CN112205991A - Method for correcting anode heel effect of X-ray machine - Google Patents
Method for correcting anode heel effect of X-ray machine Download PDFInfo
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- CN112205991A CN112205991A CN202011094622.7A CN202011094622A CN112205991A CN 112205991 A CN112205991 A CN 112205991A CN 202011094622 A CN202011094622 A CN 202011094622A CN 112205991 A CN112205991 A CN 112205991A
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- intensity distribution
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- 230000000694 effects Effects 0.000 title claims abstract description 46
- 238000000034 method Methods 0.000 title claims abstract description 21
- 239000000463 material Substances 0.000 claims description 25
- 229910052782 aluminium Inorganic materials 0.000 claims description 10
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 10
- 230000005855 radiation Effects 0.000 claims description 5
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 claims description 5
- 229910052721 tungsten Inorganic materials 0.000 claims description 5
- 239000010937 tungsten Substances 0.000 claims description 5
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 4
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 claims description 4
- 229910052802 copper Inorganic materials 0.000 claims description 4
- 239000010949 copper Substances 0.000 claims description 4
- 229910052718 tin Inorganic materials 0.000 claims description 4
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 claims description 3
- 238000001514 detection method Methods 0.000 claims description 3
- 239000011133 lead Substances 0.000 claims description 3
- 229910052750 molybdenum Inorganic materials 0.000 claims description 3
- 239000011733 molybdenum Substances 0.000 claims description 3
- 239000011135 tin Substances 0.000 claims description 3
- 238000010187 selection method Methods 0.000 claims 1
- 238000003384 imaging method Methods 0.000 abstract description 7
- 238000001228 spectrum Methods 0.000 abstract description 3
- 229910052751 metal Inorganic materials 0.000 description 6
- 239000002184 metal Substances 0.000 description 6
- 230000003287 optical effect Effects 0.000 description 6
- 238000003745 diagnosis Methods 0.000 description 4
- 229910052790 beryllium Inorganic materials 0.000 description 3
- ATBAMAFKBVZNFJ-UHFFFAOYSA-N beryllium atom Chemical compound [Be] ATBAMAFKBVZNFJ-UHFFFAOYSA-N 0.000 description 3
- 238000012986 modification Methods 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- 238000002083 X-ray spectrum Methods 0.000 description 2
- 238000005286 illumination Methods 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000003814 drug Substances 0.000 description 1
- 238000010894 electron beam technology Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 238000002594 fluoroscopy Methods 0.000 description 1
- 230000000149 penetrating effect Effects 0.000 description 1
- 239000013077 target material Substances 0.000 description 1
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/44—Constructional features of apparatus for radiation diagnosis
Abstract
The invention discloses a method for correcting an anode heel effect of an X-ray machine. The heel effect filter HEF (heel effect filter) designed by adopting the nonlinear fitting and sectional correction method can be used for pertinently adjusting the spatial distribution difference of the X-ray intensity caused by the anode heel effect, reducing the influence caused by excessive hardening of the spectrum caused by the filter and achieving a larger uniform range of the X-ray intensity distribution, thereby improving the imaging effect and other performance parameters of the X-ray machine and having wide adaptability.
Description
Technical Field
The invention provides a method for correcting an anode heel effect of an X-ray machine, and relates to the field of correction of the heel effect of the X-ray machine.
Background
Since their discovery, X-rays have been very closely linked to people's lives. The X-ray has strong penetrating power and is widely applied to the fields of modern medical fluoroscopy diagnosis, industrial flaw detection, public place personnel security check and the like. X-ray is used in clinical medicine for the first time, and with the continuous progress of X-ray technology, it is also the most important way in medical image diagnosis, and doctors use it to observe the internal structure of human body, and the application of medical X-ray machine in medical institutions such as hospitals and physical examination centers has been quite popular. Through years of clinical application, the safety awareness of patients is gradually improved, and the extra damage caused by useless rays is hoped to be reduced, and the efficiency of working rays is hoped to be improved; meanwhile, doctors hope to reduce diagnosis errors and have higher requirements on the image quality of the X-ray machine. Resolution is one of important performance indexes of image quality of a medical diagnostic X-ray machine with an image intensifier system, although the resolution of final imaging can be improved through an algorithm, if the resolution does not meet the requirement, details in the image cannot be accurately resolved, and therefore accurate diagnosis cannot be made. In the public safety field as well, the object to be detected cannot be accurately and clearly distinguished, and potential threat to public safety is caused.
One of the important factors affecting X-ray machine imaging is the anode Heel effect (Heel effect). The anode heel effect means that the intensity of X-rays close to one end of the anode target metal is obviously lower than that of the cathode end in the axial direction of the X-ray emergent direction. The reason is that the target surface of the anode metal has an inclination angle, when X-ray photons generated after high-energy electrons are driven into the target metal are emitted from the target surface, the attenuation effect of one end of the anode on the photons is stronger and the attenuation effect of one end close to the cathode on the photons is weaker due to the difference of the thicknesses of the target metal and the photon attenuation effect caused by the difference of the thicknesses of the target metal. As shown in FIG. 1, the attenuation path d1 of the two X-rays emitted along the main emission axis of the ray machine at the same included angle θ is significantly larger than that of the X-ray emitted along the cathode side d 2. And because the thickness of the target metal is gradually transited, the intensity of the output photon is gradually transited from weak to strong from the anode end to the cathode end. This necessarily results in an excess (i.e., unnecessary dose) due to the excessive image quality on the cathode side. In view of the fundamental problem of radiation protection, it is important to minimize unnecessary doses. Therefore, the heel effect of the ray machine needs to be corrected. The prior art typically uses flat plate filters to correct for the heel effect. Because the filter often blocks the low energy portion of the X-ray spectrum, the filter does not take into account the different effects of the filter on the low and high energy portions of the X-ray spectrum, which often results in over hardening of the energy spectrum, thereby affecting the imaging performance and other applications of the optical machine.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method for correcting the anode heel effect of an X-ray machine. The anode heel effect is corrected or partially corrected by a heel effect filter HEF (heel effect filter) designed by a nonlinear fitting and sectional correction method.
The invention is realized by the following technical scheme:
a method for correcting anode heel effect of an X-ray machine is characterized by comprising the following steps:
s1, obtaining the initial X-ray intensity distribution of the plane where the X-ray detector is located;
s2, selecting a proper filter sheet material according to the initial X-ray intensity distribution;
s3, obtaining the X-ray intensity distribution caused by the flat-plate type filter plates with different thicknesses of the selected material;
and S4, carrying out nonlinear fitting on the X-ray intensity distribution obtained in the S3, and setting an X-ray intensity cut-off threshold value to obtain the thickness distribution data of the heel effect filter.
In an embodiment of the present invention, the detection range of the X-ray detector in S1 includes the entire radiation field of the optical machine in the plane where the X-ray detector is located.
In one embodiment of the present invention, the filter material in S2 may be tungsten, molybdenum, lead, tin, copper, aluminum.
In one embodiment of the present invention, the method for selecting the filter sheet material in S2 is: on the light path between the X-ray machine and the X-ray detector plane, different material filters with the same thickness covering all radiation fields are placed at the same position to obtain the intensity distribution of the X-rays, and the material types are selected according to the intensity distribution of the X-rays.
In one embodiment of the present invention, the X-ray intensity distribution of the flat plate type filter with different thicknesses of the selected material obtained in S3 is obtained by: and arranging a flat plate type filter with a specific thickness in a light path between the X-ray machine and the detector plane, and obtaining the X-ray intensity distribution of the flat plate type filter with the specific thickness on the X-ray detector plane.
In one embodiment of the invention, the flat plate type filter sheet with the specific thickness is a filter sheet with a fixed thickness of 0.1mm to 5mm and the thickness interval is 0.1mm, and the filter sheets can be used in an overlapping way.
In an embodiment of the present invention, the method for obtaining the thickness distribution data of the heel effect filter in S4 comprises: and carrying out nonlinear fitting on the X-ray intensity distribution in the S3, setting an X-ray intensity cut-off threshold value, and obtaining the thickness distribution data of the filter in different angle sections on the anode and cathode axes through the intersection point of the threshold cut-off line and a fitting curve.
According to the technical scheme, the X-ray intensity spatial distribution difference caused by the anode heel effect can be adjusted in a targeted mode, the influence caused by excessive hardening of the spectrum caused by the filter is reduced, the larger X-ray intensity distribution uniformity range is achieved, the imaging effect and other performance parameters of the X-ray machine are improved, and the adaptability is wide.
Drawings
FIG. 1 is a schematic view of the heel effect of the present invention;
FIG. 2 is a reference schematic diagram of a method of heel effect correction of the present invention;
FIG. 3 is an axial X-ray intensity profile of the present invention;
FIG. 4 is a vertical axis X-ray intensity profile of the present invention;
FIG. 5 is an X-ray intensity distribution of the flat plate filters of the present invention of the same thickness and different materials;
FIG. 6 is an X-ray intensity distribution of aluminum flat plate filters of different thicknesses according to the present invention;
FIG. 7 is a graph of the results of a non-linear fit of the X-ray intensity for aluminum flat filters of different thicknesses in accordance with the present invention;
FIG. 8 is a graph of the thickness of the heel effect correction aluminum filter of the present invention versus spatial angle;
FIG. 9 is a comparison graph of the X-ray intensity distribution before and after the heel effect correction of the present invention;
figure 10 is a comparison of imaging before and after heel effect correction according to the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments. It is noted that the drawings are in greatly simplified form and that non-precision ratios are used for convenience and clarity only to aid in the description of the embodiments of the invention.
Referring to fig. 2, in one embodiment, the anode target is bombarded by a high-energy electron beam emitted from the cathode electron source, and a focal spot with a diameter of 3mm is formed on the surface of the anode target. The anode target material was tungsten with a target angle of 20 °. A round exit window is formed in the ray machine shielding box body, the maximum exit angle of the ray tube is limited to 40 degrees, meanwhile, a beryllium window of 3mm is arranged on the exit window, and part of low-energy X rays are filtered. The X-ray detector is arranged in the emergent direction of the optical machine. In the present invention, the direction of the line connecting the anode and the cathode is referred to as the axial direction, and the direction perpendicular to the axial direction of the anode and the cathode is referred to as the vertical axial direction.
S1, obtaining the initial X-ray intensity distribution of the plane where the detector is located:
specifically, first, under the condition that no filter exists in the optical path between the X-ray machine and the X-ray detector, the X-ray detector is used to obtain the initial X-ray intensity distribution of the X-ray machine. The X-ray intensity distribution in the axial direction is shown in fig. 3, and the X-ray intensity distribution in the vertical axial direction is shown in fig. 4. As can be seen from fig. 3, the intensity of X-rays gradually increases from the anode end toward the cathode end, and the X-ray intensity is highest in the direction of about 8 ° away from the main optical axis toward the cathode side, and the difference in the overall X-ray intensity distribution is large. As can be seen from fig. 4, the X-ray intensities are symmetrically distributed in the direction perpendicular to the axes of the cathode and anode, and the maximum X-ray intensity is obtained in the emission direction (0 °) of the main optical axis, so that the difference in the overall X-ray intensity distribution is small. Thereby allowing for primarily correcting for axial X-ray intensity distribution differences.
S2, selecting a proper filter material according to the initial X-ray intensity distribution:
specifically, when the anode heel effect is corrected by placing a filter sheet (attenuation sheet), an appropriate filter sheet material needs to be selected first. The filter material of the invention can be tungsten, molybdenum, lead, tin, copper and aluminum. Since the atomic numbers and densities of different filter materials are different, different filter materials with the same thickness are placed at the same position on the light path between the X-ray machine and the detector plane to obtain the intensity distribution of the X-rays, and the result is shown in FIG. 5. As can be seen from fig. 5, compared with the case without the filter, the material of the filter does not change the X-ray intensity distribution profile of the anode heel effect in the axial direction of the cathode and the anode, and the attenuation effect on the X-ray intensity is sequentially enhanced by aluminum, copper, tin, lead to tungsten. In view of the suitable thickness of the filter and the strength of the filtered X-rays, an aluminum material is most suitable in this embodiment.
S3, obtaining the X-ray intensity distribution caused by the flat plate type filter plates with different thicknesses of the selected materials:
because the material can not change the intensity line shape of the X-ray, and the part with the over-high X-ray intensity needs to be filtered, a method for differentiating the thickness distribution of the filter in the axial direction of the cathode and the anode needs to be adopted correspondingly to the filter made of the same material. The attenuation effect obtained by respectively arranging a plurality of plane aluminum filter sheets with the thickness of 0.5mm-3.5mm at the same position in front of the beryllium window is shown in figure 6.
S4, carrying out nonlinear fitting on the X-ray intensity distribution obtained in the S3, and setting an X-ray intensity cut-off threshold value to obtain the thickness distribution data of the heel effect filter plate:
in order to obtain the thickness values of the filter required for correcting the X-ray intensity to the same level in different spatial orientations, the invention performs nonlinear fitting on the curve data obtained from FIG. 6. Polynomial fitting is performed on the filter plates with different thicknesses to obtain fitting results as shown in FIG. 7. In order to ensure the irradiation effect and simultaneously inhibit the area with overhigh intensity and realize uniform illumination in the irradiation field as much as possible, the invention sets a threshold cut-off line when the intensity is reduced to 60 percent of that without the filter disc, and obtains the thickness distribution data of the aluminum filter disc in different angle sections on the axes of the anode and the cathode through the intersection point of the cut-off line and a fitting curve. Through analysis of thickness data, the anode Heel Effect Filter (HEF) is divided into three parts, and the thickness of the filter is designed in a segmented mode. Parabolic near the anode and planar in the middle, respectively. And parabolic fit was performed on the thickness data. Since the X-ray intensity near the anode-side limiting aperture stop is too low, if a filter is provided here, the X-ray intensity is further reduced, and therefore no filter is provided in the region where the X-ray intensity is less than 60%. The axial thickness profile of the resulting HEF is shown in fig. 8. Because the X-ray intensity is symmetrically distributed in the direction vertical to the axis of the cathode and the anode and the fluctuation amplitude is small, the axial thickness distribution only needs to extend to the direction vertical to the axis. And obtaining the HEF structure size corresponding to the corresponding position in front of the beryllium window through conversion of the angle and plane position relation.
The corrected X-ray intensity distribution in the cathode-anode axial direction is shown in fig. 9. Observing fig. 9, it can be seen that HEF corrects the X-ray intensity to about 60% without filtering, which is in line with design expectations, and corrects the anode heel effect well, with a maximum relative error of less than 3% in the region of uniform X-ray intensity along the anode and cathode axis.
In the range of the emergent field, a T-shaped lead block with the thickness of 1cm is arranged, and after the T-shaped lead block is corrected by a plane filter (left) and the HEF (right), the image on the imaging array surface is shown in FIG. 10. The contrast shows that the ghost image exists around the T-shaped object real image of the plane filter image, and the boundary is fuzzy. The gray image corrected by the HEF has clear boundary, accurate shape and uniform surrounding illumination.
It will be apparent to those skilled in the art that various changes and modifications may be made in the invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (7)
1. A method for correcting anode heel effect of an X-ray machine is characterized by comprising the following steps:
s1, obtaining the initial X-ray intensity distribution of the plane where the X-ray detector is located;
s2, selecting a proper filter sheet material according to the initial X-ray intensity distribution;
s3, obtaining the X-ray intensity distribution caused by the flat-plate type filter plates with different thicknesses of the selected material;
and S4, carrying out nonlinear fitting on the X-ray intensity distribution obtained in the S3, and setting an X-ray intensity cut-off threshold value to obtain the thickness distribution data of the heel effect filter.
2. The method for correcting the anode heel effect of an X-ray machine according to claim 1, wherein the detection range of the X-ray detector in S1 includes the entire radiation field of the X-ray machine in the plane of the X-ray detector.
3. The method as claimed in claim 1, wherein the filter material in S2 is selected from tungsten, molybdenum, lead, tin, copper, and aluminum.
4. The method for correcting the heel effect of the anode of the X-ray machine as claimed in claim 1, wherein the selection method of the filter sheet material in S2 comprises: on the light path between the X-ray machine and the X-ray detector plane, different material filters with the same thickness covering all radiation fields are placed at the same position to obtain the intensity distribution of the X-rays, and the material types are selected according to the intensity distribution of the X-rays.
5. The method of claim 1, wherein the method of obtaining the X-ray intensity distribution caused by the flat plate filters with different thicknesses of the selected material in S3 comprises: and arranging a flat plate type filter with a specific thickness in a light path between the X-ray machine and the detector plane, and obtaining the X-ray intensity distribution of the flat plate type filter with the specific thickness on the X-ray detector plane.
6. The method as claimed in claim 5, wherein the flat plate filter with a specific thickness comprises filter plates with a thickness of 0.1mm to 5mm and a fixed thickness of 0.1mm at intervals, and the filter plates can be stacked for use.
7. The method for correcting the heel effect of the anode of the X-ray machine according to claim 1, wherein the method for obtaining the thickness distribution data of the heel effect filter in S4 comprises the following steps: and carrying out nonlinear fitting on the X-ray intensity distribution in the S3, setting an X-ray intensity cut-off threshold value, and obtaining the thickness distribution data of the filter in different angle sections on the anode and cathode axes through the intersection point of the threshold cut-off line and a fitting curve.
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| CN202011094622.7A CN112205991A (en) | 2020-10-14 | 2020-10-14 | Method for correcting anode heel effect of X-ray machine |
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| CN202011094622.7A CN112205991A (en) | 2020-10-14 | 2020-10-14 | Method for correcting anode heel effect of X-ray machine |
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Application publication date: 20210112 |