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

Abstract

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 T 1 and T 2 relaxation times and the apparent diffusion coefficient (ADC) of water to tensile loading. The ADC was measured in directions both parallel (ADC ʈ ) and perpendicular (ADC Ќ ) 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 T 1 , T 2 , and ADC Ќ under the baseline loading condition. MR parameter maps were also generated at a second loading condition of ϳ1 MPa. At a diffusion time of 5.8 ms, there was a statistically significant increase in the rim region for both ADC Ќ (57.5%) and ADC ʈ (20.5%) upon tensile loading. The changes in core ADC (Ќ , ʈ) , as well as the relaxation parameters in both core and rim regions, were not statistically significant. The effect of diffusion time on the ADC (Ќ , ʈ) values was investigated by creating maps at three additional diffusion times (50.0, 125.0, 250.0 ms) using a diffusion-weighted, stimulatedecho (DW-STE) pulse sequence. At longer diffusion times, ADC (Ќ , ʈ) values increased rather than approaching a constant value. This observation was attributed to T 1 spin-editing during the DW-STE pulse sequence, which resulted in the loss of short-T 1 components (with correspondingly lower ADCs) at longer diffusion times (corroborating the results from earlier spectroscopic work). The T 1 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.

Three-dimensional morphology and strain of the Achilles free tendon immediately following eccentric heel drop exercise

“…Our results provide the first evidence that links acute changes in transverse morphology to corresponding changes in tendon length after exercise. Short-term changes in Achilles free tendon transverse morphology after exercise (Fahlstrom and Alfredson, 2010;Grigg et al, 2010Grigg et al, , 2009Grigg et al, , 2012Ooi et al, 2015;Wearing et al, 2011Wearing et al, , 2013Wearing et al, , 2008 may therefore be indicative of transient mechanical creep of the tendon (Lichtwark et al, 2013;Obst et al, 2015), whereby increased collagen fibril packing linked to longitudinal creep and reduction of collagen crimp could promote fluid redistribution within, and out of, the tendon (Grigg et al, 2009;Hannafin and Arnoczky, 1994;Wellen et al, 2005). It should be noted that although we did not detect any change in tendon volume at rest or during 70%…”

“…These short-term reductions in AP diameter after exercise have been suggested to reflect fluid exudation from the tendon core to the peri-tendinous space as a result of the creation of positive hydrostatic pressure within the tendon when tendon fibres stretch and pack under tensile load (Grigg et al, 2009;Hannafin and Arnoczky, 1994). While in vitro studies demonstrate load-dependent changes in fluid content and tendon dimensions in response to repeated loading (Hannafin and Arnoczky, 1994;Helmer et al, 2006;Wellen et al, 2005), in vivo studies of the human Achilles tendon report mixed findings with respect to exercise-induced changes in tendon volume (Pingel et al, 2013a, b;Shalabi et al, 2004;Syha et al, 2013) and crosssectional area (CSA) (Burgess et al, 2009;Farris et al, 2012;Neves et al, 2014;Ooi et al, 2015); discrepancies that may reflect different exercise interventions, populations or imaging methods used to assess tendon morphology. It is also currently unclear whether changes in transverse morphology and strain following exercise are uniformly distributed across the length of the tendon, occur along the medio-lateral (ML) diameter, related to changes in longitudinal deformation, or are more pronounced under tensile load.…”

“…We computed tendon diameter along the tendon length by analysing the shape and dimensions of each consecutive 2D tendon cross-section determined from manual segmentation of the original transverse B-mode images. As a consequence, while our method minimises measurement errors due to tendon obliquity (Fornage, 1986;Sunding et al, 2014), the measures are inclusive of the peri-tendinous space (as opposed to Grigg et al, 2009Grigg et al, , 2012 and therefore are unlikely to detect small changes in transverse dimensions due to possible movement of fluid from the tendon core to the peri-tendinous space (Grigg et al, 2009(Grigg et al, , 2012Wellen et al, 2005). Effect of exercise on Achilles free tendon longitudinal and transverse strain under load…”

A finite element model predicts the mechanotransduction response of tendon cells to cyclic tensile loading

“…However, it has been suggested that permeability is strain (Lai et al 1981;Weiss and Maakestad 2006;Yin and Elliott 2004), porosity (Chen et al 1998) and/or voids ratio (van der Voet 1997) dependent. Higher water content in the peripheral rim compared to the tendon core suggests that the porosity or voids ratio may also be depth dependent within a tendon (Wellen et al 2005). The permeability in tendon is also believed to be anisotropic with a higher permeability along the fiber direction than across the fibers Chen et al 1998;Han et al 2000).…”

Magnetic resonance in porous media: Recent progress

“…23 The novelty of the work from Komlosh et al is that they experimentally demonstrated that the microscopic anisotropy of macroscopically isotropic sample, which is not accessible with conventional single direction PGSE method, can be detected at low q regime using double PGSE. Such techniques may be useful for studying porous media and biological tissues, such as tendons 24,25 and brain gray matter with potential clinical applications because of its sensitivity in the low q regime compatible with clinically available gradient strength. 23 …”