Localization And Quantification Of Intramuscular Damage Using Statistical Parametric Mapping And Skeletal Muscle Parcellation

Abstract

In the present study, we proposed an original and robust methodology which combines the spatial normalization of skeletal muscle images, the statistical parametric mapping (SPM) analysis and the use of a specific parcellation in order to accurately localize and quantify the extent of skeletal muscle damage within the four heads of the quadriceps femoris. T 2 maps of thigh muscles were characterized before, two (D2) and four (D4) days after 40 maximal isometric electrically-evoked contractions in 25 healthy young males. On the basis of SPM analysis of coregistrated T 2 maps, the alterations were similarly detected at D2 and D4 in the superficial and distal regions of the vastus medialis (VM) whereas the proportion of altered muscle was higher in deep muscle regions of the vastus lateralis at D4 (deep: 35 ± 25%, superficial: 23 ± 15%) as compared to D2 (deep: 18 ± 13%, superficial: 17 ± 13%). The present methodology used for the first time on skeletal muscle would be of utmost interest to detect subtle intramuscular alterations not only for the diagnosis of muscular diseases but also for assessing the efficacy of potential therapeutic interventions and clinical treatment strategies.Unaccustomed exercises and neuromuscular diseases can lead to the occurrence of skeletal muscle damage 1-7 . These alterations are associated with several physiological events leading to inflammatory processes within muscle 1,6,[8][9][10][11] . Magnetic resonance imaging (MRI) appears as a method of choice to investigate in vivo the extent of muscle damage in healthy subjects [12][13][14][15][16] or in patients with neuromuscular diseases 4,7,17,18 . MRI is a powerful non-invasive tool allowing for a spatially-resolved analysis of muscle tissue 4,15,19 . The increase in muscle proton transverse relaxation time (T 2 ) has been identified as a relevant biomarker of muscle damage 15,[19][20][21][22] illustrating an inflammatory/edematous process 6,13,[23][24][25][26][27][28] . Different T 2 changes among muscles have been already reported after exercise-induced muscle damage 15,21,22 and in dystrophic boys 4 . In most of these studies, the averaged T 2 value was calculated in regions of interest within a given muscle thereby ignoring any spatial information. Although local T 2 changes were assessed along muscles 19,22 , no study provided information on the accurate localization and extent of intramuscular damage into the three dimensions (3D) of a skeletal muscle.Yet, accurate localization and quantification of muscle damage should provide more robust indices in diagnosis and longitudinal follow-ups of diseases or injuries. So far, only one study has reported information related to the distribution of intramuscular damage in dystrophic boys 7 . However, the analysis was only performed on a limited muscle volume (i.e., three MRI slices) and no information was provided on the localization of the most damaged areas within the muscle 7 . Moreover, we recently showed that neuromuscular electrostimulation (NMES) induced spatially heterogeneous T...