Spatial characterization of T1 and T2 relaxation times and the water apparent diffusion coefficient in rabbit Achilles tendon subjected to tensile loading

• Published in: Magnetic resonance in medicine Vol. 53; no. 3; pp. 535 - 544
• Main Authors: Wellen, J., Helmer, K. G., Grigg, P., Sotak, C. H.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.03.2005
• Subjects: Achilles Tendon - anatomy & histology; Achilles Tendon - metabolism; Animals; Body Water - metabolism; Diffusion Magnetic Resonance Imaging; Image Processing, Computer-Assisted; In Vitro Techniques; mechanical loading; MRI; rabbit Achilles tendon; Rabbits; Signal Processing, Computer-Assisted; T1 and T2 relaxation times; Tensile Strength; water apparent diffusion coefficient (ADC); water transport
• ISSN: 0740-3194; 1522-2594
• DOI: 10.1002/mrm.20361

Tendons exhibit viscoelastic mechanical behavior under tensile loading. The elasticity arises from the collagen chains that form fibrils, while the viscous response arises from the interaction of the water with the solid matrix. Therefore, an understanding of the behavior of water in response to the application of a load is crucial to the understanding of the origin of the viscous response. Three‐dimensional MRI mapping of rabbit Achilles tendons was performed at 2.0 T to characterize the response of T1 and T2 relaxation times and the apparent diffusion coefficient (ADC) of water to tensile loading. The ADC was measured in directions both parallel (ADC∥) and perpendicular (ADC⟂) to the long axis of the tendon. At a short diffusion time (5.8 ms) MR parameter maps showed the existence of two regions, here termed “core” and “rim”, that exhibited statistically significant differences in T1, T2, and ADC⟂ under the baseline loading condition. MR parameter maps were also generated at a second loading condition of ∼1 MPa. At a diffusion time of 5.8 ms, there was a statistically significant increase in the rim region for both ADC⟂ (57.5%) and ADC∥ (20.5%) upon tensile loading. The changes in core ADC(⟂, ∥), as well as the relaxation parameters in both core and rim regions, were not statistically significant. The effect of diffusion time on the ADC(⟂, ∥) values was investigated by creating maps at three additional diffusion times (50.0, 125.0, 250.0 ms) using a diffusion‐weighted, stimulated‐echo (DW‐STE) pulse sequence. At longer diffusion times, ADC(⟂, ∥) values increased rather than approaching a constant value. This observation was attributed to T1 spin‐editing during the DW‐STE pulse sequence, which resulted in the loss of short‐T1 components (with correspondingly lower ADCs) at longer diffusion times (corroborating the results from earlier spectroscopic work). The T1 spin‐editing effect was observed both in the core and in the rim regions of the tendon and hence was not solely due to the redistribution of water from the core to the rim upon loading. A measure reflective of the regional change in proton density was noted to be consistent with tensile‐load‐induced water transport from the central to the peripheral tendon region. Magn Reson Med 53:535–544, 2005. © 2005 Wiley‐Liss, Inc.