WO2013006057A1 - Imaging system displaying an image in a mri scanner - Google Patents

Imaging system displaying an image in a mri scanner Download PDF

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Publication number
WO2013006057A1
WO2013006057A1 PCT/NL2012/050480 NL2012050480W WO2013006057A1 WO 2013006057 A1 WO2013006057 A1 WO 2013006057A1 NL 2012050480 W NL2012050480 W NL 2012050480W WO 2013006057 A1 WO2013006057 A1 WO 2013006057A1
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WO
WIPO (PCT)
Prior art keywords
calibration
imaging system
screen
eye
objects
Prior art date
Application number
PCT/NL2012/050480
Other languages
French (fr)
Inventor
Albert Victor VAN DEN BERG
Original Assignee
Stichting Katholieke Universiteit
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Stichting Katholieke Universiteit filed Critical Stichting Katholieke Universiteit
Publication of WO2013006057A1 publication Critical patent/WO2013006057A1/en

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Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
    • A61B3/02—Subjective types, i.e. testing apparatus requiring the active assistance of the patient
    • A61B3/024—Subjective types, i.e. testing apparatus requiring the active assistance of the patient for determining the visual field, e.g. perimeter types
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
    • A61B3/02—Subjective types, i.e. testing apparatus requiring the active assistance of the patient
    • A61B3/028—Subjective types, i.e. testing apparatus requiring the active assistance of the patient for testing visual acuity; for determination of refraction, e.g. phoropters
    • A61B3/032—Devices for presenting test symbols or characters, e.g. test chart projectors
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
    • A61B3/10—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions
    • A61B3/113—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for determining or recording eye movement
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
    • A61B3/0016—Operational features thereof
    • A61B3/0033—Operational features thereof characterised by user input arrangements
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves  involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging

Definitions

  • the invention relates to an imaging system for displaying an image in a MRI scanner.
  • the imaging system comprises a projector for projecting the image, a screen for displaying the image, a supporting device constructed and arranged to hold the screen - in use - in a display position in the proximity of an eye of a person positioned in the MRI scanner.
  • Such an imaging system is often referred to as wide field visual projection for a MRI scanner.
  • the screen in general displays the image at a distance of around and between 3 - 6 cm from the eye of the person laying in the MRI scanner. By displaying the image in the proximity of the eye, a large visual field for the eye is created. Said visual field in general extends up to 120 degrees in width and 90 degrees in height.
  • Such a wide visual field in an MRI scanner is advantageous to diagnose problems of the visual system of a person.
  • a testing method named visual perimetry is often used.
  • the person keeps the gaze of the eye fixed while images are presented at various places in the visual field. This way the images are projected at different locations on the retina of the eye.
  • the projections on the retina result in an activity in the visual parts of the brain.
  • the MRI scanner is able to detect said activities in the brain. This allows the detection of defects in the visual system of a person. Such defects may for example be caused by brain damage as a result of a stroke.
  • a imaging system which comprises a projector for projecting the image, a screen for displaying the image, a supporting device constructed and arranged to hold the screen - in use - in a display position in the proximity of an eye of a person positioned in the MRI scanner, a calibration device constructed and arranged to - in use - establish the rotation centre of the eye and comprising at least two calibration objects located at a distance from the screen, wherein the imaging system is constructed and arranged to project at least two corresponding calibration objects on the screen and to allow the person to align a first calibration object with a first corresponding calibration object in a first view direction of the eye and to align a second calibration object with a second corresponding calibration object in a different second view direction of the eye.
  • the rotation centre of the eye can be determined on basis of the position of the aligned calibration objects and the corresponding calibration. Knowing the position of the rotation centre of the eye allows an accurate projection on the retina of the image displayed on the screen. This makes an accurate testing of the visual system of a person possible.
  • the calibration device comprises a third calibration object located at a distance from the screen, the imaging system is constructed and arranged to project a third corresponding calibration object on the screen and to allow the person to align the third calibration object with the third corresponding calibration object in a different third view direction of the eye.
  • the imaging system may be constructed and arranged to allow the person to move the corresponding calibration objects projected on the screen.
  • the calibration device may be constructed and arranged to keep the calibration objects in a fixed position relative to the screen.
  • the supporting device may be constructed and arranged to keep the screen in a fixed position relative to the eye of the person.
  • the calibration device may comprise a measuring unit constructed and arranged to measure the position of the calibration objects and corresponding calibration objects and a calculating unit constructed and arranged to communicate with the measuring unit and to calculate the rotation centre of the eye while using the measured positions of the aligned calibration objects and corresponding calibration objects.
  • the imaging system is constructed and arranged to allow the person to move the calibration objects and the screen relative to each other.
  • the calibration device is constructed and arranged to move the calibration objects relative to the screen.
  • the imaging system is constructed and arranged to keep the projected corresponding calibration objects in a fixed position relative to the eye of the person.
  • the supporting device is constructed and arranged to move the screen relative to the calibration objects.
  • the imaging system is constructed and arranged to keep the calibration objects in a fixed position relative to the eye of the person.
  • corresponding calibration objects comprise lines.
  • corresponding calibration objects each comprise at least three lines.
  • At least one of said at least three lines extends transverse to the other lines.
  • corresponding calibration objects each comprise at least two lines extending substantially parallel to each other.
  • corresponding calibration objects each comprise at least two lines extending traverse to each other.
  • corresponding calibration objects comprise lines extending substantially vertical when seen by the person.
  • corresponding calibration objects comprise lines extending substantially horizontal when seen by the person.
  • corresponding calibration object substantially have the same orientation.
  • the calibration objects and/or the corresponding calibration objects comprise dots.
  • the calibration objects comprise dots and the corresponding calibration objects comprise calibration rings.
  • the calibration objects comprise calibration rings and the corresponding calibration objects comprise dots.
  • the corresponding calibration objects are positioned behind the screen in the view direction of the person.
  • the screen is constructed and arranged to allow the person to observe the corresponding calibration objects through the screen.
  • the screen is translucent to allow the person to observe the corresponding calibration objects.
  • the screen comprises openings allowing the person to observe the corresponding calibration objects.
  • the corresponding calibration objects are positioned in front of the screen in the view direction of the person.
  • the distance D2 between the calibration objects and the screen is around and between 5 and 30 mm. In an embodiment of the imaging system, the distance D2 between the calibration objects and the screen is around and between 10 and 15 mm.
  • the calibration device comprises a calibration screen constructed and arranged to replace the screen and to perform the tasks of the screen.
  • the calibration screen is positioned in the display position when the calibration device is held by the supporting device and the at least two calibration objects are located at a distance from the calibration screen.
  • the screen, supporting device, and calibration device are formed from materials suitable for use in a MRI scanner.
  • the invention further relates to a calibration device for calibrating an imaging system for displaying an image in a MRI scanner, which imaging system comprises a projector for projecting the image, a screen for displaying the image, a supporting device constructed and arranged to hold the screen - in use - in a display position in the proximity of an eye of a person positioned in the MRI scanner, wherein the imaging system is constructed and arranged to project at least two corresponding calibration objects on the screen, and wherein the calibration device comprises at least two calibration objects - in use - located at a distance from the screen and is constructed and arranged to establish the rotation centre of the eye by aligning a first calibration object with a first corresponding calibration object in a first view direction of the eye and a second calibration object with a second corresponding calibration object in a different second view direction of the eye.
  • the calibration device comprises a third calibration object located at a distance from the screen and is constructed and arranged to establish the rotation centre of the eye by aligning the third calibration object with the third corresponding calibration object in a different third view direction of the eye.
  • the calibration device comprises a measuring unit constructed and arranged to measure the position of the calibration objects and corresponding calibration objects and a calculating unit constructed and arranged to communicate with the measuring unit and to calculate the rotation centre of the eye while using the measured positions of the aligned calibration objects and corresponding calibration objects.
  • the invention further relates to a calibration device as defined in the accompanying claims.
  • the invention further relates to a method for calibrating an imaging system according to the invention, wherein the method comprises the steps of projecting at least two corresponding calibration objects on the screen, establishing the rotation centre of the eye by aligning a first calibration object with a first corresponding calibration object in a first view direction of the eye and a second calibration object with a second corresponding calibration object in a different second view direction of the eye.
  • the invention further relates to a method for calibrating an imaging system according to the invention, wherein the method comprises the steps of projecting three corresponding calibration objects on the screen, establishing the rotation centre of the eye by aligning a first calibration object with a first corresponding calibration object in a first view direction of the eye, a second calibration object with a second corresponding calibration object in a different second view direction of the eye, and a third calibration object with a third corresponding calibration object in a different third view direction of the eye.
  • the invention further relates to a method for calibrating an imaging system for displaying an image in a MRI scanner, which imaging system comprises a projector for projecting the image, a screen for displaying the image, a supporting device constructed and arranged to hold - in use - the screen in a display position in the proximity of an eye of a person positioned in the MRI scanner, a calibration device constructed and arranged to position at least two calibration objects at a distance from the screen, wherein
  • the method comprises the steps of projecting at least two corresponding calibration objects on the screen, and establishing the rotation centre of the eye by aligning a first calibration object with a first corresponding calibration object in a first view direction of the eye and a second calibration object with a second corresponding calibration object in a different second view direction.
  • the calibration device comprises a third calibration object located at a distance from the screen
  • the imaging system is constructed and arranged to project a third corresponding calibration object on the screen and the method comprises aligning the third calibration object with the third corresponding calibration object in a different third view direction of the eye.
  • the method may comprise moving the corresponding calibration objects projected on the screen.
  • the method may comprise moving the calibration objects and the screen relative to each other.
  • the method may comprise measuring the position of the aligned calibration objects and corresponding calibration objects and calculating the rotation centre of the eye while using the measured positions of the aligned calibration objects and corresponding calibration objects.
  • the invention further relates to a calibration device for calibrating a imaging system for displaying an image in a MRI scanner, which imaging system comprises a projector for projecting the image, a screen for displaying the image, a supporting device constructed and arranged to hold the screen - in use - in a display position in the proximity of an eye of a person positioned in the MRI scanner, wherein the imaging system is constructed and arranged to project at least two corresponding calibration objects on the screen and to allow the person to move the corresponding calibration objects, and wherein the calibration device is constructed and arranged to establish the rotation centre of the eye and comprises at least two calibration objects - in use - located at a distance from the screen.
  • the invention further relates to a calibration device for calibrating an imaging system for displaying an image in a MRI scanner, which imaging system comprises a projector for projecting the image, a screen for displaying the image, a supporting device constructed and arranged to hold the screen - in use - in a display position in the proximity of an eye of a person positioned in the MRI scanner, wherein the imaging system is constructed and arranged to project at least two corresponding calibration objects on the screen, and wherein the calibration device comprising at least two calibration objects - in use - located at a distance from the screen and is constructed and arranged to establish the rotation centre of the eye by moving the calibration objects and the screen relative to each other.
  • the invention further relates to an use of an imaging system according to the invention.
  • the invention further relates to an use of a calibration device according to the invention.
  • Fig. 1 schematically shows an embodiment of the imaging system according to the invention
  • Fig. 2 schematically shows an enlarged view of part of the imaging system of fig. 1 comprising a screen
  • Fig. 3A-C schematically show the screen of fig. 2,
  • Fig. 4 schematically shows an enlarged view of part of the imaging system of fig. 1 comprising a first embodiment of the calibration device
  • Fig. 5A-C schematically show the calibration device of fig. 4,
  • Fig. 6 schematically shows an enlarged view of part of the imaging system of fig. 1 comprising a second embodiment of the calibration device
  • Fig. 7A-C schematically show the calibration device of fig. 6,
  • Fig. 8A-C schematically shows a calculation of the rotation centre in the situation of the fig. 5.
  • FIG 1 shows an embodiment of the imaging system 1 according to the invention.
  • the imaging system 1 for displaying an image in a MRI scanner 3 comprises a projector 4 for projecting the image, a screen 5 for displaying the image, a supporting device 6 constructed and arranged to hold the screen 5 - in use - in a display position 7 in the proximity of an eye 8 of a person 9 positioned in the MRI scanner 3.
  • Figure 1 shows a cross sectional view of the coil 24 of a MRI scanner 3.
  • the person 9 is positioned in the coil opening 25 of the coil 24.
  • the person 9 is positioned on a platform 27 which can move the person 9 in and out the coil opening 25.
  • the imaging system 1 further comprises a calibration device 10 constructed and arranged to - in use - establish the rotation centre 14 of the eye 8.
  • the calibration device 10 comprises at least two calibration objects 1 1 located at a distance D2 from the screen 5.
  • the imaging system 1 is constructed and arranged to project at least two corresponding calibration objects 12 on the screen 5 and to allow the person to align a first calibration object 1 1A with a first corresponding calibration object 12A in a first view direction 13A of the eye 8 and to align a second calibration object 11 B with a second corresponding calibration object 11 B in a different second view direction 13B of the eye 8.
  • the calibration device 10 comprises a measuring unit 22 constructed and arranged to measure the position of the calibration objects 1 1 and corresponding calibration objects 12 and a calculating unit 23 constructed and arranged to communicate with the measuring unit 22 and to calculate the rotation centre 14 of the eye 8 while using the measured positions of the aligned calibration objects 11 and corresponding calibration objects 12.
  • the measuring unit 22 is connected to the calculating unit 23 via a communication connection 32, such as a data line, a wireless connection, or the like.
  • the measuring unit 22 may comprise any electronic measuring device, optical measuring device or acoustical measuring device suitable for determining the location of the calibration objects 11 and corresponding calibration objects 12
  • the calculating unit 23 may comprise a computer or the like which is coupled to the measuring unit 22.
  • the imaging system comprises a control unit 34 constructed and arranged to move the corresponding calibration objects 12 projected on the screen 5 (or calibration screen 21 ).
  • the control unit 34 is connected to and communicates with the projector 4 via a control connection 33.
  • the control unit 34 is manually controlled by the person 9, but may also be controlled by another person or system based on input from the person, for example by spoken instructions of the person 9.
  • Figure 2 shows an enlarged view of part of the imaging system 1 according the invention.
  • the supporting device 6 holds a screen 5 in the display position 7.
  • the distance D1 between the eye 8 and the screen 5 is around and between 30 - 60 mm.
  • the projection of the projector 4 is reflected by a mirror 26 onto the screen. More specifically, the distance D1 relates to the distance between the image projected on the screen 5 and the eye 8.
  • the situation shown is used to provide a wide visual field to the eye 8 of the person 9.
  • the supporting device 6 is supported by the platform 27.
  • the supporting device 6 comprises an adjusting unit 29 to adjust the distance between the platform 27 and the part of supporting device 6 holding the screen 5.
  • the screen 5 may be formed by a hard material with a plate like form.
  • the screen 5 may be formed by a flexible material with a sheet like form.
  • the figures 3A-C show a front view, side view (in the direction of arrow IV-B) and top view (in the direction of arrow IV-C) of the screen 5 of fig. 2, respectively.
  • C the eye 8 of the person 9 is shown and the screen 5 is positioned in the display position 7 at distance D1.
  • fig. 3B is the width of the visual field of alpha degrees indicated, which is around and between 100 - 160 degrees.
  • In fig. 3C is the height of the visual field of beta degrees indicated, which is around and between 70 - 100 degrees.
  • FIG. 4 shows an enlarged view of part of the imaging system according the invention.
  • the supporting device 6 holds a first embodiment of the calibration device 10 according the invention.
  • the calibration device 10 comprises calibration screen 21 located in the display position 7 at a distance D1 of the eye 8.
  • the calibration device 10 comprises calibration objects 11 located at a distance from the calibration screen 21.
  • the figures 5A-C show a front view, side view (in the direction of arrow V-B) and top view (in the direction of arrow V-C) of the calibration device 10 of fig. 4, respectively.
  • the calibration device 10 comprising five calibration objects 1 1 A-E located at a distance D2 from the calibration screen 21. Five corresponding calibration objects 12A-E are projected on the calibration screen 21.
  • C the eye 8 of the person 9 is shown and the calibration screen 21 is positioned in the display position 7 at distance D1.
  • the person 9 is able to move the corresponding calibration objects 12A-E over the calibration screen 21.
  • the horizontal line of the first calibration object 1 1 A with the horizontal line of the first corresponding calibration object 12A in a first view direction 13A of the eye 8 (see fig. 5B)
  • one establishes that the rotation centre 14 of the eye 8 is located in a first plane extending through the lines of the aligned first calibration object 11 A and the first corresponding calibration object 12A.
  • This procedure may be repeated for the remaining three sets of calibration objects 11 C-E and their corresponding calibration objects 12C-E.
  • the rotation centre 14 is located in the position where the established planes intersect. Establishing three planes in three different view directions 13 is sufficient to establish the location of the rotation centre 14.
  • the calculating unit 23 calculates the location of the rotation centre 14 of the eye 8. The mathematical principals for the required calculations of the algorithm used by the calculating unit 23 are known to the person skilled in the art. Establishing additional planes can be used to control whether the established location of the rotation centre 14 is correct.
  • the first, second and third set of calibration objects 11 A-C and their corresponding calibration objects 12A-C are in general used to establish the location of the rotation centre 14 of the right eye 8 of the person.
  • the third, fourth and fifth set of calibration objects 11 C-E and their corresponding calibration objects 12C-E are in general used to establish the location of the rotation centre 14 of the left eye 8 of the person.
  • Figure 6 shows an enlarged view of part of the imaging system according the invention.
  • the supporting device 6 holds a screen 5 and a second embodiment of the calibration device 10 according the invention.
  • the screen 5 is located in the display position 7 at a distance D1 of the eye 8.
  • the calibration device 10 is held near the screen 5 and comprises calibration objects 1 1 located at a distance from the calibration screen 21. Once the location of the rotation centre 14 of the eye 8 is established, the calibration device 10 is removed out of the sight of the eye 8 while the screen 5 remains in the display position 7.
  • the figures 7A-C show a front view, side view (in the direction of arrow Vll-B) and top view (in the direction of arrow Vll-C) of the calibration device 10 of fig. 6, respectively.
  • the calibration device 10 is in a detachable manner connected to the screen 5. It is of course also possible to attach the calibration device 10 to a different object, such as the supporting device, as long as the calibration objects 11 are positioned at a distance D2 from the screen 5.
  • the calibration device 10 comprises two calibration objects 1 1A, B, each comprising a calibration ring 31A, B. Each calibration ring 31A, B is facing the screen 5. Two
  • Each corresponding calibration object 12A, B is projected on the screen 5.
  • Each corresponding calibration object 12A, B has the form of a dot 35A, B.
  • C the eye 8 of the person 9 is shown and the screen 5 is positioned in the display position 7 at distance D1 .
  • the person 9 is able to move the corresponding calibration objects 12A, B over the screen 5.
  • the first calibration object 1 1 A is aligned with the first corresponding calibration objects 12A in a first view direction 13A of the eye 8 by placing the first dot 35A in the first calibration ring 31A (see fig. 5B, C). This way one establishes that the rotation centre 14 of the eye 8 is located on a first line extending through the aligned first calibration ring 31A and first dot 35A.
  • the second calibration object 11 B is aligned with the second corresponding calibration object 12B in a second view direction 13B of the eye 8 - which is different from the first view direction 13A - (see fig. 5C).
  • the rotation centre 14 of the eye 8 is located on a second line extending through the aligned second calibration ring 31 B and second dot 35B.
  • the rotation centre 14 is located in the position where the established lines intersect. Establishing two lines in two different view directions 13 is sufficient to establish the location of the rotation centre 14.
  • the measuring unit 22 measures the position of the aligned calibration object 1 1 A, B and corresponding calibration objects 12A, B. With the use of an algorithm based on standard mathematical relations between the measured positions, the calculating unit 23 calculates the location of the rotation centre 14 of the eye 8. The mathematical principals for the required calculations of the algorithm used by the calculating unit 23 are known to the person skilled in the art. Additional lines can be used to control whether the established location of the rotation centre 14 is correct.
  • Fig. 8A-C shows a calculation of the rotation centre in the situation of the fig. 5.
  • the shown example relates to the rotation centre of the right eye. This involves the calibration objects 1 1 C, 1 1 D and 1 1 E and the projected corresponding calibration objects 12C, 12D and 12E.
  • the calibration objects 1 1 B, 1 1 C and 1 1 A and the projected corresponding calibration objects 12B, 12C and 12A are relevant.
  • the corresponding calibration objects are set by the person and are referred to as gauge lines in the following description.
  • the calibration objects are formed by a reference line with a fixed position relative to the centre O defined by row vector L. The direction thereof is given by the direction vector P.
  • Reference line and gauge line together define the gauge plane with unit normal (column) vector ti.
  • a gauge plane Y is defined by n i, i.e. the normal vector to the plane through the reference line (Li) and its correspondin gaugeline (Si) after the setting :
  • Position coordinate along their direction is set to zero (0) for all lines, because settings are perpendicular to the direction of the line.
  • Reference line element in picture position vector direction vector of reference line of reference line is set to zero (0) for all lines, because settings are perpendicular to the direction of the line.
  • I2C S 3 ⁇ 0, 3 ⁇ 4 i> ⁇

Abstract

Imaging system for displaying an image in a MRI scanner, which imaging system comprises a projector for projecting the image, a screen for displaying the image, a supporting device constructed and arranged to hold the screen - in use - in a display position in the proximity of an eye of a person positioned in the MRI scanner, a calibration device constructed and arranged to - in use - establish the rotation centre of the eye and comprising at least two calibration objects located at a distance from the screen, wherein the imaging system is constructed and arranged to project at least two corresponding calibration objects on the screen and to allow the person to align a first calibration object with a first corresponding calibration object in a first view direction of the eye and to align a second calibration object with a second corresponding calibration object in a different second view direction of the eye.

Description

Title: IMAGING SYSTEM DISPLAYING AN IMAGE IN A MRI SCANNER
The invention relates to an imaging system for displaying an image in a MRI scanner. The imaging system comprises a projector for projecting the image, a screen for displaying the image, a supporting device constructed and arranged to hold the screen - in use - in a display position in the proximity of an eye of a person positioned in the MRI scanner.
Such an imaging system is often referred to as wide field visual projection for a MRI scanner. The screen in general displays the image at a distance of around and between 3 - 6 cm from the eye of the person laying in the MRI scanner. By displaying the image in the proximity of the eye, a large visual field for the eye is created. Said visual field in general extends up to 120 degrees in width and 90 degrees in height.
Such a wide visual field in an MRI scanner is advantageous to diagnose problems of the visual system of a person. For testing the visual system a testing method named visual perimetry is often used. During this test, the person keeps the gaze of the eye fixed while images are presented at various places in the visual field. This way the images are projected at different locations on the retina of the eye. In healthy persons, the projections on the retina result in an activity in the visual parts of the brain. The MRI scanner is able to detect said activities in the brain. This allows the detection of defects in the visual system of a person. Such defects may for example be caused by brain damage as a result of a stroke.
Displaying the image in the proximity of the eye makes the testing method very sensitive for errors. It requires that it is exactly known where the eye is positioned relative to the displayed image. Any small unwanted displacement (in the width and/or height direction) of the displayed image results in relatively large displacement of the projection on the retina of the eye. This leads to errors in the perimetric measurements and associated activity of the visual parts of the brain. As a result of such errors it will be possible that a wrong diagnostic conclusion relating the visual system of a person will be made.
It is an object of the invention to provide an improved - or at least an alternative - imaging system for displaying an image in a MRI scanner. Said object is achieved by a imaging system which comprises a projector for projecting the image, a screen for displaying the image, a supporting device constructed and arranged to hold the screen - in use - in a display position in the proximity of an eye of a person positioned in the MRI scanner, a calibration device constructed and arranged to - in use - establish the rotation centre of the eye and comprising at least two calibration objects located at a distance from the screen, wherein the imaging system is constructed and arranged to project at least two corresponding calibration objects on the screen and to allow the person to align a first calibration object with a first corresponding calibration object in a first view direction of the eye and to align a second calibration object with a second corresponding calibration object in a different second view direction of the eye.
Once the calibration objects and the corresponding calibration objects are aligned, the rotation centre of the eye can be determined on basis of the position of the aligned calibration objects and the corresponding calibration. Knowing the position of the rotation centre of the eye allows an accurate projection on the retina of the image displayed on the screen. This makes an accurate testing of the visual system of a person possible.
In an embodiment of the imaging system according the invention, the calibration device comprises a third calibration object located at a distance from the screen, the imaging system is constructed and arranged to project a third corresponding calibration object on the screen and to allow the person to align the third calibration object with the third corresponding calibration object in a different third view direction of the eye.
The imaging system may be constructed and arranged to allow the person to move the corresponding calibration objects projected on the screen. The calibration device may be constructed and arranged to keep the calibration objects in a fixed position relative to the screen. The supporting device may be constructed and arranged to keep the screen in a fixed position relative to the eye of the person.
The calibration device may comprise a measuring unit constructed and arranged to measure the position of the calibration objects and corresponding calibration objects and a calculating unit constructed and arranged to communicate with the measuring unit and to calculate the rotation centre of the eye while using the measured positions of the aligned calibration objects and corresponding calibration objects.
In an embodiment of the imaging system, the imaging system is constructed and arranged to allow the person to move the calibration objects and the screen relative to each other.
In an embodiment of the imaging system, the calibration device is constructed and arranged to move the calibration objects relative to the screen.
In an embodiment of the imaging system, the imaging system is constructed and arranged to keep the projected corresponding calibration objects in a fixed position relative to the eye of the person.
In an embodiment of the imaging system, the supporting device is constructed and arranged to move the screen relative to the calibration objects.
In an embodiment of the imaging system, the imaging system is constructed and arranged to keep the calibration objects in a fixed position relative to the eye of the person.
In an embodiment of the imaging system, the calibration objects and the
corresponding calibration objects comprise lines. In an embodiment of the imaging system, the calibration objects and the
corresponding calibration objects each comprise at least three lines.
In an embodiment of the imaging system, at least one of said at least three lines extends transverse to the other lines.
In an embodiment of the imaging system, the calibration objects and the
corresponding calibration objects each comprise at least two lines extending substantially parallel to each other.
In an embodiment of the imaging system, the calibration objects and the
corresponding calibration objects each comprise at least two lines extending traverse to each other.
In an embodiment of the imaging system, the calibration objects and the
corresponding calibration objects comprise lines extending substantially vertical when seen by the person.
In an embodiment of the imaging system, the calibration objects and the
corresponding calibration objects comprise lines extending substantially horizontal when seen by the person.
In an embodiment of the imaging system, each calibration object and its
corresponding calibration object substantially have the same form.
In an embodiment of the imaging system, each calibration object and its
corresponding calibration object substantially have the same orientation.
In an embodiment of the imaging system, the calibration objects and/or the corresponding calibration objects comprise dots.
In an embodiment of the imaging system, the calibration objects comprise dots and the corresponding calibration objects comprise calibration rings.
In an embodiment of the imaging system, the calibration objects comprise calibration rings and the corresponding calibration objects comprise dots.
In an embodiment of the imaging system, the corresponding calibration objects are positioned behind the screen in the view direction of the person.
In an embodiment of the imaging system, the screen is constructed and arranged to allow the person to observe the corresponding calibration objects through the screen.
In an embodiment of the imaging system, the screen is translucent to allow the person to observe the corresponding calibration objects.
In an embodiment of the imaging system, the screen comprises openings allowing the person to observe the corresponding calibration objects.
In an embodiment of the imaging system, the corresponding calibration objects are positioned in front of the screen in the view direction of the person.
In an embodiment of the imaging system, the distance D2 between the calibration objects and the screen is around and between 5 and 30 mm. In an embodiment of the imaging system, the distance D2 between the calibration objects and the screen is around and between 10 and 15 mm.
In an embodiment of the imaging system, the calibration device comprises a calibration screen constructed and arranged to replace the screen and to perform the tasks of the screen.
In an embodiment of the imaging system, the calibration screen is positioned in the display position when the calibration device is held by the supporting device and the at least two calibration objects are located at a distance from the calibration screen.
In an embodiment of the imaging system, the screen, supporting device, and calibration device are formed from materials suitable for use in a MRI scanner.
The invention further relates to a calibration device for calibrating an imaging system for displaying an image in a MRI scanner, which imaging system comprises a projector for projecting the image, a screen for displaying the image, a supporting device constructed and arranged to hold the screen - in use - in a display position in the proximity of an eye of a person positioned in the MRI scanner, wherein the imaging system is constructed and arranged to project at least two corresponding calibration objects on the screen, and wherein the calibration device comprises at least two calibration objects - in use - located at a distance from the screen and is constructed and arranged to establish the rotation centre of the eye by aligning a first calibration object with a first corresponding calibration object in a first view direction of the eye and a second calibration object with a second corresponding calibration object in a different second view direction of the eye.
In an embodiment of the calibration device, the calibration device comprises a third calibration object located at a distance from the screen and is constructed and arranged to establish the rotation centre of the eye by aligning the third calibration object with the third corresponding calibration object in a different third view direction of the eye.
In an embodiment of the calibration device, the calibration device comprises a measuring unit constructed and arranged to measure the position of the calibration objects and corresponding calibration objects and a calculating unit constructed and arranged to communicate with the measuring unit and to calculate the rotation centre of the eye while using the measured positions of the aligned calibration objects and corresponding calibration objects.
The invention further relates to a calibration device as defined in the accompanying claims.
The invention further relates to a method for calibrating an imaging system according to the invention, wherein the method comprises the steps of projecting at least two corresponding calibration objects on the screen, establishing the rotation centre of the eye by aligning a first calibration object with a first corresponding calibration object in a first view direction of the eye and a second calibration object with a second corresponding calibration object in a different second view direction of the eye.
The invention further relates to a method for calibrating an imaging system according to the invention, wherein the method comprises the steps of projecting three corresponding calibration objects on the screen, establishing the rotation centre of the eye by aligning a first calibration object with a first corresponding calibration object in a first view direction of the eye, a second calibration object with a second corresponding calibration object in a different second view direction of the eye, and a third calibration object with a third corresponding calibration object in a different third view direction of the eye.
The invention further relates to a method for calibrating an imaging system for displaying an image in a MRI scanner, which imaging system comprises a projector for projecting the image, a screen for displaying the image, a supporting device constructed and arranged to hold - in use - the screen in a display position in the proximity of an eye of a person positioned in the MRI scanner, a calibration device constructed and arranged to position at least two calibration objects at a distance from the screen, wherein
the method comprises the steps of projecting at least two corresponding calibration objects on the screen, and establishing the rotation centre of the eye by aligning a first calibration object with a first corresponding calibration object in a first view direction of the eye and a second calibration object with a second corresponding calibration object in a different second view direction.
In an embodiment of the method according the invention, the calibration device comprises a third calibration object located at a distance from the screen, the imaging system is constructed and arranged to project a third corresponding calibration object on the screen and the method comprises aligning the third calibration object with the third corresponding calibration object in a different third view direction of the eye.
The method may comprise moving the corresponding calibration objects projected on the screen. The method may comprise moving the calibration objects and the screen relative to each other. The method may comprise measuring the position of the aligned calibration objects and corresponding calibration objects and calculating the rotation centre of the eye while using the measured positions of the aligned calibration objects and corresponding calibration objects.
The invention further relates to a calibration device for calibrating a imaging system for displaying an image in a MRI scanner, which imaging system comprises a projector for projecting the image, a screen for displaying the image, a supporting device constructed and arranged to hold the screen - in use - in a display position in the proximity of an eye of a person positioned in the MRI scanner, wherein the imaging system is constructed and arranged to project at least two corresponding calibration objects on the screen and to allow the person to move the corresponding calibration objects, and wherein the calibration device is constructed and arranged to establish the rotation centre of the eye and comprises at least two calibration objects - in use - located at a distance from the screen.
The invention further relates to a calibration device for calibrating an imaging system for displaying an image in a MRI scanner, which imaging system comprises a projector for projecting the image, a screen for displaying the image, a supporting device constructed and arranged to hold the screen - in use - in a display position in the proximity of an eye of a person positioned in the MRI scanner, wherein the imaging system is constructed and arranged to project at least two corresponding calibration objects on the screen, and wherein the calibration device comprising at least two calibration objects - in use - located at a distance from the screen and is constructed and arranged to establish the rotation centre of the eye by moving the calibration objects and the screen relative to each other.
The invention further relates to an use of an imaging system according to the invention.
The invention further relates to an use of a calibration device according to the invention.
The present invention will be more readily appreciated as the same becomes better understood by reference to the following detailed description and considered in connection with the accompanying drawings in which like reference symbols designate like parts and in which:
Fig. 1 schematically shows an embodiment of the imaging system according to the invention,
Fig. 2 schematically shows an enlarged view of part of the imaging system of fig. 1 comprising a screen,
Fig. 3A-C schematically show the screen of fig. 2,
Fig. 4 schematically shows an enlarged view of part of the imaging system of fig. 1 comprising a first embodiment of the calibration device,
Fig. 5A-C schematically show the calibration device of fig. 4,
Fig. 6 schematically shows an enlarged view of part of the imaging system of fig. 1 comprising a second embodiment of the calibration device,
Fig. 7A-C schematically show the calibration device of fig. 6, and
Fig. 8A-C schematically shows a calculation of the rotation centre in the situation of the fig. 5.
Figure 1 shows an embodiment of the imaging system 1 according to the invention. The imaging system 1 for displaying an image in a MRI scanner 3 comprises a projector 4 for projecting the image, a screen 5 for displaying the image, a supporting device 6 constructed and arranged to hold the screen 5 - in use - in a display position 7 in the proximity of an eye 8 of a person 9 positioned in the MRI scanner 3. Figure 1 shows a cross sectional view of the coil 24 of a MRI scanner 3. The person 9 is positioned in the coil opening 25 of the coil 24. The person 9 is positioned on a platform 27 which can move the person 9 in and out the coil opening 25.
The imaging system 1 further comprises a calibration device 10 constructed and arranged to - in use - establish the rotation centre 14 of the eye 8. As shown in the fig. 4-7, the calibration device 10 comprises at least two calibration objects 1 1 located at a distance D2 from the screen 5. The imaging system 1 is constructed and arranged to project at least two corresponding calibration objects 12 on the screen 5 and to allow the person to align a first calibration object 1 1A with a first corresponding calibration object 12A in a first view direction 13A of the eye 8 and to align a second calibration object 11 B with a second corresponding calibration object 11 B in a different second view direction 13B of the eye 8.
The calibration device 10 comprises a measuring unit 22 constructed and arranged to measure the position of the calibration objects 1 1 and corresponding calibration objects 12 and a calculating unit 23 constructed and arranged to communicate with the measuring unit 22 and to calculate the rotation centre 14 of the eye 8 while using the measured positions of the aligned calibration objects 11 and corresponding calibration objects 12. The measuring unit 22 is connected to the calculating unit 23 via a communication connection 32, such as a data line, a wireless connection, or the like.
The measuring unit 22 may comprise any electronic measuring device, optical measuring device or acoustical measuring device suitable for determining the location of the calibration objects 11 and corresponding calibration objects 12 The calculating unit 23 may comprise a computer or the like which is coupled to the measuring unit 22.
The imaging system comprises a control unit 34 constructed and arranged to move the corresponding calibration objects 12 projected on the screen 5 (or calibration screen 21 ). The control unit 34 is connected to and communicates with the projector 4 via a control connection 33. The control unit 34 is manually controlled by the person 9, but may also be controlled by another person or system based on input from the person, for example by spoken instructions of the person 9.
Figure 2 shows an enlarged view of part of the imaging system 1 according the invention. The supporting device 6 holds a screen 5 in the display position 7. The distance D1 between the eye 8 and the screen 5 is around and between 30 - 60 mm. The projection of the projector 4 is reflected by a mirror 26 onto the screen. More specifically, the distance D1 relates to the distance between the image projected on the screen 5 and the eye 8. The situation shown is used to provide a wide visual field to the eye 8 of the person 9. The supporting device 6 is supported by the platform 27. The supporting device 6 comprises an adjusting unit 29 to adjust the distance between the platform 27 and the part of supporting device 6 holding the screen 5.
The screen 5 may be formed by a hard material with a plate like form. The screen 5 may be formed by a flexible material with a sheet like form. The figures 3A-C show a front view, side view (in the direction of arrow IV-B) and top view (in the direction of arrow IV-C) of the screen 5 of fig. 2, respectively. In the fig. 3B, C the eye 8 of the person 9 is shown and the screen 5 is positioned in the display position 7 at distance D1. In fig. 3B is the width of the visual field of alpha degrees indicated, which is around and between 100 - 160 degrees. In fig. 3C is the height of the visual field of beta degrees indicated, which is around and between 70 - 100 degrees.
Figure 4 shows an enlarged view of part of the imaging system according the invention. The supporting device 6 holds a first embodiment of the calibration device 10 according the invention. The calibration device 10 comprises calibration screen 21 located in the display position 7 at a distance D1 of the eye 8. The calibration device 10 comprises calibration objects 11 located at a distance from the calibration screen 21. Once the location of the rotation centre 14 of the eye 8 is established, the calibration device 10 is removed and a screen 5 is placed in the display position 7.
The figures 5A-C show a front view, side view (in the direction of arrow V-B) and top view (in the direction of arrow V-C) of the calibration device 10 of fig. 4, respectively. The calibration device 10 comprising five calibration objects 1 1 A-E located at a distance D2 from the calibration screen 21. Five corresponding calibration objects 12A-E are projected on the calibration screen 21. In the fig. 5B, C the eye 8 of the person 9 is shown and the calibration screen 21 is positioned in the display position 7 at distance D1.
With the use of the control unit 34, the person 9 is able to move the corresponding calibration objects 12A-E over the calibration screen 21. By aligning the horizontal line of the first calibration object 1 1 A with the horizontal line of the first corresponding calibration object 12A in a first view direction 13A of the eye 8 (see fig. 5B), one establishes that the rotation centre 14 of the eye 8 is located in a first plane extending through the lines of the aligned first calibration object 11 A and the first corresponding calibration object 12A.
By aligning the vertical line of the second calibration object 1 1 B with the vertical line of the second corresponding calibration object 12B in a second view direction 13B of the eye 8 - which is different from the first view direction 13A (see fig. 5C) -, one establishes that the rotation centre 14 of the eye 8 is located in a second plane extending through the lines of the aligned second calibration object 11 B and the second corresponding calibration object 12B.
This procedure may be repeated for the remaining three sets of calibration objects 11 C-E and their corresponding calibration objects 12C-E. This results in five planes in the rotation centre 14 of the eye 8 is located. The rotation centre 14 is located in the position where the established planes intersect. Establishing three planes in three different view directions 13 is sufficient to establish the location of the rotation centre 14. With the use of an algorithm based on generally known rules of linear algebra between the measured positions, the calculating unit 23 calculates the location of the rotation centre 14 of the eye 8. The mathematical principals for the required calculations of the algorithm used by the calculating unit 23 are known to the person skilled in the art. Establishing additional planes can be used to control whether the established location of the rotation centre 14 is correct.
In the calibration device of fig. 5, the first, second and third set of calibration objects 11 A-C and their corresponding calibration objects 12A-C are in general used to establish the location of the rotation centre 14 of the right eye 8 of the person. The third, fourth and fifth set of calibration objects 11 C-E and their corresponding calibration objects 12C-E are in general used to establish the location of the rotation centre 14 of the left eye 8 of the person.
Figure 6 shows an enlarged view of part of the imaging system according the invention. The supporting device 6 holds a screen 5 and a second embodiment of the calibration device 10 according the invention. The screen 5 is located in the display position 7 at a distance D1 of the eye 8. The calibration device 10 is held near the screen 5 and comprises calibration objects 1 1 located at a distance from the calibration screen 21. Once the location of the rotation centre 14 of the eye 8 is established, the calibration device 10 is removed out of the sight of the eye 8 while the screen 5 remains in the display position 7.
The figures 7A-C show a front view, side view (in the direction of arrow Vll-B) and top view (in the direction of arrow Vll-C) of the calibration device 10 of fig. 6, respectively. The calibration device 10 is in a detachable manner connected to the screen 5. It is of course also possible to attach the calibration device 10 to a different object, such as the supporting device, as long as the calibration objects 11 are positioned at a distance D2 from the screen 5.
The calibration device 10 comprises two calibration objects 1 1A, B, each comprising a calibration ring 31A, B. Each calibration ring 31A, B is facing the screen 5. Two
corresponding calibration objects 12A, B are projected on the screen 5. Each corresponding calibration object 12A, B has the form of a dot 35A, B. In the fig. 5B, C the eye 8 of the person 9 is shown and the screen 5 is positioned in the display position 7 at distance D1 .
With the use of the control unit 34, the person 9 is able to move the corresponding calibration objects 12A, B over the screen 5. The first calibration object 1 1 A is aligned with the first corresponding calibration objects 12A in a first view direction 13A of the eye 8 by placing the first dot 35A in the first calibration ring 31A (see fig. 5B, C). This way one establishes that the rotation centre 14 of the eye 8 is located on a first line extending through the aligned first calibration ring 31A and first dot 35A.
By placing the second dot 35B in the second calibration ring 31 B the second calibration object 11 B is aligned with the second corresponding calibration object 12B in a second view direction 13B of the eye 8 - which is different from the first view direction 13A - (see fig. 5C). The rotation centre 14 of the eye 8 is located on a second line extending through the aligned second calibration ring 31 B and second dot 35B.
The rotation centre 14 is located in the position where the established lines intersect. Establishing two lines in two different view directions 13 is sufficient to establish the location of the rotation centre 14. The measuring unit 22 measures the position of the aligned calibration object 1 1 A, B and corresponding calibration objects 12A, B. With the use of an algorithm based on standard mathematical relations between the measured positions, the calculating unit 23 calculates the location of the rotation centre 14 of the eye 8. The mathematical principals for the required calculations of the algorithm used by the calculating unit 23 are known to the person skilled in the art. Additional lines can be used to control whether the established location of the rotation centre 14 is correct.
Fig. 8A-C shows a calculation of the rotation centre in the situation of the fig. 5. The shown example relates to the rotation centre of the right eye. This involves the calibration objects 1 1 C, 1 1 D and 1 1 E and the projected corresponding calibration objects 12C, 12D and 12E. For the right eye the calibration objects 1 1 B, 1 1 C and 1 1 A and the projected corresponding calibration objects 12B, 12C and 12A are relevant. The corresponding calibration objects are set by the person and are referred to as gauge lines in the following description.
Notations:
- Vectors are indicated with BOLD face.
- Unit vectors are indicated as a
- All position vectors refer to centre O of the calibration screen and the reference frame with unit direction vectors:
Figure imgf000011_0001
e2 = {01 ,0}
e3 = {0,0, 1 }. Definitions:
(1 ) The calibration objects are formed by a reference line with a fixed position relative to the centre O defined by row vector L. The direction thereof is given by the direction vector P.
(2) The corresponding calibration objects are formed by a gauge line projected on the calibration screen. The alignment of this gauge line with the reference line by the person is called a 'setting'.
After the setting the position of the gauge line is indicated by row vector S.
(3) Reference line and gauge line together define the gauge plane with unit normal (column) vector ti.
(4) The rotation point of the eye is characterised by the row vector r.
Calculation: (0) A gauge plane Y is defined by ni, i.e. the normal vector to the plane through the reference line (Li) and its correspondin gaugeline (Si) after the setting :
Figure imgf000012_0001
.wherein Λρ denotes the direction of the reference line. (1 ) Each gauge plane T constrains the location of r as follows:
Figure imgf000012_0002
(2) Three settings together define the location of the rotation centre as follows: r = { L\ » if » -½ * ¾ 7 ^3 * ¾ } ^- 1
.wherein Λ ' is the inverse of the matrix ^ l **2
Tables with relations between the above vectors and fig. 8A-C
Position coordinate along their direction is set to zero (0) for all lines, because settings are perpendicular to the direction of the line. Reference line element in picture position vector direction vector of reference line of reference line
Figure imgf000012_0003
Remarks: -d2 negative distance because reference line is placed behind centre O,
-h2 negative distance because reference line is placed left of centre O, in fig . 8A, distance h3 = 0 because 1 1 C is aligned with centre O.
Gauge line element m picture position vector of sause line 1 I2E S] ={0,0 -,n }
2 12D S2 =.{0 - 52 ,0}
3 . I2C S3={0, ¾ i>}
Remarks: -St because downward relative centre O
-s2 because leftward relative centre O
in fig . 8A, distance s3 = 0 because 12C aligned with centre O. Alternative embodiments of the imaging system, calibration device and method according the invention are defined in the accompanying claims.
It will be apparent to those skilled in the art that various modifications can be made to the invention without departing from the scope of the invention.

Claims

Claims
Imaging system for displaying an image in a MRI scanner, wherein the imaging system comprises;
- a projector for projecting the image,
- a screen for displaying the image,
- a supporting device constructed and arranged to hold the screen - in use - in a display position in the proximity of an eye of a person positioned in the MRI scanner,
- a calibration device constructed and arranged to - in use - establish the rotation centre of the eye and comprising at least two calibration objects located at a distance from the screen, wherein
- the imaging system is constructed and arranged to project at least two corresponding calibration objects on the screen and to allow the person to align a first calibration object with a first corresponding calibration object in a first view direction of the eye and to align a second calibration object with a second corresponding calibration object in a different second view direction of the eye.
Imaging system according to claim 1 , wherein the calibration device comprises a third calibration object located at a distance from the screen, the imaging system is constructed and arranged to project a third corresponding calibration object on the screen and to allow the person to align the third calibration object with the third corresponding calibration object in a different third view direction of the eye.
Imaging system according to claim 1 or 2, wherein the imaging system is constructed and arranged to allow the person to move the corresponding calibration objects projected on the screen.
Imaging system according to any of the preceding claims, wherein the calibration device is constructed and arranged to keep the calibration objects in a fixed position relative to the screen.
Imaging system according to any of the preceding claims, wherein the supporting device is constructed and arranged to keep the screen in a fixed position relative to the eye of the person.
6. Imaging system according to any of the preceding claims, wherein the imaging system is constructed and arranged to allow the person to move the calibration objects and the screen relative to each other.
7. Imaging system according to any of the preceding claims, wherein the calibration device is constructed and arranged to move the calibration objects relative to the screen.
8. Imaging system according to claim 7, wherein the imaging system is constructed and arranged to keep the projected corresponding calibration objects in a fixed position relative to the eye of the person.
9. Imaging system according to any of the claims 1 -6, wherein the supporting device is constructed and arranged to move the screen relative to the calibration objects.
10. Imaging system according to claim 9, wherein the imaging system is constructed and arranged to keep the calibration objects in a fixed position relative to the eye of the person.
11 . Imaging system according to any of the preceding claims, wherein the calibration objects and the corresponding calibration objects comprise lines.
12. Imaging system according to any of the preceding claims, wherein the calibration objects and the corresponding calibration objects each comprise at least two lines extending substantially parallel to each other.
13. Imaging system according to any of the preceding claims, wherein the calibration objects and the corresponding calibration objects each comprise at least two lines extending traverse to each other.
14. Imaging system according to any of the preceding claims, wherein the calibration objects and the corresponding calibration objects comprise lines extending substantially vertical when seen by the person.
15. Imaging system according to any of the preceding claims, wherein the calibration objects and the corresponding calibration objects comprise lines extending substantially horizontal when seen by the person.
16. Imaging system according to any of the preceding claims, wherein each calibration object and its corresponding calibration object substantially have the same form.
17. Imaging system according to any of the preceding claims, wherein each calibration object and its corresponding calibration object substantially have the same orientation.
18. Imaging system according to any of the preceding claims, wherein the calibration objects and/or the corresponding calibration objects comprise dots.
19. Imaging system according to any of the preceding claims, wherein the calibration objects comprise dots and the corresponding calibration objects comprise calibration rings.
20. Imaging system according to any of the preceding claims, wherein the calibration objects comprise calibration rings and the corresponding calibration objects comprise dots.
21 . Imaging system according to any of the preceding claims, wherein the corresponding calibration objects are positioned behind the screen in the view direction of the person.
22. Imaging system according to any of the preceding claims, wherein the screen is
constructed and arranged to allow the person to observe the corresponding calibration objects through the screen.
23. Imaging system according to any of the preceding claims, wherein the screen is
translucent to allow the person to observe the corresponding calibration objects.
24. Imaging system according to any of the preceding claims, wherein the screen comprises openings allowing the person to observe the corresponding calibration objects.
25. Imaging system according to any of the claims 1 -20, wherein the corresponding
calibration objects are positioned in front of the screen in the view direction of the person
26. Imaging system according to any of the preceding claims, wherein the distance D2
between the calibration objects and the screen is around and between 5 and 30 mm.
27. Imaging system according to any of the claims 1 -26, wherein the distance D2 between the calibration objects and the screen is around and between 10 and 15 mm.
28. Imaging system according to any of the preceding claims, wherein the calibration device comprises a calibration screen constructed and arranged to replace the screen and to perform the tasks of the screen.
29. Imaging system according to any of the preceding claims, wherein the calibration screen is positioned in the display position when the calibration device is held by the supporting device and the at least two calibration objects are located at a distance from the calibration screen.
30. Imaging system according to any of the preceding claims, wherein the screen, supporting device, and calibration device are formed from materials suitable for use in a MRI scanner.
31 . Imaging system according to any of the preceding claims, wherein the calibration device comprises a measuring unit constructed and arranged to measure the position of the calibration objects and corresponding calibration objects and a calculating unit constructed and arranged to communicate with the measuring unit and to calculate the rotation centre of the eye while using the measured positions of the aligned calibration objects and corresponding calibration objects.
32. Calibration device according to any of the preceding claims.
33. Calibration device for calibrating an imaging system for displaying an image in a MRI scanner, which imaging system comprises a projector for projecting the image, a screen for displaying the image, a supporting device constructed and arranged to hold the screen - in use - in a display position in the proximity of an eye of a person positioned in the MRI scanner, wherein the imaging system is constructed and arranged to project at least two corresponding calibration objects on the screen, and wherein
- the calibration device comprises at least two calibration objects - in use - located at a distance from the screen and is constructed and arranged to establish the rotation centre of the eye by aligning a first calibration object with a first corresponding calibration object in a first view direction of the eye and a second calibration object with a second corresponding calibration object in a different second view direction of the eye.
34. Calibration device according to claim 33, wherein the calibration device comprises a third calibration object located at a distance from the screen and is constructed and arranged to establish the rotation centre of the eye by aligning the third calibration object with the third corresponding calibration object in a different third view direction of the eye.
35. Calibration device according to claim 33 or 34, wherein the calibration device comprises a measuring unit constructed and arranged to measure the position of the calibration objects and corresponding calibration objects and a calculating unit constructed and arranged to communicate with the measuring unit and to calculate the rotation centre of the eye while using the measured positions of the aligned calibration objects and corresponding calibration objects.
36. Use of an imaging system according to any of the claims 1 -31.
37. Use of a calibration device according to any of the claims 32-35.
38. Method for calibrating an imaging system according to any of the claims 1-31 , wherein the method comprises the steps of;
- projecting at least two corresponding calibration objects on the screen,
- establishing the rotation centre of the eye by aligning a first calibration object with a first corresponding calibration object in a first view direction of the eye and a second calibration object with a second corresponding calibration object in a different second view direction of the eye.
39. Method for calibrating an imaging system according to any of the claims 2-31 , wherein the method comprises the steps of;
- projecting three corresponding calibration objects on the screen,
- establishing the rotation centre of the eye by aligning a first calibration object with a first corresponding calibration object in a first view direction of the eye, a second calibration object with a second corresponding calibration object in a different second view direction of the eye, and a third calibration object with a third corresponding calibration object in a different third view direction of the eye.
40. Method for calibrating an imaging system for displaying an image in a MRI scanner, which imaging system comprises;
- a projector for projecting the image,
- a screen for displaying the image,
- a supporting device constructed and arranged to hold - in use - the screen in a display position in the proximity of an eye of a person positioned in the MRI scanner,
- a calibration device constructed and arranged to position at least two calibration objects at a distance from the screen, wherein
the method comprises the steps of;
- projecting at least two corresponding calibration objects on the screen,
- establishing the rotation centre of the eye by aligning a first calibration object with a first corresponding calibration object in a first view direction of the eye and a second calibration object with a second corresponding calibration object in a different second view direction.
41 . Method according to claim 40, wherein the calibration device comprises a third calibration object located at a distance from the screen, the imaging system is constructed and arranged to project a third corresponding calibration object on the screen and the method comprises aligning the third calibration object with the third corresponding calibration object in a different third view direction of the eye.
42. Method according to claim 40 or 41 , wherein the method comprises moving the
corresponding calibration objects projected on the screen.
43. Method according to any of the claims 40-42, wherein the method comprises moving the calibration objects and the screen relative to each other.
44. Method according to any of the claims 40-43, wherein the method comprises measuring the position of the aligned calibration objects and corresponding calibration objects and calculating the rotation centre of the eye while using the measured positions of the aligned calibration objects and corresponding calibration objects.
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