Patient monitoring during scanning

Abstract

An imaging system for capturing images of a patient during a medical scan. A set of one or more cameras captures images of the patient such that, after applying deformation and perspective correction steps, pixel rows correspond to positions along an axis parallel to the direction of movement of a 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 direction of the pixel columns between sequentially captured images. A measure of patient motion can then be derived.

Description

Technical Field

[0001] The present invention relates to monitoring patients during medical scans and, in particular, to detecting movement. Background Art

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

[0003] For example, it is desirable to detect respiration-related movement to prevent and correct motion artifacts, ensure optimal image quality, and support respiration-triggered scanning. In fact, unwanted patient motion is one of the leading causes of image quality issues and safety events such as pinched fingers.

[0004] Furthermore, for these monitoring applications it is particularly important to monitor a predetermined region of interest of the patient. For example, if respiratory motion should be monitored, the patient's chest needs to be monitored, or if the patient's health should be monitored, the patient's face needs to be monitored. Since during certain medical imaging procedures (such as CT imaging procedures or MR imaging procedures) the patient may be moved through the imaging device, in order to monitor the patient's region of interest, it is necessary to track this region of the patient in the provided monitoring images.

[0005] One of the problems with tracking a patient's region of interest in a monitoring image when the patient is moved through a medical imaging device during a medical scanning procedure is that the shape and position of the region of interest in the monitoring image may change during the imaging procedure due to changes in the viewing angle of the monitoring camera relative to the region of interest. This makes purely image-based tracking of the region of interest to be monitored more difficult. Another problem with tracking the region of interest using conventional monitoring cameras is the presence of occlusions, particularly due to the couch moving through the bore. Thus, for example, with conventional monitoring cameras mounted on a scanning room wall, it is very difficult to have a free, unobstructed view of the patient's face throughout the examination.

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

[0007] In the approach of mounting the camera on the wall or ceiling of the room, at best only a partial view can be provided to the patient during scanning. Due to the shape of the patient himself, the limited diameter of the bore through the scanning system, and the presence of positioning equipment or medical equipment, large parts of the anatomy may be obscured.

[0008] Therefore, the monitoring system is unable to provide a continuous view of the relevant body part of the patient throughout the examination, particularly as the patient support travels through the scanning system.

[0009] The advantage of mounting the camera at the front or rear end of the patient support is that it provides a stable view of the patient while the patient support is moving. However, this option is undesirable because these parts of the patient support are used to position the medical device or the head support. Moreover, in the case of obese patients, the view of the upper or lower part of the patient is likely to be blocked by the abdomen.

[0010] Therefore, there is a need for an imaging system that can better capture images of patients during medical scans. These images can undergo manual inspection to assess patient movement. However, in some cases, automatic patient motion detection can be used as an input to image reconstruction algorithms and / or used to drive the scanning process. This is also an important clinical input parameter for respiratory gating and respiratory triggered scanning (such as lung scanning and 4D CT scanning used in CT simulation of radiotherapy).

[0011] One option is to place the camera on the scanning system, such as on a gantry facing the patient. The main challenge in this case is to distinguish between the apparent motion that occurs in spiral CT scans due to horizontal displacement of the patient support and the real patient motion. Since the patient is lying down, patient motion usually has a significant forward-backward component. However, due to the projection geometry of the camera system, these two motions overlap in the final camera image, making it difficult to extract the motion.

[0012] Therefore, there remains a need for a motion sensing solution that handles 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 images of the patient. The position and shape of the region of interest are mapped while the patient support moves.

[0014] EP 3832602 discloses an apparatus for monitoring an object during imaging. A region of interest is determined using two monitoring units at different support positions and based on a position map of a calibration target at a calibration support position. Summary of the invention

[0015] The invention is defined by the claims.

[0016] According to an example of an aspect of the present invention, there is provided an imaging system for capturing an image of a patient during a medical scan using a scanner having a scanning system and a patient support, the imaging system comprising:

[0017] a set of one or more cameras for mounting in a fixed position relative to the scanning system toward the patient support to capture images, wherein each camera in the set has an optical axis orthogonal to a direction of displacement of the patient support in use of the scanner, and wherein rows of pixels of an image captured by each camera correspond to positions along an axis parallel to a direction of movement of the patient support;

[0018] A processor, wherein the processor is configured to:

[0019] performing image post-processing to correct for distortion within the captured images due to the width of the field of view of the one or more cameras and to provide perspective correction;

[0020] identifying patient motion based on image movement in a pixel column direction between sequentially captured images; and

[0021] Output a measure of patient motion.

[0022] The imaging system captures images in which the patient support body moves resulting in a displacement in the direction of the pixel rows. This displacement is orthogonal to typical patient movement, which in the case of breathing is mainly in the vertical direction. Therefore, the movement is in the direction of the pixel columns. This makes motion analysis simpler, because the motion can be extracted simply based on the analysis of the image changes in the direction of the pixel columns, that is, the patient motion is identified based only on the image movement in the direction of the pixel columns between the sequentially captured images. The anterior-posterior component of the patient motion is the main component in the patient motion of the supine examination, so the anterior-posterior component of the patient motion can be best detected and quantified. Perspective correction takes into account the fact that due to inaccuracies in positioning and orientation, the camera may not be completely orthogonal to the main axis of the frame (which is also the direction of the table movement) 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 motion detected in the pixel column (vertical) direction. If the viewing angle is not correctly aligned, the patient support body movement will also cause a small movement in the pixel column direction, which should also be avoided.

[0023] For example, the processor is configured to:

[0024] identifying at least one region of interest within the image; and

[0025] Patient motion is identified for the at least one region of interest.

[0026] In this way, specific areas of the patient can be monitored for movement, for example areas that move with breathing.

[0027] For example, the processor is further configured to track at least one region of interest of the patient during displacement of the patient support.Thus, the same region may be monitored over time to detect local movement.

[0028] The processor may be configured to perform the tracing in the following manner:

[0029] using input indicative of movement of the patient support; or

[0030] Based on image-based feature recognition and tracking.

[0031] Thus, the tracking may be based on image processing, or it may use external patient support position information from the scanner.

[0032] For example, the one or more regions of interest include the abdomen.Therefore, the respiratory motion signal may be derived based on image processing.

[0033] For example, the region of interest may include a region containing a scan plane area of ​​the imaging system, ie, the portion of the imaging system that acquires data for image formation.

[0034] For example, at least one camera in the group includes a fisheye lens with a field of view greater than 150 degrees.Thus, the patient support (and the patient on the patient support) can be imaged by a small group of cameras (or even just a single camera).

[0035] The processor may also be configured to calculate the depth of the moving part relative to the camera. Based on the depth, the motion may be quantified, meaning that the physical magnitude and direction of the motion may be calculated. The spatial coordinates of points belonging to the moving part may be calculated. Additionally, based on the depth, a 3D model may be calculated as needed.

[0036] To calculate the depth map, principles known from stereo vision are applied. The input are two images with the stage acquired at two different positions. The corresponding stage displacement (e.g. a number in mm) is obtained from the scanning system and is input. Since the perspective corrected images result in stage displacements only along the rows of the image, the correspondence between the two images is found by calculating the horizontal offset between corresponding pixels. This is the disparity. The depth is calculated from this disparity using the camera intrinsic parameters (such as focal length).

[0037] For example, the processor is further configured to:

[0038] Determine the location and magnitude of local patient motion; and

[0039] A global movement is derived from the local patient motion.

[0040] The processor may be configured to perform a calibration process involving imaging one or more calibration images. The calibration process can implement distortion and perspective corrections for analyzing movement of different patient regions at different locations within the field of view at different times.

[0041] The calibration is usually performed once after the camera is installed. It can be repeated whenever necessary (e.g. after a service visit), but not every time a motion is calculated.

[0042] The present invention also provides a medical scanner, comprising:

[0043] Scanning system;

[0044] a patient support extending through the scanning system;

[0045] a drive system for driving the patient support through the scanning system; and the imaging system as defined above.

[0046] For example, each camera in the group is mounted to the scanning system in an orientation such that the optical axis is orthogonal to the direction of displacement of the patient support during use of the medical scanner, and wherein rows of pixels of an image captured by each camera correspond to positions along an axis parallel to the direction of movement of the patient support.

[0047] This provides for the desired alignment of pixel rows with the scanner patient support movement axis so that pixel columns contain relevant patient movement information.

[0048] The present invention also provides an imaging processing method for processing an image of a patient during a medical scan using a scanner, the scanner having a scanning system, a patient support and a set of one or more cameras, the one or more cameras being mounted in a fixed position relative to the scanning system towards the patient support, wherein each camera in the set has an optical axis orthogonal to the direction of displacement of the patient support during use of the scanner, the method comprising:

[0049] receiving an image from the one or more cameras in the set, wherein rows of pixels of the image correspond to positions along an axis parallel to a direction of movement of a patient support;

[0050] performing image post-processing to correct for distortion within the captured images due to the width of the field of view of the one or more cameras and to provide perspective correction;

[0051] identifying patient motion based on image movement in a pixel column direction between sequentially captured images; and

[0052] Output a measure of patient motion.

[0053] The method may include:

[0054] identifying at least one region of interest within the image; and

[0055] Patient motion is identified for the at least one region of interest.

[0056] The region of interest includes, for example, the thorax.

[0057] The method may also include performing a calibration process by imaging one or more calibration images.

[0058] For example, the offset in the horizontal direction is also calculated to obtain depth information and quantify the motion (magnitude, orientation and spatial coordinates).

[0059] The present invention also provides a computer program, comprising computer program code, wherein the computer program code is suitable for implementing the above method when the program is run on the processor of the above program system.

[0060] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] For a better understanding of the invention, and to show more clearly how it may be put into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

[0062] Figure 1 An example of a medical scanner is schematically shown;

[0063] Figure 2 An example of three images in a sequence of warping-corrected images is shown;

[0064] Figure 3 shows a side view of a CT scanner having a single camera located on one side of the gantry;

[0065] Figure 4 A side view of a CT scanner having two cameras is shown; a first camera is located on one side of the gantry and a second camera is located on the opposite side of the gantry;

[0066] Figure 5 Two cameras are shown located in lateral positions within the bore of the frame;

[0067] Figure 6 The pattern used for the calibration phase is shown;

[0068] Figure 7 A second example of a medical scanner is shown;

[0069] Figure 8 The cameras and their fields of view are shown to explain Figure 8 a design aspect of a scanner; and

[0070] Fig. 9 A sequence of images of a patient is shown, and the region of interest is shown as a box in the abdominal area. DETAILED DESCRIPTION

[0071] The present invention will be described with reference to the accompanying drawings.

[0072] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, system and method, are intended for illustrative purposes only and are not intended to limit the scope of the invention. These and other features, aspects and advantages of the apparatus, system and method of the present invention will become better understood from the following description, the appended claims and the accompanying drawings. It should be understood that the drawings are only schematic and not drawn to scale. It should also be understood that the same reference numerals are used throughout the drawings to indicate the same or similar parts.

[0073] 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 such that after applying deformation and perspective correction steps, pixel rows correspond to positions along an axis parallel to the direction in which the patient support moves, while pixel columns correspond to positions along an axis perpendicular to the direction in which the patient support moves. Patient motion of interest can then be identified based on image movement in the direction of the pixel columns between sequentially captured images. A measure of patient motion can then be derived.

[0074] The present invention generally relates to the analysis of the movement of a patient. Two aspects related to the analysis of movement are described below. The first aspect relates to the generation of an image set that most easily allows visual inspection of the movement. The second aspect relates to automatically deriving a measure of the amount of movement of the patient, and for example, this can be used to trigger an imaging process.

[0075] These two aspects can be implemented separately or in combination. Although both aspects are described below, the present invention is particularly related to the second aspect.

[0076] Figure 1 Schematically shown is an example of a medical scanner 100 for acquiring medical images of an object and which additionally comprises an imaging system for capturing optical images of a patient during the medical scan. The images are generated for the purpose of determining patient movement.

[0077] The medical scanner 100 includes a scanning system, such as a CT imaging system 140, which is adapted to acquire medical images (i.e., CT images in this example) of a patient 121 positioned 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. For this purpose, the medical scanner has a drive system 124 for driving the patient support through the scanning system.

[0078] The imaging system includes an optical camera 130 and a processor 150, the optical camera 130 being adapted to acquire monitoring images of a patient 121 during a CT imaging procedure. The operation of the system will be explained with a single camera, but there may be multiple cameras, as further explained below. The camera may be a color or monochrome camera. It may use visible light or infrared light.

[0079] The camera 130 has a wide field of view so that it captures a complete view of the patient support 120, or at least the portion of the patient support 140 on which the patient's region of interest will be located. Furthermore, the movement of the patient support 120 means that a wider field of view is required so that the desired portion of the patient support remains in the field of view of the camera (which is statically mounted to the scanning system) throughout the medical scan.

[0080] For example, the camera includes a fisheye lens with a field of view greater than 150 degrees (e.g., 160 degrees or greater).Thus, the patient support (and the patient on the patient support) may be imaged by a single camera as shown or by a small group of cameras.

[0081] Wide angle lenses cause image distortion so that the shape of objects appears different at different areas of the camera's field of view. Therefore, when the position of objects or regions of interest in the camera's field of view changes due to movement of the patient support, the shape of those objects or regions of interest will change.

[0082] To address this problem, the processor 150 performs image post-processing to correct those deformations within the captured image, namely those deformations due to the width of the camera's field of view. This is shown as a post-processor unit 160. For post-processing purposes, the cameras are calibrated so that the geometric deformations are corrected by post-processing and the position and orientation of each camera relative to the scanner coordinate system is known.

[0083] According to a first aspect, the processor tracks at least one region of interest of the patient during displacement of the patient support. This is implemented by a tracking unit 162. The region of interest (or each region of interest) is a body part to be monitored, such as the face, an area to be scanned, an IV injection area or a hand. The position of the region of interest in the initial image can be defined manually or automatically by a suitable algorithm (such as using a key point detection algorithm) that locates selected anatomical features of interest.

[0084] The processor then generates a sequence of distortion corrected images of the region of interest (or each region of interest). This is performed by an image sequence generator 164 .

[0085] The movement of the patient support is used for tracking and for generating a deformation corrected image sequence. For example, the movement of the patient support is provided by a scanning system. Alternatively, the tracking of the region of interest may be based on an automatic image-based detection and tracking algorithm.

[0086] The sequence of distortion corrected images is provided as output 170 for display on a display 180. The display 180 may be part of the medical scanner, or it may be a separate device, such as a technician's mobile device, or it may be part of a remote operations center to which the image data is transmitted by wired or wireless data transfer.

[0087] The output 170 comprises a continuous video stream. There may be one or more video streams of a region of interest.

[0088] Figure 2 An example of three images in a deformation corrected image sequence is shown, where the region of interest is the face of a patient. There may be separate image sequences for separate regions of interest.

[0089] As shown, the camera (or each camera) is oriented toward the patient support and covers a wide range of viewing angles. The position, orientation and intrinsic parameters of the camera are obtained by a calibration step, which is performed once when the system is installed. This calibration enables the required image post-processing to be derived, which in turn enables tracking of the region of interest during displacement of the patient support.

[0090] For example, a deformation-corrected image sequence is an enlarged crop of the overall deformation-corrected camera image, and it provides consecutive views of the same anatomical structure.

[0091] like Figure 2 As can be seen in FIG. 1 , despite the movement of the patient support relative to the camera, the region of interest is located at a stationary position within the image cropped from the distortion-corrected image sequence. Due to the table displacement, the region of interest moves within the distortion-corrected image. After tracking the region of interest, a cropped image around the region of interest is generated so that the body part within the region of interest appears stationary. Thus, the cropped distortion-corrected image sequence appears to have been obtained from a camera that traveled with the patient support during the scan. However, the perspective will change because the region of interest is viewed from different directions due to the movement.

[0092] In the most basic version, perspective changes are tolerable because movement occurring within the region of interest will still be easily discernible.

[0093] More preferably, the perspective is corrected by adjusting the three-dimensional tilt of the output image so that it has a specified scene viewing angle. The perspective correction provides fixation to a single z-plane (where z is the depth from the camera viewpoint). Since the motion to be detected occurs in an area wider than this single plane, the overall perspective will still change. However, when the perspective is corrected relative to the central plane, the perspective changes around it are reduced to a minimum so that actual movement can still be detected.

[0094] In this way, the display output provides a means of accurately monitoring the position and movement of a patient during a medical scan, which has been difficult to do in the past, especially during scans where the patient support moves back and forth. The system ensures optimal image quality and safe examination conditions.

[0095] For camera placement, various options exist. Figure 3 A side view of a CT scanner is shown with a single camera 130 located on one side of a gantry 200 having an opening 202 through which a patient support 120 extends.

[0096] The field of view of the camera 130 is wide enough in the length direction of the patient support to cover the entire length of the patient support, and is wide enough in the width direction of the patient support to cover the entire width of the patient support. In addition, the field of view fully covers the patient support throughout its range of motion (thus, represented by the entire range of positions that the patient support 120 can assume). Figure 3 120).

[0097] Instead, the camera field of view may cover only those areas of the patient support where the region of interest will be located, such as the face and abdomen, but also include the full position of those areas of the patient support during displacement of the patient support.

[0098] Figure 4 A side view of a medical scanner with two cameras is shown; a first camera 130a is located on one side of a gantry 200, and a second camera 130b is located on an opposite side of the gantry, where the "two sides" are at different locations along a patient support, i.e., one side faces the head end of the patient support and one side faces the foot end of the patient support.

[0099] There may be multiple cameras even at the same location along the patient support. Figure 5Two cameras 130c, 130d are shown, which may be located within the bore of the gantry, or on one side of the gantry. However, they face the patient support from the lateral side, rather than from directly above the patient support. As further explained below, this ensures that vertical motion is clear in the image. For example, the cameras may be oriented at 90 degrees relative to each other (in a plane perpendicular to the long axis of the patient support).

[0100] Thus, the camera or cameras face the patient laterally and from above.

[0101] As explained above, the calibration process is used to derive post-processing requirements to correct for image distortion. One approach is to apply a known pattern to the patient support, such as Figure 6 . The image distortion (particularly prominent 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 using this checkerboard pattern and combining the calibration results with the respective position of the patient support provided by the scanning system, the region of interest for one or more body parts can be tracked over time even when the patient support moves, as explained above.

[0102] The second aspect also uses a scanning system, calibration method, and one or more cameras with a wide field of view as discussed above.

[0103] Figure 7 An example of a medical scanner according to the second aspect is shown.

[0104] like Figure 1 The medical scanner 300 includes a scanning system, such as a CT system 140, which is adapted to acquire CT images of a patient 121 positioned on a patient support 120. The patient support 120 is adapted to be moved through the CT imaging system 140 by a drive system 124.

[0105] Wide field of view camera 130 is adapted to acquire monitoring images of patient 121 during a CT imaging procedure, and processor 150 processes the images.

[0106] The processor 150 performs image post-processing to correct for distortion within the captured image due to the width of the field of view of the camera or cameras, as discussed above. This is also performed by the post-processing unit 160, and the same calibration may be performed as explained above to achieve post-processing.

[0107] In this regard, there is automatic recognition of patient motion by the motion detection unit 210 based on image movement.

[0108] A measure of patient motion 212 is output by the system.

[0109] This aspect relies on a specific configuration of the camera (or cameras) to simplify the automatic extraction of motion signals.

[0110] Figure 8 A camera 130 and its field of view 220 are shown. The camera has a central axis 222 extending to the center of the field of view. This is the optical axis of the camera. For example, the optical axis 222 is a vector normal to the plane of the array of image sensing elements and is projected from the center of the array of imaging sensing elements.

[0111] The optical axis 222 is orthogonal to the direction in which the patient support is displaced during use of the scanner, for example the length of a patient support (in the form of a couch). Furthermore, the pixel rows of the image captured by the camera correspond to positions along an axis parallel to the direction in which the patient support is moving. A line 224 that crosses the field of view is mapped to a pixel row in the generated image, and this line 224 within the field of view (for example when the camera is imaging an empty patient support) is parallel to the direction in which the patient support is displaced, i.e. parallel to the length of the patient support.

[0112] This defines a specific orientation of the camera relative to the patient support. It means that in a captured image of an empty patient support, the pixel rows correspond to horizontal lines along the length of the patient support, while the pixel columns comprise a vertical component.

[0113] Therefore, movement can be automatically measured by analyzing the change in position of the patient in the direction of the pixel columns between sequentially captured images.

[0114] For this purpose, the camera should not be directly overhead, as this would not capture vertical displacements. For example, Figure 5 An arrangement in which two cameras capture a partial lateral view of the patient, such that vertical patient movement will result in a movement component in the pixel column direction in the captured images.

[0115] There may be one or more cameras on only one side of the rack, or there may be one or more cameras on each side of the rack, as explained above.

[0116] The imaging system thus captures images in which patient support movement results in displacements in the direction of the pixel rows, whereas typical patient movement (such as breathing) is in orthogonal directions, primarily the vertical direction.

[0117] In the same manner as described above, the processor may additionally identify at least one region of interest within 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 global horizontal pixel shift caused by patient support motion between consecutive frames is corrected using the known patient support movement. The vertical motion component between consecutive regions of interest is then calculated as a measure of patient motion. The images are processed in real time or retrospectively to detect patient motion between consecutive frames.

[0118] Figure 7 A module 230 for tracking a region of interest is shown.

[0119] Different algorithms can be applied to detect movement in the direction of pixel columns, such as optical flow algorithms or cross-correlation algorithms.

[0120] In this way, the movement of a specific area of ​​the patient, such as an area that moves with breathing, is automatically monitored. For breathing detection, for example, one or more regions of interest include the abdomen. Thus, a respiratory motion signal can be derived based on image processing. The processor can track at least one region of interest of the patient during displacement of the patient support.

[0121] As explained above, tracking may use input indicative of patient support motion, or it may be based on image-based feature recognition and tracking.

[0122] Fig. 9 A sequence of images of a patient is shown and a region of interest 240 is shown as a box in the abdominal region. A motion signal is derived specifically for this region of interest and it can be used for gating or triggering purposes in a known manner.

[0123] An optional additional image processing step can be applied based on the known horizontal offset between consecutive frames during couch displacement. This step creates a mapping from 2D images to 3D (world) coordinates. Specifically, the sequence of images is from different viewpoints relative to the patient, so that over time even a single camera can behave like multiple cameras. Thus, a 3D image can be generated based on stereo principles. In this way, the position and amplitude of parts of the moving object can be calculated.

[0124] 3D modeling uses known table movement as a premise. It is assumed that there is no movement in the x-axis (pixel row) direction except for the movement of the patient support. Based on the relationship between the pixel offset of each pixel obtained from the motion detection algorithm, and the actual movement of the table (in mm), the relative size of the pixel (in mm) can be derived. Adding the focal length of the camera (known from the calibration step), this relative size can be converted into a value indicating the distance from the camera, which is equal to the depth. Since the calculation only uses the detected changes in the pixel row direction, the movement in the pixel column direction has no direct effect on the 3D modeling. Therefore, patient movement between different images does not hinder the generation of 3D images.

[0125] As mentioned above, a calibration procedure is used. The output of the calibration process is a set of camera intrinsic parameters that describe the optical properties and lengths of the sensor, such as focal length, optical center and deformation coefficients. These parameters can then be used as input to calculate the undeformed image. The calibration process also allows the calculation of the exact position and orientation of the camera relative to the scanner coordinate system, which is usually associated with the isocenter of the scanner. This step is called calculating the extrinsic parameters of the camera (pose matrix) and allows correction of perspective effects.

[0126] Based on the extrinsic parameters, the spatial coordinates of the moving part can be expressed in the scanner coordinate system. In particular, this allows detecting whether the motion occurs on or near the scan plane.

[0127] A simplified way of calculating the physical amplitude of the motion is described here. For each pixel, the horizontal and vertical offsets between two images acquired at two consecutive time points are first calculated using methods known from the prior art (such as optical flow or cross-correlation). The horizontal offset is due to the table displacement. The vertical offset is due to patient motion (if any). The pixel amplitude of the horizontal offset depends on the depth of the corresponding part relative to the camera: the closer the part is to the camera, the larger the pixel offset will be. In other words, together with the value of the table displacement between the two images, the amplitude of the horizontal offset provides the physical optical resolution of the camera at this position. Therefore, it can be used to calculate the physical amplitude of the vertical offset. This last step is simply obtained by dividing the vertical pixel offset by the horizontal pixel offset and multiplying the quotient by the table displacement (in mm).

[0128] Based on the position and amplitude of patient movement in one or more regions of interest, an overall motion signal for the scan time can be derived, and thus significant patient motion can be detected. The motion signal calculated in this way can then be used to inform the operator of patient motion 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 reconstruction data (such as gating or motion correction) and for 4D CT scanning.

[0129] The present invention also applies to any medical scanner that moves a patient support during an imaging procedure, such as a PET imaging device, an MR imaging device, a SPECT imaging device, and a CT scanner as described above. The medical scanner may include a C-arm or a closed bore. One or more cameras may be located within the bore or on the inner surface of the C-arm, or outside the bore or C-arm envelope. However, in all cases, the camera is stationary relative to the body of the scanning system, and therefore the patient support moves relative to the camera. The camera may not be mounted directly to the medical scanner, but may be located in a fixed position relative to the medical scanner by a separate mounting.

[0130] Although in the above-described embodiments the patient support is always a patient support on which a patient lies during acquisition of medical images, the patient support may also be configured for a sitting or standing patient.

[0131] Those skilled in the art can understand and implement various variations of the disclosed embodiments when practicing the claimed invention based on 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.

[0132] The functions implemented by a processor may be implemented by a single processor or by multiple separate processing units, which may be considered to collectively constitute a “processor.” In some cases, these processing units may be remote from each other and communicate with each other in a wired or wireless manner.

[0133] 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.

[0134] The computer program may be stored / distributed on suitable media such as optical storage media or solid-state media provided together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0135] If the term "suitable for" is used in the claims or the specification, it should be noted that the term "suitable for" is intended to be equivalent to the term "configured to". If the term "device" is used in the claims or the specification, it should be noted that the term "device" is intended to be equivalent to the term "system" and vice versa.

[0136] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. An imaging system for capturing an image 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 (130) for mounting in a fixed position relative to the scanning system toward the patient support to capture images, wherein each camera in the set has an optical axis orthogonal to a direction of displacement of the patient support in use of the scanner, and wherein rows of pixels of an image captured by each camera correspond to positions along an axis parallel to the direction of movement of the patient support; A processor (150), wherein the processor is configured to: performing image post-processing to correct for distortion within the captured images due to the width of the field of view of the one or more cameras and to provide perspective correction; identifying patient motion based solely on image movement in the direction of pixel columns between sequentially captured images; and Output a measure of patient motion.

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

3. The imaging system of claim 1 or 2, wherein: The processor (150) is configured to: identifying at least one region of interest within the image; identifying patient motion with respect to the at least one region of interest; as well as The at least one region of interest of the patient is tracked during displacement of a patient support.

4. The imaging system of claim 3, wherein: The processor (150) is configured to perform the tracking in the following manner: using input indicative of movement of the patient support; or Based on image-based feature recognition and tracking.

5. The imaging system of any one of claims 3 to 4, wherein: The one or more regions of interest include the abdomen.

6. The imaging system of any one of claims 1 to 5, wherein: At least one camera (130) in the set includes a fisheye lens having a field of view greater than 150 degrees.

7. The imaging system of any one of claims 1 to 6, wherein: The processor (150) is also configured to calculate the depth of the moving part relative to the camera.

8. The imaging system of any one of claims 1 to 7, wherein: The processor (150) is further configured to: Determine the location and magnitude of local patient motion; and A global movement is derived from the local patient motion.

9. The imaging system of any one of claims 1 to 8, wherein: The processor (150) is configured to perform a calibration process involving imaging one or more calibration images.

10. A medical scanner comprising: Scanning system (140); a patient support (120) extending through the scanning system; a drive system (124) for driving the patient support through the scanning system; and An imaging system as claimed in any one of claims 1 to 9.

11. The medical scanner of claim 10, wherein: Each camera in the set is mounted to the scanning system in an orientation such that an optical axis is orthogonal to a direction of displacement of the patient support during use of the medical scanner, and wherein rows of pixels of an image captured by each camera correspond to positions along an axis parallel to the direction of movement of the patient support.

12. An imaging processing method for processing an image 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 toward the patient support, wherein: Each camera in the set has an optical axis orthogonal to a direction of displacement of the patient support in use of the scanner, the method comprising: receiving an image from the one or more cameras in the set, wherein rows of pixels of the image correspond to positions along an axis parallel to a direction of movement of a patient support; performing image post-processing to correct for distortion within the captured images due to the width of the field of view of the one or more cameras and to provide perspective correction; identifying patient motion based solely on image movement in the direction of pixel columns between sequentially captured images; and Output a measure of patient motion.

13. The method of claim 12, comprising: identifying at least one region of interest within the image; as well as Patient motion is identified for the at least one region of interest.

14. A method as claimed in claim 12 or 13, comprising performing the calibration process by imaging a calibration image.

15. A computer program comprising computer program code adapted to implement the method of any of claims 12 to 14 when said program is run on the processor of the imaging system of any of claims 1 to 9.

Images