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`Smith & Nephew Ex. 1073
`IPR Petition - USP 9,295,482
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`US 7,634,119 B2
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`2002/0087274 A1
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`3/2004 Bonutti
`3/2004 Carignan et al.
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`1/2006 Tamez-Pena et al.
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`2/2005 TfiIT1eZ'PeI13 Gt €11~
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`5/2002 Bradbury etal.
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`7/2002 Alexander et al.
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`TameZ'Pe“aa 1 6‘ 31» “MR{,1S°”°Pi°_ ReS°1“‘i°“ RGEHSHUCHOH
`F“’.m TW° O.“h°g°“"1S°.*“‘S’ Pr?’°ee°.““gS °“h‘°' SHE The Inter‘
`national Society for Optical Engineering SPIE-INT. V01. 4322, pp.
`8797, 2001.
`Blazina, MD et al. “Patellofemoral Replacement: Utilizing acust0m-
`ized Femoral Groove Replacement”, Techniques Orthop, 5(1):53-55
`(1990)
`* cited by examiner
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`US 7,634,119 B2
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`1
`FUSION OF MULTIPLE IMAGING PLANES
`FOR ISOTROPIC IMAGING IN MRI AND
`QUANTITATIVE IMAGE ANALYSIS USING
`ISOTROPIC OR NEAR-ISOTROPIC IMAGING
`
`PRIORITY CLAIM
`
`This application claims the benefit of U.S. Provisional
`Patent Application Ser. No. 60/431,176, filed Dec. 4, 2002,
`the entirety of which is herein incorporated by reference.
`
`STATEMENT AS TO RIGHTS TO INVENTIONS
`MADE UNDER FEDERALLY SPONSORED
`RESEARCH AND DEVELOPMENT
`
`Certain aspects of the invention described below were
`made with United States Government
`support under
`Advanced Technology Program 70NANBOH3016 awarded
`by the National
`Institute of Standards and Technology
`(NIST). The United States Government may have rights in
`certain of these inventions.
`
`TECHNICAL FIELD
`
`This invention relates generally to medical imaging, and
`more specifically to medical imaging that facilitates analysis
`in more than one dimension, e.g. magnetic resonance imaging
`(MRI). More particularly the invention relates to isotropic
`imaging techniques used in medical imaging, such as MRI, to
`improve quantitative image analysis.
`
`BACKGROUND OF THE INVENTION
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`Magnetic resonance imaging (MRI) is a noninvasive imag-
`ing technique that provides clinicians and diagnosticians with
`information about the anatomical structure and condition of a
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`region of interest within a subject. See, for example, U.S. Pat.
`No. 5,671,741 to Lang et al. issued Sep. 30, 1997 for “Mag-
`netic Resonance Imaging Technique for Tissue Characteriza-
`tion,” U.S. Pat. No. 6,219,571 B1 to Hargreaves et al. issued
`Apr. 17, 2002, for “Magnetic Resonance Imaging Using
`Driven Equilibrium Fourier Transform,” U.S. Pat. No. 6,479,
`996 to Hoogeveen et al. issued Nov. 12, 2002 for “Magnetic
`Resonance Imaging of Several Volumes,” U.S. patent appli-
`cation Ser. No. 2002/0087274 A1 to Alexander et al. pub-
`lished Jul. 4, 2002 for “Assessing the Condition of a Joint and
`Preventing Damage.” Commonly, in MRI, a substantially
`uniform temporally constant main magnetic field (B0) is set
`up in an examination region in which a subject being imaged
`or examined is placed. Via radio frequency (RF) magnetic
`field (B1) excitation and manipulations, selected magnetic
`dipoles in the subject that are otherwise aligned with the main
`magnetic field are tipped to excite magnetic resonance. The
`resonance is typically manipulated to induce detectable mag-
`netic resonance echoes from a selected region of the subject.
`In imaging, the echoes are spatially encoded via magnetic
`gradients set up in the main magnetic field. The raw data from
`the MRI scanner is collected into a matrix, commonly known
`as k-space. By employing inverse Fourier, two-dimensional
`Fourier, three-dimensional Fourier, or other known transfor-
`mations, an image representation of the subject is recon-
`structed from the k-space data.
`Conventional MRI scans produce a data volume, wherein
`the data volume is comprised of voxels having three-dimen-
`sional characteristics. The voxel dimensions are determined
`
`by the physical characteristics of the MRI machine as well as
`user settings. Thus, the image resolution of each voxel will be
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`limited in at least one dimension, wherein the loss of resolu-
`tion in at least one dimension may lead to three-dimensional
`imaging problems.
`There are many applications in which depth or three-di-
`mensional (“3D”) information is useful for diagnosis and
`formulation of treatment strategies. For example, in imaging
`blood vessels, cross-sections merely show slices through ves-
`sels, making it difficult to diagnose stenosis or other abnor-
`malities. Likewise, interventional imaging, such as needle
`tracking, catheter tracking, and the like, requires 3D informa-
`tion. Also, depth information is useful in the so-called inter-
`active imaging techniques in which images are displayed in
`real or near-real time and in response to which the operator
`can adjust scanning parameters, such as view angle, contrast
`parameters, field of view, position, flip angle, repetition time,
`and resolution.
`
`imaging generally involves either
`Three-dimensional
`acquiring multiple two-dimensional or slice images that are
`combined to produce a volumetric image or, alternately, the
`use of three-dimensional imaging techniques. Much effort at
`improving the efficiency ofvolume imaging has been focused
`on speeding up the acquisition. For example, many two-
`dimensional fast scan procedures have been adapted to three-
`dimensional imaging. Likewise, efforts have been made to
`improve reconstruction speed and efiiciency, for example,
`through the use of improved reconstruction algorithms. Nev-
`ertheless, three-dimensional imaging remains relatively slow.
`However, current MRI acquisition techniques do not pro-
`vide high resolution in all planes and quantitative image
`analysis using isotropic or near-isotropic imaging. Accord-
`ingly, the present invention contemplates new and improved
`magnetic resonance imaging techniques.
`An additional problem not addressed by current 3D MRI
`scanning methods is the reduction of partial volume effects.
`Partial volume effects are caused when a voxel falls within the
`
`boundary between two scarmed objects. For example, if a
`patient’s knee is being sagittally scarmed, a voxel may be
`orientated such that part of the voxel falls within the femur
`and part falls within a space outside ofthe femur. MR imaging
`will average the overall gray value over the entire voxel. The
`lower the scanning resolution the greater the partial volume
`effects. In a 3D scan, where there is low resolution in at least
`one plane of the scan impact of the partial volume effects is
`greatly increased. Thus, there is a need for methods of form-
`ing 3D MRI scans with reduced impact of partial volume
`effects.
`
`Still further, an additional shortcoming of conventional 3D
`MRI scarming procedures is that boundaries of scarmed
`objects may be missed due to scanning resolution and scan
`orientation. This may occur when a boundary of an object
`being scanned lies between the slice thickness of the scan or
`the boundary of an object is parallel to the imaging plane.
`Therefore there is a need for improved methods for reducing
`the likelihood of missed boundaries.
`
`SUMMARY OF THE INVENTION
`
`The invention addresses the problem that with current 3D
`image acquisition techniques the in-plane (x-y plane) resolu-
`tion ofthe slices is usually at least 3 times higher than the slice
`thickness (in z-dimension). The low resolution between the
`slices (typically in Z-direction) leads to limitations with
`respect to 3D image analysis and visualization. The structure
`of 3-dimensional objects carmot be described with the same
`accuracy in all three dimensions. Partial volume effects affect
`interpretation and measurements in the z-dimension to a
`greater extent than in the x-y plane. Thus, resolution and
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`accuracy of multiplanar reformations depend on the slicing
`direction through the volumetric data.
`In addition,
`the invention also addresses the issue of
`increasing accuracy of tissue segmentation and/or quantita-
`tive analysis of images, such as MR images. For example,
`after obtaining an isotropic or near-isotropic three-dimen-
`sional MR image (e.g., using pulse sequence acquisition tech-
`niques described herein and known in the field), particular
`tissues can be extracted from the image with greater accuracy
`and, moreover are quantitative. Currently available subjective
`visual inspection techniques are not quantitative and, addi-
`tionally, are often inaccurate.
`Thus, in one aspect, a method of improving resolution of
`images, such as MR images, is provided. In certain embodi-
`ments, the method includes, for example, obtaining at least
`two MR scans (e.g., scans in perpendicular planes) of a body
`part and merging the scans, thereby increasing resolution. In
`any of the methods described herein, the scans may be in any
`plane, for example, sagittal, coronal and/or axial imaging
`planes. Preferably, the second or subsequent scans contain a
`sufficient number of slices to cover the entire field of view of
`
`the first scan. Furthermore, in any of the methods described
`herein, the data obtained from the two or more scans are
`subsequently merged to form a new data volume, which is
`isotropic (or near-isotropic) and has a resolution correspond-
`ing to the in-plane resolution of S1 and S2. Merging may
`include, for example, determining a gray value for each voxel
`(V) of the new (merged) data volume. In certain embodi-
`ments, the gray values are obtained by: (a) determining the
`position in 3D space for V; (b) obtaining (e.g., from the
`original scans) gray values of the scans prior to fusion at this
`position; (c) interpolating (combining) gray values from S1
`and S2 into a single gray value (G); and (d) assigning G to V.
`In any of the methods described herein, any living tissue
`can be imaged, including, but not limited to, joints, bones
`and/or organs (e.g., brain, liver, kidney, heart, blood vessels,
`GI tract, etc.).
`In accordance with the present invention there is provided
`a MRI scanning method, the method comprising, performing
`a first MRI scan ofa body part in a first plane, wherein the first
`MRI scan generates a first image data volume; performing a
`second MRI scan of the body part in a second plane, wherein
`the second MRI scan generates a second image data volume;
`and combining the first and second image data volumes to
`form a resultant image data volume, wherein the resultant
`image data volume is isotropic.
`In accordance with another embodiment of the present
`invention there is provided a method for producing isotropic
`or near-isotropic image data, the method comprising: obtain-
`ing a first image data volume from a first MRI scan in a first
`plane; obtaining a second image data volume from a second
`MRI scan in a second plane; extracting boundary image data
`from each of the first and second image data volumes; com-
`bining said extracted boundary image data to form a resultant
`image data volume.
`In accordance with the present invention there is provided
`a method for generating a three dimensional data volume, the
`method comprising: acquiring at least two data volumes from
`at least two MRI scans performed in two different planes;
`combining the data volumes to form a resultant data volume;
`selecting a therapy in response to the resultant data volume;
`and deriving a shape for an implant.
`The system includes an image analysis method. The image
`analysis is performed by obtaining a first image of a body part
`in a first plane, wherein the first image generates a first image
`data volume; obtaining a second image of the body part in a
`second plane, wherein the second image generates a second
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`image data volume; and combining the first and second image
`data volumes to form a resultant image data volume, wherein
`the resultant image data volume is isotropic. Additionally,
`first and second gray values can be obtained from the first and
`second image data volumes at one or more three-dimensional
`positions. That data can then be interpolated to provide a
`resultant gray value which is then assigned to a voxel in the
`three-dimensional position of the resultant data volume. As
`will be appreciated by those of skill in the art, the angle
`between the images can range from about 0° to 180°, or from
`0° to 90°. Once these values have been obtained, a therapy or
`treatment can be selected to complement the data volume. A
`person of skill in the art will appreciate that at least one
`additional image of a body part taken in a plane different than
`any previous plane used can be taken used to generate addi-
`tional image volume. From that image volume, data volume is
`generated which can then be combined with the first and
`second image data volumes to form a resultant data volume.
`Of course, extracting a boundary image data volume from the
`resulting image data volume can also be performed,
`if
`desired.
`
`A method is also described for producing isotropic or near-
`isotropic image data from images. This method generally
`comprises: obtaining a first image data volume from a first
`image in a first plane; obtaining a second image data volume
`from a second image in a second plane; extracting boundary
`image data from each of the first and second image data
`volumes; and combining the extracted boundary image data
`to form a resultant image data volume. Of course, it is pos-
`sible to also obtaining at least one additional image data
`volume from at least one additional image in a plane different
`than the first plane and the second plane; extracting an addi-
`tional boundary image data from the additional image data
`volume; and combining the additional boundary image data
`volume with the resultant image data volume. This resultant
`data can be isotropic or near-isotropic. As will be appreciated,
`the first plane can be at an angle relative to the second plane;
`that angle can be from about 0° to 180° or from about 0° to
`90°.
`
`A method is included for generating a three dimensional
`data volume. Generally, this method includes acquiring at
`least two data volumes from at least two images performed in
`two different planes; combining the data volumes to form a
`resultant data volume; selecting a therapy in response to the
`resultant data volume; selecting an implant; and deriving a
`shape for an implant. The combining step can further include
`obtaining gray values for each data point in each of the data
`volumes; interpolating a resultant gray value from gray val-
`ues; and assigning the resultant value to each data point ofthe
`resultant data volume. Prior to combining the data, data cor-
`responding to any surface can be scarmed in each plane and
`extracted.
`
`Another method for generating three dimensional data is
`also disclosed. This method includes obtaining a first image
`in a first plane producing a first data volume with a default
`resolution; obtaining a second image in a second plane pro-
`ducing a second data volume with the default resolution;
`combining the first and second data volumes to produce a
`resultant data volume, the resultant data volume having a
`resultant resolution. As will be appreciated, the resultant reso-
`lution is greater than the default resolution.
`An image analysis method is disclosed that includes the
`steps of obtaining at least one image of a body part in at least
`a first plane and a second plane, wherein the first plane gen-
`erates a first image data volume and the second plane gener-
`ates a second image data volume; and combining the first and
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`US 7,634,119 B2
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`5
`second image data volumes to form a resultant image data
`volume, wherein the resultant image data volume is isotropic.
`An alternative image analysis method is also disclosed that
`includes obtaining at least one image of a body part in at least
`a first plane and a second plane, wherein the first plane gen-
`erates a first image data volume and the second plane gener-
`ates a second image data volume; and combining the first and
`second image data volumes to form a resultant image data
`volume, wherein the resultant image data volume is near-
`isotropic.
`In accordance with the present invention there is provided
`a method for generating three dimensional MRI scan data, the
`method comprising: performing a first MRI scan in a first
`plane producing a first data volume with a default resolution;
`performing a second MRI scan in a second plane producing a
`second data volume with the default resolution; combining
`the first and second data volumes to produce a resultant data
`volume, the resultant data volume having a resultant resolu-
`tion.
`
`BRIEF DESCRIPTION OF THE FIGURES
`
`FIG. 1 illustrates two MRI scans illustrating data volumes
`S1 and S2; each ofthe scans shows a plurality of image slides
`taken in planes parallel to the initial scan.
`FIG. 2 illustrates a set ofthree voxels produced by an image
`scan illustrating an increased z-axis length.
`FIG. 3 illustrates a first set of three voxels produced by an
`image scan illustrating a z-axis component.
`FIG. 4 illustrates a second set of three voxels produced by
`an image scan illustrating a z-axis component.
`FIG. 5 illustrates a resultant set ofnine voxels generated by
`the methods in accordance with the present invention.
`FIG. 6 illustrates a combined boundary image data
`extracted from two image scans.
`FIG. 7 illustrates a three-dimensional implant design gen-
`erated from at least two image scans.
`FIGS. 8A-C illustrate flow charts illustrating processes of
`the invention.
`
`DETAILED DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`The following description is presented to enable any per-
`son skilled in the art to make and use the invention. Various
`
`modifications to the embodiments described will be readily
`apparent to those skilled in the art, and the generic principles
`defined herein can be applied to other embodiments and
`applications without departing from the spirit and scope of
`the present invention as defined by the appended claims.
`Thus, the present invention is not intended to be limited to the
`embodiments shown, but is to be accorded the widest scope
`consistent with the principles and features disclosed herein.
`To the extent necessary to achieve a complete understanding
`of the invention disclosed, the specification and drawings of
`all issued patents, patent publications, and patent applications
`cited in this application are incorporated herein by reference.
`As will be appreciated by those of skill in the art, methods
`recited herein may be carried out in any order of the recited
`events which is logically possible, as well as the recited order
`of events. Furthermore, where a range of values is provided,
`it is understood that every intervening value, between the
`upper and lower limit of that range and any other stated or
`intervening value in that stated range is encompassed within
`the invention. Also, it is contemplated that any optional fea-
`ture ofthe inventive variations described may be set forth and
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`claimed independently, or in combination with any one or
`more of the features described herein.
`
`The present invention is of a method of image analysis that
`can be used for improving tissue segmentation and/or quan-
`tifying image analysis. Specifically, the present invention
`combines two or more images to achieve high resolution in all
`three-dimensional directions. The principles and operation of
`the method according to the present invention may be better
`understood with reference to the accompanying descriptions.
`1.0 General Overview
`
`According to the present invention, a method of improving
`resolution and/or tissue segmentation of images taken of a
`body part is described. This method typically involves acquir-
`ing at least two images in different planes and combining the
`images to achieve the same (e.g., high) degree ofresolution in
`all directions. The images can be acquired, for example, by
`using an MRI. However, as other imaging devices become
`available, those of skill in the art will appreciate that these
`techniques can be provided to other imaging devices as well,
`without departing from the scope of the invention.
`The methods described herein provide isotropic or near-
`isotropic resolution which results in improved tissue segmen-
`tation. Unlike currently employed visual inspection, which is
`highly subjective, the methods and compositions described
`herein are quantitative and, accordingly, increase the accu-
`racy of diagnosis and design of treatment regimes.
`1.1 Magnetic Resonance Imaging (MRI)
`Describing MRI in general terms, all protons within living
`tissues have an inherent magnetic moment and spin randomly
`giving rise to no net magnetization or direction. When a
`specimen is placed within the magnetic field of the MR scan-
`ner, the protons continue to spin but align themselves parallel
`or anti-parallel to the direction ofthe field (BO) corresponding
`to low and high-energy states respectively. In the course of an
`MR examination, a radiofrequency (RF) pulse (B 1) is applied
`to the sample from a transmitter coil orientated perpendicular
`to B0 and the protons are momentarily tilted out of alignment;
`the precession of the induced net transverse magnetization
`around the axis ofthe static BO field produces a voltage across
`the ends of the receiver coil which is detected as the MR
`
`signal. For a general discussion of the basic MRI principles
`and techniques, see MRI Basic Principles and Applications,
`Second Edition, Mark A. Brown and Richard C. Semelka,
`Wiley-Liss, Inc. (1999); see, also, U.S. Pat. No. 6,219,571 to
`Hargreaves, et a1.
`1.1 High Resolution 3D MRI Pulse Sequences
`MRI employs pulse sequences that allow for better contrast
`of different parts of the area being imaged. Different pulse
`sequences are better suited for visualization of different ana-
`tomic areas. More than one pulse sequence can be employed
`at the same time. A brief discussion of different types ofpulse
`sequences is provided in International Patent Publication WO
`02/22014 to Alexander et al. published Mar. 21, 2002.
`Routine MRI pulse sequences are available for imaging
`tissue,
`such as cartilage,
`include conventional T1 and
`T2-weighted spin-echo imaging, gradient recalled echo
`(GRE)
`imaging, magnetization transfer contrast
`(MTC)
`imaging, fast spin-echo (FSE) imaging, contrast enhanced
`imaging, rapid acquisition relaxation enhancement, (RARE)
`imaging, gradient echo acquisition in the steady state,
`(GRASS), and driven equilibrium Fourier transform (DEFT)
`imaging. As these imaging techniques are well known to one
`of skill in the art, e. g. someone having an advanced degree in
`imaging technology, each is discussed only generally herein-
`after.
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`US 7,634,119 B2
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`7
`1.2. Measurement of T1 and T2 Relaxation
`
`As a result of random thermal motion, the proton spins
`within a sample lose coherence with one another. This loss of
`coherence results in signal decay. The time taken for the MR
`signal to return to zero depends on many factors, one is the
`rate at which the energized spins lose excess energy relative to
`their immediate environment. This phenomenon called spin-
`lattice, or T1 relaxation, affects mainly magnetization parallel
`to B0 and leads to a net loss of energy from the spin system.
`Another phenomenon that is observed is that the spins of
`neighboring protons tend to drift out of alignment with one
`another as a result of slight differences in frequency. This
`causes a loss in phase coherence, referred to as spin- spin or T2
`relaxation. T2 relaxation affects the transverse component of
`the magnetization but does not cause a net loss of energy.
`Conventional T1 and T2 -weighted MRI depict living tissue
`such as articular cartilage, and can demonstrate defects and
`gross morphologic changes. One of skill in the art could
`readily select a T1 or T2-weighted MRI depending on the
`structure to be imaged. For example, T1-weighted images
`show excellent intra-substance anatomic detail of certain tis-
`
`sue such as hyaline cartilage while T2-weighted imaging
`provides a better depiction ofjoint effusions and thus surface
`cartilage abnormalities.
`1.3 Gradient-Recalled Echo (GRE) Imaging
`Gradient-recalled echo (GRE) imaging has 3D capability
`and the ability to provide high resolution images with rela-
`tively short scan times. Fat suppressed 3D spoiled gradient
`echo (FS-3D-SPGR) imaging has been shown to be more
`sensitive than standard MR imaging for the detection of hya-
`line cartilage defects such as those typically occurring in the
`knee.
`
`1.4 Magnetization Transfer Contrast Imaging
`Magnetization transfer imaging can be used to separate
`articular cartilage from adj acent joint fluid and inflamed syn-
`ovium.
`
`1.5 Fast Spin-Echo (FSE) Imaging
`Fast spin-echo (FSE) imaging is another useful pulse
`sequence MRI technique. Incidental magnetization transfer
`contrast contributes to the signal characteristics of on fast
`spin-echo images and can enhance the contrast between tis-
`sues. Sensitivity and specificity of fast spin-echo imaging
`have been reported to be 87% and 94% in a study with
`arthroscopic correlation.
`1.6 Echo Planar Imaging (EPI)
`Echo planar imaging (EPI) is an imaging technique in
`which a series of echoes is rapidly induced following a single
`radiofrequency (RF) pulse. More specifically, an RF pulse
`and a slice select gradient are applied to excite resonance in a
`selected slice and a phase encode gradient is applied to phase
`encode the resonance. A series of frequency encode or read
`gradients of alternating polarity is applied in successive fash-
`ion. During each read gradient, a magnetic resonance signal
`or echo is read out. Between each read gradient, a short pulse
`or blip along the phase encode gradient axis is applied to
`increment the phase encoding ofthe resonance by a line in the
`selected slice. A one-dimensional inverse Fourier transform
`
`of each echo provides a projection of the spin distribution
`along the read axis. A second inverse Fourier transform along
`the phase encoded echoes provides a second dimension of
`spatial encoding. Typically, the phase encode gradient blips
`are selected of an appropriate magnitude that data for a com-
`plete field of view is taken following each RF pulse. The total
`sampling time is determined by the number of sampled points
`per read gradient and the number of phase encode gradient
`steps.
`
`8
`Echo volume imaging extends echo planar imaging tech-
`niques to multiple planes. After performing the above-de-
`scribed echo planar imaging sequence, a pulse or blip along a
`secondary phase encoding axis is applied. Typically, the sec-
`ondary phase encoding blips step the phase encoding along an
`axis perpendicular to the primary phase encode and read axes.
`Thereafter, phase encode gradient blips are applied between
`each read gradient to step line by line in the primary phase
`encode direction. Because the phase encode blips in the first
`k-space plane move the phase encoding to one extreme edge
`of the field of view, the phase encoding blips in the second
`k-space plane in the secondary phase encode direction are
`typically of the opposite polarity to step the phase encoding
`back in the opposite direction. In this manner, the multiple
`planes are aligned, but offset in steps in the z-direction. One
`disadvantage of the above echo planar imaging and echo
`volume imaging techniques is that the trajectory through
`k-space is reversed in time for alternate phase encode lines or
`views. This causes phase discontinuities that can result in
`ghosting.
`Spiral echo planar imaging techniques are also known, in
`which the applied x- and y-gradient pulses, i.e., along the
`traditional read and phase encode axes, are sinusoidally vary-
`ing and linearly increasing. In this manner, data sampling
`commences at the center of the field of view and spirals
`outward, covering the field of view along a spiral k-space
`trajectory. One of the drawbacks of spiral echo planar imag-
`ing, however, is that it is a single slice technique. To obtain
`multiple slices, the spiral echo planar imaging technique is
`repeated multiple times. An RF excitation pulse and slice
`select gradient followed by sinusoidally varying and linearly
`increasing x and y-gradients are applied for each slice to
`achieve coverage of the volume of interest.
`1.7 Contrast Enhancing Imaging
`The use of gadolinium in imaging has been applied in
`several different forms. For example, direct magnetic reso-
`nance (MR) arthrography, wherein a dilute solution contain-
`ing gadolinium is injected directly into a tissue (e.g., joint),
`improves contrast between cartilage and the arthrographic
`fluid. Indirect MR arthrography, with a less invasive intrave-
`nous injection, can also been applied. Gadolinium enhanced
`imaging has the potential to monitor glycosaminoglycan con-
`tent, which may have implications for longitudinal evalua-
`tions of injured soft tissue such as cartilage.
`1.8 Driven Equilibrium Fourier Transformation
`Another 3D imaging method that has been developed is
`based on the driven equilibrium Fourier transform (DEFT)
`pulse sequence (US. Pat. No. 5,671,741 to Lang et al. issued
`Sep. 30, 1997), and may be specifically utilized for soft tissue
`(e.g., cartilage) imaging. DEFT provides an effective tradeoff
`between T2/T1 weighting and spin density contrast that
`delineates the structures of interest. Contrast-to-noise ratio
`
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`may, in certain tissues/structures, be greater with DEFT than
`with spoiled gradient echo (SPGR). DEFT is an alternative
`approach to SPGR. DEFT contrast is very well suited to
`imaging articular cartilage. Synovial fluid is high in signal
`intensity, and articular cartilage intermediate in signal inten-
`sity. Bone is dark, and lipids are suppressed using a fat satu-
`ration pulse.
`1.9 A Representative Example of MR Imaging
`A MR image can be performed using a whole body magnet
`operating at a field strength of 1.5 T (GE Sigma, for example,
`equipped with the GE SR-120 high speed gradients [2.2
`Gauss/cm in 184 p.sec risetimes]). Prior to MR imaging,
`external markers filled with Gd-DTPA (Magnevist®, Berlex
`Inc., Wayne, N.J.) doped water (T1 relaxation time approxi-
`mately 1.0 sec) can be applied to the skin. External markers
`._4
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`US 7,634,119 B2
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`9
`can be included in the field of View of all imaging studies.
`Patients can be placed in the scarmer in supine position and
`the appropriate area imaged. After an axial scout sequence,
`coronal and sagittal T1-weighted images can be acquired
`using the body coil (spin-echo, TR:500 msec, TE:15 msec,
`1 excitation (NEX), matrix 256>128 elements, field of View
`(FOV) 48 cm, slice thickness 7 mm, interslice spacing 1 mm).
`The scarmer table can then be moVed to obtain coronal and
`
`sagittal images using the same sequence parameters. These
`T1-weighted scans can be employed to identify axes that can
`be used later for defining the geometry of the tissue. A rapid
`scout scan can be acquired in the axial plane using a gradient
`echo sequence (GRASS, 2D Fourier Transform (2DFT),
`TR:50 msec, TE:10 msec,
`flip angle 40°,
`1 excitation
`(NEX), matrix 256><128 elements, field ofView (FOV) 24 cm,
`slice thickness 7 mm, interslice spacing 3 mm). This scout
`scan can be used to determine all subsequent high resolution
`imaging sequences centered oVer the body part. Additionally,
`using the graphic, image based sequence prescription mode
`provided with the scanner software, the scout scan can help to
`ensure that all external markers are included in the field of
`
`View of the high resolution MR sequences.
`There are seVeral issue