Quantative MRI predicts tendon mechanical behavior, collagen composition, and organization

Abstract

Quantitative magnetic resonance imaging (qMRI) measures have provided insights into the composition, quality, and structure-function of musculoskeletal tissues. Low signal-to-noise ratio has limited application to tendon. Advances in scanning sequences and sample positioning have improved signal from tendon allowing for evaluation of structure and function. The purpose of this study was to elucidate relationships between tendon qMRI metrics (T1, T2, T1ρ and diffusion tensor imaging [DTI] metrics) with tendon tissue mechanics, collagen concentration and organization. Sixteen human Achilles tendon specimens were collected, imaged with qMRI, and subjected to mechanical testing with quantitative polarized light imaging. T2 values were related to tendon mechanics [peak stress (r_sp = 0.51, p = 0.044), equilibrium stress (r_sp = 0.54, p = 0.033), percent relaxation (r_sp = -0.55, p = 0.027), hysteresis (r_sp = -0.64, p = 0.007), linear modulus (r_sp = 0.67, p = 0.009)]. T1ρ had a statistically significant relationship with percent relaxation (r = 0.50, p = 0.048). Collagen content was significantly related to DTI measures (range of r = 0.56-0.62). T2 values from a single slice of the midportion of human Achilles tendons were strongest predictors of tendon tensile mechanical metrics. DTI diffusivity indices (mean diffusivity, axial diffusivity, radial diffusivity) were strongly correlated with collagen content. These findings build on a growing body of literature supporting the feasibility of qMRI to characterize tendon tissue and noninvasively measure tendon structure and function. Statement of Clinical Significance: Quantitative MRI can be applied to characterize tendon tissue and is a noninvasive measure that relates to tendon composition and mechanical behavior.

Keywords: Achilles; diagnostic imaging; diffusion tensor imaging; mechanical properties; musculoskeletal imaging.

Figure 1.

Representative image of tendons in agarose mold on transverse, T1 weighted image (A). Representative T1 (B), T2 (C), and T1rho (D) maps.

Figure 2.

Between scan repeatability of T1 (A), T2 (B), and T1 rho (C) measures in ex vivo bovine deep digital flexor tendon.

Figure 3.

Representative tendon on quantitative polarized light imaging (QPLI) showing degree of linear polarization (DoLP, top) and angle of polarization (AoP, bottom).

Figure 4.

Scatterplots showing relationships between qMRI metrics [T1ρ (A) and T2 (B-E) and tendon tensile mechanics. Percent relaxation and hysteresis are displayed as decimals and not percentages.

Figure 5.

Scatterplots showing relationships between diffusivity indices (A) and fractional anisotropy (B) with collagen concentration as well as fractional anisotropy and measures of collagen organization on quantitative polarized light imaging (C,D). Diffusivity indices are in x10-3 mm2/s, collagen per wet weight is in ng/mg.