Smith & Nephew Ex. 1079
`IPR Petition - USP 8,657,827
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`The invention was made by an agency of the United States Government or under a contract with
`an agency of the United States Government.
`X No.
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`Yes, the name of the U.S. Government agency and the Government contract
`number are:
`
`Respectfully submitted,
`
`Date:
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`By:
`
`
`
`Dalma S. Pasternak
`
`Registration No. 41,411
`Attorney for Applicants
`
`ROBINS & PASTERNAK LLP
`545 Middlefield Road, Suite 180
`Menlo Park, CA 94025
`Tel; (650) 325-7812
`Fax: (650) 325-7823
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`U.S. Provisional Patent Application
`
`of
`
`Daniel STEINES
`
`for
`
`FUSION OF MULTIPLE IMAGING PLANES FOR ISOTROPIC
`
`IMAGING IN MRI AND QUANTITATIVE IMAGE ANALYSIS
`
`USING ISOTROPIC OR NEAR ISOTROPIC IIVIAGING
`
`Atty Docket No.: 6750-001 2P
`
`ROBINS & PASTERNAK LLP
`
`545 Middlefield Road, Suite 180
`Menlo Park, CA 94025
`Te1.: (650) 325-7812
`Fax: (650)325-7823
`
`-111-
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`6750-001 2P
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`FUSION OF MULTIPLE Il\/IAGING PLANES FOR ISOTROPIC IMAGING IN MRI
`
`AND QUANTITATIVE IMAGE ANALYSIS USING ISOTROPIC OR NEAR
`
`ISOTROPIC IMAGING
`
`TECHNICAL FIELD
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`This invention relates generally to magnetic resonance imaging (MRI), and more
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`particularly the invention relates to isotropic imaging techniques in MRI, thereby
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`improving quantitative image analysis.
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`BACKGROUND
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`Magnetic resonance imaging (MRI) is a noninvasive imaging technique that
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`provides clinicians and diagnosticians with information about the anatomical structure
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`and condition of a region of interest within a subject. See, for example, U.S. Patent No.
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`5,671,741; U.S. Patent No. 6,219,571 B1; U.S. Patent No. 6,479,996; U.S. Patent
`
`Application No. 2002/0087274 A1. Commonly, in MRI, a substantially unifonn
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`temporally constant main magnetic field (B0) is set up in an examination region in which
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`a subject being imaged or examined is placed. Via radio frequency (RF) magnetic field
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`(B1) excitation and manipulations, selected magnetic dipoles in the subject that are
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`otherwise aligned with the main magnetic field are tipped to excite magnetic resonance.
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`The resonance is typically manipulated to induce detectable magnetic resonance echoes
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`from a selected region of the subject. In imaging, the echoes are spatially encoded via
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`magnetic gradients set up in the main magnetic field. The raw data from the MRI
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`scanner is collected into a matrix, commonly known as k-space. By employing inverse
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`Fourier, two-dimensional Fourier, three—dimensional Fourier, or other known
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`transformations, an image representation of the subject is reconstructed from the k-space
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`data.
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`There are many applications in which depth or 3D infomiation is useful for
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`diagnosis and formulation of treatment strategies. For example, in imaging blood vessels,
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`cross—sections merely show slices through vessels, making it difficult to diagnose stenosis
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`or other abnormalities. Likewise, interventional imaging, such as needle tracking,
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`catheter tracking, and the like, requires 3D information. Also, depth information is useful
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`in the so-called interactive imaging techniques in which images are displayed in real or
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`near—real time and in response to which the operator can adjust scanning parameters, such
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`as view angle, contrast parameters, field of view, position, flip angle, repetition time, and
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`resolution.
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`Three-dimensional imaging generally involves either acquiring multiple two-
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`dimensional or slice images that are combined to produce a volumetric image or,
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`alternately, the use of three-dimensional imaging techniques. Much effort at improving
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`the efficiency of volume imaging has been focused on speeding up the acquisition. For
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`example, many two-dimensional fast scan procedures have been adapted to three-
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`dimensional imaging. Likewise, efforts have been made to improve reconstruction speed
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`and efficiency, for example, through the use of improved reconstruction algorithms.
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`Nevertheless, three-dimensional imaging remains relatively slow.
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`However, current MRI acquisition techniques do not provide high resolution in all
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`planes and quantitative image analysis using isotropic or near isotropic imaging.
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`Accordingly, the present invention contemplates new and improved magnetic resonance
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`imaging techniques.
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`SUMMARY OF THE INVENTION
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`The invention addresses the problem that with current MRI acquisition techniques
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`the in—plane (x-y plane) resolution of the slices is usually at least 3 times higher than the
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`slice thickness (in z—dimension). The low resolution between the slices (typically in z-
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`direction) leads to limitations with respect to 3D image analysis and visualization. The
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`structure of 3—dimensional objects cannot be described with the same accuracy in all three
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`dimensions. Partial volume effects affect interpretation and measurements in the z-
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`dimension to a greater extent than in the x—y plane. Resolution and accuracy of
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`multiplanar reforrnations depend on the slicing direction through the volumetric data set.
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`In addition, the invention also addresses the issues of increasing accuracy of
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`tissue segrnentalion and/or quantitative analysis of MR images. For example, after
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`obtaining an isotropic or near isotropic three-dimensional MR image (e.g., using pulse
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`sequence acquisition techniques described herein and known in the field), particular
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`6750-00 1 2P
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`tissues can be extracted from the image with greater accuracy and, moreover are
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`quantitative. Currently available subjective visual inspection techniques are not
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`quantitative and, additionally, are often inaccurate.
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`Thus, in one aspect, a method of improving resolution of MR images is provided.
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`In certain embodiments, the method includes obtaining at least two MR scans (e.g., scans
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`in perpendicular planes) of a body part and merging the scans, thereby increasing
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`resolution. In any of the methods described herein, the scans may be in any plane, for
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`example, sagittal, coronal and/or axial imaging planes. Preferably, the second or
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`subsequent scans contain a sufficient number of slices to cover the entire field of view of
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`the first scan. Furthermore, in any of the methods described herein, the data obtained
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`from the two or more scans are subsequently merged to form a new data Volume, which
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`is isotropic (or near-isotropic) and has a resolution corresponding to the in-plane
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`resolution of S1 and S2. Merging may include, for example, determining a gray value for
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`each voxel (V) of the new (merged) data volume.
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`In certain embodiments, the gray
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`values are obtained by: (a) determining the position in 3D space for V; (b) obtaining (e.g.,
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`from the original scans) gray values of the scans prior to fusion at this position; (c)
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`interpolating (combining) gray values from S1 and S2 into a single gray value (G); and
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`(d) assigning G to V.
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`In any of the methods described herein, any living tissue may be imaged,
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`including, but not limited to, joints, bones and/or organs (e.g., brain, liver, kidney, heart,
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`blood vessels, GI tract, etc.).
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`Still further advantages of the present invention will become apparent to those of
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`ordinary skill in the art upon reading and understanding the following detailed description
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`of the preferred embodiments.
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`DETAILED DESCRIPTION
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`The present invention is of a method of magnetic resonance imaging that can be
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`used improving tissue segmentation and/or quantifying image analysis. Specifically, the
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`present invention combines two or more magnetic resonance scans to achieve high
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`resolution in all three-dimensional directions. The principles and operation of the
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`method according to the present invention may be better understood with reference to the
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`accompanying descriptions.
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`Before explaining various embodiments of the invention in detail, it is to be
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`understood that the invention is not limited in its application to the details of construction
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`and the arrangement of the components set forth in the following description. The
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`invention is capable of other embodiments or of being practiced or carried out in various
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`ways. Also, it is to be understood that the phraseology and terminology employed herein
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`is for the purpose of description and should not be regarded as limiting.
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`All publications, patents and patent applications cited herein, whether supra or
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`infra, are hereby incorporated by reference in their entirety.
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`As used in this specification and the appended claims, the singular forms "a," "an"
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`and "the" include plural references unless the content clearly dictates otherwise.
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`General Overview
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`Thus, according to the present invention there is provided a method of improving
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`resolution and/or tissue segmentation of magnetic resonance images of a body part by
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`acquiring at least two MR scans in different planes and combining the scans to achieve
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`the same (e.g., high) degree of resolution in all directions. In addition, the methods
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`described herein provide isotropic or near isotropic resolution which results in improved
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`tissue segmentation. Unlike currently employed visual inspection, which is highly
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`subjective, the methods and compositions described herein are quantitative and,
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`accordingly, increase the accuracy of diagnosis and design of treatment regimes.
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`Additional objects, advantages, and novel features of the present invention will
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`become apparent to one ordinarily skilled in the art upon examination of the following
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`description, which is not intended to be limiting.
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`Ma
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`etic Resonance lma in
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`MRI
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`Describing MRI in general terms, all protons within living tissues have an
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`inherent magnetic moment and spin randomly giving rise to no net magnetization or
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`direction. When a specimen is placed within the magnetic field of the MR scanner, the
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`protons continue to spin but align themselves parallel or antiparallel to the direction of
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`the field (B0) corresponding to low and high energy states respectively. In the course of
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`an MR examination, a radiofrequency (RF) pulse (B1) is applied to the sample from a
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`transmitter coil orientated perpendicular to B0 and the protons are momentarily tilted out
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`of alignment; the precession of the induced net transverse magnetization around the axis
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`of the static Bo field produces a voltage across the ends of the receiver coil which is
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`detected as the MR signal. For a general discussion of the basic MRI principles and
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`techniques, see MRI Basic Principles and Applications, Second Edition, Mark A. Brown
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`and Richard C. Semelka, Wiley-Liss, Inc. (1999); see, also, U.S. Patent No. 6,219,571.
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`1.0. High Resolution 3D MRI Pulse Sequences
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`MRI employs pulse sequences that allow for better contrast of different parts of
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`the area being imaged. Different pulse sequences are better suited for visualization of
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`different anatomic areas. More than one pulse sequence can be employed at the same
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`time. A brief discussion of different types of pulse sequences is provided in International
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`Patent Publication WO O2/22014, incorporated by reference in its entirety herein.
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`Routine MRI pulse sequences are available for imaging tissue, such as cartilage,
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`include conventional T1 and T2-weighted spin-echo imaging, gradient recalled echo
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`(GRE) imaging, magnetization transfer contrast (MTC) imaging, fast spin-echo (FSE)
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`imaging, contrast enhanced imaging, rapid acquisition relaxation enhancement, (RARE)
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`imaging, gradient echo acquisition in the steady state, (GRASS), and driven equilibrium
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`Fourier transform (DEFT) imaging. As these imaging techniques are well known to one
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`of skill in the art, e. g. someone having an advanced degree in imaging technology, each is
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`discussed only generally hereinafter.
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`1.1. Measurement of T1 and T2 Relaxation
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`As a result of random thermal motion, the proton spins within a sample lose
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`coherence with one another and the signal decays. The time taken for the MR signal to
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`return to zero depends on many factors, one is the rate at which the energized spins lose
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`their excess energy to their immediate environment, called spin-lattice or T1 relaxation
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`which affects mainly magnetization parallel to B0 and leads to a net loss of energy from
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`the spin system.
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`Another is the slight difference in frequency in the spins of neighboring protons
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`that tend to drift out of alignment with one another losing their phase coherence and this
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`is called the spin—spin or T2 relaxation. This therefore affects the transverse component of
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`the magnetization but does not cause a net loss of energy.
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`Conventional T1 and T2-weighted MRI depicts living tissue such as articular
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`cartilage, and can demonstrate defects and gross morphologic changes. One of skill in
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`the art could readily select T1 or T2—weighted MRI depending on the structure to be
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`imaged. For example, Tl—weighted images show excellent intra—substance anatomic
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`detail of certain tissue such as hyaline cartilage while T2-weighted imaging demonstrates
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`joint effusions and thus surface cartilage abnonnalities.
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`1.2. Gradient-recalled Echo Imaging
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`Gradient-recalled echo imaging has 3D capability and ability to provide high
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`resolution images with relatively short scan times. Fat suppressed 3D spoiled gradient
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`echo (F S—3D—SPGR) imaging has been shown to be more sensitive than standard MR
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`imaging for the detection of hyaline cartilage defects in the knee.
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`1.3 Magnetization Transfer Contrast Imaging
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`Magnetization transfer imaging can be used to separate articular cartilage from
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`adj accnt joint fluid and inflamed synovium.
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`1.4. Fast Spin—ech0 Imaging
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`Fast spin—echo imaging is another useful pulse sequence MRI technique.
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`Incidental magnetization transfer contrast contributes to the signal characteristics of on
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`fast spin-echo images and can enhance the contrast between tissues. Sensitivity and
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`specificity of fast spin-echo imaging have been reported to be 87% and 94% in a study
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`with arthroscopic correlation.
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`1.5. Echo planar imaging §EPI)
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`Echo planar imaging (EPI) is an imaging technique in which a series of echoes is
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`rapidly induced following a single radiofrequency (RF) pulse. More specifically, an RF
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`pulse and a slice select gradient are applied to excite resonance in a selected slice and a
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`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 fashion. During
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`each read gradient, a magnetic resonance signal or echo is read out. Between each read
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`gradient, a short pulse or blip along the phase encode gradient axis is applied to
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`increment the phase encoding of the resonance by a line in the selected slice. A one-
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`dimensional inverse Fourier transform of each echo provides a projection of the spin
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`distribution along the read axis. A second inverse Fourier transform along the phase
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`encoded echoes provides a second dimension of spatial encoding. Typically, the phase
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`encode gradient blips are selected of an appropriate magnitude that data for a complete
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`field of View is taken following each RF pulse. The total sampling time is determined by
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`the number of sampled points per read gradient and the number of phase encode gradient
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`steps.
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`Echo volume imaging extends echo planar imaging techniques to multiple planes.
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`After performing the above—described echo planar imaging sequence, a pulse or blip
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`’ along a secondary phase encoding axis is applied. Typically, the secondary phase
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`encoding blips step the phase encoding along an axis perpendicular to the primary phase
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`encode and read axes. Thereafter, phase encode gradient blips are applied between each
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`read gradient to step line by line in the primary phase encode direction. Because the
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`phase encode blips in the first k-space plane move the phase encoding to one extreme
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`edge of the field of view, the phase encoding blips in the second k-space plane in the
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`secondary phase encode direction are typically of the opposite polarity to step the phase
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`encoding back in the opposite direction. In this manner, the multiple planes are aligned,
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`but offset in steps in the z—direction. One disadvantage of the above echo planar imaging
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`and echo volume imaging techniques is that the trajectory through k-space is reversed in
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`time for alternate phase encode lines or views. This causes phase discontinuities that can
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`result in ghosting.
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`Spiral echo planar imaging techniques are also known, in which the applied x-
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`and y—gradient pulses, i.e., along the traditional read and phase encode axes, are
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`sinusoidally varying and linearly increasing. In this manner, data sampling commences at
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`the center of the field of view and spirals outward, covering the field of view along a
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`spiral k-space trajectory. One of the drawbacks of spiral echo planar imaging, however, is
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`that it is a single slice technique. To obtain multiple slices, the spiral echo planar imaging
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`technique is repeated multiple times. An RF excitation pulse and slice select gradient
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`followed by sinusoidally varying and linearly increasing x and y-gradients are applied for
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`each slice to achieve coverage of the volume of interest.
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`1.6. Contrast Enhanced Imaging
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`The use of gadolinium in imaging has been applied in several dil'ferent forms.
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`For example, direct magnetic resonance (MR) arthrography, wherein a dilute solution
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`containing gadolinium is injected directly into a tissue (e.g., joint), improves contrast
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`between cartilage and the arthro graphic fluid.
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`Indirect MR arthrography, with a less
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`invasive intravenous injection, can also been applied. Gadolinium enhanced imaging has
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`the potential to monitor glycosaminoglycan content, which may have implications for
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`longitudinal evaluations of injured soft tissue such as cartilage.
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`1.7. Driven Egibrium Fourier Transform
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`Another 3D imaging method that has been developed is based on the driven
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`equilibrium fourier transform (DEFT) pulse sequence (U.S. Pat. No. 5,671,741), and may
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`be specifically utilized for soft tissue (e.g., cartilage) imaging. DEFT provides an
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`effective tradeoff between T2/Tl weighting and spin density contrast that delineates the
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`structures of interest. Contrast—to-noise ratio may, in certain tissues/structures, be greater
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`with DEFT than with spoiled gradient echo (SPGR). DEFT is an alternative approach to
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`SPGR. DEFT contrast is very well suited to imaging articular cartilage. Synovial fluid is
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`high in signal intensity, and articular cartilage intermediate in signal intensity. Bone is
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`dark, and lipids are suppressed using a fat saturation pulse.
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`A25
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`1.8. A Representative Example of MR Imaging
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`A MR image can be performed using a whole body magnet operating at a field
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`strength of 1.5 T (GE Signa, for example, equipped with the GE SR-120 high speed
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`gradients [2.2 Gauss/cm in 184 .1nu.sec risetimes]). Prior to MR imaging, external
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`30
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`markers filled with Gd—DTPA (Magnevist.RTM., Berlex lnc., Wayne, N.J.) doped water
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`(Tl relaxation time approximately 1.0 sec) can be applied to the skin. External markers
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`675 0—O012P
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`can be included in the field of View of all imaging studies. Patients can be placed in the
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`scanner in supine position and the appropriate area imaged. After an axial scout
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`sequence, coronal and sagittal T1-weighted images can be acquired using the body coil
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`(spin-echo, TR=500 msec, TE=l5 msec, 1 excitation (NEX), matrix 256.times.l28
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`elements, field of View (FOV) 48 cm, slice thickness 7 mm, interslice spacing 1 mm).
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`The scanner table can then be moved to obtain coronal and sagittal images using the same
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`sequence parameters. These T1-weighted scans can be employed to identify axes that
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`can be used later for defining the geometry of the tissue. A rapid scout scan can be
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`acquired in the axial plane using a gradient echo sequence (GRASS, 2D Fourier
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`Transform (ZDFT), TR=50 msec, TE=l 0 msec, flip angle 40°, 1 excitation (NEX), matrix
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`256.times.l28 elements, field of View (FOV) 24 cm, slice thickness 7 mm, interslice
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`spacing 3 mm). This scout scan can be used to determine all subsequent high resolution
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`imaging sequences centered over the body part. Additionally, using the graphic, image
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`based sequence prescription mode provided with the scanner software, the scout scan can
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`help to ensure that all external markers are included in the field of view of the high
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`resolution MR sequences.
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`There are several issues to consider in obtaining a good image. One issue is good
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`contrast between different tissues in the imaged area in order to facilitate the delineation
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`and segmentation of the data sets. In addition, if there are external markers, these must
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`be visualized. One way to address these issues is to use a three—dimensional spoiled
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`gradient-echo sequence in the sagittal plane with the following parameters (SPGR, 3DFT,
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`fat-saturated, TR=60 msec, TE=5 msec, flip angle 40.degree., 1 excitation (NEX), matrix
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`256.times.l60 elements, rectangular FOV 16.times.12 cm, slice thickness 1.3 mm, 128
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`slices, acquisition time approximately 15 min). Using these parameters, one can obtain
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`complete coverage across the body area and the external markers both in mediolateral
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`and antcroposterior direction while achieving good spatial resolution and contrast—to—
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`noise ratios. The fat-saturated 3D SPGR sequences can be used for rendering many
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`tissues in three dimensions. The 3D SPGR sequence can then be repeated in the sagittal
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`plane without fat saturation using the identical parameters and slice coordinates used
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`during the previous acquisition with fat saturation. The resultant non—fat-saturated 3D
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`SPGR images demonstrate good contrast between low signal intensity cortical bone and
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`high signal intensity bone marrow thereby facilitating 3D rendering of the femoral and
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`tibial bone contours. It is to be understood that this approach is representative only for
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`joints and should not be viewed as limiting in any way.
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`1.8. Magnetic Resonance Imaging—-Vertically Open Magnet (0.5T)
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`MR imaging can also be performed using a 0.5 T vertically open MR unit (GE
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`Signa SP, General Electric, Milwaukee, Wis.) and a MR tracking system. Prior to MR
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`imaging, external markers filled with Gd-DTPA (MagneVist.RTM., Berlex l11c., Wayne,
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`N.J.) doped water (T1 relaxation time approximately 1.0 sec) can be applied to the skin.
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`The subject can be placed in upright position inside the magnet. The body part can be
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`perpendicular to the main magnetic field. A 2DFT fast spin echo pulse sequence can be
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`acquired in the sagittal plane (FSE, TR=4000 msec, TE=25 msec, bandwidth 7.8 kHz,
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`echo train length 8, 3 excitations, slice thickness 4 mm, interslice spacing 0.5 mm, matrix
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`256.times.l92 elements, field of View 24 cm). For rapid scan acquisition with scan plane
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`tracking, a fast single slice gradient-echo pulse sequence can be acquired in the sagittal
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`plane or in the axial plane (GRASS, TR=14 msec, TE=5 msec, flip angle 40 degrees,
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`bandwidth 32 kHz, 1 excitation, slice thickness 4 mm, matrix 256.times.l28 elements,
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`field of view 20 cm, temporal resolution 2 sec/image). A field of View of 20 cm can be
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`chosen in order to achieve sufficient anatomic coverage in superoinferior.
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`2.0 Fusing Images
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`Despite the existence of these imaging techniques, resolution in more than one
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`plane remains difficult. To overcome the problems caused by different resolutions in the
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`imaging dimensions, a second scan S2 with an imaging plane oriented perpendicular to
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`the first scan S1 is typically obtained. Additional scans in other planes or directions may
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`25
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`also be obtained. For example, if the S1 is acquired in the sagittal direction, a second
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`scan in the coronal or axial imaging plane is acquired. S2 has the same in-plane
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`resolution as S1. It also contains a sufficient number of slices to cover the entire field of
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`view of S 1. This results in two data volumes with information from the same 3D space.
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`The two data volumes are subsequently merged into a third data volume. This
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`30
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`data volume is isotropic or near isotropic with a resolution corresponding to the in-plane
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`resolution of S1 and S2. The gray value for each voxel V of the third data volume is
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`6750-00121’
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`preferably calculated as follows: (a) determine the position in 3D space for V; (b)
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`determine (e.g., look up) the gray values in S1 and S2 at this position; (c) employ an
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`appropriate interpolation scheme to combine the two gray values into a single gray value
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`G; and (d) assign G to V.
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`These manipulations may be repeated for more scans. Furthermore, to
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`compensate for differences in positioning between S1 and S2 of the scanned subject, e.g.
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`due to motion, a registration technique such as principal-axis or volume-based matching
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`can be applied.
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`3 .0 Tissue Segmentation
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`Segmentation means the classification of pixels or voxels of an electronic
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`image into distinct groups. Tissue segmentation means can be applied to extract one or
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`more tissues from one or more images. This can be achieved with classification of pixels
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`or voxels of an electronic anatomical image (e. g. x-ray, CT, MR1) into distinct groups,
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`where each group represents a tissue or anatomicalistructure or combination of tissues
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`or anatomical structures or image background.
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`In another embodiment of the invention, a 3D MRI image is obtained using any
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`suitable technique, for example using pulse sequence acquisition parameters that provide
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`a 3D rather than a 2D Fourier Transform acquisition with isotropic or near isotropic
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`resolution, or by using fusion of two or more 2D acquisitions. As used herein, isotropic
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`resolution refers to an MRI image in which the slice thickness is equal to the in-plane
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`resolution. Similarly, the term "near isotropic resolution" refers to an image in which the
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`slice thickness does not exceed more than 2x the in-plane resolution, more preferably not
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`more than 1.5x the in-plane resolution and even more preferably not more than l.25x the
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`in-plane resolution. The isotropic or near isotropic 3DFT imaging pulse sequence has
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`advantages with regard to partial volume averaging. Partial volume averaging is
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`typically not greater in slice direction (z—direction) than in the imaging plane (x and y-
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`direction).
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`Non—limiting examples of pulse sequences suitable for obtaining near isotropic or
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`isotropic images include 3DFSE, 3DMFAST, 3DFIESTA, 3DFEMR, and 3DSSFP.
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`The preferred in-plane resolution of the 3DFT isotropic or near isotropic imaging
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`sequence is less than 0.5mm and the preferred slice thickness is less than 0.8 mm,
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`preferably less than 0.5mm.
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`Subsequently, these isotropic or near isotropic resolution images are used to
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`increase the accuracy of segmentation and any subsequent visualizations and/or
`
`quantitative measurements of the body part, (e.g., measurement of cartilage thickness or
`
`size of cartilage defects).
`
`Thus, the invention described herein allows, among other things, for increased
`
`resolution and efficiency of tissue segmentation. Following the manipulations described
`
`herein (e.g., merging of multiple images, isotropic or near isotropic resolution imaging),
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`commercially available segmentation software can be used, for example software that
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`includes seed—growing algorithms and active-contour algorithms that are run on standard
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`PC's.
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`For example, articular cartilage shown in the 3D MR images may be analyzed. A
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`sharp interface is present between the high signal intensity bone marrow and the low
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`signal intensity cortical bone thereby facilitating seed growing.
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`One exemplary, but not limiting, approach uses a 3D surface detection technique
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`that is based on a 2D edge detector (Wang—Binford) that has been extended to 3D. This
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`surface detection technique can generate surface points and their corresponding surface
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`normal. To smooth the contour, the program samples 25 percent of the surface points
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`and fits a cubic spline to the sample points. The program can compute the curvature
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`along sample spline points and find two sample points that have the maximum curvature
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`and are separated by about half the number of voxels on the contour. These points
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`partition the spline into two subcontours. For each subcontour, the program can compute
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`the average distance between the points and the center of the mass.
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`Programs can allow the user, through the use of the mouse and/or keyboard, the
`
`ability to observe the scene from arbitrary angles; to start and stop the animation derived
`
`from the3D data. Additionally, the user can derive quantitative information on the scene
`
`through selecting points with the mouse.
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`The software programs can be written in the C++ computer language and can be
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`compiled to run, for example on Silicon Graphics Workstations or Windows/Intel
`
`personal computers.
`
`4.0 Three-Dimensional Images
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`5
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`Afier the 3D MR image is obtained, by either using a 3D acquisition or by fusing
`
`two or more 2D scans as described above, and after one or more anatomical objects have
`
`been extracted using segmentation techniques, for example, the object information can be
`
`transformed to a surface representation using a computer program. The program can, for
`
`example, be developed in AVS Express (Advanced Visual Systems, Ine., Waltham,
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`10 Mass.). Every voxel has a value of zero if it is not within an object of interest or a value
`
`ranging from one to 4095, depending on the signal intensity as recorded by the 1.5 T MR.
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`An isosurface can then be calculated that corresponds to the boundary elements of the
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`volume of interest. A tesselation of this isosurface is calculated, along with the outward
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`pointing normal of each polygon of the tesselation. These polygons can be written to a
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`15
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`file in a standard graphics format (e. g. Virtual Reality Modeling Language Version 1.0:
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`VRML output language) and visualized on a computer screen.
`
`Visualization programs are also available, for example, user controllable 3D
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`visual analysis tools. These programs read in a scene, which scene consists of the various
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`3D geometric representations or "actors." The program allows the user, through the use
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`20
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`of the mouse and/or keyboard, the ability to observe the scene from arbitrary angles; to
`
`start and stop the animation derived from the 3D data. Additionally, the user may derive
`
`quantitative information on the scene through selecting points with the mouse.
`
`The software programs can be written in the C++ computer language and be
`
`compiled to run, for example, on Silicon Graphics Workstations and Windows/Intel
`
`25
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`personal computers. Biochemical constituents, for example of cartilage, may also be
`
`visualized, for example as described in W0 O2/22014.
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`The invention has been described with reference to the preferred embodiments.
`
`Obviously, modifications and alterations will occur to others upon reading and
`
`understanding the preceding detailed description.
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