A method and apparatus for evaluating the stability of a gantry of a CT scanner

Abstract

The application provides a CT scanner gantry stability evaluation method and device, at least comprising the following steps: obtaining projection images of a preset to-be-tested phantom under M gantry angles; wherein M is greater than or equal to 3; the to-be-tested phantom comprises N beads, and the N steel beads are arranged in a 'one' shape; obtaining projection coordinates of the to-be-tested phantom under each gantry angle according to the projection images; obtaining projection coordinates of effective steel beads according to the projection coordinates of each steel bead under all gantry angles; and evaluating the stability of the gantry according to all gantry angles corresponding to the effective steel beads. According to the application, any external measuring machine is not needed to verify the motion stability of the gantry, so that the cost is reduced, meanwhile, the calculated gantry angle is more accurate, so that the mechanical design of the CT scanner can be more accurately verified.

Description

TECHNICAL FIELD

[0001] The present application relates to CT technology, in particular to a CT scanner gantry stability evaluation method and device. BACKGROUND

[0002] Computer tomography (CT) technology can obtain the internal three-dimensional structure information of the detected object non-destructively and lowly, reconstruct the three-dimensional image of the object, and is widely used in non-destructive testing, medical diagnosis and other fields.

[0003] In the imaging of the rotating CT technology, the light source and the detector are fixed, the object is moved, the projection of the imaged object is collected, and the three-dimensional image of the object is obtained by reconstructing the collected projection through a reconstruction algorithm. The real gantry angle needs to be considered in image reconstruction, and the mechanical design can also be verified by the pure image method of image reconstruction. Therefore, the gantry angle has great reference value for image reconstruction and verification of mechanical design.

[0004] At present, there are two ways in the calculation process of the gantry angle:

[0005] First, the geometric parameters of the corresponding CT system are calculated through the projection image of a known geometric body under the CT system, and then a three-dimensional data is constructed. For example, a cylindrical phantom with multiple equally distributed steel balls is used. The difference between the projection data obtained by the rotation of the gantry and the geometric properties of the steel balls is the consistency of the gantry angle. However, in order to achieve the purpose of obtaining the gantry angle by using this cylindrical phantom, there are complex restrictions on the positioning of the cylindrical phantom, the size of the phantom and the relationship between the field of view (FOV, which refers to the range of objects that can be irradiated by X-rays), and a simple geometric phantom cannot be used to verify any size of CT system. In addition, the mechanical design control is not perfect to achieve equal angle change, so the applicability and accuracy of this method are not good.

[0006] Second, the current gantry angle is calculated by real-time acquisition of parameters. For example, the patent with the publication number CN101496726B calculates the current gantry angle by real-time acquisition of the gantry rotation speed and the initial angle, which is beneficial to the real-time measurement of the gantry motion state and angle during scanning. However, additional measuring devices need to be added to the mechanical structure to measure the real-time gantry rotation speed, which increases the cost. SUMMARY

[0007] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a CT scanner gantry stability evaluation method and device to solve the problem of inaccurate gantry stability evaluation results in the prior art.

[0008] To achieve the above object and other related objects, the present application provides a CT scanner gantry stability evaluation method, which comprises at least the following steps:

[0009] Obtaining projection images of a preset test phantom under M gantry angles, wherein M≥3; the test phantom comprises N beads arranged in a "one" shape;

[0010] Obtaining projection coordinates of the test phantom under each gantry angle according to the projection images;

[0011] Obtaining projection coordinates of effective beads according to the projection coordinates of each bead under all gantry angles;

[0012] Evaluating the stability of the gantry according to all gantry angles corresponding to the effective beads.

[0013] Preferably, obtaining projection coordinates of the test phantom under each gantry angle according to the projection images comprises:

[0014] Processing the first projection image according to the maximum pixel value to obtain the projection coordinates of each bead in the first projection image;

[0015] Processing all the remaining projection images according to the projection coordinates of each bead in the first projection image to obtain the projection coordinates of all beads in the projection images.

[0016] Preferably, processing the first projection image according to the maximum pixel value to obtain the projection coordinates of each bead in the first projection image comprises:

[0017] Obtaining the pixel corresponding to the maximum gray value in the first projection image as a first pixel point;

[0018] Calculating the projection coordinates of the first bead corresponding to the first pixel point according to the first pixel point;

[0019] Setting the gray value of the first pixel point to zero and continuing to find the maximum gray value in the first projection image until the maximum gray value is less than the set threshold value of the bead.

[0020] Preferably, obtaining projection coordinates of effective beads according to the projection coordinates of each bead under all gantry angles comprises:

[0021] Constructing a relationship model based on the projection images of the light source and the test phantom, wherein the light source and the projection image are on the two sides of the yz plane, and the projection image is parallel to the yz plane;

[0022] Determining the limiting range of each bead based on the relationship model;

[0023] Determine the position of the projection coordinates in the xy plane according to the projection coordinates of each bead at all rack angles and the light source;

[0024] Processing the position of the projection coordinates in the xy plane according to the restriction range to obtain the projection coordinates of each bead at all rack angles; the valid beads are the beads that meet the set requirements among all beads;

[0025] The projection coordinates of the effective beads are processed to obtain all corresponding rack angles.

[0026] Preferably, processing the position of the projection coordinates in the xy plane according to the restricted range to obtain the projection coordinates of each bead at all rack angles includes:

[0027] Fitting the position of the projection coordinates in the xy plane according to the restricted range to obtain a fitting result for each bead;

[0028] The projection coordinates of valid beads are screened out according to each fitting result.

[0029] Preferably, the fitting result is a minimum variance fitting loss function.

[0030] Preferably, when the minimum variance fitting loss function value is less than a set threshold, the beads corresponding to the minimum variance fitting loss function value are valid beads.

[0031] To achieve the above-mentioned and other related objectives, the present invention further provides a gantry stability evaluation device for a CT scanner. The device includes a processor and a memory. The memory stores a computer program executable on the processor. When the computer program is executed by the processor, the steps of the gantry stability evaluation method for a CT scanner are implemented as described in any one of claims 1 to 7.

[0032] As described above, the CT scanner gantry stability evaluation and device of the present invention has the following beneficial effects:

[0033] The present invention first processes the projection images of all beads at all mechanical angles to obtain the coordinates of each bead at all mechanical angles. These coordinates are then fitted to obtain bead trajectories. If the fitted trajectory of a bead at all mechanical angles is circular or elliptical, the bead is considered to represent the gantry angle trajectory of the CT scanner and is considered a valid bead. This is then evaluated using bead parameters. This eliminates the need for external measurement equipment to verify the gantry's motion stability, reducing costs. Furthermore, the calculated gantry angles are more accurate, enabling more precise verification of the CT scanner's mechanical design. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A flowchart of a method for evaluating the stability of a gantry of a CT scanner is shown.

[0035] Figure 2 A flowchart of a method for obtaining the projection coordinates of the beads in the phantom by maximum processing of the first projection image is shown.

[0036] Figure 3 A flowchart of a method for obtaining the projection coordinates of the effective beads from the projection coordinates of each bead at all gantry angles is shown.

[0037] Figure 4 A schematic diagram of a relationship model between the projection image of the phantom and the light source is shown.

[0038] Figure 5 A schematic diagram of a set of positions of the projection coordinates in the xy plane is shown.

[0039] Figure 6 A schematic diagram of a gantry stability evaluation device for a CT scanner is shown. DETAILED DESCRIPTION

[0040] The above description is only used to illustrate the specific embodiments of the present application. Those skilled in the art can easily understand other advantages and effects of the present application from the above description. The present application can also be implemented or applied in different specific embodiments, and the details in the description can be modified or changed based on different views and applications without departing from the spirit of the present application.

[0041] Reference will now be made to the drawings Figures 1-6 It should be noted that the diagrams provided in the embodiments only schematically illustrate the basic concepts of the present application, and the diagrams only show the components related to the present application, not the number, shape and size of the components in actual implementation. The shapes, number and proportions of the components in actual implementation can be arbitrarily changed, and the layout of the components can be more complex.

[0042] In order to better verify the mechanical design of the CT scanner, the present application proposes a method for evaluating the stability of the gantry of the CT scanner by using a row of beads. The projection image of the row of beads is collected at a fixed interval, and the gantry angle of the projection image is obtained. In theory, the gantry angle obtained by processing the projection image collected at a fixed interval should also be equally spaced. However, due to the jitter or vibration during the rotation of the gantry, the gantry angle is not equally spaced. Therefore, the consistency of the gantry angle can be used to evaluate the stability of the gantry rotation. Based on this technical concept, the present application proposes a method and device for evaluating the stability of the gantry of the CT scanner.

[0043] First, the projection images of all the beads at all mechanical angles are processed to obtain the coordinates of each bead at all mechanical angles, and the bead trajectory is fitted. When the bead trajectory of a certain bead fitted at all mechanical angles is circular, it is considered that the bead trajectory of the bead represents the gantry angle trajectory of the CT scanner. The gantry angle obtained in this way is more accurate, so that the mechanical design of the CT scanner can be verified more accurately.

[0044] Method embodiment:

[0045] For the CT scanner, the object to be measured is fixed on the gantry of the CT scanner, and the object to be measured rotates with the rotation of the gantry angle, and the image is acquired during the rotation. During this process, the rotation electric angle of the object to be measured is consistent with the gantry angle. Figure 1 The flowchart of the gantry stability evaluation method of the CT scanner of the present application is shown. Combined with Figure 1 The process of the gantry stability evaluation method of the CT scanner of the present application is described in detail. The evaluation method comprises at least the following steps:

[0046] S1, obtaining the projection images of a preset object to be measured at M gantry angles; wherein M≥3;

[0047] In the embodiment of the present application, the preset object to be measured includes N beads, and the N beads are arranged in a "one" shape. Specifically, the N beads are arranged in a non-equidistant vertical arrangement, wherein N≥4. Single-row beads are used as the phantom, which has a simple structure and no restrictive requirements for the installation of the phantom, and can be placed in a glass cup. In this embodiment, the beads are specifically steel beads, but the material of the beads is not limited in the present application.

[0048] The object to be measured is scanned by the CT scanner. During the scanning of the object to be measured, the object to be measured is rotated by 360°. During the rotation, the detector of the CT scanner acquires the projection images of the object to be measured at fixed intervals;

[0049] Specifically, the CT scanner is a flat panel CBCT scanner. During the rotation of the object to be measured by 360°, the X-ray flat panel detector is used to acquire M projection images of the object to be measured, i.e. M frames of projection images. The gray value of each pixel point on the Mth image is I M (u,v) is a two-dimensional matrix element, u is the row number, and v is the column number. M is the number of acquisition at fixed intervals during the rotation of 360°, which is also the number of gantry angles, i.e. one projection image corresponds to one gantry angle.

[0050] S2, obtaining the projection coordinates of the object to be measured at each gantry angle according to the projection images;

[0051] In the embodiment of the present application, the centroid method is used to extract the coordinates of all the beads in each projection image. Specifically, the coordinates of all the beads in the first projection image are obtained, and then the same processing is performed on the remaining projection images according to the coordinates in the first projection image to obtain the coordinates of all the beads in the remaining projection images, thereby obtaining the coordinates of all the beads in the test phantom at each gantry angle.

[0052] S21, processing the first projection image according to the maximum value of the pixels to obtain the projection coordinates of each bead in the first projection image;

[0053] In this step, the coordinates of each bead in one of the projection images are obtained to provide data reference for subsequent calculation of the bead coordinates in the remaining projection images.

[0054] The first projection image is processed by maximum value to obtain the projection coordinates of the beads in the test phantom, as shown in Figure 2 .

[0055] In this step, the coordinates of all (N) beads in the test phantom are calculated.

[0056] S211, obtaining the pixel corresponding to the maximum value of the gray scale in the first projection image as a first pixel point;

[0057] In this embodiment, the gray scale value corresponding to each pixel point on the first projection image is I1(u, v). Wherein, u, v are natural numbers.

[0058] The gray scale values of all the pixel points in the first projection image are compared to find the maximum gray scale value; if the maximum gray scale value is greater than the set threshold value of the bead, it is indicated that the maximum gray scale value is the projection pixel of a bead in the test phantom, and therefore the pixel point corresponding to the maximum gray scale value is determined as the data for calculating the bead.

[0059] S212, calculating the projection coordinates of the first bead corresponding to the first pixel point according to the first pixel point;

[0060] In this step, the pixel point corresponding to the maximum gray scale value is taken as the center, and a set distance is taken as the size of the first window of the pixel point, and the centroid of the first window is calculated, wherein the set distance is k, which is slightly larger than and close to the diameter of the bead. The calculation of the centroid is a prior art, which will not be described in detail in the present application.

[0061] In the present application, the centroid of the first window is the coordinates R1(u CM ,v CM ) of the corresponding first bead.

[0062] S213, setting the gray value of the first pixel point to zero, and continuing to search for the maximum gray value in the first projection image until the maximum gray value is less than the set threshold of the beads, indicating that the projection coordinates of all beads in the current projection image have been calculated.

[0063] When the coordinates of the first bead are calculated, to avoid repeated calculation of the post group, the gray value of the first pixel point corresponding to the first bead is set to zero, so as not to affect the processing and calculation of the remaining beads in the projection image. Then, steps S3121 and S3122 are repeatedly executed to calculate the projection coordinates of the remaining beads in the first projection image.

[0064] At this point, the projection coordinates of all beads in the measured model obtained through the first projection image are R1(u CM ,v CM ), R2(u CM ,v CM ), R3(u CM ,v CM )……R N (u CM ,v CM ).

[0065] S22, according to the projection coordinates of each bead in the first projection image, processing all the remaining projection images to obtain the projection coordinates of all beads in the projection image.

[0066] The method of processing all the remaining projection images (2nd to Mth) in this step is the same. In this embodiment, the second projection image is taken as an example to illustrate the process of processing all the remaining projection images to obtain the bead coordinates.

[0067] According to the projection coordinates of each bead in the first projection image, processing the second projection image to obtain the projection coordinates of all beads in the projection image includes the following steps:

[0068] First, obtain the projection coordinates of all beads in the first projection image, and take the projection coordinates of each bead as the center of the corresponding position bead in the second projection image; then, according to the same set distance, define the window size of each bead for each bead coordinate in the second projection image; finally, perform centroid calculation on the window size of each bead to obtain the centroid coordinates of each bead in the second projection image, i.e. the projection coordinates of each bead in the second projection image.

[0069] The third projection image, …, the Nth projection image are processed in turn by using the same processing method as the second projection image. Using this processing method can quickly locate the position of each bead, thereby improving the calculation speed of the bead coordinates.

[0070] Since each projection image corresponds to one gantry angle, the coordinates of all beads under all gantry angles can be obtained after processing all projection images.

[0071] S3, obtaining the projection coordinates of the effective beads according to the projection coordinates of each bead under all gantry angles; a flowchart is shown in Figure 3 Figure 3 The process is described in detail as follows:

[0072] S31, constructing a relationship model based on the projection image and the light source and the to-be-measured phantom; the light source and the projection image are on the two sides of the yz plane respectively, and the projection image is parallel to the yz plane.

[0073] Since the light source emits laser light within a fixed interval of time, the beads in the to-be-measured phantom rotate with the gantry according to 360°, and the detector acquires the projection image within a fixed interval of time, therefore, the relationship model shown in Figure 4 is constructed.

[0074] S32, determining the limit range of each bead based on the relationship model;

[0075] In this step, by determining the limit range of each bead, the fitting parameters can be limited when fitting the fitting track of each bead in the subsequent fitting, thereby accelerating the fitting effect. Corresponding to all gantry angles, one bead corresponds to one limit range.

[0076] S321, determining the position of the projection coordinates in the yz plane according to the projection coordinates of each bead under all gantry angles and the light source;

[0077] Specifically, the line connecting the projection coordinates of each bead and the light source, and the intersection point of the line and the yz plane is the position (x, y, z) of the projection coordinates in the yz plane;

[0078] The coordinates of the light source are (x0, y0, z0) T , the coordinates of the projection are (x1, y1, z1) T , and the normal vector of the yz plane is (x, y, z) = (x_target, 0, 0)

[0079]

[0080] S322, determining the limit range according to the position of the projection coordinates in the yz plane;

[0081] Since the set of the positions of the projection coordinates in the yz plane is perpendicular to the xy plane, the limit range is the upper limit and the lower limit on the z axis, and the maximum value on the z axis is taken as the upper limit threshold, and the minimum value on the z axis is taken as the lower limit threshold.

[0082] ​Restricting the fitting parameters, accelerating the speed of the least squares fitting and optimizing the fitting effect.

[0083] S33, determining the position of the projection coordinates in the xy plane according to the projection coordinates of each bead at all gantry angles and the light source;

[0084] Specifically, the intersection of the line connecting the projection coordinates of each bead and the light source and the xy plane is the position (x, y, z) of the projection coordinates in the xy plane; wherein the normal vector of the xy plane is (0, 0, z_target)

[0085]

[0086] The set of intersection coordinates of each bead at all gantry angles, i.e. the position of the projection coordinates in the xy plane, is similar to a circle or an ellipse as shown in Figure 5 .

[0087] S34, processing the position of the projection coordinates in the xy plane according to the restricted range to obtain the projection coordinates of the effective beads at all gantry angles; the effective beads are the beads that meet the set requirements among all the beads;

[0088] S341, fitting the position of the projection coordinates in the xy plane according to the restricted range to obtain the fitting result of each bead; the fitting result is the least squares fitting loss function;

[0089] The least squares fitting loss function is obtained by fitting the position of the projection coordinates in the xy plane using the least squares of the projection polar coordinate radius variance, which is actually the standard deviation of the position of the projection coordinates in the xy plane under the polar coordinate.

[0090] S342, screening the projection coordinates of the effective beads according to the fitting result of each bead;

[0091] The smaller the standard deviation of the radius under the xy plane, the closer the shape of the motion trajectory formed by the position of the projection coordinates in the xy plane to a true circle.

[0092] If the least squares fitting loss function value is greater than the set threshold value, it means that the bead trajectory is not circular or elliptical, that is, the position coordinate noise is too large and unstable, resulting in an inaccurate motion trajectory, so the fitting result of the current bead needs to be discarded or removed; if the least squares fitting loss function value is less than the set threshold value, it is considered that the motion trajectory of the bead is circular or elliptical, that is, the fitting result of the bead corresponding to the least squares fitting loss function value meets the set requirements, so the bead that meets the set requirements is considered as an effective bead, and then the motion trajectory parameters of the effective bead at all gantry angles are extracted.

[0093] S35, processing the projection coordinates of the effective beads to obtain all gantry angles corresponding to the effective beads.

[0094] The minimum value of the minimum variance fitting loss function value corresponds to the xy plane closest to a circle. Taking (0, 0, z) as the origin, the position coordinates of the projection coordinates in the xy plane are converted to polar coordinates under the xy plane, i.e. taking (0, 0) as the center, to obtain the gantry angle corresponding to the required bead coordinates, and as the actual gantry angle to be calculated corresponding to each bead coordinate. fit ) as the origin, the position coordinates of the projection coordinates in the xy plane are converted to polar coordinates under the xy plane, i.e. taking (0, 0) as the center, to obtain the gantry angle corresponding to the required bead coordinates, and as the actual gantry angle to be calculated corresponding to each bead coordinate.

[0095] S4, evaluating the stability of the gantry according to all gantry angles corresponding to the effective beads.

[0096] In the embodiment of the application, since the time interval for obtaining the projection image is fixed, the theoretically obtained gantry angle interval should also be equidistant, but due to the jitter or vibration during the rotation of the gantry, the gantry angle is not equidistant. Therefore, the stability of the gantry rotation can be evaluated by the consistency of the gantry angle.

[0097] In this step, the gantry angle calculated according to the effective beads is more accurate. In the embodiment of the application, since the beads are arranged in a linear manner, the gantry angle corresponding to the projection coordinates on the same projection image is the same regardless of the number of effective beads, so a gantry angle sequence is finally obtained.

[0098] In the evaluation process, if the gantry angles are equidistant, the stability of the gantry is considered to be the best, if they are not equidistant, the closer the interval difference is to the stability, the better the stability is, and the larger the interval difference is, the worse the stability is.

[0099] Device embodiment:

[0100] To solve the problems in the prior art, the application further provides a gantry stability evaluation device for a CT scanner, as shown in the drawings, comprising a processor and a memory, the memory stores a computer program executable on the processor, and the computer program is executed by the processor to realize the steps of the gantry stability evaluation method for the CT scanner. Figure 6

[0101] The principles and specific steps of the steps of the gantry stability evaluation method for the CT scanner executed by the processor have been described in detail in the method embodiment, and will not be repeated here.

[0102] ​The processor can be a general processor, including a central processing unit (CPU), a network processor (NP), etc., and can also be a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, a discrete gate or transistor logic device, a discrete hardware component. The disclosed methods, steps and logic block diagrams in the embodiments of the present application can be implemented or executed. The general processor can be a microprocessor or the processor can be any conventional processor.

[0103] It should be noted that, according to the needs of implementation, each component / step described in the embodiments of the present application can be split into more components / steps, or two or more components / steps or part of the operation of the components / steps can be combined into a new component / step, to achieve the purpose of the embodiments of the present application.

[0104] In summary, the present application does not need to use any external measuring machine to verify the motion stability of the gantry, thereby reducing the cost, and the calculated gantry angle is more accurate, thereby the mechanical design of the CT scanner can be more accurately verified. Therefore, the present application effectively overcomes the various shortcomings in the prior art and has high industrial utilization value.

[0105] The above embodiments only exemplarily illustrate the principles and effects of the present application, and are not used to limit the present application. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes completed by those skilled in the art without departing from the spirit and technical thought disclosed by the present application should be covered by the claims of the present application.

Claims

1. A method for evaluating the stability of a CT scanner frame, characterized in that: At least the following steps are included: Obtaining projection images of a preset phantom under M rack angles; wherein M ≥ 3; the phantom under test includes N beads, and the N beads are arranged in a straight line; Obtaining the projection coordinates of the phantom to be measured at each rack angle according to the projection image; The projection coordinates of the effective beads are obtained according to the projection coordinates of each bead at all rack angles; The stability of the rack was evaluated based on all rack angles corresponding to the valid beads; Obtaining the projection coordinates of the phantom to be tested at each rack angle according to the projection image includes: processing the first projection image according to the maximum value of the pixel to obtain the projection coordinates of each bead in the first projection image; processing all other projection images according to the projection coordinates of each bead in the first projection image to obtain the projection coordinates of all beads in the projection image; Processing the first projection image according to the pixel maximum value to obtain the projection coordinates of each bead in the first projection image includes: obtaining a pixel corresponding to the grayscale maximum value in the first projection image as a first pixel point; calculating the projection coordinates of the first bead corresponding to the first pixel point based on the first pixel point; setting the grayscale value of the first pixel point to zero, and continuing to search for the grayscale maximum value in the first projection image until the grayscale maximum value is less than a set threshold value for the bead; Obtaining the projection coordinates of valid beads according to the projection coordinates of each bead at all rack angles includes: constructing a relationship model based on the projection image of the light source and the phantom to be measured; wherein the light source and the projection image are respectively on both sides of the yz plane, and the projection image is parallel to the yz plane; determining the restriction range of each bead based on the relationship model; determining the position of the projection coordinates in the xy plane according to the projection coordinates of each bead at all rack angles and the light source; processing the position of the projection coordinates in the xy plane according to the restriction range to obtain the projection coordinates of each bead at all rack angles; the valid beads are the beads that meet the set requirements among all beads; processing the projection coordinates of the valid beads to obtain all corresponding rack angles.

2. The CT scanner gantry stability evaluation method according to claim 1, characterized in that: The projection coordinates of each bead at all rack angles are obtained by processing the position of the projection coordinates in the xy plane according to the restriction range, including: Fitting the position of the projection coordinates in the xy plane according to the restricted range to obtain a fitting result for each bead; The projection coordinates of valid beads are screened out according to each fitting result.

3. The CT scanner gantry stability evaluation method according to claim 2, characterized in that: The fitting result is the minimum variance fitting loss function.

4. The method for evaluating gantry stability of a CT scanner according to claim 3, wherein: When the minimum variance fitting loss function value is less than a set threshold, the beads corresponding to the minimum variance fitting loss function value are valid beads.

5. A CT scanner gantry stability evaluation device, characterized in that: The device includes a processor and a memory, wherein the memory stores a computer program that can be run on the processor, and when the computer program is executed by the processor, the steps of the CT scanner gantry stability evaluation method according to any one of claims 1 to 4 are implemented.

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