Monitoring system for a magnetic resonance examination system with a video camera and a non-metallic mirror

Abstract

A magnetic resonance examination system has an examination region (11) and comprises a camera (21) and a non-metallic mirror (22), in particular within the examination region (11), through which a light path (23) is arranged between a portion of the examination region (11) and the camera (21). The camera can obtain image information from the portion even if a direct line of sight (28) is blocked. The non-metallic mirror is a dielectric mirror having a macroscopic grid base.

Description

TECHNICAL FIELD

[0001] The invention relates to a monitoring system with a camera for monitoring an examination region of a magnetic resonance examination system. BACKGROUND

[0002] It is known from US patent application US 2017 / 0146619 to have such a monitoring system. The known monitoring system is formed by a camera mounted outside the bore of a magnetic resonance imaging (MRI) device and adjacent to the protective shield of the MRI device. The camera is arranged to image a patient to be examined during operation of the MRI device.

[0003] JP H0928689 discloses a mirror mounted in the bore of an MRI system and a TV camera for taking an image of a subject mirrored on the mirror. A computer analyzes the image and detects motion of the subject. The computer determines whether to discard, acquire again or collect MR data, for example, depending on whether the subject moved out of a limit. Alternatively, MRI parameters can be optimized to eliminate the effects of subject motion.

[0004] JP 2018-042892 discloses an MRI system including a patient table, a screen, a reflection plate, and a frame. The patient table is movable within the bore of the system along a central axis of the bore. The frame on the patient table supports the reflection plate so that a subject placed on the patient table can see an image projected through the reflection plate onto the screen.

[0005] US 2017 / 123020 discloses a medical image diagnosis system including a stand, a table, a reflection plate, and a processing circuit. The reflection plate reflects an image output from an image output device. In a first case where the image is not displayed to an observer through the reflection plate, the processing circuit outputs a first image signal related to a first image to the image output device. In a second case where the image is displayed to the observer through the reflection plate, the processing circuit outputs a second image signal related to a second image to the image output device.

[0006] JP 2004-041411 discloses a method of presenting visual stimuli in an MRI system. A dichroic mirror is used in the optical path of light incident on the eyeball of a subject from a substantially frontal direction to present visual stimuli from a projector and a screen. The eyeball is illuminated by an infrared light, and the motion of the eyeball is monitored by an infrared camera through the dichroic mirror, i.e. using a configuration in which the visual stimuli in the optical wavelength spectrum are reflected by the dichroic mirror while the infrared light for illuminating and monitoring the eye passes through. SUMMARY

[0007] It is an object of the present invention to provide a camera-based monitoring system for a magnetic resonance examination system, which has a more effective range in the examination region of the magnetic resonance examination system.

[0008] According to the invention, this object is achieved by a magnetic resonance examination system having an examination region and comprising:

[0009] a monitoring system having:

[0010] a camera sensitive to infrared radiation and

[0011] at least one non-metallic mirror, in particular located within the examination region, through which the optical path is arranged between a portion of the examination region and the camera. The non-metallic mirror is a dielectric mirror having a macroscopic grating base. The macroscopic grating base comprises a plurality of patches which are tilted with respect to the normal to the planar extension of the base such that the orientation of the individual patches determines an effective tilt with respect to the reflection angle of light from and / or to the examination region.

[0012] The monitoring system of the invention functions to monitor the examination region based on images acquired by the camera, either by a single image frame or by a dynamic image. The camera has a (volume) range or field of view to which the camera is sensitive to acquire image information therefrom. The non-metallic mirror is arranged with respect to the light path between a portion of the examination region and the camera such that the camera can obtain image information from that portion. The non-metallic mirror can be positioned within the examination region, for example by being mounted to an inner wall of the examination region. The non-metallic mirror can also be provided on an auxiliary device within the examination region, for example on a local radio frequency (RF) coil that is positioned on a patient support. It is practical, for example, to mount the non-metallic mirror on the RF head coil. Furthermore, the non-metallic mirror can be provided on a separate frame outside the examination region. It is noted that, if no measures are taken, the problematic portion would be blocked from the range of the camera. Such an obstruction is formed by an opaque object that is located in the direct line of sight of the camera into the examination region. The object blocks a portion of the examination region from the field of view of the camera. Such an obstruction can be an auxiliary device placed in the examination region, for example a local radio frequency (RF) transmit or receive (T / R) antenna. Some parts of the patient body to be examined can also cause an obstruction. The non-metallic mirror creates a light path that bypasses the obstruction or obstructions between the camera and the portion of the examination region. By providing a plurality of non-metallic mirrors on the inner wall of the examination region, a more complex bypass light path can be formed. For example, the invention provides more frontal views of the patient to be examined, even if there is an obstruction in the examination region. According to the invention, less or no portion of the examination region is potentially blocked by an object that potentially obstructs the direct line of sight of the camera to the examination region is excluded from the range of the camera. The non-metallic mirror is easy to mount on the inner wall of the examination region. The non-metallic mirror is inexpensive to manufacture. The mounting of the non-metallic mirror is easy to adapt to various imaging environments and positions of obstructions, for example local RF T / R antennas in the examination region or the size and position of the patient to be examined. The arrangement of a single camera and several non-metallic mirrors is relatively inexpensive, for example compared to the use of multiple cameras, where each camera can view a respective portion of the examination region.

[0013] The non-metallic mirror does not (electromagnetically) interfere with the radio frequency operation of the magnetic resonance examination system. That is, the sensitive RF acquisition of the weak magnetic resonance signals is not affected by the non-metallic mirror. Further, the non-metallic mirror does not interfere with the magnetic field and the radio frequency dynamic transmission field of the magnetic resonance examination system. The non-metallic mirror is formed as a dielectric mirror. Such a dielectric mirror comprises a stack of layers with different refractive indices. These layers can be glass layers with different refractive indices between adjacent layers forming a dielectric resonator. These stacked layers lead to an interference of light reflected from the interfaces of adjacent layers in the stack. In a simple implementation, the dielectric mirror can be a glass plate, preferably coated on one side with a dark coating. Such a coated glass plate can be mounted with the uncoated side directed towards the examination region. The reflectivity of such a single layer glass plate is about 4-5%, which also allows the camera to acquire image information from the examination region even at low light intensities.

[0014] These and other aspects of the application will be further elucidated with reference to the embodiments defined in the dependent claims.

[0015] The non-metallic mirror is a dielectric mirror with a macroscopic grating base. The non-metallic mirror can be formed from a stack of dielectric layers deposited on the macroscopic grating base. The macroscopic grating base can have a plurality of patches, each patch being at an equal oblique angle to the normal of the lateral extension of the base. This macroscopic grating structure induces an oblique effective reflection from the layered stack of the non-metallic mirror. This oblique provides additional degrees of freedom for configuring the optical path to and from the non-metallic mirror. The mounting of the dielectric mirror can be arranged to be easy to mount and remove, so that a dielectric mirror with the appropriate obliquity can be used for each examination, each examination having a specific configuration of patient and auxiliary equipment to be examined. That is, a dielectric mirror with an oblique angle can be selected that provides the best optical path from the examination region to the camera, and without or with very few obstacles. To this end, the mounting can be a simple mechanical sliding mechanism with a clamp to attach / detach the dielectric mirror.

[0016] It is noted that the effective reflection, e.g. induced by the oblique of the patches of the grating base, can be different from the reflection with respect to the normal of the lateral extension of the base, so that the positioning (e.g. orientation) of the mirror is less limited. For example, a good reflection along the optical path can be achieved, while the mirror does not need to protrude excessively into the confined space of the scanner bore, e.g. can remain flush with the wall of the examination region, or at least extends from the wall of the examination region to a smaller extent.

[0017] In another example of the magnetic resonance examination system of the application, the non-metallic mirror can be mounted in an adjustable manner, for example by a hinge or a pivot. This enables to change the orientation of the non-metallic mirror with respect to the inner wall or with respect to the main axis of the examination region. This provides an additional degree of freedom for configuring the optical path from the examination region through the non-metallic mirror to the camera. This enlarges the range to bypass obstacles in the examination region and thus further avoids that parts of the examination region are obscured out of the view of the camera.

[0018] Preferably, the monitoring system consisting of the camera and the non-metallic mirror and optionally one or more light sources is operated in a narrow wavelength range and outside the visible wavelength range. A preferred example is to operate the system at (infrared (IR)) wavelengths, for example greater than 800 nm, for example with a wavelength of about 850 nm + / - 20 nm. The multi-layer stack can be configured to be reflective in this narrow wavelength range and to have a high reflectivity for a wide range of incidence angles or at least for a range of incidence angles. This enables to configure the optical path to achieve a good coverage of the examination region of the camera, despite possible obstacles in the examination region. This also enables to monitor the patient using IR light in case of low or dark visible light levels, which seems to be comfortable for many patients. For such a setup, a separate IR light source is installed for IR illumination of the examination region.

[0019] In another example of the magnetic resonance examination system, the light source is configured and positioned for directing its light beam into the examination region through the non-metallic mirror. This configuration allows to illuminate several different regions on the patient with one common light source. This light source can be located next to the camera to illuminate the examination region through the non-metallic mirror using the optical path. In particular, the optical path from the light source to the examination region and from the examination region to the camera can have one or more common non-metallic mirrors. This enables to position the light source as well as the camera outside the examination region, which simplifies the configuration of the magnetic resonance examination system and provides a larger free bore width within the examination region. In this way, for example in a cylindrical magnetic resonance examination system, one end of the bore, i.e. the examination region, is freely accessible for a staff member to position auxiliary equipment, to connect the auxiliary equipment (for example by electrodes) to the patient. The free end of the examination region also reduces the impact of claustrophobia. The wider the free bore space, the less discomfort a (claustrophobic) patient experiences, while a wider bore results in a more expensive arrangement of the main magnetic field coils and the gradient magnetic field coils of the magnetic resonance examination system.

[0020] In another example of the present invention, the non-metallic mirror is transparent in the visible wavelength range. In the framework of this example of the present invention, transparent means for example a reflectivity of less than 10% in the visible wavelength range of 400 nm to 800 nm. Such a non-metallic mirror transparent in the visible spectrum appears unobtrusive and almost invisible to an observer, such as an operator and a patient to be examined. This visual transparency reduces the disturbance for the operator and the patient to be examined. This can be particularly advantageous to avoid confusing or distressing scenarios presented to the patient and / or to provide a clear (unobstructed) view for the operator entering the examination room and / or to allow additional system components to provide visual stimulation or entertainment for the patient without obstructing the observation system.

[0021] As another example, the monitoring system according to embodiments of the present invention can be used to obtain information of the patient, such as vital signs of the patient and / or motion of the patient and / or signs of distress of the patient (or more generally, patient emotion detection) and / or photoplethysmography (PPG) and / or video-based speech detection (or speech recognition, e.g. recognition of simple words or instructions based on facial features). Information about the motion of the patient can include for example respiratory motion and / or cardiac motion, e.g. indicating the respiratory phase and / or the cardiac cycle phase. For example, information about the motion of the patient can be obtained from image information of the patient's body enclosure. These information can 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. Respiratory and / or cardiac phase information can be applied to the reconstructor to either motion- gated magnetic resonance signals or to apply motion correction to the reconstructed magnetic resonance images. For example, a cardiac trigger signal can be determined based on a video signal from a video camera. Cardiac triggering is particularly useful for cardiac MRI for obvious reasons, but can 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 can be suppressed or reduced by such triggering techniques or other compensation methods based on the cardiac phase signal. This can also be used for quantitative measurement of blood flow in the carotid artery. Furthermore, a PPG signal can be extracted from a video signal by analyzing subtle intensity changes of skin pixels, such as on the subject's face, e.g. at the forehead or the cheeks.

[0022] The present invention also relates to a monitoring system for observing an examination region of a magnetic resonance examination system by a video camera. The monitoring system of the present invention comprises:

[0023] a video camera, and

[0024] A non-metallic mirror for placement in an examination region to arrange an optical path between a portion of the examination region and a camera through the non-metallic mirror. The non-metallic mirror is a dielectric mirror having a macroscopic grating base. The macroscopic grating base comprises a plurality of patches that are tilted with respect to a normal of a planar extension of the base such that the orientation of an individual patch determines an effective tilt with respect to a reflection angle of light from and / or to the examination region.

[0025] These and other aspects of the application will be apparent from and elucidated with reference to the embodiments described hereinafter and with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 A schematic side view is shown of an example of a magnetic resonance examination system incorporating the application;

[0027] Figure 2 A schematic side view is shown of another example of a magnetic resonance examination system incorporating the application, and

[0028] Figure 3 Details are shown of an example of a non-metallic mirror incorporated in a monitoring system. DETAILED DESCRIPTION

[0029] Figure 1 A schematic side view is shown of an example of a magnetic resonance examination system incorporating the application. The magnetic resonance examination system comprises a main magnet structure 10 defining an examination region. A patient 13 to be examined can be positioned on a patient support 14, such as a patient couch, and enter the examination region. The main magnet structure comprises a frame holding magnet windings to produce a static, uniform magnetic field in the examination region. The examination region can be a cylindrical space enclosed by a set of coaxial (superconducting) windings. Acquired magnetic resonance signals are applied to a reconstructor 15 that reconstructs magnetic resonance images from the magnetic resonance signals. The reconstructed magnetic resonance images are eventually output 16 for viewing, processing or storage. Ancillary equipment such as an RF T / R head coil 12 is placed in the examination region, especially to acquire magnetic resonance signals from the head of the patient 13. For example, brain, cranial and / or cervical scans can typically be performed with the aid of such a head coil, which can (at least to a large extent) completely enclose the head and neck of the patient such that direct observation by a camera is largely obstructed.

[0030] The monitoring system 20 is used to obtain information from the patient to be examined, in particular information about vital signs and motion. It is noted that respiratory motion and cardiac motion can be derived from image information of the patient's body shell. The camera 21 can be mounted at a position close to one entrance of the examination region. For example, the camera can be integrated in or mounted on a flange of the MR bore (e.g. such that the available free bore diameter is not affected or only minimally reduced, and / or to avoid or minimize interference with the MR system operation).

[0031] A camera controller 25 is provided to control the camera 21, in particular with respect to the direction in which the camera's range extends into the examination region and the focal length of the camera. The images of the interior of the examination region 11 acquired by the camera 21 can be displayed on a display 26. In this way, a staff member or operator can visually monitor the patient to be examined which is in the examination region. The image information acquired by the camera 21 can also be applied to a motion detector 27 (which can be implemented in software, for example) to derive physiological information from the image information acquired by the camera 21 as respiratory and / or cardiac cycle phase of the patient to be examined. The respiratory and / or cardiac phase information can be applied to the reconstructor 15 to correct the acquired magnetic resonance signals for motion and / or to impose motion correction on the reconstructed magnetic resonance images.

[0032] The monitoring system 20 further comprises a non-metallic mirror 22 which can be mounted to an inner wall 17 of the examination region, e.g. to an inner wall of the magnet bore shell. The monitoring system can comprise a pivot 24 for mounting the non-metallic mirror such that the orientation of the non-metallic mirror can be controlled by the adjustable pivot. The non-metallic mirror 22 can be mounted directly to the inner wall 17 such that the non-metallic mirror only occupies a small space within the examination region. The non-metallic mirror creates an (additional) optical path 23 from a portion of the patient to be examined to the camera. This additional optical path 23 through the camera can bypass obstacles such as Figure 1 and Figure 2 the RF T / R head coil 12 shown as an example in Fig. 1. Thus, the non-metallic mirror enables that multiple portions of the patient to be examined can be monitored, even if the direct line of sight 28 of the camera is blocked by, for example, the RF T / R head coil 12.

[0033] Alternatively (or additionally), the non-metallic mirror can be mounted on or formed as part of a head T / R coil, e.g. for a neck, cranial and / or neuro-radiological MR examination. It is noted that integrating the mirror in or on a head coil can avoid expensive or complex modifications to existing equipment, e.g. the bore of a scanner. Although the relatively large distance between the camera, e.g. mounted on the flange of the bore, can result in a very limited field of view, e.g. showing only the forehead or a part thereof, this can be sufficient for certain applications to monitor blood pulsation, e.g. by slight changes in pixel intensity.

[0034] Figure 2 A schematic side view is shown of another example of a magnetic resonance examination system incorporating the application. Figure 2 The monitoring system of the shown magnetic resonance examination system is similar to Figure 1 the monitoring system of the shown magnetic resonance examination system. Figure 2 The monitoring system of the shown magnetic resonance examination system is similar to

[0035] Figure 3 Details of an example of a non-metallic mirror 22 incorporated in the monitoring system are shown. The non-metallic mirror 22 comprises a substrate 31 and has a macroscopic grating base 33 on one side of the substrate 31. The macroscopic grating base 31 has a plurality of patches 34 which are tilted with respect to the normal 35 of the planar extension of the substrate. That is, each patch is angled θ g with respect to the normal 35 of the planar extension of the substrate. The lateral dimension of a single patch is much larger than the wavelength of the (IR) light from the examination region. Hence, the patches induce an effective tilt of the angle of reflection with respect to the light from / to the examination region. This effective tilt can be determined by the orientation of a single patch.

Claims

1. A magnetic resonance imaging (MRI) system having an inspection area (11), the MRI system comprising a monitoring system including a camera (21) positioned outside the inspection area and a non-metallic reflector (22) mounted on an inner wall of the inspection area, wherein an optical path (23) is arranged between a portion of the inspection area and the camera via the non-metallic reflector located within the inspection area. Its features are: The non-metallic reflector is a dielectric reflector with a macro-grid substrate (33). The macro-grid substrate includes a plurality of patches (34) that are tilted relative to the normal (35) of the planar extension of the substrate, such that the orientation of a single patch determines an effective tilt relative to the angle of reflection of light from and / or arriving at the inspection area. The magnetic resonance imaging system also includes a light source (29) positioned outside the examination area, for guiding a light beam into the examination area via the non-metallic reflector (22); The non-metallic reflector is reflective of infrared radiation; and The optical path from the light source to the inspection area and the optical path from the inspection area to the camera both share the non-metallic reflector.

2. The magnetic resonance imaging system according to claim 1, wherein, The monitoring system is adapted to obtain information from the patient based on the image output of the camera (21), wherein the information includes at least one of the following: The patient's vital signs. The patient's body movements, The patient's expression of pain or emotion, Respiratory cycle phase, and Cardiac cycle phase.

3. The magnetic resonance imaging system according to claim 1 or 2, wherein, The optical path (23) bypasses the auxiliary equipment placed in the inspection area.

4. The magnetic resonance imaging system according to claim 1 or 2, wherein, A stack of dielectric layers is deposited on the macro-grid substrate, resulting in effective reflection of the tilted surface from the layered stack.

5. The magnetic resonance imaging system according to claim 1 or 2, wherein, Each of the patches (34) forms an equal angle of inclination relative to the normal (35) of the lateral extension of the substrate.

6. The magnetic resonance imaging system according to claim 1 or 2, wherein, The non-metallic reflector (22) is adjustablely mounted so that its orientation relative to the inner wall of the inspection area can be changed.

7. The magnetic resonance imaging system according to claim 1 or 2, wherein, The monitoring system includes multiple non-metallic reflectors.

8. The magnetic resonance imaging system according to claim 1 or 2, wherein, The camera is sensitive to infrared radiation.

9. The magnetic resonance imaging system according to claim 1 or 2, wherein, The non-metallic mirror (22) is transparent in the visible wavelength range.

10. A monitoring system for observing the examination area of ​​a magnetic resonance imaging (MRI) system via a camera, the monitoring system comprising: Camera (21), which is positioned outside the inspection area, A non-metallic reflector (22) is used to mount on the inner wall of the inspection area so as to arrange an optical path between a portion of the inspection area and the camera via the non-metallic reflector located within the inspection area. A light source (29), positioned outside the inspection area, is used to guide a light beam into the inspection area via the non-metallic reflector (22). The non-metallic reflector is a dielectric reflector with a macro-grid substrate (33). The macro grid substrate includes a plurality of patches (34) that are tilted relative to the normal (35) of the planar extension of the substrate, such that the orientation of a single patch determines an effective tilt relative to the angle of reflection of light from and / or arriving at the inspection area. The non-metallic reflector is reflective of infrared radiation; and The optical path from the light source to the inspection area and the optical path from the inspection area to the camera both share the non-metallic reflector.

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