Patient monitoring during scanning

Abstract

The imaging system is for capturing images of a patient during a medical scan. A set of one or more cameras captures images of the patient, after applying distortion and perspective correction steps, such that pixel rows correspond to positions along an axis parallel to a direction of movement of the patient support and pixel columns correspond to positions along an axis perpendicular to the patient support. Patient motion of interest can then be identified based on image movement in the pixel column direction between successive captured images. A measure of patient motion can then be derived.

Description

[Technical field]

[0001] The present invention relates to monitoring a patient during a medical scan, and in particular to detecting movement. [Background technology]

[0002] In many medical imaging procedures, it is important to monitor the patient during the imaging procedure, for example to monitor the patient's movements during the procedure or to monitor the patient's health during the imaging procedure. Surveillance images, such as video images provided by a camera, such as a wide field of view camera, are used for monitoring.

[0003] As an example, it is desirable to detect respiratory-related motion to prevent and correct motion artifacts, ensure optimal image quality, and support respiratory-induced scanning. Indeed, undesirable patient motion is one of the main reasons for image quality problems and safety events (such as finger pinching).

[0004] Moreover, in these monitoring applications, it is particularly important to monitor a certain region of interest of the patient. For example, if the respiratory movement is to be monitored, the patient's chest must be monitored, or if the patient's health condition is to be monitored, the patient's face must be monitored. In order to monitor the patient's region of interest during certain medical imaging procedures, such as CT or MR imaging procedures, the patient must be tracked in the provided monitoring images. Summary of the Invention [Problem to be solved by the invention]

[0005] One of the problems in tracking the patient's region of interest in the monitoring image is that, as the patient is moved through the medical imaging device during the medical scan procedure, the shape and position of the region of interest changes in the monitoring image during the imaging procedure due to changes in the perspective of the monitoring camera relative to the region of interest. This makes a purely image-based tracking of the region of interest to be monitored more difficult. Another problem in tracking the region of interest using a regular monitoring camera is the presence of occlusions, especially as the treatment couch is moving through the bore. Thus, it is very difficult to obtain a free, unoccluded view of the patient's face throughout the examination, for example, using a regular monitoring camera mounted on the wall of the scanning room.

[0006] Typically, two or more surveillance cameras are mounted in the scanning room to capture both the front and rear views of the scanner, for example, mounted at an angle such that there is at least a partial view through the scanning system, e.g., through the bore of the CT scanner gantry.

[0007] Approaches in which the camera is mounted on the wall or ceiling of a room can provide, at best, only a partial view of the patient during scanning, with much of the anatomy likely to be occluded by the patient's own shape, the limited diameter of the bore through the scanning system, and positioning or the presence of medical devices.

[0008] Thus, the surveillance system does not have a continuous view of the relevant body parts of the patient throughout the entire examination, especially as the patient support moves through the scanning system.

[0009] Mounting a camera on the front or rear end of the patient support has the advantage of providing a stable view of the patient while the patient support is moving. However, this option is not desirable since these parts of the patient support are used to position medical devices or head supports. Furthermore, with a heavy patient, the view to either the upper or lower part of the patient will most likely be occluded by the abdomen.

[0010] Thus, there is a need for imaging systems that can better capture images of patients during medical scans. These images may be subject to manual inspection to assess patient motion. However, in some cases, automatic patient motion detection may be used as input for image reconstruction algorithms and / or to drive the scanning process. It is also an important clinical input parameter for respiratory-gated and respiratory-triggered scans, such as lung and 4D CT scans used for CT simulation of radiation therapy.

[0011] One option is to place the camera on the scanning system, for example on the gantry facing the patient. The main challenge then is to separate the apparent motion due to horizontal displacements of the patient support from the true patient motion, as occurs during helical CT scanning. Because the patient is lying down, the patient motion typically has a significant anterior-posterior motion component. However, due to the projection geometry of the camera system, these two motions are superimposed in the final camera image, making the motion extraction difficult.

[0012] Therefore, there is also a need for a motion sensing solution that accounts for different patient orientations and patient support positions.

[0013] WO 2021 / 110613 discloses a system and method for monitoring a patient during a medical scan. It uses a wide field of view camera to capture an image of the patient. The position and shape of the region of interest are mapped while the patient support moves.

[0014] EP 3 832 602 discloses an apparatus for monitoring an object during imaging, in which a region of interest is determined using two monitoring units at different support positions as well as a position map based on a calibration object at a calibration support position. [Means for solving the problem]

[0015] The invention is defined by the claims.

[0016] According to an example according to one aspect of the present invention, there is provided an imaging system for capturing images of a patient during a medical scan using a scanner having a scanning system and a patient support, the imaging system comprising: a set of one or more cameras for mounting in a fixed position relative to the scanning system directed towards the patient support to capture images, each camera of the set having an optical axis orthogonal to a direction of displacement of the patient support when the scanner is in use, and a row of pixels in an image captured by each camera corresponds to a position along an axis parallel to the direction of movement of the patient support; A processor, the processor comprising: performing image post-processing to correct distortion in the captured images due to a width of field of view of the one or more cameras and to provide perspective correction; identifying patient motion based on image motion in the pixel column direction between successive captured images; outputting the patient movement measurements; a processor configured to execute An imaging system is provided having the following:

[0017] The imaging system captures images in which the movement of the patient support results in a displacement in the pixel row direction, which is orthogonal to typical patient movements, which in the case of respiration are mainly vertical. This movement is therefore in the pixel column direction. This makes the movement analysis simpler in that the movement can be extracted simply from the analysis of the image changes of the pixel columns, i.e. the patient movement is identified based on the image movement of only the pixel columns between successive captured images. In this way, the anterior-posterior component of the patient movement, which is the main component of the patient movement for recumbent examinations, can be optimally detected and quantified. Perspective correction accounts for the fact that the camera may not be oriented exactly perpendicular to the main axis of the gantry (which is also the direction of the table movement) due to inaccuracies in positioning and orientation. After perspective correction, the direction of the table movement is exactly along the desired axis (line) of the output image. By ensuring the correct orientation of the viewing angle of the output image, it is possible to quantify the detected movement in the pixel column (vertical) direction. If the viewing angle is not correctly aligned, the movement of the patient support will also result in small movements in the pixel column direction, which should be avoided.

[0018] The processor is configured, for example, to identify at least one region of interest in the image and to identify patient motion relative to the at least one region of interest.

[0019] In this way, the movement of particular regions of the patient can be monitored, for example regions that move with breathing.

[0020] The processor may, for example, be further configured to track at least one region of interest on the patient during displacement of the patient support, such that the same region can be monitored over time to detect localized motion.

[0021] The processor may be configured to perform the tracking.

[0022] It may use input indicative of patient support motion or may be based on image-based feature identification and tracking.

[0023] Thus, the tracking may be based on image processing or may use external patient support position information from a scanner.

[0024] The region of interest includes, for example, the abdomen. Thus, the respiratory motion signal can be derived from image processing.

[0025] The region of interest can include, for example, the region of the scan plane area of the imaging system, i.e., the part of the imaging system where data is acquired for image formation.

[0026] At least one camera of the set is equipped with, for example, a fisheye lens having a field of view exceeding 150 degrees. Thus, the patient support (and the patient on the patient support) can be imaged by a small set of cameras, even if it is a single camera.

[0027] The processor can be further configured to calculate the depth of the movable part with respect to the camera. Based on the depth, the movement can be quantified in the sense that the physical amplitude and direction of the movement can be calculated. The spatial coordinates of the points belonging to the movable part can be calculated. Further, based on the depth, a 3D model can be calculated as needed.

[0028] To calculate the depth map, the principles known from stereo vision are applied. The input is two images acquired using the table at two different positions. The corresponding table displacements (e.g., numbers in millimeters) are obtained from the scan system and input. Since the perspective-corrected images are such that the table displacement is only along the lines of the image, the correspondence between the two images is found by calculating the horizontal shift between the corresponding pixels. This is the parallax. The depth is calculated from the parallax using camera intrinsic parameters (e.g., focal length).

[0029] The processor is further configured, for example, to determine the position and magnitude of the local patient's movement and to derive the overall movement from the local patient's movement.

[0030] The processor may be configured to perform a calibration process that involves taking one or more calibration images that allow distortion and perspective correction to be performed for analysis of motion of different patient regions at different positions within the field of view at different times.

[0031] Calibration is typically performed once after installation of the camera. It can be repeated as needed (e.g. after a service visit), but is not required every time movements are calculated.

[0032] The present invention also provides A scanning system; a patient support extending through the scanning system; a drive system for driving the patient support through the scanning system; an imaging system as defined above; The present invention provides a medical scanner including:

[0033] Each camera of the set is, for example, mounted on the scanning system with its optical axis oriented perpendicular to the direction of displacement of the patient support when the medical scanner is in use, and the pixel rows of the image captured by each camera correspond to positions along an axis parallel to the direction of movement of the patient support.

[0034] This provides the desired pixel row alignment with the scanner patient support motion axis so that the pixel columns contain associated patient motion information.

[0035] The invention also provides an imaging processing method for processing images of a patient during a medical scan using a scanner having a scanning system, a patient support and a set of one or more cameras mounted in a fixed position relative to the scanning system directed towards the patient support, each camera of the set having an optical axis orthogonal to a direction of displacement of the patient support when the scanner is in use, the method comprising: receiving an image from one or more cameras of the set, rows of pixels in the image corresponding to positions along an axis parallel to a direction of motion of the patient support; performing image post-processing to correct distortion in the captured images due to a width of field of view of the one or more cameras and to provide perspective correction; identifying patient motion based solely on image motion in the pixel column direction between successive captured images; outputting the patient movement measurements; The present invention provides a method comprising:

[0036] The method is: identifying at least one region of interest within the image; identifying patient motion relative to the at least one region of interest; may have the following structure:

[0037] The region of interest may, for example, include the thorax.

[0038] The method may also include performing a calibration process by capturing one or more calibration images.

[0039] Horizontal shifts are also calculated, for example, to obtain depth information and to quantify the movement (magnitude, orientation, and spatial coordinates).

[0040] The invention also provides a computer program comprising computer program code adapted, when the program is executed on a processor of an imaging system as defined above, to perform the above method.

[0041] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0042] For a better understanding of the invention and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings in which: [Brief description of the drawings]

[0043] [Figure 1] 1 illustrates a schematic diagram of an example medical scanner; [Diagram 2] 3 shows an example of three images of a rectified image sequence. [Diagram 3] FIG. 1 shows a side view of a CT scanner having a single camera located on one side of the gantry. [Figure 4] FIG. 1 shows a side view of a CT scanner having two cameras, a first camera located on one side of the gantry and a second camera located on the opposite side of the gantry. [Diagram 5] 1 shows two cameras positioned within the gantry bore with lateral positions. [Figure 6] 4 shows a pattern for use in the calibration phase. [Figure 7] 2 shows a second example of a medical scanner. [Figure 8] 1 shows a camera and its field of view to illustrate one design of the scanner. [Figure 9] A series of images of a patient are shown, showing the region of interest as a block in the abdominal region. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] The present invention will now be described with reference to the drawings.

[0045] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the devices, systems, and methods, are for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the devices, systems, and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the figures to denote the same or similar parts.

[0046] The present invention provides an imaging system for capturing optical images of a patient during a medical scan. A set of one or more cameras captures images of the patient, after applying distortion and perspective correction steps, such that pixel rows correspond to positions along an axis parallel to the direction of movement of the patient support and pixel columns correspond to positions along an axis perpendicular to the direction of movement of the patient support. Patient motion of interest can then be identified based on image movement in the pixel column direction between successive captured images. A measure of patient motion can then be derived.

[0047] The present invention generally relates to the analysis of patient motion. Two aspects are described below in relation to motion analysis. The first aspect relates to the generation of a set of images that most easily allows motion to be visually inspected. The second aspect relates to automatically deriving a measure of the amount of patient movement, which can be used, for example, to trigger an imaging process.

[0048] The two aspects may be implemented separately or in combination, and although both aspects are described below, the invention particularly relates to the second aspect.

[0049] 1 shows a schematic diagram of an example of a medical scanner 100 for acquiring medical images of a subject, the medical scanner further comprising an imaging system for capturing optical images of the subject during a medical scan, the images being generated for the purpose of determining patient motion.

[0050] The medical scanner 100 comprises a scanning system, such as a CT imaging system 140 adapted to acquire medical images, i.e. in this example CT images, of a patient 121 arranged on a patient support 120. The patient support 120 is adapted to move the patient 121 through the CT imaging system 140 during a CT imaging procedure. To this end, the medical scanner has a drive system 124 for driving the patient support through the scanning system.

[0051] The imaging system comprises an optical camera 130 adapted to acquire surveillance images of the patient 121 during a CT imaging procedure, and a processor 150. The operation of the system with a single camera is described, although there may be multiple cameras as described further below. The camera may be a color or monochrome camera. Visible or infrared light may be used.

[0052] The camera 130 has a wide field of view so as to capture a full view of the patient support 120, or at least the portion of the patient support 120 where the patient's region of interest is located. Furthermore, the movement of the patient support 120 means that an even wider field of view is required in order for the desired portion of the patient support to remain within the field of view of the camera (which is statically attached to the scanning system) throughout the medical scan.

[0053] The camera may, for example, be equipped with a fisheye lens having a field of view of more than 150 degrees, such as 160 degrees or more. Thus, the patient support (and the patient on the patient support) may be imaged by a single camera, as shown, or by a small set of cameras.

[0054] Wide angle lenses introduce image distortion such that the shapes of objects appear differently in different regions of the camera's field of view, and as a result, the shapes of objects or regions of interest change when the position of those objects or regions of interest changes within the camera's field of view as a result of patient support movement.

[0055] To address this issue, processor 150 performs image post-processing to correct distortions in the captured images, i.e. distortions resulting from the width of the camera's field of view, shown as post-processing unit 160. For the purposes of post-processing, the cameras are calibrated so that geometric distortions are corrected by post-processing, and the position and orientation of each camera relative to the scanner coordinate system is known.

[0056] According to a first aspect, the processor tracks at least one region of interest of the patient during the displacement of the patient support. This is performed by a tracking unit 162. The (or each) region of interest is a body part to be monitored, such as the face, the area to be scanned, the area of ​​IV injection, or the hand. The location of the region of interest in the initial image can be defined manually or automatically by a suitable algorithm (e.g. using a keypoint detection algorithm) that locates a selected anatomical feature of interest.

[0057] The processor then generates a distortion-corrected image sequence of the (or each) region of interest. This is performed by image sequence generator 164.

[0058] The patient support movement is used for tracking and for generating the distortion-corrected image sequence. The patient support movement can be provided, for example, by the scanning system. Alternatively, tracking of the region of interest can be based on automated image-based detection and tracking algorithms.

[0059] The distortion corrected image sequence is provided as output 170 for display on a display 180. This display 180 may be part of the medical scanner, or may be a separate device such as a technician's mobile device, or may be part of a remote operation center where the image data is transmitted by wired or wireless data transfer.

[0060] The output 170 includes a continuous video stream. There may be video streams of one or more regions of interest.

[0061] Figure 2 shows an example of three images of an image sequence where the region of interest has been dewarped with the patient's face. There may be separate image sequences for separate regions of interest.

[0062] As shown, the camera (or each camera) is oriented towards the patient support and covers a wide range of views. The camera's position, orientation and intrinsic parameters are obtained by a calibration step performed once at the time of system installation. This calibration makes it possible to derive the necessary image post-processing, which allows to track the region of interest during displacements of the patient support.

[0063] The dewarped image sequence may, for example, be a zoomed-in crop of the global dewarped camera images, providing successive views of the same anatomical structures.

[0064] As can be seen in Fig. 2, despite the movement of the patient support relative to the camera, the region of interest is located at a stationary position in the images cropped from the distortion-corrected image sequence. The region of interest moves in the distortion-corrected images as a result of the table displacement. After tracking the region of interest, a cropped image is generated around the region of interest such that the body part within this region of interest appears to be static. The cropped distortion-corrected image sequence thus appears to have been obtained from a camera that moved with the patient support during the scan. However, the viewpoint changes since the region of interest is viewed from different directions as a result of the movement.

[0065] In the most basic version, perspective changes are tolerated since the motion occurring within the region of interest is still easily discernible.

[0066] More preferably, the perspective is corrected by adapting the tilt of the output image to three dimensions so that it has a specified viewing angle of the scene. Perspective correction provides fixation to a single z-plane (where z is the depth from the camera's viewpoint). Since the motion to be detected occurs within an area larger than this single plane, the overall perspective still changes. However, when correcting the perspective to a central plane, the perspective changes around it are reduced to a minimum so that the actual motion can still be detected.

[0067] In this way, the display output provides a way to accurately monitor the patient's position and activity during a medical scan, which has been particularly difficult during scans where the patient support is moving back and forth. The system ensures optimal image quality and safe examination conditions.

[0068] There are various options for camera placement: Figure 3 shows a side view of a CT scanner with a single camera 130 located on one side of a gantry 200 having an opening 202 through which the patient support 120 passes.

[0069] The camera 130 has a field of view wide enough along the length of the patient support to cover the entire length of the patient support, and wide enough along the width of the patient support to cover the entire width of the patient support, and the field of view covers the entire patient support over its range of motion (thus, the patient support 120 is represented in FIG. 3 by the full range of positions it may adopt).

[0070] The camera field of view may instead cover only those areas of the patient support where the regions of interest are located, e.g., the face and abdomen, but still include all positions of these areas of the patient support during displacement of the patient support.

[0071] FIG. 4 shows a side view of a medical scanner having two cameras, a first camera 130a located on one side of the gantry 200 and a second camera 130b located on the opposite side of the gantry, where the "sides" are at different positions along the patient support, i.e., one side facing the head end of the patient support and one side facing the foot end patient support.

[0072] There may also be multiple cameras, even at the same location along the patient support. Figure 5 shows two cameras 130c, 130d, which may be located in the gantry bore or on one side of the gantry. They face the patient support, but from the side, not directly above. As explained further below, this ensures that vertical movement is evident in the image. For example, the cameras may be oriented 90 degrees to each other (in a plane perpendicular to the long axis of the patient support).

[0073] The cameras are therefore pointing to the side and above the patient.

[0074] As explained above, a calibration process is used to derive post-processing requirements to correct image distortion. One approach is to apply a known pattern to the patient support, such as the checkerboard pattern shown in FIG. 6. Image distortion, particularly noticeable at the edges of the field of view, can be corrected by deriving a correction function that returns the captured image to a known "correct" image. By calibrating the camera with this checkerboard pattern and combining the calibration results with the respective positions of the patient support provided by the scanning system, as described above, regions of interest of one or more body parts can be tracked over time, even when the patient support is moving.

[0075] The second embodiment also uses a scanning system, calibration approach, and one or more cameras with a wide field of view, as described above.

[0076] FIG. 7 shows an example of a medical scanner according to the second embodiment.

[0077] 1, the medical scanner 300 includes a scanning system, such as a CT system 140, adapted to acquire CT images of a patient 121 disposed on a patient support 120. The patient support 120 is adapted to move the patient 121 through the CT imaging system 140 by a drive system 124.

[0078] The wide field camera 130 is adapted to acquire surveillance images of the patient 121 during a CT imaging procedure, and the processor 150 processes the images.

[0079] Processor 150 performs image post-processing, as described above, to correct distortions in the captured images due to the width of the camera or the field of view of the camera. This is again performed by post-processing unit 160, and to enable post-processing, the same calibrations can be performed as described above.

[0080] In this embodiment, the motion detection unit 210 provides automatic identification of patient motion based on image motion.

[0081] A measurement 212 of the patient's movement is output by the system.

[0082] This aspect relies on the specific configuration of the camera (or cameras) to simplify the automatic extraction of the motion signal.

[0083] 8 shows a camera 130 and its field of view 220. The camera has a central axis 222 that extends to the center of the field of view. This is the optical axis of the camera. This optical axis 222 is, for example, a vector that is perpendicular to the plane of the array of image sensing elements and projects from the center of the array of image sensing elements.

[0084] The optical axis 222 is perpendicular to the direction of displacement of the patient support when the scanner is in use, e.g. the length of the patient support in the form of a treatment couch. Furthermore, a row of pixels in the image captured by the camera corresponds to a position along an axis parallel to the direction of movement of the patient support. A line 224 across the field of view is mapped to a row of pixels in the generated image, and this line 224 in the field of view (e.g. when the camera is imaging an empty patient support) is parallel to the direction of displacement of the patient support, i.e. parallel to the length of the patient support.

[0085] This defines a particular orientation of the camera relative to the patient support, meaning that in a captured image of an empty patient support, pixel rows correspond to horizontal lines along the length of the patient support, while pixel columns include a vertical component.

[0086] Thus, motion can be measured automatically by analyzing the change in patient position in the pixel column direction, such as between successive captured images.

[0087] For this purpose, the cameras should not be directly overhead, as they will not capture vertical displacement. The configuration of Figure 5 may be used, for example, with two cameras capturing a partial lateral view of the patient, such that vertical patient movement results in a component of pixel column-wise movement in the captured image.

[0088] As mentioned above, there may be one or more cameras on only one side of the gantry, or there may be one or more cameras on each side of the gantry.

[0089] This imaging system thereby captures images in an orthogonal direction, primarily vertical, with typical patient movements, such as respiration, resulting in displacements in the pixel row direction as the patient support movements result.

[0090] As above, the processor may additionally identify at least one region of interest in the image or divide the image into blocks and then identify patient motion for at least one region of interest or block. For each region of interest, the overall horizontal pixel shift induced by the patient support motion between successive frames is corrected by using the known patient support motion. The vertical motion component between successive regions of interest is then calculated as a measure of patient motion. The images may be processed in real time or retrospectively to detect patient motion between successive frames.

[0091] FIG. 7 shows a module 230 for tracking a region of interest.

[0092] Different algorithms can be applied to detect the motion along the pixel columns, such as optical flow algorithms or cross-correlation algorithms.

[0093] In this way, certain regions of the patient, e.g., regions that move with respiration, are automatically monitored for movement. For respiration detection, the region of interest includes, e.g., the abdomen. Thus, a respiration movement signal can be derived from image processing. The processor can track at least one region of interest of the patient during displacement of the patient support.

[0094] As explained above, tracking can use inputs indicative of patient support motion, or can be based on image-based feature identification and tracking.

[0095] 9 shows a series of images of a patient, showing a region of interest 240 as a block in the abdominal region. A motion signal can be derived specifically for this region of interest and used for gating or triggering purposes, in known manner.

[0096] Based on the known horizontal shift between successive frames during the couch displacement, an optional additional image processing step can be applied. This step creates a mapping from the 2D images to 3D (world) coordinates. In particular, the sequence of images is from different viewpoints relative to the patient, so that even a single camera can function as a time-multiplexed camera system. Thus, a 3D image can be generated based on the stereo principle. In this way, the position and size of the moving subject parts can be calculated.

[0097] In 3D modeling, a known table movement is used as a prerequisite. The assumption is that there is no movement in the x-axis (pixel row) direction away from the patient support movement. From the relationship between the pixel shift per pixel, obtained from the motion detection algorithm, and the true table movement (in mm), the relative size of the pixel in mm can be derived. Together with the focal length of the camera (known from the calibration step), this relative size can be converted into a value indicating the distance to the camera that is equal to the depth. As this calculation only uses the detected changes in the pixel row direction, the movement in the pixel column direction does not directly affect the 3D modeling. Therefore, the patient movement between different images does not prevent the generation of the 3D image.

[0098] As mentioned above, a calibration procedure is used. The output of the calibration process is a set of camera-specific parameters that describe the optical properties and lengths of the sensor, such as focal length, optical center, and distortion coefficients. These parameters can be used as input to calculate an undistorted image. The calibration process also makes it possible to calculate the exact position and orientation of the camera relative to the scanner coordinate system, which is typically linked to the isocenter of the scanner. This step is called calculating the extrinsic parameters (pose matrix) of the camera, and makes it possible to correct for perspective effects.

[0099] Based on external parameters the spatial coordinates of the moving parts can be expressed in the scanner coordinate system, which in particular makes it possible to detect whether the movement is taking place in the scan plane or in the vicinity of the scan plane.

[0100] Here we describe a simplified method for calculating the physical amplitude of the movement. For each pixel, the lateral and vertical shift between two images acquired at two successive time points is first calculated using means known from the state of the art such as optical flow or cross-correlation. The horizontal shift is due to the table displacement. The vertical shift is due to the patient movement (if any). The amplitude of the horizontal shift pixel depends on the depth of the corresponding part relative to the camera: the closer the part is to the camera, the larger the pixel shift. In other words, the amplitude of the horizontal shift together with the value of the table displacement between the two images provides the physical optical resolution of the camera at this position. It can therefore be used to calculate the physical amplitude of the vertical shift. This last step is obtained simply by dividing the vertical pixel shift by the horizontal pixel shift and multiplying this quotient by the table displacement in millimeters.

[0101] Based on the location and magnitude of patient motion in one or more regions of interest, a global motion signal can be derived over the time of the scan, and thus significant patient motion can be detected. This calculated motion signal can then be used to inform the operator about patient motion, either before or during the scan. It can be used to predict which slices of the imaged volume will be affected by motion. It can also be used as input for data reconstruction (e.g., gating or motion correction) and for 4D CT scans.

[0102] The present invention can be applied to any medical scanner in which the patient support is moved during the imaging procedure, such as PET imaging devices, MR imaging devices, SPECT imaging devices, and the above-mentioned CT scanner. The medical scanner can include a C-arm or closed bore. One or more cameras can be located within the bore, or on the inner surface of the C-arm, or outside the bore or C-arm envelope. In all cases, however, the camera is static relative to the body of the scanning system, and thus the patient support moves relative to the camera. The camera does not have to be directly attached to the medical scanner, but instead may be in a fixed position relative to the medical scanner by a separate attachment.

[0103] Although in the above described embodiments the patient support is always the patient support on which the patient lies during acquisition of medical images, the patient support can also be configured for a sitting or standing patient.

[0104] Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

[0105] The functions implemented by a processor may be implemented by a single processor or by multiple separate processing units, which may be considered to constitute a "processor". Such processing units may possibly be remote from each other and in communication with each other in a wired or wireless manner.

[0106] The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0107] The computer program may be stored / distributed on a suitable medium, such as an optical storage medium or a solid-state medium, provided together with or as part of other hardware, but may also be distributed in other forms, such as over the Internet or other wired or wireless telecommunications systems.

[0108] It should be noted that when the term "adapted for" is used in the claims or description, it is intended to be equivalent to the term "configured for." When the term "apparatus" is used in the claims or description, it is intended to be equivalent to the term "system," and vice versa.

[0109] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. 1. An imaging system for capturing images of a patient during a medical scan using a scanner having a scanning system and a patient support, the imaging system comprising: a set of one or more cameras for mounting in a fixed position relative to the scanning system directed towards the patient support to capture images, each camera of the set having an optical axis orthogonal to a direction of displacement of the patient support when the scanner is in use, and a row of pixels in an image captured by each camera corresponds to a position along an axis parallel to the direction of movement of the patient support; A processor, the processor comprising: performing image post-processing to correct distortion in the captured images due to a width of field of view of the one or more cameras and to provide perspective correction; identifying patient motion based solely on image motion in the pixel column direction between successive captured images; outputting the patient movement measurements; a processor configured to execute An imaging system comprising:

2. The imaging system of claim 1 , wherein each camera of the set of cameras faces the patient support from the side and from above.

3. The processor, identifying at least one region of interest within the image; identifying patient motion relative to the at least one region of interest; tracking at least one region of interest on the patient during displacement of the patient support; 3. The imaging system of claim 1, configured to:

4. The processor, using an input indicative of movement of the patient support; or Based on the image-based feature identification and tracking, The imaging system of claim 3 configured to perform the tracking.

5. The imaging system of claim 3 , wherein the region of interest comprises an abdomen.

6. 6. The imaging system of claim 1, wherein at least one camera of the set is equipped with a fisheye lens having a field of view greater than 150 degrees.

7. 7. The imaging system of claim 1, wherein the processor is further configured to calculate a depth of a moving part relative to the camera.

8. The processor further comprises: determining the location and magnitude of local patient motion; deriving global motion from the local patient motions; 8. The imaging system of claim 1 , configured to:

9. 9. The imaging system of claim 1, wherein the processor is configured to perform a calibration process comprising capturing one or more calibration images.

10. 1. A medical scanner comprising: A scanning system; a patient support extending through the scanning system; a drive system for driving the patient support through the scanning system; The imaging system according to any one of claims 1 to 9.

1. A medical scanner comprising:

11. 11. The medical scanner of claim 10, wherein each camera of the set is mounted on the scanning system with an orientation such that the optical axis is perpendicular to a direction of displacement of the patient support when the medical scanner is in use, and a row of pixels in an image captured by each camera corresponds to a position along an axis parallel to the direction of movement of the patient support.

12. 1. An imaging processing method for processing images of a patient during a medical scan using a scanner having a scanning system, a patient support, and a set of one or more cameras mounted in a fixed position relative to the scanning system directed towards the patient support, each camera of the set having an optical axis perpendicular to a direction of displacement of the patient support when the scanner is in use, the method comprising: receiving an image from one or more cameras of the set, rows of pixels in the image corresponding to positions along an axis parallel to a direction of motion of the patient support; performing image post-processing to correct distortion in the captured images due to a width of field of view of the one or more cameras and to provide perspective correction; identifying patient motion based solely on image motion in the pixel column direction between successive captured images; outputting the patient movement measurements; The method comprising:

13. identifying at least one region of interest within the image; identifying patient motion relative to the at least one region of interest; 13. The method of claim 12, comprising:

14. 14. A method according to claim 12 or 13, comprising the step of performing a calibration process by taking a calibration image.

15. A computer program comprising a computer program code adapted to carry out the method according to any one of claims 12 to 14, when the program is run on a processor of an imaging system according to any one of claims 1 to 9.

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