Assessment of Human Skeletal Muscle Contraction and Force by Diffusion Tensor Imaging

Junichi Hata,Haruyuki Nagata,Masakazu Sato,Yuji Komaki,Kazuo Yagi,Tomokazu Numano,Kazuki Endo

doi:10.4236/ojrad.2015.54026

Abstract

We aimed to investigate the association between mobility and skeletal muscle strength by using magnetic resonance diffusion tensor imaging (DTI). This study included 20 healthy male volunteers (mean age, 21.8 ± 1.1 years). The maximum voluntary strength (MVC) of each participant was measured with the ankle joint in plantar and dorsal flexion using an instrument for measuring muscle strength. Moreover, magnetic resonance imaging (MRI) was performed with the ankle joint at rest, in plantar flexion, and in dorsal flexion. For imaging, a 1.5-T MRI device was used, and a diffusion-weighted stimulated echo-planar imaging pulse sequence. Tensor eigenvalues (λ), fractional anisotropy (FA), and the apparent diffusion coefficient (ADC) were calculated from data obtained by DTI. The resulting MRI data were compared to the data on muscle mobility or strength and statistically analyzed. Regarding changes in DTI indices during muscle movements, anisotropy of the tibialis anterior was significantly increased from rest to plantar flexion (P < 0.01), whereas no significant change was observed in dorsal flexion (n.s.). In contrast, the extent of significant changes in anisotropy of the medial gastrocnemius (mGC) and soleus (SOL) was small at plantar flexion (mGC, P < 0.01; SOL, n.s.), whereas the indices were significantly increased at dorsal flexion (P < 0.01). Regarding the correlation between MVC of each skeletal muscle and the DTI indices, FA and λ3 were significantly correlated in movements involving the muscles, whereas no significant correlation was observed in movements not involving them. Changes in intramuscular water molecules by elongation and contraction of the skeletal muscle fibers could be assumed to affect changes in diffusional anisotropy. When muscles contract, the space between myocytes was reduced and they might become increasingly dense. Moreover, diffusional anisotropy increased with increasing MVC, whereas ADC remained unchanged. DTI was suggested to produce measurements similar to the degree of muscle strength.

Highlights

Diffusion tensor imaging (DTI) is a technique that allows calculation of the diffusion direction of water molecules into the body [1]
The skeletal muscles are directly associated with quality of life (QOL) and activities of daily living (ADL) and comprise a medically important organ that is affected by age-related disease and mobility impairments
Changes in the DTI indices of the skeletal muscles of the lower leg with the ankle joint positioned at dorsal flexion and rest

Summary

Introduction

Diffusion tensor imaging (DTI) is a technique that allows calculation of the diffusion direction of water molecules into the body [1]. Fractional anisotropy (FA) can be calculated from values called apparent diffusion coefficient (ADC) determined by measuring the long axis of tissue (λ1) and two vertical lines to the axis (λ2 and λ3). This FA is considered extremely useful for assessing nerve-like fibrous tissue [2]-[4]. Many studies of the skeletal muscles using MRI have been reported, including assessments of muscle morphology [5] [6], muscle metabolism with hydrogen (1H) or phosphorus (31P) by magnetic resonance spectroscopy (MRS) [7]-[9], and muscle function by the measurement of T2 values [10]-[13]. DTI, on which the present study focuses, has been reported in studies on the assessment of muscle morphology, such as measurement of pennation angle by tensor tractography [14], depiction of orientation [15]-[17], and assessment of muscle damage [18]

Objectives

Methods

Results

Conclusion