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Noninvasive Quantification of Human Nucleus Pulposus Pressure with Use of T1ρ-Weighted Magnetic Resonance Imaging
An M. Nguyen, BS1; Wade Johannessen, PhD1; Jonathon H. Yoder, MS1; Andrew J. Wheaton, PhD2; Edward J. Vresilovic, MD, PhD3; Arijitt Borthakur, PhD4; Dawn M. Elliott, PhD1
1 Department of Orthopaedic Surgery, McKay Orthopaedic Research Laboratory, University of Pennsylvania, 424 Stemmler Hall, Philadelphia, PA 19104-6081. E-mail address for D.M. Elliott: delliott@mail.med.upenn.edu
2 Toshiba Medical Research Institute USA, 777 Beta Drive, Mayfield, OH 44143
3 Milton S. Hershey Medical Center (MSHMC) Orthopaedics, 500 University Drive, Hershey, PA 17033-0850
4 Department of Radiology, Metabolic Magnetic Resonance Research and Computing Center (MMRRCC), Department of Radiology, University of Pennsylvania, B1 Stellar-Chance Labs, 422 Curie Boulevard, Philadelphia, PA 19104-6100
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Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from the National Institute of Arthritis and Musculoskeletal and Skin Diseases (Grant AR 050052) and the National Football League Charities (Medical Research Grant). Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.
Investigation performed at the University of Pennsylvania, Philadelphia, Pennsylvania

The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2008 Apr 01;90(4):796-802. doi: 10.2106/JBJS.G.00667
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Background: Early diagnosis is a challenge in the treatment of degenerative disc disease. A noninvasive biomarker detecting functional mechanics of the disc is needed. T1?-weighted imaging, a spin-lock magnetic resonance imaging technique, has shown promise for meeting this need in in vivo studies demonstrating the clinical feasibility of evaluating both intervertebral discs and articular cartilage. The objectives of the present study were (1) to quantitatively determine the relationship between T1? relaxation time and measures of nucleus pulposus mechanics, and (2) to evaluate whether the quantitative relationship of T1? relaxation time with the degenerative grade and glycosaminoglycan content extend to more severe degeneration. It was hypothesized that the isometric swelling pressure and compressive modulus would be directly correlated with the T1? relaxation time and the apparent permeability would be inversely correlated with the T1? relaxation time.

Methods: Eight cadaver human lumbar spines were imaged to measure T1? relaxation times. The nucleus pulposus tissue from the L1 disc through the S1 disc was tested in confined compression to determine the swelling pressure, compressive modulus, and permeability. The glycosaminoglycan and water contents were measured in adjacent tissue. Linear regression analyses were performed to examine the correlation between the T1? relaxation time and the other measured variables. Mechanical properties and biochemical content were evaluated for differences associated with degeneration.

Results: A positive linear correlation was observed between the T1? relaxation time on the images of the nucleus pulposus and the swelling pressure (r = 0.59), glycosaminoglycan content per dry weight (r = 0.69), glycosaminoglycan per wet weight (r = 0.49), and water content (r = 0.53). No significant correlations were observed between the T1? relaxation time and the modulus or permeability. Similarly, the T1? relaxation time, swelling pressure, glycosaminoglycan content per dry weight, and water content were significantly altered with degeneration, whereas the modulus and permeability were not.

Conclusions: T1?-weighted magnetic resonance imaging has a strong potential as a quantitative biomarker of the mechanical function of the nucleus pulposus and of disc degeneration.

Clinical Relevance: Several in vivo studies have previously demonstrated the clinical feasibility of using T1?-weighted imaging to evaluate both intervertebral discs and articular cartilage. Its application for the diagnosis of disc degeneration looks promising.

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    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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