MR elastography monitoring of tissue-engineered constructs

• Published in: NMR in biomedicine Vol. 25; no. 3; pp. 452 - 463
• Main Authors: Othman, Shadi F., Curtis, Evan T., Plautz, Sarah A., Pannier, Angela K., Butler, Stephanie D., Xu, Huihui
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.03.2012
• Subjects: Animals; biomechanics; Elasticity Imaging Techniques - instrumentation; Elasticity Imaging Techniques - methods; elastography; Humans; Implants, Experimental; Magnetic Resonance Imaging - instrumentation; Magnetic Resonance Imaging - methods; Mesenchymal Stromal Cells - cytology; Mesenchymal Stromal Cells - physiology; Models, Theoretical; MR elastography; shear wave; Stem Cell Transplantation; Stress, Mechanical; tissue engineering; Tissue Engineering - methods
• ISSN: 0952-3480; 1099-1492
• DOI: 10.1002/nbm.1663

The objective of tissue engineering (TE) is to create functional replacements for various tissues; the mechanical properties of these engineered constructs are critical to their function. Several techniques have been developed for the measurement of the mechanical properties of tissues and organs; however, current methods are destructive. The field of TE will benefit immensely if biomechanical models developed by these techniques could be combined with existing imaging modalities to enable noninvasive, dynamic assessment of mechanical properties during tissue growth. Specifically, MR elastography (MRE), which is based on the synchronization of a mechanical actuator with a phase contrast imaging pulse sequence, has the capacity to measure tissue strain generated by sonic cyclic displacement. The captured displacement is presented in shear wave images from which the complex shear moduli can be extracted or simplified by a direct measure, termed the shear stiffness. MRE has been extended to the microscopic scale, combining clinical MRE with high‐field magnets, stronger magnetic field gradients and smaller, more sensitive, radiofrequency coils, enabling the interrogation of smaller samples, such as tissue‐engineered constructs. The following topics are presented in this article: (i) current mechanical measurement techniques and their limitations in TE; (ii) a description of the MRE system, MRE theory and how it can be applied for the measurement of mechanical properties of tissue‐engineered constructs; (iii) a summary of in vitro MRE work for the monitoring of osteogenic and adipogenic tissues originating from human adult mesenchymal stem cells (MSCs); (iv) preliminary in vivo studies of MRE of tissues originating from mouse MSCs implanted subcutaneously in immunodeficient mice with an emphasis on in vivo MRE challenges; (v) future directions to resolve current issues with in vivo MRE in the context of how to improve the future role of MRE in TE. Copyright © 2011 John Wiley & Sons, Ltd. Tissue engineered (TE) construct development in vitro and regeneration in vivo can be monitored by probing their mechanical properties using high resolution magnetic resonance elastography (MRE). In this paper a description of the MRE system, theory, and in vitro MRE work for monitoring osteogenic and adipogenic tissues is described. TE constructs are then implanted in a mouse model and preliminary in vivo studies are presented demonstrating the future role of MRE in tissue engineering. Finally, MRE technical hurdles are discussed.