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WO2006059089A1 - Imagerie par résonance magnétique oculaire - Google Patents

Imagerie par résonance magnétique oculaire Download PDF

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Publication number
WO2006059089A1
WO2006059089A1 PCT/GB2005/004577 GB2005004577W WO2006059089A1 WO 2006059089 A1 WO2006059089 A1 WO 2006059089A1 GB 2005004577 W GB2005004577 W GB 2005004577W WO 2006059089 A1 WO2006059089 A1 WO 2006059089A1
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Prior art keywords
eye
image
magnetic resonance
acquired image
processing
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Ceased
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PCT/GB2005/004577
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English (en)
Inventor
Krishna Singh
Bernard Gilmartin
Nicola Logan
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Aston University
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Aston University
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    • 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
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/5608—Data processing and visualization specially adapted for MR, e.g. for feature analysis and pattern recognition on the basis of measured MR data, segmentation of measured MR data, edge contour detection on the basis of measured MR data, for enhancing measured MR data in terms of signal-to-noise ratio by means of noise filtering or apodization, for enhancing measured MR data in terms of resolution by means for deblurring, windowing, zero filling, or generation of gray-scaled images, colour-coded images or images displaying vectors instead of pixels

Definitions

  • the present invention relates to a method and apparatus for imaging the human eye or a portion thereof. More particularly, the invention relates to a method and apparatus able to produce a three dimensional image of the eye or a portion thereof.
  • Certain human medical conditions result in, or are a result of, anomalous ocular growth.
  • myopia is due to excessive growth of the posterior segment of the eye - in essence the eye outgrows the focusing power provided by the cornea and internal crystalline lens.
  • the increased prevalence of myopia in young adolescent children has reached epidemic levels - in some East Asian societies prevalence levels of 80% are not uncommon.
  • Prevalence in western industrialised societies has reached at least 25% and is rising. Obtaining an understanding of the nature of ocular growth is central to an understanding of myopia and other conditions.
  • Eye volume is an important variable in relation to choroidal blood flow (which accounts for 85% of intraocular blood flow). Interpretation of these measures would be facilitated by accurate determination of eye volume rather than using the relatively coarse approximations in current instrumentation.
  • 3-D modelling of the eye could also assist in the design of image shells generated by a variety of ophthalmic appliances ranging from spectacle lenses, contact lenses, intraocular lenses and corneal inlays. Of special interest would be the potential to couple 3-D modelling of posterior eye shape with profiles of wave front aberration (expressed as Zernike coefficients) and to consider whether this would have utility in wave front guided laser corneal surgery.
  • Wave front aberration of the human eye is principally a consequence of the interaction between the quality of corneal optics, crystalline lens optics and posterior eye shape.
  • new surgical techniques develop (e.g. clear lens extraction as a method of treating presbyopia and myopia) there will be a need to understand the relative contribution of cornea and posterior eye shape to the formation of the retinal image.
  • Ocular Magnetic Resonance Imaging has been previously used for 2-dimensional depiction of the human eye to investigate, for example, changes in the diameter of the ciliary smooth muscle collar with accommodation. Studies have used this information to comment on mechanisms of presbyopia (i.e. the ageing process that causes a need for reading glasses at around 45 years of age). Others have used 2-D MRI depiction to comment on posterior segment contour of the eye with a very recent paper using 2-D MRI representation to investigate separately posterior retinal shape in horizontal and vertical meridians. This work is described in the following:
  • a method of imaging a human or animal eye comprising: configuring a magnetic resonance imaging instrument to provide high contrast between fluid and non-fluid materials; acquiring a three-dimensional image of the eye and its surroundings using the magnetic resonance imaging instrument when so configured; and processing the acquired image to obtain a three-dimensional envelope of the eye or a portion thereof.
  • Embodiments of the present invention provide a means for generating a 3-D representation of the eye that is spatially manipulable. The invention allows calculation of eye shape and curvature at any selected point across the whole surface of the eye.
  • embodiments of the invention may provide results that can be utilised to assist surgeons to locate accurately an area of the eye requiring ocular surgery. Similar applications can be envisaged for assisting in retinal detachment surgery (myopic individuals are especially susceptible to retinal detachment) and to squint surgery whereby re-insertion of extraocular muscles could be mapped accurately to globe dimensions.
  • Said step of processing the acquired image may comprise identifying the outer boundaries of the fluid filled chambers of the eye.
  • posteriorly the envelope corresponds approximately to the position of the retina that encompasses the posterior vitreous chamber and anteriorly to the surface of the corneal endothelium that encompasses the anterior chamber.
  • the initial envelope may be further modified so that it corresponds to another boundary separating different tissue types, for example the outer surface of the sclera.
  • the magnetic resonance imaging instrument is configured to provide a T2 weighted volume scan.
  • the instrument may also be configured to provide a T1 -weighted scan, said step of processing the acquired image comprising incorporating features obtained from the T1 scan into the image obtained from the T2 scan.
  • the step of processing the acquired image comprises adjusting the brightness and contrast of the acquired image data to distinguish the eye or portion of the eye from the surrounding regions.
  • the adjusted image data may then be flood-filled.
  • the step of generating the envelope may comprise identifying the flood-filled area of the image data, and applying a shrink-wrap algorithm. More particularly, the step comprises generating a sphere mesh around the identified area, centred on the geometrical centre of the eye. Using an iterative procedure, the vertices of the sphere mesh are shrunk until the vertices contact the surface of the identified area.
  • a smoothing algorithm is applied to the shrunk mesh.
  • the method may comprise using a second imaging procedure to measure one or more dimensional properties of the eye, and using the measured property or properties to correct the acquired image before or during processing.
  • said second procedure may be used to measure an axial length of the eye, with the image of the eye obtained using the magnetic resonance imaging instrument being adjusted so that the axial length of the eye corresponds to the measured length.
  • the method may comprise processing the obtained envelope of the eye to assign colours to the surface of the envelope in dependence upon the properties of a surface region, e.g. distance from a certain point, radius of curvature, etc.
  • apparatus for imaging a human or animal eye comprising: a magnetic resonance imaging instrument configured to a provide high contrast between fluid and non-fluid materials; data processing means coupled to said magnetic resonance imaging instrument for receiving therefrom an acquired three-dimensional image of the eye and its surroundings and arranged to process the acquired image to obtain a three-dimensional envelope of the eye or a portion of the eye.
  • a computer storage medium having recorded thereon a computer program for configuring a magnetic resonance imaging instrument to provide high contrast between fluid and non-fluid materials, for acquiring a three-dimensional image of the eye and its surroundings using the magnetic resonance imaging instrument when so configured, and for processing the acquired image to obtain a three-dimensional envelope of the eye or a portion thereof.
  • Figure 1A illustrates a transverse cross-section through a 3-D image of the front of a human head acquired using T2-weighted MRI configuration
  • Figure 1 B illustrates a transverse cross-section through a 3-D image of the front of a human head acquired using a T1 -weighted MRI configuration
  • Figure 2 illustrates a flood-fill processing step applied to the image of Figure
  • Figure 3 illustrates a shrink wrapping mesh applied to an eye contained in the processed image of Figure 2;
  • Figure 4 illustrates a smoothing process applied to the wrapped eye of Figure
  • Figure 5 is a flow diagram illustrating key steps in the 3-D image acquisition and processing procedure
  • Figure 6 illustrates two different views of a processed image of a normal eye, dressed to show distance of the surface from the corneal pole;
  • Figure 7 illustrates two different views of a processed image of a strongly myopic eye, dressed to show distance of the surface from the corneal pole;
  • Figure 8 illustrates two different views of a processed image of a normal eye, dressed to show radius of curvature of the surface;
  • Figure 9 illustrates a view of a processed image of a strongly myopic eye, dressed to show radius of curvature of the surface
  • Figure 10 illustrates schematically a lateral cross-section through the eye showing various axial dimensions that can be used to correct a scanned image
  • Figure 11 is a schematic block diagram of apparatus according to the invention.
  • Magnetic Resonance Imaging is now a well-established technique for obtaining three-dimensional images of the human or animal body. Using MRI instruments, images with a resolution of a fraction of a millimetre can be obtained. A description of the theory underlying MRI and of MRI instruments is beyond the scope of this document. For this purpose reference might be made to: MRI from Picture to Proton. By Donald W. McRobbie, Elizabeth A. Moore, Martin J. Graves, Martin R. Prince. Publisher: Cambridge University Press (December 5, 2002). ISBN: 0521523192; MRI : Basic Principles and Applications. By Mark A. Brown, Richard C. Semelka. Publisher: Wiley-Liss; 3 edition (September 5, 2003). ISBN: 0471433101.
  • FIGS. 1A and 1 B show transverse cross-sections of 3-D images of the eye acquired using a Siemens Trio 3-Tesla MRI scanner, with scanning sequences that are optimised for revealing detail in the eye.
  • Figure 1A The sequence described above for Figure 1A, is known as a HASTE sequence - Half Fourier Acquisition Single Shot Turbo Spin Echo.
  • This technique is a heavily T2 weighted, high speed sequence using a partial Fourier technique, and has high sensitivity for fluid detection and an acquisition time which is faster than conventional spin-echo sequences.
  • the rapidity of the acquisition is important because of the need to acquire a complete image of the eye in a short period of time, so that the patient is able to maintain a relatively stable ocular fixation, thus reducing motion-induced blurring.
  • Figure 1A was acquired in 5.5 minutes.
  • the enhanced fluid sensitivity is created by choosing relatively long TR and TE timing parameters. Because the eyes contain fluid-filled chambers, they are seen to be extremely bright, with high contrast relative to the surroundings, in the HASTE image. This means they can be automatically identified and extracted from the MR image using the procedures described below.
  • Both scans are spin-echo sequences (to reduce susceptibility distortions), and employ local shimming around the acquisition volume. Again, shimming locally around the eyes increases the spatial integrity of the images.
  • the images were acquired using a whole-head radio frequency coil array, which allows parallel-acquisition techniques to be used (GRAPPA 4 in the image of Figure 1A). This again allows rapid acquisition of the images.
  • GRAPPA 4 in the image of Figure 1A.
  • a dedicated ocular imaging coil consisting of a small single coil placed directly over the eye.
  • Such coils are typically custom-made to order, and are not standard items supplied by the MRI manufacturer.
  • the image shown in Figure 1 B is a T1 -weighted scan which reveals the fine detail of the eye, particularly the lens and ciliary body. Whilst this image may be extremely useful for certain applications, it is not easy to generate from it accurate data relating to the envelope or tunic of the eyeball.
  • the boundaries between sclera surface and the orbit are not as well defined as in the image of Figure 1A. Note that the two images shown in Figures 1A and 1 B are optimised for different purposes. It is proposed to use the T2-weighted images, as in 1A, for automatic segmentation and 3D characterisation of the shape of the eye.
  • T1 weighted images such as 1 B
  • the fine soft-tissue anatomical detail revealed by T1 weighted images can also be used to provide other morphological information about the eye, such as the position and dimensions of the lens, configuration and dimensions of the ciliary body, the thickness of the sclera, and most importantly the position of the optic nerve and the fovea.
  • These anatomical parameters can also be used to inform the visualisation of the 3D eye models described in this document.
  • the position of the Fovea determined using the T1 weighted image shown in Figure 1 B, can be "painted on" to the visualisations shown in Figures 6 to 9 discussed below.
  • the 3-D MRI images collected by the scanner are loaded into a modified version of a program called "mri ⁇ dX".
  • the basic program has been developed for analysing MR images of the brain, and is available for download from the web site of the Aston University, Birmingham, UK (www.aston.ac.uk).
  • the program used here is modified to include some features for morphometric eye-shape analysis as will be described.
  • the brightness and contrast of the image are adjusted so that the eye takes on a uniform white appearance. This may be done manually, with an operator adjusting the viewed image to optimise these qualities, or may be performed automatically.
  • the resulting image allows automatic segmentation (i.e. identification) of the eye from the rest of the image.
  • the operator places the crosshairs in the centre of the bright eye and selects a flood-fill option, which causes those areas of the image having a brightness within some specified range (e.g. 25%) of the brightness of the location of the crosshairs, to be filled with a uniform colour.
  • a flood-fill option which causes those areas of the image having a brightness within some specified range (e.g. 25%) of the brightness of the location of the crosshairs, to be filled with a uniform colour.
  • the entire globe of the eye, including anterior and posterior chambers, is then filled with this colour.
  • This procedure is illustrated in Figure 2, which shows a 2-D section through the acquired 3-D image. This procedure may be fully automatic, making use of some pattern recognition software to locate the approximate centre of an eye, and performing the flood-fill based upon the brightness at this centre.
  • a surface mesh is fitted to the outside of the eye.
  • Many algorithms are available for this purpose.
  • a preferred algorithm is however a "shrink-wrap" algorithm, in which a triangular mesh model of a simple sphere is first constructed. [ see van Overveld, K., Wyvill., B. (2004). "Shrinkwrap: An efficient adaptive algorithm for triangulating an iso-surface. The Visual Computer: International Journal of Computer Graphics. 20(6). 362 - 379.] This sphere consists of over 32000 vertices and is centred on the geometrical centre of the eye, such that the sphere encloses the whole of the shaded eye.
  • the constructed eye model clearly looks like an eye, but is jagged in nature. This is because the shrink-wrapping tightly wraps around the sharp edges of the voxels that make up the MRI image. These voxels might be, for example, 0.5x0.5x1 mm in dimension. This might appear to be a fundamental limit on the resolution of the approach described here, were it not for the fact that the eye's surface should be locally smooth.
  • smoothing the mesh e.g. taking a weighted sum of the local vertex positions at each point of the mesh, a greatly improved image can be obtained. The result is illustrated in Figure 4.
  • this process can be thought of as using a mesh that has elasticity, so that it does not turn tightly round the edges of the voxels in the MRI image. It is thus possible to construct a representation of the eye that actually has an intrinsically higher-resolution than does the initial scan.
  • Figure 5 is a flow diagram illustrating the key steps in the 3-D image processing procedure.
  • a 3-dimensional model of the eye we can use it to calculate morphological parameters of interest and colour-code the model for 3-D visualisation.
  • a software package such as GEOMVIEW (a general mesh viewer) may be used to visualise the 'dressed' models. Visualisation allows the model to be rotated in real-time so that the eye can be viewed from any angle
  • this shows a model, obtained using the above procedure, of an emmetrope (i.e. no refractive error).
  • the image has been colour coded based on the distance of the surface from the corneal pole, where Dark green (5) ⁇ 20 mm, Lighter Green (4) 20-21 mm, Light Green (3) 21-22 mm, Blue 22-23 (2) mm, Magneta (1 ) 23-24 mm, Cyan 24-25 mm, Yellow 25-26 mm, Orange 26-27 mm, Dark Orange 27-28 mm, Red 28+ mm.
  • the contours also give the viewer a feeling of eye shape.
  • Figure 7 shows a model obtained for an eye of a person who is strongly myopic (-6.5D).
  • the increased axial length can clearly be seen (the red region (6) represents > 28 mm). This is a known characteristic of myopia.
  • FIG. 8 shows the radius of curvature for an emmetropic eye (no refractive error) by way of a colour coding scheme.
  • the blue region 10 identifies a region in which the eye is "pushed-in” compared to the mean radius of curvature (i.e. radius of curvature flatter than the mean), whilst red colours 11 are regions that are "bulging” out (i.e. radius of curvature steeper than the mean).
  • the image shown in Figure 9 shows the same kind of curvature analysis, but this time for a -6.5D myopic eye. Images such as these can prove extremely valuable for determining how the shape of the eye is modified as myopia develops.
  • MRI computed tomography
  • other, more accurate imaging technologies can be used to correct MRI images.
  • these techniques cannot themselves provide a complete 3D model of the eye, they allow some critical dimensions of the eye to be accurately measured (sub mm). Examples of some such dimensions are depicted in Figure 10. If these critical dimensions are known, the segmented MRI data can be post-hoc corrected using an affine spatial co-ordinate transform that best fits the MRI model to the measured lengths. Ocular dimensions are obtained for each eye, non-invasively, using one or more of the following:
  • the ORBSCAN (Bausch & Lomb) takes 40 slit-sections of the cornea during 2 scans, each scan lasting 0.7 seconds. Each slit section is similar to an optical section viewed through a slit lamp. The instrument thus provides a full detailed surface topography of corneal radius, corneal apex location and central and peripheral corneal thickness.
  • the IOLMASTER uses partial coherent interferometry to provide high-resolution measures of overall axial length. Measurement of the anterior chamber depth is by image analysis of an Optical section'. In addition the instrument can measure corneal radius and visible iris diameter.
  • the ACMASTER again uses partial coherent interferometry to provide high-resolution measures of lens thickness, corneal thickness and anterior chamber depth.
  • the Oculus PENTACAM system (Oculus, Giessen, Germany) uses a rotating Scheimpflug principle to provide measures of anterior chamber volume and height. Central and peripheral measures of corneal thickness and corneal volume are also available.
  • the apparatus 10 can comprise an MRI system such as a Siemans Trio 3-Tesla MRI scanner, consisting of a 3 tesla magnet 12 with associated gradient coils, a transmit/receive body coil and a patient bed 16, coupled with a phased-array radio-frequency (RF) head coil 14 capable of collecting high resolution images of the head and eyes.
  • MRI system such as a Siemans Trio 3-Tesla MRI scanner, consisting of a 3 tesla magnet 12 with associated gradient coils, a transmit/receive body coil and a patient bed 16, coupled with a phased-array radio-frequency (RF) head coil 14 capable of collecting high resolution images of the head and eyes.
  • the gradients are switched using a set of gradient amplifiers 18 and the coils are driven and monitored using RF amplifiers and receivers 20.
  • computers 24 and 26 can comprise a processor for data analysis and image processing.
  • the apparatus 10 is configured so as to allow the collection and analysis of high-resolution T1 and T2-weighted images of the eye in 3-dimensions.

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Abstract

Procédé d’imagerie d’un œil humain ou animal, comprenant la configuration d’un instrument d’imagerie par résonance magnétique pour mettre à disposition un contraste élevé entre des matières fluides et non fluides, l’acquisition d’une image tridimensionnelle de l’œil et de ses environs à l’aide de l’instrument d’imagerie par résonance magnétique lorsqu’il est configuré ainsi, et le traitement de l’image acquise pour obtenir une enveloppe tridimensionnelle de l’œil ou d’une partie de celui-ci.
PCT/GB2005/004577 2004-11-30 2005-11-30 Imagerie par résonance magnétique oculaire Ceased WO2006059089A1 (fr)

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GB0426243.2 2004-11-30

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CN116636925A (zh) * 2023-05-29 2023-08-25 天津医科大学眼科医院 基于3d打印技术的眼球模型条带设计方法

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Cited By (16)

* Cited by examiner, † Cited by third party
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US10258285B2 (en) 2004-05-28 2019-04-16 St. Jude Medical, Atrial Fibrillation Division, Inc. Robotic surgical system and method for automated creation of ablation lesions
US9566119B2 (en) 2004-05-28 2017-02-14 St. Jude Medical, Atrial Fibrillation Division, Inc. Robotic surgical system and method for automated therapy delivery
US10863945B2 (en) 2004-05-28 2020-12-15 St. Jude Medical, Atrial Fibrillation Division, Inc. Robotic surgical system with contact sensing feature
US8206383B2 (en) 2004-05-28 2012-06-26 St. Jude Medical, Atrial Fibrillation Division, Inc. Radio frequency ablation servo catheter and method
US8551084B2 (en) 2004-05-28 2013-10-08 St. Jude Medical, Atrial Fibrillation Division, Inc. Radio frequency ablation servo catheter and method
US8528565B2 (en) 2004-05-28 2013-09-10 St. Jude Medical, Atrial Fibrillation Division, Inc. Robotic surgical system and method for automated therapy delivery
US7974674B2 (en) * 2004-05-28 2011-07-05 St. Jude Medical, Atrial Fibrillation Division, Inc. Robotic surgical system and method for surface modeling
US9782130B2 (en) 2004-05-28 2017-10-10 St. Jude Medical, Atrial Fibrillation Division, Inc. Robotic surgical system
US9204935B2 (en) 2004-05-28 2015-12-08 St. Jude Medical, Atrial Fibrillation Division, Inc. Robotic surgical system and method for diagnostic data mapping
US8755864B2 (en) 2004-05-28 2014-06-17 St. Jude Medical, Atrial Fibrillation Division, Inc. Robotic surgical system and method for diagnostic data mapping
US8407023B2 (en) 2005-05-27 2013-03-26 St. Jude Medical, Atrial Fibrillation Division, Inc. Robotically controlled catheter and method of its calibration
US9237930B2 (en) 2005-05-27 2016-01-19 St. Jude Medical, Atrial Fibrillation Division, Inc. Robotically controlled catheter and method of its calibration
US8155910B2 (en) 2005-05-27 2012-04-10 St. Jude Medical, Atrial Fibrillation Divison, Inc. Robotically controlled catheter and method of its calibration
WO2008045828A3 (fr) * 2006-10-12 2008-08-28 St Jude Medical Atrial Fibrill Système chirurgical robotique et méthode de modelage de surface
CN116636925A (zh) * 2023-05-29 2023-08-25 天津医科大学眼科医院 基于3d打印技术的眼球模型条带设计方法
CN116636925B (zh) * 2023-05-29 2024-05-10 天津医科大学眼科医院 基于3d打印技术的眼球模型条带设计方法

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