P.303Ultrashort-TE magnetic resonance imaging does not reveal alterations of short-T2-signal fraction in patients with congenital myopathies

Abstract

To look for alterations of the short-T2 NMR-signal fraction in the skeletal muscle of patients with congenital myopathies (CM). Non-invasive quantification of endomysial fibrosis would constitute an important biomarker of disease progression and response to treatments, but it still remains an open problem. It has been previously stated that the short-T2 signal observed in UTE MRI could reflect extra cellular matrix content, suggesting UTE as a good candidate to fulfil this objective. Fat-fraction (FF), T2*, and short-T2-fraction (sT2f) maps were extracted in the calf of 16 controls and 10 patients with CM. Regions of interest (ROIs) were traced in the Soleus, Gastrocnemius Lat. and Med. muscles, which presented no visible aponeurosis. The average and standard deviation, of FF, T2* and sT2f were calculated for each ROI. Both quantities were compared between the two groups (Ctrl and CM) using one-way ANOVA. FF, FF heterogeneity and T2* heterogeneity were increased in CM patients (p<0.001). T2* correlated with FF (r=-0.24, p<0.001) and FF heterogeneity (r=-0.33, p<0.001). T2* heterogeneity correlated with FF (r=0.70, p<0.001) and FF heterogeneity (r=0.58, p<0.001). No differences were observed for sT2f and T2*. sT2f correlated with FF (r=-0.50, p<0.001) and FF heterogeneity (r=-0.33, p<0.001). Increased T2* heterogeneity probably reflects the differences of T2* characterizing muscle and adipose tissue, as evidenced by the positive correlation between T2* heterogeneity and FF. Also, an increase of the local magnetic susceptibility gradients induced by fatty infiltration might lead to a reduction of T2*. Although fibrosis is one of the pathologic features of CM, no alteration of sT2f was observed in patients. One possible explanation is that the short-T2 signal observed in UTE MRI arises from a large ensemble of macromolecules, including the contractile apparatus, and/or their hydration layers. So the replacement of myofibers by connective tissue might not significantly impact on the observed sT2f.