Dental radiography method with enhanced material characterization - Patents.com

Abstract

A method for forming a radiographic image of a subject's oral anatomical structure includes exposing the subject to radiation along a radiation path. At each location on a detector array in the radiation path, the number of photons received from the radiation passing through the subject is counted, and the detector maintains a first photon count for photons having a first energy above a first energy threshold and at least a second photon count for photons having a second energy above a higher energy threshold. One or more materials in the subject's mouth are identified by performing a material decomposition process according to two or more reference materials, and natural oral anatomical features and engineered materials in the subject's mouth are differentiated according to the material decomposition process. The adjusted image content enhances the differentiation of natural oral anatomical features and engineered materials according to the material decomposition.

Description

[Technical field]

[0001] The present disclosure relates generally to dental radiography, and more particularly to the use of spectral radiography in dentistry and cephalometric imaging for characterization and differentiation of materials in the image content of a sample, and enhanced visualization of intra-oral features according to their corresponding materials. [Background technology]

[0002] Conventional dental x-ray imaging is widely recognized to be a valuable tool to show the internal condition of the teeth and underlying supporting structures and to assist in the introduction and evaluation of various procedures and dental appliances, including crowns, implants, and other devices. Not only are dental x-rays extremely useful in supporting certain procedures, but they can also serve as a useful tool in monitoring the health of the oral cavity as part of routine imaging procedures.

[0003] The intraoral environment presents a great challenge for radiographic characterization. The mouth contains a wide range of materials and tissue types, ranging from fluids and soft tissues to bone and tooth materials of variable density. In addition, various dental treatments and procedures can introduce multiple and diverse materials, from dental fillings to crowns, implants, and other prosthetics, including materials used in endodontics, periodontics, and other specialties. A wide range of materials, including various metals, ceramics, plastics, composites, and other materials, can be temporarily or permanently introduced into, around, or even in place of various intraoral structures, amid the surrounding teeth and supporting structures.

[0004] The very small size of the patient's mouth, concerns for patient comfort and safety during imaging, constraints on detector array size, placement, and support, and the need to work with or around a variety of prosthetic devices, compounded by the need to minimize dose to the lowest possible levels, can make it particularly difficult to obtain radiographic images that provide the information desired by the physician at the optimal energy levels needed to provide information related to intra-oral features and the patient's overall condition.

[0005] Further complicating the problem is that the imaging content for different types of tissue and other materials is itself highly dependent on the energy level of the radiation delivered, such that lower energy levels that are optimal for characterizing, for example, gum tissue may produce insufficient or even unusable results for imaging tooth or bone structures or features formed from metal or implant materials.

[0006] X-ray imaging provides image content according to the attenuation coefficients of image features located in the path of the x-ray beam. Using standard radiography, it can be very difficult to ascertain the material composition of the imaged anatomical structures unless only one predominant type of tissue or material is present.

[0007] The ability to distinguish material types would be highly beneficial in multiple dental applications. It may be useful for dentists to have the ability to separately visualize features such as metal or synthetic material fillings in addition to and within the surrounding tooth structure. This ability would also allow virtual material removal, so that structures of different materials can be more easily segmented from each other and then restored and displayed separately. For example, procedures for root canal therapy would benefit from improved segmentation of soft tissues from surrounding structures, allowing the practitioner to visualize the pulp chamber walls separately from the gutta-percha fillings. Segmentation of metal crowns for endodontic therapy could also take advantage of enhanced imaging capabilities for materials, and virtual material removal would allow for more careful analysis of the underlying bone structure away from the crown. Virtual material removal could improve osseointegration assessment of implant preparation and status, allowing the ability to more clearly distinguish material types from each other.

[0008] Incomplete records and other factors can make it difficult for physicians to determine what substances may have been used in a patient's previous treatment by other physicians. Current practice can require meticulous tooth-by-tooth observations to evaluate and analyze a patient's medical history.

[0009] In these and other applications, practitioners would clearly benefit from being able to visually separate materials within the mouth in order to better assess the overall condition and arrangement of various naturally occurring and engineered features and structures. Without this ability, dentists may be required to interpret some x-rays using a degree of guesswork and approximation, which risks errors of judgment and potentially jeopardizing safe and effective patient treatment.

[0010] It would therefore be appreciated that dental radiography tools and techniques would be beneficial that enhanced the practitioner's ability to separate and view various materials and features in a patient's mouth according to material properties. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] International Publication No. 2021 / 034891 [Patent Document 2] International Publication No. 2020 / 077166 Summary of the Invention [Problem to be solved by the invention]

[0012] It is an object of the present disclosure to advance the art of dental radiography. One embodiment of the present disclosure specifically addresses the need to distinguish specific materials in a patient's mouth and use this knowledge for improved characterization of intra-oral features, and to enable virtual material removal for improved visibility of natural and synthetic structures.

[0013] Another object of the present application is to address, in whole or in part, at least the above-mentioned and other deficiencies in the related art.

[0014] A related object of the present application is to provide, in whole or in part, at least the advantages described herein.

[0015] These objectives are given for purposes of illustration only, and such objectives are exemplary of one or more embodiments of the present application. Other desirable objectives and advantages inherently achieved by the disclosed method will occur or become apparent to those skilled in the art. The invention is defined in the appended claims. In addition, it will be appreciated that dental practitioners would benefit from enhanced capabilities to measure dimensions of both tissue and additional materials. Dimensional criteria can relate to measures of linear range (such as height, width, and depth), circumference, surface area, or volume, for example. [Means for solving the problem]

[0016] According to one aspect of the present disclosure, there is provided a method of producing a radiographic image of an oral anatomy of a subject, comprising: a) exposing an object to radiation along an X-ray radiation path; b) obtaining image content by counting the number of photons received on the detector array in the radiation path from the radiation passing through the object at each of a plurality of positions; acquiring, wherein the detector maintains a first photon count for photons having a first energy above a first energy threshold and further maintains at least a second photon count for photons having a second energy above a higher energy threshold; c) identifying one or more materials in the subject's mouth by performing a material decomposition process according to two or more reference materials previously characterized according to at least a first and a second photon count, and distinguishing between natural oral anatomical features and engineered materials in the subject's mouth according to the material decomposition process; and d) displaying adjusted image content that enhances differentiation between identified natural oral anatomical features and engineered materials within the mouth according to the material decomposition.

[0017] The above and other objects, features and advantages of the present invention will become apparent from the following more particular description of the embodiments of the present disclosure, which are illustrated in the accompanying drawings. The elements of the drawings are not necessarily to scale relative to each other. [Brief description of the drawings]

[0018] [Figure 1] 1 is a schematic diagram of a dental imaging system for performing an X-ray scan of a patient to generate a 3D volumetric reconstruction of a portion of the patient in accordance with the present disclosure. [Figure 2A] FIG. 2 is a schematic diagram showing a photon counting sequence. [Figure 2B] FIG. 2 is a schematic diagram illustrating a photon counting sequence with multiple thresholds. [Diagram 3] 1 is a graph showing the placement of energy bins defined across an energy spectrum. [Figure 4A] 1 is a graph illustrating exemplary linear attenuation characteristics for two different materials. [Figure 4C] 1 is a graph showing exemplary linear absorption characteristics for two different materials. [Figure 4D] 1 is a graph showing curves of relative attenuation coefficients for water, bone, and calcium. [Figure 5A] FIG. 1 is a logic flow diagram illustrating an overview of an imaging process according to one embodiment of the present disclosure. [Figure 5B] FIG. 11 is a logic flow diagram illustrating the setup steps in more detail. [Figure 5C] 11A-11C illustrate some of the variations possible for the acquiring step using the procedures of the present disclosure. [Figure 5D] FIG. 1 illustrates an aspect of a material characterization step. [Figure 5E] FIG. 2 illustrates a logic flow for some portions of the processing and evaluation steps according to one embodiment of the present disclosure. [Figure 5F] 1 is a flow diagram illustrating a sequence of steps for acquiring and processing image content for virtual material removal according to one embodiment of the present disclosure using spectral imaging. [Figure 6A] FIG. 13 illustrates, by way of example, the use of scout image content for populating a dental chart for a patient. [Figure 6B] FIG. 13 illustrates another method that may be used to edit the bin definition thresholds on a user interface associated with the X-ray imaging system. [Figure 6C] FIG. 1 is a diagram showing a sequence for generating a material-separated projection image. [Figure 6D]FIG. 1 is a schematic diagram of a sequence for processing material-separated projection images. [Figure 7A] FIG. 1 is a schematic diagram of a dental phantom scanned using spectral X-rays to generate a 3D volumetric reconstruction. [Figure 7B] FIG. 7B shows attenuation restoration for gutta-percha material in the dental phantom of FIG. 7A. [Figure 7C] FIG. 3D volume reconstruction obtained using HA (hydroxyapatite) as reference material. [Figure 7D] FIG. 3D volume reconstruction obtained using titanium (Ti) as reference material. [Figure 8A] FIG. 1 shows an example of a restoration from a tooth having gutta-percha material. [Figure 8B] FIG. 1 shows an example of a restoration from a tooth having gutta-percha material. [Figure 8C] FIG. 8C compares axial views from the reconstructions of FIG. 8A and FIG. 8B for conventional attenuation, soft tissue density, and connective soft tissue (ST) and HA density. [Figure 8D] FIG. 8C compares coronal views from the reconstructions of FIG. 8A and FIG. 8B for conventional attenuation, soft tissue density, and combined ST and HA density. [Figure 9A] FIG. 13 shows the placement of a titanium post partially seated within a SiO2 crown on a dental phantom. [Figure 9B] FIG. 9B illustrates a conventional restoration based on the feature decay of FIG. 9A. [Figure 9C] FIG. 13 shows an exemplary reconstruction for a representative Ti / SiO2 structure in a phantom using HA and Ti densities. [Figure 9D] FIG. 13 shows an exemplary reconstruction for a representative Ti / SiO2 structure in a phantom using HA and Ti densities. [Figure 10A] FIG. 1 shows a dental phantom arrangement used to image a gold crown placed against tooth material. [Figure 10B]FIG. 13 shows ray tracing projection images for a phantom gold crown at different angular orientations. [Figure 10C] FIG. 13 shows an axial view of the restoration of a phantom tooth with a gold crown using the basic attenuation restoration. [Figure 10D] FIG. 13 shows the reconstruction of a phantom tooth using the density of HA reference material. [Figure 10E] FIG. 13 shows the reconstruction of a phantom tooth using the density of titanium as a reference material. [Figure 11A] FIG. 1 shows a tooth with a metal crown. [Figure 11B] FIG. 11B shows an X-ray projection image of the tooth of FIG. 11A. [Figure 11C] FIG. 2 shows restoration under HA density. [Figure 11D] FIG. 13 shows a reconstruction using Ti density. [Figure 12A] FIG. 1 shows a tooth reconstruction from an imaging phantom simulating a gold-filled cavity embedded in HA material. [Figure 12B] FIG. 1 shows a tooth restoration with an amalgam cavity. [Figure 12C] FIG. 13 shows a restoration of a phantom dentition created using total attenuation, having both gold and amalgam fillings along with gutta-percha fillings and titanium posts. [Figure 12D] FIG. 13. Reconstructions made using HA basal density. [Figure 12E] FIG. 13 shows a reconstruction formed using Ti ground density to separate gold and Ti features from less dense structures. [Figure 13A] 1 shows photographs of teeth with metal fillings imaged relative to different reference materials using the method of the present disclosure. [Figure 13B] FIG. 13 is a reconstructed image of a tooth produced using total attenuation. [Figure 13C] FIG. 1 shows reconstruction of dental bone tissue using the density of HA reference material. [Figure 13D]FIG. 13 shows the reconstruction of metal fillings using the density of titanium as a reference material. [Figure 14A] FIG. 1 illustrates reconstruction using conventional attenuation imaging. [Figure 14B] FIG. 1 shows reconstruction for soft tissue visualization using soft tissue (ST) reference material. [Figure 14C] FIG. 13. Reconstruction for soft tissue visualization using a blend of ST and HA densities. [Figure 15A] FIG. 13 shows a reconstruction of a polyethylene block with water-filled pores produced using lower energy spectral image content. [Figure 15B] FIG. 13 shows restoration for a polyethylene component with water removed from the image content. [Figure 15C] FIG. 1 shows the resilience to moisture of a segmented polyethylene block. [Figure 16A] FIG. 13 shows projection images of a head phantom acquired using ST as the reference material. [Figure 16B] FIG. 1 shows projection images of a head phantom acquired using a 50% ST-50% HA composite. [Figure 17A] FIG. 13 illustrates an exemplary acquisition parameter setting screen. [Figure 17B] FIG. 1 illustrates an exemplary material parameter setting screen according to an embodiment of the present disclosure. [Figure 18] FIG. 13 illustrates an exemplary decomposition selection screen for selecting aspects of projection decomposition at a level of detail. [Figure 19] FIG. 13 illustrates an exemplary decomposition selection screen for selecting aspects of projection decomposition at a level of detail. [Figure 20] FIG. 1 is an illustration of multiple channels that can be applied to a single spectral scan. [Figure 21] FIG. 13 illustrates a composite user interface display that allows channel selection and different views of acquired image content. [Figure 22]FIG. 13 illustrates an operator interface that uses a mouse or other pointer to scroll through data by channel number. [Figure 23] FIG. 13 illustrates an alternative method of user channel selection using icons. [Figure 24] FIG. 1 illustrates how channel parameter selection can be used to provide improved segmentation. [Diagram 25] FIG. 1 illustrates the selection of specific channels that allow visualization or removal of specific materials in 2D or 3D views. [Figure 26] FIG. 13 illustrates a hypothetical removal of sealant material deposited on a dentition. [Figure 27] FIG. 1 illustrates the virtual removal of repair material. [Figure 28] FIG. 13 is a diagram showing an example of virtual tooth extraction. [Figure 29] FIG. 1 shows an example with virtual tooth extraction as an aid to root canal treatment. [Diagram 30] FIG. 1 illustrates virtual orthodontic removal in orthodontic treatment. [Diagram 31] FIG. 1 shows a representation of separated or decomposed calcifications and soft tissue. [Diagram 32] FIG. 13 shows material separation displayed with highlighting of alveolar bone structure. [Diagram 33] FIG. 1 illustrates the virtual removal of dentures and surgical guides in restorative dentistry. [Diagram 34] FIG. 1 illustrates different 3D renderings of different materials for different types of anatomical structures. [Diagram 35] FIG. 1 is an exemplary 3D rendering of intra-oral features. [Diagram 36] FIG. 1 illustrates the use of spectral enhanced imaging in bone grafting for repair and implant procedures. [Figure 37] FIG. 13 shows imaging for evaluating osseointegration. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Following below is a detailed description of exemplary embodiments, reference is made to the drawings in which like reference numerals identify like structural elements in each of the several views. As used in the context of this disclosure, the terms "first," "second," and the like do not necessarily indicate any relationship with respect to order, sequence, or priority, but are merely used to more clearly distinguish one step, an element, or a set of elements from another, unless otherwise specified.

[0020] In the context of this disclosure, the terms "pixel" and "voxel" may be used interchangeably to refer to individual digital image data elements, i.e., single values ​​representing measured image signal intensity. Conventionally, individual digital image data elements are referred to as voxels in the case of three-dimensional volumetric images, and pixels in the case of two-dimensional images. Volumetric images, such as images from a CT or CBCT device, are formed by acquiring multiple 2D images consisting of pixels taken at different relative angles, and then combining the image data to form corresponding 3D voxels. For purposes of description herein, the terms voxel and pixel refer to image element datums that can be considered equivalent overall and can have a wide range of numerical values. Voxels and pixels have the attributes of both spatial location and image data code value.

[0021] In the context of the present invention, the terms "digital sensor" and "digital detector" are considered equivalent and refer to the panel that acquires image data in a digital radiography system.

[0022] The term "highlighting" of a displayed feature has its conventional meaning as understood by those skilled in the art of information and image display. Generally, highlighting uses some form of local display enhancement to attract the viewer's attention. Highlighting of a portion of an image, such as an individual organ, bone, or structure, or the path from one cavity to the next, can be accomplished in any of a number of ways, including, but not limited to, displaying a note, displaying nearby or overlapping symbols, drawing an outline or trace, displaying in a different color or significantly different intensity or grayscale value from other image or information content, flashing or animating a portion of the display, or displaying with greater sharpness or contrast.

[0023] An "adjusted" image has been modified in some way by image processing software, such as to enhance or suppress the visibility of various imaged features according to material composition as described herein. The term "technique" is a technical term in radiography and relates to exposure settings and adjustments for acquiring an X-ray image.

[0024] The schematic diagram of Figure 1 shows an extraoral scanning imaging device 100 that can be used for 2D or 3D imaging of teeth and other intraoral features. In 2D imaging, a single image can be acquired, or multiple 2D images can be acquired, such as in panoramic imaging, where a series of two or more 2D images are acquired and images of adjacent content are arranged to form a larger image. For 3D imaging modes, such as tomography, computed tomography volumetric imaging, or cone beam computed tomography (CBCT) imaging, multiple 2D images are acquired sequentially and used to reconstruct features for dental, ENT, and related head imaging applications.

[0025] In the schematic diagram of Fig. 1, a rotatable mount 130 is provided on a column 118, preferably adjustable in height to accommodate the size of the patient 12. The mount 130 maintains an X-ray source 110 and a radiation sensor 121 on either side of the patient's 12 head, and optionally rotates to orbit the source 110 and the sensor 121 in a scanning pattern around the head. The mount 130 rotates about an axis Q that corresponds to a central portion of the patient's head, and thus the components mounted on the mount 130 orbit around the head. A sensor 121, a photon-counting sensor according to an embodiment of the invention, is coupled to the mount 130 on the opposite side of the X-ray source 110 that emits a radiation pattern suitable for 2D imaging, tomosynthesis imaging, or CT or CBCT volumetric imaging. An optional head support 136, such as a chin rest or bite element, provides stabilization of the patient's head during image acquisition. A computer 106 has an operator interface 104 and a display 108 for accepting operator commands and displaying volumetric images acquired by the imaging device 100. The computer 106 provides signals for controlling the source 110 and, optionally, the rotational actuator 112 for the components of the mount 130, in signal communication with the sensor 121 for acquiring image data. One or more height sensors 134 are also sensed by the computer 106 to obtain an initial height setting and to track the relative vertical displacement of the sensor 121 with respect to the patient's head during the helical scan. The computer 106 is also in signal communication with a memory 132 for storing image data. An optional alignment device 140 is provided to assist in proper alignment of the patient's head for the imaging process. The alignment device 140 may include a laser that provides one or more line references for positioning the head according to an embodiment of the present invention. In alternative embodiments, the alignment device 140 includes a visible light beam or other marker, or a mechanical or other positioning device. The imaging device 100 may also have the capability of panoramic or cephalometric imaging using the x-ray source 110 and sensor 121 or other imaging sensor.

[0026] There may be multiple variable scan patterns depending on the imaging type required. For example, tomosynthesis typically uses less than 180 degree scanning around the patient. CBCT scanning may require a helical scan pattern with one or more rotations around the patient's head. An optional adjustment mechanism 142 is provided to adjust the source-to-image (SID) distance between the x-ray source 110 and the sensor 121 to tailor the scan pattern to different patients or imaging types.

[0027] As previously discussed in the background section, conventional radiography provides image content based on the attenuation coefficients along each path of the x-ray beam. In images with multiple different materials, such as dental x-ray or cephalometric images, conventional x-ray provides very limited information about the materials in the imaging path. Conventionally used integrated x-ray sensors are spatially digitized and provide an analog output that represents the accumulated charge received for each pixel during the exposure interval. This imaging method is typically susceptible to noise.

[0028] Spectral X-ray imaging uses an alternative approach to image capture in which radiation across a relatively broad spectral range, or radiation in two or more energy ranges, is directed through an object. Each energy range is detected at a pixel or other region, and the combination of received energies can be used to characterize the material composition of the object in that region.

[0029] Notable types of spectral, polychromatic, or "color" x-ray imaging include: (i) dual-energy imaging, in which two x-ray images of the same target anatomy are acquired in rapid succession, each at a different energy level, and the images are merged; and (ii) photon counting, which counts incoming X-ray photons above and below different thresholds to provide image data for each pixel; Includes:

[0030] The embodiments of the present disclosure can use either dual energy or photon counting x-ray devices for dental imaging. Spectral x-ray imaging can provide accurate information about the actual density of the imaged material (e.g.,

number

[0031] Advantages of Photon Counting Spectral X-ray using photon-counting detector arrays provides low-cost and low-dose color X-ray imaging. Photon counting advantageously has high immunity to noise, provided the pulse intensity exceeds the background noise level. FIG. 2A shows a photon-counting sequence in schematic form. Incoming photons generate a pulse 80 at a predefined energy level. For each array location or "pixel", the energy of the pulse 80 is compared to a threshold by a comparator 82 and shaped by a pulse shaper 84 to form a shaped pulse 88. A counter 86 then records the pulse event and provides a digital output, a pulse count value 90. A separate pulse count value 90 is obtained for each pixel element in the array of the imaging sensor 70. The threshold value can be adjustable or selectable from a wide range of values, depending on the photon energy of interest. Photon-counting X-ray detectors provide suitable performance at low signal levels, thus allowing the X-ray dose given to the patient to be reduced.

[0032] A further advantage of pulse counting relates to its ability to count pulses 80 at multiple thresholds at each pixel location. With reference to the schematic diagram of FIG. 2B, two comparators 82a and 82b are shown for measuring pulse energy. In this particular configuration, comparator 82a, pulse shaper 84a, and counter 86a provide values ​​of count 90a for all pulses received at that pixel location with energies above a first threshold, and similarly comparator 82b, pulse shaper 84b, and counter 86b indicate only pulse energies above a higher second threshold and provide count 90b accordingly. A simple subtraction then identifies the different power levels achieved for each pulse. It will be appreciated that a corresponding arrangement of comparator circuits can be used to measure three or more threshold levels at a pixel, allowing pulse counts corresponding to photon energies in an energy range defined by any of the multiple thresholds. In addition, some systems allow the thresholds to be selectable, such as adjustable to fine-tune the response of the imaging sensor 70 to various photon energy levels. Thus, for example, an operator may use a set of pre-set thresholds to differentiate between softer tissue and denser tissue in the final conditioned image.

[0033] The graph in FIG. 3 shows an arrangement of six energy bins 150 defined across an energy (keV) range. The boundaries and width of each bin 150 are selected to facilitate material characterization in response to incident x-ray energy. An embodiment of the present disclosure may provide one or more default bin distributions selectable by an end user according to the type of exam or patient condition. An embodiment of the present disclosure may alternatively use information from imaging results to specify or adjust the kV thresholds that define the boundaries of the bins 150.

[0034] In addition to setting a minimum threshold, embodiments of the present invention can also provide the option of measuring photon energy using an upper or maximum threshold for enumerating photons. This capability can be used for multiple functions, including reducing the generation of excessive noise signals from metal artifacts or x-rays passing directly through the detection material.

[0035] As explained with reference to FIG. 2B, the ability to distinguish and count photons of different energy thresholds allows the sensor to differentiate between energy levels obtained from illuminating the object, providing an additional dimension to the image data provided as a result of each exposure. This ability is described as multispectral or "color" x-ray imaging and allows information to be obtained about the material composition of the object pixel. As shown for a typical metal in the simplified graph of FIG. 4A, two materials A and B have different attenuation coefficients μ, which vary with the radiation energy level shown as exposure E. At a given exposure value shown as a KeV value, material A attenuates photons with an energy absorption corresponding to material A, as shown by value A1. Similarly, radiation hitting material B attenuates photons with an energy corresponding to material B, as shown by value B1. This variable characteristic of the imaged material can be considered a kind of spectral "signature" for the material, which will be used as described later in this disclosure. If these photons of different energy values ​​can be differentiated from each other, it is possible to identify one or both materials within the same pixel or voxel image element of the acquired image. This same fundamental behavior in response to radiation also allows some ability to differentiate between tissue and material types.

[0036] As an example, the graph in FIG. 4C shows the relative attenuation coefficient for two different bone densities. The graph in FIG. 4D shows curves of the relative attenuation coefficient for water, bone, and calcium. Over a wide range of keV values, steepness of the curve indicates higher attenuation and therefore material inclusions. As FIG. 4C and FIG. 4D suggest, different linear absorption characteristics allow differentiation of various types of tissues, such as bone types, and different types of materials.

[0037] One major difference from conventional larger area image detection is that photon counting architectures generally use reduced size image detectors and typically require scanning sequences even when only 2D images are acquired. For volumetric or 3D imaging, such as the sequences required for CT or cone beam CT (CBCT) imaging, it may be necessary not only to scan in the same plane but also to provide a three-dimensional helical scan in addition.

[0038] Example Applications The enhanced information made available using spectral radiography allows for the ability to perform image adjustments such as virtual material removal as described herein, as well as improved results in material identification and mapping, more precise segmentation, improved 3D reconstructions, and more accurate material decomposition data, which can be used to address multiple dental procedures and conditions, including: Root canal geometry assessment, allowing visualization with removal of root canal filling material from the image content and allowing visibility of the inner surface of the root canal; -Evaluation of implant osseointegration by visualizing bone structures distinct from integrated titanium features; · Visualization of tooth structure with crown removal to accommodate endodontic treatment; · Cavity assessment by visibility of tooth structure separate from filling material; Soft tissue only images for root canal and pulp chamber evaluation, Soft tissue only images for gingival assessment, Cephalometric analysis with soft tissue and bone / tooth only images; Visualization of intraoral features where braces or other prosthetic devices have been removed; Bone structure assessment, including the ability to characterize bone mineral density and other features of overall bone health; Graft volume assessment, Improved identification of materials used in various types of treatments, including, for example, metals, ceramics, plastics, and sealants, as well as precise information about the spatial positioning of various features for use in generating and updating patient chart data; · highlighting of substances used in the mouth according to type, 3D reconstruction for visualization of features according to material type, Implant interface evaluation, and Visualization in 2D or 3D according to material profiles or "channel" settings, Measuring the dimensions of the implant or the bone in which the implant is inserted; Measurement of the dimensions of the filling material or tissue filled or proposed to be filled.

[0039] Various Image Types The types of radiographic images that can be acquired and used for improved material characterization using embodiments of the present disclosure include: Scout images acquired by 3D dental scanner, Panoramic images, Tomosynthesis images acquired with a fixed detector and by moving the source (or using multiple source foci); Intraoral imaging with a detector held in the patient's mouth, Intraoral tomosynthesis images, A portion of the reconstructed volume, such as an axial, coronal, or sagittal view, or any slice of any orientation, from the reconstructed volume of an image from a 3D scan; and Head measurement image may include.

[0040] Application of the ALARA principle Embodiments of the present disclosure can help address the principle of "as low as reasonably practicable" (ALARA) dose for radiation imaging. For example, the use of low-dose scout images can provide substantial information regarding intra-oral features and material composition of fillings and prostheses, thus keeping dose levels for the entire imaging sequence as low as possible.

[0041] Profile or "Channel" Settings The embodiments of the present disclosure take advantage of the spectral "signatures" available for different natural materials used to replace, adjust, repair, or restore intra-oral features that can be imaged using radiography tools, as well as processed or prepared artificial or "engineered" materials. As briefly illustrated in the exemplary graphs of FIGS. 4A-4D, different materials exhibit different levels of attenuation for various wavelengths of X-ray energy, or alternatively, various photon energy levels. Thus, considering the graph of FIG. 4A for example, it is possible to determine the material composition of a subject by analyzing its attenuation over a wide range of wavelengths, and to distinguish subject materials "A" and "B," for example, to distinguish one metal from another, one type of biological tissue from another, or one composite filling material type from another composite filling material type.

[0042] The variable attenuation caused by spectral X-ray exposure across the spectrum, or even across specific portions of the spectral region, is characteristic of each imaged material, whether it is naturally "intrinsic" to the oral anatomy, or somehow processed, treated, shaped, and constructed from suitable materials and permanently or temporarily positioned within the mouth. The embodiments of the present disclosure take advantage of an additional dimension of spectral imaging by enabling the use of channels. A channel can be considered as a predefined area mapping optimized to collect and measure photon energy across a sufficient number of energy levels to characterize the material content of the imaged object. From a related aspect, a channel can refer to a density profile, where the spectral response to one or more density values ​​is characteristic of the reference material. The channel mapping can enable the observer to distinguish both natural and synthetic materials from each other. According to one embodiment, each channel identifies a specific combination of one or more reference materials used in the material decomposition processing of the resulting image.

[0043] Considering the simplified attenuation coefficient graphs for materials A and B in FIG. 4A, it can be seen that collecting photon data at a particular threshold can provide sufficient information to characterize and distinguish material A from B within a given object. Using this capability, channels can be set up that identify unique energy "bins," each bin defining a unique energy range for collecting photon data, which also provide the data required for the material decomposition process to identify materials, as well as for use in display enhancement and restoration.

[0044] A channel can alternatively be considered as an arrangement of reference materials or energy bands used as reference coefficients for material decomposition. The channel provides a means for interpreting relative photon energy levels as they relate to specific materials within the imaged object. As known to those skilled in the art of photon counting technology, material decomposition can be performed by analyzing energy information obtained at different photon energy levels obtained using the channel features described herein.

[0045] The channel set thus defines an arrangement of spectral regions sufficient to characterize one or more substances within the acquired image content according to photon energy levels and quantization settings. How these channels can be used advantageously is described in more detail later in this disclosure. The steps for channel setup are: (i) defining a number of energy bins for photons detected when irradiating a material; (ii) relating the defined arrangement of energy bins to a set of reference materials that serve as benchmarks for the imaged materials; (iii) relating these reference materials to actual materials found in the oral environment, whether naturally occurring (bone, teeth, or other tissues) or not native to the oral environment, such as man-made or engineered materials and features; (iv) storing the resulting values ​​obtained from steps (i)-(iii) as decomposition coefficients for processing the intraoral radiography image content.

[0046] According to one embodiment of the present disclosure, channel settings can have multiple default settings assigned at the time of manufacture, and these settings can be modified by a physician at a specific location to make the channel more useful for a particular patient or performance requirements.

[0047] Spectral radiography can also utilize the k-edge material response for various materials subjected to incident radiation, as shown in Figures 4A and 4B. Elements such as barium, hafnium, and gold exhibit a characteristic steep k-edge response at characteristic radiation energies. The k-edge is 34.7 kV for barium, 65.35 kV for hafnium, and 80.72 kV for gold. This response can be useful in identifying the presence of materials such as barium, hafnium, or gold in, for example, dental coatings or sealants or other materials.

[0048] Substance of interest In addressing the above and other dental applications where visualization according to material type may be useful, there are several different materials of particular interest for dental radiography, both intrinsic to the anatomical structure and processed and added temporarily or permanently, including soft tissue, bone, tooth enamel, gutta-percha, sealants, veneers, and various polymers, compositions, ceramics, and metals. Within this set, each of these types of materials has a corresponding spectral range that is optimal for characterization in radiography, both for 2D radiography and acquisition of 2D projection images, typically expressed in KeV, and used for subsequent 3D reconstruction and material decomposition processing, providing information about the material composition of various features. The embodiments of the present disclosure are directed to certain materials among a portion of materials typically used in dental treatment and medicine, both for acquisition and subsequent processing and visualization. This includes, but is not limited to, the materials listed in Table A.

[0049] As a practical approach to characterizing imaged materials typical of the intra-oral environment, embodiments of the present disclosure may use a set of two or more reference materials as a reference set for determining energy levels for X-ray exposure based on the energy detected from the exposure, and as coefficients for performing the processing required for material decomposition processing. The reference materials provide a known standard against which certain measurements of the imaged sample can be evaluated. In practice, the approach used in embodiments of the present disclosure accommodates the selection of the reference materials through energy binning and corresponding quantization.

[0050] Unlike other forms of intraoral imaging, an embodiment of the present disclosure facilitates detection and differentiation of sealants, including glass ionomers (acid-base reactive), resin-modified glass ionomers, polyacid-modified resins (compomers), and composite resins. Spectral imaging can be used to distinguish non-eugenol sealants, including calcium hydroxide-based, resin-based, solvent-based, nogenol-based, silicone-based, calcium phosphate-based, urethane methacrylate-based, and MTA-based sealers, from eugenol sealers. Some types of eugenol sealers include sealers containing zinc oxide eugenol, Kerr-Pulp Canal Sealer from Kerr Corporation, Brea CA, Grossman's sealer, TubliSeal™ from Kerr Corporation (SyberonEndo), Brea, CA, Endofill Root Canal Filling Material from Dubai Medical Equipment, Sharjah, UAE, and Zical® Root Canal Sealant from Prevest Denpro (Bahadurgarh, Haryana, India).

[0051] [Table 1]

[0052] Denture materials that can be detected using the techniques described herein can include hard rubber, nitrocellulose, chrome cobalt, porcelain, and various synthetic resins.

[0053] Typical restorative materials may include, for example, gold, porcelain, composite resins, amalgams, ceramics, and zirconia.

[0054] Gutta percha is a polymeric product derived from plants that is processed through an extraction and purification process that separates it from other substances.

[0055] How to use Basal Density Generally, spectral X-ray imaging by itself is not useful for accurate differentiation of different types of soft tissues and fluids due to the relatively close atomic number values ​​for the predominant constituent atoms in these materials, such as carbon (6), nitrogen (7), and oxygen (8). The use of reference materials helps to compensate for this problem in the material breakdown process.

[0056] The reference material provides a useful basis for relating the signal acquired from the measured energy attenuation (i.e., the number of photons acquired) to the relative density of the material. Decomposition using different soft-tissue-like reference materials helps to enhance the usefulness of the signal content for distinguishing various types of soft tissue from one another. The resulting images can be noisy, but noise reduction methods allow some correction to compensate for these effects.

[0057] Reference material images can be used to automatically detect regions of distinctive soft tissue types. 2D imaging modalities are particularly beneficial because overlapping bone and dental inclusions can be easily removed from the images.

[0058] Table B lists exemplary reference materials and corresponding materials for typical applications. The decomposition process can be performed according to these or other suitable reference materials, each of which provides a useful reference for relating acquired photon energy levels and photon counts to specific materials in an image.

[0059] [Table 2]

[0060] Imaging sequence 5A-5F are flow diagrams illustrating a sequence of steps for acquiring and processing image content for material and feature characterization according to one embodiment of the present disclosure. The exemplary process illustrated in FIG 5A provides an overview of the imaging process according to one embodiment of the present disclosure.

[0061] 5A, a setting step S500 sets the energy level for photon counting, which includes defining the number of bins 150 (FIG. 3) and the energy range associated with each bin as determined by an energy threshold setting. Step S500 can also include defining radiography technique settings for acquiring image content.

[0062] An object to be imaged (alternatively referred to as a "target" for imaging) is exposed by a radiography system and corresponding image data is collected in an acquisition step S510. A material characterization step S520 then provides a decomposition calculation for the acquired image data. The decomposition logic may use, for example, a variable set of reference materials. A processing step S536 processes the data for 2D or 3D display according to the acquired data content. An evaluation step S570 then enables manual or computer-assisted evaluation of the patient's condition and treatment strategy relative to the processed image content.

[0063] Bin Settings The logic flow sequence of Figure 5B shows the setting step S500 in more detail. In a bin definition step S502, threshold settings are set that define the energy levels and resolution for the photon-counting detector. The threshold settings can be provided from stored preset values, and multiple sets of energy threshold settings are pre-prepared and indexed according to factors such as the patient's age and personal condition, physical size, medical and dental history, treatment indications, and other factors.

[0064] The patient chart can be used as input to the bin definition calculations, i.e., for energy threshold setting that corresponds to the bin boundaries. The presence of crowns or post-and-core appliances in the patient's mouth can help determine how best to measure the photon energy from the exposure process.

[0065] Alternatively, an initial low-dose scout image of the subject can be acquired and used to generate a rough determination of material composition for intra-oral features that is sufficiently accurate to define threshold settings for energy bins and to update patient chart data.

[0066] 6A illustrates, by way of example, the use of scout image content to populate a dental chart 160 for a patient, in addition to defining or adjusting thresholds for bins 150. The scout image allows the detection of stainless steel dams 152, gutta-percha points 154, and metal posts 156, which can be suitably enhanced or annotated to the chart 160. In the example of FIG. 6A, the dental chart 160 has been labeled by the system to indicate the location of materials detected from the scout image.

[0067] 6B shows another method that can be used to edit the bin-defining energy thresholds on a user interface associated with an X-ray imaging system. A set of selection buttons 170 allows for selection of default bin threshold settings according to specialization type or treatment. Alternatively, a manual adjustment interface 174 can be used, allowing the user to input values ​​that set or adjust the thresholds that define each bin. This mechanism can allow for adding or combining bins as needed, including, for example, technique settings.

[0068] In addition to the scout image, other image results may be used, such as recent images acquired from the same patient, etc. In an optional technique setting step S504, settings for the exposure current and voltage potentials to be used may be set or adjusted.

[0069] Image acquisition Following binning, an acquisition step S510 is then performed to generate one or more images of the subject patient, as shown in the diagram of Figure 5C. Depending on the imaging device used and the needs of the patient, various types of images can be acquired including, for example, static x-ray images, panoramic images, tomosynthesis projection images, intraoral images, intraoral projection images, and cephalometric images.

[0070] Material decomposition processing The image data includes attenuation information, which can be decomposed in a process to determine the type of naturally occurring or engineered material receiving the exposure radiation of the object. As shown in FIG. 5D, the processing required for material identification can then be performed in a material characterization step S520 in a decomposition step S522, and mapping and reporting is provided in a mapping and identification step S524. One or more reference materials 200 are defined to the image processing system as representative or "benchmark" materials for modeling the attenuation response of real materials in the object. For example, water can serve as a reference material for many types of body fluids and many types of soft tissue (ST) features, since soft tissue contains negligible mineral content, and hydroxyapatite (HA) can serve as a reference material for tooth or bone features. Often, values ​​from two or more reference materials are used to identify a particular material.

[0071] For purposes of describing the exemplary embodiments herein, the mineral content of bone-like tissue (e.g., bone-like tissue with varying mineral density) is preferably modeled by the mineral hydroxyapatite (HA), which serves as a useful reference material 200. However, the definition of the mineral content of bone-like tissue may vary. The density ρ of all points in the object is calculated by the density of the soft tissue (ST) and HA, ρ, respectively, as shown in Equation (1): ST and ρ HA has a density value which is the sum of multiplied by a weighting factor. ρ=f ST ρ ST +f HA ρ HA (1) In the above formula, the weighting factor f ST and f HA are decimal values ​​for soft tissue and hydroxyapatite, respectively.

[0072] Using the model expressed in equation (1), the x-ray attenuation coefficient μ of every point in the exposed object is given by equation (2).

number

number

number

[0073] In this example, HA and ST are used as two representative reference materials 200. It will be appreciated that any number of additional reference materials may be utilized to provide enhanced resolution to the material decomposition process. The corresponding calculations of the reference materials provided by the material characterization process of step S520 may be used to identify a collection or "library" of materials.

[0074] The mapping and identification of materials in the patient's mouth can be performed automatically and can provide the practitioner with an input dental chart. For example, this capability can provide a chart for a new patient or can be used to update an existing dental chart.

[0075] Display and Reporting Process Processing step S536 serves to provide further analysis for display with the acquired 2D image, as shown in more detail in FIG. 5E. In the case of a 3D volumetric image, the 2D image is a projection image, which is used to generate the volumetric image in a reconstruction process S538. The reconstruction process may further include a step of differentiating materials and highlighting areas of the image where different materials of interest may be present. Improved segmentation may enable 3D visibility according to materials, thus providing an image that includes or excludes only a desired set of materials, for example.

[0076] In the evaluation step S570, additional display and analysis tools may be provided to assist in identifying the patient's condition and planning treatment.

[0077] Example Workflow for Material Removal 5F shows an exemplary logic flow for a material removal process in a radiographic scan. The process uses spectral imaging to characterize the material inclusions of an imaged object using photon counting S580 according to attenuation data in two energy regions acquired in the scan step S500. A single threshold is used to define a lower energy bin 50 for capturing photons with energies below the threshold and a higher energy bin 52 for photons with energies above the threshold. Photon attenuation at two or more different energy levels can then be used to characterize the material inclusions of each portion of the object.

[0078] The acquisition of photon energy itself can involve scanning the image by applying a suitable spectral range of X-ray energy, including lower and higher energy values. Other scanning methods can include alternating lower and higher energy values ​​within the same scan, or applying different energies in separate successive scans. However, the photon counting method is advantageous because it allows the collection of spectral data in a single scan of an intraoral object by applying exposure energy distributed over a wide spectral range and detecting energy decay according to the measured relative energy levels. Although two energy levels are shown in the sequence of FIG. 5F, the photon counting detector can allow the use of multiple thresholds and can allow the use of additional bins to measure photon data at additional energy levels.

[0079] The next part of the sequence relates to the selected reference material and processing the acquired image content according to the reference material.In a material characterization step S520, the photon data is used to determine the material composition according to the acquired image content.

[0080] In the example of Figure 5F, two reference materials are defined for mapping corresponding attenuation data. In a density calculation step S584, density information is obtained for the first reference material. In a density calculation step S586, density is obtained for the second reference material. Then, in a material removal step S588, segmentation and visualization or removal of materials in the acquired or reconstructed image is performed.

[0081] By "removal" is meant the masking or suppression of image data content specific to a particular material or group of materials. The removal process involves, for example, identifying individual pixels believed to represent the material of interest. The values ​​for these pixels are adjusted to normalize the pixels to the surrounding content so that features formed by the material of interest are not visible or are sufficiently suppressed to allow visibility of the surrounding features. This can be equivalent to varying the opacity of the pixels or voxels of the image, for example adjusting the opacity to a very low value or zero transparency.

[0082] The overall sequence of FIG. 5A allows for multiple alternatives suitable for imaging various types of materials in acquiring both 2D and 3D images. In the scan step S500, the operator can select two or more appropriate energy levels for material discrimination based on the imaging type and material of interest. For example, a lower energy value used for bin 50 can be optimized for imaging soft tissue. A higher energy value used for bin 52 can be optimized for bone.

[0083] Following acquisition, image processing of FIG. 5F proceeds to use two reference materials selected for the particular imaging application. The two reference materials are typically selected from water, soft tissue, bone, tooth enamel, gutta-percha, and a collection of various ceramics and metals, as previously described. One selected reference material has a lower attenuation coefficient and a lower density. Processing on the lower density reference material can distinguish the selected material and materials of relatively lower density than the selected material from materials of higher attenuation.

[0084] Other selected reference materials have higher attenuation coefficients and higher densities, and processing on the higher density reference materials can distinguish the selected material and materials with relatively higher attenuation than the selected material from materials with lower densities.

[0085] 5A-5F works best when the practitioner has at least some prior knowledge regarding the different materials present in the mouth being examined. This information helps tailor various aspects of the image acquisition process, including, for example, the selection of reference materials and corresponding energy levels.

[0086] The sequence of Figures 5A-5F has been illustrated and described with respect to dual energy acquisition. The scanning and acquisition applies lower and upper energy thresholds to the received photon energy, such that all photons related to materials below the lower threshold contribute primarily to the less dense material image content, and all photons corresponding to materials above the upper threshold contribute primarily to the more dense material image content. A similar sequence applies to photon counting techniques that use three, four, or more energy levels to characterize intra-oral features of various materials. The use of additional energy levels can allow for greater accuracy and differentiation of more types of materials. Each energy level used has a corresponding reference material.

[0087] Various materials can be distinguished according to their relationship to the reference material. The following example shows the results of processing image data acquired according to different sets of reference materials.

[0088] 3D volume reconstruction The 3D volume reconstruction can be performed in one of two ways for material removal. Using one approach, material segmentation and / or removal is applied to the acquired 2D projection images prior to reconstruction. The processed 2D projection images can then be used to form a reconstruction for the selected material type. In an alternative approach, a volume reconstruction can first be performed using photon attenuation information for all material types, followed by decomposition of the 3D volume using discrimination according to reference materials.

[0089] It will be appreciated that the combination of reference materials used for image processing can be changed following image acquisition, as shown in the example of Figure 5F. Thus, for the same image content, a portion of the reference materials can be used for optimizing image acquisition, and then a different portion of the reference materials can be used for material decomposition processing. This allows flexibility for acquiring and processing image data under variable conditions, allowing different views and applications of the acquired image content.

[0090] Target material separation in 2D projection The embodiments of the present disclosure allow clear identification of various tissues and synthetic materials, and allow these materials to be distinguished from each other in the projection image content. Such identification of individual materials can then be used for subsequent 3D volume reconstruction. Figure 6C shows a sequence of applying decomposition to 2D projection images to generate material-separated projection images. The reconstruction process then uses the multi-channel volume data to generate 3D volume content.

[0091] The decomposition can also be provided according to user selection, as shown in the example user interface of FIG. 6D. One or more menu selections can provide the required information for the reference material and threshold definition used in the material decomposition. The restoration can then be selectively applied to desired portions of the multi-channel data from the material separated projections.

[0092] Exemplary Results – Root Canal Geometry Assessment FIG. 7A shows a schematic diagram for a dental phantom scanned using spectral X-rays to generate the 3D volumetric reconstructions depicted in FIG. 7B, FIG. 7C, and FIG. 7D. The phantom shows for a tooth 30 a pulp chamber filled with gutta-percha material and a root canal structure with the same gutta-percha material. FIG. 7B shows a conventional 3D attenuation reconstruction from a volumetric imaging device such as that shown in FIG. 1, obtained from a set of projection images acquired with X-rays at a single energy level. As can be clearly seen, the imaging technique and X-ray energy used are more closely optimized for gutta-percha material rather than tooth or metal material. The features and edges of the tooth structure are less distinct.

[0093] Figures 7C and 7D show examples of reconstructions produced when using the spectral X-ray imaging technique by processing two different reference materials. Figure 7C shows a 3D volume reconstruction obtained with HA (hydroxyapatite), the material permeating different levels with respect to the dental bone and enamel. Figure 7D shows a reconstruction produced using titanium (Ti) as the reference material.

[0094] Figures 8A and 8B show examples of restorations from teeth with gutta-percha material. The gutta-percha filling material can be removed for evaluation of the root canal geometry as shown in the example images. Figure 8A shows a photographic image of the tooth with gutta-percha points inserted for reference.

[0095] FIG. 8B shows an axial view from a lower energy spectral reconstruction. The top image in FIG. 8B shows a portion of a tooth showing tooth enamel with an associated attenuation coefficient of cm -1 The bottom image in Figure 8B shows the unit of 1.99 cm -1 Gutta-percha in and 0.77 cm -1 A comparison with dentin material in is shown.

[0096] Figure 8C shows axial views from the tooth restoration of Figure 8A using different reference materials. The image on the left is from total attenuation and no photon energy threshold is considered. The image restoration in the middle uses soft tissue (ST) as the reference material. The restoration on the right uses the indicated percentages of ST and HA materials.

[0097] Figure 8D shows a coronal view from the tooth restoration of Figure 8A using the set of reference materials used in Figure 8C. The image on the left is from total attenuation and no photon energy threshold is considered. The image restoration in the middle uses soft tissue (ST) as the reference material. The restoration on the right uses the indicated percentages of ST and HA materials.

[0098] Exemplary Results – Titanium Post Visualization 9A-9D show examples of titanium (Ti) segmentation and removal, such as those useful for implant osseointegration assessment. Metal artifact reduction has been applied. FIG. 9A shows a phantom placement for a titanium post partially located within a SiO2 crown. FIG. 9B is a conventional reconstruction based on attenuation in the full spectral range.

[0099] 9C and 9D show example reconstructions for a representative Ti / SiO2 structure in a phantom using HA and Ti densities, respectively.

[0100] Exemplary Results - Visualization of Tooth Structure Under Metal Crown Due to its large atomic number (79), gold has very high photoelectric absorption, making it difficult to image crowns and other structures with gold inclusions, as well as features adjacent to such structures. Figure 10A shows a dental phantom arrangement used to image a gold crown positioned adjacent to tooth material.

[0101] FIG. 10B shows ray tracing projection images for the phantom gold crown on tooth #1 at different angular orientations using a 14-bit detector.

[0102] FIG. 10C shows an axial view of the restoration of a phantom tooth with a gold crown using a base attenuation restoration.

[0103] FIG. 10D shows the reconstruction of a phantom tooth using the density of the HA reference material.

[0104] FIG. 10E shows the reconstruction of a phantom tooth using the density of titanium as a reference material.

[0105] 11A-11D show images of metal crown restorations for endodontic treatment. FIG. 11A shows a tooth with a metal crown. FIG. 11B shows an X-ray projection image for the tooth in FIG. 11A. FIG. 11C shows a restoration under HA density. FIG. 11D shows a restoration using Ti density. FIG. 10E shows a phantom tooth restoration using titanium as the reference material.

[0106] FIG. 11A shows a tooth with a metal crown.

[0107] FIG. 11B shows an X-ray projection image of the tooth of FIG. 11A.

[0108] Figure 11C shows a tooth restoration using HA as the base density, and Figure 11D shows a restoration of similar content using Ti density.

[0109] Exemplary Results - Visualization for Caries Assessment with Virtual Filling Removal A useful feature of the methods described herein relates to the ability to visualize the filling material separately from its corresponding cavity structure and surface. Figure 12A shows a tooth from an imaging phantom simulating a gold-filled cavity 20 embedded in HA material. Figure 12B shows a similar amalgam cavity 22.

[0110] 12C shows a restoration of a phantom dentition created using total attenuation, having both gold and amalgam fillings with gutta-percha fillings and titanium posts. As can be easily seen, features are presented but cannot be easily distinguished from the surrounding tooth structure.

[0111] Figure 12D shows a restoration created using HA base density, where features having bone density are evident and more easily distinguishable from metal and other features.

[0112] FIG. 12E shows a reconstruction formed using the Ti ground density to separate the gold and Ti features from the less dense structures.

[0113] FIG. 13A shows photographs of a tooth with a metal filling imaged relative to different reference materials using the method of the present disclosure.

[0114] FIG. 13B shows a diagram of a reconstructed image of a tooth produced using total attenuation.

[0115] FIG. 13C shows reconstruction of dental bone tissue using the density of HA reference material.

[0116] FIG. 13D shows the reconstruction of the metal filling using the density of titanium as a reference material.

[0117] Exemplary Results - Soft Tissue Only Assessment Benefits of the methods of the present disclosure relate to enhanced capabilities for imaging of soft tissues, such as for evaluation of root canals and pulp chambers as well as evaluation of gingiva.

[0118] FIG. 14A shows the reconstruction using conventional attenuation imaging.

[0119] FIG. 14B shows a reconstruction for soft tissue visualization using a soft tissue (ST) fiducial.

[0120] FIG. 14C shows restoration for soft tissue visualization using a blend of ST and HA densities.

[0121] Gingival assessment requires the ability to accurately and precisely characterize tissue density. An embodiment of the present disclosure is able to more clearly distinguish tissue densities as shown in the simulated examples of Figures 15A-C. The object is a polyethylene block with water-filled pores. Figure 15A shows a reconstruction of the object produced using lower energy spectral image content. Figure 15B shows a reconstruction for the polyethylene component with water removed from the image content.

[0122] FIG. 15C shows the recovery to moisture of a segment made from a polyethylene block.

[0123] Spectral X-rays allow to create virtual monochromatic reconstructions at high energies where the material contrast is high. The difference in attenuation between PE (polyethylene) and water is 12% in low energy spectral reconstructions and 24% in the virtual monochromatic range at 30 kV.

[0124] Virtual Material Removal for Panoramic and Cephalometric Image Content According to an embodiment of the present disclosure, the virtual material removal method can also be applied to panoramic and cephalometric image content. As an example, FIG. 16A shows a projection image of a head phantom acquired using ST as a reference material. FIG. 16B shows a projection image of a head phantom acquired using a 50% ST-50% HA composite. The combined results of the ST and HA reconstructions are then displayed. The combination can include adding, weighting, averaging, and other methods for calculating an image density value from multiple related values.

[0125] User Interface Features As shown in FIG. 17A and in the examples below, a graphical user interface (GUI) can be provided for configuring scan acquisition settings, decomposition variables, and display options.

[0126] 17A illustrates an exemplary acquisition parameter setting screen 1600 according to one embodiment of the present disclosure. A bin assignment section 1610 allows a user to set an energy threshold (kV) for each of a number of energy bins for the photon counting system. As previously mentioned, the bin energy levels relate to the reference material selected for exposure and subsequent decomposition functions. The screen 1600 may also display the tube voltage and allow adjustment of the current value for the exposure device.

[0127] Multiple pre-set acquisition parameters may be available for selection and may be prepared according to the patient's size, age, or other characteristics, or according to the particular type of information required by a particular specialist, as shown in the screen of Figure 16. Thus, for example, separate sets of default parameters may be available for child or adult patients, or for periodontists, orthodontists, oral pathologists, oral surgeons, and other specialists. The pre-sets may include bin thresholds, which may be adjustable, for example, by the operator.

[0128] The acquisition parameter setting screen 1600 may also include an anatomical structure selection section 1620 that allows the operator to specify areas of the mouth or jaw that are of particular interest. With a mouse click or other selection mechanism, the operator selects a particular anatomical structure, which is highlighted on the display. The selected area may be used, for example, by the system to adjust pre-set thresholds.

[0129] An optional display area 1630 may show the currently acquired image or a previous image of the area of ​​interest specified by the operator.

[0130] Channel Settings As previously indicated, a channel is used that provides a convenient tool for characterizing a larger set of materials using a smaller set. The larger set of materials is found within the oral environment and includes many types of metals, ceramics, polymers, and composite materials, as well as various types of hard and soft tissues. The smaller set of reference materials has known properties for incident radiation in the x-ray spectrum.

[0131] The channel setup allows profiling of materials according to their spectral response in two or more reference materials. For intra-oral materials, the relative weightings or percentages from two or more reference materials can be used for the setup of acquisition parameters as well as for the decomposition processing and display functions.

[0132] A number of default channels are provided for typical combinations of reference materials. A user interface utility allows channel settings, prompting the user to specify a channel name (e.g., "7", "Gingival Tissue, Adult", "Composite Filler") and the corresponding weights, ratios, or percentages (e.g., HA:8, ST:2) assigned to each of any number of reference materials. The observer can then store the channel settings and edit them as needed. As can be seen, channel parameter selections can be provided for various purposes, such as segmentation, tissue enhancement, gingival enhancement, etc.

[0133] FIG. 17B illustrates an exemplary material parameter setting screen 1640 according to one embodiment of the present disclosure. Among its features, the parameter setting screen 1640 gives the observer the option to select different volumetric presentations using a channel paradigm and modify not only the combination of materials included, but also the relative intensity of each material within the volume. The setting screen 1640 allows for the setting of channel icons 1650 that the physician can use to adjust material parameters and to store a desired set of parameters and settings. For example, a set of material selections 171, 173, 175, 177, 178, and 179 can be defined for a particular patient or condition based on the patient chart. The various material selections can be identified by the image shown in the display area 1630 and selectively modified to depict similar anatomical features. Fine tuning for enhancement of a particular material can be added by first identifying the material, such as by selecting one of the material selections 171, 173, 175, 177, 178, 179, such as by using a mouse cursor or a touch screen. After a particular material selection is made, the required enhancement or suppression level of image content for the selected material can be provided by use of an adjustment tool 172, such as a slide bar. This adjustment can be performed for each of the various materials by using the image displayed in the display area 1630 as a guide for the resulting image rendering. A Save button 1634 can be provided to give the physician the option to name and save a channel setting with customized settings 176 that are suitable for a particular patient or that are particularly suited to a job or specialty. The newly saved channel setting can be displayed, for example, along with the channel settings that were pre-configured at the time of manufacture.

[0134] Image Acquisition and Decomposition Using Channel Functions Figures 18, 19, 20 and 21 show various ways in which the channel structure can be used for material decomposition and to modify image restoration and display to visualize different materials represented in the acquired image content.

[0135] 18 and 19 show decomposition selection screens 1700, 1800 for choosing aspects of the projection decomposition at a detailed level. A 2D reconstruction review panel 1710 can provide images of the reconstructed 2D projections along with a menu list of reference materials that can be applied to the reconstruction algorithm. Further controls can allow adjustment of highlighting effects. A 3D volume reconstruction review panel 1720 can then show a representative image volume reconstructed according to the selected projection variables. An image storage area 1730 stores temporary results from operator manipulation of patient image content.

[0136] The decomposition selection screen 1800 of FIG. 19 also provides a working area for projection decomposition in an alternative format. A selection menu 1810 allows the operator to select the decomposition parameters according to a specialty such as orthodontics, endodontics, periodontics, etc. In addition, menu selections can also be provided for one or more user-defined parameter sets, including, for example, parameters defined in a previous examination. A 3D volume reconstruction panel 1820 can then show a representative image volume reconstructed according to the selected projection variables. Advantageously, multiple volumes can be stored with different material decomposition coefficients, making it possible to provide a substantial amount of data regarding the material composition of oral anatomical features for a patient in a single scan.

[0137] FIG. 20 shows an illustration of multiple channels that can be applied to a single spectral scan. Channels can be used individually or in combination to aid in visualizing the acquired image content as a 2D image or 3D volumetric reconstruction. As shown in FIG. 20, channel #1 is used to more clearly show the segmentation boundaries. Channel #2 shows enhanced tissue to allow clear identification and extraction of key features. Channel #3 provides enhancement of gingival tissue. Channel #4 provides enhancement of cortical bone features. Another channel can also provide the bound volume as a default.

[0138] FIG. 21 shows a composite user interface display that allows channel selection and different views of acquired image content. FIG. 21 also shows alternative views of spectral volumes that can be generated by an embodiment of the present disclosure. This can include 2D projections or 3D reconstruction volumes from the same acquisition scan using any combination of material decomposition coefficients. Multiple viewing tools can be provided for view angle and rotation, zoom, and measurement. Numbered channel icons allow selection to view a particular volume.

[0139] FIG. 22 shows an operator interface that uses a mouse or other pointer to scroll through different views of the data by channel number.

[0140] FIG. 23 shows a portion of an operator interface display that may provide an alternative method of user channel selection and combination using icons 1650. By way of example, seven channels are listed in the channel icons 1650. The operator may select one or more channels for display using a mouse cursor or touch screen selection, or a mouse wheel, or the like. For each selected channel, multiple logical operations are provided for combination, such as, for example, addition, subtraction, AND, OR, Max., and Min. functions. This user interface arrangement is more complex than the arrangement for channel adjustment shown in FIG. 17B, and may support the viewer with multiple channel combinations of channels, such as combining channels using addition, subtraction, or other logical operations as shown.

[0141] FIG. 24 illustrates how channel parameter selection can be used to provide improved segmentation. For example, segmentation can substantially distinguish tooth components from gingival tissue and surrounding alveolar bone structures. Channel #1 provides an enhanced tooth view for segmentation. Channel #2 shows an enhanced bone volume. Channel #3 provides a full volume view.

[0142] Virtual Removal The virtual removal capability allows enhanced visualization of selected portions of image content according to material composition. With reference to FIG. 25, the selection of specific channels allows visualization or removal of specific materials within the presented 2D or 3D view. Removal can be equivalent to reducing opacity to a minimum level or substantially zero. This can include, for example, virtual material removal of crown, gutta-percha, and post materials from the oral anatomy, allowing the observing physician to evaluate the biological tissue interfaces and surfaces around the restoration. Features formed from artificial or engineered materials, rather than materials native to the oral cavity or oral environment, can be distinguished from tissues and supporting anatomical structures within the imaged oral anatomy.

[0143] The left side of Figure 25 is a combined image, made available by the Channel #1 setting, with material components including various attenuation characteristics. The second image corresponds to the Channel #2 setting and has been adjusted to provide a view of the image content with the gutta-percha component removed from the image. The third channel setting, Channel #3 in Figure 25, shows the adjustment of the image content due to the removal of tooth and dentin, thus showing the gutta-percha features more clearly.

[0144] FIG. 26 shows a virtual removal of the sealant material deposited on the dentition. Removal of the sealant inclusions can allow for an evaluation of the treatment process of the affected teeth. In the exemplary diagrams shown, channel #1 provides a view with the sealant removed. Channel #2 provides an image with only the dental appliances and other features removed. Channel #3 shows a combined image that allows visibility of the teeth, dental appliances, and sealant features. FIG. 26 shows an exemplary sealant position relative to any filling material.

[0145] FIG. 27 shows the virtual removal of restorative material. This feature allows the observing clinician to more clearly visualize the fracture or decay in the tooth. Channel #1 shows an image with the restoration enhanced. Channel #2 shows an image with the restorative content virtually removed. Channel #3 shows the bond volume including the restorative features. Typical restorative materials can include, for example, gold, porcelain, composite resin, amalgam, ceramics, and zirconia.

[0146] FIG. 28 shows an example of a virtual tooth extraction. This feature allows for improved visibility of nearby supporting structures, which may be useful prior to a surgical procedure. Selection of channel #1 allows the decomposition software to separate the tooth from the surrounding features. Channel #2 can provide a bone-enhanced image. Channel #3 can provide a combined volume showing the tooth and nearby features.

[0147] Figure 29 shows an example with virtual tooth extraction as an aid to root canal treatment. Selection of channel #1 shows tooth content only. Channel #2 shows extracted root material only. Channel #3 shows bond volume.

[0148] FIG. 30 shows virtual bracket removal in orthodontic treatment. Selection of channel #1 provides an image with brackets enhanced. Channel #2 shows an image with bracket content suppressed or removed. Channel #3 shows the bonded volume for viewing. Brackets that can be identified include traditional metal brackets, including ceramic brackets, color brackets, lingual brackets, brackets that face the back of the teeth or toward the tongue, and clear aligners.

[0149] Figure 31 shows a display of separated or resolved calcification and soft tissue with channel settings useful for highlighting carotid artery calcification and tumor. Selection of channel #1 provides a combined panoramic image. Selection of channel #2 shows an image with enhanced calcium inclusions.

[0150] FIG. 32 shows the displayed material separation, with highlighting of the alveolar bone to aid in the evaluation and qualification of the alveolar bone structure relative to the implant material. As shown, bone types can be identified within the acquired image content. Selection of channel #1 provides an image with the alveolar bone separated. Selection of channel #2 results in an image of the instrument only. Channel #3 provides the combined volume for viewing. Bone quality can be classified into groups. Type I- Homogeneous cortical bone. Type II - thick cortical bone with medullary cavity. Type III- Thin cortical bone with dense cancellous bone of good strength. Type IV - Very thin cortical bone with low density cancellous bone of weak strength.

[0151] Assessment and Planning FIG. 33 illustrates the virtual removal of dentures and surgical guides in restorative dentistry.

[0152] Figure 34 shows different 3D renderings of different materials for different types of anatomical structures. A user interface checklist 24 provides a utility for selecting materials for display.

[0153] 35 shows an exemplary 3D rendering 28 of separate components including the tooth, alveolar bone, implant structure, nerve canal, and crown. Another 3D rendering 30 shows the separated dentin, crown, and root within the restored volume.

[0154] FIG. 36 illustrates the use of spectral enhanced images in bone grafting for restorative and implant procedures. This capability can be used, for example, to evaluate socket grafts, block bone grafts, or sinus lift procedures. Channel #1 provides a bone enhanced image. Channel #2 provides a restoration enhanced image. Channel #3 provides a combined image.

[0155] Figure 37 shows imaging for osseointegration assessment. Virtual removal of the implant from the surrounding alveolar bone tissue allows for a more accurate assessment of the osseointegration process.

[0156] The present exemplary embodiments disclosed herein are therefore considered in all respects to be illustrative and not restrictive. The scope of the present disclosure is indicated by the appended claims, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.

[0157] Consistent with at least one exemplary embodiment, the exemplary method / apparatus may employ a computer program having stored instructions executed on image data accessed from an electronic memory. As can be appreciated by those skilled in the image processing art, the computer program of the exemplary embodiments herein may be utilized by a suitable general-purpose computer system, such as a personal computer or a workstation. However, many other types of computer systems may be used to execute the computer program of the exemplary embodiments described, including, for example, a single processor or an arrangement of networked processors.

[0158] The computer program for executing the method of the specific exemplary embodiment described herein can be stored in a computer-readable storage medium. The medium can include, for example, a magnetic storage medium such as a magnetic disk, for example a hard drive or a removable device or a magnetic tape, an optical storage medium such as an optical disk, an optical tape, or a machine-readable optical encoding, a solid-state electronic storage device such as a random access memory (RAM) or a read-only memory (ROM), or any other physical device or medium used to store a computer program. The computer program for executing the exemplary method of the described embodiment can also be stored on a computer-readable storage medium connected to the image processor by the Internet or other network or communication medium. It will be further readily understood by those skilled in the art that the equivalent of such a computer program product can also be constructed in hardware.

[0159] It should be noted that in the context of this application, the term "memory" equivalent to "computer-accessible memory" can refer to any type of temporary or longer-term data storage workspace used to store and operate on image data, such workspace being accessible to a computer system, including, for example, a database. Memory can also be non-volatile, using long-term storage media such as magnetic or optical storage devices. Alternatively, memory can be more volatile, using electronic circuitry such as random access memory (RAM) used as a temporary buffer or workspace by a microprocessor or other control logic processor device. For example, display data is typically stored in a temporary storage buffer that can be directly associated with a display device, and such temporary storage buffer is periodically refreshed as needed to provide the displayed data. This temporary storage buffer can also be considered to be a memory as the term is used in this application. Memory is also used as a data workspace to perform and store intermediate and final results of calculations and other processing. Computer-accessible memory can be volatile, non-volatile, or a hybrid combination of volatile and non-volatile types.

[0160] It will be appreciated that the computer program products for the exemplary embodiments herein may employ various well-known image manipulation algorithms and / or processes. It will be further appreciated that the exemplary computer program product embodiments herein may implement algorithms and / or processes not specifically shown or described herein but useful for implementation. Such algorithms and processes may include conventional utilities within the art of image processing technology. Additional aspects of such algorithms and systems, as well as hardware and / or software, that create and otherwise process images or cooperate with the computer program products of the present application may be selected from such algorithms, systems, hardware, components, and elements not specifically shown or described herein but known in the art.

[0161] Exemplary embodiments according to the present application can include various features described herein (either individually or in any combination).

[0162] Although the present invention has been described with respect to one or more implementations, changes and / or modifications can be made to the described examples without departing from the spirit and scope of the appended claims. In addition, while a particular feature of the present invention may be disclosed with respect to only one of several implementations / exemplary embodiments, such feature can be combined with one or more other features of other implementations / exemplary embodiments as may be desired and advantageous for any given or specific function. The term "a" or "at least one of" is used to mean that one or more of the listed items may be selected. The term "about" indicates that the listed values ​​may be modified to some extent as long as such modification does not result in non-compliance of the process or structure with the exemplary embodiment being described. Finally, "exemplary" indicates that the description is not intended to be ideal, but is used as an example. Other embodiments of the present invention will be apparent to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the appended claims.

Claims

1. 1. A method for producing a radiographic image of an oral anatomy of a subject, comprising: a) exposing the object to radiation along an X-ray radiation path; b) acquiring image content by counting the number of photons received on a detector array in the radiation path from the radiation passing through the object at each of a plurality of positions; acquiring, wherein the detector maintains a first photon count for photons having a first energy above a first energy threshold and further maintains at least a second photon count for photons having a second energy above a higher energy threshold; c) identifying one or more materials in the subject's mouth by performing a material decomposition process according to two or more reference materials previously characterized according to the at least first and second photon counts, and distinguishing natural oral anatomical features and engineered materials in the subject's mouth according to the material decomposition process; and d) displaying adjusted image content that enhances the distinction between the identified natural oral anatomical features and engineered materials within the mouth according to the material decomposition.

2. 10. The method of claim 1, further comprising accepting an operator-input instruction specifying one or more reference materials for material decomposition.

3. 10. The method of claim 1, wherein the adjusted image content reduces opacity of one or more of the natural oral anatomical features and processed substances within the mouth.

4. 2. The method of claim 1, wherein the image content is a 3D reconstruction formed from a set of two-dimensional radiographic images acquired over a set of projection angles around the object.

5. The method of claim 1 , wherein the image content is a 2D projected image.

6. 2. The method of claim 1, wherein the reference material is taken from the group consisting of a fluid, hydroxyapatite, and a metal.

7. 10. The method of claim 1, further comprising accepting at least the first energy threshold value input by a user.

8. 2. The method of claim 1, wherein the detector further accumulates photon energies located between the higher energy threshold and a third energy threshold.

9. 10. The method of claim 1, further comprising: responding to a user command to modify at least one or both of the first energy threshold and the higher energy threshold.

10. 10. The method of claim 1, wherein the first energy threshold is obtained using material information from a patient's dental chart.

11. 2. The method of claim 1, wherein the first energy threshold is obtained from an initial image of the object.

12. 10. The method of claim 1, further comprising setting an exposure value for X-ray radiation according to the initial image.

13. 2. The method of claim 1, wherein the first energy threshold is a predetermined value.

14. 2. The method of claim 1, wherein displaying adjusted image content includes enhancing visibility of features of a first material in the image and suppressing visibility of features of a second material.

15. 15. The method of claim 14, wherein enhancing and suppressing are controlled on a user interface display.

16. 15. The method of claim 14, wherein the first material is a natural feature of the target anatomical structure and the second material is engineered.

17. 17. The method of claim 16, wherein the second material has a k-edge for attenuation within a spectral range of the radiation.

18. 2. The method of claim 1, wherein the processed material forms a root canal filling material.

19. 10. The method of claim 1, wherein the fabricated material forms an implant.

20. 2. The method of claim 1, wherein the fabrication material is an encapsulant.

21. 10. The method of claim 1, wherein the fabricated material is a dental filling material.

22. 10. The method of claim 1, wherein the workpiece is a restorative material.

23. 10. The method of claim 1, wherein the workpiece forms a dental crown.

24. 10. The method of claim 1, wherein the fabricated material forms a denture.

25. 2. The method of claim 1, wherein displaying the adjusted image content according to the material decomposition further comprises responding to a user selection of a channel, the channel identifying one or more reference material combinations and corresponding densities used in the material decomposition process.

26. 1. A method for producing a radiographic image of an oral anatomy of a subject, comprising: a) exposing the object to X-ray radiation; b) acquiring image content by acquiring photon energy from the radiation passing through the object at a detector array that accumulates at each of a plurality of array locations a first photon number for photons having a first energy above a first energy threshold and at least a second photon number for photons having a second energy above a higher energy threshold; c) performing a material decomposition process on the acquired image content according to the at least first and second photon counts to form an adjusted image content, the material decomposition distinguishing natural oral anatomical features and engineered materials in the subject's mouth against two or more reference materials characterized according to the at least first and second photon counts; d) storing the adjusted image content; and e) identifying at least first and second substances within the imaged oral anatomical structure according to the adjusted image content; and f) repeating steps a) to e) at a wide range of angles around the object; and g) reconstructing and displaying a 3D image of the object from the stored image content.

27. 27. The method of claim 26, further comprising highlighting at least the first material in the reconstructed 3D image.

28. 27. The method of claim 26, further comprising selecting the one or more reference materials according to patient chart data.

29. 27. The method of claim 26, further comprising selecting the one or more reference materials according to an initial scout image.

30. 27. The method of claim 26, wherein performing the material decomposition process includes responding to an operator selection of channels defining a set of reference materials.

31. 31. The method of claim 30, further comprising storing the reconstructed 3D image according to the selected channel.

32. 27. The method of claim 26, wherein performing the material decomposition process includes responding to an operator specification of a dental specialty.

33. 27. The method of claim 26, further comprising presenting alternative views of the adjusted image content according to attenuation characteristics of the imaged material.

34. 31. The method of claim 30, wherein a first channel selection shows an image in which the encapsulant feature is visible and a second channel selection shows an image in which the encapsulant feature is transparent.

Images