Evaluation of tissue displacement and regional strain in the Achilles tendon using quantitative high-frequency ultrasound

<div><p>The Achilles tendon has a unique structure-function relationship thanks to its innate hierarchical architecture in combination with the rotational anatomy of the sub-tendons from the triceps surae muscles. Previous research has provided valuable insight in global Achilles tendon mechanics, but limitations with the technique used remain. Furthermore, given the global approach evaluating muscle-tendon junction to insertion, regional differences in tendon mechanical properties might be overlooked. However, recent advancements in the field of ultrasound imaging in combination with speckle tracking have made an intratendinous evaluation possible. This study uses high-frequency ultrasound to allow for quantification of regional tendon deformation. Also, an interactive application was developed to improve clinical applicability. A dynamic ultrasound of both Achilles tendons of ten asymptomatic subjects was taken. The displacement and regional strain in the superficial, middle and deep layer were evaluated during passive elongation and isometric contraction. Building on previous research, results showed that the Achilles tendon displaces non-uniformly with a higher displacement found in the deep layer of the tendon. Adding to this, a non-uniform regional strain behavior was found in the Achilles tendon during passive elongation, with the highest strain in the superficial layer. Further exploration of tendon mechanics will improve the knowledge on etiology of tendinopathy and provide options to optimize existing therapeutic loading programs.</p></div

2D US image of volunteer with selected regions of interest (1) and subregions (2–7) delimited in red.

<p>2D US image of volunteer with selected regions of interest (1) and subregions (2–7) delimited in red.</p

Absolute difference in mean displacement of superficial versus deep layer (** = p = 0,002).

<p>Absolute difference in mean displacement of superficial versus deep layer (** = p = 0,002).</p

US images of an Achilles tendon acquired with different central frequencies.

<p><b>(a) 10MHz transducer, (b) 21MHz transducer (c) 40MHz transducer</b>. Tendon width, length and corresponding image resolution is annotated in yellow.</p

Interactive application.

<p>Interactive application.</p

Close-up of Fig 1.

<p>Speckle pattern width is measured for the 10MHz image (a), 21MHz image(b) and 40MHz image(c).</p

Non-uniform displacement along the major deformation direction (*** = p < 0.001).

<p>Non-uniform displacement along the major deformation direction (*** = p < 0.001).</p

Non-uniform regional strain along the major deformation direction (** = p = 0.002 / *** = p < 0.001 / n.s. = non significant).

<p>Non-uniform regional strain along the major deformation direction (** = p = 0.002 / *** = p < 0.001 / n.s. = non significant).</p

Comparison of the mean Dice-scores and their standard deviation between different initialization methods for the UZ Ghent dataset.

<p>The highest Dice-score per NMF method and per tissue class is marked in bold. * indicates statistically significantly higher Dice-scores with SPA initialization compared to direct SPA endmember extraction (right column), using a one-tailed Wilcoxon signed rank test (<i>p</i> < 0.05).</p

Comparison of the mean Dice-scores and their standard deviation between different initialization methods for the UZ Leuven dataset.

<p>The highest Dice-score per NMF method and per tissue class is marked in bold. * indicates statistically significantly higher Dice-scores with SPA initialization compared to direct SPA endmember extraction (right column), using a one-tailed Wilcoxon signed rank test (<i>p</i> < 0.05).</p