference, and the second ray filter layer (4) has a substantially uniform radial thickness. ) has the same radial thickness at all locations along the circumference; the number of the first ray filter layers (3) is two, and the two first ray filter layers (3) are respectively arranged on both sides of the second ray filter layer (4); in dual-energy scanning with dual filtration, the scanning protocol is modified in accordance with the scanning scene to realize the acquisition of dual-energy images; by modifying the pitch value of the spiral scanning, the image obtained by rotating the detector (2) and the radiation source (1) for one circle coincides with the image at the starting position; the arc lengths of the first ray filter layer (3) and the second ray filter layer (4) are equal; the side of the second ray filter layer (4) close to the radiation source (1) is flush with the side of the first ray filter layer (3) close to the radiation source (1), and the second ray filter layer (4) is flush with both ends of the first ray filter layer (3).

2. The dual-energy filter according to claim 1, characterized in that: It also comprises a support layer (5), wherein the support layer (5) is connected to the first ray filtering layer (3) and the second ray filtering layer (4).

3. The dual-energy filter according to claim 2, characterized in that: The support layer (5) is arranged on a side of the second ray filter layer (4) away from the radiation source (1), and the side of the support layer (5) away from the radiation source (1) is flush with a side of the first ray filter layer (3) away from the radiation source (1).

4. The dual-energy filter according to claim 1, characterized in that: The thickness of the second ray filtering layer (4) in the radial direction is smaller than the thickness of the first ray filtering layer (3) in the radial direction.

5. The dual-energy filter according to claim 1, characterized in that: The atomic number of the material in the second ray filtering layer (4) is higher than the atomic number of the material in the first ray filtering layer (3).

6. The dual-energy filter according to any one of claims 1 to 5, characterized in that: It also comprises a shielding layer (6) for shielding radiation, wherein the shielding layer (6) is arranged between the first ray filtering layer (3) and the second ray filtering layer (4).

7. A dual-energy CT, characterized in that: It comprises a radiation source (1), a detector (2) and a dual-energy filter according to any one of claims 1 to 6, wherein the dual-energy filter is arranged between the radiation source (1) and the detector (2).

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