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In vivo intervertebral disc deformation: intratissue strain patterns within adjacent discs during flexion-extension. Sci Rep 2021; 11:729. [PMID: 33436667 PMCID: PMC7804136 DOI: 10.1038/s41598-020-77577-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Accepted: 11/10/2020] [Indexed: 01/29/2023] Open
Abstract
The biomechanical function of the intervertebral disc (IVD) is a critical indicator of tissue health and pathology. The mechanical responses (displacements, strain) of the IVD to physiologic movement can be spatially complex and depend on tissue architecture, consisting of distinct compositional regions and integrity; however, IVD biomechanics are predominately uncharacterized in vivo. Here, we measured voxel-level displacement and strain patterns in adjacent IVDs in vivo by coupling magnetic resonance imaging (MRI) with cyclic motion of the cervical spine. Across adjacent disc segments, cervical flexion-extension of 10° resulted in first principal and maximum shear strains approaching 10%. Intratissue spatial analysis of the cervical IVDs, not possible with conventional techniques, revealed elevated maximum shear strains located in the posterior disc (nucleus pulposus) regions. IVD structure, based on relaxometric patterns of T2 and T1ρ images, did not correlate spatially with functional metrics of strain. Our approach enables a comprehensive IVD biomechanical analysis of voxel-level, intratissue strain patterns in adjacent discs in vivo, which are largely independent of MRI relaxometry. The spatial mapping of IVD biomechanics in vivo provides a functional assessment of adjacent IVDs in subjects, and provides foundational biomarkers for elastography, differentiation of disease state, and evaluation of treatment efficacy.
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Cai L, Nauman EA, Pedersen CBW, Neu CP. Finite deformation elastography of articular cartilage and biomaterials based on imaging and topology optimization. Sci Rep 2020; 10:7980. [PMID: 32409711 PMCID: PMC7224212 DOI: 10.1038/s41598-020-64723-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2019] [Accepted: 04/17/2020] [Indexed: 01/17/2023] Open
Abstract
Tissues and engineered biomaterials exhibit exquisite local variation in stiffness that defines their function. Conventional elastography quantifies stiffness in soft (e.g. brain, liver) tissue, but robust quantification in stiff (e.g. musculoskeletal) tissues is challenging due to dissipation of high frequency shear waves. We describe new development of finite deformation elastography that utilizes magnetic resonance imaging of low frequency, physiological-level (large magnitude) displacements, coupled to an iterative topology optimization routine to investigate stiffness heterogeneity, including spatial gradients and inclusions. We reconstruct 2D and 3D stiffness distributions in bilayer agarose hydrogels and silicon materials that exhibit heterogeneous displacement/strain responses. We map stiffness in porcine and sheep articular cartilage deep within the bony articular joint space in situ for the first time. Elevated cartilage stiffness localized to the superficial zone is further related to collagen fiber compaction and loss of water content during cyclic loading, as assessed by independent T2 measurements. We additionally describe technical challenges needed to achieve in vivo elastography measurements. Our results introduce new functional imaging biomarkers, which can be assessed nondestructively, with clinical potential to diagnose and track progression of disease in early stages, including osteoarthritis or tissue degeneration.
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Affiliation(s)
- Luyao Cai
- Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, 47907, US
| | - Eric A Nauman
- Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, 47907, US
- School of Mechanical Engineering, Purdue University, West Lafayette, IN, 47907, US
- Department of Basic Medical Sciences, Purdue University, West Lafayette, IN, 47907, US
| | | | - Corey P Neu
- Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, 47907, US.
- Department of Mechanical Engineering, University of Colorado Boulder, Boulder, CO, 80309, US.
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Chan DD, Cai L, Butz KD, Nauman EA, Dickerson DA, Jonkers I, Neu CP. Functional MRI can detect changes in intratissue strains in a full thickness and critical sized ovine cartilage defect model. J Biomech 2018; 66:18-25. [PMID: 29169631 PMCID: PMC5767131 DOI: 10.1016/j.jbiomech.2017.10.031] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2017] [Revised: 10/02/2017] [Accepted: 10/27/2017] [Indexed: 02/07/2023]
Abstract
Functional imaging of tissue biomechanics can reveal subtle changes in local softening and stiffening associated with disease or repair, but noninvasive and nondestructive methods to acquire intratissue measures in well-defined animal models are largely lacking. We utilized displacement encoded MRI to measure changes in cartilage deformation following creation of a critical-sized defect in the medial femoral condyle of ovine (sheep) knees, a common in situ and large animal model of tissue damage and repair. We prioritized visualization of local, site-specific variation and changes in displacements and strains following defect placement by measuring spatial maps of intratissue deformation. Custom data smoothing algorithms were developed to minimize propagation of noise in the acquired MRI phase data toward calculated displacement or strain, and to improve strain measures in high aspect ratio tissue regions. Strain magnitudes in the femoral, but not tibial, cartilage dramatically increased in load-bearing and contact regions especially near the defect locations, with an average 6.7% ± 6.3%, 13.4% ± 10.0%, and 10.0% ± 4.9% increase in first and second principal strains, and shear strain, respectively. Strain heterogeneity reflected the complexity of the in situ mechanical environment within the joint, with multiple tissue contacts defining the deformation behavior. This study demonstrates the utility of displacement encoded MRI to detect increased deformation patterns and strain following disruption to the cartilage structure in a clinically-relevant, large animal defect model. It also defines imaging biomarkers based on biomechanical measures, in particular shear strain, that are potentially most sensitive to evaluate damage and repair, and that may additionally translate to humans in future studies.
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Affiliation(s)
- Deva D Chan
- Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN 47907, United States; Department of Biomedical Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180, United States
| | - Luyao Cai
- Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN 47907, United States
| | - Kent D Butz
- School of Mechanical Engineering, Purdue University, West Lafayette, IN 47907, United States
| | - Eric A Nauman
- Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN 47907, United States; School of Mechanical Engineering, Purdue University, West Lafayette, IN 47907, United States; BioRegeneration Technologies, Inc., West Lafayette, IN 47907, United States
| | - Darryl A Dickerson
- School of Mechanical Engineering, Purdue University, West Lafayette, IN 47907, United States; BioRegeneration Technologies, Inc., West Lafayette, IN 47907, United States
| | - Ilse Jonkers
- Kinesiology Department, KU Leuven, Leuven, Belgium
| | - Corey P Neu
- Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN 47907, United States; Department of Mechanical Engineering, University of Colorado Boulder, Boulder, CO 80309, United States.
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Chan DD, Cai L, Butz KD, Trippel SB, Nauman EA, Neu CP. In vivo articular cartilage deformation: noninvasive quantification of intratissue strain during joint contact in the human knee. Sci Rep 2016; 6:19220. [PMID: 26752228 PMCID: PMC4707486 DOI: 10.1038/srep19220] [Citation(s) in RCA: 86] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2015] [Accepted: 12/08/2015] [Indexed: 12/25/2022] Open
Abstract
The in vivo measurement of articular cartilage deformation is essential to understand how mechanical forces distribute throughout the healthy tissue and change over time in the pathologic joint. Displacements or strain may serve as a functional imaging biomarker for healthy, diseased, and repaired tissues, but unfortunately intratissue cartilage deformation in vivo is largely unknown. Here, we directly quantified for the first time deformation patterns through the thickness of tibiofemoral articular cartilage in healthy human volunteers. Magnetic resonance imaging acquisitions were synchronized with physiologically relevant compressive loading and used to visualize and measure regional displacement and strain of tibiofemoral articular cartilage in a sagittal plane. We found that compression (of 1/2 body weight) applied at the foot produced a sliding, rigid-body displacement at the tibiofemoral cartilage interface, that loading generated subject- and gender-specific and regionally complex patterns of intratissue strains, and that dominant cartilage strains (approaching 12%) were in shear. Maximum principle and shear strain measures in the tibia were correlated with body mass index. Our MRI-based approach may accelerate the development of regenerative therapies for diseased or damaged cartilage, which is currently limited by the lack of reliable in vivo methods for noninvasive assessment of functional changes following treatment.
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Affiliation(s)
- Deva D Chan
- Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, 47907
| | - Luyao Cai
- Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, 47907
| | - Kent D Butz
- School of Mechanical Engineering, Purdue University, West Lafayette, IN, 47907
| | - Stephen B Trippel
- Departments of Orthopaedic Surgery and Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, IN, 46202
| | - Eric A Nauman
- Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, 47907.,School of Mechanical Engineering, Purdue University, West Lafayette, IN, 47907
| | - Corey P Neu
- Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, 47907.,Department of Mechanical Engineering, University of Colorado, Boulder, CO, 80309
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Chan DD, Neu CP. Intervertebral disc internal deformation measured by displacements under applied loading with MRI at 3T. Magn Reson Med 2015; 71:1231-7. [PMID: 23650022 DOI: 10.1002/mrm.24757] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
PURPOSE Noninvasive assessment of tissue mechanical behavior could enable insights into tissue function in healthy and diseased conditions and permit the development of effective tissue repair treatments. Measurement of displacements under applied loading with MRI (dualMRI) has the potential for such biomechanical characterization on a clinical MRI system. METHODS dualMRI was translated from high-field research systems to a 3T clinical system. Precision was calculated using repeated tests of a silicone phantom. dualMRI was demonstrated by visualizing displacements and strains in an intervertebral disc and compared to T2 measured during cyclic loading. RESULTS The displacement and strain precisions were 24 µm and 0.3% strain, respectively, under the imaging parameters used in this study. Displacements and strains were measured within the intervertebral disc, but no correlations were found with the T2 values. CONCLUSION The translation of dualMRI to a 3T system unveils the potential for in vivo studies in a myriad of tissue and organ systems. Because of the importance of mechanical behavior to the function of a variety of tissues, it's expected that dualMRI implemented on a clinical system will be a powerful tool in assessing the interlinked roles of structure, mechanics, and function in both healthy and diseased tissues.
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Affiliation(s)
- Deva D Chan
- Weldon School of Biomedical Engineering, College of Engineering, Purdue University, West Lafayette, Indiana, USA
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Chan DD, Gossett PC, Butz KD, Nauman EA, Neu CP. Comparison of intervertebral disc displacements measured under applied loading with MRI at 3.0 T and 9.4 T. J Biomech 2014; 47:2801-6. [PMID: 24968943 DOI: 10.1016/j.jbiomech.2014.05.026] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2014] [Revised: 05/26/2014] [Accepted: 05/30/2014] [Indexed: 11/25/2022]
Abstract
The purpose of this study was to compare displacement behavior of cyclically loaded cadaveric human intervertebral discs as measured noninvasively on a clinical 3.0 T and a research 9.4 T MRI system. Intervertebral discs were cyclically compressed at physiologically relevant levels with the same MRI-compatible loading device in the clinical and research systems. Displacement-encoded imaging was synchronized to cyclic loading to measure displacements under applied loading with MRI (dual MRI). Displacements from the two systems were compared individually using linear regression and, across all specimens, using Bland-Altman analysis. In-plane displacement patterns measured at 3.0 T and 9.4 T were qualitatively comparable and well correlated. Bland-Altman analyses showed that over 90% of displacement values within the intervertebral disc regions of interest lay within the limits of agreement. Measurement of displacement using dual MRI using a 3.0 T clinical system is comparable to that of a 9.4 T research system. Additional refinements of software, technique implementation, and image processing have potential to improve agreement between different MRI systems. Despite differences in MRI systems in this initial implementation, this work demonstrates that dual MRI can be reliably implemented at multiple magnetic field strengths, permitting translation of dual MRI for a variety of applications in the study of tissue and biomaterial biomechanics.
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Affiliation(s)
- Deva D Chan
- Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, USA
| | - Paull C Gossett
- Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, USA
| | - Kent D Butz
- School of Mechanical Engineering, Purdue University, West Lafayette, IN, USA
| | - Eric A Nauman
- Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, USA; School of Mechanical Engineering, Purdue University, West Lafayette, IN, USA
| | - Corey P Neu
- Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, USA.
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Zignego DL, Jutila AA, Gelbke MK, Gannon DM, June RK. The mechanical microenvironment of high concentration agarose for applying deformation to primary chondrocytes. J Biomech 2013; 47:2143-8. [PMID: 24275437 DOI: 10.1016/j.jbiomech.2013.10.051] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2013] [Revised: 10/25/2013] [Accepted: 10/31/2013] [Indexed: 11/16/2022]
Abstract
Cartilage and chondrocytes experience loading that causes alterations in chondrocyte biological activity. In vivo chondrocytes are surrounded by a pericellular matrix with a stiffness of ~25-200kPa. Understanding the mechanical loading environment of the chondrocyte is of substantial interest for understanding chondrocyte mechanotransduction. The first objective of this study was to analyze the spatial variability of applied mechanical deformations in physiologically stiff agarose on cellular and sub-cellular length scales. Fluorescent microspheres were embedded in physiologically stiff agarose hydrogels. Microsphere positions were measured via confocal microscopy and used to calculate displacement and strain fields as a function of spatial position. The second objective was to assess the feasibility of encapsulating primary human chondrocytes in physiologically stiff agarose. The third objective was to determine if primary human chondrocytes could deform in high-stiffness agarose gels. Primary human chondrocyte viability was assessed using live-dead imaging following 24 and 72h in tissue culture. Chondrocyte shape was measured before and after application of 10% compression. These data indicate that (1) displacement and strain precision are ~1% and 6.5% respectively, (2) high-stiffness agarose gels can maintain primary human chondrocyte viability of >95%, and (3) compression of chondrocytes in 4.5% agarose can induce shape changes indicative of cellular compression. Overall, these results demonstrate the feasibility of using high-concentration agarose for applying in vitro compression to chondrocytes as a model for understanding how chondrocytes respond to in vivo loading.
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Affiliation(s)
- Donald L Zignego
- Department of Mechanical and Industrial Engineering, Montana State University, Bozeman, MT 59718-3800, USA
| | - Aaron A Jutila
- Department of Mechanical and Industrial Engineering, Montana State University, Bozeman, MT 59718-3800, USA
| | - Martin K Gelbke
- Bridger Orthopedic and Sports Medicine, Bozeman, MT 59715, USA
| | - Daniel M Gannon
- Bridger Orthopedic and Sports Medicine, Bozeman, MT 59715, USA
| | - Ronald K June
- Department of Mechanical and Industrial Engineering, Montana State University, Bozeman, MT 59718-3800, USA; Department of Cell Biology and Neuroscience, Montana State University, Bozeman, MT 59718-3800, USA.
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