Camera-Based Patient Monitoring in Medical Imaging

Abstract

The present invention relates to a medical imaging system comprising a camera for monitoring a subject under examination in an examination zone of the system, and a mirror assembly in the examination zone for reflecting light from a target area on the subject's body onto the camera, the mirror assembly comprising a curved reflective surface and / or multiple reflective surfaces oriented in different directions, such that light is reflected from the target area into the camera by magnifying the reflected image and / or by projecting multiple copies of the same target area onto different areas of the camera image and / or by reflecting light from a light source at different positions onto the target area as the camera reflects the light from the target area into the camera.

Description

[Technical field]

[0001] The present invention relates to the field of medical imaging, such as magnetic resonance imaging, computed tomography imaging, and more particularly to medical imaging (or diagnostic imaging) systems adapted for camera-based observation and / or monitoring of patient parameters, such as vital signs and / or movement, based on camera observation, and related methods. [Background technology]

[0002] Surveillance systems for monitoring the examination zone of a medical imaging system, for example a magnetic resonance imaging system, by means of a camera are generally known in the art. Such systems can be used for various purposes, such as visual patient monitoring by an operator or automatic monitoring based on image processing, for example to monitor a patient undergoing an examination while inside the magnet bore of an MRI system. For example, a camera for imaging a patient during a magnetic resonance imaging examination can be mounted outside the bore of the MRI system, for example on or adjacent to a protective cover of the system, for example on a flange of the bore, to keep the complexity of the integration into the MRI system as low as possible and / or to avoid a reduction in the free bore diameter.

[0003] Many variations and extensions of this concept are known as well. For example, a mirror may be installed in the bore of the MRI system so that the camera can observe the patient, e.g., the patient's face, even if a direct line of sight is not available or difficult to achieve. In many configurations, the camera system is mounted relatively far from the region to be observed, and the optical axis of the camera may generally be oriented in the direction of the longitudinal axis of the magnet bore, or may have a predominant component. The use of such a mirror may be particularly advantageous to provide a better view of the camera system, since patients are typically, or at least very often, examined with the longitudinal axis of the body substantially aligned with the longitudinal axis of the bore.

[0004] In addition to allowing an operator to observe the patient, for example to detect signs of distress, ensure that the patient remains awake, or assess compliance with the imaging protocol (e.g. in functional imaging of the brain), the camera system may be used in conjunction with an image analysis system to determine useful parameters, for example to detect and / or quantify movement, respiration, heart rate or other cardiac parameters, and / or other vital signs and / or parameters indicative of the patient's condition in general. For example, when movement is detected in a general sense, or specifically inferred from the detected respiratory and / or cardiac movement or phase, data simultaneously acquired by the MRI system may be discarded, annotated, collated as a function of the detected (respiratory / cardiac) phase, and / or corrected to compensate for the detected movement.

[0005] Other exemplary applications may include remote photoplethysmography (rPPG), mood detection, video-based talking detection, etc. Furthermore, it is noted that cardiac triggering is not only useful for cardiac MRI, but may also be applied to a variety of other MRI imaging protocols. A common application in neuroimaging is suppressing artifacts in head and neck scans caused by pulsatile flow of blood and cerebrospinal fluid. Another common application is the quantitative measurement of blood flow in the carotid arteries.

[0006] For example, JP H0928689 discloses a mirror installed in the bore of an MRI system and a television camera for capturing an image of an object mirrored on the mirror. A computer analyzes the image and detects the subject's motion. The computer decides whether to discard, reacquire, or collect MR data depending on, for example, whether the subject moves outside the limited range. Alternatively, MRI parameters can be optimized to offset the effects of subject motion.

[0007] US2020 / 289075A1 discloses a mirror system including a curved mirror for monitoring patient movement within the bore of an imaging device. Summary of the Invention [Problem to be solved by the invention]

[0008] It is an object of embodiments of the present invention to provide good and efficient means and methods for monitoring a subject in a medical imaging system (e.g., a magnetic resonance imaging system, a computed tomography imaging system, a positron emission imaging system, a single photon emission computed tomography system, without limitation to these examples) using a camera system and / or for quantifying vital signs, movement and / or other parameters of interest indicative of the subject based on the output of the camera system. [Means for solving the problem]

[0009] It is an advantage of embodiments of the present invention that better illumination of the area of ​​the body being imaged being observed by the camera system may be achieved.

[0010] An advantage of embodiments of the present invention is that by allowing optimization of the light path from the light source to the target area and / or from the target area to the camera, high flexibility, e.g., more degrees of freedom, can be achieved in the configuration of the camera system, e.g., with respect to both the illumination of the target area and the field of view of the camera. It is therefore also advantageous that the camera system can be easily adapted to different use cases, e.g., imaging protocols and variations in the properties of the object to be imaged.

[0011] An advantage of embodiments of the present invention is that, based on images acquired e.g. by camera observation, good signals indicative of the respiratory and / or cardiac motion of a subject can be derived, advantageously with a low signal-to-noise ratio and / or in a robust and reproducible manner, such that such signals can be advantageously used to improve the quality of imaging procedures, e.g. for respiratory triggered MRI, motion compensation in the reconstruction process, etc.

[0012] An advantage of embodiments of the present invention is that obstacles in the examination zone (e.g. inside the scanner bore), such as auxiliary coils, parts of the subject's body and / or other equipment used during the imaging process, can be avoided by the mirror or mirrors to allow good illumination of the target area on the body and its image by the camera. Furthermore, it is advantageous that the use of additional mirrors for configuring such optical paths can be avoided and / or the mirrors used can be configured without blocking each other's optical paths, while still achieving, for example, good illumination and camera field of view.

[0013] An advantage of embodiments of the present invention is that the subject under examination can see the information or entertainment presented on the screen and / or by the projector, and the camera observation does not block the subject's view or may even enable (e.g., at least contribute to) such view as its additional feature.

[0014] An advantage of embodiments of the present invention is that pre-installed, e.g. commonly used MRI systems can be easily retrofitted in accordance with embodiments of the present invention, e.g. by simply replacing the mirror or mirror assembly of an existing camera system (and by fine-tuning already configurable optical and / or software settings).

[0015] An advantage of embodiments of the present invention is that the available camera detector area of ​​the camera system, e.g., available pixels (for example, but not limited to, the same principles apply to analog systems), can be more optimally utilized by magnifying the part of the subject's body of interest using a mirror or mirrors that provide magnification.

[0016] An advantage of embodiments of the present invention is that a better view of the target area to be observed by the camera can be achieved without reducing the distance of the camera to the target area. For example, it may be preferable to locate the camera (and / or illumination source) outside the examination zone (e.g., outside or at the edge of the scanner bore) so as not to interfere with, or at least minimize the effect of, the electromagnetic (radio frequency) and / or magnetic field characteristics of the system.

[0017] An advantage of embodiments of the present invention is that physiological or other (e.g. motion-related) parameters of a subject can be monitored accurately and robustly during an MRI examination. For example, subtle intensity changes in the camera images or features derived therefrom can be analyzed to extract cardiac, respiratory and / or (more general) motion signals. For example, in some such applications it may be desirable to have a wide field of view of the subject's body parts, e.g. the face and / or head, whereas when installed in practical and technically less confounding positions, e.g. at the end of the magnet bore flange, a long distance between the cameras may typically reduce the viewing angle, e.g. such that the number of image pixels available for processing may be significantly lower. Furthermore, achieving good illumination of the monitored body parts may be difficult or less efficient. These challenges may be overcome or at least reduced by embodiments according to the present invention.

[0018] Systems and methods according to embodiments of the present invention achieve the above objectives.

[0019] In a first aspect, the invention relates to a medical imaging system, such as a magnetic resonance imaging system, a computed tomography imaging system, and / or other such diagnostic imaging system. The system comprises a camera for monitoring a subject when undergoing an examination while positioned in an examination zone of the system by acquiring at least one image. The system comprises a mirror assembly arranged in the examination zone to reflect light from a target area on the subject's body onto the camera. The mirror assembly comprises a curved reflective surface and / or a plurality of reflective surfaces oriented in different directions. The curved reflective surface and / or the plurality of reflective surfaces are adapted to reflect light from a target area to the camera by magnifying the reflected image and / or by projecting multiple copies of the same target area onto different areas of the image acquired by the camera and / or by both reflecting light from the target area to the camera and reflecting light from at least one light source located differently from the camera to the target area. An image processor is adapted to process image information acquired by the camera to derive a photoplethysmography signal from the image acquired by said camera.

[0020] Thus, the curved reflective surface and / or multiple reflective surfaces may be adapted to reflect light from a target area to a camera by magnifying the reflected image.

[0021] Additionally or alternatively, the curved reflective surface and / or multiple reflective surfaces may be adapted to reflect light from the target area to the camera by projecting multiple copies of the same target area onto different areas of the image captured by the camera.

[0022] Additionally or alternatively, the curved reflective surface and / or the multiple reflective surfaces may be adapted to reflect light from the target area to the camera as well as to reflect light from at least one light source at a different location from the camera to the target area. In other words, one reflective surface may reflect light from a light source onto the target area and from the target area onto the camera, or one reflective surface may reflect light from a light source onto the target area and a different reflective surface may reflect light from the target area onto the camera. Obviously, this does not preclude the use of two or more reflective surfaces, one each involved in both the inbound and outbound paths to the target (or a subset thereof), nor does it preclude the use of two or more dedicated reflective surfaces and / or two or more dedicated reflective surfaces for illumination of the outbound light path from the target to the camera.

[0023] In a medical imaging system according to an embodiment of the invention, a mirror assembly can comprise a first mirror portion, the first mirror portion comprising at least one reflective surface adapted to provide a view of the target area to a camera.

[0024] In a medical imaging system according to an embodiment of the present invention, the first mirror portion may include multiple reflective surfaces, each reflective surface adapted to reflect the same target area onto the camera, the target area being replicated via different optical paths in the acquired image.

[0025] In a medical imaging system according to an embodiment of the present invention, the first part may comprise a reflective surface forming a converging mirror to provide a camera with a magnified view of the target area.

[0026] In medical imaging systems according to embodiments of the present invention, the converging mirror may be a spherical or parabolic mirror, or may have a spherical or parabolic profile in at least one direction.

[0027] A medical imaging system according to an embodiment of the present invention may include at least one light source for emitting a light beam within an examination zone, and the mirror assembly includes a second mirror portion (e.g., different from the first mirror portion) having at least one reflective surface oriented differently from the reflective surface of the first mirror portion for reflecting light from the light source onto a target area.

[0028] In a medical imaging system according to an embodiment of the present invention, the second mirror portion may comprise multiple reflective surfaces having different orientations such that light from multiple light sources is reflected onto a target area by corresponding reflective surfaces of the second mirror portion.

[0029] In a medical imaging system according to an embodiment of the present invention, the mirror assembly may comprise a third mirror portion for reflecting an image presented by a screen (which may be part of the imaging system) outside the examination zone to the subject so that the subject can visually receive entertainment, instructions and / or information through said screen.

[0030] A medical imaging system according to an embodiment of the present invention may include a radio frequency transmitter / receiver head coil assembly for acquiring magnetic resonance signals from a head region of a subject, and the mirror assembly may be adapted to be attached to the head coil assembly or may be integrated therein.

[0031] A medical imaging system according to an embodiment of the invention may comprise, for example, an arm assembly, comprising one or more flexible structures and / or joints for providing some degree of freedom in configuration of orientation and / or position, adapted to be fixed (or attached) to a mounting point on (a stationary part of) a gantry or magnet bore enclosure, or on a patient treatment couch or other auxiliary equipment, for use in an examination zone of the medical imaging system. The arm attachment is thus adapted to be mounted (e.g. attached to or attached to, e.g. removably attached to) in or on the medical imaging system. The mirror assembly may be adapted to be mounted to the arm assembly, for example, such that the mirror assembly is supported by the mounting point via the arm assembly, or may be attached to the arm assembly. The arm assembly may be a rigid structure, but may be adapted to provide a degree of freedom to configure the position and / or orientation of the mirror assembly relative to the mounting point, for example via one or more hinges, other types of mechanical joints (having at least a degree of freedom), and / or flexible or pliable structures, as already mentioned.

[0032] In medical imaging systems, and in particular magnetic resonance imaging systems, according to embodiments of the invention, a camera may be integrated into or attached to a flange end region of the magnet bore housing of the system, and a light source may be integrated into or attached to the flange end region.

[0033] A medical imaging system according to an embodiment of the present invention may comprise an image processor adapted to process image information acquired by the camera to derive information about the subject.

[0034] In a medical imaging system according to an embodiment of the present invention, the target area may be a part of the subject's forehead or cheek, or a portion thereof, and the image processor may be adapted to derive a photoplethysmography signal from an image acquired by said camera.

[0035] In a second aspect, the present invention relates to a head coil mount adapted to be attached to a radio frequency transmitter / receiver head coil assembly for acquiring magnetic resonance signals from a head region of a subject when examined by a magnetic resonance imaging system. The head coil mount comprises a mirror assembly for reflecting light from a target region on the body of the subject onto a camera of the magnetic resonance imaging system. The mirror assembly comprises a curved reflective surface and / or a plurality of reflective surfaces oriented in different directions. The curved reflective surface and / or the plurality of reflective surfaces are adapted to reflect light from the target region to the camera by magnifying the reflected image and / or by projecting multiple copies of the same target region onto different regions of an image acquired by the camera, and / or to reflect light from the target region to the camera when reflecting light from at least one light source located differently from the camera onto the target region as the camera.

[0036] In a further aspect, the invention relates to an arm mount, for example with one or more flexible structures and / or joints to provide some degree of freedom in orientation and / or position configuration, adapted to mount to a mounting point on a (stationary part) of a gantry or magnet bore enclosure, or on a patient treatment couch or other auxiliary equipment, for use in an examination zone of a medical imaging system. The arm mount is thus adapted to be fixed (e.g. attached to, optionally removably attached to) in or on a medical imaging system for examining a subject when placed in the examination zone of the system. The arm mount comprises a mirror assembly for reflecting light from a target area on the subject's body onto a camera of the medical imaging system. The mirror assembly comprises a curved reflective surface and / or multiple reflective surfaces oriented in different directions. The curved reflective surface and / or the multiple reflective surfaces are adapted to reflect light from the target area to the camera by magnifying the reflected image and / or by projecting multiple copies of the same target area onto different areas of the image captured by the camera, and / or to reflect light from the target area to the camera when reflecting light from at least one light source located differently from the camera to the target area as the camera.

[0037] In a third aspect, the present invention relates to a radio frequency transmitter / receiver coil assembly for acquiring magnetic resonance signals from a body of a subject when examined by a magnetic resonance imaging system. The radio frequency transmitter / receiver coil assembly comprises a mirror assembly for reflecting light from a target area on the body of the subject onto a camera of the magnetic resonance imaging system. The mirror assembly comprises a curved reflective surface and / or a plurality of reflective surfaces oriented in different directions. The curved reflective surface and / or the plurality of reflective surfaces are adapted to reflect light from the target area to the camera by magnifying the reflected image and / or by projecting multiple copies of the same target area onto different areas of an image acquired by the camera, and / or to reflect light from the target area to the camera when reflecting light from at least one light source located differently from the camera onto the target area as the camera.

[0038] In a fourth aspect, the present invention relates to a method for monitoring a subject undergoing a medical imaging examination (e.g. MRI, CT or other type of medical imaging examination) while the subject is positioned in an examination zone of a medical imaging system, the method comprising the steps of providing a mirror assembly in the examination zone, illuminating a target area on the subject's body, and acquiring at least one image by a camera to view the target area through a reflective surface of a first part of the mirror assembly, where illuminating the target area comprises reflecting light from a light source onto the target area through a reflective surface of a second part of the mirror assembly, and / or acquiring the image comprises viewing the target area magnified by a curved reflective surface of the first part of the mirror assembly, and / or viewing the target area replicated in different areas of the acquired image by reflection through a plurality of differently oriented reflective surfaces of the first part of the mirror assembly.

[0039] The independent and dependent claims set out particular and preferred features of the invention. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not necessarily as explicitly set out in the claims. [Brief description of the drawings]

[0040] [Figure 1] 1 illustrates a medical imaging system, for example a magnetic resonance imaging system, in accordance with an embodiment of the present invention. [Diagram 2] 1 shows a photograph of a flange portion of an MRI scanner bore with integrated camera and light source according to an embodiment of the present invention. [Diagram 3] A camera image is shown, whereby the reflection of the patient's forehead can be monitored via a mirror on the head coil of the MRI system. [Figure 4] The light path from the light source to the patient's forehead, and from the patient's forehead to the camera by a mirror, is shown in a mirror configuration as known in the art. [Diagram 5] 1 illustrates a light path from a light source to a patient's forehead and from the patient's forehead to a camera, each of which is facilitated by a separate reflective surface, according to an embodiment of the present invention. [Figure 6] 1 shows an MRI head coil having a front opening through which the patient's face (or part thereof) can be viewed, as is known in the art. [Figure 7] 1 illustrates a mirror assembly with multiple reflective surfaces for replicating a target region of interest on a subject's body onto different areas of an image acquired by a camera during an MRI examination, according to an embodiment of the present invention. [Figure 8] 1 shows a further example of a mirror assembly comprising multiple reflective surfaces that reflects light from a light source onto a target area of ​​interest on a subject's body during an MRI examination and reflects a view of the target area onto a camera, according to an embodiment of the present invention. [Figure 9] 1 illustrates a ray geometry of a curved mirror for use in a system or apparatus according to an embodiment of the present invention. [Figure 10] 1 illustrates a method according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] The drawings are schematic and non-limiting. Elements in the drawings are not necessarily drawn to scale. The present invention is not necessarily limited to the particular embodiment of the invention shown in the drawings.

[0042] Notwithstanding the exemplary embodiments described below, the present invention is limited only by the claims appended hereto, which are expressly incorporated into this detailed description, and each claim, and each combination of claims permitted by the substructure defined by the claims, forms a separate embodiment of the present invention.

[0043] The term "comprising", when used in the claims, is not limited to the features, elements, or steps described below, but does not exclude additional features, elements, or steps. Thus, it specifies the presence of a stated feature without excluding the further or additional presence of one or more features.

[0044] In this detailed description, numerous specific details are presented. Embodiments of the present invention may be practiced without these specific details. Additionally, well-known features, elements, and / or steps are not necessarily described in detail for the sake of clarity and conciseness of the present disclosure.

[0045] In a first aspect, the invention relates to a medical imaging system, for example a magnetic resonance imaging system, comprising an examination zone and a camera system for monitoring a subject as it undergoes an examination whilst located in the examination zone.

[0046] Although aspects of the invention are discussed in detail with respect to a magnetic resonance imaging system, it will be understood that embodiments of the invention may be equally applied to different types of medical imaging systems, such as computed tomography imaging systems, single photon emission computed tomography systems, positron emission tomography systems, and / or other medical imaging systems. It will also be understood that the imaging system may be combined with other medical systems, for example, to perform a therapy (e.g., radiation therapy), to assist a surgical procedure, or to perform another type of medical intervention. Thus, images of the object may be acquired by the system to guide the therapy or other medical intervention. Furthermore, when referring to typical components of a magnetic resonance imaging system, such as a magnet bore enclosure, it will be understood that other embodiments may relate to different imaging modalities, and such components may be replaced by similar components, e.g., having similar or identical functions, or having a generally similar or identical form. For example, when a magnet bore enclosure is referenced, this may be considered similar to a gantry of a computed tomography imaging system, and it will be understood that the similarity makes sense so far. Similarly, where reference is made to a head coil assembly, it will be understood that this may be similar to a head enclosure for use in other types of systems (or different types of head enclosures that may likewise be used in MRI), such as a stereotactic head frame for use in planning and performing radiotherapy or surgical procedures, radiotherapy masks, etc. These remarks apply equally to further aspects of the invention discussed further below, e.g., methods according to embodiments.

[0047] 1 shows diagrammatically a magnetic resonance imaging system 1 according to an embodiment of the invention. The magnetic resonance examination system comprises a primary magnet assembly 10 defining an examination zone 11, which may for example be formed by a volume in which magnetic field conditions, as substantially generated and controlled by the magnet assembly, are suitable for magnetic resonance imaging. The examination zone may thus correspond to (at least a usable portion of) the volume enclosed by the magnet bore of the system (for example, but not limited to, the principles of the invention apply equally to open bore systems and other, less frequently used magnet assembly configurations).

[0048] A subject to be examined, e.g. a patient 13, may be positioned on a patient treatment couch 14 within the examination zone when the system is in use. The primary magnet assembly may comprise magnet windings, e.g. coaxial (e.g. superconducting) windings, for generating a fixed homogenous magnetic field within the examination zone. The examination zone may be a cylindrical volume enclosed by these magnet windings.

[0049] The system may comprise a reconstructor 15 for reconstructing a magnetic resonance image, for example a tomographic MRI image, from magnetic resonance signals acquired by the system in use. The reconstructed image may be provided via output 16 for display, processing or storage.

[0050] An auxiliary device such as an RF T / R head coil 12 may be placed in the examination zone to acquire magnetic resonance signals from the subject's head, in use. Typically the signals may also be received by a receiver coil already integrated within the housing of the primary magnet assembly, although other auxiliary coil configurations may be used to acquire signals from other body parts or for different use cases.

[0051] It will be appreciated that in other embodiments the system may be a medical imaging system for different imaging modalities, such as, but not limited to, a computed tomography system.

[0052] The system comprises a camera system comprising a camera 21. The camera system is adapted to acquire information from the subject being examined, for example to acquire vital signs, movement, indications of distress, etc. Acquiring this information may refer to simply acquiring images to be presented to an operator for evaluation, i.e. deriving information by observing the images, and / or may refer to acquiring images for processing by, for example, an electronic processing device to determine a useful value or indicator representative of a parameter or parameters of interest.

[0053] The camera 21 may be mounted near the entry of one of the examination zones. For example, the camera may be integrated into or attached to a flange of the MR bore (for example, so that the usable free bore diameter is not affected or is only minimally reduced and / or so as to avoid or minimize interference with the operation of the MR system). This is illustrated for example by the photograph of FIG. 2, which also shows the integration of an (optional) illumination light 29 in this flange. The camera system may also comprise a camera control unit 25 for controlling the camera 21, for example to adjust parameters such as the orientation of the optical axis, the focal length, etc., and the camera system may comprise a display 26 for displaying images of the interior of the inspection zone 11 acquired by the camera 21 (either raw or after suitable processing), thereby enabling an operator to visually monitor the specimen within the inspection zone.

[0054] Images acquired by camera 21 may be provided to an image processor 27 (which may be implemented in software, for example) for deriving information about the subject from the acquired camera images.

[0055] The image processor 27 may be adapted to process image information acquired by the camera system and may be adapted to perform static or dynamic image analysis in order to obtain information from the patient, such as, for example, the patient's vital signs, and / or the patient's movements, and / or the patient's signs of distress (or more generally, the patient's mood detection), and / or photoplethysmography (PPG), and / or video-based detection of voice (or, for example, speech recognition of simple words or commands based on facial features). Information about the patient's movements may include, for example, information indicative of respiratory and / or cardiac movements, for example, respiratory and / or cardiac cycle phases. For example, information about the patient's movements may be derived from image information of the patient's body hull. The information may be determined by processing (for example, by an image-based movement detector) and / or by (direct) visual monitoring of the patient via the system by an operator or staff member.

[0056] Respiratory and / or cardiac phase information (and / or more general information indicative of motion) may be provided to the reconstructor 15 to correct the acquired magnetic resonance signals for motion and / or to apply motion correction to the reconstructed magnetic resonance images. For example, a cardiac trigger signal may be determined based on a video signal from the camera. Cardiac triggering is particularly useful for cardiac MRI for obvious reasons, but may also be applied more generally. For example, in neuroimaging, artifacts in head and / or neck scans caused by pulsatile flow of blood and / or cerebrospinal fluid may be suppressed or reduced by such triggering techniques or other compensation approaches based on the cardiac phase signal. This may also be useful for quantitative measurements of blood flow in the carotid arteries. Furthermore, a PPG signal may be extracted from the video signal, for example by analyzing subtle intensity changes of skin pixels on the subject's face, such as the forehead and cheeks.

[0057] In magnetic resonance imaging systems according to embodiments of the present invention, the camera system may also include one or more light sources 29. It will be appreciated by those skilled in the art that lighting conditions may be better controlled and imaging may be more effective when using active lighting, although embodiments relying on passive lighting for imaging are not necessarily excluded.

[0058] The light source 29 may be configured and positioned to direct its light beam directly into / onto the inspection zone, possibly supported by a mirror or reflective surface. Additionally, the use of multiple mirrors (or faceted mirrors) or curved mirrors may allow different areas on the object to be effectively illuminated with a single light source even if the camera and light are not in the same location or very close to each other, and / or allow illumination light from the light source to be both reflected onto a target area of ​​the object and observed by the camera (via the reflected image).

[0059] The light source and / or the camera may be located outside the examination zone, or on or near its edge region. This can simplify the setup of the magnetic resonance imaging system (e.g., avoid or reduce interference with the RF and magnetic field operation of the system) and provide a more flexible bore width in the examination zone. For example, in the case of a cylindrical bore system, the camera and / or the light source may both be located in a flange of the bore enclosure at one end of the bore, which can leave the other end substantially free, for example allowing unhindered access to the examination zone (to bring the patient and / or ancillary equipment into the examination zone) and reducing potential claustrophobic effects and therefore possible discomfort for the subject while being imaged by the system.

[0060] The light sources 29 may be located, for example, adjacent to each other at the flange end of the bore, or generally in the same flange area in the longitudinal direction, separated, for example, by an angle about the longitudinal axis, see, for example, FIG. 2, next to or near the camera. If the light sources and the camera are located relatively close together, mirrors or reflective surfaces may be used, for example, so that the same mirror is effectively used twice in the optical path to direct the emitted light from the light source to the examination zone (e.g., the body part being observed) and back again from the observed examination zone to the camera, thus reducing the number of mirrors required (but not limited to this). Locating the light sources and the camera close to each other may have further advantages, such as minimizing the (reduction of) the impact on the available bore width, and optionally sharing cables or conduits for power and / or control signals (which may also simplify the design of the system in terms of avoiding or reducing RF and / or magnetic field interference). However, it is an advantage of the embodiment that good illumination by the camera as well as good visibility by a camera having only a single mirror can be achieved even when the camera and light source are separated by a substantial distance, for example at different angular positions around the longitudinal axis (e.g. at least a 10° separation, for example at least a 20° separation, or even substantially greater, for example in the range of 30° to 120°, for example in the range of 45° to 90°, for example in the range of 30° to 60°).

[0061] In a magnetic resonance imaging system according to an embodiment of the invention, a camera (or multiple cameras) may be adapted to operate (e.g., be substantially exclusively sensitive to) light within a (e.g., narrow) infrared wavelength range and outside the visible wavelength range.

[0062] In a magnetic resonance imaging system according to an embodiment of the invention, the camera (or cameras) may be adapted to operate (e.g., be substantially exclusively sensitive) in the visible wavelength range, e.g., be sensitive to a broad white light spectrum or portions thereof, e.g., color bands. The camera may be adapted to acquire monochrome information, or may be a color camera, e.g., adapted to detect different color components, e.g., but not limited to, red, green and blue components, preferably independently and substantially simultaneously. The camera may also be adapted to detect a relatively large number of spectral components (e.g., more than three), e.g., a multispectral camera.

[0063] The light source can emit light in a spectrum suitable for the camera, for example, a broadband white light can provide illumination for a monochrome or color camera operating in the visible range. Similarly, an infrared light source can be used to emit infrared light in the spectral range to which the infrared camera is sensitive. It will be appreciated that the spectra of the light source and the camera need not necessarily be identical or even closely related, for example, the spectrum of the light source can be broader, so long as there is sufficient overlap with the spectrum to which the camera is sensitive.

[0064] The camera may be an analog camera, or preferably a digital camera, including, for example, an array of pixelated photodetectors.

[0065] The system comprises a mirror assembly 22 arranged in the examination zone to reflect light from a body part of the subject, such as the face or parts thereof (e.g. eyes or eyeballs, forehead area, ...) to the camera and / or to reflect light from a light source to said body part. The mirror assembly 22 comprises one or more mirrors and / or reflective surfaces. The mirror assembly may comprise a (e.g. non-metallic) mirror. The use of the term "mirror" should not be narrowly interpreted, for example the mirror assembly may be composed of components acting as mirrors and / or reflectors, i.e. reflecting light within a spectral range of interest. The mirror assembly comprises at least a part adapted to reflect an image from the body part of interest towards the camera (not necessarily excluding additional mirrors along its path towards the camera), i.e. a part suitable for reflecting light without substantial scattering and / or diffusion so that an image of reasonable quality can be formed. The mirror assembly may comprise another part(s) that reflects light from the light source(s) onto the body part of interest, although the requirements for this second part(s) may be more relaxed, e.g., scattering or diffusion of the reflected light may be acceptable.

[0066] The mirror assembly 22 can be mounted, for example, on the inner wall of the examination zone of the magnet bore enclosure and / or on auxiliary devices such as a patient table (or patient treatment couch) or a head coil assembly. For example, the mirror assembly may be attached to the patient table via an arm assembly. Thus, the mirror assembly can be attached to or formed as part of a head T / R coil, for example to be used for neck MR examinations, head MR examinations, head MR examinations, and / or neuroradiology MR examinations. It is noted that integrating the mirror in or on the head coil can avoid expensive or complex modifications of existing devices, for example the scanner bore. Although a relatively large distance between the cameras, mounted, for example, on the flange of the bore, may result in a very limited field of view, showing, for example, only the forehead or parts thereof, this may be sufficient for some applications, for example monitoring blood pulsation by slight variations in pixel intensity.

[0067] A medical imaging system according to an embodiment of the invention may comprise an arm assembly adapted to be fixed (or attached) to a mounting point on (a stationary part of) a gantry or magnet bore enclosure, and / or a patient treatment couch and / or other ancillary equipment for use in an examination zone of the medical imaging system. The arm attachment is thus adapted to be fixed (e.g., attached or mounted, e.g., removably mounted) in or on the medical imaging system or a part thereof (e.g., a patient treatment couch). The mirror assembly may be adapted to be attached to the arm assembly, for example, such that the mirror assembly is supported by the mounting point via the arm assembly, or may be attached to the arm assembly. The arm assembly may be a rigid structure, but may also be adapted to provide a degree of freedom to configure the position and / or orientation of the mirror assembly relative to the mounting point, for example via one or more hinges, other types of mechanical joints (having at least one degree of freedom), and / or a flexible or pliable structure.

[0068] Further embodiments are described below relating to a mirror assembly that is integrated within or attached (or attachable) to the head coil, although it will be appreciated that the same principles apply to different designs of ancillary equipment with similar results being obtained when the mirror assembly is attached to the (inner) wall of the examination zone. For example, instead of supporting the mirror assembly by the head coil, the mirror assembly could equally be supported by a bore wall above the head coil (or the head if a head coil is not used), or above another body part of interest that is to be observed by the camera.

[0069] (a) The use of mirrors / reflectors can be particularly advantageous when the region of interest for observation is blocked from direct view by the camera. For example, the obstruction can be formed by an opaque object, e.g., an auxiliary device such as a local radio frequency (RF) transmit or receive (T / R) antenna, located in the direct line of sight of the camera to the inspection zone. Other possible obstructions include parts of the subject's body.

[0070] Preferably, the mirror assembly 22 does not interfere with the radio frequency operation of a magnetic resonance imaging system and / or does not disrupt the magnetic and RF dynamic transmission fields of an MRI system. Non-metallic mirrors are particularly suited to achieving this advantage. For example, the non-metallic mirror may be a dielectric mirror including, for example, a stack of layers of different refractive index, such that, for example, a dielectric resonator is formed by the stack. Although such devices are particularly suited for a narrow wavelength range, it will be appreciated that varying the thickness of layers in the stack can accommodate reflection of different wavelengths, such that broadband reflection (or an approximation thereof) or reflection of multiple color components can also be readily achieved.

[0071] In a magnetic resonance imaging system according to an embodiment of the invention, the mirror assembly may be particularly adapted to reflect light to enable formation of an image of a body part of interest on an imaging plane of the camera (for camera observation) and / or to reflect light from a light source to the body part of interest. Optionally, the mirror assembly, or at least parts thereof, may be transparent or semi-transparent to light in the (human) visual range, i.e. when different spectral ranges are used for illumination and camera image, such as infrared.

[0072] The mirror assembly 22 may thus position an optical path between a portion of the examination zone, i.e., the portion where the body part is located when the subject is undergoing examination, and the camera, so that the camera can obtain image information from that portion. The mirror assembly may be located within the examination zone, for example, by mounting to an inner wall of the magnet bore enclosure. Alternatively, the mirror assembly may be located on ancillary equipment within the examination zone, such as on a local radio frequency (RF) coil, for example when the mirror assembly is located on a patient treatment couch within the examination zone. For example, it may be practical to mount the mirror assembly to an RF head coil.

[0073] For example, neuroscans are typically performed with the patient's head placed inside a head coil located at the isocenter of the magnet. The neurocoil substantially completely surrounds the patient's head and neck, so that a direct camera view of the head is largely obscured. For example, as shown in FIG. 2, a camera may be mounted on the flange of the bore. A view of the patient positioned within the head coil is shown in view 3. A small portion of the patient's forehead may be observed by a mirror mounted on top of the head coil, for example, as shown by area 41. The substantial enclosure of the head by the head coil poses a problem by allowing a limited view, e.g., only a small portion of the forehead in this example, making it more difficult to adequately illuminate the target area. For example, it may be difficult to directly illuminate the forehead with a bore light (e.g., see FIG. 2), such that only indirect light scattered by the bore walls reaches the area of ​​interest. The fact that the camera and the bore light are located at different locations on the flange of the bore may also contribute to the problem of insufficient illumination. A single flat mirror 43, as shown in FIG. 4, cannot effectively (or sufficiently) reflect the light from the light source 29 onto the target area (e.g., the forehead) as well as the light from the target area onto the camera 21. In other words, the mirror cannot effectively or efficiently project the light from the bore light onto the same area to get a good view of the target area by the camera.

[0074] Thus, the mirror assembly 22 is curved or faceted in embodiments according to the invention. A faceted mirror assembly may comprise multiple reflective surfaces that are not parallel to each other, such that differently oriented portions can reflect light from different volumes in space onto substantially the same target area, or vice versa. Thus, light from a light source can be reflected onto a target area, the target area can be observed by the cameras at different positions, and / or light from different light sources can be directed towards the target area. Similarly, different cameras can use differently oriented mirror facets to view the same area in a multi-camera setup, or the same target area can be replicated within the camera images acquired by the cameras to increase the number of available pixels corresponding to the target area, for example, for algorithmic processing purposes.

[0075] For example, Fig. 5 shows a schematic of a setup with a faceted mirror. The mirror assembly 22 comprises a first mirror 43 and at least a second mirror 44, or multiple additional mirrors. In other words, one or multiple additional mirrors or mirror segments 44 are added to the first mirror 43 shown in Fig. 4 to form such a faceted mirror, this second mirror having a different tilt angle. The second mirror can be tilted to reflect light from the light source through the first mirror to the area of ​​the forehead seen by the camera.

[0076] In addition to tilting about a horizontal axis (perpendicular to the longitudinal axis of the scanner system, i.e. about the transverse axis), this second mirror may also be tilted about a vertical axis (the frontal axis when the patient is imaged in a conventional supine position in use), as shown by the plane A of the second mirror not coinciding with the plane of the first mirror. This is obviously advantageous in embodiments where the camera and the light source are arranged at different angular positions in the same flange area, see for example FIG. 2, to project light onto a target area and image the target area by the camera. The second mirror facet may for example comprise a number of different mirror facets with different angles (tilts) to project light from different light sources onto the target area. In the example of FIG. 2, the light sources are arranged at substantially the same vertical position (height), and for example the bores are arranged at the same longitudinal position (the flange end of the bore) and are widest in the horizontal plane (not limited to this), but on different sides relative to the center. Thus, in this example, the two second mirrors 44 may have the same angle with respect to the vertical, but are tilted differently about this vertical axis (e.g., symmetrically about a vertical plane through the isocenter), e.g., each having a different tilt about the axis A shown.

[0077] Thus, a mirror assembly according to an embodiment may comprise at least two facet portions, which may be separate mirrors or reflective surfaces, or may form part of a single connected mirror and / or reflector structure, with one or more facet edge lines connecting the facets (e.g., integrally formed as a single mirror). As can be seen from the above examples, a mirror or reflective surface may comprise e.g. 3-10, e.g. 3-5, e.g. 3 or 4 facet portions, e.g. at least three facet portions for each camera and at least one reflector for each light source (and possibly additional reflectors for reflecting multiple copies of a target area onto different areas in an image captured by the camera, as described in more detail below).

[0078] The size and shape of the (or each) secondary mirror (or mirror facet) 44 may be adapted to generate an illumination area that corresponds to (or strongly overlaps with) an area of ​​interest seen by the camera when illuminated by the (or corresponding) light source. The secondary mirror may be rectangular, but this is not strictly necessary and may for example deviate from a rectangular shape for this purpose. The size and shape may thus be determined based on the expected position of the mirror assembly during use of the apparatus, the size and shape of the area to be observed, and the position of the light source from which light is reflected to the target area.

[0079] It should also be noted that the use of additional secondary mirror facets to receive light from two or more light sources (e.g., such that the mirror assembly includes two or more differently oriented facets) can be advantageous to avoid shadows in areas of interest, for example, such that each area that would cast a shadow when illuminated by one light source is sufficiently illuminated by another light source.

[0080] The first mirror (facet) 43 may be larger than the second mirror 44 (e.g., each), so that the first mirror can use a larger area so that it can project a good image onto the camera, while less space is reserved for the second mirror, which has the auxiliary function of providing good illumination.

[0081] For example, the first mirror 43 may be limited (laterally) to the size of the opening of the head coil to which the mirror assembly may be attached according to the embodiment. Figure 6 shows a typical head coil assembly 12, where the front opening provides a maximum usable width d for the mirror assembly, e.g., the first mirror 43. By adapting the width of the first mirror to this width d of the opening or close to it, a good view of the (e.g., full) forehead can be achieved by the camera. This does not necessarily mean that the mirror is strictly limited to this width, e.g., optical and design considerations may motivate a (e.g., slightly) wider design. If the first mirror is curved, e.g., forming a converging mirror, it may be possible to further increase the (usable) width of the mirror.

[0082] However, such an aperture is generally quite large compared to its width, so that the primary mirror 43 can be used for the secondary mirror 44 (in the horizontal plane). Furthermore, space to either side (also in the horizontal plane) can additionally or alternatively be used, as a different angling of the second mirror may allow the light to be directed onto the area of ​​interest from a more acute angle. It is also noted that the use of two or more light sources and two or more secondary mirrors 44 may be even more advantageous when the light is projected onto the target area at a more acute angle, as a larger shadow will be cast in such a case and can be compensated for by additional illumination paths.

[0083] Thus, good illumination of the area observed by the camera can be achieved by the embodiments, which also enables more robust and / or accurate signal detection based on camera image analysis, for example based on inferring remote PPG signals from the camera images.

[0084] 8 shows an example of a mirror assembly 22 for attachment to a head coil 12 for MRI imaging, for example as may be detected by a bore camera in use. The mirror assembly comprises a first mirror 43 for reflecting an image of the target area onto the camera, and two second mirrors 44 project light from respective light sources onto the target area.

[0085] The mirror assembly 22 includes one or more mirrors and / or reflective surfaces, for example a first mirror or mirror portion 43 for reflecting light from a body part of the subject onto a camera. As mentioned above, the mirror assembly 22 may also include a second mirror or mirror portion 44 for reflecting light from a light source onto said body part. The mirror assembly 22 may also include a third mirror or mirror portion 45 (conceptually shown in the lower area of ​​the first portion of FIG. 8 ), which reflects an image presented by a screen to the subject (e.g., to or on the subject's eyes) for example to provide entertainment, instructions, and / or information to the subject. For example, the mirror 43 in the example of FIG. 8 may be positioned approximately above the forehead in use to observe this area by the camera, while the secondary mirror 44 may be positioned higher (in a headward sense in use) to illuminate the area. A third mirror portion 45 may be added below the first mirror (e.g. in a caudal direction in use), for example to allow the subject to view a screen (e.g. a display or projection screen) when in use, positioned above the subject's eye. The tilt angle of this third mirror (or mirror facets) may be adapted for this purpose.

[0086] An advantage of using separate mirror elements (as opposed to an integrally formed mirror assembly with multiple different tilting facets) is that each mirror element can be configured to be adjustable in position and / or orientation, for example, using a sliding or pivoting base. This can provide additional flexibility for adjusting the mirror assembly for different use cases, for example, different positions of the mirror assembly along the longitudinal scanner axis when the camera and light source are in fixed positions. Nevertheless, an integrally formed structure can provide other advantages, for example, in terms of robustness and ease of use.

[0087] Furthermore, the first mirror portion for mirroring the object of interest onto the camera can include multiple separate portions, e.g., facets or individual mirrors, each adapted to reflect substantially the same region of interest on the subject's body onto the camera, thus allowing the region of interest to be replicated via different optical paths in the acquired camera image.

[0088] For example, if the target area on the body is relatively small, e.g., the forehead or a portion thereof (e.g., the central frontal area of ​​the forehead), it may not be necessary to make individual mirror facets to image this area very widely. Other examples of areas of interest include the eye, e.g., eye tracking or wakefulness monitors. Thus, a single flat mirror for observing such an area does not need to be wider than the aperture of the MR head coil. This leaves space to add additional mirrors or mirror segments, e.g., flat mirror segments at slightly different angles relative to each other. FIG. 7 shows an example of a mirror assembly 22, e.g., a first part 43 thereof, comprising three (not limited to this number) mirrors 51, 52, 53. Thus, the mirror assembly 22 can comprise a first mirror part 43 for reflecting light from the subject's body part onto the camera, this first mirror part consisting of multiple mirrors 51, 52, 53 and / or mirror facets adapted, e.g., oriented, to reflect substantially the same target area of ​​the body part of interest onto the camera, e.g., from slightly different angles. These mirrors 51, 52, 53 of the first part may be flat or curved and may for example have a converging or focusing shape (or its equivalent achieved for example by a grating design). The (for example flat) mirrors may be oriented at different angles such that the same (for example substantially overlapping) area is projected onto the camera. Thus, effectively, the camera can observe multiple reflections of the same area, for example the forehead or parts thereof, side by side in the camera image. This image can then be processed to extract useful information such as cardiac signals, which may advantageously improve the signal to noise ratio since the sensor noise of the pixels in the camera is typically uncorrelated, or at least not strongly correlated. This can be used in an independent manner in one embodiment or in combination with the second and / or third mirror parts described above. For example, in the example shown in FIG. 7, the overall width may roughly correspond to the width of the aperture of a head coil to which the mirror assembly can be attached, while the individual mirrors are on the order of the size (and / or shape) of the area of ​​interest, for example (but not limited to) the frontal and central areas of the forehead.For example, this may correspond to region 41 shown in the situation overview of FIG.

[0089] Additionally or alternatively, the mirror assembly 22 or portions contained therein can be curved, for example to form a converging mirror, e.g., a zoom mirror. For example, a relatively large distance between the camera and the region of the patient being observed, e.g., the forehead (e.g., to enable remote PPG measurements), can result in a relatively low viewing angle, e.g., when the camera is mounted on or near the flange of the magnet bore, such that the region of interest covers only a small number of camera pixels in the acquired image. This limits the signal-to-noise ratio (SNR) for video-based extraction of signals of interest, such as cardiac signals.

[0090] This can be overcome, at least to some extent, by choosing a camera lens with a larger focal length, but this has the drawback of limiting the overall field of view of the camera, which may be useful for other applications such as motion tracking and general patient monitoring.

[0091] It should be noted that this concept can also be combined with the above-mentioned feature, where multiple mirrors or mirror segments are configured to provide cameras with views of the same area of ​​interest, e.g., substantially overlapping views onto that same body part or area of ​​interest. In other words, each of the mirror segments can be curved to provide a zoomed reflection.

[0092] Images acquired by camera 21 may be provided to an image processor 27 (which may be implemented in software, for example) for deriving information about the subject from the acquired camera images.

[0093] The image processor 27 may be adapted to process image information acquired by the camera system. For example, magnification and / or image duplication (e.g., into multiple image regions of the same target area on the patient) may provide multiple pixels in the image (especially more than are available when duplication and / or optical magnification is not applied), which are suitable for signal extraction of the signal of interest (not necessarily excluding signal processing relying on larger scale image features, e.g., edge detection, etc., which may be equally duplicated in the image when using multiple reflections or may be enhanced by magnification). Thus, signal extraction may be applied to each pixel (or pixel regions, or image features, which are duplicated in the image), and the results may be combined, for example, by (but not limited to) averaging, to generate a more robust and / or more accurate estimate of the signal of interest. It will also be apparent that such combination or aggregation may be applied at different stages in the processing algorithm, for example pixels (or other image features) may be averaged (or otherwise summarized and / or combined by a suitable measure) to obtain a less noisy representative value which may be used for subsequent processing to determine a signal of interest, or intermediate results derived from the image may be combined (over different regions representing the same image feature and / or over different intermediates obtained from different pixels etc., without limitation) before continuing the processing algorithm to arrive at the signal of interest.

[0094] It is further noted that the reflecting surface of the second part 44 for illuminating the area of ​​interest may be curved, for example, to spread the light received from the light source over the target area. The mirror of the first part for providing a view to the target area is preferably of a converging shape (at least if not flat), while the curved mirror of the second part for illumination purposes may have a converging or diverging shape, depending on the optical properties of the system. For example, when the distance to the light source is relatively small and / or the light source emits a narrow beam, e.g. a laser beam, it may be advantageous to provide a diverging mirror to spread this narrow beam over the entire target area, whereas for light beams emitting a wide beam (e.g. a focused light source), it may be advantageous to provide a converging mirror at a greater distance to capture more of the incident light and focus this incident light on the target area.

[0095] It should be noted that "curved", "converging", "diverging", etc. should be interpreted in a functional sense throughout this specification. For example, one skilled in the art knows that the properties of a curved mirror can be achieved by a flat grating or similar design using diffractive and / or structured reflective optics. In other words, a (mechanically) flat grating or similar optical structure can be considered to be "curved" in the optical sense, or at least fully equivalent thereto.

[0096] By providing a curved mirror or multiple curved mirrors, e.g. converging mirrors, e.g. parabolic mirrors, and / or by duplicating the same area of ​​interest on the body in the camera image by multiple mirrors or mirror facets, generally more pixels become available for monitoring and image processing, e.g. increasing the SNR of the values ​​derived from the image by processing, e.g. cardiac signals. This also has the advantage that no changes need to be made to the hardware of the camera or magnetic resonance imaging system (obviously, except for the mirror assembly itself if it is considered part of the system). Duplication can be achieved by several (e.g. slightly) angled mirrors and by magnification by using curved mirrors.

[0097] For example, the mirror assembly may comprise one or more curved mirrors or mirror facets. The curved mirror (or curved regions of the mirror, e.g., embodiments in which more functional mirror portions are integrated into a single integrally formed mirror) may be a concave mirror, e.g., a parabolic mirror, or a spherical mirror. Spherical mirrors may have the advantage of being easier and more cost-effective to manufacture, although embodiments are not limited thereto.

[0098] For example, but not by way of limitation, the curved mirror or curved mirror portion may have a fixed radius of curvature r in at least a first horizontal direction (e.g., a transverse direction perpendicular to the longitudinal axis of the MRI system, e.g., relative to the subject when placed in a prone position during an imaging procedure). H The second radius of curvature r V (e.g., perpendicular to the first direction), e.g., the front-to-back direction during use, e.g., the vertical direction is r H (thus forming a spherical mirror) or may be different. The radius is selected such that a single but magnified image of the target area, e.g., the forehead or part thereof, is reflected by this mirror or mirror portion to the camera. The ray geometry of such an exemplary zoom mirror is shown in FIG. 9. The patient's forehead G is placed within the focal length f=r / 2 of the mirror. This reflects a magnified virtual image B of the forehead to the camera. The Gaussian lens equation is: 1 / f=1 / g+1 / b=2 / r and b = fg / (g-f) Because of the virtual image behind the mirror, b is a negative value. The magnification m is m≡B / G=―b / g=f / (f―g) is given by:

[0099] For a given distance g between the forehead and the mirror, and a desired magnification m, the corresponding focal length f of the mirror is given by: f = mg / (m-1) is given by:

[0100] As an illustrative example, for an embodiment in which the mirror is placed on the forehead above the head coil, a distance g of 20 cm may be assumed, such that a desired magnification of, say, m=5, results in a focal length of f=25 cm and a radius of curvature of r=50 cm. The desired magnification can be changed by selecting a different value of r.

[0101] While both the exemplary embodiment of image duplication by multiple mirrors and the exemplary embodiment of image magnification by zoom mirrors may have the advantage of increasing the signal-to-noise ratio of detection of a characteristic of interest by image processing, for example, both introduce more pixels to the image collection light relevant for processing, the magnification by mirrors has the additional advantage that more details in the region of interest, for example the patient's forehead, can be resolved by the camera. This may be beneficial for certain image processing applications, such as motion detection and quantification for use in motion compensation techniques (in reconstructing and / or processing acquired MRI images). For example, motion detection may be based on pattern matching, which may be more accurate and / or robust if more details are available in the image. Motion compensation may also be particularly useful as an element of a processing algorithm adapted to determine another useful parameter from the observed camera images, for example, motion compensation of acquired camera data may improve the reliability and accuracy of cardiac signal detection based on said camera images.

[0102] With regard to the mirrors and / or mirror facets of the mirror assemblies described above, it should be noted that, according to at least some embodiments, multiple such differently oriented and / or oriented (and / or distorting by magnification) reflective surfaces placed in or near the field of view of the subject undergoing the examination may have a confusing or disruptive effect on the subject's experience. For example, the subject may see multiple replicated or distorted views of his / her environment through such mirrors. Often, the patient undergoing the examination may see video content on a screen or may be instructed to pay attention to information and / or instructions on a screen visible to the subject through a mirror in front of them. It will be appreciated that in such situations, additional mirrors and / or curved mirrors in the subject's field of view may be particularly distracting or even uncomfortable.

[0103] The use of a dielectric mirror, for example in combination with a camera image outside the visible spectrum or only in a narrow band, can overcome this problem (e.g. reducing the confusing visual information reflected to the patient to a single color that can be more easily ignored). For example, the dielectric mirror can be designed to be reflective only for a specific narrow wavelength band, for example the infrared range or a narrow color component of the visible spectrum, while being non-reflective, for example exhibiting a flat area of ​​neutral color, or being transparent, outside that narrow wavelength band. The use of the infrared spectrum can further make it possible to extend the width of this band without discomfort, since no visual information is carried by infrared light. This can be combined with adapting the light source to the spectrum used for the camera image (and corresponding to the reflective properties of the mirror), for example using infrared illumination. Obviously, these remarks do not apply to the third part and part of the previously mentioned mirror assembly, if included in the embodiment, which is specifically adapted to assist in presenting such information provided to the subject via a screen or projection.

[0104] The mirror assembly may be adapted to be attached to ancillary equipment of an MRI scanner, such as an MRI coil assembly, e.g. a head coil. The mirror assembly may alternatively be integrated into such ancillary equipment, e.g. forming a (fixed) part of a coil assembly, e.g. a head coil.

[0105] In a second aspect, the present invention relates to a head coil mount adapted to be attached to a radio frequency transmitter / receiver head coil assembly 12 for acquiring magnetic resonance signals from a head region of a subject when examined by a magnetic resonance imaging system 1. The head coil mount comprises a mirror assembly 22 for reflecting light from a target region on the subject's body onto a camera of the magnetic resonance imaging system. The mirror assembly 22 comprises a curved reflective surface and / or a plurality of reflective surfaces oriented in different directions. The curved reflective surface and / or the plurality of reflective surfaces are adapted to both reflect light from the target region to the camera by magnifying the reflected image and / or by projecting multiple copies of the same target region onto different regions of an image acquired by the camera and / or to reflect light from the target region to the camera when reflecting light from at least one light source at different positions as the camera. For example, the mirror assembly 22 may be a mirror assembly as described above with respect to the first aspect of the invention.

[0106] In a further aspect, the invention relates to an arm mount (see arm assembly discussed above) with one or more flexible structures and / or joints, for example to provide some degree of freedom in orientation and / or position configuration, which is adapted to be attached to a mounting point on a (stationary part of) a gantry or magnet bore enclosure, or on a patient treatment couch or other auxiliary equipment, for use in an examination zone of a medical imaging system. The arm mount is thus adapted to be fixed (i.e. attached) (optionally removably attached) in or on (e.g. to a component thereof, e.g. a patient couch) for examining a subject when placed in the examination zone of the system. The arm mount comprises a mirror assembly for reflecting light from a target area on the subject's body onto a camera of the medical imaging system. The mirror assembly comprises a curved reflective surface and / or a plurality of reflective surfaces oriented in different directions. The curved reflective surface and / or the multiple reflective surfaces are adapted to reflect light from the target area to the camera by magnifying the reflected image and / or by projecting multiple copies of the same target area onto different areas of the image captured by the camera, and / or to reflect light from the target area to the camera when reflecting light from at least one light source located differently from the camera to the target area as the camera.

[0107] In a third aspect, the present invention relates to a radio frequency transmitter / receiver coil assembly, e.g. a head coil assembly 12, for acquiring magnetic resonance signals from a body of a subject when examined by a magnetic resonance imaging system. The radio frequency transmitter / receiver coil assembly comprises a mirror assembly 22 for reflecting light from a target area on the body of the subject onto a camera of the magnetic resonance imaging system. The mirror assembly 22 comprises a curved reflective surface and / or a plurality of reflective surfaces oriented in different directions. The curved reflective surface and / or the plurality of reflective surfaces may be adapted to reflect light from the target area to the camera by magnifying the reflected image and / or by projecting multiple copies of the same target area onto different areas of the image acquired by the camera and / or when reflecting light from at least one light source at different positions as the camera onto the target area. For example, the mirror assembly 22 may be a mirror assembly as described above with respect to the first aspect of the present invention.

[0108] In a fourth aspect, the invention relates to a method for monitoring a subject undergoing a magnetic resonance imaging examination whilst positioned within an examination zone of a magnetic resonance imaging system, for example within the magnet bore of the system.

[0109] FIG. 10 illustrates an exemplary method 100 according to an embodiment of the present invention.

[0110] The method can include placing a subject in an MRI system for examination.

[0111] The method may include imaging a subject using an MRI system, eg, acquiring magnetic resonance signals from the subject during operation of the system.

[0112] The method includes providing 101 a mirror assembly 22 within an examination zone for monitoring a subject during examination. For example, the mirror assembly may be integrated into or attached to a coil assembly, e.g., a head coil.

[0113] The method includes illuminating 102 a target area on the subject's body using one or more light sources, such as, for example, a light source outside or at an edge region of an examination zone, such as a bore light.

[0114] The target area may be illuminated by reflecting light from a light source onto the target area via a reflective surface of a mirror assembly.

[0115] The method includes a step 103 of acquiring at least one image by a camera 21 to view the target area through a reflective surface of a first part of the mirror assembly. For example, the camera may be positioned outside the edge area of ​​the inspection zone, for example in or on a flange of the magnet bore.

[0116] Acquiring the image may include observing a target area magnified by a curved reflective surface of the mirror assembly, and / or observing a target area replicated in different regions of the acquired image by reflection through a plurality of differently oriented reflective surfaces of the mirror assembly.

[0117] Other features or details of the above-described features of the method according to an embodiment of the fourth aspect of the invention will be apparent in light of the description provided above regarding the system according to an embodiment of the first aspect of the invention.

Claims

1. A medical imaging system, a camera for monitoring a subject when undergoing an examination while positioned in an examination zone of the medical imaging system by acquiring at least one image, a mirror assembly arranged to reflect light from a target region on the body of the subject onto the camera, wherein the mirror assembly has a plurality of reflecting surfaces directed in different directions, the plurality of reflecting surfaces being configured to reflect light from the target region onto the camera by projecting a plurality of copies of the same target region onto different regions of the image acquired by the camera, the mirror assembly, an image processor configured to process image information of the target region acquired by the camera to derive a plethysmograph signal from the image acquired by the camera A medical imaging system having.

2. The medical imaging system according to claim 1, wherein the mirror assembly comprises a first mirror portion, and the first mirror portion comprises at least one reflecting surface configured to provide a view of the target region to the camera.

3. The medical imaging system according to claim 2, wherein the first mirror portion comprises a plurality of reflecting surfaces, and each of the reflecting surfaces is adapted to reflect the same target region onto the camera such that the target region is replicated via different optical paths within the acquired image.

4. The medical imaging system according to claim 2, wherein the first portion comprises a reflecting surface forming a converging mirror to provide an enlarged view of the target region to the camera.

5. The medical imaging system according to claim 4, wherein the converging mirror is a spherical or parabolic mirror, or has a spherical or parabolic profile in at least one direction.

6. The medical imaging system according to claim 2, further comprising at least one light source for emitting a light beam into the examination zone, and the mirror assembly comprises a second mirror portion comprising at least one reflecting surface oriented differently from the reflecting surface of the first mirror portion for reflecting light from the light source onto the target region.

7. The medical imaging system according to claim 6, wherein the second mirror portion comprises a plurality of reflecting surfaces having different directions such that light from a plurality of light sources is reflected onto the target region by corresponding reflecting surfaces of the second mirror portion. Claim 8 The medical imaging system according to claim 1, wherein the mirror assembly comprises a third mirror portion for reflecting an image presented by a screen outside the examination zone to the subject so that the subject can visually receive entertainment, instructions, and / or information through the screen. Claim 9 The medical imaging system according to claim 1, comprising a radio frequency transmitter / receiver head coil assembly for acquiring magnetic resonance signals from the head region of the subject, and / or an arm assembly for attachment to a mounting point on a gantry and / or on a magnet bore enclosure and / or on a patient treatment table and / or on other auxiliary devices for use in the examination zone of the medical imaging system, wherein the mirror assembly is configured to be attached to or integrated with the head coil assembly or the arm assembly. Claim 10 The medical imaging system according to claim 1, wherein the camera is integrated with or attached to a flange end region of a magnet bore housing of the system. Claim 11. The medical imaging system according to claim 10, wherein the image processor is configured to derive information indicating movement, such as respiration-based movement and / or heart phase-based movement, from an image acquired by the camera. Claim 12. A head coil attachment portion for attachment to a radio frequency transmitter / receiver head coil assembly for acquiring magnetic resonance signals from the head region of a subject when examined by a magnetic resonance imaging system, the head coil attachment portion having a mirror assembly that reflects light from a target region on the body of the subject onto a camera of the magnetic resonance imaging system, wherein the mirror assembly has a plurality of reflecting surfaces oriented in different directions, and the plurality of reflecting surfaces are configured to reflect light from the target region onto the camera by projecting a plurality of copies of the same target region onto different regions of an image acquired by the camera. Head coil attachment portion.

13. A radio frequency transmitter / receiver coil assembly for acquiring a magnetic resonance signal from a subject's body when examined by a magnetic resonance imaging system, the radio frequency transmitter / receiver coil assembly comprising a mirror assembly for reflecting light from a target region on the subject's body onto a camera of the magnetic resonance imaging system, the mirror assembly comprising a plurality of reflecting surfaces oriented in different directions, the plurality of reflecting surfaces being configured to reflect light from the target region onto the camera by projecting a plurality of copies of the same target region onto different regions of an image acquired by the camera, radio frequency transmitter / receiver coil assembly.

14. A method for monitoring a subject when undergoing a medical imaging examination while positioned in an examination zone of a medical imaging system, the method comprising the step of providing a mirror assembly within the examination zone, the step of illuminating a target region on the subject's body, the step of acquiring at least one image with a camera and observing the target region through a reflecting surface of a first portion of the mirror assembly, the step of illuminating comprising the step of reflecting light from a light source onto the target region through a reflecting surface of a second portion of the mirror assembly, and / or the step of acquiring comprising the step of observing a replicated target region in different regions of the acquired image by reflection through a plurality of reflecting surfaces of the first portion of the mirror assembly oriented in different directions, method.

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