A three-dimensional perspective automatic dimming method

Abstract

The present invention discloses a three-dimensional perspective automatic dimming method, comprising: a three-dimensional perspective automatic dimming method, characterized in that: comprising: (1) performing lateral perspective, and obtaining exposure voltage and lateral exposure current according to target light metering value; (2) performing frontal perspective with the exposure voltage obtained in step (1), and calculating the frontal exposure current according to the target light metering value; (3) constructing an ellipse model, with the position on the ellipse as the exposure position, the intersection of the major axis and the ellipse as the lateral exposure position, and the intersection of the minor axis and the ellipse as the frontal exposure position; (4) calculating the exposure current of the exposure position at different angles during the three-dimensional scanning process according to the ellipse model; (5) collecting a three-dimensional image with the exposure voltage obtained in step (1) and the exposure current obtained in step (4). The present invention utilizes the existing frontal and lateral positioning process, and can achieve relatively accurate three-dimensional automatic dimming without adding additional equipment and operation steps.

Description

Technical Field

[0001] The present invention relates to the technical field of three-dimensional image reconstruction, and in particular to a three-dimensional perspective automatic light adjustment method. Background Art

[0002] CBCT three-dimensional reconstruction technology uses an X-ray light source and a flat-panel detector to rotate and scan the object, expose and shoot when the C-arm rotates to different angles, obtains the projection of the object at the corresponding angle, and then uses a cone-beam back-projection reconstruction algorithm to obtain a three-dimensional image of the object.

[0003] The automatic perspective system (ABS) automatically adjusts the perspective exposure parameters through the detector's light-sensing recognition control, so that the exposure dose reaches the appropriate range, a clear image effect is obtained, and the automatic dimming process is realized. It greatly facilitates user operation and reduces the problem of excessive dose or poor image quality caused by improper human operation.

[0004] The automatic perspective system (ABS) requires a priori detection frames to obtain the brightness effect of the current parameters during the dimming process, and then obtains the target exposure parameters through feedback control or dimming model; however, for the three-dimensional mode, the C-arm is in a rotating state and cannot perform prior frame detection during the three-dimensional acquisition process, so other methods need to be used to achieve automatic dimming.

[0005] Due to the limited field of view of 3D measurement, users need to place the test object in the 3D imaging area. Therefore, it is necessary to first take the frontal and lateral perspective images to locate the test object so that users can adjust the position of the test object into the imaging area. However, existing dimming solutions are all for 2D imaging, and there is no automatic dimming solution for 3D imaging. Summary of the invention

[0006] Purpose of the invention: In view of the above-mentioned shortcomings, the present invention proposes a CBCT three-dimensional automatic dimming method, which uses the images generated by the frontal and lateral perspective positioning process to perform preliminary dimming and form a three-dimensional dimming model without adding additional operation processes.

[0007] Technical solution:

[0008] A three-dimensional perspective automatic dimming method, comprising:

[0009] (1) Perform lateral perspective and obtain exposure voltage and lateral exposure current according to the target light measurement value;

[0010] (2) performing a positive perspective with the exposure voltage obtained in step (1), and calculating a positive exposure current according to the target light metering value;

[0011] (3) constructing an ellipse model, with the position on the ellipse as the exposure position, the intersection of the major axis and the ellipse as the lateral exposure position, and the intersection of the minor axis and the ellipse as the frontal exposure position;

[0012] (4) Calculating the exposure current at different exposure angles during the three-dimensional scanning process based on the elliptical model;

[0013] (5) Capturing a three-dimensional image using the exposure voltage obtained in step (1) and the exposure current obtained in step (4).

[0014] The method for calculating the exposure current in step (4) is as follows:

[0015] The lateral exposure position in the constructed elliptical model is taken as 0 angle. As the rotation angle changes during image acquisition, the rotation angle of the corresponding point on the elliptical model is The exposure current is calculated using the following formula:

[0016]

[0017] Among them, I A is the side exposure current, I B In the step (1), the exposure voltage is obtained by using a 2D dimming algorithm, and the side exposure current is calculated based on the known relationship between the exposure voltage and the exposure current.

[0018] The 2D dimming algorithm is a feedback method:

[0019] Get the exposure image and calculate the metering value C of the current image t , and the target exposure value C m Compare, such as C t <C m The exposure voltage is increased by the set step length, and vice versa, the exposure voltage is decreased by the set step length;

[0020] Continue iterating until C t =C m , and obtain the exposure voltage at this time.

[0021] The 2D dimming algorithm is a model method:

[0022] The photometric values ​​of the exposure images obtained by using different exposure voltages at different thicknesses are obtained through experiments, and a three-dimensional mapping model of photometric value-exposure voltage-thickness is established accordingly;

[0023] Get the exposure image and calculate the metering value C of the current image t , the current patient thickness h is calculated according to the three-dimensional mapping model, and the current patient thickness h and the target photometric value C are used to calculate the current patient thickness h and the target photometric value C m The corresponding exposure voltage is calculated according to the three-dimensional mapping model.

[0024] It also includes an iterative step: obtaining an exposure image and calculating its photometric value using the exposure voltage and exposure current calculated once before, calculating the corresponding patient thickness h according to the three-dimensional mapping model, and calculating the corresponding exposure voltage accordingly;

[0025] The iterative steps are repeated until the difference between the obtained light metering value of the exposure image and the target light metering value is within a preset range or a preset number of iterations is reached.

[0026] The specific light metering value of the calculated image is:

[0027] Calculate the average gray value p0 of the exposure image;

[0028] The region of interest is obtained by segmentation, and a set range is selected from the lowest grayscale value in the region of interest as the darkest area of ​​the region of interest, and its average grayscale value p1 is calculated, so as to calculate the metering value C=αp0+βp1 of the exposure image, where α and β are weighting parameters respectively.

[0029] The setting range is set to 10-15%.

[0030] The step (2) is specifically:

[0031] The exposure voltage obtained in step (1) and the preset frontal exposure current I0 are used to capture the frontal image of the patient; wherein the preset frontal exposure current I0 is smaller than the lateral exposure current;

[0032] Calculate the photometric value C of the patient's positive image taken B and compare it with the target light value C m The ratio between them is proportional to the target exposure current I B , the calculation formula is: B =I0*C m / C B .

[0033] Beneficial effects: The present invention utilizes the existing frontal and lateral positioning process and can achieve relatively accurate three-dimensional automatic dimming without adding additional equipment and operating steps. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a flow chart of the automatic dimming algorithm of the present invention;

[0035] Figure 2 It is a schematic diagram of the anteroposterior and lateral positions of the C-arm machine; the solid line is the anteroposterior position, and the dotted line is the lateral position;

[0036] Figure 3 This is a schematic diagram of the elliptical dimming model constructed by the present invention. DETAILED DESCRIPTION

[0037] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments.

[0038] Figure 1 is a flow chart of the automatic dimming algorithm of the present invention, as shown in Figure 1 As shown, the CBCT three-dimensional automatic dimming method of the present invention comprises the following steps:

[0039] (1) Perform lateral perspective to obtain exposure voltage V and lateral exposure current I A ;

[0040] The present invention uses a 2D dimming algorithm to obtain the exposure voltage V and the side exposure current I A , as follows:

[0041] The C-arm is rotated to the patient's lateral position, and the patient's lateral image is taken. The 2D dimming algorithm is used to obtain the lateral exposure parameters, namely the exposure voltage V and the lateral exposure current I. A ;

[0042] Among them, 2D dimming algorithms include feedback method and model method;

[0043] Feedback method: Based on experience or prior information, the relationship curve between exposure voltage and exposure current is obtained, the exposure image is obtained, and the metering value C of the current image is calculated. t , and the target exposure value C m Compare, such as C t <C m The exposure voltage V is increased by the set step size, and vice versa, the exposure voltage V is decreased by the set step size. The side exposure current is calculated according to the relationship curve between the exposure voltage and the exposure current, and the iteration is continued until C t =C m , and obtain the exposure voltage and side exposure current at this time;

[0044] Model method:

[0045] Since the density of human body is close to that of water, the thickness of water film is used to equate to the thickness of human body for the test. The thickness direction is the direction of ray. The photometric values ​​of the exposure images obtained by using different exposure voltages under different water film thicknesses are obtained through the experiment, and a three-dimensional mapping model of photometric value-exposure voltage-water film thickness is established accordingly.

[0046] Setting exposure voltage based on experience and acquiring exposure images;

[0047] Calculate the metering value C of the current image t , and calculate the current patient thickness h according to the three-dimensional mapping model obtained above, and use the thickness h and the target photometry value C m The corresponding exposure voltage V is obtained according to the aforementioned three-dimensional mapping model, and the side exposure current I is calculated according to the known relationship between the exposure voltage V and the exposure current.A ;

[0048] In the present invention, since the current patient thickness h is calculated and may deviate from the actual thickness, in order to make the result more accurate, an iterative step can also be set: the exposure voltage V and the lateral exposure current I calculated once before are calculated. A Acquire an exposure image and repeat the above process to obtain more accurate exposure voltage V and exposure current; the iterative step is performed until the difference between the metering value of the acquired exposure image and the target metering value is within a preset range or a preset number of iterations. The preset range is determined according to actual needs and can generally be set to 2 to 3 times.

[0049] The light metering value is calculated as follows:

[0050] Calculate the average gray value p0 of the exposure image;

[0051] The region of interest is obtained by segmentation, and a set range is selected from the lowest grayscale value in the region of interest as the darkest area of ​​the region of interest, and its average grayscale value p1 is calculated, so that the metering value C=αp0+βp1 of the exposure image can be calculated, wherein α and β are weighting parameters respectively; wherein the set range is set to 10-15%.

[0052] The region of interest is the area in the image where the target object is located.

[0053] (2) performing anterior perspective to obtain anterior exposure current;

[0054] (21) The C-arm is rotated to the patient's frontal position, and an image of the patient's frontal position is captured using the exposure voltage V obtained in step (1) and a preset frontal exposure current I0; wherein the preset frontal exposure current I0 is less than I A , for example, it can be set to I A / 2;

[0055] (22) Calculate the photometric value C of the patient's positive image taken B and compare it with the target light value C m The positive exposure current I is calculated in direct proportion to the ratio between B , thus obtaining the target positive exposure current I B , the calculation formula is:

[0056] I B =I0*C m / C B

[0057] So far, the exposure voltage V of the three-dimensional automatic dimming of the present invention and the exposure current I at the thickest position (patient side position) and the thinnest position (patient front position) are obtained. A and I B ;

[0058] (3) Construct a dimming model;

[0059] The exposure current of all exposure positions (different angles) in the 3D scanning process is calculated through the constructed dimming model;

[0060] The dimming model constructed is an elliptical model, such as Figure 2 , the origin is the coordinate origin, the position on the ellipse is the exposure position, the intersection of the major axis and the ellipse is defined as the lateral exposure position, and the intersection of the minor axis and the ellipse is defined as the frontal exposure position; and the lateral exposure position in the constructed ellipse model is taken as 0 angle, then the rotation angle of the corresponding point in the ellipse model is The exposure current can be calculated using the following formula:

[0061]

[0062] (4) Using the exposure voltage V obtained in step (1) and the exposure current obtained in step (3) Acquire three-dimensional images.

[0063] Because the voltage needs to be fixed during 3D shooting, this voltage must be guaranteed to penetrate the thickest part of the patient (the patient's lateral position is thickest), so the lateral position is taken first; after the voltage is fixed, the dimming process becomes simple, so one frame of the image in the upright position is sufficient.

[0064] The present invention utilizes the existing frontal and lateral positioning process to achieve relatively accurate three-dimensional automatic dimming without adding additional equipment and operating steps.

[0065] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various equivalent transformations (such as quantity, shape, position, etc.) can be made to the technical scheme of the present invention, and these equivalent transformations all belong to the protection scope of the present invention.

Claims

1. A three-dimensional perspective automatic dimming method, characterized in that: include: (1) Perform lateral perspective and obtain exposure voltage and lateral exposure current according to the target light measurement value; (2) performing a positive perspective with the exposure voltage obtained in step (1), and calculating a positive exposure current according to the target light metering value; (3) constructing an ellipse model according to the side exposure current of step (1) and the front exposure current of step (2), with the position on the ellipse as the exposure position, the intersection of the major axis and the ellipse as the side exposure position, and the intersection of the minor axis and the ellipse as the front exposure position; (4) Calculating the exposure current at different exposure angles during the three-dimensional scanning process based on the elliptical model; (5) Capturing a three-dimensional image using the exposure voltage obtained in step (1) and the exposure current obtained in step (4).

2. The three-dimensional perspective automatic dimming method according to claim 1, characterized in that: The method for calculating the exposure current in step (4) is as follows: The lateral exposure position in the constructed elliptical model is taken as 0 angle. As the rotation angle changes during image acquisition, the rotation angle of the corresponding point on the elliptical model is The exposure current is calculated using the following formula: Among them, I A is the side exposure current, I B is the positive exposure current.

3. The three-dimensional perspective automatic dimming method according to claim 1, characterized in that: In the step (1), the exposure voltage is obtained using a 2D dimming algorithm, and the side exposure current is calculated based on the known relationship between the exposure voltage and the exposure current.

4. The three-dimensional perspective automatic dimming method according to claim 3, characterized in that: The 2D dimming algorithm is a feedback method: Get the exposure image and calculate the metering value C of the current image t , and the target exposure value C m Compare, such as C t <C m The exposure voltage is increased by the set step length, and vice versa, the exposure voltage is decreased by the set step length; Continue iterating until C t =C m , and obtain the exposure voltage at this time.

5. The three-dimensional perspective automatic dimming method according to claim 3, characterized in that: The 2D dimming algorithm is a model method: The photometric values ​​of the exposure images obtained by using different exposure voltages at different thicknesses are obtained through experiments, and a three-dimensional mapping model of photometric value-exposure voltage-thickness is established accordingly; Get the exposure image and calculate the metering value C of the current image t , the current patient thickness h is calculated according to the three-dimensional mapping model, and the current patient thickness h and the target photometric value C are used to calculate the current patient thickness h and the target photometric value C m The corresponding exposure voltage is calculated according to the three-dimensional mapping model.

6. The three-dimensional perspective automatic dimming method according to claim 5, characterized in that: It also includes an iterative step: obtaining an exposure image and calculating its photometric value using the exposure voltage and exposure current calculated once before, calculating the corresponding patient thickness h according to the three-dimensional mapping model, and calculating the corresponding exposure voltage accordingly; The iterative steps are repeated until the difference between the obtained light metering value of the exposure image and the target light metering value is within a preset range or a preset number of iterations is reached.

7. The three-dimensional perspective automatic dimming method according to any one of claims 4 to 6, characterized in that: The specific light metering value of the calculated image is: Calculate the average gray value p0 of the region of interest; A set range is selected from the lowest grayscale value in the region of interest as the darkest region of the region of interest, and its average grayscale value p1 is calculated, thereby obtaining the metering value C=αp0+βp1 of the exposure image, where α and β are weighting parameters respectively.

8. The three-dimensional perspective automatic dimming method according to claim 7, characterized in that: The setting range is set to 10-15%.

9. The three-dimensional perspective automatic dimming method according to claim 1, characterized in that: The step (2) is specifically: The exposure voltage obtained in step (1) and the preset frontal exposure current I0 are used to capture the frontal image of the patient; wherein the preset frontal exposure current I0 is smaller than the lateral exposure current; Calculate the photometric value C of the patient's positive image taken B and compare it with the target light value C m The ratio between them is proportional to the target exposure current I B , the calculation formula is: B =I0*C m / C B .

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