An intraoral imaging scanner based on silicon photomultiplier

Abstract

The present invention discloses an intraoral image scanner based on a silicon photomultiplier, which has a small overall size, low power consumption and is less likely to be disturbed by a magnetic field. An intraoral image scanner based on a silicon photomultiplier includes a laser, an optical mechanism for processing a laser beam emitted by the laser, and a scanning mechanism for moving a light spot formed by the laser beam. The intraoral image scanner also includes a fluorescence collection mechanism for collecting fluorescence excited by an image plate and a silicon photomultiplier for photoelectric conversion. The silicon photomultiplier includes an avalanche photodiode array, which is composed of a plurality of avalanche photodiodes arranged in an array. The avalanche photodiode array includes at least one row of avalanche photodiodes, and the plurality of avalanche photodiodes constituting the row of avalanche photodiodes are arranged in a direction parallel to the scanning track of the laser beam on the image plate.

Description

Technical Field

[0001] The invention belongs to the field of laser scanning imaging and relates to an image scanning device based on X-rays. Background Art

[0002] Laser scanning imaging specifically refers to recording images through X-rays and using lasers to read images recorded on a flexible imaging plate. Computed X-ray Radiography (CR) has been widely used in the field of medical health. Compared with traditional X-ray photography technology, its main feature is that it uses a flexible, erasable imaging plate (IP) instead of silver halide film, and can store and display image information using a computer. X-rays penetrate objects and irradiate the imaging plate containing light-stimulated phosphors, which will produce a frame of latent image and store it in the imaging plate. When a laser of a certain wavelength (600-700nm) is used for irradiation, the imaging plate will excite fluorescence of a specific wavelength (350-450nm), and its energy distribution characteristics are completely related to the latent image morphology. These fluorescences are collected, converted into electrical signals and digitized, thereby converting the latent image into a two-dimensional digital image that can be stored and transmitted.

[0003] In the dental industry, CR scanners are commonly used to read tooth profile information on the image plate. Intraoral image scanners used in dentistry and other fields are low-light detection instruments. Currently, the most widely used low-light detectors mainly use photomultiplier tubes (PMTs). Current intraoral image scanners have the following problems:

[0004] 1. The shape of the intraoral scanner cannot be miniaturized, which makes it inconvenient for customers to move it according to actual applications. In addition, it also increases the cost of later production mold opening and practical production materials;

[0005] 2. The operating voltage of PMT is generally several hundred to thousands of volts, which is difficult for circuit design. On the other hand, it will also cause high power consumption of the entire intraoral scanner and is easy to be damaged;

[0006] 3. Due to the limitation of photocathode, the detection efficiency is low;

[0007] 4. Sensitive to magnetic fields. The electromagnetic fields in the surrounding environment of the equipment will affect the normal operation of the equipment. As a medical imaging device, the intraoral image scanner will suffer from image quality degradation if it is interfered by electromagnetic fields. These interferences will be displayed in a certain form on the image, thus affecting the doctor's viewing of the film and the further diagnosis of the patient by the imaging doctor. Summary of the invention

[0008] In response to at least one of the above problems, the present invention provides an intraoral image scanner based on silicon photomultipliers, which has a smaller overall size, lower power consumption and is less likely to be disturbed by magnetic fields.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is:

[0010] An intraoral image scanner based on a silicon photomultiplier comprises a laser, an optical mechanism for processing a laser beam emitted by the laser, and a scanning mechanism for moving a light spot formed by the laser beam. The intraoral image scanner also comprises a fluorescence collection mechanism for collecting fluorescence excited by an image plate and a silicon photomultiplier for photoelectric conversion. The silicon photomultiplier comprises an avalanche photodiode array, which is composed of a plurality of avalanche photodiodes arranged in an array.

[0011] Preferably, the avalanche photodiode array comprises at least one row of avalanche photodiodes, and a plurality of avalanche photodiodes constituting the row of avalanche photodiodes are arranged in a direction parallel to a scanning track of the laser beam on the image plate.

[0012] More preferably, the fluorescence collecting mechanism comprises a cylindrical mirror, and a generatrix of the cylindrical mirror is parallel to a scanning trajectory of the laser beam on the image plate.

[0013] Furthermore, the NA of the cylindrical mirror is greater than 0.5, and a UV high anti-reflection film layer is coated on the surface of the cylindrical mirror.

[0014] Preferably, the fluorescence collecting mechanism comprises a cylindrical mirror, a rod mirror or a fiber optic lens.

[0015] Preferably, the intraoral image scanner further comprises a filter for filtering out the excitation laser, and the filter is arranged between the fluorescence collection mechanism and the silicon photomultiplier.

[0016] Preferably, the laser is a single-mode semiconductor laser.

[0017] Preferably, the optical mechanism comprises a collimating lens, an aperture stop and a focusing lens which are arranged in sequence.

[0018] More preferably, the collimating lens is composed of a single aspherical mirror, the focal length of the aspherical mirror is 15-25 mm, the diameter of the aperture stop is 5-10 mm, and the focal length of the focusing lens is 100-180 mm. Furthermore, the aspherical mirror is coated with a dielectric film layer.

[0019] Preferably, the scanning mechanism comprises a galvanometer mirror for reflecting the laser beam onto the image plate and a galvanometer mirror motor for driving the galvanometer mirror to deflect within a certain angle.

[0020] The present invention adopts the above technical solution, which has the following advantages compared with the prior art:

[0021] Reducing the overall size of the intraoral image scanner greatly facilitates the doctor's mobile diagnosis; the intraoral image scanner adopts silicon photomultipliers, which can reduce the cost of the entire intraoral image scanner; in actual applications, the driving voltage of the silicon photomultiplier is only tens of volts, which reduces the difficulty and cost of circuit design and power consumption; it has low sensitivity to electromagnetic fields and is not easily disturbed by them, and electromagnetic shielding can be avoided, thereby reducing the resulting cost increase. Moreover, the application of the intraoral image scanner will not be too restricted by the magnetic field, and it can still be used even in an environment with large electromagnetic interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solution of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0023] Figure 1 is a schematic structural diagram of an intraoral image scanner according to an embodiment of the present invention;

[0024] Figure 2 Schematic diagram of light propagation along the generatrix direction of the cylindrical mirror;

[0025] Figure 3 Schematic diagram of light propagation along the non-generatrix direction of the cylindrical mirror;

[0026] Figure 4 Schematic diagram of the structure of a one-dimensional array of silicon photomultipliers.

[0027] In the above-mentioned figures,

[0028] 1. Laser; 2. Optical mechanism; 21. Collimating lens; 22. Aperture; 23. Focusing lens; 3. Scanning mechanism; 31. Galvanometer; 32. Galvanometer motor; 4. Image plate; 5. Cylindrical mirror; 6. Filter; 7. Silicon photomultiplier; 71. Avalanche photodiode. DETAILED DESCRIPTION

[0029] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] This embodiment provides an intraoral image scanner based on a silicon photomultiplier. Figure 1 As shown, the intraoral image scanner includes a laser 1, an optical mechanism 2, a scanning mechanism 3, a fluorescence collection mechanism, a filter 6 and a silicon photomultiplier 7. The above components and mechanisms are arranged in sequence along the propagation path of the light. Specifically, the laser 1 emits a laser; the optical mechanism 2 processes the laser beam emitted by the laser 1 (such as collimation, focusing, etc.); the processed laser beam is reflected to the image plate 4 by the scanning mechanism 3, and at the same time, the scanning mechanism 3 will move accordingly to change the laser beam to irradiate different positions of the image plate 4, that is, change the position of the scanning spot formed by the laser beam on the image plate 4; the fluorescence collection mechanism is arranged behind the image plate 4, and the laser beam will excite and generate fluorescence after irradiating the image plate 4, and the scattered light generated by the image plate 4 is collected by the fluorescence collection mechanism; the filter 6 is arranged behind the fluorescence collection mechanism, and is used to filter out the excitation laser in the scattered light and only allow the fluorescence to pass; the silicon photomultiplier 7 is arranged behind the filter 6, and the collected fluorescence is photoelectrically converted and the corresponding electrical signal is output.

[0031] In this embodiment, the laser 1 adopts a single-mode semiconductor laser. The wavelength of the laser beam 10 emitted by the single-mode semiconductor laser is 635nm, and the size of the light-emitting surface is constant, about 1-4μm, which has excellent beam quality, ensuring that the entire intraoral impact scanner has good spatial resolution, and this will greatly reduce the difficulty of designing the laser shaping optical path, which will be described in detail below.

[0032] In this embodiment, the optical mechanism 2 includes a collimating lens 21, an aperture stop 22 and a focusing lens 23 arranged in sequence along the optical axis of the laser beam. The collimating lens 21 collimates the laser beam to form a parallel beam. Preferably, the collimating lens 21 is composed of a single aspherical mirror. That is, in this embodiment, only one aspherical lens is used to collimate the laser. The single aspherical mirror achieves better collimation phase difference control within the diffraction limit for the laser with NA of 0.2. After passing through the collimating lens 21, the laser passes through the aperture stop 22. The aperture stop 22 is a circular knife-edge design and is blackened internally, thereby effectively controlling the stray light of the system and expanding the focal depth of the entire optical system. The optical mechanism 2 in this embodiment adopts an optical design with a long working distance and a low magnification to achieve a high spatial resolution of the intraoral image scanner, that is, within the entire scanning angle range, the laser spot is very small and is within the diffraction limit of the optical system. The specific description is as follows.

[0033] In this embodiment, the collimating lens 21 is composed of an aspherical mirror, and the focal length of the aspherical mirror is 15 to 25 mm. Since a single-mode semiconductor laser is selected as the laser light source 1 in this embodiment, the slow axis and fast axis M of the laser are 2They are all close to 1, so only one aspherical mirror is used to collimate the laser. The focal length of the aspherical mirror is 15-25mm, which can achieve perfect collimation of lasers with NA of 0.2, and the aberration is controlled within the diffraction limit; at the same time, the surface of the aspherical mirror is coated with a dielectric film layer with a transmittance of about 99.5%, thereby ensuring that the laser has sufficient power. The diameter of the aperture diaphragm 22 is 5 to 10mm, thereby increasing the focal depth of the optical system. The intraoral image scanner of the present invention is a flat field scan, so the setting of the aperture size of the diaphragm (3) is very critical. Since flat field scanning will cause light at different angles to have different optical paths, that is, the laser spot size at different spatial positions of the IP board will have a large difference. In this embodiment, the diameter of the aperture diaphragm 22 is set to 5 to 10mm, which can better avoid the above problems. The focal length of the focusing lens 23 is 100 to 180mm. In order to cover the entire image plate and reduce the scanning angle of the laser, the optical system adopts a long working distance design. However, if the working distance is too long, the optical magnification of the entire optical system will inevitably increase. Since the size of the light-emitting surface of the single-mode semiconductor laser is constant, about 1-4um, if the magnification of the optical system is too large, the spot size of its image surface will also increase accordingly. Therefore, the intraoral image scanning system of this embodiment uses a focusing lens 23 with a focal length set to 100-180mm to focus the light beam, that is, to balance the optical magnification and the low scanning angle, and cooperates with a small aperture diaphragm 22 to achieve that the laser spot size is within the diffraction limit within the entire scanning angle, that is, to achieve flat field scanning without an f-θ lens, and at the same time achieve high spatial resolution of the intraoral image scanner, that is, within the entire scanning angle range, the laser spot is very small and within the diffraction limit of the optical system.

[0034] In this embodiment, the scanning mechanism 3 includes a galvanometer 31 for reflecting the laser beam onto the image plate 4 and a galvanometer motor 32 for driving the galvanometer 31 to rotate. The galvanometer 31 is fixed on the output shaft of the galvanometer motor 32, and the galvanometer motor 32 reciprocates within a certain angle, thereby driving the galvanometer 31 to reciprocate within a certain angle. Therefore, the laser spot formed by the laser beam reflected by the galvanometer 31 onto the image plate 4 also reciprocates along a track, which is the scanning track of the laser beam on the image plate 4. The scanning track in this embodiment is preferably a track extending along a straight line. Each time the galvanometer 31 rotates a stroke, the laser spot completes the scanning of one row of the image plate 4; multiple reciprocating strokes are performed until the laser spot scans the entire image plate 4.

[0035] In this embodiment, the fluorescence collection mechanism includes a cylindrical mirror 5, and the generatrix of the cylindrical mirror 5 is parallel to the scanning track of the laser beam on the image plate 4. The cylindrical mirror 5 is arranged at a position adjacent to the image plate 4, so that it can be arranged close to the image plate 4, so that more fluorescence can be collected. Figure 2 and Figure 3 As shown, a cylindrical mirror 5 is used to collect fluorescence, and the cylindrical mirror 5 only converges the light beam in one direction (non-bus direction), and the light beam in the other direction (bus direction) propagates according to the original incident direction. The NA of the cylindrical mirror 5 is greater than 0.5, and a UV high anti-reflection film layer is coated on the surface of the cylindrical mirror 5.

[0036] In some other embodiments, the cylindrical mirror 5 may also be replaced by a rod mirror or a fiber optic lens.

[0037] In this embodiment, the filter 6 is arranged between the cylindrical mirror 5 and the silicon photomultiplier 7 .

[0038] The silicon photomultiplier 7 includes an avalanche photodiode array, which is composed of a plurality of avalanche photodiodes arranged in an array. The avalanche photodiode array includes at least one row of avalanche photodiodes, and the plurality of avalanche photodiodes constituting the row of avalanche photodiodes are arranged in a direction parallel to the scanning track of the laser beam on the image plate 4. For example, if the scanning track extends horizontally from left to right, the plurality of avalanche photodiodes constituting a row of avalanche photodiodes are also arranged horizontally from left to right. In the present invention, the silicon photomultiplier 7 (Silicon photomultiplier-SiPM) is used as a photoelectric conversion device for an intraoral imaging scanner. The silicon photomultiplier 7 is composed of hundreds of avalanche photodiode (APD) units operating in Geiger mode, and each APD unit is connected in series with a resistor of about several hundred kilo-ohms to control the avalanche quenching and voltage recovery of the APD unit. Since the APD unit operates above the reverse breakdown voltage, when a certain APD unit receives a photon, the generated photogenerated carriers will trigger avalanche breakdown, and the photoelectric conversion gain can reach 10 5 ~10 6 Silicon photomultipliers 7 can detect single photons, and have advantages such as higher detection efficiency than photomultiplier tubes, lower operating voltage, higher gain, better single-photon resolution than photomultiplier tubes, insensitivity to magnetic fields, small size, low power consumption, and easy fabrication of large-scale multiplier arrays.

[0039] In this embodiment, the silicon photomultiplier 7 is a one-dimensional array, and its long side direction is parallel to the scanning track; meanwhile, the curvature of the cylindrical mirror 5 is also a one-dimensional direction, and its generatrix direction is also parallel to the scanning track. Figure 4 As shown, the silicon photomultiplier 7 includes a row of avalanche photodiodes, and a plurality of avalanche photodiodes 71 in the row are arranged at intervals in a direction parallel to the scanning track, and the energy collected by each avalanche photodiode 71 is output as the total energy. The combination of the linear scanning track, the cylindrical mirror 5, and the linear array of the silicon photomultiplier 7 can achieve excellent fluorescence collection capability while greatly reducing the size of the entire intraoral image scanning system.

[0040] The intraoral image scanner of this embodiment has the following features:

[0041] 1. Reduce the overall size of the intraoral imaging scanner, which greatly facilitates doctors' mobile diagnosis;

[0042] 2. The intraoral image scanner uses silicon photomultipliers, which can reduce the cost of the entire intraoral image scanner;

[0043] 3. In practical applications, the driving voltage of silicon photomultipliers is only tens of volts, which reduces the difficulty and cost of circuit design and power consumption;

[0044] 4. It is less sensitive to electromagnetic fields and is not easily disturbed by them. It can avoid electromagnetic shielding, thereby reducing the cost increase caused by it. In addition, the application of the intraoral imaging scanner will not be restricted too much by the magnetic field and can still be used even in an environment with large electromagnetic interference;

[0045] 5. The intraoral image scanner adopts an optical structure design with long working distance, low magnification and long focal depth to achieve high spatial resolution within the entire scanning angle.

[0046] The above embodiment is only for illustrating the technical concept and features of the present invention, and is a preferred embodiment, and its purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and it cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. An intraoral image scanner based on a silicon photomultiplier, comprising a laser, an optical mechanism for processing a laser beam emitted by the laser, and a scanning mechanism for moving a light spot formed by the laser beam, characterized in that: The intraoral image scanner further comprises a fluorescence collection mechanism for collecting fluorescence excited by the image plate and a silicon photomultiplier for photoelectric conversion, wherein the silicon photomultiplier comprises an avalanche photodiode array, wherein the silicon photomultiplier is a one-dimensional array, and the avalanche photodiode array is composed of a plurality of avalanche photodiodes arranged in an array; the avalanche photodiode array comprises at least one row of avalanche photodiodes, and the plurality of avalanche photodiodes constituting the row of avalanche photodiodes are arranged in a direction parallel to the scanning track of the laser beam on the image plate; The fluorescence collection mechanism includes a cylindrical mirror; The laser is a single-mode semiconductor laser, the size of the light-emitting surface of the single-mode semiconductor laser is 1-4 μm, the optical mechanism comprises a collimating lens, an aperture stop and a focusing lens which are arranged in sequence, the collimating lens is composed of a single aspheric mirror, the focal length of the aspheric mirror is 15-25 mm, the diameter of the aperture stop is 5-10 mm, and the focal length of the focusing lens is 100-180 mm; the surface of the aspheric mirror is coated with a dielectric film layer; The scanning mechanism includes a galvanometer for reflecting the laser beam onto an image plate and a galvanometer motor for driving the galvanometer to deflect within a certain angle, wherein the galvanometer motor is configured to rotate back and forth within a certain angle, thereby driving the galvanometer to rotate back and forth within a certain angle, so that the laser spot formed by the laser beam reflected by the galvanometer onto the image plate moves back and forth along a straight line trajectory; the generatrix of the cylindrical mirror is parallel to the straight line trajectory and the row direction of the at least one row of avalanche photodiodes, and the NA of the cylindrical mirror is greater than 0.

5.

2. The intraoral image scanner according to claim 1, characterized in that: The surface of the cylindrical mirror is coated with an ultraviolet high-reflection film layer.

3. The intraoral image scanner according to claim 1, characterized in that: The intraoral image scanner also includes a filter for filtering out the excitation laser, and the filter is arranged between the fluorescence collection mechanism and the silicon photomultiplier.

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