A dental panoramic imaging device and an automatic calibration method

Abstract

The present invention relates to the technical field of oral photography, and discloses a dental panoramic photography device and an automatic correction method. The device includes: a column, a cheek rest arm, a lifting arm, a rotating arm, a cross laser assembly and a positioning assembly. The lifting arm is slidably connected to the column, the rotating arm is rotatably connected to the lifting arm, a flat panel detector and an X-ray emitter are provided on the rotating arm. The cross laser assembly is used to locate the occlusal horizontal plane and the left-right symmetry plane of the dental arch, and the positioning assembly is used to facilitate the rapid positioning of the user. The positioning assembly includes a jaw support and a bite bar, the bite bar is slidably connected to the jaw support, and the jaw support is used to support the user's chin and define the lower edge of the panoramic photograph. The present invention facilitates the rapid and accurate positioning of the patient's head during oral photography by the user.

Description

Technical Field

[0001] The present invention relates to the technical field of oral photography, and in particular, to a dental panoramic photographing device and an automatic calibration method. Background Art

[0002] An oral panoramic film, or an orthopantomogram, can display the morphology of the entire dentition of a patient in a single two-dimensional image and plays a very important role in dental diagnosis.

[0003] Before taking a panoramic film, it is necessary to position the patient's head so that the actual dental arch surface of the patient coincides as much as possible with a preset virtual focusing surface. Compared with the shooting of CBCT, the positioning steps and accuracy requirements during panoramic shooting are much higher, and the positioning has a great influence on the scanning and reconstruction results.

[0004] At present, most panoramic scanning devices on the market use a three-laser-line scheme for head positioning, namely: the Frankfurt line, the sagittal line, and the canine laser line. Among them, the Frankfurt line is responsible for positioning the up-and-down pitch angle of the head: the laser passes through the lower edge of the orbital bone and the midpoint of the external auditory canal; the sagittal line is responsible for positioning the left-right symmetry of the head: the laser passes through the midpoint of the nose wing and the chin; the canine line is responsible for positioning the front-back position: the laser is aligned with the middle of the third canine tooth.

[0005] It is found through user feedback and actual operation that there are great problems with the three-line positioning method:

[0006] 1. The canine line generally adopts one of the two schemes of "fixed laser line and movable bite bar" or "fixed bite bar and movable laser line". For the former, the patient needs to bite the bite bar and move forward and backward with the jaw support to align with the canine line, which is cumbersome to operate. The movable jaw support is prone to problems after long-term use, and the positioning process is not user-friendly to the patient; for the latter, the patient does not need to move, and the laser line is moved to align with the patient's third canine tooth. Although this scheme is simpler and more convenient than the former, when shooting, it is necessary to calculate the offset of the gantry before and after according to the actual position of the current laser line, which introduces an additional error in the estimation of the laser offset.

[0007] 2. The positioning of the Frankfurt line and the sagittal line is relatively simple. When positioning the canine line, a large number of patients cannot easily open their lips to make the canine line irradiate the third canine tooth. Forcibly opening the lips will cause facial muscle twitching, and the nervousness is likely to cause the patient to secrete a large amount of saliva, and the repeated swallowing action will affect the positioning accuracy of the previous two laser lines.

[0008] 3. The three-line positioning takes a long time, and patients who are younger or in poor health are more likely to move their heads during the shooting process after a long positioning.

[0009] Therefore, how to provide a rapid positioning device for dental panoramic imaging and an automatic calibration method for its supporting use, so as to facilitate users to quickly and accurately complete the positioning during oral cavity photography has become a technical problem to be solved urgently. Summary of the Invention

[0010] The technical problem to be solved by the present invention is how to provide a rapid positioning device for dental panoramic imaging and an automatic calibration method for its supporting use, so as to facilitate users to quickly and accurately complete the positioning during oral cavity photography.

[0011] To this end, according to the first aspect, an embodiment of the present invention discloses a dental panoramic imaging device, including: a column, a cheek support arm, a lifting arm, a rotating arm, a cross laser component and a positioning component. The lifting arm is slidably connected to the column, the rotating arm is rotatably connected to the lifting arm. A flat panel detector and an X-ray emitter are provided on the rotating arm. The cross laser component is used to locate the occlusal horizontal plane and the left-right symmetry plane of the dental arch. The positioning component is used to facilitate the user to quickly position. The positioning component includes a jaw support and a bite bar. The bite bar is slidably connected to the jaw support. The jaw support is used to support the user's chin and define the lower edge of panoramic photography.

[0012] The present invention is further arranged such that one end of the bite bar is provided with a bite groove for the user to bite conveniently.

[0013] The present invention is further arranged such that the bite groove is arranged in an arc-shaped slope.

[0014] The present invention is further arranged to further include a calibration component for calibrating the position of the bite bar.

[0015] The present invention is further arranged such that the calibration component includes a cap sleeved on one end of the bite bar, and steel balls are embedded in the cap.

[0016] The present invention is further arranged such that the cap is made of a transparent material.

[0017] The present invention is further arranged such that both the flat panel detector and the X-ray emitter are fixedly connected to the rotating arm, and the flat panel detector and the X-ray emitter are respectively distributed at both ends of the rotating arm.

[0018] According to the second aspect, an embodiment of the present invention discloses an automatic calibration method applied to a dental panoramic imaging device, including:

[0019] Install a cap with steel balls on the bite bar;

[0020] Based on preset shooting parameters, shoot a multi-layer panoramic image once;

[0021] Automatically calculate the offset of the rotation center of the rotating arm relative to the bite bar through an automatic calibration algorithm;

[0022] Correct the distance of the center of the rotating arm at the initial scanning point along the direction of the occlusal rod according to the offset.

[0023] The present invention is further configured such that the offset of the rotation center of the rotating arm relative to the occlusal rod automatically calculated by the automatic correction algorithm includes:

[0024] Find the local region (ROI) where the steel ball cap is located in the panoramic image according to the geometric relationship;

[0025] Perform mean or median filtering on the ROI of each layer of the panoramic image;

[0026] Perform gray value normalization on the ROI;

[0027] Use binary segmentation to find the steel ball and calculate the center coordinate;

[0028] Statistically plot the gray curve along the horizontal path passing through the center of the circle, and find the gray intervals corresponding to the steel ball and the background according to the curve;

[0029] Calculate the area of the blurred region of each layer, and obtain the layer with the smallest area of the blurred region;

[0030] According to the layer with the smallest area of the blurred region, calculate the offset of the actual position of the steel ball relative to the designed center focusing surface.

[0031] The present invention is further configured such that the following formula is used to calculate the offset of the steel ball:

[0032]

[0033] where Y Offset is the offset of the steel ball, N slices is the total number of layers of the multi-layer panoramic image, N clear is the layer number of the layer with the smallest area of the blurred region or the clearest steel ball, P start is the coordinate (mm) in the Y-axis direction of the first layer panoramic focusing layer, P end is the coordinate of the last layer, N slices layers are equally spaced within this interval, and the layer numbers are from P start to P end in sequence: 1, 2,..., N slices -1, N slices .

[0034] The present invention has the following beneficial effects: the occlusal horizontal plane and the left-right symmetry plane of the dental arch are positioned by the cross laser assembly, the chin of the user is supported by the jaw support and the lower edge of the panoramic photograph is defined, and the front and rear positions of the occlusal surface can be quickly and accurately positioned by biting the occlusal bar in the positioning assembly, eliminating the cumbersome operation of the traditional canine laser line positioning. At the same time, an automatic correction method for dental panoramic is provided to facilitate automatic correction by the user only through the panoramic image with the steel ball cap when the mechanical error is too large due to certain reasons. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0036] Figure 1 is a schematic structural diagram of a dental panoramic photographing device disclosed in this embodiment;

[0037] Figure 2 is a cross-positioning schematic diagram of the cross laser assembly in a dental panoramic positioning device disclosed in this embodiment;

[0038] Figure 3 is a partial structural schematic diagram of a dental panoramic positioning device disclosed in this embodiment;

[0039] Figure 4 is a sectional view of a dental panoramic mechanical error correction tooling disclosed in this embodiment;

[0040] Figure 5 is a flowchart of an automatic correction method disclosed in this embodiment;

[0041] Figure 6 is a schematic diagram of a focusing surface in a multi-layer panoramic reconstruction method disclosed in this embodiment;

[0042] Figure 7 is an image diagram of the steel ball taken at different focusing layers (surfaces) and reconstructed at that layer;

[0043] Figure 8 is an image diagram of the steel ball taken at the same focusing layer and reconstructed for different focusing layers;

[0044] Figure 9 The gray area in is the "blurred boundary" of the steel ball in the panoramic image;

[0045] Figure 10The middle curve represents the change trend of the fuzzy boundary area of the steel balls in each layer.

[0046] Reference numerals: 1, vertical column; 2, cheek rest arm; 3, lifting arm; 4, rotating arm; 5, positioning assembly; 51, jaw rest; 52, occlusion rod; 521, occlusion groove; 6, calibration assembly; 61, cap; 62, steel ball; 7, flat panel detector; 8, X-ray emitter. Specific embodiments

[0047] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0048] In the description of the present invention, it should be noted that, unless otherwise clearly defined and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may also be the communication inside two elements. It may be a wireless connection or a wired connection. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0049] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention. In addition, the terms "first", "second", and "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0050] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0051] An embodiment of the present invention discloses a dental panoramic imaging device, as Figure 1-4As shown in the figure, it includes: a vertical column 1, a cheek rest arm 2, a lifting arm 3, a rotating arm 4, a cross laser assembly and a positioning assembly 5. The lifting arm 3 is slidably connected to the vertical column 1, the rotating arm 4 is rotatably connected to the lifting arm 3. A flat panel detector 7 and an X-ray emitter 8 are provided on the rotating arm 4. The cross laser assembly is used to locate the occlusal horizontal plane and the left-right symmetry plane of the dental arch, and the positioning assembly 5 is used to facilitate the user's quick positioning. The positioning assembly 5 includes a jaw support 51 and a bite bar 52. The bite bar 52 is slidably connected to the jaw support 51. The jaw support 51 is used to support the user's chin and define the lower edge of the panoramic photographing.

[0052] It should be noted that by using the cross laser assembly to locate the occlusal horizontal plane and the left-right symmetry plane of the dental arch, the positioning assembly 5 facilitates the user's quick positioning. By using the jaw support 51 to support the user's chin and define the lower edge of the panoramic photographing, and the user bites the bite bar 52, thus providing a quick positioning device for dental panoramic and an automatic calibration method designed based on this device to facilitate the user to quickly and accurately position during oral photographing.

[0053] As Figure 1 and Figure 3 shown in the figure, one end of the bite bar 52 is provided with a bite groove 521 for the user to bite easily.

[0054] As Figure 1 and Figure 3 shown in the figure, the bite groove 521 is arranged in an arc shape.

[0055] As Figure 1-4 shown in the figure, it further includes a calibration assembly 6 for calibrating the position of the bite bar 52.

[0056] As Figure 1-4 shown in the figure, the calibration assembly 6 includes a cap 61 sleeved on one end of the bite bar 52, and a steel ball 62 is embedded in the cap 61.

[0057] As Figure 1-4 shown in the figure, the cap 61 can be made of a transparent material to facilitate measuring the actual position of the center of the steel ball.

[0058] As Figure 1-4 shown in the figure, both the flat panel detector 7 and the X-ray emitter 8 are fixedly connected to the rotating arm 4, and the flat panel detector 7 and the X-ray emitter 8 are respectively distributed at both ends of the rotating arm 4.

[0059] The embodiment of the present invention discloses an automatic calibration method. As Figure 5 shown in the figure, it is applied to a photographing device for dental panoramic, including:

[0060] Step S100, installing the cap 61 with the steel ball 62 on the bite bar 52;

[0061] Step S200, taking a multi-layer panoramic photograph once based on preset photographing parameters;

[0062] Step S300, automatically calculate the offset of the rotation center of the rotating arm 4 in the direction of the occlusal rod 52 through an automatic calibration algorithm;

[0063] Step S400, correct the distance of the center of the rotating arm 4 at the initial scanning point in the direction of the occlusal rod 52 according to the offset.

[0064] It should be noted that

[0065] In the specific implementation process, step S300 specifically includes:

[0066] Step S301, find the local area (ROI) where the steel ball 62 and the cap 61 are located in the panoramic image according to the geometric relationship;

[0067] Step S302, perform mean or median filtering on the ROI of each layer of the panoramic image;

[0068] Step S303, perform gray value normalization processing on the ROI;

[0069] Step S304, use binary segmentation to find the steel ball 62 and calculate the center coordinates;

[0070] Step S305, statistically plot the gray curve along the horizontal path passing through the center of the circle, and find the gray intervals corresponding to the steel ball 62 and the background according to the curve;

[0071] Step S306, calculate the area of the blurred area of each layer, and obtain the layer with the smallest blurred area;

[0072] Step S307, according to the layer with the smallest blurred area, calculate the offset of the actual position of the steel ball 62 relative to the designed central focusing surface.

[0073] In the specific implementation process, the following formula is used to calculate the offset of the steel ball 62:

[0074]

[0075] where, Y Offset is the offset of the steel ball 62, N slices is the total number of layers of the multi-layer panoramic image, N clear is the layer number of the layer with the smallest blurred area or the clearest steel ball, P start is the coordinate (mm) in the Y-axis direction of the first layer panoramic focusing layer, P end is the coordinate of the last layer, N slices layers are equally spaced within this interval, and the layer numbers are from P start to P end in sequence: 1, 2,..., N slices -1, N slices .

[0076] A virtual focusing surface is set according to the shape of the human dental arch. The horizontal cross-section of this surface is represented by a dotted line in Figure 6 , and each imaging point on the line is evenly distributed. Taking this surface as the central reference surface, the focusing points are translated inward and outward along the X-ray direction ( Figure 6 represented by diverging outward line segments in ) at a certain step size, for example, translated once every 0.5 mm, and translated 10 times inward and outward respectively, thus forming 21 layers of focusing surfaces, evenly distributed between two focusing surfaces of -5 mm and 5 mm (represented by two solid curves in Figure 6 ). By taking one shot, all the above-mentioned focusing surfaces are reconstructed, which is the multi-layer panoramic view described above.

[0077] According to the method of translating the imaging points along the ray direction described above, we can know that only the imaging points on the blue dotted line surface at 0 mm in the middle satisfy the uniform and equidistant distribution. The surfaces translated outward or inward will all produce geometric deformations of stretching or shrinking to varying degrees in the horizontal direction, but at the same time, it also brings benefits: the actual physical characteristics represented by the points at the same position on different focusing surfaces will all remain unchanged. For example, if a point is a canine tooth at the 0 mm focusing layer, then it is also a canine tooth at this position on all translated layers.

[0078] According to the above characteristics, the imaging morphology of the steel ball 62 reconstructed on different focusing surfaces can be predicted. When the steel ball 62 is located at the 0 mm focusing layer shown in Figure 6 , the steel ball 62 in the reconstructed image of this layer should be a non-distorted perfect circle, as shown in the left figure of Figure 7 ; when the steel ball 62 is located at +5 mm, it corresponds to the horizontally narrowed oval in the middle figure of Figure 7 ; when the steel ball 62 is located at -5 mm, it corresponds to the horizontally stretched oval in the right figure of Figure 7 . The above are all clear reconstructed images formed by the focusing surfaces corresponding to the positions where the steel ball 62 is located. The images of the other 20 layers of focusing surfaces can be regarded as having different degrees of horizontal blurring effects on the basis of the clear layer image where the steel ball 62 is located. This is because the focusing points produce horizontal divergence. Figure 8 The three figures represent the panoramic scanning of the steel ball 62 at the same focusing layer (+5 mm), and the images of the steel ball 62 reconstructed on different focusing layers (a: +5, b: 0, c: -5).

[0079] According to the above characteristics, the following scheme can be further obtained: No matter which layer the steel ball 62 is currently in, take one shot of a multi-layer panorama including 21 layers, evenly distributed in the interval from -5 mm to +5 mm, as shown in Figure 6As shown. Find the clearest layer from these, and assume it is the nth layer. The calibration target is that the middle layer (the 11th layer) is the clearest layer (the steel ball 62 is a perfect circle). According to the formula, the current offset Y of the steel ball 62 can be calculated Offset =(5 - (-5)) / (21 - 1)*(n - 11)=(11 - n) / 2, and the result can be added to the Y-direction offset component of the rotating arm 4.

[0080] Assume that it is calculated that 0 to 0.4 represents the background, 0.6 to 1 represents the steel ball 62, then the area of 0.4 to 0.6 is the transition area formed by the horizontal blur of the steel ball 62. The smaller this area is, the clearer the steel ball 62 is.

[0081] Calculate the area of the 0.4 - 0.6 blur region for each layer. Figure 9 The medium gray area is the horizontal blur area.

[0082] Find the layer with the smallest blur region area, and it can be considered that the steel ball 62 on this layer is the clearest. Figure 10 The minimum value of the blur boundary should be at the 20.5th layer. At this time, Y Offset =(11 - 20.5) / 2 = -4.75(mm), which means that the actual position of the steel ball 62 during this scan is offset by 4.75 mm in the positive Y direction relative to the designed central focusing surface.

[0083] It should be noted that the present invention integrates the function of the canine laser line into the occlusion device, making the positioning system more streamlined. It reduces the equipment complexity and the failure rate. The present invention simplifies the process of panoramic positioning, reduces the difficulty, error and duration of positioning during use. When there is a problem with the positioning system, it is no longer necessary for engineers or customer service to go to the site for re-calibration. Only through remote operation, the user can put on the designed cap on the occlusion rod to complete the rack calibration through one shot, reducing the maintenance cost and repair duration.

[0084] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A dental panoramic imaging device, characterized in that, Including: A vertical column, a cheek rest arm, a lifting arm, a rotating arm, a cross laser assembly and a positioning assembly. The lifting arm is slidably connected to the vertical column, the rotating arm is rotatably connected to the lifting arm. A flat panel detector and an X-ray emitter are provided on the rotating arm. The cross laser assembly is used to locate the occlusal horizontal plane and the left-right symmetry plane of the dental arch. The positioning assembly is used to facilitate the user to quickly position. The positioning assembly includes a jaw support and a bite bar. The bite bar is slidably connected to the jaw support. The jaw support is used to support the user's chin and define the lower edge of the panoramic photographing. The panoramic dental photographing device adopts an automatic calibration method, including: Install a cap with a steel ball on the bite bar; Take a multi-layer panoramic photograph once based on preset photographing parameters; Automatically calculate the offset of the rotation center of the rotating arm relative to the bite bar through an automatic calibration algorithm; Correct the distance of the rotation arm center along the direction of the bite bar at the initial scanning point according to the offset; The automatically calculating the offset of the rotation center of the rotating arm relative to the bite bar through the automatic calibration algorithm includes: Find the local region ROI where the cap with the steel ball is located in the panoramic image according to the geometric relationship; Perform mean or median filtering on the ROI of each layer of the panoramic image; Perform gray value normalization processing on the ROI; Use binary segmentation to find the steel ball and calculate the center coordinates; Statistically plot the gray curve along the horizontal path passing through the center of the circle, and find the gray intervals corresponding to the steel ball and the background according to the curve; Calculate the area of the blurred region of each layer, and obtain the layer with the smallest area of the blurred region; According to the layer with the smallest area of the blurred region, calculate the offset of the actual position of the steel ball relative to the designed central focusing surface; Calculate the steel ball offset using the following formula: Among them, Y Offset is the steel ball offset, N Slices is the total number of layers of the multi-layer panorama, N Clear is the layer number of the layer with the smallest blurred area or the clearest steel ball, P Start is the coordinate in the Y-axis direction where the first-layer panorama focusing layer is located, unit mm, P End Then it is the coordinate in the Y-axis direction where the last-layer panorama focusing layer is located, N Slices The layers are evenly distributed in this interval, and the layer numbers range from P Start to P End and are in sequence: 1, 2,..., N Slices -1, N Slices .

2. The dental panoramic imaging device according to claim 1, characterized in that, One end of the bite bar is provided with a bite groove for the user to bite conveniently.

3. The dental panoramic photographing device according to claim 2, characterized in that, The bite groove is arc-shaped.

4. The dental panoramic imaging device according to claim 1, characterized in that, It further includes a calibration assembly for calibrating the position of the bite bar.

5. The dental panoramic imaging device according to claim 4, wherein, The calibration assembly includes a cap sleeved on one end of the bite bar, and a steel ball is embedded in the cap.

6. The dental panoramic imaging device according to claim 5, characterized in that, The cap is made of a transparent material.

7. The dental panoramic imaging device according to claim 1, characterized in that, Both the flat panel detector and the X-ray emitter are fixedly connected to the rotating arm, and the flat panel detector and the X-ray emitter are respectively distributed at both ends of the rotating arm.

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