CN115153595A - Three-dimensional perspective automatic dimming method - Google Patents
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Abstract
The invention discloses a three-dimensional perspective automatic dimming method, which comprises the following steps: a three-dimensional perspective automatic dimming method is characterized by comprising the following steps: the method comprises the following steps: (1) Performing side position perspective, and obtaining exposure voltage and side position exposure current according to a target photometric value; (2) Performing normal perspective on the exposure voltage obtained in the step (1), and calculating according to a target photometric value to obtain a normal exposure current; (3) Constructing an ellipse model, wherein the upper position of the ellipse is taken as an exposure position, the intersection point of the major axis and the ellipse is taken as a lateral exposure position, and the intersection point of the minor axis and the ellipse is taken as a positive exposure position; (4) Calculating exposure currents of exposure positions at different angles in the three-dimensional scanning process according to the ellipse model; (5) And (5) acquiring a three-dimensional image by using the exposure voltage obtained in the step (1) and the exposure current obtained in the step (4). The invention can realize accurate three-dimensional automatic dimming by utilizing the existing positive side positioning process without adding additional equipment and operation steps.
Description
Technical Field
The invention relates to the technical field of three-dimensional image reconstruction, in particular to an automatic dimming method for three-dimensional perspective.
Background
The CBCT three-dimensional reconstruction technology is a technology that an X-ray light source and a flat panel detector are adopted to carry out rotary scanning on an object, exposure shooting is carried out when a C arm rotates to different angles, projections of the object under corresponding angles are obtained, and then a cone-beam back projection reconstruction algorithm is used for obtaining a three-dimensional image of the object.
The automatic perspective system (abs) automatically adjusts perspective exposure parameters through photosensitive recognition control of a detector, so that the exposure dose reaches a proper range, a clear image effect is obtained, and an automatic dimming process is realized. Greatly facilitating the operation of users and reducing the problems of overhigh dosage or poor image quality caused by improper manual operation.
An automatic perspective system (abs) needs a priori detection frame to obtain the brightness effect of the current parameter in the dimming process, and then obtains a target exposure parameter through feedback control or a dimming model; however, for the three-dimensional mode, the C-arm is in a rotating state, prior frame detection cannot be performed in the three-dimensional acquisition process, and other methods are required to realize automatic dimming.
The three-dimensional measurement requires a user to place a test object in a three-dimensional imaging area due to limited shooting visual field, so that the user needs to shoot a front side perspective image to position the test object, so that the user can adjust the position of the test object to the imaging area. However, the existing dimming is the dimming for two-dimensional imaging, and an automatic dimming scheme for three-dimensional imaging is not available.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the defects, the invention provides a CBCT three-dimensional automatic dimming method, which utilizes the image generated in the front-side perspective positioning process to perform preliminary dimming and form a three-dimensional dimming model without adding an additional operation process.
The technical scheme is as follows:
a three-dimensional perspective automatic dimming method, comprising:
(1) Performing side position perspective, and obtaining exposure voltage and side position exposure current according to a target photometric value;
(2) Performing normal perspective on the exposure voltage obtained in the step (1), and calculating according to a target photometric value to obtain a normal exposure current;
(3) Constructing an ellipse model, wherein the upper position of the ellipse is taken as an exposure position, the intersection point of the major axis and the ellipse is taken as a lateral exposure position, and the intersection point of the minor axis and the ellipse is taken as a positive exposure position;
(4) Calculating exposure currents of exposure positions at different angles in the three-dimensional scanning process according to the ellipse model;
(5) And (4) acquiring a three-dimensional image by using the exposure voltage obtained in the step (1) and the exposure current obtained in the step (4).
The method for calculating the exposure current in the step (4) is as follows:
the side exposure position in the constructed elliptical model is set as an angle of 0 degree and rotates along with the image acquisition processThe rotation angle of the corresponding point on the ellipse model is determined according to the change of the rotation angle
The exposure current is calculated by the following formula
Wherein, I A For lateral exposure current, I B Is the positive exposure current. In the step (1), the exposure voltage is obtained by using a 2D dimming algorithm, and the side position exposure current is calculated according to the known relationship between the exposure voltage and the exposure current.
The 2D dimming algorithm is a feedback method:
obtaining an exposure image, and calculating a photometric value C of the current image t And the target photometric value C m Comparison, e.g. C t <C m Increasing the exposure voltage by a set step length, and conversely, decreasing the exposure voltage by the set step length;
continuously iterating until C t ＝C m The exposure voltage at this time is obtained.
The 2D dimming algorithm is a model method:
acquiring photometric values of exposure images obtained by adopting different exposure voltages under different thicknesses through experiments, and establishing a three-dimensional mapping model of the photometric values, the exposure voltages and the thicknesses according to the photometric values;
obtaining an exposure image, and calculating a photometric value C of the current image t Calculating to obtain the current patient thickness h according to the three-dimensional mapping model, and obtaining the target photometric value C according to the current patient thickness h m And calculating according to the three-dimensional mapping model to obtain the corresponding exposure voltage.
Further comprising the iterative step of: obtaining an exposure image and calculating a photometric value of the exposure image according to the exposure voltage and the exposure current obtained by previous calculation, calculating the thickness h of the corresponding patient according to the three-dimensional mapping model, and obtaining the corresponding exposure voltage according to the calculation;
and repeating the iteration step until the difference value between the photometric value of the obtained exposure image and the target photometric value is within a preset range or reaches a preset iteration number.
The specific steps for calculating the photometric value of the image are as follows:
calculating the average gray value p of the exposed image 0 ；
Obtaining an interested area by segmentation, selecting a set range from the lowest gray value in the interested area as the darkest area of the interested area, and calculating the average gray value p of the selected range 1 Thereby calculating the photometric value C = alpha p of the exposure image 0 +βp 1 Where α and β are weighting parameters, respectively.
The set range is set to 10 to 15%.
The step (2) is specifically as follows:
adopting the exposure voltage obtained in the step (1) and a preset positive exposure current I 0 Taking a patient orthostatic image; wherein the preset positive exposure current I 0 Less than the lateral exposure current;
calculating the photometric value C of the positive position image of the patient B And through it with the target photometric value C m Proportional ratio between the current values of the target positive exposure current I and the target negative exposure current I B The calculation formula is as follows: i is B ＝I 0 *C m /C B 。
Has the advantages that: the invention can realize accurate three-dimensional automatic dimming by utilizing the existing positive side positioning process without adding additional equipment and operation steps.
Drawings
FIG. 1 is a flow chart of an automatic dimming algorithm of the present invention;
FIG. 2 is a schematic side view of the C-arm machine; wherein, the solid line is a positive position, and the dotted line is a lateral position;
fig. 3 is a schematic diagram of an elliptical dimming model constructed according to the present invention.
Detailed Description
The invention is further elucidated with reference to the drawings and the embodiments.
Fig. 1 is a flowchart of an automatic dimming algorithm of the present invention, and as shown in fig. 1, the CBCT three-dimensional automatic dimming method of the present invention includes the following steps:
(1) Performing lateral perspective to obtain exposure voltage V and lateral exposure current I A ；
The invention obtains exposure voltage V and lateral exposure current I by using a 2D dimming algorithm A The method comprises the following steps:
rotate the C arm to patient side position, shoot patient side position image, adopt 2D dimming algorithm to obtain side position exposure parameter, exposure voltage V and side position exposure current I promptly A ；
The 2D dimming algorithm comprises a feedback method and a model method;
a feedback method comprises the following steps: obtaining a relation curve of exposure voltage and exposure current according to experience or prior information, obtaining an exposure image, and calculating a photometric value C of the current image t And the target photometric value C m Comparison, e.g. C t <C m Increasing the exposure voltage V by a set step length, conversely decreasing the exposure voltage V by the set step length, calculating the lateral exposure current according to the relationship curve of the exposure voltage and the exposure current, and continuously iterating until C t ＝C m Obtaining the exposure voltage and the lateral exposure current at the moment;
and (3) modeling method:
because the density of a human body is close to water, the thickness of a water film is equal to the thickness of the human body for testing, the thickness direction is the ray direction, photometric values of exposure images obtained by adopting different exposure voltages under different water film thicknesses are obtained through the test, and a three-dimensional mapping model of the photometric values, the exposure voltages and the water film thicknesses is established according to the photometric values;
setting exposure voltage according to experience to obtain an exposure image;
calculating the photometric value C of the current image t Calculating to obtain the thickness h of the current patient according to the obtained three-dimensional mapping model, and obtaining the target photometric value C according to the thickness h m Obtaining corresponding exposure voltage V according to the three-dimensional mapping model, and obtaining the relationship between the exposure voltage V and the exposure current according to the known relationshipCalculating to obtain lateral exposure current I A ；
In the invention, because the current patient thickness h is calculated and may have deviation from the actual thickness, in order to obtain more accurate results, an iteration step may be further provided: exposure voltage V and lateral exposure current I obtained by previous calculation A Acquiring an exposure image, and repeating the process to obtain more accurate exposure voltage V and exposure current; the iteration step is carried out until the difference value between the acquired photometric value of the exposure image and the target photometric value is within a preset range or preset iteration times, wherein the preset range is determined according to actual requirements and can be generally set to be 2 to 3 times.
Wherein, the photometric value is calculated as follows:
calculating the average gray value p of the exposed image 0 ；
Obtaining an interested area by segmentation, selecting a set range from the lowest gray value in the interested area as the darkest area of the interested area, and calculating the average gray value p of the selected range 1 So that the photometric value C = α p of the exposure image can be calculated 0 +βp 1 Wherein, alpha and beta are respectively weighting parameters; wherein the set range is set to 10 to 15%.
The region of interest is the region in the image where the target measurement is located.
(2) Performing positive perspective to obtain positive exposure current;
(21) Rotating the C arm to the correct position of the patient, and adopting the exposure voltage V obtained in the step (1) and the preset correct position exposure current I 0 Taking a positive image of the patient; wherein the preset positive exposure current I 0 Is less than I A E.g. can be set to I A /2；
(22) Calculating the photometric value C of the photographed patient normal image B And through it with the target photometric value C m Proportional calculation of the ratio of the current to the voltage to obtain the positive exposure current I B Thereby obtaining a target normal exposure current I B The calculation formula is as follows:
I B ＝I 0 *C m /C B
thus obtaining the exposure voltage V of the three-dimensional automatic dimming and the exposure current I of the thickest position (patient side position) and the thinnest position (patient right position) A And I B ；
(3) Constructing a dimming model;
calculating exposure currents of all exposure positions (different angles) in the three-dimensional scanning process through the constructed dimming model;
the constructed dimming model is an ellipse model, as shown in fig. 2, the origin is a coordinate origin, the upper position of the ellipse is taken as an exposure position, the intersection point of the major axis and the ellipse is defined as a lateral exposure position, and the intersection point of the minor axis and the ellipse is defined as a positive exposure position; and setting the side exposure position in the constructed elliptical model as 0 degree, aiming at the rotation angle of the corresponding point in the elliptical model
The exposure current can be calculated as follows
(4) Using the exposure voltage V obtained in the step (1) and the exposure current obtained in the step (3)
A three-dimensional image is acquired.
Because voltage needs to be fixed in the 3D shooting process, the voltage needs to ensure that the thickest part of a patient can be penetrated (the lateral position of the patient is thickest), so that the lateral position is shot firstly; after the voltage is fixed, the dimming process becomes simple, so that one frame of image can be positioned.
The invention realizes more accurate three-dimensional automatic dimming by utilizing the existing positive side positioning process without adding additional equipment and operation steps.
Although the preferred embodiments of the present invention have been described in detail, the present invention is not limited to the details of the foregoing embodiments, and various equivalent changes (such as number, shape, position, etc.) may be made to the technical solution of the present invention within the technical spirit of the present invention, and these equivalent changes are all within the protection scope of the present invention.
Claims (9)
1. A three-dimensional perspective automatic dimming method is characterized by comprising the following steps: the method comprises the following steps:
(1) Performing side position perspective, and obtaining exposure voltage and side position exposure current according to a target photometric value;
(2) Performing normal perspective on the exposure voltage obtained in the step (1), and calculating according to a target photometric value to obtain a normal exposure current;
(3) Constructing an ellipse model according to the side position exposure current in the step (1) and the positive position exposure current in the step (2), wherein the upper position of an ellipse is taken as an exposure position, the intersection point of a long axis and the ellipse is taken as a side position exposure position, and the intersection point of the short axis and the ellipse is taken as a positive position exposure position;
(4) Calculating exposure currents of exposure positions at different angles in the three-dimensional scanning process according to the ellipse model;
(5) And (5) acquiring a three-dimensional image by using the exposure voltage obtained in the step (1) and the exposure current obtained in the 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 the step (4) is as follows:
setting the side exposure position in the constructed elliptical model as 0 degree, and aiming at the rotation angle of the corresponding point on the elliptical model along with the rotation angle change in the image acquisition process
The exposure current is calculated by the following formula
Wherein, I A For lateral exposure current, I B Is the positive exposure current.
3. The three-dimensional perspective automatic dimming method according to claim 1, wherein: in the step (1), the exposure voltage is obtained by using a 2D dimming algorithm, and the side position exposure current is calculated according to 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:
obtaining an exposure image, and calculating a photometric value C of the current image t And the target photometric value C m Comparison, e.g. C t <C m Increasing the exposure voltage by a set step length, and conversely, decreasing the exposure voltage by the set step length;
continuously iterating until C t ＝C m The exposure voltage at this time is obtained.
5. The three-dimensional perspective automatic dimming method according to claim 3, wherein: the 2D dimming algorithm is a model method:
acquiring photometric values of exposure images obtained by adopting different exposure voltages under different thicknesses through experiments, and establishing a three-dimensional mapping model of the photometric values, the exposure voltages and the thicknesses according to the photometric values;
obtaining an exposure image, and calculating a photometric value C of the current image t Calculating to obtain the current patient thickness h according to the three-dimensional mapping model, and obtaining the target photometric value C according to the current patient thickness h m And calculating to obtain corresponding exposure voltage according to the three-dimensional mapping model.
6. The three-dimensional perspective automatic dimming method according to claim 5, wherein: further comprising the iterative step of: obtaining an exposure image and calculating a photometric value of the exposure image according to the exposure voltage and the exposure current obtained by previous calculation, calculating the thickness h of the corresponding patient according to the three-dimensional mapping model, and obtaining the corresponding exposure voltage according to the calculation;
and repeating the iteration step until the difference value between the photometric value of the obtained exposure image and the target photometric value is within a preset range or reaches a preset iteration number.
7. The three-dimensional perspective automatic dimming method according to any one of claims 4 to 6, characterized in that: the specific calculation of the photometric value of the image is as follows:
calculating the average gray value p of the interested region 0 ；
Selecting a set range from the lowest gray value in the region of interest as the darkest region of the region of interest, and calculating the average gray value p 1 Thereby calculating the photometric value C = alpha p of the exposure image 0 +βp 1 Where α and β are weighting parameters, respectively.
8. The three-dimensional perspective automatic dimming method according to claim 7, wherein: the set range is set to 10 to 15%.
9. The three-dimensional perspective automatic dimming method according to claim 1, characterized in that: the step (2) is specifically as follows:
adopting the exposure voltage obtained in the step (1) and a preset positive exposure current I 0 Taking a positive image of the patient; wherein the preset positive exposure current I 0 Less than the lateral exposure current;
calculating the photometric value C of the positive position image of the patient B And through it with target photometric value C m Proportional calculation of target normal exposure current I B The calculation formula is as follows: i is B ＝I 0 *C m /C B 。
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Address after: 210000 building 3, No. 34, Dazhou Road, Yuhuatai District, Nanjing, Jiangsu Province Applicant after: Tuodao Medical Technology Co.,Ltd. Address before: 210000 building 3, No. 34, Dazhou Road, Yuhuatai District, Nanjing, Jiangsu Province Applicant before: Nanjing Tuodao Medical Technology Co.,Ltd. |