Patent Grant
12004890
This is a national stage application of PCT application No. PCT/2018/057719 having an international filing date of Oct. 26, 2018, the entire contents of which are incorporated herein by reference in its entirety for all purposes.
The subject matter disclosed herein relates generally to x-ray imaging. More particularly, the subject matter disclosed herein relates to stationary intraoral tomosynthesis systems, devices, and methods for three-dimensional dental imaging.
Dental radiology has undergone important changes over the past several decades. However, the need for more precise diagnostic imaging methods continues to be a high priority. Intraoral dental X-rays were introduced only one year after Roentgen's discovery of X-ray radiation. Since that time, advances in dental imaging techniques have included more sensitive detector technology, panoramic imaging, digital imaging and Cone Beam Computed Tomography (CBCT). Computed Tomography (CT), Magnetic Resonance Imaging (MRI), Ultrasound (US), and optical techniques have also been investigated for dental imaging.
Intraoral radiography is the mainstay of dental imaging. It provides relatively high resolution, and limited field of view images for most routine dental needs. However, as a two dimensional (2D) imaging modality, the technique suffers from superimposition of overlying structures and loss of spatial information in the depth dimension. Panoramic imaging, a popular form of extraoral imaging, visualizes the entire maxilla, mandible, temporo-mandibular joints (TMJ), and associated structures in a single image. However, it is subject to considerable geometric distortion and has relatively low spatial resolution compared with intraoral radiography. CBCT as a three dimensional (3D) imaging modality has found wide acceptance in dentistry, especially for surgical planning procedures such as dental implant and orthodontic treatment planning, and evaluation of endodontic and pathological condition. There are, however, several disadvantages associated with CBCT in comparison to 2D radiography: (1) excess noise and artifacts from metal dental restorations/appliances reduce the image quality; (2) acquisition, reconstruction, and interpretation time are greatly increased, reducing clinical efficiency and increasing financial cost; and (3) significantly higher ionizing radiation doses increase the radiation burden for the patient.
Despite the many technological advances, the radiographic diagnostic accuracy for some of the most common dental conditions has not improved in many years and in some cases remains low. Examples include caries detection, root fracture detection, and assessment of periodontal bone loss.
Caries are the most common dental disease. The World Health Organizations estimates that 60-90% of school children and nearly all adults have dental caries at some point in time. If carious lesions are detected early enough, i.e. before cavitation, they can be arrested and re-mineralized by non-surgical means. When carious lesions go undetected, they can evolve into more serious conditions that may require large restorations, endodontic treatment, and, in some cases, extractions. The detection sensitivity of caries has not seen any significant improvement in the past several decades. 2D intraoral radiography is the current gold standard, with a reported sensitivity ranging from 40% to 70% for lesions into dentine and from 30% to 40% for lesions confined to enamel. CBCT does not provide significant improvement for caries detection. Beam-hardening artifacts and patient movement decrease structure sharpness and definition.
The detection of vertical root fractures (VRF) represents a clinically significant diagnostic task with important ramifications in tooth management. VRFs are considered one of the most frustrating tooth conditions associated with endodontic therapy. Overall detection of VRFs remains poor. The ability of CBCT to detect initial small root fractures is limited by its relatively low resolution.
Dental radiography provides important information for assessing tooth prognosis and making treatment decisions associated with periodontal disease. Currently, 2D intraoral radiography is the mainstay of dental imaging. It provides relatively high resolution images with a limited field of view for most routine dental needs. However, this technique is limited because of the 2D representation of 3D objects. The 2D image results in superimposition of overlying structures and loss of spatial information in the depth dimension. Consequently, important dimensional relationships are obscured, observed sharpness is reduced, objects of interest are lost, and pathology contrast is reduced. On the other hand, Panoramic imaging, a popular form of extra-oral imaging visualizes the entire maxilla, mandible, temporo-mandibular joints and associated structures on a single scan. It is subject to considerable geometric distortion, and has relatively low spatial resolution compared with intraoral radiography.
These diagnostic tasks illustrate the clinical need for a diagnostic imaging system with high resolution, 3D capabilities, reduced metal artifact and lower radiation burden to patients.
Digital tomosynthesis imaging is a 3D imaging technique that provides reconstruction slice images from a limited-angle series of projection images. Digital tomosynthesis improves the visibility of anatomical structures by reducing visual clutter from overlying normal anatomy. Some examples of current clinical tomosynthesis applications include chest, abdominal, musculoskeletal, and breast imaging.
A variation of the tomosynthesis technique, called Tuned Aperture Computed Tomography (TACT), was investigated in the late 1990's for dental imaging. TACT significantly improved the diagnostic accuracy for a number of tasks compared to conventional radiography. These included: (1) root fracture detection, (2) detection and quantification of periodontal bone loss, (3) implant site assessment, and (4) the evaluation of impacted third molars. The results for caries, however, were inconclusive.
TACT was not adopted clinically because the technology was not practical for patient imaging. Conventional x-ray tubes are single pixel devices where x-rays are emitted from a fixed point (focal spot). To acquire the multiple projection images, an x-ray source was mechanically moved around the patient. A fiduciary marker was used to determine the imaging geometry. The process was time consuming (e.g., approximately 30 minutes per scan) and required high operator skill to accomplish image acquisition. The difficulty of determining precisely the imaging geometry parameters and long imaging acquisition time due to mechanical motion of the source makes TACT impractical. Any variation of TACT for 3D intraoral imaging using a single x-ray source suffers from similar drawbacks and disadvantages.
Extra-oral tomosynthesis has been investigated in a patient study using an experimental device as well as by using CBCT. The extra-oral geometry required high radiation doses. The image quality was compromised by cross-talk of out-of-focus structures. In order to avoid high radiation doses, intraoral tomosynthesis using a single mechanically scanning x-ray source has been described in the patent literature, and investigated in a recent publication using a single conventional x-ray source and a rotating phantom. Unfortunately, the limitations described above for TACT remained the same for these approaches, which are caused primarily by the conventional single focal spot x-ray tube.
The concept of a stationary intraoral tomosynthesis system has recently been disclosed in U.S. Pat. Nos. 9,782,136, and 9,907,520. The system utilizes a distributed x-ray source array to generate all the projection images needed for reconstruction without any mechanical movement of the source or the detector. The x-ray source array is placed outside a patient's mouth and an intraoral detector placed inside the patient's mouth. Such a distributed x-ray source array can now be constructed using, for example, carbon nanotube (CNT) field emission x-ray technology. The feasibility of this technology has been demonstrated and reported in several research publications and in clinical studies.
As all existing commercial intraoral imaging systems are 2D regular radiographic imaging devices, when adopting new imaging devices such as the intraoral tomosynthesis imaging system of the present disclosure, there is a desire from dentists and practitioners that the same system be capable of performing intraoral imaging in both the tomosynthesis mode and in the regular 2D radiographic mode.
A medical imaging device should follow the principle of As Low As Reasonably Practicable (ALARP). Standard IEC 60601-2-65, requires specific collimation limits such that the majority of the radiation from the x-ray source should be directed and limited to the detector surface, thus reducing the radiation burden to the patient. This requires a collimator (also known as a beam limiting device) that precisely controls the radiation field, and alignment of the radiation field and the detector. An x-ray source array with a plurality of the spatially distributed focal spots is difficult to collimate without moving the collimation assembly because the x-ray radiation is emitted from different focal spots on the x-ray anode. Thus, a new design of a collimation system that can meet this requirement is needed.
For conventional 2D intraoral radiography, two types of collimation are commonly used. One is a circular collimator which defines a radiation field that is significantly larger than the size of the intraoral sensor used. The large radiation field makes it easier and faster for the operator in the clinic to position the intraoral sensor and to minimize the chances of image truncation (also known as “cone cut”). With the large circular collimator, it is possible for an operator to place and position the intraoral detector without the use of an alignment guide. This reduces the imaging time, which is desirable for a busy dental clinic. The use of an oversized radiation field, which exposes the patient to more radiation, is possible because most of the conventional intraoral radiography equipment and intraoral detectors are sold separately. As such, the IEC requirement, discussed hereinabove, does not apply.
The other common type of collimation for 2D intraoral radiography is a rectangular collimator which defines a small radiation field that closely matches the size of the detector. It reduces the radiation exposure to the patient. In this case an alignment guide is commonly used to ensure that the detector is precisely aligned with the radiation field, to minimize the chance of cone cuts.
For the dental clinics, it is desirable to have collimators with small and large radiation fields that are easily interchangeable at the clinics.
An intraoral tomosynthesis device requires a dynamic intraoral detector that can synchronize image capturing with x-ray exposure at a high speed. Such a detector is not commonly available in dental clinics and is supplied as an integral part of the intraoral tomosynthesis imaging system. To follow the ALARP principle and to satisfy the IEC requirement, it is necessary to invent a collimation system that can collimate the x-ray radiation from all x-ray focal spots to the detector area for tomosynthesis imaging. It is further desirable that the collimation unit for the tomosynthesis system is stationary which does not need to mechanically move as the x-ray exposure is moved from one focal spot to another.
Furthermore, it is desirable that the intraoral tomosynthesis can also be used for conventional 2D intraoral radiography. When used for 2D intraoral radiography, it is desirable that the device provides options for circular collimation with a radiation field substantially larger than the x-ray sensor for easy placement of the sensor, and/or a rectangular collimation with a radiation field that is comparable to the sensor area for reducing the radiation dose.
For an intraoral tomosynthesis device utilizing a distributed x-ray source array with one or more x-ray focal spots, it is necessary to have a control electronic unit that can regulate the x-ray tube current for each of the one or more focal spots such that x-ray radiation from each x-ray focal spot is regulated.
A goal of the present disclosure is to address these clinical needs for intraoral tomosynthesis imaging.
In accordance with the disclosure herein, stationary x-ray intraoral tomosynthesis devices, systems, and methods are provided. The present disclosure describes, in some embodiments, designs of a stationary x-ray intraoral tomosynthesis imaging device and system with a detachable collimation assembly providing a variety of radiation fields for both 3-dimensional (3D) tomosynthesis imaging and regular 2-dimensional (2D) radiography. In other embodiments, the present disclosure includes methods to control the radiation from the plurality of x-ray focal spots.
In one aspect, an x-ray intraoral tomosynthesis imaging system is provided, the system comprising: an x-ray source array comprising one or more spatially distributed x-ray focal spots; an electronic unit comprising a high voltage power supply and a current source; a switching circuit configured to connect the current source to various cathodes of the x-ray source array, one at a time, to produce a scanning x-ray beam; a collimation assembly configured to provide rectangular or circular radiation fields; a digital intraoral x-ray detector; an input panel configured to allow a user to select x-ray energy, tube current, exposure time, and imaging mode, including a two dimensional (2D) imaging mode, a three dimensional (3D) imaging mode, or a combination of the 2D imaging mode and the 3D imaging mode; and an image viewer configured to display a stack of reconstructed tomosynthesis slice images, wherein the x-ray source array is configured to produce either a scanning x-ray beam illuminating an object from different viewing angles without mechanically moving the x-ray source array for tomosynthesis, or a single 2D radiograph; and wherein the collimation assembly is further configured to substantially collimate x-ray radiation from all x-ray focal spots to the digital intraoral x-ray detector.
In another aspect, the collimation assembly comprises: a primary collimator positioned close to an exit window of the x-ray source array wherein the primary collimator comprises an array of one or more apertures, each of the one or more apertures being aligned with one corresponding x-ray focal spot of the x-ray source array, and configured to allow x-ray radiation from the one corresponding x-ray focal spot to pass through; a secondary collimator positioned in line with respect to the primary collimator, wherein the secondary collimator has one aperture configured to further confine x-ray radiation passing through the primary collimator; and a cone structure that encloses the primary collimator and the secondary collimator.
In yet another aspect of the subject matter of the present disclosure, a method for x-ray intraoral tomosynthesis imaging is provided, the method comprising: providing an x-ray source array comprising one or more spatially distributed focal spots; providing an electronic unit comprising a high voltage power supply and a current source; providing a switching circuit that is configured to connect the current source to various cathodes of the x-ray source array, one at a time, to produce a scanning x-ray beam; providing a collimation assembly configured to provide rectangular and circular radiation fields; providing a digital intraoral x-ray detector; providing an input panel that allows a user to select x-ray energy, tube current, exposure time, and imaging mode, including a 2D imaging mode, a 3D imaging mode, or a combination of the 2D imaging mode and the 3D imaging mode; illuminating an object from different viewing angles with a scanning x-ray beam generated by the x-ray source array, without mechanically moving the x-ray source array, for tomosynthesis or a single 2D radiograph; collimating x-ray radiation from all of the one or more spatially distributed focal spots to the digital intraoral x-ray detector using the collimation assembly; and providing an image viewer configured to display a stack of reconstructed tomosynthesis slice images.
Although some of the aspects of the subject matter disclosed herein have been stated hereinabove, and which are achieved in whole or in part by the presently disclosed subject matter, other aspects will become evident as the description proceeds when taken in connection with the accompanying drawings as best described hereinbelow.
Features and advantages of the present subject matter will be more readily understood from the following detailed description which should be read in conjunction with the accompanying, example drawings that are given merely by way of explanatory and non-limiting example, and in which:
The present disclosure describes a stationary x-ray intraoral tomosynthesis imaging device, and related systems and methods, with a collimation assembly that can provide a variety of radiation fields needed for different imaging modes, including, for non-limiting example, rectangular and circular fields for both 3-dimensional (3D) tomosynthesis imaging and regular 2-dimensional (2D) radiography.
In this embodiment, the x-ray source array 102 can be placed outside a patient's mouth and the intraoral x-ray detector 108 placed inside the patient's mouth wherein, the specimen 110 is positioned between the x-ray source array 102 and the intraoral x-ray detector 108. In this embodiment, the x-ray source array 102 emits x-ray beams 106 in the direction of the specimen 110 and the intraoral x-ray detector 108. The intraoral x-ray detector 108 detects the x-ray beams 106 and one or more images is/are generated based on those detections. In some embodiments, the x-ray source array 102 can be constructed using, for non-limiting example, carbon nanotube (CNT) field emission x-ray technology.
In other embodiments, the collimation assembly comprises the primary collimator 220 and the first secondary collimator 260A. In still other embodiments the collimation assembly comprises the primary collimator 220 and the second secondary collimator 260B. In some embodiments, the collimation assembly acts as a beam-limiting device for the x-ray beams emitted by the x-ray source array 102. In some embodiments, the x-ray intraoral tomosynthesis imaging device 200 is a stationary device. In other embodiments, the x-ray intraoral tomosynthesis imaging device 200 is non-stationary. In further embodiments of the present disclosure, the collimation assembly is further configured to substantially collimate x-ray radiation from all of the one or more x-ray focal spots 104 to the digital intraoral x-ray detector 108.
In some embodiments, and as briefly disclosed above, the primary collimator 220 is placed close to the exit window 230 of the x-ray source array 102. In some embodiments, the primary collimator 220 comprises one or more apertures such as apertures 240. Each of the one or more apertures 240 is aligned with a corresponding focal spot 104 of the x-ray source array 102, only allowing the x-ray radiation or x-ray beams from the corresponding focal spot 104 to pass through the corresponding aperture 240. In other words, each of the one or more apertures 240 of the primary collimator 220 is lined up with one focal spot 104 such that any x-ray radiation or x-ray beam emitted by a focal spot 104 is directed at or towards the aperture 240 that the focal spot 104 is lined up with. This is illustrated in
In some embodiments, the primary collimator 220 is mechanically fixed to the front surface 270 of the body 210 of the x-ray intraoral tomosynthesis imaging device 200 to ensure precise alignment of the one or more apertures 240 with the one or more focal spots 104. In further embodiments, the first secondary collimator 260A is configured such that it can be readily exchanged in a dental clinic, depending on the imaging needs of an operator of the x-ray intraoral tomosynthesis imaging device 200. In the embodiment shown in
In some embodiments, the primary collimator 220, the first secondary collimator 260A, and/or the second secondary collimator 260B are made of x-ray attenuating materials. In further embodiments, the primary collimator 220, the first secondary collimator 260A, and/or the second secondary collimator 260B are made of non-lead containing heavy metals. In another embodiment, the primary collimator 220, the first secondary collimator 260A, and/or the second secondary collimator 260B are made from, for non-limiting exemplary purposes, tungsten containing polymer that heavily attenuates x-ray beams or x-ray radiation, and can be made from one or more molding.
In some embodiments, the first secondary collimator 260A has a tight rectangular aperture and the second secondary collimator 260B has a large circular aperture. In further embodiments of the present disclosure, the first secondary collimator 260A has a tight rectangular aperture configured to collimate radiation generated from all of the one or more x-ray focal spots 104 to a surface of the intraoral x-ray detector 108 thereby reducing a patient's radiation dose. In some embodiments, the first secondary collimator 260A and the second secondary collimator 260B have different lengths and are configured to allow intraoral imaging at different source-to-detector distances. In some embodiments, the collimation assembly is configured to be easily detached and reattached to the x-ray intraoral tomosynthesis imaging device 200 thereby allowing imaging at different modes. In further embodiments, the collimation assembly comprises one or more attachments, including a tomosynthesis collimator configured for intraoral tomosynthesis imaging using all of the one or more x-ray focal spots 104, a radiograph collimator configured for 2D radiographic imaging using a pre-selected x-ray focal spot 104, or a combination collimation assembly configured for imaging in both 2D and tomosynthesis modes.
In some embodiments, the image viewer 420 can, for example, be separate from the input panel 400. In some embodiments, the input panel 400 can, for non-limiting example, be affixed, or attached to a wall just outside the clinic room. In further embodiments, the input panel 400 can, for non-limiting example, be on a mobile station or mobile cart that can be taken from room to room. In some embodiments, the input panel 400 is connected to the x-ray intraoral tomosynthesis imaging device 200 by suitable cabling necessary to allow electronic communication between the input panel 400 and the x-ray intraoral tomosynthesis imaging device 200. In some embodiments, the input panel 400 comprises one or more processors and a non-transitory computer readable medium comprising tomosynthesis image reconstruction software used to reconstruct the tomosynthesis slice images.
The present subject matter can be embodied in other forms without departure from the spirit and essential characteristics thereof. The embodiments described therefore are to be considered in all respects as illustrative and not restrictive. Although the present subject matter has been described in terms of certain preferred embodiments, other embodiments that are apparent to those of ordinary skill in the art are also within the scope of the present subject matter.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2018/057719 | 10/26/2018 | WO |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2020/086094 | 4/30/2020 | WO | A |
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