Camera-based monitoring system for magnetic resonance imaging equipment

Abstract

A magnetic resonance inspection system is provided that includes an inspection zone (11), a camera (21), and a non-metallic mirror (22), and in particular, an optical path (23) is arranged within the inspection zone (11) between a portion of the inspection zone (11) and the camera (21) via the non-metallic mirror (22). The camera can obtain image information from the portion even when the direct line of sight (28) is blocked. The non-metallic mirror is a dielectric mirror having a macroscopically grated base.

Description

[Technical Field]

[0001] The present invention relates to a surveillance system with a camera for monitoring an examination area of ​​a magnetic resonance examination system. [Background technology]

[0002] Such a monitoring system is known from US patent application 2017 / 0146619. The known monitoring system is formed by a camera mounted outside the bore of the magnetic resonance imaging (MRI) device, adjacent to a protective cover of the MRI device. The camera is configured to image a patient being examined during operation of the MRI device.

[0003] JP H0928689 discloses a mirror installed in the bore of an MRI system and a TV camera for capturing an image of the subject mirrored on the mirror. A computer analyzes the image and detects the subject's movement. The computer determines whether the MR data should be discarded, retrieved again, or collected depending on, for example, whether the subject moves outside the limited range. Alternatively, the MRI parameters can be optimized to counteract the effects of the subject's movement.

[0004] JP 2018042892 A discloses an MRI system including a patient bed, a screen, a reflector, and a frame. The patient bed is movable within the bore of the system along the central axis of the bore. The frame on the patient bed supports the reflector so that a subject placed on the bed can see an image projected onto the screen through the reflector.

[0005] U.S. Patent Application Publication No. 2017 / 123020 discloses a medical imaging diagnostic system including a gantry, a treatment table, a reflector, and a processing circuit. The reflector reflects an image output from an image output device. The processing circuit outputs a first image signal related to the first image to the image output device in a first case where the image is presented to the observer without the reflector. In a second case where the image is presented to the observer via the reflector, the processing circuit outputs a second image signal related to the second image to the image output device.

[0006] Japanese Patent Application Laid-Open Publication No. 2004041411 discloses a method for presenting visual stimuli in an MRI system. A dichroic mirror is used in an optical path that is incident on a subject's eye from a substantially frontal direction, and visual stimuli are presented from a projector and a screen. The eye is illuminated by an infrared lamp, and eye movements are monitored through the dichroic mirror by an infrared camera, i.e., using a setup in which infrared light is irradiated and visual stimuli of an optical wavelength spectrum are reflected by the dichroic mirror while the infrared light passes through to monitor the eye. Summary of the Invention [Problem to be solved by the invention]

[0007] SUMMARY OF THE INVENTION It is an object of the present invention to provide a camera surveillance system for a magnetic resonance examination apparatus which has a better coverage of the examination area of ​​the magnetic resonance examination apparatus. [Means for solving the problem]

[0008] This object is achieved according to the invention by a magnetic resonance examination system having an examination zone, comprising a camera sensitive to infrared light and at least one non-metallic mirror in the examination zone, the non-metallic mirror being a dielectric mirror with a macroscopically grated base, through which an optical path is formed between a part of the examination zone and the camera.

[0009] The monitoring system of the present invention functions to monitor the examination zone based on images acquired by a camera (whether by a single image frame or by dynamic images). The camera has a (volumetric) range or field of view, for which the camera is highly sensitive in order to obtain image information from that portion. A non-metallic mirror forms an optical path between a portion of the examination zone and the camera, allowing the camera to obtain image information from that portion. The non-metallic mirror can be located within the examination zone, for example, by attaching it to an inner wall of the examination zone. The non-metallic mirror may also be located on an auxiliary device within the examination zone, such as a local radio frequency (RF) coil located on the patient carrier. For example, it is practical to attach the non-metallic mirror to an RF head coil. Furthermore, the non-metallic mirror can be provided on a separate frame outside the examination zone. In particular, if no steps are taken, the portion in question would be blocked from the camera's range. Such an obstacle can be formed by an opaque object located in the camera's direct line of sight to the examination zone. This object often blocks part of the examination zone from the camera's field of view. Such an obstacle can also be an auxiliary device located within the examination zone, such as a local RF (Radio Frequency) transmit or receive (T / R) antenna. The body portion of the patient being examined may also create an obstruction. The non-metallic mirror creates an optical path that avoids one or more obstructions between the camera and portions of the examination zone. By providing multiple non-metallic mirrors on the interior walls of the examination zone, more complex avoidance optical paths can be formed. For example, the present invention provides a more frontal view of the patient being examined, even when obstructions are present in the examination zone. According to the present invention, less or no portions of the examination zone are removed from the camera's range due to objects potentially obstructing the camera's direct line of sight to the examination zone. The non-metallic mirror is simple to attach to the interior walls of the examination zone. The non-metallic mirror is inexpensive to manufacture. The attachment of the non-metallic mirror can be easily adapted to various imaging environments and obstruction locations, such as local RF T / R antennas within the examination zone, or the size and location of the patient being examined.An arrangement of a single camera and several non-metallic mirrors is, for example, relatively inexpensive compared to employing several cameras, each of which overlooks a respective part of the inspection zone.

[0010] The non-metallic mirror does not (electromagnetically) interfere with the high-frequency operation of the magnetic resonance examination system. That is, the sensitive RF acquisition of weak magnetic resonance signals is not affected by the non-metallic mirror. Furthermore, the non-metallic mirror does not perturb the magnetic field and high-frequency dynamic transmission field of the magnetic resonance examination system. The non-metallic mirror is formed as a dielectric mirror. Such a dielectric mirror includes a stack of layers with different refractive indices. The layers may be glass layers with different refractive indices between adjacent layers forming a dielectric resonator. These stacked layers cause interference of light reflected from the interfaces of adjacent layers in the stack. In a simple embodiment, the dielectric mirror may be a glass plate, preferably darkly coated on one side. This coated glass plate can be mounted with its uncoated side facing the examination zone. This single-layer glass plate has a reflectivity of around 4-5%, which allows a camera to acquire image information from the examination zone, albeit with low light intensity.

[0011] These and other aspects of the invention will be further elaborated with reference to the embodiments defined in the dependent claims.

[0012] The non-metallic mirror is a dielectric mirror having a macroscopically grated base. The non-metallic mirror can be formed by a stack of dielectric layers deposited on the macroscopically grated base. The macroscopically grated base can have patches that are each at an equal oblique angle relative to the normal to the lateral extension of the base. Such a macroscopic grating structure induces a tilted effective reflection from the layer stack of the non-metallic mirror. This tilt provides an additional degree of freedom for configuring the optical path to and from the non-metallic mirror. The mounting of the dielectric mirror can be configured to facilitate mounting and removal, so that a dielectric mirror with an appropriate tilt can be used for each examination, each with a specific configuration of patient and ancillary equipment to be examined. That is, the dielectric mirror can have a tilt angle that provides an optimal optical path from the examination zone to the camera, with no or at most minimal obstructions. To this end, the mounting can be a simple mechanical sliding mechanism with a clamp for mounting and removing the dielectric mirror.

[0013] It is noted that, for example, the effective reflection caused by the tilt of the patches of the grated base may differ from the reflection with respect to the normal to the lateral extension of the base, resulting in less constraints on the positioning (e.g., orientation) of the mirror. For example, good reflection along the optical path can be achieved while the mirror does not have to protrude too much into the constrained volume of the scanner bore, and may, for example, remain flush with the walls of the examination region or at least extend to a lesser extent.

[0014] In another example of the magnetic resonance examination system of the present invention, the non-metallic mirror may be mounted in an adjustable manner, for example by a hinge or pivot, which allows the orientation of the non-metallic mirror to be changed relative to the inner wall or relative to the main axis of the examination zone. This provides an additional degree of freedom for configuring the optical path from the examination zone through the non-metallic mirror to the camera. This increases the range in which obstacles in the examination zone can be avoided, thus further avoiding parts of the examination zone being blocked from the camera's view.

[0015] Preferably, the monitoring system, comprising a camera and non-metallic mirrors, and optionally one or more light sources, operates within a narrow wavelength range and outside the visible wavelength range. A preferred example is for the system to operate at (infrared (IR)) wavelengths, e.g., wavelengths greater than 800 nm, e.g., approximately 850 nm + / - 20 nm. The multilayer stack can then be configured to be reflective in that narrow wavelength range and have high reflectivity over a wide range of angles of incidence, or at least over a certain range of angles of incidence. This allows the optical path to be configured to achieve good coverage of the camera's examination zone despite obstacles that may be located within the examination zone. This also allows for patient monitoring using IR light while visible light levels are low or dark, which may be comfortable for many patients. For such a setup, a separate IR light source is installed for IR illumination of the examination zone.

[0016] In a further example, in a magnetic resonance imaging system, a light source is configured and arranged to direct its light beam toward the examination zone through a non-metallic mirror. This configuration allows for the illumination of several different areas on a patient using a common light source, which may be positioned next to a camera to illuminate the examination zone using an optical path through a non-metallic mirror. In particular, the optical paths from the light source to the examination zone and from the examination zone to the camera may share one or more non-metallic mirrors. This simplifies the setup of the magnetic resonance imaging system and allows for the location of the light source as well as the camera outside the examination zone, providing a more flexible bore width within the examination zone. In this way, for example, in a cylindrical magnetic resonance imaging system, one end of the bore, i.e., the examination zone, remains freely accessible for staff to position auxiliary devices and connect them to the patient, for example, via electrodes. The free end of the examination zone also reduces claustrophobic effects, allowing for a larger free bore space and less discomfort for the (claustrophobic) patient. However, a larger bore size makes the placement of the main magnetic field coils and gradient magnetic field coils of the magnetic resonance imaging system more expensive.

[0017] In another embodiment of the present invention, the non-metallic mirror is transparent in the visible wavelength range. In the context of this embodiment, transparency means, for example, a reflectance of less than 10% in the visual wavelength range of 400 nm to 800 nm. Such a non-metallic mirror that is transparent in the visual spectrum is not distracting and appears almost unnoticeable to observers, such as the operator and the patient being examined. This visual transparency reduces distractions between the operator and the patient being examined. This may be particularly advantageous to avoid confusing or painful views presented to the patient, and / or to provide a clear (unobstructed) view for the operator into the examination room, and / or to enable additional system components to provide visual stimulation or entertainment to the patient without interference from the observation system.

[0018] As another example, a monitoring system according to an embodiment of the present invention may function to obtain information from a patient, such as the patient's vital signs, and / or the patient's movements, and / or signs of patient distress (or more generally, patient mood detection), and / or photoplethysmography (PPG), and / or video-based speech detection (or, for example, speech recognition of simple words or commands based on facial features). Information regarding patient movements may include, for example, respiratory movements and / or cardiac movements (e.g., indicative of respiratory and / or cardiac cycle phases). For example, information regarding patient movements may be derived from image information of the patient's body hull. The information may be determined by processing (e.g., by an image-based motion detector) and / or by (direct) visual monitoring of the patient via the system by an operator or staff member. Respiratory and / or cardiac phase information may be applied to a reconstructor to correct acquired magnetic resonance signals for motion or to apply motion correction to reconstructed magnetic resonance images. For example, a cardiac trigger signal may be determined based on a video signal from a camera. Cardiac triggering is particularly useful for cardiac MRI for obvious reasons, but may also have more general applications. For example, in neuroimaging, artifacts in head and / or neck scans caused by pulsatile blood flow and / or cerebrospinal fluid flow can be suppressed or reduced by such triggering techniques or other compensation approaches based on cardiac phase signals. This can also be useful for quantitative measurement of blood flow in the carotid arteries. Furthermore, PPG signals can be extracted from video signals by analyzing subtle intensity variations of skin pixels on the subject's face, for example, on the forehead or cheek.

[0019] The invention also relates to a monitoring system for viewing an examination zone of a magnetic resonance examination system by means of a camera, the monitoring system comprising a camera and a non-metallic mirror for placement in the examination zone so as to define an optical path between a portion of the examination zone and the camera via the non-metallic mirror, the non-metallic mirror being a dielectric mirror having a macroscopically grated base.

[0020] These and other aspects of the invention will be elucidated with reference to the embodiments described hereinafter and with reference to the accompanying drawings. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a schematic side view of an example of a magnetic resonance examination apparatus incorporating the present invention; [Figure 2] 10 shows a schematic side elevation view of another example of a magnetic resonance examination system incorporating the present invention. [Figure 3] 10 shows details of an example of a non-metallic mirror incorporated into a monitoring system. DETAILED DESCRIPTION OF THE INVENTION

[0022] FIG. 1 is a schematic side view of an example of a magnetic resonance examination apparatus incorporating the present invention. The magnetic resonance examination system includes a main magnet structure 10 defining an examination zone. A patient 13 to be examined may be positioned within the examination zone on a patient carrier 14, e.g., a patient couch. The main magnet structure includes frame-supported magnet windings to generate a fixed, uniform magnetic field in the examination zone. The examination zone may be a cylindrical volume encompassed by a set of coaxial (superconducting) windings. Acquired magnetic resonance signals are applied to a reconstructor 15, which reconstructs a magnetic resonance image from the magnetic resonance signals. The reconstructed magnetic resonance image is ultimately output 16 for viewing, processing, or storage. Ancillary devices, such as an RF T / R head coil 12, are positioned in the examination zone, particularly to acquire magnetic resonance signals from the head of the patient 13. For example, scans of the brain, skull, and / or neck can typically be performed with the aid of such a head coil, which can completely surround (at least most of) the patient's head and neck, so that direct viewing by a camera is largely obscured.

[0023] The monitoring system 20 serves to obtain information from the examined patient, in particular regarding vital signs and movements. In particular, respiratory and cardiac movements can be derived from imaging information of the patient's body skin. The camera 21 can be mounted close to the entrance of one of the examination zones. For example, the camera may be integrated into a flange of the MR bore and mounted (e.g., in such a way that the usable free bore diameter is not affected or only minimally reduced and / or interference with the operation of the MR system is avoided or minimized).

[0024] A camera control unit 25 is provided for controlling the camera 21, in particular with respect to the focal length of the camera with respect to the direction in which the range of the camera extends within the examination zone. Images of the inside of the examination zone 11 acquired by the camera 21 may be shown on a display 26. In this way, staff or an operator can visually monitor the patient being examined in the examination zone. The image information acquired by the camera 21 may also be applied to a motion detector 27 (which may be implemented, for example, in software) in order to derive physiological information such as the respiratory and / or cardiac cycle phase of the examined patient from the image information acquired by the camera 21. The respiratory and / or cardiac phase information may be applied to a reconstructor 15 in order to motion-correct the acquired magnetic resonance signals and / or to apply motion correction to the reconstructed magnetic resonance images.

[0025] The monitoring system 20 further includes a non-metallic mirror 22 that can be attached to the inner wall 17 of the examination zone (e.g., the inner wall of the magnet bore enclosure). The monitoring system may include a pivot 24 for mounting the non-metallic mirror, and its orientation may be controlled by the adjustable pivot. The non-metallic mirror 22 can be attached directly to the inner wall 17 so that the non-metallic mirror occupies only a small amount of space within the examination zone. The non-metallic mirror generates an (additional) optical path 23 from a portion of the patient to be examined to the camera. Such an additional optical path 23 via the camera can avoid obstacles such as, for example, the RF T / R head coil 12 shown in FIGS. 1 and 2 . Thus, the non-metallic mirror achieves that the portion of the patient to be examined can be monitored even if the direct line of sight 28 of the camera is obstructed, for example, by the RF T / R head coil 12.

[0026] Alternatively (or additionally), the non-metallic mirror may be mounted on or formed as part of a head T / R coil, such as those used in neck, head, and / or neuroradiological MR examinations. It is noted that integrating the mirror into or onto the head coil may avoid costly or complex modifications to existing equipment, such as the scanner bore. For example, a relatively large distance between cameras mounted on the flange of the bore may result in a very limited field of view, showing only the forehead or a portion of the forehead, which may be sufficient for some applications, such as monitoring blood pulsation via slight fluctuations in pixel intensity.

[0027] FIG. 2 is a schematic side view of another example of a magnetic resonance examination system incorporating the present invention. The monitoring system of the magnetic resonance examination system shown in FIG. 2 is similar to that shown in FIG. 1. The monitoring system of FIG. 2 additionally includes an illumination system (part) for illuminating the inspection zone. The illumination system includes a light source 29, e.g., an infrared (IR) light source. For example, the light source can be positioned alongside the camera 21. The light source can be positioned at a distance from the camera, but can also be positioned, for example, approximately nearby. The light source can thus illuminate relevant portions of the inspection zone, for example, directly and / or via the non-metallic mirror 22. In this way, potentially obstructive portions of the inspection zone can be illuminated via the non-metallic mirror. Therefore, the non-metallic mirror can achieve effective illumination of the inspection zone despite the possible presence of obstructing objects within the inspection zone. FIG. 3 shows details of an example of a non-metallic mirror 22 incorporated into the monitoring system. The non-metallic mirror 22 includes a base plate 31 having a macroscopically lattice-shaped base 33 on one side of the base plate 31. The macroscopically grated base 31 has a plurality of patches 34 that are tilted with respect to a normal 35 to the planar extension of the base plate. That is, each patch is at an angle θ to the normal 35 to the planar extension of the base plate. The lateral dimension of each individual patch is substantially larger than the wavelength of the (IR) light from the inspection zone. Therefore, the patches induce an effective tilt in the light generation / reflection angle into the inspection zone. This effective tilt can be determined by the orientation of the individual patches.

Claims

1. a magnetic resonance examination system having an examination zone, the system comprising a monitoring system including a camera outside the examination zone, one or more non-metallic mirrors attached to an interior wall of the examination zone, the one or more non-metallic mirrors defining an optical path within the examination zone between the camera and portions of the examination zone through the one or more non-metallic mirrors, and a light source directing a light beam through the one or more non-metallic mirrors into the examination zone; the one or more non-metallic mirrors are dielectric mirrors having a base; the base has a plurality of patches tilted with respect to a normal to a planar extension of the base such that the orientation of each patch determines an effective tilt for the angle of reflection of light from and / or to the inspection zone; the one or more non-metallic mirrors are reflective to infrared light; an optical path from the light source to the inspection zone and an optical path from the inspection zone to the camera share the one or more non-metallic mirrors; Magnetic resonance imaging system.

2. The monitoring system is configured to obtain information from the patient based on the image output of the camera, the information comprising: Vital signs of the patient; a physical movement of the patient; an indicator of the patient's distress or mood; Respiratory cycle phases; Cardiac cycle phase and The magnetic resonance examination system of claim 1 , comprising at least one of:

3. 3. A magnetic resonance examination system according to claim 1, wherein the optical path avoids auxiliary devices arranged in the examination zone.

4. 4. The magnetic resonance examination system according to claim 1, wherein a dielectric layer is deposited on the base.

5. 5. The magnetic resonance examination system according to claim 1, wherein the patches are each at the same oblique angle relative to a normal to the lateral extension of the base.

6. 6. The magnetic resonance examination system of claim 1, wherein the one or more non-metallic mirrors are adjustably mounted so that their orientation relative to the inner wall can be changed.

7. A magnetic resonance examination system as described in any one of claims 1 to 6, wherein the camera is highly sensitive to infrared rays.

8. A magnetic resonance examination system as described in any one of claims 1 to 7, wherein the one or more non-metallic mirrors are transparent in the visual wavelength range.

9. A monitoring system for observing an examination zone of a magnetic resonance examination system by a camera, comprising: a camera outside the inspection zone; one or more non-metallic mirrors attached to an interior wall of the inspection zone, the one or more non-metallic mirrors for placement within the inspection zone to define an optical path between a portion of the inspection zone and the camera through the one or more non-metallic mirrors; a light source that directs a light beam through the one or more non-metallic mirrors to the inspection zone; and the one or more non-metallic mirrors are dielectric mirrors having a base; the base has a plurality of patches tilted with respect to a normal to a planar extension of the base such that the orientation of each patch determines an effective tilt for the angle of reflection of light from and / or to the inspection zone; the one or more non-metallic mirrors are reflective to infrared light; an optical path from the light source to the inspection zone and an optical path from the inspection zone to the camera share the one or more non-metallic mirrors; Surveillance system.

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