Abstract
Diffusion tensor imaging (DTI) measures water diffusion in skeletal muscle tissue and allows for muscle assessment in a broad range of neuromuscular diseases. However, current DTI measurements, typically performed using pulsed gradient spin echo (PGSE) diffusion encoding, are limited to the assessment of non-contracted musculature, therefore providing limited insight into muscle contraction mechanisms and contraction abnormalities. In this study, we propose the use of an oscillating gradient spin echo (OGSE) diffusion encoding strategy for DTI measurements to mitigate the effect of signal voids in contracted muscle and to obtain reliable diffusivity values. Two OGSE sequences with encoding frequencies of 25 and 50 Hz were tested in the lower leg of five healthy volunteers with relaxed musculature and during active dorsiflexion and plantarflexion, and compared with a conventional PGSE approach. A significant reduction of areas of signal voids using OGSE compared with PGSE was observed in the tibialis anterior for the scans obtained in active dorsiflexion and in the soleus during active plantarflexion. The use of PGSE sequences led to unrealistically elevated axial diffusivity values in the tibialis anterior during dorsiflexion and in the soleus during plantarflexion, while the corresponding values obtained using the OGSE sequences were significantly reduced. Similar findings were seen for radial diffusivity, with significantly higher diffusivity measured in plantarflexion in the soleus muscle using the PGSE sequence. Our preliminary results indicate that DTI with OGSE diffusion encoding is feasible in human musculature and allows to quantitatively assess diffusion properties in actively contracting skeletal muscle. OGSE holds great potential to assess microstructural changes occurring in the skeletal muscle during contraction, and for non-invasive assessment of contraction abnormalities in patients with muscle diseases.
Highlights
Diffusion tensor imaging (DTI) is an MRI-based technique that allows to measure the anisotropic diffusion of water molecules in muscle tissue
For the images acquired with relaxed musculature, areas of signal voids were present for each volunteer using the pulsed gradient spin echo (PGSE) sequence
Our study suggests that fully compensated PGSE waveforms (M0 = M1 = M2 = 0) could provide the same benefit as oscillating gradient spin echo (OGSE) for skeletal muscle contraction imaging, this hypothesis has to be tested
Summary
Diffusion tensor imaging (DTI) is an MRI-based technique that allows to measure the anisotropic diffusion of water molecules in muscle tissue. DTI can non-invasively provide in vivo information on tissue architecture and microstructure, either normal or in a diseased state. In a typical DTI experiment, diffusion is probed along multiple directions using diffusion encoding gradients. The application of diffusion encoding gradients results in a signal attenuation, which across several directions can be geometrically interpreted by a rank 2 tensor. This tensor can be DTI of Skeletal Muscle Contraction Using OGSE diagonalized to derive the principal directions of diffusion. Due to its exquisite sensitivity to tissue microstructure, DTI is becoming an increasing popular tool to assess skeletal muscle status in a wide range of diseases [1] and muscle injuries [2]
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