Ultrashort echo time T2∗ values decrease in tendons with application of static tensile loads

Abstract

In early stages of tendon disease, mechanical properties may become altered prior to changes in morphological anatomy. Ultrashort echo time (UTE) magnetic resonance imaging (MRI) can be used to directly detect signal from tissues with very short T2 values, including unique viscoelastic tissues such as tendons. The purpose of this study was to use UTE sequences to measure T2^∗, T1 and magnetization transfer ratio (MTR) variations of tendon samples under static tensile loads. Six human peroneal tendons were imaged before and under static loading using UTE sequences on a clinical 3T MRI scanner. Tendons were divided into two static tensile loading groups: group A that underwent one-step loading (15N) and group B that underwent two-step loading (15 and 30N). The T2^∗, T1 and MTR variations were investigated in two selected section regions of interest (ROIs), including whole and core sections. Mean T2^∗ values for the first step of loading (groups A and B) in both whole section and core section ROIs were significantly decreased by 13±7% (P=0.028) and 16±5% (P=0.017), respectively. For the second loading step (group B), there was a consistent, but non-significant reduction in T2^∗ value by 9±2% (P=0.059) and 7±5% (P=0.121) for whole and core sections, respectively. Mean T1 did not show any consistent changes for either loading steps (P>0.05). Mean MTR increased slightly, but not significantly for both loading steps (P>0.05). Significant differences were found only in T2^∗ values of tendons by static tensile load application. Therefore, T2^∗ monitoring during loading is suggested for quantitative investigation of the tendons biomechanics.

Keywords: MRI; T2(∗); Tendon; Tensile loading; Ultrashort TE.

Figure 1

MRI compatible, plastic, loading device used for applying static extension loads on peroneal tendons soaked in fomblin. (b) Mounted tendon on the fixed and sliding grippers, using plastic bolts.

Figure 2

UTE-MR images with T2* decay curves comparing the three loading conditions in sample B-1. Single component fitting of T2* decay in the whole and the core sections for (a,b) non-loaded (straight), compared with (c,d) 15 and (e,f) 30 N loaded tendons.

Figure 3

The T2* map in three selected tendon samples, A-1, B-1 and B-2 at different loading conditions (non-loaded, 15 and 30 N). The regions of higher T2* values (indicated by green to red) of all samples decreased in size within the tendons by mechanical loading.

Figure 4

The magnetization transfer ratio (MTR) maps for different loading conditions (non-loaded, 15 and 30 N) at 2 kHz frequency offset and 1500° MT pulse preparation. The MTR map indicated higher values and non-homogenous distributions for loaded tendons particularly in sample B-1. Sample A-1 and B-2 showed less variations by loading.