WO2021252751A1

WO2021252751A1 - Systems and methods for generating synthetic baseline x-ray images from computed tomography for longitudinal analysis

Info

Publication number: WO2021252751A1
Application number: PCT/US2021/036795
Authority: WO
Inventors: Krishna Seetharam Shiram; Vikram MELAPUDI
Original assignee: GE Precision Healthcare LLC
Priority date: 2020-06-10
Filing date: 2021-06-10
Publication date: 2021-12-16

Abstract

Various methods and systems are provided for X-ray imaging. In one embodiment, In one embodiment, a method includes acquiring an initial computed tomography (CT) image volume and an initial X-ray image of a subject, acquiring a subsequent X-ray image of the subject, generating a synthetic baseline X-ray image from the initial CT image volume according to the initial X-ray image, and outputting the synthetic baseline X-ray image and the subsequent X-ray image for comparison. In this way, X-ray images acquired at different times and different projection angles may be directly compared, thereby enabling a radiologist to monitor changes in imaged structures over time.

Description

SYSTEMS AND METHODS FOR GENERATING SYNTHETIC BASELINE X-RAY IMAGES FROM COMPUTED TOMOGRAPHY FOR LONGITUDINAL ANALYSIS

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to Indian Patent Application No. 202041024295, entitled “SYSTEMS AND METHODS FOR GENERATING SYNTHETIC BASELINE X-RAY IMAGES FROM CT FOR LONGITUDINAL ANALYSIS”, and filed on June 10, 2020. The entire contents of the above-listed application is hereby incorporated by reference for all purposes.

FIELD

[0002] Embodiments of the subj ect matter disclosed herein relate to medical imaging, and more particularly, to generating synthetic X-ray images from computed tomography images.

BACKGROUND

[0003] Various medical imaging systems and methods are used to obtain images of the affected regions of the subject for diagnosing the medical condition. X-ray systems are the most widely known and used for imaging the subject for detecting variety of medical conditions like cancers, bone fracture, dental conditions and pneumonia. X-ray systems are one of the most cost effective, readily available and portable imaging systems that are more frequently used than the other imaging systems like Computed Tomography (CT) for obtaining similar images. Different X-ray methods have been developed for imaging different body parts such as lungs, abdomen, teeth and bones, kidney-ureter-bladder (KUB), and chest, to name a few. Also, a variety of X-ray imaging systems are available in the market including fixed X-ray systems, portable X-ray systems and mobile X-ray systems.

[0004] Obtaining X-ray images of a subject involves projecting the X-rays towards the particular body portion of the subject and receiving the X-rays that pass through the body of the subject on a detector to generate X-ray images. During passage of X-rays through the body of the subject, each X-ray passes through a volume of the body before reaching the detector. Each X-ray contains information that represents the body volume through which it has passed. Therefore, X-ray is a summative modality where each pixel in the image contains information from many voxels encountered along the projection path of the X-ray.

[0005] Computed Tomography (CT) is another well-known medical imaging technique used to obtain detailed images of the subject body. CT imaging involves imaging body of the subject using X-rays in several different angles to obtain a three-dimensional view of the portion of the subject body. CT imaging provides more detailed view of the subject pathology than a single X-ray image. However, it is not convenient and cost effective to carry out CT imaging repeatedly to check the health status of the subject. Therefore, X-ray imaging is preferred as a more convenient and cost-effective method over CT for regular monitoring of the health condition of the subject.

BRIEF DESCRIPTION

[0006] In one embodiment, a method comprises acquiring an initial computed tomography (CT) image volume and an initial X-ray image of a subject, acquiring a subsequent X-ray image of the subject, generating a synthetic baseline X-ray image from the initial CT image volume according to the initial X-ray image, and outputting the synthetic baseline X-ray image and the subsequent X-ray image for comparison. In this way, X-ray images acquired at different times and different projection angles may be directly compared, thereby enabling a radiologist to monitor changes in imaged structures over time.

[0007] It should be understood that the brief description above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present invention will be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings, wherein below:

[0009] FIG. 1 shows a pictorial view of an exemplary computed tomography imaging system, according to an embodiment;

[0010] FIG. 2 shows a block diagram of the exemplary computed tomography imaging system, according to an embodiment;

[0011] FIG. 3 shows a block diagram of an exemplary X-ray imaging system, according to an embodiment;

[0012] FIG. 4 shows a block diagram of an exemplary medical image processing system, according to an embodiment;

[0013] FIG. 5 shows a high-level flow chart illustrating an exemplary method for evaluating changes in a subject by comparing X-ray images with synthetic baseline X-ray images, according to an embodiment;

[0014] FIG. 6 shows a high-level flow chart illustrating an exemplary method for generating synthetic baseline X-ray images, according to an embodiment;

[0015] FIG. 7 shows a set of images illustrating a comparison of subsequent X-ray images with an initial X-ray image, according to an embodiment; and [0016] FIG. 8 shows a set of images illustrating a comparison of subsequent X-ray images with synthetic baseline X-ray images, according to an embodiment.

DETAILED DESCRIPTION

[0017] The following description relates to various embodiments of X-ray imaging. In particular, systems and methods for generating synthetic X-ray images from CT images are provided. In order to determine deterioration or improvement in the medical condition of a subj ect, a radiologist compares a previous X-ray image of the subj ect with a subsequent X-ray image of the subject. One medical condition that may be monitored through X-ray imaging is pneumonia, and in some cases daily X-ray imaging is recommended to monitor progress of the infection. It is therefore important to provide X-ray images to a radiologist for early detection and monitoring of pneumonia. However, in X-ray imaging, every new image of a subject varies from the previous image due to several factors including human factors like subject alignment, subject movement, breathing, and technical factors like change in imaging system, alignment of the imaging system. It takes significant skill and efforts on part of the operator of the X-ray imaging system to obtain an image at exactly same angle as that of the previous X-ray image and further it takes significant experience for a radiologist to compare such X-ray image to a previous X-ray image. Any manual or technical alteration in imaging system by the operator would result in change in angle of the projection of the X-rays and generate an image that represents a different portion of the subject body than the portion represented by previous X-ray image. A slight difference in angle of projection of X-rays results in a change in projection path and very different X- ray image would be obtained. Such variation in representation of the subject body may result in wrong interpretation of the X-ray images by the radiologist and potentially adversely affect the further course of treatment.

[0018] As discussed further herein, an initial CT image volume of a subject or patient may be acquired with a CT imaging system, such as the CT imaging system depicted in FIGS. 1 and 2. During the same visit, the patient may also be imaged with an X-ray imaging system, such as the X-ray imaging system depicted in FIG. 3, to obtain an initial X-ray image. An image processing system, such as the image processing system depicted in FIG. 4, may use the initial X-ray image to generate synthetic baseline X-ray images from the initial CT image volume for comparison to X-ray images acquired at a later time. A method for evaluating the medical progression of a patient, such as the method depicted in FIG. 5, may include acquiring an initial CT image volume and an initial X-ray image, acquiring subsequent X-ray images at a later time, and generating synthetic baseline X-ray images corresponding to the projection angles of the subsequent X-ray images. A method for generating the synthetic baseline X-ray images, such as the method depicted in FIG. 6, may include using data from the initial X-ray image such that the synthetic baseline X-ray images are consistent with the initial X-ray image while accurately depicting the internal anatomy of the patient at a same view as the subsequent X-ray images. By generating synthetic baseline X-ray images in this way, a comparison of X-ray images acquired over time may more effectively indicate changes in the medical progression of the patient, as depicted in FIGS. 7 and 8. [0019] Referring now to FIG. 1, an exemplary imaging system 100 is depicted according to an embodiment. In the illustrated embodiment, the imaging system 100 is an X-ray imaging system configured to perform CT imaging. Though the illustrated embodiment actively acquires medical images, it is understood that other embodiments do not actively acquire medical images. Instead, embodiments may retrieve images or imaging data that was previously acquired by an imaging system and process the imaging data as set forth herein.

[0020] The imaging system 100 may be configured to image a subject 112 such as a patient, an inanimate object, one or more manufactured parts, and/or foreign objects such as dental implants, stents, and/or contrast agents present within the body. In one embodiment, the imaging system 100 may include a gantry 102, which in turn, may further include at least one X-ray source 104 configured to project a beam of X-ray radiation 106 (see FIG. 2) for use in imaging the subject 112 laying on a table 114. Specifically, the X- ray source 104 may be configured to project the X-rays 106 towards a detector array 108 positioned on the opposite side of the gantry 102. Although FIG. 1 depicts a curved detector array 108, in certain embodiments, a flat-panel detector may be employed. Further, although FIG. 1 depicts a single X-ray source 104, in certain embodiments, multiple X-ray sources and/or detectors may be employed to project a plurality of X-ray radiation beams 106 for acquiring projection data corresponding to the subject 112 at different energy levels or angular orientations. In some CT imaging embodiments, the X- ray source 104 may enable dual-energy imaging by rapid peak kilovoltage (kVp) switching. In some embodiments, the X-ray detector employed is a photon-counting detector which is capable of differentiating X-ray photons of different energies. In other embodiments, two sets of X-ray sources and detectors are used to generate dual-energy projections, with one set acquired at a low-kVp setting and the other acquired at a high-kVp setting. It should thus be appreciated that the methods described herein may be implemented with single energy acquisition techniques as well as dual energy acquisition techniques.

[0021] In certain embodiments, the imaging system 100 further includes an image processor unit 110 configured to reconstruct images of a target volume of the subject 112 using an iterative or analytic image reconstruction method, or a combination of both. For example, in some CT imaging applications, the image processor unit 110 may use an analytic image reconstmction approach such as filtered backprojection (FBP) to reconstruct images of a target volume of the patient. As another example, the image processor unit 110 may use an iterative image reconstmction approach such as advanced statistical iterative reconstmction (ASIR) or model-based iterative reconstmction (MBIR), and the like, to reconstmct images of a target volume of the subject 112. In some examples, the image processor unit 110 may use both an analytic image reconstmction approach such as FBP in addition to an iterative image reconstmction approach. In one embodiment, and as discussed in detail below, the image processor unit 110 may use an iterative image reconstmction approach leveraging one-dimensional homographic resampling transforms. [0022] In some CT imaging system configurations, an X-ray source projects a cone- shaped X-ray radiation beam which is collimated to lie within an X-Y-Z plane of a Cartesian coordinate system (generally referred to as an “imaging plane”). The X-ray radiation beam passes through an object being imaged, such as the patient or subject. The X-ray radiation beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated X-ray radiation beam received at the detector array is dependent upon the attenuation of an X-ray radiation beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement (e.g., a line integral measurement) of the X-ray beam attenuation at the detector location. The attenuation measurements from all the detector elements are acquired separately to produce a transmission profile.

[0023] In some CT imaging systems, the X-ray source and the detector array are rotated with a gantry about the imaging plane and around the object to be imaged such that an angle at which the radiation beam intersects the object constantly changes. A group of X-ray radiation attenuation measurements, e.g., projection data, from the detector array at one angular position of the gantry is referred to as a “view.” A “scan” of the obj ect includes a set of views made at different angular positions, or view angles, during one revolution of the X-ray source and detector about the object. It is contemplated that the benefits of the methods described herein accrue to many medical imaging modalities, so as used herein the term “view” is not limited to the use as described above with respect to projection data from one gantry angle. The term “view” is used to mean one data acquisition whenever there are multiple data acquisitions from different angles, whether from a CT, X-ray radiographic imaging, positron emission tomography (PET), or single-photon emission CT (SPECT) acquisition, and/or any other modality including modalities yet to be developed as well as combinations thereof in fused embodiments.

[0024] The projection data is processed to reconstruct an image that corresponds to one or more two-dimensional slices taken through the object or, in some examples where the projection data includes extended axial coverage, e.g., Z-axis illumination, a three- dimensional image volume of the object. One method for reconstructing an image from a set of projection data is referred to in the art as the filtered backprojection technique. Transmission and emission tomography reconstruction techniques also include statistical iterative methods such as maximum likelihood expectation maximization (MLEM) and ordered-subsets expectation maximization reconstruction techniques as well as iterative reconstruction techniques. This process converts the attenuation measurements from a scan into integers (called “CT numbers” or “Hounsfield units” in the case of a CT imaging system), which are used to control the brightness of a corresponding pixel on a display device.

[0025] To reduce the total scan time, a “helical” scan may be performed. To perform a “helical” scan, the patient is moved while the data for the prescribed axial coverage is acquired. Such a system generates a single helix from a cone-beam helical scan. The helix mapped out by the cone beam yields projection data from which images in each prescribed slice may be reconstructed.

[0026] As used herein, the phrase “reconstructing an image” is not intended to exclude embodiments of the present disclosure in which data representing an image is generated but a viewable image is not. Therefore, as used herein, the term “image” broadly refers to both viewable images and data representing a viewable image. However, many embodiments generate (or are configured to generate) at least one viewable image.

[0027] Referring now to FIG. 2, an exemplary imaging system 200 similar to the imaging system 100 of FIG. 1 is depicted. As shown, the imaging system 200 may include multiple components. The components may be coupled to one another to form a single structure, may be separate but located within a common room, or may be remotely located with respect to one another. For example, one or more of the modules described herein may operate in a data server that has a distinct and remote location with respect to other components of the imaging system 200.

[0028] In accordance with aspects of the present disclosure, the imaging system 200 may be configured for imaging a subject 204 (e.g., the subject 112 of FIG. 1). In one embodiment, the imaging system 200 may include the detector array 108 (see FIG. 1). The detector array 108 may further include a plurality of detector elements 202 that together sense the X-ray radiation beams 106 that pass through the subject 204 (such as a patient) to acquire corresponding projection data. Accordingly, in one embodiment, the detector array 108 may be fabricated in a multi-slice configuration including the plurality of rows of cells or detector elements 202. In such a configuration, one or more additional rows of the detector elements 202 may be arranged in a parallel configuration for acquiring the projection data.

[0029] The gantry 102 may movably support the X-ray source 104 and the detector array 108 mounted opposite to each other on opposed ends. The subject 204 may accordingly be disposed between the X-ray source 104 and the detector array 108, supported by the table 114.

[0030] It will be recognized that in some embodiments, the table 114 may further be movable to achieve a desired image acquisition. During such an acquisition of image data, the gantry 102 may be movable to change a position and/or orientation of the X-ray source 104 and/or the detector array 108 relative to the subject 204.

[0031] Accordingly, in some embodiments, the gantry 102 may remain fixed during a given imaging session so as to image a single 2D projection of the subject 204. In such embodiments, a position of the gantry 102 and/or the table 114 may be adjusted between imaging sessions so as to image another view of the subject 204.

[0032] In other embodiments, such as in CT imaging applications, the imaging system 200 may be configured to traverse different angular positions around the subject 204 for acquiring desired projection data. Accordingly, the gantry 102 and the components mounted thereon may be configured to rotate about a center of rotation 206 for acquiring the projection data, for example, at different energy levels. Alternatively, in embodiments where a projection angle relative to the subject 204 varies as a function of time, the mounted components may be configured to move along a general curve rather than along a segment of a circle.

[0033] In such embodiments, as the X-ray source 104 and the detector array 108 rotate, the detector array 108 may collect data of the attenuated X-ray beams. The data collected by the detector array 108 may undergo preprocessing and calibration to condition and process the data to represent the line integrals of the attenuation coefficients of the scanned subject 204. The processed data are commonly called projections.

[0034] In some examples, the individual detectors or detector elements 202 of the detector array 108 may include photon-counting detectors which register the interactions of individual photons into one or more energy bins. It should be appreciated that the methods described herein may also be implemented with energy-integrating detectors. [0035] The acquired sets of projection data may be used for basis material decomposition (BMD). During BMD, the measured projections may be converted to a set of material-density projections. The material-density projections may be reconstructed to form a pair or a set of material-density maps or images of each respective basis material, such as bone, soft tissue, and/or contrast agent maps. The material -density maps or images may be, in turn, associated to form a volume rendering of the basis material, for example, bone, soft tissue, and/or contrast agent, in the imaged volume.

[0036] Once reconstructed, the basis material image produced by the imaging system 200 may reveal internal features of the subject 204, expressed in the densities of two basis materials. The density image, or combinations of multiple density images, may be displayed to show these features. In traditional approaches to diagnosis of medical conditions, such as disease states, and more generally of medical events, a radiologist or physician would consider a hard copy or display of the density image, or combinations thereof, to discern characteristic features of interest. Such features might include lesions, sizes and shapes of particular anatomies or organs, and other features that would be discemable in the image based upon the skill and knowledge of the individual practitioner. [0037] In one embodiment, the imaging system 200 may include a control mechanism 208 to control movement of the components such as rotation of the gantry 102 and the operation of the X-ray source 104. In certain embodiments, the control mechanism 208 may further include an X-ray controller 210 configured to provide power and timing signals to the X-ray source 104. Additionally, the control mechanism 208 may include a gantry motor controller 212 configured to control a rotational speed and/or position of the gantry 102 or of various components thereof (e.g., the X-ray source 104, the detector array 108, etc.) based on imaging requirements.

[0038] In certain embodiments, the control mechanism 208 may further include a data acquisition system (DAS) 214 configured to sample analog data received from the detector elements 202 and convert the analog data to digital signals for subsequent processing. For photon-counting imaging systems, the DAS 214 may download measured photon counts in one or more energy bins from detector array 108. The DAS 214 may further be configured to selectively aggregate analog data from a subset of the detector elements 202 into so-called macro-detectors, as described further herein.

[0039] The data sampled and digitized by the DAS 214 may be transmitted to a computer or computing device 216. In the illustrated embodiment, the computing device 216 may be configured to interface with various components of the imaging system 200. As such, the computing device 216 may be configured to control operation of the imaging system 200. In various embodiments, the computing device 216 may take the form of a mainframe computer, server computer, desktop computer, laptop computer, tablet device, network computing device, mobile computing device, mobile communication device, etc. In one embodiment, the computing device 216 may take the form of an edge device for interfacing between the various components of FIG. 2. In some embodiments, the one or more components of the imaging system 200 configured to acquire X-ray radiation may be considered an X-ray imaging subsystem (e.g., the X-ray source 104, the detector array 108, etc.) of the overall imaging system 200, which may be a computing system further configured to interface with a user and perform a variety of computational processes (e.g., imaging or non-imaging). Accordingly, other components (e.g., the computing device 216, etc.) of the imaging system 200 may be communicably coupled to the X-ray imaging subsystem.

[0040] In some embodiments, the computing device 216 may store the data in a storage device or mass storage 218, either included in the computing device 216 (in such examples, the computing device 216 may be referred to as a controller) or a separate device communicably coupled to the computing device 216 (in such examples, the computing device 216 may be referred to as a processor). The storage device 218 may include removable media and/or built-in devices. Specifically, the storage device 218 may include one or more physical, non-transitory devices configured to hold data and/or instructions executable by the computing device 216 to implement the herein described methods. Accordingly, when such methods are implemented, a state of the storage device 218 may be transformed (for example, to hold different, or altered, data). The storage device 218, for example, may include magnetoresistive random-access memory (MRAM), a hard disk drive, a floppy disk drive, a tape drive, a compact disk-read/write (CD-R/W) drive, a Digital Versatile Disc (DVD) drive, a high-definition DVD (HD-DVD) drive, a Blu-Ray drive, a flash drive, and/or a solid-state storage drive. It will be appreciated that the storage device 218 may be a non-transitory storage medium.

[0041] Additionally, the computing device 216 may provide commands and parameters to one or more of the DAS 214, the X-ray controller 210, and the gantry motor controller 212 for controlling system operations such as data acquisition and/or processing. In certain embodiments, the computing device 216 controls system operations based on operator input, e.g., via a user interface 234. The computing device 216 receives the operator input, for example, including commands and/or scanning parameters via an operator console 220 operatively coupled to the computing device 216. The operator console 220 may include a physical keyboard, mouse, touchpad, and/or touchscreen to allow the operator to specify the commands and/or scanning parameters.

[0042] Although FIG. 2 illustrates only one operator console 220, more than one operator console 220 may be coupled to the imaging system 200, for example, for inputting or outputting system parameters, requesting examinations, plotting data, and/or viewing images. Further, in certain embodiments, the imaging system 200 may be coupled to multiple displays, printers, workstations, and/or similar devices located either locally or remotely, for example, within an institution or hospital, or in an entirely different location via one or more configurable wired and/or wireless networks such as the Internet and/or virtual private networks, wireless telephone networks, wireless local area networks, wired local area networks, wireless wide area networks, wired wide area networks, etc.

[0043] In one embodiment, for example, the imaging system 200 may either include, or may be coupled to, a picture archiving and communications system (PACS) 224. In an exemplary implementation, the PACS 224 may further be coupled to a remote system such as radiological information systems (e.g., RIS), electronic health or medical records and/or hospital information systems (e.g., EHR/HIS), and/or to an internal or external network (not shown) to allow operators at different locations to supply commands and parameters and/or gain access to the image data.

[0044] The computing device 216 may use the operator-supplied and/or system- defined commands and parameters to operate a table motor controller 226, which in turn, may control a table 114 which may be a motorized table. Specifically, the table motor controller 226 may move the table 114 for appropriately positioning the subject 204 in the gantry 102 for acquiring projection data corresponding to the target volume of the subject 204.

[0045] As previously noted, the DAS 214 samples and digitizes the projection data acquired by the detector elements 202. Subsequently, an image reconstructor 230 uses the sampled and digitized X-ray data to perform high-speed reconstruction. Although FIG. 2 illustrates the image reconstructor 230 as a separate entity, in certain embodiments, the image reconstructor 230 may form part of the computing device 216. Alternatively, the image reconstructor 230 may be absent from the imaging system 200 and instead the computing device 216 may perform one or more functions of the image reconstructor 230. Moreover, the image reconstructor 230 may be located locally or remotely, and may be operatively connected to the imaging system 200 using a wired or wireless network. For example, one embodiment may use computing resources in a “cloud” network cluster for the image reconstructor 230.

[0046] In one embodiment, the image reconstructor 230 may store the images reconstructed in the storage device 218, either via the computing device 216 as shown in FIG. 2 or via a direct connection (not shown). Alternatively, the image reconstructor 230 may transmit the reconstructed images to the computing device 216 for generating useful patient information for diagnosis and evaluation. In certain embodiments, the computing device 216 may transmit the reconstructed images and/or the patient information to a display or display device 232 communicatively coupled to the computing device 216 and/or the image reconstructor 230. In some embodiments, the reconstructed images may be transmitted from the computing device 216 or the image reconstructor 230 to the storage device 218 for short-term or long-term storage.

[0047] The various methods or processes (such as the methods described below with reference to FIGS. 5 and 6) described further herein may be stored as executable instructions in non-transitory memory on a computing device (or controller), or in communication with a computing device (or processor), in the imaging system 200. In one embodiment, the image reconstructor 230 may include such executable instructions in non- transitory memory, and may apply the methods described herein to reconstruct an image from scanning data. In another embodiment, the computing device 216 may include the instructions in non-transitory memory, and may apply the methods described herein, at least in part, to a reconstructed image after receiving the reconstructed image from the image reconstructor 230. In yet another embodiment, the methods and processes described herein may be distributed across the image reconstructor 230 and the computing device 216.

[0048] In operation, the computing device 216 may acquire imaging data and other medical data, which may be translated for display to a user (e.g., a medical professional) via the user interface 234, for example, on the display device 232. As an example, the medical data may be transformed into and displayed at the display device 232 as a userfacing graphical and/or textual format, which may be standardized across all implementations of the imaging system 200 or may be particular to a given facility, department, profession, or individual user. As another example, the imaging data (e.g., three-dimensional (3D) volumetric data sets, two-dimensional (2D) imaging slices, etc.) may be used to generate one or more images at the computing device 216, which may then be displayed to the operator or user at the display device 232. As such, the display device 232 may allow the operator to evaluate the imaged anatomy. The display device 232 may also allow the operator to select a volume of interest (VOI) and/or request patient information, for example, via a graphical user interface (GUI) for a subsequent scan or processing.

[0049] Turning now to FIG. 3, a block diagram of an X-ray imaging system 300 in accordance with an embodiment is shown. The X-ray imaging system 300 includes an image acquisition unit 302 and an operating console 342. The operating console 342 includes a processor 381, a memory 382, an X-ray controller 387, an X-ray data acquisition unit 391, and an image processor 392 communicatively coupled via a bus 390. The operating console 342 is communicatively coupled to a user interface 383 and a display device 395, as depicted, though it should be appreciated that in some examples the operating console 342 may further comprise one or more of the user interface 383 and the display device 395. In some examples, the X-ray imaging system 300 comprises a mobile X-ray imaging system, such that the image acquisition unit 302 and the operating console 342 are portable or mobile.

[0050] The image acquisition unit 302 includes a radiation source such as an X-ray source 304. The X-ray source 304 is configured to emit a radiation beam such as an X-ray beam 306 having a field-of-view towards an object 310. In the example of FIG. 3, the object 310 is an anatomical region or a region of interest in a subject such as a patient 312. [0051] In some examples, the X-ray imaging system 300 further includes a patient table (not shown) configured to support the patient 312. The X-ray beam 306 upon impinging on the anatomical region 310 may be attenuated differently by portions of the anatomical region 310. An X-ray detector 308 that is disposed in the field-of-view of the X-ray beam 306 acquires the attenuated X-ray beam. The X-ray detector 308 may comprise, as non-limiting examples, an X-ray exposure monitor, an electric substrate, and so on. The X-ray detector 308 is moveable by an operator of the mobile X-ray imaging system 300 for manually positioning relative to the X-ray beam 306.

[0052] The operating console 342 comprises a processor 381, a memory 382, an X- ray controller 387, an X-ray data acquisition unit 391, and an image processor 392. X-ray image data acquired by the X-ray detector 308 is transmitted from the X-ray detector 308 and is received by the X-ray data acquisition unit 391. The collected X-ray image data are image-processed by the image processor 392. A display device 395 communicatively coupled to the operating console 342 displays an image-processed X-ray image thereon. The X-ray controller 387 supplies power of a suitable voltage current to the X-ray source 304 for powering the X-ray source 304.

[0053] The image acquisition unit 302 is further configured to generate an X-ray image corresponding to the object 310 based on the detected X-ray beam. In the example of FIG. 3, the X-ray image is a projection of the anatomical region 310 of the subject 312 in a detector plane of the X-ray detector 308.

[0054] The image processor 392 is communicatively coupled to the X-ray data acquisition unit 391 and configured to receive X-ray image data from the X-ray data acquisition unit 391. In some examples, the image processor 392 is configured to identify a medical condition of the anatomical region 310 of the subject 312 based on the X-ray image. In one embodiment, the image processor 392 is configured to display the X-ray image, the identified medical condition, or a combination thereof on the display device 395. To that end, the image processor 392 processes the X-ray image with one or more image processing techniques, including but not limited to segmentation techniques, deep learning techniques, and so on.

[0055] In some examples, the display device 395 may be integrated with the user interface 383. For example, the display device 395 may comprise a touch-sensitive display device or a touchscreen, such that the display device 395 may display a graphical user interface and detect inputs by an operator.

[0056] Further, the processor 381 is communicatively coupled to the memory unit 382 and the image processor 392 via a communication bus 390 and configured to provide computing and control functionalities. The processor 381 includes at least one of a central processing unit (CPU), a graphics processing unit (GPU), a digital signal processor, and a controller. In other embodiments, the processor 381 includes a customized processor element such as, but not limited to, an application-specific integrated circuit (ASIC) and a field-programmable gate array (FPGA). The processor 381 may be further configured to receive commands and/or parameters from an operator via the user interface 383. In some embodiments, the processor 381 may perform one or more functions of at least one of the image acquisition unit 302 and the image processor 392. The processor 381 may include more than one processor cooperatively working with each other for performing the functions described herein. The processor 381 may also be configured to store and retrieve contents into and from the memory 382. In one example, the processor 381 is configured to initiate and control the functionality of at least one of the image acquisition unit 302 and the grid artifact correction unit 393. [0057] In one embodiment, the memory 382 comprises a random-access memory (RAM), read-only memory (ROM), flash memory, or any other type of computer-readable memory accessible by one or more of the image acquisition unit 302, the image processor 392, and the processor 381. Also, in some examples, the memory 382 comprises a non- transitory computer-readable medium encoded with a program having a plurality of instructions to instruct at least one of the image acquisition unit 302, the image processor 392, and the processor 381 to perform a sequence of steps to generate the X-ray image. The program may further instruct the display device 395 to display the corrected X-ray image to the operator for evaluation of the corrected X-ray image.

[0058] Referring to FIG. 4, a medical image processing system 400 is shown, in accordance with an exemplary embodiment. Medical image processing system 400 comprises image processing device 402, display device 420, user input device 430, and a plurality of medical imaging devices including a CT imaging system 440 and an X-ray imaging system 450. In some embodiments, at least a portion of medical image processing system 400 is disposed at a remote device (e.g., edge device, server, etc.) communicably coupled to one or more of the medical imaging devices 440 and 450 via wired and/or wireless connections. In some embodiments, at least a portion of image processing device 402 is disposed at a separate device (e.g., a workstation) configured to receive images from a storage device which stores images acquired by the CT imaging system 440 and the X- ray imaging system 450. In some examples, one or more of the CT imaging system 440 and the X-ray imaging system 450 may be communicatively coupled to the image processing device 402 via a network 435, which may comprise a wired or wireless network. [0059] Image processing device 402 includes a processor 404 configured to execute machine readable instructions stored in non-transitory memory 406. Processor 404 may be single core or multi-core, and the programs executed thereon may be configured for parallel or distributed processing. In some embodiments, the processor 404 may optionally include individual components that are distributed throughout two or more devices, which may be remotely located and/or configured for coordinated processing. In some embodiments, one or more aspects of the processor 404 may be virtualized and executed by remotely-accessible networked computing devices configured in a cloud computing configuration. [0060] Non-transitory memory 406 may store a synthetic image generation module 408, an artificial intelligence module 412, and image data 414. The synthetic image generation module 408 may include instructions for generating synthetic baseline X-ray images from CT image data. The synthetic image generation module 408 is configured to generate synthetic baseline X-ray images from CT image data 416, for example, that are suitable for comparison with acquired X-ray image data 418 that is acquired during a subsequent time. For example, when a subject is being initially examined, the subject may be imaged with the CT imaging system 440 and the X-ray imaging system 450 to acquire CT image data 416 and X-ray image data 418. The synthetic image generation module 408 may use one or more artificial intelligence algorithms, such as one or more deep learning models stored in the artificial intelligence module 412, trained to generate synthetic baseline X-ray images from the CT image data 416. In some examples, the synthetic image generation module 408 may generate a plurality of synthetic baseline X-ray images using the CT image data 416 by rotating the CT image volume at several different angles and obtaining synthetic baseline X-ray images at desired angles. A deep learning model may be trained to identify a synthetic baseline X-ray image with a given projection angle corresponding to a projection angle of a subsequently-acquired X-ray image. As another example, the deep learning model may determine a projection angle of a subsequent X-ray image relative to the initial CT image volume, and the synthetic image generation module 408 may generate a synthetic baseline X-ray image from the CT image data 416 corresponding to the projection angle of the subsequent X-ray image. Methods for the synthetic image generation module 408 are described further herein with regard to FIGS. 5 and 6.

[0061] Artificial intelligence module 412 may include trained and/or un-trained deep neural networks, as an illustrative and non-limiting example. In some embodiments, the artificial intelligence module 412 is not disposed at the image processing device 402, but is disposed at a remote device communicably coupled with image processing device 402 via wired or wireless connection. Artificial intelligence module 412 may include various deep neural network metadata pertaining to the trained and/or un-trained networks. In some embodiments, the deep neural network metadata may include an indication of the training data used to train a deep neural network, a training method employed to train a deep neural network, and an accuracy/validation score of a trained deep neural network. In some embodiments, artificial intelligence module 412 may include metadata for a trained deep neural network indicating a type of anatomy, and/or a type of imaging modality, to which the trained deep neural network may be applied. In some examples, the artificial intelligence module 412 may further comprise machine executable instructions for training one or more of the deep neural networks stored in artificial intelligence module 412. In one embodiment, the artificial intelligence module 412 may include gradient descent algorithms, loss functions, and rules for generating and/or selecting training data for use in training a deep neural network.

[0062] It should be appreciated that in some examples, one or more operations such as identifying projection angles and comparing X-ray images to baseline X-ray images may be performed without the use of the artificial intelligence module 412.

[0063] Non-transitory memory 406 may further store image data 414, comprising medical images/imaging data acquired by medical imaging devices such as the CT imaging system 440 and the X-ray imaging system 450. Image data 414 may further comprise medical images/imaging data received from other medical imaging systems, via communicative coupling with the other medical imaging systems. The medical images stored in image data 414 may comprise medical images from various imaging modalities or from various models of medical imaging devices, and may comprise images of various views of anatomical regions of one or more patients. In some embodiments, medical images stored in image data 414 may include information identifying an imaging modality and/or an imaging device (e.g., model and manufacturer of an imaging device) by which the medical image was acquired. In some embodiments, image data 414 may comprise X- ray images acquired by an X-ray device, MR images captured by an MRI system, CT images captured by a CT imaging system, PET images captures by a PET system, and/or one or more additional types of medical images. For example, as depicted, the image data 414 may comprise CT image data 416 acquired via the CT imaging system 440 and X-ray image data 418 acquired via the X-ray imaging system 450.

[0064] In some embodiments, the non-transitory memory 406 may include components disposed at two or more devices, which may be remotely located and/or configured for coordinated processing. In some embodiments, one or more aspects of the non-transitory memory 406 may include remotely-accessible networked storage devices configured in a cloud computing configuration.

[0065] Medical image processing system 400 further includes one or more medical imaging devices, which may comprise substantially any type of medical imaging device, including X-ray, MRI, CT, PET, hybrid PET/MR, ultrasound, etc. As depicted, the medical image processing system 400 includes medical imaging devices such as the CT imaging system 440 and the X-ray imaging system 450. The imaging systems 440 and 450 may acquire measurement data of an anatomical region of a patient, which may be used to generate medical images. The medical images generated from measurement data acquired by the medical imaging devices 440 and 450 may comprise two-dimensional (2D) or three- dimensional (3D) imaging data, wherein said imaging data may comprise a plurality of pixel intensity values (in the case of 2D medical images) or voxel intensity values (in the case of 3D medical images). The medical images acquired by medical imaging devices 440 and 450 may comprise gray scale, or color images, and therefore the medical images stored in image data 414 may comprise a single color channel for gray scale images, or a plurality of color channels for colored medical images.

[0066] Medical image processing system 400 may further include user input device 430. User input device 430 may comprise one or more of a touchscreen, a keyboard, a mouse, a trackpad, a motion sensing camera, or other device configured to enable a user to interact with and manipulate data within image processing device 402.

[0067] Display device 420 may include one or more display devices utilizing virtually any type of technology. In some embodiments, display device 420 may comprise a computer monitor configured to display medical images of various types and styles. Display device 420 may be combined with processor 404, non-transitory memory 406, and/or user input device 430 in a shared enclosure, or may be a peripheral display device and may comprise a monitor, touchscreen, projector, or other display device known in the art, which may enable a user to view medical images of a subj ect acquired at different times according to one or more embodiments of the current disclosure, and/or interact with various data stored in non-transitory memory 406. [0068] It should be understood that medical image processing system 400 shown in FIG. 4 is for illustration, not for limitation. Another appropriate medical imaging system 400 may include more, fewer, or different components.

[0069] FIG. 5 shows a high-level flow chart illustrating an exemplary method 500 for evaluating changes in a subject by comparing X-ray images with synthetic baseline X-ray images, according to an embodiment. Method 500 is described with regard to the systems and components of FIGS. 1-4, though it should be appreciated that method 500 may be implemented with other systems and components without departing from the scope of the present disclosure. Method 500 may be implemented as executable instructions stored in non-transitory memory, such as the non-transitory memory 406, and may be executed by a processor, such as the processor 404, to perform the actions described herein.

[0070] Method 500 begins at 505. At 505, method 500 obtains an initial CT image volume for a subject at an initial time tO. For example, method 500 may obtain the initial CT image volume for the subject at the initial time tO by controlling a CT imaging system, such as the imaging system 200, to acquire a CT image volume. Alternatively, method 500 may retrieve, from non-transitory memory, the initial CT image volume for the subject acquired at the initial time tO with a CT imaging system. Further, at 510, method 500 obtains an initial X-ray image for the subject at the initial time tO. For example, method 500 may obtain the initial X-ray image for the subject at the initial time tO by controlling an X-ray imaging system, such as the X-ray imaging system 300, to acquire the initial X- ray image of the subject. The time tO corresponds to an imaging session and thus may comprise a time duration during which the subject is being examined, rather than a singular point in time. For example, the time tO may refer to a duration such as a specific day or hour during which the subject is imaged with the CT imaging system and the X-ray imaging system. In this way, subsequent times (e.g., a time tl, a time t2, and so on) may refer to similar durations of time, such as a subsequent day or hour depending on the specification of the time tO. Further, although only a CT modality and an X-ray modality are mentioned, it should be appreciated that a greater number of images may be obtained using more imaging modalities in a bigger testing facility and may be processed in a similar manner as described herein. At 515, method 500 stores the initial CT image volume and the initial X-ray image in non-transitory memory. The initial CT image volume and the initial X-ray image serve as baseline images for evaluating the health progression of the subject.

[0071] At 520, method 500 updates a synthetic X-ray model according to the initial X-ray image and the initial CT image volume. For example, method 500 may determine the projection angle of the initial X-ray image, data regarding the detectors and sources used to obtain the initial X-ray image and the initial CT image volume, and determine a mapping between Hounsfield units (HUs) of the initial CT image volume to the attenuation values a of the initial X-ray image. Method 500 may store the updated synthetic X-ray model for the pairing of the initial X-ray image and the initial CT image volume in non- transitory memory.

[0072] At 525, method 500 acquires one or more subsequent X-ray image(s) of the subject at a time tl. For example, method 500 may control an X-ray imaging system, such as the X-ray imaging system 300, to acquire one or more subsequent X-ray image(s) of the subject at the time tl. As mentioned hereinabove, the time tl comprises a time duration subsequent to the time duration tO. It should be appreciated that the time tl may comprise any time duration subsequent to the time duration tO. The length of the time durations tO and tl may be selected such that the initial CT image volume and the initial X-ray image may both be acquired within the time tO. Further, the times tO and tl may indicate the specific date and time interval of the acquisition(s). For example, the health progression of a subject may be evaluated throughout a day and so the subject may be imaged multiple times in the day, and in this example the times tl and tO may refer to different hours or blocks of minutes in the day. As another example, the health progression of the subject may be evaluated over a greater amount of time, such as on different days, different months, or even different years. The subsequent X-ray image(s) may be acquired via the same X- ray imaging system used to acquire the initial X-ray image, though it should be appreciated that different X-ray imaging system(s) may be used to acquire the subsequent X-ray image(s).

[0073] At 530, method 500 identifies projection angle(s) for the one or more subsequent X-ray image(s). In some examples, method 500 may input the initial X-ray image and the subsequent X-ray image(s) to the artificial intelligence module 412, for example, to identify the projection angle(s) for the initial X-ray image and the subsequent X-ray image(s) with a deep learning model. For example, method 500 may identify the projection angle for the initial X-ray image, and the deviations of each subsequent X-ray image from the projection angle of the initial X-ray image.

[0074] At 535, method 500 generates, for each of the one or more subsequent X-ray image(s), a synthetic baseline X-ray image for the corresponding projection angle from the initial CT image volume and the synthetic X-ray model. For example, method 500 uses the synthetic X-ray model to generate a two-dimensional image corresponding to the projection angle from the initial CT image volume. By using the synthetic X-ray model that characterizes the relationship between the initial CT image volume and the initial X- ray image, the resulting two-dimensional image comprises an X-ray image that accurately resembles the initial X-ray image while being consistent with the projection angle of the subsequent X-ray image. Further, by using the initial CT image volume acquired at the time tO to generate the synthetic baseline X-ray image, the synthetic baseline X-ray image depicts the internal structures of the subject at the time tO. In this way, differences between the synthetic baseline X-ray image(s) and the subsequent X-ray image(s) indicate changes in the subject between the times tO and tl. An example method for generating a synthetic baseline X-ray image is described further herein with regard to FIG. 6.

[0075] At 540, method 500 displays the synthetic baseline X-ray image(s) and the subsequent X-ray image(s). Method 500 may display the synthetic baseline X-ray image(s) and the subsequent X-ray image(s) adjacent to each other, as one example, via a display device such as the display device 420. Additionally or alternatively, method 500 may overlay the synthetic baseline X-ray image(s) and the subsequent X-ray image(s) and depict the overlay via the display device 420.

[0076] At 545, method 500 determines a change between the synthetic baseline X-ray image(s) and the subsequent X-ray image(s). For example, method 500 may subtract the synthetic baseline X-ray image(s) from the subsequent X-ray image(s) to obtain one or more difference image(s) depicting the difference between the synthetic baseline X-ray image(s) and the subsequent X-ray image(s). In another example, method 500 may input the synthetic baseline X-ray image(s) and the subsequent X-ray image(s) to the artificial intelligence module 412, and an artificial intelligence algorithm such as a deep learning model may be configured to identify differences between the synthetic baseline X-ray image(s) and the subsequent X-ray image(s). The artificial intelligence module 412 may output an image that highlights the region of change in the pathology of the subject, for example. The comparable images (i.e., the synthetic baseline X-ray image(s) and the subsequent X-ray image(s)) may be processed using known techniques of attenuation and projecting the image for visualization.

[0077] At 550, method 500 displays the change between the synthetic baseline X-ray image(s) and the subsequent X-ray image(s). For example, method 500 displays the highlighted region of change and/or the difference image(s) via the display device 420. In this way, a radiologist may obtain a faster understanding of the medical condition of the subject. Method 500 then returns.

[0078] FIG. 6 shows a high-level flow chart illustrating an exemplary method 600 for generating synthetic baseline X-ray images, according to an embodiment. Method 600 is described with regard to the systems, components, and methods of FIGS. 1-5, though it should be appreciated that method 600 may be implemented with other systems, components, and methods without departing from the scope of the present disclosure. Method 600 may be implemented as executable instructions stored in non-transitory memory, such as the non-transitory memory 406, and may be executed by a processor, such as the processor 404, to carry out the actions described herein.

[0079] Method 600 begins at 605. At 605, method 600 obtains an initial CT image volume for a subject. For example, method 600 obtains the initial CT image volume obtained at 505. At 610, method 600 rotates the initial CT image volume according to a projection angle of a subsequent X-ray image. At 615, method 600 converts HU values of the rotated CT image volume to attenuation values according to the synthetic X-ray model that maps the HU values of the initial CT image volume to the attenuation values of the initial X-ray image. At 620, method 600 performs an orthographic projection of the converted CT image volume with an attenuation-based decay function, such as e^~Aa, where A is a selectable parameter for projecting the converted and rotated initial CT image volume to a two-dimensional image and where a is the attenuation value. At 625, method 600 quantizes the projection to the X-ray image range to obtain a synthetic baseline X-ray image. Thus, the synthetic baseline X-ray image is generated from the initial CT image volume, and comprises a two-dimensional image at a view corresponding to the projection angle of a subsequent X-ray image, with pixel values accurately derived from the HU values of the initial CT image volume and the attenuation values of the initial X-ray image. In this way, the synthetic baseline X-ray image is directly comparable to the subsequent X-ray image, and such a comparison indicates differences in the subject between the acquisition time of the initial CT image volume and the acquisition time of the subsequent X-ray image. By generating a synthetic baseline X-ray image from the three-dimensional CT image volume rather than rotating the initial X-ray image via skewing operations for example, the synthetic baseline X-ray image accurately depicts how the internal anatomy of the subject would look if an X-ray image were acquired at the same projection angle as the subsequent X-ray image but at the initial time tO.

[0080] To illustrate the advantages of the systems and methods for generating synthetic baseline X-ray images described herein, FIGS. 7 and 8 illustrate comparisons of images without synthetic baseline X-ray images and with synthetic baseline X-ray images. In particular, FIG. 7 shows a set of images 700 illustrating a comparison of an initial X-ray image 705 to subsequent X-ray images 710 including a first subsequent X-ray image 712 and a second subsequent X-ray image 714. The initial X-ray image 705 is acquired at an initial time tO, for example. The subsequent X-ray images 710 may be acquired at a subsequent time tl . When imaging the subject at time tl, the operator of the X-ray imaging system may have difficulty capturing a same exact view of the subject as depicted in the initial X-ray image 705, due to the time passed between tO and tl. The first X-ray image 712 may be rotated twenty degrees along a first axis relative to the initial X-ray image 705, for example, while the second X-ray image 714 may be rotated twenty degrees along a second axis relative to the initial X-ray image 705. These rotations may occur due to changes in the angle at which X-rays are projected or the angle at which the subject is aligned with respect to incident X-rays. Due to these small rotations, a direct comparison of the initial X-ray image 705 and the subsequent X-ray images 710 is not useful. For example, the images 700 include overlays 720 of the images, including an overlay 722 of the initial X-ray image 705 and the first subsequent X-ray image 712, and an overlay 724 of the initial X-ray image 705 and the second subsequent X-ray image 724. Artifacts may occur in the overlays 720 due to the difference in projection angles between the subsequent X-ray images 710 and the initial X-ray image 705. Further, difference images 730 further emphasize the errors that arise during a direct comparison between the subsequent X-ray images 710 and the initial X-ray image 705. The difference images 730 include a first difference image 732 comprising a difference between the first subsequent X-ray image 712 and the initial X-ray image 705, and a second difference image 734 comprising a difference between the second subsequent X-ray image 714 and the initial X-ray image 705. As depicted, the difference images 730 indicate substantial differences between the initial time tO and the subsequent time tl. A radiologist may find it difficult to identify pathological changes in such difference images due to these substantial differences that solely arise due to the difference in projection angles between the times tO and tl.

[0081] To overcome these limitations of X-ray imaging systems with regard to monitoring medical progression of a subject over time, synthetic baseline X-ray images may be used for comparison as described herein. FIG. 8 shows a set of images 800 illustrating a comparison of subsequent X-ray images with synthetic baseline X-ray images, according to an embodiment. In addition to acquiring the initial X-ray image 705 of the subject, an initial CT image volume 807 is acquired at the same time tO. Synthetic baseline X-ray images 810 are generated from the initial CT image volume 807, where a first synthetic baseline X-ray image 812 and a second synthetic baseline X-ray image 814 are generated with the same projection angles as the subsequent X-ray images 712 and 714, respectively. Further, by using the initial X-ray image 705 in generating the synthetic baseline X-ray images 810, the attenuation values of the synthetic baseline X-ray images 810 are consistent with the attenuation values of the initial X-ray image 705, thereby improving the ability of the synthetic baseline X-ray images 810 to be compared with the subsequent X-ray images 710. The set of images 800 includes overlay images 820, including an overlay image 822 of the subsequent X-ray image 712 overlaid or superimposed on the synthetic baseline X-ray image 812, and an overlay image 824 of the subsequent X-ray image 714 overlaid on the synthetic baseline X-ray image 814. The set of images 800 further include difference images 830, including a difference image 832 comprising a difference between the subsequent X-ray image 712 and the synthetic baseline X-ray image 812, and a difference image 834 comprising a difference between the subsequent X-ray image 714 and the synthetic baseline X-ray image 814. As the synthetic baseline X-ray images 810 are aligned with the subsequent X-ray images 710, a radiologist evaluating the overlay images 820 and/or the difference images 830 is able to make a meaningful comparison between the images and thus to identify progression of medical conditions such as pneumonia.

[0082] While subsequent images acquired at a time tl are described herein, it should be appreciated that a plurality of subsequent images may be acquired at a plurality of subsequent times t2, t3, t4, and so on in some examples. Such subsequent images may be compared to synthetic baseline X-ray images generated from the initial CT image volume obtained at the initial time tO. If and when a subsequent CT image volume is acquired, X- ray images acquired subsequent to the subsequent CT image volume may be compared to synthetic baseline X-ray images generated from the subsequent CT image volume as well as synthetic baseline X-ray images generated from the initial CT image volume.

[0083] A technical effect of the disclosure includes the generation of a synthetic X- ray image from CT image data. Another technical effect of the disclosure includes the comparison of a synthetic X-ray image to an X-ray image. Yet another technical effect of the disclosure includes the synthetic rotation of an X-ray image based on CT image data. [0084] In one embodiment, a method comprises acquiring an initial computed tomography (CT) image volume and an initial X-ray image of a subject, acquiring a subsequent X-ray image of the subject, generating a synthetic baseline X-ray image from the initial CT image volume according to the initial X-ray image, and outputting the synthetic baseline X-ray image and the subsequent X-ray image for comparison.

[0085] In a first example of the method, the initial CT image volume and the initial X-ray image are acquired during a first time duration, and the subsequent X-ray image is acquired during a second time duration subsequent to the first time duration. In a second example of the method optionally including the first example, the method further comprises identifying a projection angle of the subsequent X-ray image. In a third example of the method optionally including one or more of the first and second examples, generating the synthetic baseline X-ray image from the initial CT image volume according to the initial X-ray image comprises generating the synthetic baseline X-ray image from the initial CT image volume at the projection angle of the subsequent X-ray image. In a fourth example of the method optionally including one or more of the first through third examples, the projection angle of the subsequent X-ray image is different from a projection angle of the initial X-ray image. In a fifth example of the method optionally including one or more of the first through fourth examples, generating the synthetic baseline X-ray image from the initial CT image volume according to the initial X-ray image comprises mapping Hounsfield unit (HU) values of the initial CT image volume to attenuation values of the initial X-ray image, rotating the initial CT image volume according to a desired view, and converting the HU values of the rotated initial CT image volume to attenuation values according to the mapping. In a sixth example of the method optionally including one or more of the first through fifth examples, the method further comprises performing an orthographic projection of the converted rotated initial CT image volume to generate the synthetic baseline X-ray image. In a seventh example of the method optionally including one or more of the first through sixth examples, the method further comprises determining a change between the synthetic baseline X-ray image and the subsequent X-ray image, and outputting the determined change to a display device. In an eighth example of the method optionally including one or more of the first through seventh examples, the method further comprises inputting the synthetic baseline X-ray image and the subsequent X-ray image to a deep learning model trained to determine the change between the synthetic baseline X- ray image and the subsequent X-ray image. In a ninth example of the method optionally including one or more of the first through eighth examples, determining the change between the synthetic baseline X-ray image and the subsequent X-ray image comprises calculating a difference between the synthetic baseline X-ray image and the subsequent X- ray image, wherein outputting the determined change to the display device comprises outputting an image comprising the difference to the display device.

[0086] In another embodiment, a method comprises acquiring an initial CT image volume and an initial X-ray image of a subject during a first time duration, acquiring a subsequent X-ray image during a second time duration, updating a synthetic X-ray model based on a mapping of the initial CT image volume to the initial X-ray image, generating a synthetic baseline X-ray image from the initial CT image volume according to the updated synthetic X-ray model, comparing the synthetic baseline X-ray image to the subsequent X-ray image, and outputting the comparison of the synthetic baseline X-ray image to the subsequent X-ray image. [0087] In a first example of the method, the method further comprises identifying a projection angle of the subsequent X-ray image, wherein the projection angle of the subsequent X-ray image is different from a projection angle of the initial X-ray image. In a second example of the method optionally including the first example, the method further comprises generating the synthetic baseline X-ray image from the initial CT image volume according to the projection angle of the subsequent X-ray image. In a third example of the method optionally including one or more of the first and second examples, the method further comprises generating a plurality of synthetic baseline X-ray images from the initial CT image volume with a corresponding plurality of projection angles, and selecting the synthetic baseline X-ray image from the plurality of synthetic baseline X-ray images to match the projection angle of the subsequent X-ray image.

[0088] In yet another embodiment, a system comprises an X-ray imaging system configured to acquire X-ray images, a CT imaging system configured to acquire CT image volumes, and a processor communicatively coupled to the X-ray imaging system and the CT imaging system, the processor configured with instructions in a non-transitory memory that when executed cause the processor to: acquire, via the CT imaging system, an initial CT image volume of a subject during a first time duration; acquire, via the X-ray imaging system, an initial X-ray image of the subject during the first time duration; acquire, via the X-ray imaging system, a subsequent X-ray image of the subject during a second time duration; generate a synthetic baseline X-ray image from the initial CT image volume according to the initial X-ray image; and output the synthetic baseline X-ray image and the subsequent X-ray image for comparison.

[0089] In a first example of the system, the processor is further configured with instructions in the non-transitory memory that when executed cause the processor to identify a projection angle of the subsequent X-ray image. In a second example of the system optionally including the first example, the processor is further configured with instructions in the non-transitory memory that when executed cause the processor to generate the synthetic baseline X-ray image from the initial CT image volume at the proj ection angle of the subsequent X-ray image. In a third example of the system optionally including one or more of the first and second examples, to generate the synthetic baseline X-ray image, the processor is further configured with instructions in the non-transitory memory that when executed cause the processor to map Hounsfield unit (HU) values of the initial CT image volume to attenuation values of the initial X-ray image, rotate the initial CT image volume according to a desired view, and convert the HU values of the rotated initial CT image volume to attenuation values according to the mapping. In a fourth example of the system optionally including one or more of the first through third examples, the processor is further configured with instructions in the non-transitory memory that when executed cause the processor to perform an orthographic projection of the converted rotated initial CT image volume to generate the synthetic baseline X-ray image.

[0090] As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising,” “including,” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property. The terms “including” and “in which” are used as the plain-language equivalents of the respective terms “comprising” and “wherein.” Moreover, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements or a particular positional order on their objects.

[0091] This written description uses examples to disclose the invention, including the best mode, and also to enable a person of ordinary skill in the relevant art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claims

CLAIMS:

1. A method, comprising: acquiring an initial computed tomography (CT) image volume and an initial X-ray image of a subject; acquiring a subsequent X-ray image of the subject; generating a synthetic baseline X-ray image from the initial CT image volume according to the initial X-ray image; and outputting the synthetic baseline X-ray image and the subsequent X-ray image for comparison.

2. The method of claim 1, wherein the initial CT image volume and the initial X-ray image are acquired during a first time duration, and wherein the subsequent X-ray image is acquired during a second time duration subsequent to the first time duration.

3. The method of claim 1, further comprising identifying a projection angle of the subsequent X-ray image.

4. The method of claim 3, wherein generating the synthetic baseline X-ray image from the initial CT image volume according to the initial X-ray image comprises generating the synthetic baseline X-ray image from the initial CT image volume at the projection angle of the subsequent X-ray image.

5. The method of claim 4, wherein the projection angle of the subsequent X-ray image is different from a projection angle of the initial X-ray image.

6. The method of claim 1 , wherein generating the synthetic baseline X-ray image from the initial CT image volume according to the initial X-ray image comprises: mapping Hounsfield unit (HU) values of the initial CT image volume to attenuation values of the initial X-ray image; rotating the initial CT image volume according to a desired view; and converting the HU values of the rotated initial CT image volume to attenuation values according to the mapping.

7. The method of claim 6, further comprising performing an orthographic projection of the converted rotated initial CT image volume to generate the synthetic baseline X-ray image.

8. The method of claim 1, further comprising determining a change between the synthetic baseline X-ray image and the subsequent X-ray image, and outputting the determined change to a display device.

9. The method of claim 8, further comprising inputting the synthetic baseline X-ray image and the subsequent X-ray image to a deep learning model trained to determine the change between the synthetic baseline X-ray image and the subsequent X-ray image.

10. The method of claim 8, wherein determining the change between the synthetic baseline X-ray image and the subsequent X-ray image comprises calculating a difference between the synthetic baseline X-ray image and the subsequent X-ray image, wherein outputting the determined change to the display device comprises outputting an image comprising the difference to the display device.

11. A method, compri sing : acquiring an initial CT image volume and an initial X-ray image of a subject during a first time duration; acquiring a subsequent X-ray image during a second time duration; updating a synthetic X-ray model based on a mapping of the initial CT image volume to the initial X-ray image; generating a synthetic baseline X-ray image from the initial CT image volume according to the updated synthetic X-ray model; comparing the synthetic baseline X-ray image to the subsequent X-ray image; and outputting the comparison of the synthetic baseline X-ray image to the subsequent X-ray image.

12. The method of claim 11, further comprising identifying a projection angle of the subsequent X-ray image, wherein the projection angle of the subsequent X-ray image is different from a projection angle of the initial X-ray image.

13. The method of claim 12, further comprising generating the synthetic baseline X- ray image from the initial CT image volume according to the projection angle of the subsequent X-ray image.

14. The method of claim 12, further comprising generating a plurality of synthetic baseline X-ray images from the initial CT image volume with a corresponding plurality of projection angles, and selecting the synthetic baseline X-ray image from the plurality of synthetic baseline X-ray images to match the projection angle of the subsequent X-ray image.

15. A system, comprising: an X-ray imaging system configured to acquire X-ray images; a CT imaging system configured to acquire CT image volumes; and a processor communicatively coupled to the X-ray imaging system and the CT imaging system, the processor configured with instructions in a non-transitory memory that when executed cause the processor to: acquire, via the CT imaging system, an initial CT image volume of a subject during a first time duration; acquire, via the X-ray imaging system, an initial X-ray image of the subject during the first time duration; acquire, via the X-ray imaging system, a subsequent X-ray image of the subject during a second time duration; generate a synthetic baseline X-ray image from the initial CT image volume according to the initial X-ray image; and output the synthetic baseline X-ray image and the subsequent X-ray image for comparison.

16. The system of claim 15, wherein the processor is further configured with instructions in the non-transitory memory that when executed cause the processor to: identify a projection angle of the subsequent X-ray image.

17. The system of claim 16, wherein the processor is further configured with instructions in the non-transitory memory that when executed cause the processor to: generate the synthetic baseline X-ray image from the initial CT image volume at the projection angle of the subsequent X-ray image.

18. The system of claim 15, wherein, to generate the synthetic baseline X-ray image, the processor is further configured with instructions in the non-transitory memory that when executed cause the processor to: map Hounsfield unit (HU) values of the initial CT image volume to attenuation values of the initial X-ray image; rotate the initial CT image volume according to a desired view; and convert the HU values of the rotated initial CT image volume to attenuation values according to the mapping.

19. The system of claim 18, wherein the processor is further configured with instructions in the non-transitory memory that when executed cause the processor to: perform an orthographic projection of the converted rotated initial CT image volume to generate the synthetic baseline X-ray image.

20. The system of claim 15, wherein the processor is further configured with instructions in the non-transitory memory that when executed cause the processor to: determine a change between the synthetic baseline X-ray image and the subsequent X-ray image; and output the determined change to a display device.