Patent Description:
In medical x-ray imaging, for example, body composition and/or bone densitometry systems, an x-ray source and an x-ray detector are generally mounted on opposing ends of a substantially C-shaped gantry. A scanning radiographic technique, such as typically employed with densitometry, uses a narrowly collimated beam of radiation formed into, for example a fan beam. The emitted fan beam of radiation, typically x-rays, are incident on and detectable by the x-ray detector, although other configurations of x-ray imaging systems are known. This typically uses a smaller array for the x-ray detector, and the x-ray source and the x-ray detector are moved relative to the patient. In embodiments, this enables scanning or collection of data from a broad area of the patient, including the entire patient, as compared to other conventional radiography techniques. The source and the detector are positioned such that when an object (e.g., part of a human body) is interposed there between and is irradiated with x-rays, the detector produces data representative of characteristics of the interposed object.

In the particular application of densitometry, when two (or more) energies of x-rays are used, bone and tissue information can be acquired due to the differences in the absorption of the x-rays of different energies. Measurements of the x-ray absorption by an object at two different x-ray energies can reveal information about the composition of that object as decomposed into two selected basis materials. In the medical area, the selected basis materials are frequently bone and soft tissue. The ability to distinguish bone from surrounding soft tissue allows x-ray images to yield quantitative information about in vivo bone density for the diagnosis of osteoporosis and other bone disease.

As depicted in <FIG> an exemplary x-ray system, such as a dual energy x-ray absorptiometry (DXA or DEXA)/densitometry system <NUM> may be configured to include a substantially C-shaped or semi-circular gantry, or C-arm <NUM>. The C-arm <NUM> movably supports a source <NUM> and a detector <NUM> mounted opposite to each other on opposed ends. The patient <NUM> is disposed between the source <NUM> and the detector <NUM>, such as on a table <NUM>. In many systems <NUM>, the positions of the source <NUM> and detector <NUM> are variable in order to accommodate different patient morphologies, different orientations of the source <NUM> and the detector <NUM> for imaging different portions of the patient, etc. The movement of the source <NUM> and the detector <NUM> is normally controlled by a motor (not shown) located within the system <NUM> to control and maintain the alignment of the source <NUM> and the detector <NUM> during the operation and/or alteration of the orientation of the system <NUM>.

In order to assist with and/or improve one or more of the proper positioning of the patient on the table <NUM>, automatic positioning of the source <NUM> and detector <NUM> relative to the patient, and/or the determination of the current field of view (FOV) of the source <NUM> relative to the position of the patient <NUM>, the system <NUM> can employ a camera <NUM> disposed outside of the system <NUM>, such as on a ceiling in a room in which the system <NUM> is disposed. The camera <NUM> provides optical images of the system <NUM> and the patient in order to provide information to the system <NUM> and/or operator of the system <NUM> to streamline the operation of the system <NUM> and reduce errors.

In order to enable the camera <NUM> to provide the relevant information on the relative position of the source <NUM>/detector <NUM> and the patient, the camera <NUM> must be calibrated with regard to the system <NUM>, such that the position of objects in the images obtained by the camera <NUM> can be referenced with regard to the same objects in the images obtained by the system <NUM>.

In order to perform the calibration, the system <NUM> can employ a calibration optical marker <NUM>, such as that disclosed in <CIT> entitled Optical Geometry Calibration Devices, Systems, And Related Methods For Three-Dimensional X-Ray Imaging (the '<NUM> patent). The calibration optical marker <NUM> is positioned on a portion of the system <NUM>, i.e., on the table <NUM>, and has a configuration, such as a chessboard pattern with known characteristics, e.g., square locations and sizes, that is able to be imaged by the camera <NUM> and which location is known in regards to the image area <NUM> or the table <NUM>.

In the calibration procedure, an image of the optical marker <NUM> is obtained via the camera <NUM>. Using the known distances between the detector <NUM> or the table <NUM> and the marker <NUM> and subsequently all squares intersection points on <NUM> as a result of the known position, i.e., height, of the detector <NUM> relative to the table <NUM> and the position of the detector <NUM> along the table <NUM> caused by the movement of the motor (not shown) as controlled by the system <NUM>, and the calculated distances of the camera <NUM> to the optical marker <NUM> determined from the camera images such as those disclosed in the '<NUM> patent, it is possible to register the camera images to the detector images to correlate coordinates in the camera images directly with coordinates in the detector images. With this registration, in any subsequent imaging procedure using the system <NUM>, images obtained by the camera <NUM> can be used to determine the location of the patient relative to the source <NUM>/detector <NUM> and the FOV of the source <NUM> in order to provide the operator with any necessary adjustments to the position of the patient on the table <NUM> to allow the system <NUM> to provide the desired x-ray images of the patient.

However, while the use of the optical marker <NUM> enables the calibration of the camera <NUM> with regard to the system <NUM> as described previously, the requirement for the optical marker <NUM> is undesirable as it creates the need for an additional component that must be manufactured and sent to the deployment location for the system <NUM> for use in the calibration procedure.

As a result, it desirable to develop a system and method for the calibration of a camera with regard to a DXA/DEXA imaging system that avoids the need for a separate optical marker.

<CIT> describes a method which makes it possible to record the location of a laser or of the laser fan beam relative to the x-ray geometry, and an x-ray device suitable for carrying out the method. Imaging facilities attached to video cameras are used to establish the relationship between x-ray geometry and laser. The structure of the corresponding x-ray device typically features a movable C-arm, a laser positioning device mounted on the C-arm, typically in the form of two laser fan beam projectors mounted on the housing of the x-ray detector, and one or more video cameras mounted on the C-arm. The cameras are aligned in the direction of the laser beams. In a calibration method the relationship between x-ray geometry and laser fan beams can be determined by an image of a calibration phantom being recorded both by the video cameras and also by the x-ray imaging system. Advantageously the calibration phantom features both x-ray-absorbing markers and also structures visible in the camera image, the relative position of the structures is known in relation to a coordinate system assigned to the calibration phantom and the surface geometry of the x-ray phantom is known and likewise described in the above-mentioned coordinate system. For a C-arm angulation the location of the video cameras relative to the x-ray geometry can be determined by the projection geometry of the x-ray imaging system being determined by means of the x-ray-absorbing marker from an x-ray image of the calibration phantom by known methods, the relative position of the video cameras in relation to the calibration phantom can be determined from video images of the camera(s) by known methods and all relative locations between the video cameras and the x-ray geometry can be computed from the now computable locations of the x-ray geometry and of the video cameras in relation to the same coordinate system. The location of the laser relative to the x-ray geometry is calculated for example during an installation, by video images being recorded with the laser positioning device switched on, the laser projection on the calibration phantom being automatically extracted in the recorded video images, the 3D location of the projection lines in the coordinate system of the calibration phantom being determined using the known surface geometry and the relative location of the video cameras in relation to the same coordinate system (this is possible with at least one camera) and the alignment of the planes described by the laser fan beams being reconstructed from the projection lines. In order to be able to follow changes in the laser adjustments after the installation of the x-ray device, if there are at least two video cameras present, the exact laser geometry relative to the C-arm can be determined via video images from at least two cameras being recorded during the patient procedure, the lines generated by projection of the laser fan beams on the patient's surface are extracted from the video images, the 3D line is reconstructed from the individual 2D lines of the video images using the known locations of the video cameras relative to the coordinate system which was determined in the first step by the calibration phantom and the alignment of the planes described by the laser fan beams is computed from the reconstructed 3D lines.

According to one aspect of an exemplary embodiment of the disclosure, an x-ray system includes a support surface, and a gantry operably connected to the support surface and including an x-ray source, an x-ray detector alignable with the x-ray source, and a laser disposed on the gantry adjacent the x-ray detector, the gantry defining a system referential, an image processing system operably connected to the gantry to control the operation of laser, and the x-ray source and x-ray detector to generate x-ray image data, the image processing system including a processing unit for processing the x-ray image data from the detector, a database operably connected to the processing unit and storing instructions for operation of a calibration system, a display operably connected to the image processing system for presenting information to a user, and a user interface operably connected to the image processing system to enable user input to the image processing system and a camera-based feature detection system including a camera spaced from the gantry and operably connected to the image processing system, the camera defining a camera referential within which the support surface and gantry are positioned and operable to generate one or more camera images of the support surface and gantry, wherein the calibration system is operable to register the camera referential to the system referential, wherein the calibration system is configured to determine a number of positions of the indication within the camera image referential, to determine a number of positions of the indication within the system referential, and to register the camera referential to the system referential.

According to still another aspect of an exemplary embodiment of the present disclosure, a method for calibrating a camera-based feature detection system for an x-ray system including the steps of providing an x-ray system having a support surface, and a gantry operably connected to the support surface and including an x-ray source, an x-ray detector alignable with the x-ray source, and a laser disposed on the gantry adjacent the x-ray detector, the gantry defining a system referential, an image processing system operably connected to the gantry to control the operation of laser, and the x-ray source and x-ray detector to generate x-ray image data, the image processing system including a processing unit for processing the x-ray image data from the detector, a database operably connected to the processing unit and storing instructions for operation of a calibration system, a display operably connected to the image processing system for presenting information to a user, and a user interface operably connected to the image processing system to enable user input to the image processing system and a camera-based feature detection system including a camera spaced from the gantry and operably connected to the image processing system, the camera defining a camera referential within which the support surface and gantry are positioned and operable to generate one or more camera images of the support surface and gantry, wherein the calibration system is operable to register the camera referential to the system referential, operating the laser to position an indication on the support surface, obtaining a number of camera images of the indication on the support surface, determining a number of positions of the indication within the camera image referential, determining a number of positions of the indication within the system referential, and registering the camera referential to the system referential.

These and other exemplary aspects, features and advantages of the invention will be made apparent from the following detailed description taken together with the drawing figures.

The drawings illustrate the best mode currently contemplated of practicing the present invention.

Furthermore, any numerical examples in the following discussion are intended to be non-limiting, and thus additional numerical values, ranges, and percentages are within the scope of the disclosed embodiments.

The description herein relates to various embodiments of medical imaging systems. In particular, methods and systems are provided for use as a single energy x-ray absorptiometry (SXA) system, as is exemplarily used to measure breast density or a dual-energy x-ray absorptiometry (DXA) used to measure bone mineral density. Examples of DXA are used herein although it will be recognized that in other embodiments, other modalities of radiography and/or medical imaging may be employed. For example, these may include, but are not limited to: PET, SPECT, C-arm angiography, mammography, ultrasound, and so forth. The present discussion of DXA is provided as an example of one suitable application.

Referring to <FIG> and <FIG>, an exemplary embodiment of the system <NUM>, such as that disclosed in <CIT>, entitled Variable Distance Imaging, may be utilized to measure at least an area of a bone, a length of bone, a bone mineral content (BMC), a bone mineral density (BMD), or a tissue thickness or density. The BMD is calculated by dividing the BMC by the area of a bone. During operation, an x-ray beam with broadband energy levels is utilized to scan an object, for example, to scan a human patient to image the bones of the patient. The acquired images of the bones are used to diagnose a medical condition, for example osteoporosis. The images may be generated in part from determined bone density information acquired during a dual-energy x-ray scan. As described in further detail herein, the positions of the source <NUM>, detector <NUM>, and/or table can be adjusted to achieve further desired imaging purposes, including but not limited to magnification, increasing image resolution, or spatial resolution. For exemplary purposes, the imaging system <NUM> may be described as a dual-energy x-ray absorptiometry (DXA) system, although it will be recognized that a variety of other systems may also be implemented in a similar manner.

The imaging system <NUM> is shown as including a gantry <NUM>. Gantry may be a substantially C shaped or semi-circular gantry, or C-arm gantry. The gantry <NUM> movably supports a source <NUM> and a detector <NUM> mounted opposite to each other on opposed ends. Further, a subject <NUM> is disposed between the source <NUM> and the detector <NUM>.

Gantry <NUM> includes an x-ray source <NUM> that projects a beam of x-rays <NUM> toward detector array <NUM>. The gantry <NUM> exemplarily includes a lower end <NUM> that is positioned below a subject <NUM>, such as a patient, and an upper end <NUM> that is positioned above the subject <NUM>. The x-rays pass through the subject <NUM> to generate attenuated x-rays. As depicted in <FIG>, the x-ray source <NUM> may be secured to the upper end <NUM> and the x-ray detector <NUM> secured to the lower end <NUM>. As depicted in <FIG>, the detector <NUM> may be secured to the upper end <NUM> and the x-ray source <NUM> may be secured to the lower end <NUM>. Each detector element <NUM> is exemplarily, but not limited to a cadmium telluride (CdTe) detector element, which produces an electrical signal that represents an intensity of the attenuated x-rays.

During a scan to acquire image data, gantry <NUM> and/or components mounted on gantry <NUM> are movable relative to the subject <NUM> and/or a table <NUM>. The table <NUM> may include a scanning surface on which the subject <NUM> may be positioned. For example, during an acquisition of image data, the gantry <NUM> is movable to change a position and/or orientation of the source <NUM> and/or detector <NUM> relative to the patient. In an exemplary embodiment, the gantry <NUM> may move the source <NUM> and the detector <NUM> in a transverse scanning path, a progressive overlapping scanning path, or a zig-zag (e.g. raster) scanning path <NUM> that moves along both the long axis <NUM> and the short axis <NUM> of the table <NUM>, as shown in <FIG> and <FIG>. It will be recognized that other forms of image data acquisition may utilize other forms of scanning paths, which may include, but are not limited to rotation or tilt of the gantry <NUM>. It will be recognized that in other exemplary imaging systems within the present disclosure, one of the source or detector may remain in a fixed position while the other of the source or detector is movable with respect to the patient. In still other exemplary embodiments as disclosed herein, the table, which is configured to support the patient, is further movable to achieve a desired image acquisition.

Movement of the gantry <NUM> and an operation of x-ray source <NUM> are governed by an imaging controller <NUM> of imaging system <NUM>. Imaging controller <NUM> includes an x-ray controller <NUM> that provides power and timing signals to x-ray source <NUM>. The x-ray controller <NUM> may further provide operational and/or control signals to the adjustable collimator <NUM> to shape the beam of x-rays from the source <NUM> in accordance with the imaging procedure to be performed. In some embodiments, the x-ray beam may be shaped (collimated) as a fan beam. In an exemplary embodiment, the fan beam <NUM> may be a narrow fan beam such as to limit the divergence between x-rays in the beam, which has been shown to improve parallax and image overlap blurring.

The imaging controller <NUM> further includes a gantry motor controller <NUM> that controls a motion, speed, and position of gantry <NUM> via one or more suitable motors (not shown) operably connected to the gantry <NUM> or specified portions thereof and the gantry motor controller <NUM>. In some embodiments, gantry motor controller <NUM> may control movement of the gantry <NUM> in multiple degrees of freedom utilizing the one or more motors, including a tilt angle of gantry <NUM>. The system <NUM> can also include a table motor controller <NUM> is operably connected to the table <NUM> through a table motor (not shown) and to the imaging controller <NUM>. The table motor is operable, under control signals from the table motor controller <NUM>, to translate, rotate, and/or tilt the table <NUM> in a plurality of degrees of freedom of movement. In an embodiment, the table motor is operable to move the table <NUM> in three degrees of freedom, (e.g. horizontal, vertical, and depth translation) while in another embodiment, rotational degrees of freedom of movement (e.g. pitch, yaw, and roll) may be available. It will be recognized that the table motor may include one or more mechanical or electromechanical systems to carry out these movements of the table <NUM>, including but not limited to tack and opinion, screw, or chain driven actuators.

The x-ray source <NUM> and the x-ray detector <NUM>, i.e., the gantry <NUM>, may be moved in a raster pattern <NUM> so as to trace a series of transverse scans <NUM> of the subject <NUM> during which dual energy x-ray data is collected by the x-ray detector <NUM>. The transverse scanning procedure generates either a single image or quantitative data set, form a plurality of scan images acquired across a patient, wherein the x-ray source <NUM> and the detector <NUM> are either longitudinally aligned with the superior-inferior axis of the patient or transversely from the patient's left to right. Scanning a patient using a transverse motion facilitates minimizing the time between acquisitions of adjacent scan images because the transverse direction across the patient is shorter than the longitudinal direction across the patient. Thus transverse scanning can reduce the severity of patient motion artifacts between scan images allowing the images to be more accurately merged.

The transverse scanning motion is produced by coordination between the motion control of the gantry <NUM>, x-ray source <NUM>, and the x-ray detector <NUM> by the gantry motor controller <NUM> as well as optional control of the table <NUM> by the table motor controller <NUM> which operates the table <NUM> through the table motor. During operation, the x-ray source <NUM> produces a fan beam <NUM> having a plane that is exemplarily parallel to the longitudinal axis <NUM>. Optionally, the fan beam <NUM> may have a plane that is perpendicular to the longitudinal axis <NUM>. The raster pattern <NUM> is adjusted such that there is some overlap (e.g., an overlap of <NUM>%) between successive scan lines of the fan beam <NUM>. Further, the range of motion of the gantry <NUM> and the source14/detector <NUM> define a system referential <NUM> encompassing the space able to the viewed/imaged by the system <NUM>.

A data acquisition system (DAS) <NUM> in the imaging controller <NUM>, samples and digitizes the data from detector elements <NUM> and converts the data to sampled and digitized data for subsequent processing. In some embodiments, DAS <NUM> may be positioned adjacent to detector array <NUM> on gantry <NUM>. Pre-processor <NUM> receives the sampled and digitized data from DAS <NUM> to pre-process the sampled and digitized data. In one embodiment, pre-processing includes, but is not limited to, an offset correction, a primary speed correction, a reference channel correction, an air-calibration, and/or applying a negative logarithmic operation. As used herein, the term processor is not limited to just those integrated circuits referred to in the art as a processor, but broadly refers to a controller, a microcontroller, a microcomputer, a programmable logic controller, an application specific integrated circuit, and any other programmable circuit, and these terms are used interchangeably herein. Pre-processor <NUM> pre-processes the sampled and digitized data to generate pre-processed data.

An image processor <NUM> receives the pre-processed data from pre-processor <NUM> and performs image analysis, including that of densitometry and/or absorptiometry through one or more image processing operations. The acquired bone and tissue information, for example, image and density information may be processed and displayed in real time though operations to the image processor <NUM> and/or the processing unit <NUM>. The processing unit <NUM> exemplarily operates to store the reconstructed image in a mass storage device <NUM>, where the mass storage device <NUM> may include, as non-limiting examples, a hard disk drive, a floppy disk drive, a compact disk-read/write (CD-R/W) drive, a Digital Versatile Disc (DVD) drive, a flash drive, and/or a solid-state storage device. As used herein, the term computer is not limited to just those integrated circuits referred to in the art as a computer, but broadly refers to a processor, a microcontroller, a microcomputer, a programmable logic controller, an application specific integrated circuit, and any other programmable circuit, and these terms are used interchangeably herein. It will be recognized that any one or more of the processors and/or controllers as described herein may be performed by, or in conjunction with the processing unit <NUM>, for example through the execution of computer readable code stored upon a computer readable medium accessible and executable by the processing unit <NUM>. For example, the computer/processing unit <NUM> may include a processor configured to execute machine readable instructions stored in the mass storage device <NUM>, which can be non-transitory memory. Processor unit/computer <NUM> may be single core or multi-core, and the programs executed thereon may be configured for parallel or distributed processing. In some embodiments, the processing unit <NUM> 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 processing unit <NUM> may be virtualized and executed by remotely-accessible networked computing devices configured in a cloud computing configuration. According to other embodiments, the processing unit/computer <NUM> may include other electronic components capable of carrying out processing functions, such as a digital signal processor, a field-programmable gate array (FPGA), or a graphic board. According to other embodiments, the processing unit/computer <NUM> may include multiple electronic components capable of carrying out processing functions. For example, the processing unit/computer <NUM> may include two or more electronic components selected from a list of electronic components including: a central processor, a digital signal processor, a field-programmable gate array, and a graphic board. In still further embodiments the processing unit/computer <NUM> may be configured as a graphical processing unit (GPU) including parallel computing architecture and parallel processing capabilities.

Processing unit <NUM> also receives commands and scanning parameters from a user, such as an operator, via a console <NUM> that includes a user interface device, such as a keyboard, mouse, voice-activated controller, touchscreen or any other suitable input apparatus. An associated display <NUM> allows a user, such as an operator, to observe the image and densitometry data from processing unit <NUM>. The commands and scanning parameters are used by processing unit <NUM> to provide control signals and information the imaging controller <NUM>, including the DAS <NUM>, x-ray controller <NUM>, and gantry motor controller <NUM>. In addition, processing unit <NUM> may operate a table motor controller <NUM> exemplarily of the imaging controller <NUM> which controls a movable subject support, which is exemplarily a motorized table <NUM>, to position subject <NUM> within gantry <NUM>. Particularly, table motor controller <NUM> adjusts table <NUM> to move portions of subject <NUM>.

During operation, the system <NUM> is configured to operate in either a dual energy x-ray mode or a single energy x-ray mode. In the single energy mode, the x-ray source <NUM> emits x-rays at a narrow band of energies of a few keV and in the diagnostic imaging range of approximately <NUM>-<NUM> keV. In the dual-energy mode, the x-ray source <NUM> emits radiation at two or more bands of energy emitted simultaneously or in rapid succession. The x-ray source <NUM> may also be configured to emit a single broadband energy of more than a few keV over the diagnostic imaging range. The system <NUM> may be switched between the dual energy mode and the single energy mode by increasing or decreasing the x-ray source <NUM> voltage and/or current. The system <NUM> may also be switched between the dual energy mode and the single energy mode with a K-edge filter and energy discriminating detector. It should be noted that the x-ray source <NUM> may emit x-rays at different energies or ranges of energies.

The x-ray source <NUM> may be configured to output a fan beam <NUM> of x-rays. The x-ray source <NUM> may also be configured to output a pencil beam of x-rays (not shown), a cone beam of x-rays, or other configurations. In some embodiments, the processing unit <NUM> controls the system <NUM> to operate in the single energy mode or dual-energy mode to determine the bone or tissue information of at least some of the scanned body. In general, an image resolution in the system <NUM> may be based on a detector element size, a source focal spot size, and an object to detector distance. The acquired images may then be used to measure, for example, bone density or other bone and tissue characteristics or content. As discussed above, the dual-energy x-ray scan may be a rectilinear scan of the entire patient body, which may be performed in a transverse-type scanning sequence as described above. During the dual-energy x-ray scan an image of the entire body of the patient may be acquired, which includes image information relating to the bones and tissue in the body. The full body or total body scan of the entire body may be performed as a single scanning operation, which may be a low dose mode scan. In some embodiments, instead of a full body or total body scan, individual rectangular regions of the body may be scanned, which may be single sweep scans. Once the scan of the patient, or a portion thereof, is completed, the dual energy signals provided by the detector <NUM> are deconstructed into images of two basis materials, such as bone and soft tissue. The high and low energy signals can also be combined to provide a single energy mode having superior signal to noise ratio for imaging purposes.

The system <NUM> additionally includes a camera <NUM> disposed on a surface <NUM> of the room within which the system <NUM> is located. In the exemplary embodiment of <FIG>, the camera <NUM> is disposed in a ceiling <NUM> above the system <NUM>, such that the system <NUM> and imaged volume <NUM> are entirely positioned within the area viewable by the camera <NUM>, which defines the camera referential <NUM>. The camera <NUM> is operably connected to the computer/processing unit <NUM> to forms a part of a camera-based feature detection system <NUM> for the system <NUM> that can be operated to detect and provide information regarding the proper positioning of the patient <NUM> on the table <NUM>, automatic positioning of the source <NUM> and detector <NUM> relative to the area of interest of the patient <NUM>, and/or the determination of the current field of view (FOV) of the source <NUM> relative to the position of the patient <NUM>. The camera <NUM> can be operated in response to signals sent from the computer/processing unit <NUM> to the camera <NUM>, with the data forming the images obtained by the camera <NUM> being able to be transmitted to the computer/processing unit <NUM>. The camera <NUM> can be any suitable type of camera for obtaining images of the system <NUM> and the patient <NUM> located on the system <NUM>, such as an RBG-IR-Depth camera capable of obtaining images in the visible and infrared spectrums, and providing depth information among others.

The images from the camera <NUM> are transmitted to the camera-based feature detection system <NUM> within the computer/processing unit <NUM> which can be utilized to provide information of one or more of the proper positioning of the patient <NUM> on the table <NUM>, automatic positioning of the source <NUM> and detector <NUM> relative to the patient <NUM>, and/or the determination of the current field of view (FOV) of the source <NUM> relative to the position of the patient <NUM>. This information is calculated utilizing a known relationship or registration between the frame of reference for the system <NUM> or system referential <NUM>, as defined by the components of the system <NUM>, e.g., the gantry <NUM>, the source <NUM> and the detector <NUM>, and the frame of reference for the camera <NUM> or camera referential <NUM>, as defined by the location of the camera <NUM>. With this known relationship, the computer/processing unit <NUM> can correlate information/data provided by the images from the camera <NUM>, e.g., the location of the patient <NUM> and/or body part of interest (e.g., a knee) on the table <NUM>, with the known location of the source <NUM> and detector <NUM> from the system <NUM> in order to make adjustments to the position of the source <NUM>/detector <NUM> and/or patient <NUM>/table <NUM> prior to and/or during any imaging procedure performed on the patient <NUM> using the system <NUM>.

In order to provide the known relationship between the system referential and the camera referential, there must be a registration or calibration of the position of the system <NUM> and the components thereof within the camera referential <NUM>. As best shown in <FIG>, the upper end <NUM> of the gantry <NUM> includes a light source <NUM>, such as a target laser <NUM> disposed adjacent the detector <NUM>. When operated, the laser <NUM> projects a light beam <NUM> onto the table <NUM> or portion of the patient <NUM> on the table <NUM> to provide an indication <NUM> of the point where the x-rays from the source <NUM> are to pass through the table <NUM> on a path to the detector <NUM>.

When the laser <NUM> is operated, as best shown in <FIG> the location of the indication <NUM> generated by the laser <NUM> relative to the components of the system <NUM>, e.g., the source <NUM>, detector <NUM> and table <NUM>, is known within the system referential <NUM> as a result of the construction of the system <NUM> and the positioning of the components under the control of the computer/processing unit <NUM>. Further, the position of the indication <NUM> can also be determined within the camera image referential <NUM> using an image obtained by the camera <NUM> of the indication <NUM> as projected onto the table <NUM>. By moving the gantry <NUM> along the long axis table <NUM> and moving the detector <NUM> within the gantry <NUM> to move the indication to different points along the short axis of the table <NUM> as different points along the long axis, as shown in <FIG>, the camera <NUM> can obtain a number of images of the indication <NUM> along the path of the gantry <NUM>, providing multiple reference points for the indication <NUM> within the camera image referential <NUM> that have a correspondence with known locations of the indication <NUM> within the system referential <NUM>. Depending upon the position of the camera <NUM>, there may be an area <NUM> of the table <NUM> that is obstructed by the gantry <NUM> such that the indication <NUM> cannot be viewed by the camera <NUM>. However, the number of points for the location of the indication <NUM> that can be obtained to either side of the area <NUM> are sufficient to calculate the necessary correspondence between the locations of the indication <NUM> in the system referential <NUM> and in the camera image referential <NUM> and thus registering camera referential <NUM> to system referential <NUM>.

In a particular exemplary embodiment of the invention, each camera image of the indication <NUM> can be obtained using the camera <NUM> operated in the visible spectrum and/or in the infrared spectrum, such as when the camera <NUM> utilized is an Intel® RealSense™ camera, in order to obtain the best view of the location of the indication <NUM>. Using a suitable 2D to 3D pose or model correspondence procedure, the localization in 2D image(s) of the indication <NUM> obtained by the camera <NUM>, along with the corresponding 3D coordinates of the indication in the system referential can be employed to determine the pose/position of the camera <NUM> relative to system <NUM>.

Further, in other exemplary embodiments illustrated in <FIG>, the location of the indication <NUM> within the camera image referential <NUM> can be determined by obtaining a first camera image of the system <NUM> with no indication <NUM> present, which can be a first infrared camera image, subsequently operating the laser <NUM> at the same location for the gantry <NUM> and obtaining a second camera image of the system <NUM> including the indication <NUM>, which can be a second infrared image, and then subtracting the pixels in the first image without the indication <NUM> from the second image including the indication <NUM> to produce a third image of only the indication <NUM> within the camera image referential <NUM>.

With the images of the indication <NUM> from the camera <NUM> and the corresponding indication coordinates into the system referential <NUM>, with a minimum of three (<NUM>) images being required, a transformation matrix can be computed to establish the correspondence of any points in the camera referential <NUM> to points within the system referential <NUM>. For example, for each camera image, the location of the indication <NUM> is known in each of the X, Y and Z axes of the system referential <NUM> as a result of the known location of the laser <NUM> due to the known position of the gantry <NUM> based on the construction of the gantry <NUM> (and position of the laser <NUM> thereon) in conjunction with any movement of the gantry <NUM> via suitable motors under the control of the imaging controller <NUM> and/or computer/processing unit <NUM>, thus determining the position of the indication <NUM> in the X and Y axes, with the Z axis position being defined as <NUM>, i.e., the surface of the table <NUM>. With these known coordinates of the indication <NUM> in the system referential <NUM>, along with the corresponding location of the indication in the camera image referential <NUM>, it is possible to register the camera referential <NUM> with regard to the system referential <NUM> such as by employing any suitable known manner of determining the solution for the Perspective-n-Point (PnP) for the camera <NUM>.

For example, as shown in the exemplary embodiment of <FIG>, the calibration system <NUM> can be operated in step <NUM> to obtain one or more camera images of the indication <NUM>, such as described previously and/or in an infrared or visible spectrum modes of operation for the camera <NUM>. In step <NUM> the one or more images are subjected to image processing by the system <NUM>, such as by the processing unit <NUM>, where the X and Y coordinates of the indication <NUM> in the image(s) are determined based on image processing algorithms or manual detection. Simultaneously, in step <NUM> the gantry <NUM> is moved to a desired location using the one or more motors such that the position of the gantry <NUM> within the system referential <NUM> is known based on the precise operation of the motor(s) to position the gantry <NUM>. Correspondingly, the location or coordinates where the emitted x-rays pass through the table <NUM>, i.e., is known from the structure and position of the gantry <NUM>. In step <NUM>, which can be performed prior to, simultaneously with, or subsequent to step <NUM>, the computer/processing unit <NUM> can utilize the precise location of the laser <NUM> relative to the detector <NUM>, i.e., the laser offset, to determine the exact position of the indication <NUM> within the system referential <NUM> relative to the position of the x-ray intersection point on the table <NUM>. This process through steps <NUM>-<NUM> can be repeated for a number of different locations of the indication <NUM> on the table <NUM> to provide a sufficient number of coordinate pairs <NUM> for the indication <NUM> in both the camera image referential <NUM> and the system referential <NUM>, e.g., at least three coordinate pairs for use with a P3P algorithm employed within the calibration system <NUM>.

With a specified number of coordinate pairs, in step <NUM> the computer/processing unit <NUM> can provide the coordinate pairs <NUM> as an input to a suitable algorithm <NUM>, such as a random sample consensus, or RANSAC algorithm, or a PnP solution, or a combination thereof, such as a that described at: https://en. org/wiki/Perspective-n-Point, along with various intrinsic parameters <NUM> for the camera <NUM>, in order to create or output from the artificial intelligence/algorithm <NUM> a transformation matrix <NUM> for converting coordinates in the system referential <NUM> to the camera referential <NUM> and vice versa.

Looking now at <FIG>, this transformation matrix <NUM>/registration enables the computer/processing unit <NUM> to associate images from the camera <NUM> with images and/or proposed images from the detector <NUM> in order to accurately identify the position of anatomical structures of the patient <NUM> shown in a camera image within the system referential <NUM>. In particular, in a camera image <NUM> obtained by the camera <NUM> of a point of interest P on the patient/subject <NUM>, the image provides pixel information (X,Y) and depth information (Z) on the point of interest P that provides coordinates (X,Y,Z) for the point of interest P in the camera referential <NUM>. The transformation matrix <NUM> can be applied to the coordinates for the point P in the camera referential <NUM> to convert the coordinates into coordinates within the system referential <NUM> for use by the system <NUM>.

Further, as the system and method requires no additional components for the performance of the camera calibration, i.e., no optical marker, the camera calibration system and method of the present disclosure provides a much more highly efficient calibration process than employed previously.

Claim 1:
A method for calibrating a camera-based feature detection system for an x-ray system (<NUM>), the method comprising the steps of:
a. providing an x-ray system (<NUM>) comprising:
i. a support surface (<NUM>), and a gantry (<NUM>) operably connected to the support surface (<NUM>) and including an x-ray source (<NUM>), an x-ray detector (<NUM>) alignable with the x-ray source (<NUM>), and a light source (<NUM>) disposed on the gantry (<NUM>) adjacent the x-ray detector (<NUM>), the gantry (<NUM>) defining a system referential (<NUM>);
ii. an image processing system (<NUM>) operably connected to the gantry to control the operation of light source, and the x-ray source (<NUM>) and x-ray detector (<NUM>) to generate x-ray image data, the image processing system (<NUM>) including a processing unit (<NUM>) for processing the x-ray image data from the detector (<NUM>), a database (<NUM>) operably connected to the processing unit (<NUM>) and storing instructions for operation of a calibration system (<NUM>), a display (<NUM>) operably connected to the image processing system (<NUM>) for presenting information to a user, and a user interface (<NUM>) operably connected to the image processing system (<NUM>) to enable user input to the image processing system (<NUM>); and
iii. a camera-based feature detection system (<NUM>) including a camera (<NUM>) spaced from the gantry (<NUM>) and operably connected to the image processing system (<NUM>), the camera (<NUM>) defining a camera referential (<NUM>) within which the support surface (<NUM>) and gantry (<NUM>) are positioned and operable to generate one or more camera images of the support surface (<NUM>) and gantry (<NUM>), wherein the calibration system (<NUM>) is operable to register the camera referential (<NUM>) to the system referential (<NUM>);
b. operating the light source (<NUM>) to position an indication (<NUM>) on the support surface (<NUM>);
c. obtaining a number of camera images of the indication (<NUM>) on the support surface (<NUM>);
d. determining a number of positions of the indication (<NUM>) within the camera image referential (<NUM>);
e. determining a number of positions of the indication (<NUM>) within the system referential (<NUM>); and
f. registering the camera referential (<NUM>) to the system referential (<NUM>).