Magnetic resonance imaging phantom device and method of use thereof

Abstract

A phantom device (10) for magnetic resonance imaging (MRI) comprises target structures (22) in the form of tubular channels for optical stimulation during MRI measurements, and a chamber (20) surrounding the target structures (22) and to be filled with MRI contrast medium. The device (10) enables indirect visualisation of target structures (22) that provide no contrast, by providing a target-surrounding contrast agent chamber (20), to separate contrast agent from the target structure (22). The device (10) enables determining an orientation of an eye, by providing a viewable target that itself may not provide MRI signal, such as light passing through channels of the target structures (22).

Description

[0001] Imaging device and method of use thereof

[0002] Field of the Invention

[0003] The present invention relates to magnetic resonance imaging (MRI), specifically to an imaging target or phantom configured to exhibit contrast better distinguishable on MR images for use as a reference structure during MRI imaging. More specifically, the invention relates to an imaging target comprising an arrangement of non-contrast or low- signal areas, and MRI-contrast or high-signal areas, the MRI-contrast areas being arranged to enable location of non-contrast areas.

[0004] Background

[0005] Magnetic resonance imaging (MRI) enables the imaging of organs including the brain and eyes.

[0006] A challenge for MRI studies is that equipment and stimulus devices need to be compatible and safe for use within the magnetic fields of an MRI system. For instance, light stimuli can be provided using fibre-optics light guides while a study participant is being imaged.

[0007] The present invention seeks to provide additional improvements for magnetic resonance imaging targets.

[0008] Summary of the Invention

[0009] In accordance with a first aspect of the invention, there is provided a phantom device as defined in claim 1 , for use with a magnetic resonance imaging device, the device comprising an arrangement of one or more target structures and of one or more reference structures, wherein at least one of the target structures and the reference structures comprises a contrast-agent chamber for containing an MRI contrast agent.

[0010] A target structure, herein, is understood to be a target to be identified during, or as part of, an MRI scan procedure. An appreciation underlying the development of the present invention is that some target structures of interest during an MRI scan may exhibit no, or

[0011] Version 2025-07-18 low, MRI signal. Furthermore, some target structures of interest may be of a size or scale that cannot be spatially resolved, sufficiently, by the available resolution of typical MRI devices.

[0012] The reference structure is, herein, considered a structure to assist with location and / or characterisation of the target structure. Specifically, one of the reference structure and the target structure may be configured to exhibit greater MRI signal, and the other may have less, or no MRI signal.

[0013] The idea underlying the present invention is to form either the reference structure, or the target structure, in the form of a chamber adjacent to, or in a known position relative to, the respective other of the reference structure or target structure. In this manner, the chamber may be filled or provided with contrast medium or contrast agent, such as a liquid. An area free of contrast medium or contrast agent may be considered an agent- free region, which may be a solid structure not filled, in use, with contrast agent, or may be a cavity isolated from a contrast agent chamber. For the purposes of the present disclosure, the expression “agent-free” is used for a region not provided with contrast medium. The chamber may surround the agent-free structure. Vice versa, the agent- free structure may surround a chamber to be filed with contrast agent.

[0014] In other words, the reference structure and the target structure of the phantom may not necessarily be the actual agent-free target structure or reference structure, or the actual signal-generating contrast-agent target or reference. For instance, the agent-free structure may be provided by a passage for light, wherein light stimuli may be used during performance of an MRI measurement, and the signal-providing structure containing contrast agent may be provided by a chamber suitable for holding liquid during performance of an MRI measurement, surrounding the passage for light.

[0015] The MRI contrast agent will be understood to be any suitable substance, typically a liquid, providing MRI contrast, and includes herein contrast media such as saline. A wide range of suitable contrast materials will be known to a skilled person and is not discussed in detail herein. For instance, a widely used MRI contrast agent is Gadolinium, available under the name Dotarem (RTM). Other widely available contrast agents and contrast media include cod liver oil or other suitable oils, or other contrast media such as saline.

[0016] Version 2025-07-18 In some embodiments, at least one contrast-agent chamber provides a reference structure adjacent to at least one target structure.

[0017] In some embodiments, at least one contrast-agent chamber provides a target structure adjacent to at least one reference structure.

[0018] In some embodiments, the contrast-agent chamber at least partially surrounds at least one of the one or more target structures and the one or more target reference structures.

[0019] In some embodiments, at least one of the target structures and reference structures comprises a hollow portion fluid-tightly separated from the contrast-agent chamber.

[0020] A fluid-tight separation may be provided by a circumferentially extending wall, such as a tubular wall structure to provide a hollow portion, e.g. a lumen within the tubular wall, separated from a volume outside the tubular wall. In that manner, fluid provided in the contrast-agent chamber is kept separate from the lumen. As will be appreciated, the void of the lumen may provide no MRI signal, however a passage may be visualised within an MRI data set as a region surrounded by a signal-generating fluid volume.

[0021] In some embodiments, the hollow portion comprises free ends providing one or more passages for light.

[0022] The free end may provide an inlet for light to be shone into the passage. The free end may provide an attachment location or receptacle for a light guide, such as an optical fibre end. The other free end may be formed as a pinhole structure.

[0023] In some embodiments, one or more passages are provided as channels passing through the contrast-agent chamber.

[0024] The channels may be elongate, straight passages. In some embodiments, the channels may be annular and / or comprise annular geometry along at least a portion of their elongate extension. The channels may comprise more complex geometry and / or may comprise along their elongate extension a complex cross-section, such as a polygonal or cruciform cross section, or others. As such, channels may be of even cross-section along their longitudinal extension, for instance cylindrical, or alternatively may have a

[0025] Version 2025-07-18 narrowing cross-section, for instance of conical shaping, or frustoconical shaping, providing a pinhole at one free end.

[0026] The chamber may comprise a lid or other closing mechanism. The chamber may be sealable to contain liquid.

[0027] In some embodiments, the device is comprised of a material that is compatible with an MRI environment.

[0028] In some embodiments, the device is comprised of a non-magnetic material.

[0029] As will be appreciated, the entire body of the device may be of a material that is nonmagnetic, or other material that is sufficiently safe and / or compatible for use with an MRI system.

[0030] In some embodiments, the device comprises a plurality of target structures spaced apart by one or more reference structures.

[0031] In some embodiments, the plurality of target structures comprises a plurality of elongate structures.

[0032] The elongate structures may be provided by straight passages. The elongate passages may be defined by voids of tubular structures, walls of the tubular structures providing a separation structure to keep fluid from the contrast-agent chamber from permeating into the voids, specifically voids intended to remain agent-free. In this manner, the inner volume of the tubular structures can remain free from contrast agent.

[0033] In some embodiments, the elongate structures are angled towards a common focus point.

[0034] The elongate structures, e.g. the light passages, may provide a line-of-sight target. The angle of the elongate structures relatively to each other may be such that the focus point is located at an eye structure of interest, e.g. a retina, lens, or otherwise. To this end, the common focus point may be a predetermined distance, e.g. spaced at least 2 cm, 3 cm, 4 cm, 5 cm, 6 cm, 7 cm, 8 cm, 9 cm, or at least 10 cm from the free ends of the

[0035] Version 2025-07-18 passages. Likewise, the common focus point may be spaced no more than 15 cm, 14 cm, 13 cm, 12 cm, 11 cm, 10 cm, 9 cm, 8 cm, 7 cm, 6 cm, or no more than 5 cm from the free ends of the passages. The distance may be chosen such that the phantom device fits within the scan range of an MRI device, to facilitate depiction of both the phantom device and one or two eyes in one scan data set.

[0036] In some embodiments, the or each contrast-agent chamber is individually fillable and sealable.

[0037] The device may comprise a single contrast-agent chamber within which the target structures are located. Respectively, the contrast-agent chamber may surround each one of the target structures. Alternatively, the device may comprise separate contrastagent chambers. The different chambers may be used with different contrast media during the same MRI scan.

[0038] In some embodiments, surfaces of the contrast-agent chamber comprise hydrophobic surface properties.

[0039] In some embodiments, surfaces of the contrast-agent chamber comprise hydrophilic surface properties.

[0040] The device may be made from sufficiently inert or robust materials to withstand repeated cleaning with typical cleaning agents, disinfectants and / or autoclave conditions that may be experienced by devices used in an MRI setting. In alternative embodiments, the device is provided as a disposable device, e.g. a single-use device, and may be provided in sealed packaging, sealed to maintain the device sterile until use. In that case, the device may be made from a material that is suitable for recycling. For instance, the device may be made from a unitary body of a single type of material, avoiding a need for separation of components prior to recycling.

[0041] In accordance with a second aspect of the present invention, there is provided a mount for use with MRI procedures, the mount comprising one or more devices according to any one of the embodiments of the first aspect.

[0042] Version 2025-07-18 In accordance with a third aspect of the present invention, there is provided a mount for use with MRI procedures, the mount comprising a receptacle structure for anchoring one or more devices according to any one of the embodiments of the first aspect, wherein the one or more devices comprise an anchoring portion shaped for complementary engagement with the receptacle structure.

[0043] The mount will be understood to be configured or shaped to provide a receptacle shaped to receive the phantom device in a manner that maintains target and / or contrast structures viewable by a participant during imaging. In embodiments comprising angled passages with common focus region, the mount will be understood to permit positioning of the phantom device such that the common focus region can intersect with an eye structure of interest.

[0044] In some embodiments of the second and third aspects, the mount is provided by an MRI coil. For instance, an MRI coil may comprise one or more integrally shaped phantom devices and / or one or more integrally shaped anchoring portions for one or more phantom devices.

[0045] As will be appreciated, the MRI coil will typically be a head coil or coil suitable for head measurements.

[0046] Embodiments of the second and third aspect may comprise an adjustment mechanism to allow the position and / or angular orientation of the phantom device to be adjusted. As will be appreciated, the adjustment mechanism may allow the position and / or angular orientation to be adjusted while the phantom device is mounted on the mount or coil, as the case may be.

[0047] In accordance with a fourth aspect of the present invention, there is provided a method of identifying an optical axis from an MRI data set, the method comprising providing an MRI data set comprising an image of an eye and of a phantom device comprising one or more target structures according to any one of the preceding claims, determining the orientation and / or movement of the eye in the MRI data set, determining the position of said one or more target structures in the MRI data set, determining a parameter indicative of the orientation and / or movement of the eye relative to the position of the one or more target structures, and presenting an output indicative of the parameter.

[0048] Version 2025-07-18 As will be appreciated, a target structure in such an embodiment may be constituted by data points with no, or practically no signal, adjacent to or surrounded by reference structures exhibiting signal.

[0049] In some embodiments, the parameter is one of a line of sight, a visual axis, and a fixation axis. The MRI data set may also allow determining biometry of the eye, such as a volume of an anterior section and / or posterior section (region in front of and / or behind the natural lens), length, surface areas, and / or combinations thereof and / or ratios thereof.

[0050] In some embodiments, the method comprises presenting the output as overlay on image data derived from the MRI data set.

[0051] In some embodiments, the method is carried out using a machine learning algorithm.

[0052] In accordance with a further aspect of the invention, there is disclosed a computer program product comprising machine readable instructions that, when loaded into a memory of a computer having a processor, executes the method according to any one of the embodiments of the fourth aspect. The computer program may be provided on a non-transitory storage medium.

[0053] Embodiments of the fourth aspect may be provided in the form of a computer- implemented method.

[0054] Features described in relation to any one or more of the embodiments of the first aspect may be combined with features of any one or more of the further aspects. One or more embodiments of the fourth or further aspects may be implemented in the form of software instructions, which may be incorporated in a device, which may be a device according to any one or more of the embodiments of the second or third aspect. The device may comprise a processor and software instructions implemented by the processor to carry out the functionality of the other aspects.

[0055] Version 2025-07-18 of the Figures

[0056] Exemplary embodiments of the invention will now be described with reference to the Figures, in which:

[0057] Figure 1 is an isometric view of a phantom device;

[0058] Figure 2 is an end view of the Figure 1 phantom device;

[0059] Figure 3 is another end view of the Figure 1 phantom device;

[0060] Figure 4 is a view of a lid component for use with the Figure 1 phantom device;

[0061] Figure 5 is a schematic illustration of an MRI system configured with an embodiment;

[0062] Figure 6 is an illustration of MRI data obtained from the phantom device; and

[0063] Figure 7 shows a sequence of exemplary steps of a data processing method.

[0064] Figures 1 to 3 show a phantom device 10, here in the form of a vessel or cup, comprising a body 12 of generally cylindrical form, the body 12 comprising a peripheral wall 14, here in the shape of a cylindrical mantle, a base 16, here disc shaped, and a distal wall edge 18 defining a free peripheral edge of an open side of the body 12. The generally cylindrical geometry of the body 12 is exemplary and other geometries may be used.

[0065] The body 12 is hollow and comprises a cavity 20 having a free volume defined by the inner base surface 16b and the inner surface 14b of the peripheral wall 14. Within the cavity 20, the body 12 comprises an arrangement of, here, five tubular structures 22 extending from the base 16 to a height defined by the wall edge 18. The five tubular structures are arranged in a cruciform layout comprising one central tubular structure and four peripheral tubular structures that are, here, equally radially-spaced from the central tubular structure and equally circumferentially spaced at a 90° central angle between adjacent peripheral tubular structures. The tubular structures 22 are spaced apart from each other such that the cavity 20 provides a single continuous void, or chamber, surrounding the tubular structures 22. As will be appreciated, the spaced apart tubular structures 22 are provided as one example of a suitable target structure geometry. Different shapes and / or different arrangements, including complex interlinked structures, may be used in other embodiments.

[0066] Version 2025-07-18 Each of the tubular structures 22 comprises a generally cylindrical wall portion defining a hollow lumen providing a passage 24 extending along a passage axis 26 from a first passage end 24a to a second passage end 24b. The first passage ends 24a provide openings in the base 16. The second passage ends 24b are located at free ends of the tubular structures 22 and provide openings on the open side of the body 12. The second passage ends 24b are structurally separated by the walls of the tubular structures 22 from the free volume of the cavity 20.

[0067] The body 12 is made from a material suitable for use with MRI scanners. As such, the body 12 is understood to be from a non-magnetic material. The body may be formed by 3D printing, moulding, or any other suitable manufacturing method. The body 12 may have an outer diameter of around 3 cm, 4 cm, 5 cm, 6 cm, 7 cm, 8 cm, 9 cm, or other suitable diameter to allow it to be depicted in full within an MRI imaging area. The body 12 provides a fluid-tight vessel for a liquid to be supplied, specifically for a liquid providing MRI contrast. For instance, the liquid may be a lipid (oil) or other suitable contrast agent such as commercially available contrast media. In preparation for an MRI scan, contrast material such as a liquid is provided in the cavity 20 or part thereof. In that manner, contrast material is contained in the cavity 20 while remaining separated from the passages 24 defined by the tubular structures 22.

[0068] In the illustrated embodiment, the tubular structures 22 are arranged at an angle relative to each other, such that their passage axes 26 are angled towards a common focus point 30. As will be appreciated, the focus point 30, which may be at a position in a range between 15 cm to 2 cm from the base 16, provides a line of sight through each of the first passage ends 24a, through each of the passages 24, and through the second passage ends 24b. The tubular walls of the tubular structures 22 are, here, of even wall thickness, such that also the tubular outer mantle surfaces of the tubular structures are aligned according to the passage axes 26. The first passage ends 24a may have a relatively small diameter, of no more than 5 mm, 4 mm, 3 mm, 2 mm, or no more than 1 mm, to provide a pinhole aperture. Thereby, the five passage ends 24a provide an arrangement of pinhole apertures.

[0069] Figure 4 illustrates a lid 40 that may be used to close the body 12 of the phantom device 10. The lid 40 comprises a lid body 42 including an arrangement of, here, five openings 44 located corresponding to the second free ends 24b. Although illustrated as openings

[0070] Version 2025-07-18 44, the openings 44 may be designed in the form of sockets or attachment locations for instrumentation, such as optical fibre connectors. Although not necessarily required in all embodiments, the openings 44 may comprise a window transparent to wavelengths used for optical stimuli during an MRI procedure. The lid 40 may be used in registration with the second passage ends 24b to close the cavity 20. To this end, the lid 40 may comprise a seal 46, e.g. a peripheral seal or other suitable sealing mechanism. The lid 40 may be made from the same material as the body 12, and / or a different material.

[0071] Figure 5 illustrates, schematically, a system setup incorporating the phantom device 10. An MRI system 100 comprises a bed 102 for a study participant P. The MRI system 100 is provided with a head coil 90 comprising one or more phantom devices 10. For instance, the head coil 90 may be provided with two phantom devices 10, and / or with a single phantom device comprising two sets of tubular structures, each set comprising a focal point alignment. The operation of an MRI system as such is, herein, considered well known to a skilled person and not described in more detail herein. For the purposes of the present disclosure, the invention provides a novel phantom device for use with an MRI system. The phantom device may be integrated with, or provided for use with, an MRI-compatible mount providing a support structure. Conveniently, the mount is integral with, or provided by, an MRI coil, specifically a head coil or other suitable coil used for eye measurements. However, it will be understood that this is not necessarily a requirement of every embodiment of the invention.

[0072] The phantom device is preferably dimensioned to fit within an MRI scanning area, e.g. to allow it to be positioned sufficiently close to an eye such that a contrast agent chamber is depicted in full in a scanned image. Likewise, individual regions of the phantom device are preferably dimensioned to enable the device to be used in an appropriate distance, or proximity, to the eye, and to allow the phantom device to be used alongside another, like, device for the study of two eyes simultaneously. For instance, the angle of the passages may be chosen such that the focus point 30 is sufficiently close to allow the phantom device 10 to be positioned no more than a few centimetres from an eye to be measured.

[0073] The MRI system 100 is provided with a stimulus generator in the form of a light source 92 operated by a controller, the light source 92 providing stimuli via a light guide 94 such as an array of optical fibres to shine light via the passages 24. The invention is not

[0074] Version 2025-07-18 necessarily limited to use with optical fibres and light stimuli may be provided by several different methods, however the use of optical fibres was found to facilitate use of MRI- compatible materials, while enabling individual illumination of different passages independently of other passages that may or may not be illuminated contemporaneously.

[0075] Figure 6 shows illustrative data from a portion of an MRI scan, reproduced in three- dimensional image form. The image shows an MRI representation of an eye E, whereas it will be appreciated that MRI contrast is generated by liquid bodies of the eye, such as the vitreous body VB, anterior chamber AC, and other structures (not illustrated in Figure 6) that may be visible in section, such as posterior chamber, lens, tarsal plate, optical nerve, and others. The measurement may be carried out such that the entire eye is represented within a data set. The spatial resolution is preferably high enough to allow a lens, typically a natural crystalline lens or a pseudophakic lens, to be depicted. Likewise, the resolution may be chosen sufficiently high to allow a non-contrast target, e.g. the passages 24, to be depicted, here in the form on non-signal linear structures surrounded by signal-generating medium. Conversely, the passages may be dimensioned of sufficient diameter and length for a given MRI setup to ensure they can be depicted in an MRI data set. Such parameters may be selected according to study requirement and some embodiments may use different parameters, resolution and / or imaging regions, as well as phantom geometry. For instance, in some embodiments the invention may be provided in the form of a kit of phantom devices, the kit comprising a set of different phantom devices each comprising one or more target structures of different thicknesses for use with different imaging resolutions.

[0076] The MRI data set comprises phantom data 50, representing a body of fluid MRI contrast agent contained in the phantom device 10 during a scan. It will be appreciated that an MRI scan may have been obtained of a study participant observing the phantom device from underneath, looking upward. In that case, the “top” of the data set is on the righthand side of Figure 6 in its reading orientation.

[0077] The phantom data 50 comprises data points identifying a volume 52, the volume 52 being generally disc shaped and corresponding to a volume taken up by a liquid in the cavity 20. As such, the volume 52 comprises an eye-facing base 58 corresponding to the geometry of the inner base surface 16b, and is intersected by five passages 54 whose diameter and angle corresponds to the mantle outer surfaces of the tubular structure 22.

[0078] Version 2025-07-18 The five passages 54 are, in the direction from the free peripheral edge towards the base 16, angled relatively to each other such that their axes 56 converge on a common focal point. It will be appreciated that the thickness of the disc shaped volume 52 depends on the amount of fluid contained in the phantom device 10 during an MRI scan. For instance, the thickness of the volume 52 and the length of the passages 54 may be greater, and may potentially permit more accurate geometric measurements, when the phantom device 10 is sufficiently large for it to be filled with a larger amount of contrast agent.

[0079] The phantom data 50 may be used in combination with study data or records. For instance, during a study, participants may be asked to indicate on which one of the first passage ends 24a they focused during a measurement. To provide an illustrative scenario, during a study, a participant P may see, lying on their back and looking upward, the in-use underside of the phantom device 10, i.e. the base 16, and an arrangement of one or more of five lights or light spots corresponding to the first passage ends 24a. The participant P may be asked to focus on one of the first passage ends, e.g. on a central light spot, corresponding to the central passage end 24a, and / or may be asked to move the focus in a pattern, such as clockwise along different light spots. Alternatively, or in addition, lights may flash in one or more different sequences, and / or different wavelengths (colours), and / or intensities, to be identified, traced and / or to be confirmed by a participant. Furthermore, a participant may be asked to focus on one passage end 24a, and to confirm whether or not they notice variations of light patterns in one or more other passage ends 24a on which the participant is not focusing. The participant may be asked to keep the eye still, or to focus, for a predetermined period of time or until a signal or command is provided to relax the eye or to focus on another target.

[0080] Such light stimuli are understood to provide no MRI signal or resulting image contrast. To the best of the inventors’ knowledge, it was hitherto not possible to confirm visually within an MRI data set on which one of several stimuli an eye of a study participant was focused. Hitherto, any movement or angular orientation of an eye image could practically not be correlated with the location of a non-contrast target or non-signal target. The provision of phantom data 50 allows non-contrast stimuli, such as light, to be correlated with the position of reference contrast, here in the form of volume of a liquid body surrounding a non-contrast target.

[0081] Version 2025-07-18 As such, the phantom device 10 comprises an arrangement of target structures, here in the form of passages 20 for light, which do not necessarily provide MRI signal, and an arrangement of reference structures, here in the form of a void to be filled with contrast agent, providing MRI signal, wherein the reference structures allow identification and location of the target structures.

[0082] Figure 7 describes steps of a method 60 of using a phantom device. In an optional step 62, the method comprises arranging an MRI scan comprising a setup including one or more phantom devices as described hereinbefore. The step 62 is optional because it may be omitted, for instance, if the method 60 acquires a data set from a different source, e.g. in the form of a training data set or historical data set copied from data storage.

[0083] In step 64, the method acquires an MRI data set comprising data of an eye, and data of a phantom device comprising MRI contrast agent. The data set may comprise data of two eyes. For instance, the data set may comprise data including sections of a head. Step 64 may comprise a step of ensuring the data of each or of at least one eye is of sufficient quality, e.g. by ensuring the entire eye is depicted, and / or that target structures of interest are depicted and / or discernible. In step 66, the location, orientation and / or movement of the, or each, eye is determined. In step 68, the position of one or more target structures in the MRI data set is determined. In step 70, the method analyses the position of the one or more target structures relative to the position, orientation, and / or movement of the, or each, eye. As will be appreciated, steps 66 and 68 may be carried out in a different order and / or simultaneously. Likewise, step 70 may be carried out simultaneously with steps 66 and 68, or steps 66 and 68 may be carried out as a subroutine of step 70. In step 72, an output is provided that is representative of one or more parameters determined in step 70.

[0084] In an optional step 74, the output of step 72 is presented as an overlay on an image calculated from the MRI data set. In an optional step 76, at least one of a line of sight, a visual axis, and a fixation axis is determined for the, or each, eye. Step 76 may be carried out one or more times as part of step 70. In step 78, the method returns to one of the earlier steps, e.g. to step 62, to step 64, and / or to one of the subsequent steps, to repeat the method for different parameters, a different eye, and / or different phantom configurations. To provide an illustrative example, knowledge of the line of sight is believed to enable, or facilitate with greater accuracy, a determination of the location of

[0085] Version 2025-07-18 a macula, and / or the location of the fovea. As will be appreciated, the location of the macula and / or fovea may be determined by extrapolation of target structure geometries, such as the axes 56 of the passages 54, using a plurality of such axes 56 to extrapolate an intersection or focus point. The fovea is a pit in the macula in which vision is usually the sharpest, and the fovea can be taken as being aligned with central axis of the lens (crystalline lens or pseudophakic lens), and so extrapolation of the axis of suitable target structures facilitates location of the fovea or macula.

[0086] Steps 64 to 76, and step 78 where included, may be embodied in a computer program product comprising machine readable instructions that, when loaded into a memory of a computer having a processor, executes the method according to any one of the preceding claims. The computer program may be comprised in an MRI system 100 as described above, and / or may be provided on a separate workstation remote from an MRI system.

[0087] While the exemplary setup refers to emitted light stimuli, this is believed to be one of several practical implementations. For instance, other stimuli, such as images, may be used in other embodiments.

[0088] The exemplary embodiment shows contrast-agent-free targets, here in the form of passages for light, surrounded by reference structures, here in the form of tubular structures separating a void providing a chamber for contrast agent. As will be appreciated, a phantom device could comprise different arrangements of a target and reference structure. For instance, a target could be provided by a void comprising contrast agent, such as a conical cavity providing a point end, surrounding by an annular light guide structure. In that manner, a study participant may be asked to focus on a ‘dark’ area within a light ring. Different designs of target structure may be defined in one phantom, for instance the passage ends 24a may have different shapes such as straight slit structures, undulating slit structures, and multi-arm slit structures and or multi-dot patterns.

[0089] The phantom device may be made from a material that is easy to clean and maintain, e.g. from a material comprising a coating, and / or having hydrophobic properties, or lipophobic properties, so as to facilitate cleaning, and / or from a material sufficiently robust to withstand repeated exposure to cleaning agents and / or sterilization conditions.

[0090] Version 2025-07-18 The phantom device may be integral with a support structure, head coil or other appropriate coil for MRI imaging. The phantom device may be provided as component to be added to an MRI coil, for instance to be attachable to a receptacle location of the MRI coil. In that case, the receptacle location and / or the phantom device may comprise an adjustment mechanism to facilitate position and / or angular alignment while mounted on the MRI coil.

[0091] The exemplary geometry of the phantom device is generally cylindrical, comprising five spaced-apart tubular passages in cruciform arrangement. As will be appreciated, the phantom device may comprise any suitable geometry, such as renal shapes that may be suited for eye studies. The shape, number and arrangement of target structures may differ and may include linear shapes such as slits, crosshair structures, arcuate shapes, and others. An arrangement of target structures distributed across a plane, generally perpendicular to the assumed line of sight, is believed to facilitate measurement of eye orientations in three dimensions.

[0092] Whilst the principle of the invention has been illustrated using exemplary embodiments, it will be understood that the invention is not so limited, and that the invention may be embodied by other variants defined within the scope of the appended claims.

[0093] Version 2025-07-18

Claims

CLAIMS:

1. A phantom device for use with a magnetic resonance imaging device, the device comprising an arrangement of one or more target structures and of one or more reference structures, wherein at least one of the target structures and the reference structures comprises a contrast-agent chamber for containing an MRI contrast agent.

2. The device according to claim 1, wherein at least one contrast-agent chamber provides a reference structure adjacent to at least one target structure.

3. The device according to claim 1 or 2, wherein at least one contrast-agent chamber provides a target structure adjacent to at least one reference structure.

4. The device according to any one of the preceding claims, wherein the contrastagent chamber at least partially surrounds at least one of the one or more target structures and the one or more target reference structures.

5. The device according to any one of the preceding claims, wherein at least one of the target structures and reference structures comprises a hollow portion fluid-tightly separated from the contrast-agent chamber.

6. The device according to claim 5, wherein the hollow portion comprises free ends providing one or more passages for light.

7. The device according to claim 6, wherein the one or more passages are provided as channels passing through the contrast-agent chamber.

8. The device according to any one of the preceding claims, comprised of a material that is compatible with an MRI environment.

9. The device according to any one of the preceding claims, comprised of a nonmagnetic material.

10. The device according to any one of the preceding claims, comprising a plurality of target structures spaced apart by one or more reference structures.Version 2025-07-1811 . The device according to any one of the preceding claims, wherein the plurality of target structures comprises a plurality of elongate structures.

12. The device according to claim 11 , wherein the elongate structures are angled towards a common focus point.

13. The device according to any one of the preceding claims, wherein the or each contrast-agent chamber is individually fillable and sealable.

14. The device according to any one of the preceding claims, wherein surfaces of the contrast-agent chamber comprise hydrophobic surface properties.

15. The device according to any one of claims 1 to 13, wherein surfaces of the contrast-agent chamber comprise hydrophilic surface properties.

16. A mount for use with MRI procedures, the mount comprising one or more devices according to any one of the preceding claims.

17. A mount for use with MRI procedures, the mount comprising a receptacle structure for anchoring one or more devices according to any one of the preceding claims, wherein the one or more devices comprise an anchoring portion shaped for complementary engagement with the receptacle structure.

18. The mount according to claim 16 or 17, constituted by an MRI coil.

19. A method of identifying an optical axis from an MRI data set, the method comprising providing an MRI data set comprising an image of an eye and of a phantom device comprising one or more target structures according to any one of the preceding claims, determining the orientation and / or movement of the eye in the MRI data set, determining the position of said one or more target structures in the MRI data set, determining a parameter indicative of the orientation and / or movement of the eye relative to the position of the one or more target structures, andVersion 2025-07-18presenting an output indicative of the parameter.

20. The method according to claim 19, wherein the parameter is one of a line of sight, a visual axis, and a fixation axis.

21. The method according to claim 19 or 20, comprising presenting the output as overlay on image data derived from the MRI data set.

22. The method according to any one of claim 19 to 21 , carried out using a machine learning algorithm.

23. A computer program product comprising machine readable instructions that when loaded into a memory of a computer having a processor executes the method according to any one of claims 19 to 22.Version 2025-07-18

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