MAGNETIC RESONANCE IMAGING METHOD AND DEVICE

Abstract

The present invention relates to a magnetic resonance eye imaging method, wherein an eye image is obtained from magnetic resonance image data acquired while the eye is moving, comprising determining eye orientation information data during magnetic resonance image data acquisition; binning the acquired magnetic resonance image data into groups according to eye orientation information data; and constructing a magnetic resonance image eye image from a selection of groups of magnetic resonance image data.

Claims

1. A magnetic resonance eye imaging method, wherein an eye image is obtained from magnetic resonance image data acquired while the eye is moving, comprising determining eye orientation information data during magnetic resonance image data acquisition; binning the acquired magnetic resonance image data into groups according to eye orientation information data; and constructing a magnetic resonance image eye image from a selection of groups of magnetic resonance image data.

2. The magnetic resonance eye imaging method according to claim 1, wherein the magnetic resonance image data are acquired with a free running magnetic resonance image and/or in a manner not triggered by an eye orientation determined.

3. The magnetic resonance eye imaging method according to claim 1, wherein the eye image is obtained from magnetic resonance image data acquired intermittent to or simultaneous with an eye motion.

4. The magnetic resonance eye imaging method according to claim 1, wherein determining eye orientation information data during magnetic resonance image data acquisition comprises tracking the orientation of the eye or the orientation of a surface related to the eye.

5. The magnetic resonance eye imaging method according to claim 1, wherein determining eye orientation information data during magnetic resonance image data acquisition comprises causing the eye to orient in space according to a known pattern.

6. The magnetic resonance eye imaging method according to claim 1, wherein determining eye orientation information data during magnetic resonance image data acquisition comprises determination of eye orientation information data according to a two-dimensional pattern.

7. The magnetic resonance eye imaging method according to claim 1, wherein binning the acquired magnetic resonance image data into groups according to eye orientation information data comprises a two-dimensional binning.

8. The magnetic resonance eye imaging method according to claim 1, wherein constructing a magnetic resonance image from a selection of groups of magnetic resonance image data comprises constructing a 3D image having a number of planes.

9. The magnetic resonance eye imaging method according to claim 1, wherein constructing a magnetic resonance eye image from a selection of groups of magnetic resonance image data comprises constructing a sequence of images constructed according to a sequence of orientations.

10. The magnetic resonance eye imaging method according to claim 1, wherein a body part is scanned comprising the entire visceral cavity wherein the eye is located.

11. The magnetic resonance eye imaging method according to claim 1, wherein the eye orientation is determined by a showing a pattern to be followed.

12. A magnetic resonance eye imaging system, comprising a magnetic resonance image data acquisition arrangement adapted to acquire magnetic resonance image data from a region of interest including the eye and while the eye is moving, and an eye orientation information data determination arrangement adapted for determining eye orientation information data during magnetic resonance image data acquisition in a manner allowing to assign an orientation of the eye to different parts of the magnetic resonance image data.

13. The magnetic resonance eye imaging system according to claim 12, the magnetic resonance eye imaging system further comprising an image constructing arrangement adapted to bin the acquired magnetic resonance image data into groups according to eye orientation information data; and to construct a magnetic resonance image eye image from a selection of groups of magnetic resonance image data.

14. A magnetic resonance eye image construction arrangement for constructing eye images from magnetic resonance imaging data acquired during movement of the eye, the eye image construction arrangement comprising an input for inputting magnetic resonance image data acquired from a region of interest including the eye and while the eye is moving, and for inputting eye orientation information data relating to eye orientation information data determined during magnetic resonance image data acquisition, and an image constructing arrangement adapted to bin the acquired magnetic resonance image data into groups according to eye orientation information data; and to construct a magnetic resonance image eye image from a selection of groups of magnetic resonance image data.

Description

[0123] The invention will now be described by way of example only with respect to the drawing. In the drawing,

[0124] FIG. 1 represents a comparison between the horizontal angular orientation of the Eye determined from the reconstructed images and the orientation according to the eye tracker used in the experimental setup;

[0125] FIG. 2 represents a comparison between the vertical angular orientation of the Eye determined from the reconstructed images and the orientation according to the eye tracker used in the experimental setup;

[0126] FIG. 3 represents trajectories determined with the Eye-Tracker;

[0127] FIG. 4 a 2D eye images obtained from example 1 for two different sections through the head with the white point showing the direction into which the test person is looking;

[0128] FIG. 4 b same as FIG. 4a, but with the test person looking into another direction;

[0129] FIG. 4 c same as FIG. 4a, but with the test person looking into yet another direction;

[0130] FIG. 4 d an enlarged part of one of the sections through the head shown in FIG. 4 a-c;

[0131] FIG. 5 a magnetic resonance eye imaging system according to the invention.

[0132] FIG. 6 represents a comparison between an image reconstructed according to the method of the present invention, and that reconstructed using the same amount of data collected in a consecutive period of time.

[0133] In FIG. 5, reference numeral 1 generally refers to a magnetic resonance eye imaging system 1 comprising a magnetic resonance image data acquisition arrangement 2 adapted to acquire magnetic resonance image data 3 from a region of interest 4 including the eye 5 and while the eye is moving, and eye orientation information data determination arrangement 6 adapted for determining eye orientation information data during magnetic resonance image data acquisition in a manner allowing to assign an orientation of the eye to different parts of the magnetic resonance image data. The magnetic resonance eye imaging system 1 also comprises an image constructing arrangement 7 adapted to bin the acquired magnetic resonance image data into groups according to eye orientation information data and to construct a magnetic resonance image eye image from a selection of groups of magnetic resonance image data.

[0134] Note that although in FIG. 5, the image constructing arrangement 7 is shown in close proximity to the magnetic resonance image data acquisition arrangement 2, it would be well possible to space the image constructing arrangement 7 far apart from the magnetic resonance image data acquisition arrangement 2. In particular, it would be possible to acquire the data in a medical practice and communicate the data to a remote center for analysis and/or diagnosis.

[0135] The magnetic resonance image data acquisition arrangement 2 shown in FIG. 5 can be based on a commercially available device. In a practical embodiment, a standard MAGNETOM Prismafit 3T clinical MRI scanner by Siemens Healthcare AG was used as a magnetic resonance image data acquisition arrangement 2. This MRI scanner can be operated using a number of different definable pulse sequences and with different receiving antenna coils; in the practical embodiment, an antenna coil arrangement was used adapted for skull imaging. The signals received with the antenna coils will vary over time in a manner depending from both the excitation pulses used and the anatomical details of the person examined; the signals are conditioned e.g. amplified appropriately and then digitized using conventional suitable circuitry so that magnetic resonance image data 3 is acquired from which by proper magnetic resonance image data processing in an image constructing arrangement 7 a magnetic resonance image eye image can be constructed. Accordingly, the magnetic resonance image data acquisition arrangement 2 was adapted to acquire magnetic resonance image data 3 from a region of interest 4 including the eye.

[0136] Furthermore, in a practical implementation, the MAGNETOM Prismafit 3T clinical MRI scanner by Siemens Healthcare AG used as a magnetic resonance image data acquisition arrangement 2 is adapted to generate an uninterrupted gradient recalled echo (GRE) sequence with lipid-insensitive binomial off-resonant RF excitation (LIBRE) for fat suppression was applied and the acquisition used a 3D radial phyllotaxis sampling pattern with spiral trajectories rotated by the golden-angle for uniform k-space coverage over a field-of view of (192 mm)3 with 1 mm3 isotropic resolution.

[0137] Within the tube of the a magnetic resonance image data acquisition arrangement 2, a display 6a constituting a part of the eye orientation information data determination arrangement 6 is placed capable of showing to a person examined a white circle on a black background at different positions. The size of the display is selected such that the person examined has to look up, down, left and right respectively when the white circle is shown close to the border of the display. In a practical embodiment, the display can be controlled by a programmable computer 6b in a manner such that changing images as changing stimuli to the patient can be shown that each have a duration of e.g. 5 seconds. (For the record: such duration is not limiting and other durations are obviously possible; also note that rather than using a separate computer 6b, the hardware of e.g. the image constructing arrangement 7 could also be used where this is a computer). For each distinct visual stimulus, the white circle was shown at a different position. In a practical embodiment the computer can be programmed such that each stimulus was repeated 6 times during an examination for a total of 96 trials opportunely randomized.

[0138] Furthermore, a commercial eye-tracker 6c constituting a further part of the eye orientation information data determination arrangement 6 is placed in the tube of the magnetic resonance image data acquisition arrangement 2, the eye-tracker 6c being arranged for observing the direction to which the person examined is looking during operation of the as magnetic resonance image data acquisition arrangement 2. In a practical implementation, an eye tracker EyeLink 1000Plus eye-tracking system has been used. The eye tracker was operated in parallel to the generation of the uninterrupted gradient recalled echo (GRE) sequence and a Syncbox 8 by NordicNeuroLab was provided to synchronize the measurements with the MRI scanner, i.e time stamps for both the eye orientation information data and the magnetic resonance image data 3 are generated by Syncbox 8.

EXAMPLE 1

[0139] For healthy adult volunteers, magnetic resonance image data were acquired using a standard MAGNETOM Prismafit 3T clinical MRI scanner by Siemens Healthcare AG.

[0140] An uninterrupted gradient recalled echo (GRE) sequence with lipid-insensitive binomial off-resonant RF excitation (LIBRE) for fat suppression was applied and the acquisition used a 3D radial sampling pattern rotated by the golden-angle for uniform k-space coverage. The field-of view was (192 mm).sup.3 with 1 mm.sup.3 isotropic resolution.

[0141] During acquisition of magnetic resonance image data, sixteen distinct visual stimuli were randomly presented six times to each volunteer.

[0142] Each stimulus had a duration of 5 seconds and consisted of a white circle on a black background; for each distinct visual stimulus, the white circle was shown at a different position. Each stimulus was repeated 6 times during the experiment for a total of 96 trials opportunely randomized to ensure uniform sampling distribution of the readouts in k-space.

[0143] Simultaneous with the presentation of the sixteen distinct visual stimuli, eye movements were tracked using an Eye-tracker EyeLink 1000Plus eye-tracking system that was synchronized with the MRI scanner via a Syncbox by NordicNeuroLab. An example of the trajectories extracted with the Eye-Tracker is shown in FIG. 3.

[0144] The post-processed Eye-tracker data were then used for binning the data obtained during the time interval spent in a given orientation state and for matching the k-space readouts corresponding to the same stimulus presentation.

[0145] Orientation-resolved 5D image reconstruction (x-y-z-α-β dimensions, where α and β represent the angular displacement of the eye in the up-down and left-right directions) was performed using a k-t sparse SENSE algorithm that exploits sparsity both along the α and β directions.

[0146] For all volunteers, 3D orientation-resolved images of the eye with 1 mm.sup.3 isotropic resolution could be successfully acquired and reconstructed. Despite the fact that each stimulus had a 5 second duration which is long compared to fast movements of the eye occurring sometimes during prolonged observations of a target, the images were void of orientation artifacts and eye orientations across the presentation of the different visual stimuli were clearly reconstructed (FIG. 4).

[0147] It was found that the horizontal angular orientation of the Eye deduced from the reconstructed Images corresponds closely to the determination of eye orientation based on the eye tracker, cmp. FIG. 1.

[0148] Furthermore, it was also found that the angular orientation of the Eye deduced from the reconstructed Images corresponds closely to the determination of eye orientation based on the eye tracker, cmp. FIG. 2.

[0149] Magnetic resonance images obtained in this manner are shown in FIG. 4 a-c for three different orientations. FIG. 4d depicts an enlarged view of a section as shown in FIG. 4a-c.

[0150] It can be concluded that the proposed method allows to obtain high quality orientation resolved eye images using a free running, uninterrupted MR excitation sequence and additional eye orientation information data.

[0151] As will be obvious from the above description, the present invention thus allows to reconstruct magnetic resonance images of an object while moving. It is inter alia suggested in one embodiment to provide magnetic resonance eye images based on a known pattern to be followed; accordingly, a stimulation protocol is implemented leading to a stimulated eye orientation. However, not only is in a preferred embodiment a suitable stimulation protocol implemented, but also the data acquired are treated in a specific manner overcoming limitations of prior part ophtalmic technologies requiring anesthesia.

EXAMPLE 2

[0152] Images were acquired using a 3T clinical MRI scanner (MAGNETOM Prisma.sup.fit, Siemens Healthcare AG) with a 22-channel head coil, using a prototype uninterrupted gradient recalled echo (GRE) sequence with lipid-insensitive binomial off-resonant RF excitation (LIBRE) for fat suppression. The acquisition used a 3D radial sampling pattern, the spiral phyllotaxis trajectory where each interleaf is rotated by the golden-angle to allow uniform k-space coverage. Eye movements were tracked using an eye-tracking system (EyeLink 1000Plus, SR Research) synchronized with the MRI scanner via Syncbox (NordicNeuroLab). An Experiment builder (EyeLink) program was developed and used to control the calibration of the Eye-Tracker from outside the scanner room and to correctly synchronize the different hardware components of the experiment. Eye-tracked trajectories, together with related trial number and temporal synchronization information, were extracted from the eye-tracking software. The right eye was the one tracked during the acquisition. Eye movement trajectories were recorded using infrared, with a sampling rate of 2000 Hz, through a mirror positioned inside the scanner bore, replacing the standard head-coil mirror usually available, which is not infrared compatible. The FoV was 192 mm.sup.3 with 1 mm.sup.3 isotropic resolution, TR/TE=6.4/2.94 ms, receiver bandwidth BW=501 Hz/px, and radiofrequency excitation angle FA=5°. The stimulation protocol was divided into 3 distinct phases, all consisting of a grey circle positioned at specific locations on a black background. These circular stimuli guided the eye movements. First, an initial period of fixation was performed, where the image presented to the participant was the static grey circle positioned at the centre of the screen. This first part of the experiment allowed for performing the sequence localizer while the eye was in a static position. Second, 96 visual stimuli were presented to each participant. Each stimulus corresponded to one among 16 different locations the grey circle on a 4×4 grid.

[0153] Each presentation had a duration of 5 seconds and was repeated 6 times in distinct and randomized moments during the experiment. This part of the acquisition lasted for 8 minutes in total. Third, the fixation circle was presented again, as in the first part of the experiment, to conclude the acquisition. The presentations during the second phase of the experiment were opportunely randomized to ensure a uniform sampling distribution of the readouts in k-space during the following retrospective motion-resolved reconstruction step. A total of 81906 readout profiles, divided into 3723 interleaves, were acquired.

[0154] The continuously acquired data, as enabled by the free-running approach to data collection, can be arbitrarily partitioned into different bins thanks to the golden-angle distribution properties. The processed eye-tracker data were used to bin the time intervals of each motion state and to match the k-space readouts corresponding to the same stimulus presentation, hence leading to the same motion-resolved 3D image. Motion-resolved 5D image reconstruction (x-y-z-α-β dimensions, where α and β represent the eye angular rotations in the horizontal and vertical directions, respectively) was performed using a k-t sparse SENSE algorithm (image under-sampling 8.8%), exploiting sparsity both along the α and β directions. The values of α and β are deduced from the eye-tracker recordings and correspond to those determined from the reconstructed images, once normalized. For one selected subject and eye position, a typical reconstructed image is shown in FIG. 6 in panels A and B.

REFERENCE EXAMPLE 2

[0155] The dataset of Example 1 is used in Reference Example 2, wherein no binning according to eye orientation information data is performed. Instead of performing a 5D k-t sparse SENSE reconstruction, we perform a 4D reconstruction (NO k-t sparse SENSE) having the time t as fourth dimension. The sections shown on the right are composed by readouts acquired continuously for 30 s, matching the bin size of the previous compressed sensing reconstruction. The resulting reconstruction is shown in FIG. 6 panel C and D.

[0156] As it can be seen, from comparing panels A and C, as well as B and D in FIG. 6, binning of MRI data according to eye orientation information data allows for reconstructions that are less blurred and comprise higher level of detail.