Effective Focus Measurement Method and Device Based on Dynamic Translation of Shutter

Abstract

The present invention discloses a method and device for measuring an effective focus based on dynamic translation of a shielding plate, including: Step 1, collecting bright-field data; Step 2, adjusting the normal direction of the shielding plate to be parallel to the main direction of X-ray propagation, and the center of the shielding plate and the center of the X-ray source focus are located on the same horizontal line. Taking the side of the light-emitting window of the X-ray source as the starting point of movement, moving according to a preset step value until the shielding plate completely blocks the light-emitting window and stops moving. During the movement, use a detector to collect the photon energy distribution data after each movement of the shielding plate; Step 3, use the photon energy distribution data to inversely calculate the energy proportion of each sub-focus in the entire X-ray source focus, so as to obtain the size, shape and normalized intensity distribution of the X-ray source focus. The method of the present invention requires fewer additional devices and has high focus measurement accuracy. Higher spatial resolution images can be obtained using the focus information measured by this method.

Description

Technical Field

[0001] The present invention relates to the technical field of X-ray CT imaging, and particularly to an effective focal spot measurement method and device based on dynamic translation of a shielding plate. Background Art

[0002] The focal spot of an X-ray source is an important factor affecting spatial resolution. Especially when the focal spot is relatively large compared to the detector unit size, the shape and intensity of the focal spot cannot be ignored. Although the effective focal spot is measured according to the EN 12543 standard or the IEC 60336 standard when the X-ray source leaves the factory, due to factors such as long-term use of the X-ray source, directly using the measured effective focal spot size may not be reliable, and the characteristics of the effective focal spot are different under different voltages, currents, etc. Therefore, when performing high-resolution imaging based on the focal spot model, in order to better ensure the detail resolution ability of the reconstructed image, it is necessary to further measure the effective focal spot on-site.

[0003] Currently, the measurement methods for the characteristics of the effective focal spot of an X-ray source include the scanning method, the pinhole method, the slit method, the edge method, the star card method, and the small focal spot and micro focal spot measurement methods. Among them, the methods applicable to on-site measurement are the pinhole method, the slit method, and the edge method. The specific implementation steps of the methods are specified in detail in the EN 12543 standard, the IEC 60336 standard, and the ASTM E165 standard. The pinhole method is a commonly used measurement method, but its use will be restricted when the X-ray energy is high or the aperture of the pinhole baffle used is small. The principle of the slit method is similar to that of the pinhole method, and it has a better measurement effect on focal spots with a nominal value less than 0.3 mm. The edge method is a method of indirectly measuring the focal spot size by measuring the geometric unsharpness and is not used as an accurate focal spot measurement method.

[0004] With the wide application of CT imaging technology in the fields of medicine, industry, etc., high-precision focal spot measurement technology plays an important role. For imaging systems where the focal spot dominates spatial resolution, this paper proposes a high-precision dynamic translation effective focal spot measurement method. This method first uses a high-precision electric displacement stage to control the dynamic movement of a shielding plate made of a high-absorption material to obtain multiple sets of data. Then, a discrete focal spot model is established, and by solving the model, the shape and intensity information of the effective focal spot are restored. On the one hand, this method uses a high-precision displacement stage to reduce the systematic error of the measurement device. On the other hand, by iteratively solving the linear equations, the accuracy of the approximate solution is improved, and the transmission influence at high X-ray energies is reduced. Summary of the Invention

[0005] The object of the present invention is to provide an effective focus measurement method based on dynamic translation measurement. A shutter made of a high-absorption material is controlled by a high-precision electric displacement table to move dynamically, multiple groups of data are obtained, and then a discrete focus model is established. By solving the model, the size, shape and normalized intensity distribution of the X-ray source focus are obtained.

[0006] To achieve the above object, the present invention provides an effective focus measurement method based on dynamic translation of a shutter, which includes:

[0007] Step 1, collecting bright-field data I0;

[0008] Step 2, adjusting the normal direction of the shutter to be parallel to the main direction of X-ray propagation, and the center of the shutter and the center of the X-ray source focus are on the same horizontal line. Taking the light-emitting window side of the X-ray source as the starting point of movement, moving according to a preset step value until the shutter completely blocks the light-emitting window and stops moving. During the movement, the detector is used to collect the photon energy distribution data I1,…,I n …,I N ; where I1, I n , I N respectively represent the photons detected by the detector during the 1st, nth, and Nth translations

[0009] Step 3, using the photon energy distribution data to inversely calculate the energy proportion of each sub-focus in the entire X-ray source focus, so as to obtain the size, shape and normalized intensity distribution of the X-ray source focus; where all the discrete sub-foci constitute the focus of the X-ray source.

[0010] Further, in step 3, the energy proportion of each sub-focus in the entire X-ray source focus is calculated using the following formula (6):

[0011]

[0012] In the formula, J represents the total number of sub-foci, w j represents the energy proportion of the jth sub-focus in the entire X-ray source focus, μ represents the linear attenuation coefficient per unit length under standard density, and l n,j represents the matrix of the straight-line length of the ray passing through the shutter from the jth sub-focus to each detector unit on the detector during the nth translation.

[0013] Further, step 3 specifically includes:

[0014] Step 31, obtaining l n,j and μ;

[0015] Step 32, calculating the energy proportion of each sub-focus in the entire X-ray source focus according to the following formula (2):

[0016]

[0017] Further, in step 31, l n,j is obtained by the following method:

[0018] Step 311: Establish a coordinate system. Take the focal center of the X-ray source as the coordinate origin, the straight line connecting the origin and the center of the detector as the x-axis, and the direction from the origin to the detector as the positive direction of the x-axis. Take the straight line passing through the origin and parallel to the plane where the detector is located and perpendicular to the x-axis as the y-axis, and the upward direction as the positive direction of the y-axis. Take the straight line passing through the origin and perpendicular to the x-y plane as the z-axis;

[0019] Step 312: Determine the coordinates of each sub-focus and the coordinates of the detector units. Among them, multiple detector units with the same detection area form the detector;

[0020] Step 313: Determine whether the straight line formed between the current sub-focus and the detector unit intersects the shielding plate. If so, calculate l according to the distance formula of the two intersection points formed between the straight line and the shielding plate n,j ; if not, l n,j = 0.

[0021] Further, the length and width of the shielding plate are slightly larger than the length and width of the light output window.

[0022] The present invention also provides an effective focal spot measuring device based on the dynamic translation of the shielding plate, which includes:

[0023] A data acquisition unit, which includes an electrically controlled displacement stage and a detector. Among them, the normal direction of the detector is parallel to the main direction of X-ray propagation, and is used to collect bright field data I0, and collect photon energy distribution data I1,..., I n …, I N ; among them, I1, I n , I N respectively represent the photon energies detected by the detector during the 1st, nth, and Nth translations;

[0024] The electrically controlled displacement stage: includes a displacement stage and a shielding plate fixed on the displacement plate. The normal direction of the shielding plate is adjusted to be parallel to the main direction of X-ray propagation, and its center is on the same horizontal line as the center of the X-ray source focus. Take one side of the light output window of the X-ray source as the starting point of movement, and move according to a preset step value until the shielding plate completely shields the light output window and stops moving;

[0025] A calculation unit, which is used to inversely calculate the energy proportion of each sub-focus in the entire X-ray source focus by using the photon energy distribution data, so as to obtain the size, shape and normalized intensity distribution of the X-ray source focus; wherein, all the discretized sub-foci constitute the focus of the X-ray source.

[0026] Further, the calculation unit uses the following formula (6) to calculate the energy proportion of each sub-focus in the entire X-ray source focus:

[0027]

[0028] In the formula, J represents the total number of sub-foci, w j represents the energy proportion of the j-th sub-focus in the entire X-ray source focus, μ represents the linear attenuation coefficient per unit length under the standard density, and l n,j represents the straight-line length matrix of the j-th sub-focus and the straight line passing through the shielding plate where each detector unit on the detector is located during the n-th translation.

[0029] Further, the calculation unit specifically includes:

[0030] An intersection line length calculation subunit, which is used to obtain l n,j ;

[0031] An energy proportion calculation subunit, which is used to calculate the energy proportion of each sub-focus in the entire X-ray source focus according to the following formula (2) and μ:

[0032]

[0033] Further, the method for the intersection line length calculation subunit to obtain l n,j includes:

[0034] Step 311, establish a coordinate system: Establish a coordinate system: Take the focus center of the X-ray source as the coordinate origin, take the straight line connecting the origin and the detector center as the x-axis, and the direction from the origin to the detector as the positive direction of the x-axis, take the straight line passing through the origin and parallel to the plane where the detector is located and perpendicular to the x-axis as the y-axis, and take the upward direction as the positive direction of the y-axis, and take the straight line passing through the origin and perpendicular to the x-y plane as the z-axis;

[0035] Step 312, determine the coordinates of each sub-focus and the coordinates of the detector unit; wherein, a detector is composed of multiple detector units with the same detection area.

[0036] Step 313, determine whether there is an intersection point between the straight line formed between the current sub-focus and the detector unit and the shielding plate. If so, calculate l n,j according to the distance formula of the two intersection points formed between the straight line and the shielding plate; if not, l n,j = 0.

[0037] Furthermore, the length and width of the baffle are slightly larger than those of the light exit window.

[0038] The present invention can be used for the measurement of the effective focal spot, with few additional devices required, high measurement accuracy of the focal spot, and higher spatial resolution images can be obtained using the focal spot information measured by this method. Description of the Drawings

[0039] Figure 1 is a diagram of the device for measuring the effective focal spot of the present invention;

[0040] Figure 2 is a schematic diagram of the device for the mechanical zero point of the effective focal spot measurement of the present invention;

[0041] Figure 3 is a schematic diagram of the device after stepping a certain step size during the effective focal spot measurement of the present invention;

[0042] Figure 4 A in is a schematic diagram of the coordinate system during the effective focal spot measurement of the present invention;

[0043] Figure 4 B1 in is a front view when the sub-focal spot is at the origin of the coordinates and the baffle is translated below the x-axis (h < 0);

[0044] Figure 4 B2 in is a partial enlarged schematic diagram of B1;

[0045] Figure 4 C1 in is a front view when the sub-focal spot is at the origin of the coordinates and the baffle is translated below the x-axis (h = 0);

[0046] Figure 4 C2 in is a partial enlarged schematic diagram of C1;

[0047] Figure 4 D1 in is a front view when the sub-focal spot is at the origin of the coordinates and the baffle is translated below the x-axis (h > 0);

[0048] Figure 4 D2 in is a partial enlarged schematic diagram of D1;

[0049] Figure 5 is the intensity distribution image in the horizontal direction of the effective focal spot used in an embodiment of the present invention;

[0050] Figure 6 is the intensity distribution of the effective focal spot restored by the method of the present invention under different numbers of sub-focal spots in an embodiment of the present invention;

[0051] Figure 7 is the intensity distribution of the effective focal spot restored by the method of the present invention under different step sizes in an embodiment of the present invention;

[0052] Figure 8 The focal image measured by using the method of the present invention for an embodiment of the present invention;

[0053] Figure 9 The true and effective focal intensity distribution restored by using the traditional method and the method of the present invention for an embodiment of the present invention;

[0054] Figure 10 The linear attenuation coefficient map reconstructed from the effective focal point information restored by using different methods for an embodiment of the present invention. Detailed implementation manners

[0055] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0056] The method of the present invention includes the following steps:

[0057] Step 1: Set the tube voltage and tube current of the X-ray tube. After the X-ray source is preheated and reaches a stable state, collect bright-field data. Herein, the "stable state" can be understood as that the number of photons emitted by the X-ray source is basically stable within a certain period of time.

[0058] Step 2: Adjust the normal direction of the shielding plate to be parallel to the main direction of X-ray propagation, and the center of the shielding plate and the center of the focal point of the X-ray source are located on the same horizontal line. Taking the side of the light-emitting window of the X-ray source as the starting point of movement, move according to a preset step value until the shielding plate completely blocks the light-emitting window and stops moving. During the movement, use the detector to collect the photon energy distribution data I1,..., I n …, I N ;

[0059] Among them, I1, I n , I N respectively represent the photon energies detected by the detector during the 1st, nth, and Nth translations. It should be noted that the shielding plate is fixed on a high-precision electric displacement table. As Figure 1 shown, the high-precision electric displacement table is composed of a translation stage, a lifting stage, a manual angular stage, etc., and the minimum adjustment accuracy can reach 0.001 mm. By adjusting the high-precision electric displacement table, the movement command can be executed through a motion controller or software, and the pose and displacement of the shielding plate can be controlled.

[0060] The shielding plate is a high-ray-absorbing material plate with a certain thickness and uniform material. Its material is determined according to the tube voltage and tube current of the X-ray tube, and its function is to block the photons emitted from the focal point of the X-ray source. Preferably, the length and width of the shielding plate are slightly larger than the length and width of the light-emitting window of the X-ray source, so as to ensure complete photon blocking and avoid phenomena such as photon diffraction and scattering that may occur at the boundary where the shielding plate is perpendicular to the translation direction and close to the focal point center.

[0061] As shown Figure 4 in the figure, the detector is composed of multiple detector units with the same detection area.

[0062] Step 3: Using the photon energy distribution data, inversely calculate the energy proportion of each sub-focus in the entire X-ray source focus, so as to obtain the focus size, shape, and normalized intensity distribution of the X-ray source. Among them, the focus of the X-ray source generates a conical beam, dividing the plane perpendicular to the main direction of X-ray propagation into multiple sub-planes with equal areas, and each sub-plane can be called a sub-focus. All the sub-foci after discretization can be understood as constituting the focus of the X-ray source.

[0063] For example: As shown Figure 2 and Figure 3 in the figure, the number of sub-foci after discretization is J. The number of photons received by each detector unit should be the sum of the photons emitted by J sub-foci. When the number of discretizations is large and the reflection, scattering, and absorption that may occur to photons in the transmission medium air are ignored, the embodiment of the present invention can consider that the angular distribution of the radiation field within the solid angle of each sub-focus is approximately uniform. Therefore, assuming that the X-ray is composed of monoenergetic photons and the influence of factors such as scattered photons and electronic noise is not considered, the process of attenuation when the ray of the i-th detector unit passes through the baffle during the n-th translation can be described by the Beer-Lambert law. Step 3 specifically includes:

[0064] Step 31: Obtain l n,j and μ;

[0065] Step 32: According to the following formula (1), calculate the energy proportion of each sub-focus in the entire X-ray source focus:

[0066]

[0067] In formula (1), I n,i represents the remaining number of photons detected by the i-th detector unit during the n-th translation, J represents the total number of sub-foci, w j represents the energy proportion of the j-th sub-focus in the entire X-ray source focus, I 0,i represents the initial number of photons corresponding to the i-th detector unit, ∫ L μ n,j,i dl represents the line integral of the linear attenuation coefficient of the object being scanned along the straight line L where the j-th sub-focus and the i-th detector unit are located during the n-th translation.

[0068] In one embodiment, in step 3, for simplicity, step 32 can also calculate the energy proportion of each sub-focus in the entire X-ray source focus according to the following formula (2):

[0069]

[0070] Where: I n represents the data collected by the detector during the nth movement, I0 represents the bright-field data, l n,j expresses the straight-line length of the ray passing through the baffle plate where the jth sub-focus and the detector are located, w j , μ, and l n,j are unknowns, where μ and l n,j can be obtained through calculation, w j is the variable to be solved. When the material of the baffle plate is known to be uniform, μ can be obtained from NIST (National Institute of Standards and Technology, hereinafter referred to as NIST, Chinese: National Institute of Standards and Technology of the United States), and μ is then a known quantity. l n,j is l n,j represents the matrix of the straight-line lengths of the rays passing through the baffle plate where the jth sub-focus and each detector unit on the detector are located during the nth translation. When the thickness δ of the baffle plate is known, l n,j in step 31 can be obtained by the following methods:

[0071] Step 311, establish a coordinate system: As Figure 4 shown, take the focus center of the X-ray source as the coordinate origin, such as Figure 4 the Focus of A in [figure reference], which can also be understood as the focus center of the X-ray source. Take the straight line connecting the origin and the center of the detector as the x-axis, and the direction from the origin to the center of the detector as the positive direction of the x-axis. The detector is like Figure 4 the Detector of A in [figure reference]. Take the straight line passing through the origin and perpendicular to the plane where the x-axis is located as the y-axis, and the direction away from the origin and upward as the positive direction of the y-axis. The z-axis is perpendicular to the xy plane, and the direction perpendicular to the paper and outward can be taken as the positive direction of the z-axis.

[0072] Step 312, determine the coordinates of each sub-focus and the coordinates of the detector unit. Taking two dimensions as an example, the coordinates of the sub-focus are denoted as (0, j), and the coordinates where the detector unit is located are denoted as (fdd, y d ).

[0073] Step 313, determine whether the straight line formed between the current sub-focus and the detector unit intersects the baffle plate. If so, calculate l n,j according to the distance formula between the two intersection points formed by the straight line and the baffle plate; if not, l n,j = 0.

[0074] Taking two dimensions as an example, when the coordinates of the sub-focus are (0, j), the intersection line length l jIt can be calculated by the following formulas (3)-(5), where Δh is the step value, the moving distance of the shutter is h = n*Δh, δ is the width of the shutter, fod is the distance from the X-ray source focal center to the side of the shutter close to the X-ray source, fdd is the distance from the X-ray source focal center to the detector center, and y d is the distance from the current detector unit in the vertical direction to the detector center.

[0075] As Figure 4 shown by B1 and B2 in, the shutter is below the x-axis, h is less than 0, l n,j The calculation formula of is formula (3), as Figure 4 shown by C1 and C2 in, the shutter is below the x-axis, h is equal to 0, l n,j The calculation formula of is formula (4), as Figure 4 shown by D1 and D2 in, the shutter is above the x-axis, h is greater than 0, l n,j The calculation formula of is formula (5)

[0076]

[0077]

[0078]

[0079] In the formula, Δh is the step value, the moving distance of the shutter is h = n*Δh, δ is the width of the shutter, fod is the distance from the X-ray source focal center to the side of the shutter close to the X-ray source, fdd is the distance from the X-ray source focal center to the detector center, and y d is the distance from the current detector unit in the vertical direction to the detector center.

[0080] In one embodiment, in step 3, after N translations, the energy proportion of the sub-focus in the entire X-ray source focus can be calculated inversely and expressed as the following formula (6):

[0081]

[0082] Let When J = N, the exact solution of the above linear equation can be obtained. When J ≠ N, the above formula is an underdetermined or overdetermined linear equation. By adding constraint conditions and using methods such as the least squares method to iterate and solve, the shape of the focus and the photon distribution intensity can be obtained.

[0083] The present invention uses the data measured each time, based on the discrete focus model, and obtains the size, shape and intensity distribution of the focus by solving j . Compared with the traditional method, the present invention obtains it by solving the model instead of directly obtaining it after measurement, which ensures the accuracy of the focus. At the same time, the influence of photon transmission is reduced.

[0084] In one embodiment, the termination conditions for solving formula (6) include, but are not limited to, the maximum number of iterations, and the weight difference obtained in two iterations is less than a set threshold.

[0085] An embodiment of the present invention further provides an effective focal spot measurement device based on the dynamic translation of a shielding plate, which includes:

[0086] A data acquisition unit, which includes an electrically controlled displacement stage and a detector. Among them, the normal direction of the detector is parallel to the main direction of X-ray propagation, and is used to collect bright field data I0, and collect photon energy distribution data I1, …, I n …, I N ; Among them, I1, I n , I N respectively represent the photon energies detected by the detector during the 1st, nth, and Nth translations;

[0087] The electrically controlled displacement stage: includes a displacement stage and a shielding plate fixed on the displacement plate. The normal direction of the shielding plate is adjusted to be parallel to the main direction of X-ray propagation, and its center is on the same horizontal line as the center of the X-ray source focal spot. Taking the side of the light exit window of the X-ray source as the starting point of movement, and moving according to a preset step value until the shielding plate completely blocks the light exit window and stops moving;

[0088] A calculation unit, which is used to inversely calculate the energy proportion of each sub-focal spot in the entire X-ray source focal spot by using the photon energy distribution data, so as to obtain the size, shape and normalized intensity distribution of the X-ray source focal spot; among them, all the discretized sub-focal spots constitute the focal spot of the X-ray source.

[0089] In one embodiment, the calculation unit uses the energy proportion of each sub-focal spot in the entire X-ray source focal spot in the above formula (6).

[0090] In one embodiment, the calculation unit specifically includes:

[0091] An intersection line length calculation sub-unit, which is used to obtain l n,j ;

[0092] An energy proportion calculation sub-unit, which is used to calculate the energy proportion of each sub-focal spot in the entire X-ray source focal spot according to the above formula (2) and μ.

[0093] In one embodiment, the method for the intersection line length calculation sub-unit to obtain l n,j includes:

[0094] Step 311, establish a coordinate system: Take the focus center of the X-ray source as the coordinate origin, take the straight line connecting the origin and the center of the detector as the x-axis, and the direction from the origin to the center of the detector as the positive direction of the x-axis. Take the straight line passing through the origin and parallel to the plane where the detector is located and perpendicular to the x-axis as the y-axis, and take the straight line passing through the origin and perpendicular to the x-y plane as the z-axis;

[0095] Step 312, determine the coordinates of each sub-focus and the coordinates of the detector units; among them, multiple detector units with the same detection area form the detector;

[0096] Step 313, determine whether the straight line formed between the current sub-focus and the detector unit intersects with the baffle. If so, calculate l according to the distance formula of the two intersection points formed between the straight line and the baffle n,j ; if not, l n,j = 0.

[0097] The following uses a specific embodiment to illustrate the specific implementation process of an effective focus measurement method based on dynamic translation of the baffle proposed by the present invention.

[0098] Figure 5 This is the intensity distribution image in the horizontal direction of the effective focus used in this specific embodiment. Figure 6 、 Figure 7 This is the effective focus information recovered under different numbers of sub-foci and different steps in the discrete focus model in this specific embodiment.

[0099] The numerical experiment parameters are set as follows: Assume that the effective focus is a rectangle with a size of 1x0.4mm 2 , and the horizontal direction weight distribution is as shown in the reference curve of Figure 5 . The uniform material of the baffle is tungsten, with a length and width of 120mm and a thickness δ = 2mm. The initial number of photons is 10 6 . The length and width of the light exit window are 100mm respectively. The geometric parameters of the CT system are fod = 164mm and fdd = 550mm. The line detector is composed of 1024 detector units, and the size of each detector unit is 0.2mm.

[0100] The specific implementation steps are as follows:

[0101] Step 1, discretize the focus of the X-ray source into J sub-foci with intensities of w1,…w j …,w J . The linear attenuation coefficient of tungsten is u = 28.8702mm -1 . The baffle is translated from the side of the light exit window of the X-ray source until it completely blocks the focus of the X-ray source and stops. The step value Δh = 0.01mm, and the number of translations is N = 1000;

[0102] Step 2: Use the Siddon method to obtain the intersection line length corresponding to each translation. The calculation formulas for the intersection line length are (6) - (8), and the intersection line length for each movement is l 1,j …l n,j …l N,J 。

[0103] Step 3: According to Equation (1), obtain the number of photons of the detector as [I1, I2, I3, …, I N ;

[0104] Step 4: Let In the process of inverse-solving w j When Δh = 0.01mm, J = 20, J = 60, J = 100, and J = 80, Δh = 0.3mm, Δh = 0.1mm, Δh = 0.01mm, respectively, use the traditional ART method to iteratively solve X until the iterative termination condition is met, and then stop the iteration.

[0105] From Figure 6 and Figure 7 the results, it can be seen that the method of the present invention can restore the information of the effective focus.

[0106] The following uses a specific embodiment to compare the measurement effects of the method of the present invention and existing patent documents.

[0107] Figure 8 This is the focus image measured using the method of the present invention in an embodiment of the present invention, Figure 8 which is the measured focus image.

[0108] Figure 9 This is the true effective focus intensity distribution restored using the traditional method and the method of the present invention in an embodiment of the present invention, Figure 9 where the full width at half maximum of the curve is taken as the focus size, Figure 9 and the intensity distribution w of the focus in j 。

[0109] Figure 10 This is the linear attenuation coefficient map reconstructed from the effective focus information restored using different methods in an embodiment of the present invention.

[0110] The experimental scanning parameters are set as follows: The distance from the effective focus of the X-ray source to the center of the shielding plate is 164mm, the distance from the effective focus of the X-ray source to the detector is 1000mm, the tube voltage is 160kV, the tube current is 2.6mA, the step value is Δh = 0.01, the shielding plate is a tungsten plate with a uniform material thickness of 5mm, and the length and width of the device are 120mm. The detector consists of 2048 detector units, and the size of each detector unit is 0.2mm.

[0111] The specific implementation steps are as follows:

[0112] Step 1: Set the tube voltage and tube current of the X-ray tube. After the X-ray source is preheated and reaches a stable state, collect bright-field data.

[0113] Step 2: Fix the baffle on the high-precision electric displacement stage, adjust the position of the baffle so that its normal direction is parallel to the main direction of X-ray propagation. Then, driven by the high-precision electric displacement stage, move the baffle from the side of the light exit window of the X-ray source, and use the detector to collect data after each movement.

[0114] Step 3: When the baffle completely blocks the focus of the X-ray source, stop data collection.

[0115] Step 4: Use the data collected each time to inversely calculate the energy proportion of each sub-focus in the entire focus of the X-ray source, so as to obtain the size, shape and normalized intensity distribution of the X-ray source focus.

[0116] Figure 9 The horizontal intensity distribution of the true and effective focus restored by the boundary method and the method of this article. It can be clearly seen that the effective focus results measured by the two methods are different under the same CT system parameters. To further compare the two methods, in the embodiments of the present invention, under the same CT system geometric parameters during measurement, when the distance from the X-ray source to the turntable is 500 mm and the scanning angle is 1800, a standard CT performance phantom is scanned to obtain projection data. Then, under the effective focus information measured by different methods, the same reconstruction algorithm is used for reconstruction respectively, and the best result of the reconstructed image quality is as Figure 10 shown. Through comparison, the embodiments of the present invention find that the images reconstructed by the method of the present invention have better discrimination ability at high resolutions.

[0117] Those of ordinary skill in the art can understand that the drawings are only schematic diagrams of one embodiment, and the modules or processes in the drawings are not necessarily essential for implementing the present invention.

[0118] Those of ordinary skill in the art can understand that this embodiment is carried out on the calibrated size (EN 12543) of the X-ray source focus 1x0.4 mm 2 but the method of the present invention can also be used for on-site measurement of other foci.

[0119] Finally, it should be pointed out that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Those of ordinary skill in the art should understand that the technical solutions recorded in the foregoing embodiments can be modified, or some of the technical features can be equivalently replaced; these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An effective focal spot measurement method based on dynamic translation of a shielding plate, characterized in that, Including: Step 1, collecting bright-field data I0; Step 2: Adjust the normal direction of the baffle to be parallel to the main X-ray propagation direction, and ensure that the center of the baffle and the center of the X-ray source focus are on the same horizontal line. Starting from the side of the light exit window of the X-ray source as the starting point of movement, move according to the preset step value until the baffle completely blocks the light exit window and stops moving. During the movement process, use the detector to collect the photon energy distribution data I1, …, I n …, I N ; where I1, I n , I N respectively represent the photon energies detected by the detector during the 1st, nth, and Nth translations; Step 3, using the photon energy distribution data to inversely calculate the energy proportion of each sub-focus in the entire X-ray source focus, so as to obtain the size, shape and normalized intensity distribution of the X-ray source focus; wherein, all the discretized sub-foci constitute the focus of the X-ray source.

2. The effective focus measurement method based on dynamic translation of the shielding plate according to claim 1, wherein, In Step 3, the following formula (6) is used to obtain the energy proportion of each sub-focus in the entire X-ray source focus: Where J represents the total number of sub-foci, and w j represents the energy proportion of the j-th sub-focus in the entire X-ray source focus, μ represents the linear attenuation coefficient per unit length under standard density, and l n,j represents the straight-line length matrix of the ray passing through the shielding plate where the j-th sub-focus and each detector unit on the detector are located during the n-th translation.

3. The effective focal spot measurement method based on dynamic translation of the shielding plate according to claim 1 or 2, characterized in that Step 3 specifically includes: Step 31, obtain l n,j and μ; Step 32, according to the following formula (2), calculating the energy proportion of each sub-focus in the entire X-ray source focus:

4. The effective focus measurement method based on dynamic translation of the shielding plate according to claim 3, wherein The obtaining method of l in step 31 n,j includes: Step 311, establishing a coordinate system: taking the center of the focus of the X-ray source as the coordinate origin, taking the straight line connecting the origin and the center of the detector as the x-axis, and the direction from the origin to the detector as the positive direction of the x-axis, taking the straight line passing through the origin and parallel to the plane where the detector is located and perpendicular to the x-axis as the y-axis, and taking the upward direction as the positive direction of the y-axis, taking the straight line passing through the origin and perpendicular to the x-y plane as the z-axis; Step 312, determining the coordinates of each sub-focus and the coordinates of the detector unit; wherein, the detector is composed of multiple detector units with the same detection area. Step 313, determine whether there is an intersection point between the straight line formed by the current sub-focus and the detector unit and the baffle. If so, calculate l according to the distance formula of the two intersection points formed between the straight line and the baffle n,j ; if not, l n,j = 0.

5. The effective focal spot measurement method based on dynamic translation of the shielding plate according to claim 3, characterized in that, The length and width of the baffle are slightly larger than the length and width of the light exit window.

6. An effective focus measurement device based on dynamic translation of a baffle, characterized in that, Including: The data acquisition unit includes an electrically controlled displacement stage and a detector. Among them, the normal direction of the detector is parallel to the main direction of X-ray propagation, and it is used to collect bright-field data I0 and the photon energy distribution data I1, …, I n …, I N ; among them, I1, I n , I N respectively represent the photon energies detected by the detector during the 1st, nth, and Nth translations; Electrically controlled displacement stage: including a displacement stage and a baffle fixed on the displacement plate, the normal direction of the baffle is adjusted to be parallel to the main direction of X-ray propagation, and its center is on the same horizontal line as the center of the X-ray source focus, taking one side of the light exit window of the X-ray source as the starting point of movement, and moving according to a preset step value until the baffle completely blocks the light exit window and stops moving; A calculation unit, which is used to inversely calculate the energy proportion of each sub-focus in the entire X-ray source focus by using the photon energy distribution data, so as to obtain the size, shape and normalized intensity distribution of the X-ray source focus; wherein, all the discretized sub-foci constitute the focus of the X-ray source.

7. The effective focal spot measuring device based on dynamic translation of the shielding plate according to claim 6, wherein The calculation unit uses the following formula (6) to obtain the energy proportion of each sub-focus in the entire X-ray source focus: where J represents the total number of sub-foci, and w j represents the energy proportion of the j-th sub-focus in the entire X-ray source focus, μ represents the linear attenuation coefficient per unit length under standard density, and l n,j represents the matrix of the straight-line lengths of the rays passing through the shielding plate from the j-th sub-focus to each detector unit on the detector during the n-th translation.

8. The effective focus measurement device based on the dynamic translation of the baffle according to claim 6 or 7, characterized in that, The calculation unit specifically includes: The intersection line length calculation subunit is configured to obtain l n,j ; An energy proportion calculation sub-unit, which is used to calculate the energy proportion of each sub-focus in the entire X-ray source focus according to the following formula (2) and μ:

9. The effective focus measuring device based on the dynamic translation of the baffle according to claim 8, wherein The intersection line length calculation subunit obtains l n,j The method includes: Step 311, establishing a coordinate system: Establishing a coordinate system: taking the center of the focus of the X-ray source as the coordinate origin, taking the straight line connecting the origin and the center of the detector as the x-axis, and the direction from the origin to the detector as the positive direction of the x-axis, taking the straight line passing through the origin and parallel to the plane where the detector is located and perpendicular to the x-axis as the y-axis, and taking the upward direction as the positive direction of the y-axis, taking the straight line passing through the origin and perpendicular to the x-y plane as the z-axis; Step 312, determining the coordinates of each sub-focus and the coordinates of the detector unit; wherein, the detector is composed of multiple detector units with the same detection area. Step 313, determine whether there is an intersection point between the straight line formed by the current sub-focus and the detector unit and the baffle. If there is, calculate l according to the distance formula of the two intersection points formed between the straight line and the baffle n,j ; if not, l n,j = 0.

10. The effective focus measurement device based on the dynamic translation of the shielding plate according to claim 8, wherein The length and width of the baffle are slightly larger than the length and width of the light exit window.

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