A solution for a CT dental x-ray imaging of an object

Abstract

The invention relates to a dental X-ray imaging system (100) for a computed tomography (CT) dental X-ray imaging of an object (300). The system (100) comprises: a dental X-ray imaging unit (102) comprising: an X-ray source part (114), an X-ray imaging detector part (116), and a gantry part (112); and a control system (106). The control system (106) is configured to: receive scan request comprising an indication of at least one region of interest (ROI); control the parts of the dental X-ray imaging unit (102) to acquire one X-ray scout image (302) of the object (300); detect at least one anatomical structure of the object (300) from the X-ray scout image (302) by applying at least one trained detection model (616); define at least one target structure of the object (300) associated with the at least one ROI based on the detected at least one anatomical structure and anatomical a priori data (618); define field of view (FOV) data of the dental X-ray imaging unit (102) at least partially based on the at least one target structure; and control the parts of the dental X-ray imaging unit (102) to implement the defined FOV data for a CT scan the object (300) in order to acquire dental CT X-ray image data of the object (300). The invention relates also to a method for a computed tomography (CT) dental X-ray imaging, a computer program and a tangible non-volatile computer- readable medium.

Description

[0001] A solution for a CT dental X-ray imaging of an object

[0002] TECHNICAL FIELD

[0003] The invention concerns in general the technical field of dental X-ray imaging. Especially the invention concerns computed tomography (CT) dental X-ray imaging.

[0004] BACKGROUND

[0005] A dental X-ray imaging unit typically comprises a gantry part, i.e. a rotating part, having an X-ray source part and an X-ray imaging detector part. The X-ray source part provides an X-ray beam that travels through an object, e.g. a head of a patient, to the X-ray imaging detector part. In a computed tomography (CT) dental X-ray imaging, the X-ray beam forms a cylindrical field of view (FOV) around a vertical rotation axis, when the gantry part is arranged to rotate around the object. The position and the dimensions of the cylindrical FOV should be defined so that anatomical structures of the object to be included in the CT scan are inside the cylindrical FOV.

[0006] Patient supporting accessories are typically used to support the head of the patient as stationary as possible. The use of patient supporting accessories intended for certain specific regions (i.e. certain specific anatomical structures of the patient) of the object (e.g. front teeth and / or temporomandibular joints (TMJs)) enable that said certain specific regions are in a known position with respect the dental X-ray imaging unit and thus the 3D location of the FOV may be known a priori. However, this enables only that said specific regions may be imaged reliably, but there are not patient supporting accessories for other regions. Furthermore, the assembly of the patient supporting accessories for these certain specific regions is time consuming.

[0007] One traditional FOV positioning and dimensioning approach is based on using X-ray scout images, i.e. a set of two X-ray projection images taken typically at 90 degrees angle, wherein a user, e.g. an operator, of the dental X-ray imaging unit manually positions and dimensions the FOV by means of the X-ray scout images. The manual FOV positioning and dimensioning by the operator is time consuming and requires anatomy knowledge and skills by the operator. Another known FOV positioning and dimensioning approach is based on using optical scout image, wherein the user of the dental X-ray imaging unit manually positions and dimensions the FOV by means of the optical scout image. However, the optical scout image -based FOV positioning and dimensioning is inaccurate, because the dental anatomical structures of the patient are not shown in the optical scout image. Thus, the X-ray scout image -based FOV positioning and dimensioning is also needed in addition to the optical scout image -based FOV positioning and dimensioning, which, in turn, increases the imaging time. Moreover, the optical scout image -based FOV positioning and dimensioning requires that the X-ray dental imaging unit comprises one or more optical cameras, which increases the price of the X-ray dental imaging unit.

[0008] SUMMARY

[0009] The following presents a simplified summary in order to provide basic understanding of some aspects of various invention embodiments. The summary is not an extensive overview of the invention. It is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of exemplifying embodiments of the invention.

[0010] An objective of the invention is to present a dental X-ray imaging system and a method for a computed tomography (CT) dental X-ray imaging of an object. Another objective of the invention is that the dental X-ray imaging system and the method for the CT dental X-ray imaging of an object enables reducing imaging time and improving imaging accuracy.

[0011] The objectives of the invention are reached by a dental X-ray imaging system, a method, a computer program, and a tangible non-volatile computer-readable medium as defined by the respective independent claims.

[0012] According to a first aspect, a dental X-ray imaging system for a computed tomography (CT) dental X-ray imaging of an object is provided, wherein the system comprises: a dental X-ray imaging unit comprising: an X-ray source part for emitting X-rays, an X-ray imaging detector part for receiving the X-rays from the source part, and a gantry part comprising the X-ray source part and the X-ray imaging detector part, and a control system configured to: receive scan request comprising an indication of at least one region of interest (ROI); control the parts of the dental X-ray imaging unit to acquire one X-ray scout image of the object; detect at least one anatomical structure of the object from the X-ray scout image by applying at least one trained detection model; define at least one target structure of the object associated with the at least one ROI based on the detected at least one anatomical structure and anatomical a priori data; define field of view (FOV) data of the dental X-ray imaging unit at least partially based on the at least one target structure; and control the parts of the dental X-ray imaging unit to implement the defined FOV data for a CT scan the object in order to acquire dental CT X-ray image data of the object.

[0013] The FOV data may comprise a FOV position and a FOV size.

[0014] The X-ray scout image of the object may be a lateral (LAT) view angle X-ray scout image.

[0015] The defining of the at least one target structure associated with the at least one ROI may comprise that the control system may be configured to align the anatomical a priori data with the object by using the detected at least one anatomical structure in the alignment.

[0016] The alignment of the anatomical a priori data with the object may comprise that the control system may be configured to: define from the anatomical a priori data at least one anatomical structure being a counterpart for the detected at least one anatomical structure, and define aligned anatomical a priori data by align the at least one anatomical structure defined from the anatomical a priori data with the object, wherein the detected at least anatomical structure may be used to evaluate a cost function of the alignment.

[0017] The control system may be configured to extract the at least one target structure associated with the at least one ROI from the aligned anatomical a priori data.

[0018] Alternatively or in addition, the control system may further be configured to: obtain imaging geometry data representing an imaging geometry of the dental X- ray imaging unit respective to the X-ray scout image; and further use the obtained imaging geometry data in the alignment of the anatomical a priori data with the object.

[0019] The scan request may further comprise object data representing at least one object related parameter and / or imaging program data representing required imaging program, wherein the object data and / or the imaging program data may be used in the defining of the FOV data.

[0020] The at least one trained detection model may be a machine learning (ML) model or an artificial intelligence (Al) model.

[0021] Alternatively or in addition, the at least trained detection model may depend on a region of the object imaged in the X-ray scout image.

[0022] The detecting the at least one anatomical structure of the object from the X-ray scout image may be based on landmark -based detection, bounding box -based detection, and / or object segmentation -based detection.

[0023] In the landmark -based detection at least one landmark may be detected from the X-ray scout image by applying the at least one trained detection model.

[0024] According to a second aspect, a method for a computed tomography (CT) dental X-ray imaging is provided, wherein the method is performed by an X-ray dental imaging system described above, wherein the method comprises: receiving scan request comprising an indication of at least one region of interest (ROI); controlling the parts of the dental X-ray imaging unit to acquire one X-ray scout image of the object; detecting at least one anatomical structure of the object from the X-ray scout image by applying at least one trained detection model; defining at least one target structure of the object associated with the at least one ROI based on the detected at least one anatomical structure and anatomical a priori data; defining field of view (FOV) data of the dental X-ray imaging unit at least partially based on the at least one target structure; and controlling the parts of the dental X-ray imaging unit to implement the defined FOV data for a CT scan of the object in order to acquire CT dental X-ray image data of the object.

[0025] According to a third aspect, a computer program is provided, wherein the computer program comprises instructions which, when the program is executed by an X-ray dental imaging system described above, cause the X-ray dental imaging system to carry out the method described above.

[0026] According to a fourth aspect, a tangible non-volatile computer-readable medium is provided, wherein the computer-readable medium comprises instructions which, when executed by an X-ray dental imaging system described above, cause the X-ray dental imaging system to carry out the method described above. Various exemplifying and non-limiting embodiments of the invention both as to constructions and to methods of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific exemplifying and non-limiting embodiments when read in connection with the accompanying drawings.

[0027] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of unrecited features. The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” or “an”, i.e. a singular form, throughout this document does not exclude a plurality.

[0028] BRIEF DESCRIPTION OF FIGURES

[0029] The embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings.

[0030] Figure 1 illustrates schematically an example of a dental X-ray imaging system for dental X-ray imaging of an object.

[0031] Figure 2 illustrates schematically an example of a method for CBCT dental imaging of an object.

[0032] Figure 3A illustrates schematically an example of lateral (LAT) imaging of an object.

[0033] Figure 3B illustrates schematically an example of a posterior-anterior (PA) imaging an object.

[0034] Figure 3C illustrates schematically an example of a LAT scout image of an object.

[0035] Figure 3D illustrates schematically an example of a PA scout image of an object.

[0036] Figure 4A illustrates schematically a non-liming example of landmarks intended for detecting maxillary teeth from a LAT scout image of an object.

[0037] Figure 4B illustrates schematically a non-liming example of landmarks intended for detecting maxillary teeth from a PA scout image of an object. Figure 5A illustrates schematically an example of adjusting a horizontal dimension of a field-of-view (FOV).

[0038] Figure 5B illustrates schematically an example of adjusting a vertical dimension of the FOV.

[0039] Figure 6 illustrates schematically an example of a control system of a dental X- ray imaging system.

[0040] DESCRIPTION OF THE EXEMPLIFYING EMBODIMENTS

[0041] In this description we use the following vocabulary concerning different phases of a dental X-ray imaging process. The term radiating means the phase comprising merely the irradiation, i.e. the phase when an X-ray source is providing an X-ray beam that travels through an object to an X-ray imaging detector. The object may be expected to remain as still, i.e. immobile, as possible during the radiating. During the radiating one or more parts of the dental X-ray imaging unit may move. The term scanning, in turn, means the phase comprising the radiating and moving of one or more parts of the dental X-ray imaging unit. The scanning does not comprise positioning of one or more parts of the X-ray imaging unit in a correct place for providing X-ray images. The term imaging means the whole process comprising radiating, scanning and positioning.

[0042] Figure 1 illustrates an example of a dental X-ray imaging system 100 for dental X-ray imaging of an object 300, e.g. a patient (for sake of clarity the object 300 is not shown in Figure 1 ). The imaging system 100 comprises a dental X-ray imaging unit 102 for acquiring X-ray image data from the object 300 or calibration target, in dental X-ray imaging, e.g. in extraoral dental X-ray imaging. The acquired X-ray image data is used to reconstruct a three-dimensional (3D) X- ray volume from at least part of the imaged object 300. The dental X-ray imaging system 100 further comprises a control system 106. The control system 106 may be electrically and / or communicatively coupled to the dental X-ray imaging unit 102. The implementation of the control system 106 may be done as a standalone unit or as a distributed control environment between a plurality of standalone units providing distributed controlling resource. Preferably, the control system 106 may be an embedded computer. The control system 106 may for example comprise a control unit of the dental X-ray imaging unit 102. The control system 106 may further comprise one or more computing units being external to the dental X-ray imaging unit 102. The control unit of the dental X-ray imaging unit 102 is configured to control the operation of the dental X-ray imaging unit 102 at least in part. The control unit of the dental X-ray imaging unit 102 may be located proximate to the dental X-ray imaging unit 102 or the control unit of the dental X-ray imaging unit 102 may be embedded withing the dental X-ray imaging unit 102.

[0043] The dental X-ray imaging unit 102 is configured to perform computed tomography (CT) imaging procedure (i.e. imaging mode). The CT imaging may for example be a cone beam CT (CBCT) imaging, wherein the beam is a cone-shaped beam, or other type of CT imaging for example, wherein the beam is a pyramidal-shaped beam, half-moon -shaped cone beam, or any other shaped beam. The CT imaging results (i.e. produces) the X-ray image data for the reconstruction of the 3D volume from the at least part of the imaged object 300. Figure 1 illustrates only one example of a dental X-ray imaging unit 102 for use with the concepts in the present disclosure.

[0044] The dental X-ray imaging unit 102 comprises a carriage part 101 that may be moveably supported on a support column 103. The carriage part 101 may be moved up and down in a vertical direction (V) by means of a guide motor (not shown in Figure 1 ) that is configured to move the carriage 101 up and down along the supporting column 103 in the vertical direction. An upper shelf, 110 is configured to support a gantry part, i.e. a rotating part, 112, which is rotatable in a horizontal (H) plane with respect to the upper shelf 110. The upper shelf 110 and / or the gantry part 112 may comprise a rotating motor (not shown in Figure 1 ) configured to rotate the gantry part 112. Alternatively or in addition, the upper shelf 110 and / or the gantry part 112 may comprise a pivot motor (not shown in Figure 1 ) configured to pivot the upper shelf 110 around the column 103. The upper shelf 110 and / or the gantry part 112 may alternatively or in addition comprise at least one linear motor (not shown in Figure 1 ) configured to provide linear movement(s). Alternatively or in addition, the dental X-ray imaging unit 102 may be mounted to a supporting structure (not shown in Figure 1 ) exemplarily a wall to being supported by the column 103.

[0045] The dental X-ray imaging unit 102 comprises further an X-ray source part 114 and an X-ray imaging detector part 116, which are used in the acquisition of the X-ray image data. The gantry part 112 embodies and supports the source part 114 and the imaging detector part 116. The gantry part 112 may have substantially a form of letter C, as presented in Figure 1 , whereupon the source part 114 may be attached on one end of the gantry part 112 and the imaging detector part 116 may be attached on the other end of the gantry part 112 so that the source part 114 and the imaging detector part 116 are opposed from each other. The X-ray source part 114 comprises an X-ray source that emits X-rays (i.e. generates the X-ray beam) through the object 300 being imaged, e.g. a head of the patient, to the X-ray imaging detector part 116, which comprises at least one X-ray detector that receives the emitted X-rays from the source part 114. The X- ray imaging detector part 116 further generates the X-ray image data from the X-ray exposed, i.e. imaged object.

[0046] The dental X-ray imaging unit 102 also comprises a collimator 506 (not shown in Figure 1 ) for the X-ray source part 114 to restrict and / or shape the beam of X- rays. The X-rays pass through a portion of the object 300, for example the patient’s anatomy, e.g. patient’s head. The anatomical structures through which the X-rays pass may absorb varying amounts of the X-ray energy. After passing through the object 300, the attenuated X-rays are received by the X-ray imaging detector part 116. The X-ray imaging detector part 116 is configured to convert the magnitude of the received X-ray energy and to produce a digitized output, i.e. the X-ray image data, representative of the unabsorbed X-rays at the at least one X-ray detector. The collection of digitized outputs from the X-ray imaging detector part 116 that correspond to a single emission of a beam of X-rays from the X-ray source part 114 may be referred to a projection image of the object 300 being imaged, for example the head of the patient 300.

[0047] Furthermore, the dental X-ray imaging unit 102 may comprise patient support parts 124, 126 (as presented in Figure 1 , but not necessarily) that may be used for supporting the patient. The patient support parts 124, 126 may comprise a chin support part 124 and / or a head support part 126. The chin support part 124 may support a tip of a chin of patient and the head support part 126 may support a forehead or temple of the patient. The dental X-ray imaging unit 102 may comprise a lower shelf 122 that extends from the carriage 101 . The lower shelf 122 may comprise the chin support part 124 as in the example dental X-ray imaging unit 102 of Figure 1 . The head support part 126 may extend from the upper shelf 110 through the gantry part 112 as in the example dental X-ray imaging unit 102 of Figure 1 . Alternatively, the lower shelf 122 may also comprise the head support part 126. The patient support parts, i.e. the chin support part 124 and / or the head support part 126, may be optional, and positioning of the patient may be carried out in other manners. The dental X-ray imaging unit 102 may further comprise handles 128 for the patient to grasp.

[0048] The gantry part 112 may be rotated by a rotating motor, for example. The rotation of the gantry part 112 rotates the X-ray source part 114 and the X-ray imaging detector part 116 around the object to be imaged, for example around a rotation axis along a motion path. The X-ray beam emitted by the X-ray source part 114 forms a 3D cylindrical field-of-view (FOV) around the rotation axis, when the gantry part 112 rotates around the patient. The 3D cylindrical FOV should be dimensioned and positioned so that the anatomical structure(s) of the object 300 to be included in the scan is / are inside the 3D cylindrical FOV. As the X-ray source part 114 and the X-ray imaging detector part 116 are rotated around the object 300, the dental X-ray imaging unit 102 operates to acquire a plurality of projection images of the object 300 taken at incremental angles of rotation. The dental X-ray image may be formed from the plurality of projection images by reconstructing the X-ray image data to the dental X-ray image.

[0049] Next at least some example aspects of a method for CT dental X-ray imaging of an object 300, e.g. a patient, are defined referring to Figure 2. Figure 2 illustrates the method as a flow chart. The method is performed by the dental X-ray system 100 discussed above. The CT dental imaging of the object 300 may preferably be CBCT dental imaging.

[0050] At a step 210, the control system 106 receives a scan request. The scan request comprises an indication of at least one region of interest (ROI). The at least one ROI represents at least one region (e.g. at least one target anatomical structure) of the object 300 to be included in the CT scan. For example, the at least one ROI may comprise, but is not limited to, at least one of the following: a single tooth, a range of teeth, a dental arch (either maxillary or mandibular), both dental arches (maxillary and mandibular), a temporomandibular joint (TMJ), both TMJs, a whole dentition and TMJs. The scan request may further comprise object data representing at least one object related parameter (e.g. age, size, etc.) and / or imaging program data representing required imaging program (e.g. dose information including an indication of a dose to be used in the scan, resolution information including an indication of a resolution to be used in the scan, etc.). The scan request may also comprise patient identification data (for example, a patient name, a patient identification number, photograph, fingerprint, retinal scan, facial recognition, and / or other biometric data, etc.). The scan request may be received locally or remotely via a user interface part 140a, 140b. The user interface part 140a may for example be located at the same location as the dental X-ray imaging unit 102 is located, i.e. the scan request may be received locally. For example, the dental X-ray imaging unit 102 may comprise the user interface part 140a, e.g. a touch screen, as in the example dental X-ray imaging unit 102 of Figure 1 . An operator of the dental X-ray imaging unit 102 may input the scan request via the user interface part 140a. Alternatively or in addition, the user interface part 140b may for example be located at another location than the location where the dental X-ray imaging unit 102 is located, i.e. the user interface part 140b may be located remotely from the dental X-ray imaging unit 102, and be communicatively coupled with the control system 106. In that case the scan request may be received remotely. According to an example, initial FOV data may be defined based on the received scan request. The initial FOV data may comprise initial position of the FOV and initial size of the FOV (i.e. initial dimensions of the FOV).

[0051] At a step 220 the control system 106 controls the parts of the dental X-ray imaging unit 102 to acquire an X-ray scout image 302 of the object 300. The use of only one X-ray scout image 302 enables reducing the imaging time, as there is no need to control the gantry part 112 of the dental X-ray imaging unit 102 to move from the scout image acquisition position into other position(s) for acquisition of further scout images before going to a scan start position (i.e. a starting position of the CT scan). The X-ray scout image 302 is a two-dimensional (2D) X-ray projection image. Preferably, the scout image acquisition position is selected so that the movement time between different gantry positions is minimized, when the gantry part 112 moves from a patient positioning position through the scout image acquisition position into the scan start position. The X- ray scout image 302 may be acquired from any scout image acquisition position (i.e. scout imaging direction). For example, the scout image may be a lateral (LAT) view angle X-ray scout image 302, i.e. a LAT scout image, of the object 300 or a posterior-anterior (PA) view angle X-ray scout image, i.e. a PA scout image. Typically, the scout image acquisition position for the LAT scout image 302 is close to the scan start position. In that case, the use of the LAT scout image 302 enables reducing the imaging time for example in comparison to the PA scout image 304. Figure 3A illustrates schematically an example of the lateral imaging of the object 300 for acquiring the LAT scout image 302 of the object 300. Figure 3B illustrates schematically an example of the posterior- anterior imaging of the object 300 for acquiring the PA scout image 302 of the object 300. Figure 3C illustrates schematically an example of the LAT scout image 302 of the object 300 acquired by the lateral imaging. Figure 3D illustrates schematically an example of the PA scout image 302 of the object 300 acquired by the posterior-anterior imaging.

[0052] At as step 230, the control system 106 detects at least one anatomical structure of the object 300 from the X-ray scout image 302 by using automated detection. The automated detection comprises applying at least one trained detection model 616 for the X-ray scout image 302. In other words, at the step 230 the control system 106 detects the at least one anatomical structure of the object 300 by applying at least one trained detection model 616 for the X-ray scout image 302. The X-ray scout image 302 is used as the input data of the at least one trained detection model 616 and the at least one anatomical structure of the object 300 is obtained as the output data of the at least one trained detection model 616. The detection of the at least one anatomical structure of the object 300 means that the at least one anatomical structure is localized i.e. its spatial location in the X-ray scout image 302 is defined, and its identity (e.g. name of label) is known. The detected at least one anatomical structure is used in a definition of at least one target structure of the object 300 associated with the at least one ROI indicated in the scan request as will be described later in the disclosure. More specifically, the detected at least one anatomical structure is used in alignment of anatomical a priori data with the object 300 to define the at least one target structure as will also be described later in the disclosure. The alignment is possible with one anatomical structure detected from the X-ray scout image 302. However, by increasing the number of the detected anatomical structures, the accuracy of the alignment may be increased. Thus, it is profitable to use in the alignment as many anatomical structures detected from the X-ray scout image 302 as possible. The number of the anatomical structures detected from the X-ray scout image 302 may also depend on degree of freedom (DoF) used in the alignment. The higher the DoF is, the more anatomical structures detected from the X-ray scout image 302 are needed. For example, if the DoF of the alignment is one, only one anatomical structure detected from the X-ray scout image 302 is needed. According to another example, if the DoF is six, at least three anatomical structures detected from the X-ray scout image 302 are needed, but even more anatomical structures (e.g. 20) detected from the X-ray scout image 302 may be used to achieve more accurate alignment. The at least one trained detection model 616 may depend on a region of the object 300 imaged in the X-ray scout image 302. In other words, different trained detection models 616 may be trained for different regions of the object 300. For example, at least one trained detection model 616 may be trained for at least one of the following regions of the object 300: the region of maxillary teeth, the region of mandibular teeth, the region of both maxillary and mandibular teeth, and / or the region of TMJs, etc. Depending on the region of the object 300 imaged in the X-ray scout image 302, appropriate at least one trained detection model 616 for the X-ray scout image 302 may be selected.

[0053] The at least one trained detection model 616 may be formed by using training data. The training of the at least one detection model 616 may preferably be supervised training, i.e. supervised learning, but also other training paradigms may be used, e.g. unsupervised learning, reinforcement learning, or hybrid paradigms comprising two or more training paradigms. In the supervised training, the training data comprises input training data and output training data. The input training data may for example comprise a plurality of X-ray scout images. The plurality of X-ray scout images comprised in the input training data may for example comprise previously collected X-ray scout images. The previously collected X-ray scout images may preferably comprise X-ray scout mages of patients. Alternatively or in addition, the previously collected X-ray scout images may comprise X-ray scout images of phantoms (e.g. dry skulls). Alternatively or in addition, the plurality of X-ray scout images comprised in the input training data may comprise simulated and / or artificial X-ray scout images. The output training data may for example comprise annotation data representing annotations of the anatomical structures, e.g. the positions and the identities of the anatomical structures. The output training data may be generated in a manual process, e.g. by a human expert, in a semi-automated process, or in a fully automated process. Data augmentation may also be used to increase the size of the training data.

[0054] The at least one trained detection model 616 may be based on one or more machine learning (ML) methods or one or more artificial intelligence (Al) methods. In other words, the at least one trained detection model 616 may be a ML model or an Al model. For example, the at least one trained detection model 616 may be based on a tree-based machine learning (ML) methods, e.g. decisions trees, and especially regression trees. To leverage the power of a single tree, multiple trees may be combined (i.e. ensemble). Preferably, the at least one trained detection model 616 may be based on ensemble of regression trees ML method. Alternatively, the at least one trained detection model 616 may be based on convolutional neural networks (CNNs). The at least one trained detection model 616 may be stored into a memory part 608 of the control system 106.

[0055] The detection of the at least one anatomical structure of the object 300 from the X-ray scout image 302 may be based on landmark -based detection, bounding box -based detection, and / or object segmentation -based detection. A combination of the landmark -based detection and the bounding box -based detection may comprise bounding box detection of a region in the X-ray scout image 302 followed by the landmark -based detection applied inside the detected region. In the landmark -based detection at least one landmark related to the at least one anatomical structure of the object 300 is detected from the X-ray scout image 302 by using the automated detection, i.e. by applying the at least one trained detection model 616 for the X-ray scout image 302. In other words, the X-ray scout image 302 may be used as the input data of the at least one trained detection model 616 and the at least one landmark 402 may be obtained as the output data of the at least one trained detection model 616. Some non-limiting examples of the at least one landmark 402 may comprise mandibular teeth, maxillary teeth, the TMJs, anterior nasal spine (ANS), posterior nasal spine (PNS), and / or any other mandibular, maxillary or cranial structure. Figure 4A illustrates schematically a non-liming example of the landmarks 402 intended for detecting the maxillary teeth from the LAT scout image 302. Figure 4B illustrates schematically a non-liming example of the landmarks 402 intended for detecting the maxillary teeth from the PA scout image 302. In the examples of Figures 4A and 4B the small circles inside the dashed ellipse represent the landmarks 402.

[0056] At a step 235, the control system 106 defines at least one target structure of the object 300 (e.g. at least one anatomical target structure of the object 300) associated with the at least one ROI indicated in the scan request based on the detected at least one anatomical structure of the object 300 and anatomical a prior data. The defining of the at least one target structure associated with the at least one ROI may comprise aligning (i.e. registering) the anatomical a priori data 618 with the object 300 by using the at least one anatomical structure detected at the step 230 in the alignment.

[0057] The anatomical a priori data 618 represents dental related anatomical data formed from anatomical data acquired from at least one dental database. The dental database may for example be a dental atlas. The anatomical a priori data 618 may be stored into the memory part 608 of the control system 106.

[0058] The anatomical a priori data 618 comprises information relating to one or more anatomical structures. This information both identifies and localizes anatomical structure(s). In other words, the anatomical a priori data may comprise a location information of the one or more anatomical structures and identity information of the one or more anatomical structures. The one or more anatomical structures may comprise, but are not limited to, one or more of the following anatomic structures: teeth (e.g. maxillary teeth and / or mandibular teeth), the TMJ(s), one or more mandibular structures (e.g. coronoid(s), condyle(s), chin menton, and / or any other mandibular structures), one or more eye socket structures (e.g. lower orbit(s) and / or any other eye socket structures), auditory canal(s), one or more nose and / or skull structures (e.g. ANS, PNS, and / or any other nose and / or skull structures), and / or any other anatomically relevant structures. In addition to the location and identity information, the anatomical a priori data may further comprise other anatomical information of the one or more anatomical structures, for example information on structure location variations (e.g. statistical shape modes or similar).

[0059] The anatomical a priori data 618 may be derived (i.e. extracted) from radiological or dental images, such as CT- images (e.g. CBCT-images), medical CT images, magnetic resonance images (MRI), and / or other radiological or dental images. Preferably, these images are 3D images, but the images may also be 2D or 4D images. The anatomical a priori data 618 may be extracted from images of a single subject or from images of multiple subjects. Thus, the one or more anatomical structures may present a single subject anatomy or a mean anatomy of multiple subjects. In case of multiple subjects, the anatomical a priori data 618 may comprise information on anatomy variations within the subjects (e.g. statistical information, probability information etc.). The anatomical a priori data 618 may also be created without real image data. For example, by using anthropometric measurements or any other information on human anatomy generic and / or artificial anatomical structure(s) may also be constructed. It is also possible to use both image and non-image data for constructing the anatomical a priori data 618.

[0060] As discussed above, the control system 106 defines the at least one target structure of the object 300 associated with the at least one ROI by aligning the anatomical a priori data 618 with object 300 so that the detected at least one anatomical structure is used in the alignment. For the alignment the control system 106 defines from the anatomical a priori data 618 at least one anatomical structure being a counterpart for the at least one anatomical structure detected from the X-ray scout image 302. In other words, the control system 106 selects from the anatomical a priori data 618 at least one anatomical structure which is a counterpart for the at least one anatomical structure detected from the X-ray scout image 302. From now on in this disclosure the at least one anatomical structure defined from the anatomical a priori data 618 is called as at least one a priori anatomical structure and the at least one anatomical structure detected from the X-ray scout image 302 is called as at least one scout image anatomical structure. The at least one a priori anatomical structure may be aligned with the object 300 by using the at least one scout image anatomical structure in the alignment. The at least one scout image anatomical structure may be used in the alignment to evaluate a cost function of the alignment. The cost function measures the goodness of the alignment. As a result of the alignment aligned anatomical a priori data may be defined. The at least one target structure of the object 300 associated with the at least one ROI may then be extracted from the aligned anatomical a priori data. Preferably, all target structures of the object 300 associated with at least one ROI are extracted from the aligned anatomical a priori data. For example, if the at least one ROI indicated in the scan request comprises a range of teeth, teeth of the object 300 corresponding to the range of teeth indicated in the scan request are extracted from the aligned anatomical a priori data. The defining of the at least one target structure of the object 300 associated with the at least one ROI may also comprise defining a location of the at least one target structure of the object associated with the at least one ROI. For example, if the at least one ROI indicated in the scan request is a single tooth, the location of the tooth of the object 300 corresponding to the tooth indicated in the scan request may be extracted from the aligned anatomical a priori data.

[0061] The at least one a priori anatomical structure is represented as 3D points in 3D imaging device coordinates. The control system 106 may further use in the alignment imaging geometry data representing an imaging geometry of the dental X- ray imaging unit 102 respective to the X-ray scout image 302. The control system 106 may for example obtain the imaging geometry data when the X-ray scout image 302 is acquired, i.e. in connection with the acquirement of the X- ray scout image 302, at the step 220. The control system 106 may then use the obtained imaging geometry data to project the at least one a priori anatomical structure presented in the 3D imaging device coordinates into the X-ray scout image coordinate space. When the at least one scout image anatomical structure and the at least one a priori anatomical structure are both located in the same coordinate space, the cost function measuring the goodness of the alignment may be evaluated. In a simple case, the cost function may be a distance measure (e.g. a sum of distances between corresponding scout image anatomical structures and projected a priori anatomical structures). The smaller the distance is, the smaller the alignment cost is, and the better the alignment between the anatomical a priori data 618 and the object 300 is.

[0062] The alignment (i.e. registration) may for example be solved by using an iterative registration framework. By defining a transformation model, the cost function and an optimization method, the optimization finds an optimal transformation that minimizes the cost function. Above, as the common coordinate space for evaluating the cost function the X-ray scout image coordinate space is used. This, however, is not the only option, but any other known coordinate space may also be used assuming that a meaningful cost function may be formulated in that common coordinate space.

[0063] Transforming the at least one a priori anatomical structure with the optimal transformation aligns these structures with corresponding at least one structure of the object 300. In the aligned anatomical a priori data, the at least one a priori anatomical structure is aligned with the corresponding at least one anatomical structure of the object 300. In other words, after the alignment the a priori anatomical structures are aligned with the corresponding anatomical structures of the patient 300. This enables that the at least one target structure associated with the at least one ROI indicated in the scan request may be extracted from the aligned anatomical a priori data as discussed above. At a step 240, the control system 106 defines FOV data of the dental X-ray imaging unit 102 at least partially based on the at least one target structure defined at the step 235. The FOV data may comprise a FOV position and a FOV size (i.e. dimensions of the FOV). The FOV position may comprise a vertical FOV position and a horizontal FOV position. Preferably, at the step 240, the control system 106 defines the FOV data based on the detected at least one target structure. Alternatively, if the initial FOV data is defined based on the scan request as discussed above, the control system 106 may define the FOV data partially based on the detected at least one target structure and partially based on the initial FOV data. For example, the FOV size (or at least one dimension of the FOV) may be defined based on the initial FOV data or the FOV position may for example be defined based on the initial FOV data. According to a non-limiting example, the FOV position may be defined based on the detected at least one target structure and the FOV size may be defined based on the initial FOV data, or vice versa.

[0064] The vertical FOV position may be defined by defining by using a reference point. The reference point may for example be one of the following: the most inferior point of the FOV (i.e. FOV bottom point), the middle point of the FOV (i.e. FOV middle point), the most superior point of the FOV (i.e. FOV top point). For example, if the most inferior point of the FOV is used as the reference point, to define the most inferior point of the FOV the control system 106 may define the most inferior point of the defined at least one target structure and assign vertical FOV position (i.e. the most inferior point of the FOV) at the same vertical level with the most inferior point of the defined at least one target structure. The other reference points may be used similarly to define the vertical FOV position.

[0065] The horizontal FOV position may for example be a center vertical axis of the FOV (i.e. the FOV center axis). The horizontal FOV position may be solved in a horizontal plane. To define the horizontal FOV position, the defined at least one target structure of the object 300 may be projected in any horizontal plane in the imaging device coordinates. The location of the FOV center axis in this horizontal plane may be defined as a location where the FOV with smallest horizontal dimension fully includes the projection of the defined at least one target structure. The horizontal FOV position in the horizontal plane is the center of the smallest circle that fully encloses the at least one target structures in this projection plane. If the at least one target structure comprises a single structure (e.g. a single tooth), the control system 106 may define the horizontal FOV position so that the FOV center axis goes (i.e. passes) through the center of the single structure. Alternatively, if the at least one target structure comprises two structures, the control system 106 may define the horizontal FOV position so that the FOV center axis goes through a middle point on a line connecting the two structures. Alternatively, if the at least one target structure comprises multiple structures (e.g. multiple teeth), the control system 106 may define the horizontal FOV position so that the FOV center axis goes through the center of the multiple structures. The center of the multiple structures may for example be derived by averaging the projected locations of target structures (e.g. arithmetic mean, geometric mean, or weighted mean, etc.). According to an example an iterative optimization may be used for defining a more precise location. In the iterative optimization, for each iteration the distance from the FOV center into each target structure is defined in the projected horizontal plane. The maximum of these distances is the radius for a circle. Using the optimization method the circle center coordinates may be optimized until the radius minimum is reached. The optimized center coordinates provide the horizontal location for the FOV center axis. Instead of the iterative optimization, also analytical optimization methods may be used for defining the horizontal FOV position.

[0066] The dimensions of the FOV may for example comprise a horizontal dimension of the FOV (e.g. a width of the FOV, i.e. a diameter of the FOV, or a radius of the FOV), and a vertical dimension of the FOV (e.g. a vertical height of the FOV). The control system 106 may for example estimate the horizontal dimension of the FOV by defining for each structure the distance from the defined FOV center axis and the maximum of these distances may be used as the radius of the FOV. The width of the FOV, i.e. the diameter of the FOV, may be defined based on the radius of the FOV. The vertical dimension of the FOV may be defined based on a most superior point of the FOV and a most inferior point of the FOV. To define the most superior point of the FOV, the control system 106 may define the most superior point of the at least one target structure and assign the top of the FOV at the same level, i.e. the defined most superior point of the at least one target structure is assigned as the most superior point of the FOV. If the at least one target structure comprises multiple structures, the most superior point of all of these multiple structures may be assigned as the most superior point of the FOV. To define the most inferior point of the FOV, the control system 106 may define the most inferior point of the at least one target structure and assign the bottom of the FOV at the same level, i.e. the defined most inferior point of the at least one target structure is assigned as the most inferior point of the FOV. If the at least one target structure comprises multiple structures, the most inferior point of all of these multiple structures may be assigned as the most inferior point of the FOV.

[0067] According to an example, a safety margin may be added to the horizontal dimension of the FOV and to the vertical dimension of the FOV. The size of the safety margin may for example be fixed or it may depend on the object 300, the ROI, and / or the imaging program data. The safety margin may be the same for the horizontal dimension of the FOV and for the vertical dimension of the FOV. Alternatively, different safety margins may be added to the horizontal dimension and to the vertical dimension of the FOV. According to an example, the object data and / or the imaging program data may be used in the defining of the FOV data, e.g. in the defining of the safety margin.

[0068] After the defining of the FOV data, at an optional step 250, the control system 106 may output via one or more user interface devices, e.g. the user interface part 140a, the defined FOV data to the operator of the dental X-ray imaging unit 102 for a review and approval. This enables that the operator may review the correctness of the defined FOV data. If the operator is satisfied with the defined FOV data, the operator may approve the defined FOV data. Alternatively, if the operator is not satisfied with the defined FOV data, the operator may manually adjust the FOV position and / or at least one dimension of the FOV via the user interface part 140a before approving the FOV data. One example to visualize the FOV data is to superimpose it on top of the X-ray scout image 302. In addition to FOV data, also some of the anatomical structures detected from the X- ray scout image 302 may be superimposed on top X-ray scout image 302.

[0069] At a step 260, the control system 106 controls the parts of the dental X-ray imaging unit 102 to implement the defined FOV data for the CT scan of the object 300 in order to acquire dental CT X-ray image data of the object 3OO.The control system 106 controls the gantry part 112 of the dental X-ray imaging unit 102 to move into the starting position of the CT scan. In case of a symmetrical CT imaging, in the starting position of the CT scan the rotation axis is aligned with the central axis of the FOV defined at the step 240. The rotation axis may be a mechanical rotation axis of the gantry part 112 or a virtual rotation axis. The virtual rotation axis may be obtained, for example, by moving the mechanical rotation axis of the gantry part 112 along a circular path, whereupon the virtual rotation axis may be formed in the centre of said circular path. In case of an offset CT-imaging, the starting position of the CT scan may be off-set from the central axis of the FOV defined at the step 240 by a known amount in a known direction, i.e. by a known off-set vector. The control system 106 may adjust the horizontal dimension 504 of the FOV 502 to correspond to the defined horizontal dimension of the FOV by means of the collimator 506 of the X-ray source part 114. The vertical dimension 510 of the FOV 502 may be adjusted to correspond to the defined vertical dimension of the FOV by means of the collimator 506. For example, vertical dimension 510 of the FOV 502 may be adjusted by controlling the collimator 506 of the X-ray source part 114 so that the most superior point of the FOV 502 corresponds to the defined most superior point of the FOV and / or that the most inferior point of the FOV 502 corresponds to the defined most inferior point of the FOV. The collimator 506 of the X-ray source part 114 may comprise an adjustable slit. The size and / or the position of the slit of the collimator 506 may be adjusted. The size of the slit of the collimator 506 may be adjusted in the horizontal direction to adjust the horizontal dimension 504 of the FOV 502 and in the vertical direction to adjust the vertical dimension 510 of the FOV 502. Figure 5A illustrates schematically an example of adjusting the horizontal dimension 504 of the FOV 502. The horizontal dimension 504 in this example is the width of the FOV 502, i.e. the diameter of the FOV 502. The diameter 504 of the of the FOV 502 may be adjusted by adjusting the size of the slit of the collimator 506 in the horizontal direction. The size of the slit of the collimator 506 in the horizontal direction, i.e. the width of the slit, is illustrated in Figure 5A with the dashed arrow 508. The larger the slit of the collimator 506 is in the horizontal direction the larger the diameter 504 of the FOV 502 is. In other words, by closing the slit of the collimator 506 in the horizontal direction, the diameter 504 of the FOV 502 may be adjusted smaller and by opening the slit of the collimator 506 in the horizontal direction, the diameter 504 of the FOV 502 may be adjusted larger. Figure 5B illustrates schematically an example of adjusting the vertical dimension 510 of the FOV 502. The vertical dimension 510 in this example is the height of the FOV 502. The height 510 of the of the FOV 502 may be adjusted by adjusting the size of the slit of the collimator 506 in the vertical direction. The size of the slit of the collimator 506 in the vertical direction, i.e. the height of the slit, is illustrated in Figure 5B with the dashed arrow 512. The larger the slit of the collimator 506 is in the vertical direction, the larger the height 510 of the FOV 502 is. In other words, by closing the slit of the collimator 506 in the vertical direction, the height 510 of the FOV 502 may be adjusted smaller and by opening the slit of the collimator 506 in the vertical direction, the height 510 of the FOV 502 may be adjusted larger.

[0070] At a step 270, after the rotation axis is moved into the starting position of the CT scan and the horizontal dimension and the vertical dimension of the FOV are adjusted at the step 260, the control system 106 controls the parts of the dental X-ray imaging unit 102 to scan the object (300) in order to acquire the dental CT X-ray image data of the object 300. The controlling at the step 270 may comprise controlling the gantry part 112 to rotate according to a motion path of the CT scan around the rotation axis in order to acquire the dental CT X-ray image data of the object 300. The motion path may for example be a circular path or a noncircular path, e.g. an elliptic path, around the rotation axis. The circular path or the non-circular path may be full rotation or partial rotation around the rotation axis. The non-circular rotation path may be produced, for example, by moving the gantry part 112 along a motion path deviating from the circular path, for example an elliptic path. Other techniques or alignments for the rotation axis may also be used as will be recognized by a person or ordinary skill in the art.

[0071] Figure 6 illustrates a schematic example of the control system 106 of the dental X-ray imaging system 100. The control system 106 may comprise a processor part 602, a data transfer part 604, a user interface part 606, and a memory part 608. The processor part 602 is configured to perform user and / or computer program (software) initiated instructions, and to process data. The processor part 602 may comprise at least one processor. The memory part 608 is configured to store and maintain data. The data may be instructions, computer programs, the at least one trained detection model 616, the anatomical a priori data 618, and any data files. The memory part 608 may comprise at least one memory. The memory part 608 may further comprise at least a data transfer application 610 in order to control the data transfer part 604, a user interface application 612 in order to control the III part 606, and a computer program (code) 614 in order to control the operations of the control system 106. The memory part 608 and the computer program 614, together with the processor part 602, may cause the control system 106 at least to implement one or more method steps and / or operations of the control system 106 as described above. The data transfer part 604 may be configured to send control commands other units, e.g. the dental X- ray imaging unit 102. In addition, the data transfer part 604 may receive data from other units, e.g. the dental X-ray imaging unit 102, the user interface part 140b, a database(s) and / or any other external units. The user interface (III) part 606 may be configured to input control commands, to receive information and / or instructions, and to display information. The III part 606 may comprise at least a display, a screen, a touchscreen, at least one function key, a keyboard, a wired or wireless remote controller, or any other user input and / or output device. The computer program 614 may be a computer program product that may be comprised in a tangible, non-volatile (non-transitory) computer-readable medium bearing the computer program code 614 embodied therein for use with a computer, e.g. the control system 106. The CT dental X-ray imaging method described above enables reducing the imaging time, because manual FOV positioning by the operator of the dental X-ray imaging unit 102 is not needed. Furthermore, the FOV positioning does not depend on the anatomy knowledge and skills by the operator of the dental X-ray imaging unit 102. Therefore, the CT dental X-ray imaging method described above improves the imaging accuracy. Although the FOV positioning does not depend on the anatomy knowledge and skills by the operator, the CT dental X- ray imaging method described above provides support for the skills of the operator. The specific examples provided in the description given above should not be construed as limiting the applicability and / or the interpretation of the appended claims. Lists and groups of examples provided in the description given above are not exhaustive unless otherwise explicitly stated.

Claims

CLAIMS1 . A dental X-ray imaging system (100) for a computed tomography (CT) dental X-ray imaging of an object (300), the system (100) comprising: a dental X-ray imaging unit (102) comprising: an X-ray source part (114) for emitting X-rays, an X-ray imaging detector part (116) for receiving the X-rays from the source part (114), and a gantry part (112) comprising the X-ray source part (114) and the X-ray imaging detector part (116); and a control system (106) configured to: receive scan request comprising an indication of at least one region of interest (ROI); control the parts of the dental X-ray imaging unit (102) to acquire one X- ray scout image (302) of the object (300); detect at least one anatomical structure of the object (300) from the X-ray scout image (302) by applying at least one trained detection model (616); define at least one target structure of the object (300) associated with the at least one ROI based on the detected at least one anatomical structure and anatomical a priori data (618); define field of view (FOV) data of the dental X-ray imaging unit (102) at least partially based on the at least one target structure; and control the parts of the dental X-ray imaging unit (102) to implement the defined FOV data for a CT scan the object (300) in order to acquire dental CT X-ray image data of the object (300).

2. The dental X-ray imaging system (100) according to claim 1 , wherein the FOV data comprises a FOV position and a FOV size.

3. The dental X-ray imaging system (100) according to any of the preceding claims, wherein the X-ray scout image (302) of the object (300) is a lateral (LAT) view angle X-ray scout image (302).

4. The dental X-ray imaging system (100) according to any of the preceding claims, wherein the defining of the at least one target structure associated with the at least one ROI comprises that the control system (106) is configured to align the anatomical a priori data (618) with the object (300) by using the detected at least one anatomical structure in the alignment.

5. The dental X-ray imaging system (100) according to claim 4, wherein the alignment of the anatomical a priori data (618) with the object (300) comprises that the control system (106) is configured to: define from the anatomical a priori data (618) at least one anatomical structure being a counterpart for the detected at least one anatomical structure, and define aligned anatomical a priori data by align the at least one anatomical structure defined from the anatomical a priori data (618) with the object (300), wherein the detected at least anatomical structure is used to evaluate a cost function of the alignment.

6. The dental X-ray imaging system (100) according to claim 5, wherein the control system (106) is configured to extract the at least one target structure associated with the at least one ROI from the aligned anatomical a priori data.

7. The dental X-ray imaging system (100) according to any of claims 4 to 6, wherein the control system (106) is further configured to: obtain imaging geometry data representing an imaging geometry of the dental X-ray imaging unit (102) respective to the X-ray scout image (302); and further use the obtained imaging geometry data in the alignment of the anatomical a priori data (618) with the object (300).

8. The dental X-ray imaging system (100) according to any of the preceding claims, wherein the scan request further comprises object data representing at least one object related parameter and / or imaging program data representing required imaging program, wherein the object data and / or the imaging program data is used in the defining of the FOV data.

9. The dental X-ray imaging system (100) according to any of the preceding claims, wherein the at least one trained detection model (616) is a machine learning (ML) model or an artificial intelligence (Al) model.

10. The dental X-ray imaging system (100) according to any of the preceding claims, wherein the at least trained detection model (616) depends on a region of the object (300) imaged in the X-ray scout image (302).11 . The dental X-ray imaging system (100) according to any of the preceding claims, wherein the detecting the at least one anatomical structure of the object (300) from the X-ray scout image (302) is based on landmark -based detection, bounding box -based detection, and / or object segmentation -based detection.

12. The dental X-ray imaging system (100) according to claim 11 , wherein in the landmark -based detection at least one landmark (402) is detected from the X-ray scout image (302) by applying the at least one trained detection model (616).

13. A method for a computed tomography (CT) dental X-ray imaging, the method is performed by an X-ray dental imaging system (100) according to any of the preceding claims, wherein the method comprises: receiving (210) scan request comprising an indication of at least one region of interest (ROI); controlling (220) the parts of the dental X-ray imaging unit (102) to acquire one X-ray scout image (302) of the object (300); detecting (230) at least one anatomical structure of the object (300) from the X-ray scout image (302) by applying at least one trained detection model (616); defining (235) at least one target structure of the object (300) associated with the at least one ROI based on the detected at least one anatomical structure and anatomical a priori data (618); defining (240) field of view (FOV) data of the dental X-ray imaging unit (102) at least partially based on the at least one target structure; and controlling (260) the parts of the dental X-ray imaging unit (102) to implement the defined FOV data for a CT scan of the object (300) in order to acquire CT dental X-ray image data of the object (300).

14. A computer program (614) comprising instructions which, when the program (614) is executed by an X-ray dental imaging system (100) according to any of claims 1 to 12, cause the X-ray dental imaging system (100) to carry out the method according to claim 13.

15. A tangible non-volatile computer-readable medium comprising instructions which, when executed by an X-ray dental imaging system (100) according to any of claims 1 to 12, cause the X-ray dental imaging system (100) to carry out the method according to claim 13.

Images