A diffusion tensor-based method facilitating volumetric assessment of fiber orientations in skeletal muscle

Abstract

Background The purpose of this study was to develop a DTI-based method to quantitatively assess fiber angles and changes therein in leg muscles in order to facilitate longitudinal studies on muscle fiber architectural adaptations in healthy subjects. Methods The upper legs of five volunteers were scanned twice on the same day. The right lower legs of five volunteers were scanned twice with the ankle in three positions, i.e. -15° dorsiflexion, 0° neutral position, and 30° plantarflexion. The MRI protocols consisted of a noise scan, a 3-point mDixon scan and a DTI scan. Fiber-angle color maps were generated for four muscles in the upper legs and two muscles in the lower leg. Voxel-wise fiber angles (θ) were calculated from the angle between the principal eigenvector of the diffusion tensor and a reference line defined between the origo and insertion points of each muscle. Bland-Altman analysis, intraclass correlation coefficient (ICC), coefficient of variation (CV%), minimal detectable change (MDC), standard error (SE) and Friedman test were used for assessing the feasibility of this method and in order to have an indication of the repeatability and the sensitivity. Results Bland-Altman analysis showed good repeatability (CV%<10 and 0.7≤ICC≤0.9) with exception of the Tibialis Anterior (TA) muscle in dorsiflexion position(CV%: 12.2) and the Semitendinosus (ST) muscle (left leg) (CV%: 11.4). The best repeatability metrics were found for the SOL muscle in neutral position (CV%: 2.6). Changes in average θ in TA and SOL with ankle positions were observed in accordance with expected agonist and antagonist functions of both muscles. For example, for the anterior left compartment the change in fiber angle Δθ with respect to the neutral position Δθ = -1.6° ± 0.8° and 2.2° ± 2.8° (p = 0.008), for dorsiflexion and plantarflexion, respectively. Conclusion Our method facilitates fast inspection and quantification of muscle fiber angles in the lower and upper leg muscles in rest and detection of changes in lower-leg muscle fiber angles with varying ankle angles.

Effect of two eccentric hamstring exercises on muscle architectural characteristics assessed with diffusion tensor MRI

“…26 With custom-built DTI data analysis methods and tractography software, fascicle length and orientation can be reliably determined in lower limb muscles. [27][28][29][30] The aim of this study was to evaluate the effect of the Nordic hamstring exercise and Diver hamstring exercise on muscle fascicle length and orientation in the biceps femoris long head, semitendinosus and semimembranosus through DTI. Secondary aims were to evaluate the effect of these hamstring exercises on strength, flexibility, and individual hamstring muscle volume.…”

“…Water diffusion in healthy muscle tissue is anisotropic, which means that the majority of water molecules diffuse along the longitudinal axis of the muscle fibers 26 . With custom‐built DTI data analysis methods and tractography software, fascicle length and orientation can be reliably determined in lower limb muscles 27–30 …”

“…Primary outcome measure: fascicle orientation Fascicle orientation maps were determined for the volume of the biceps femoris long head, semitendinosus and semimembranosus individually 30. The orientation maps consisted of one angle per voxel within the hamstring muscles, with respect to a reference line, placed on the proximal intramuscular tendon of the individual hamstring muscle.…”

Advanced MRI Approaches for Evaluating Common Lower Extremity Injuries in Basketball Players: Current and Emerging Techniques

“…63 Another study demonstrated the reproducibility of 3D muscle pennation angle and fascicle length measurements using DTI with different leg positions and time points during a training intervention. 64 The latter study also illustrated the importance of successfully registering the diffusion scan to the anatomical reference for strong repeatability results when using DTI. DTI shows promise for detailed insight into muscle status at the fiber level.…”

“…Repeatability of standard DTI in upper leg muscles of healthy adults showed the highest repeatability (within‐subject coefficient of variations) with MD (4.5%), and then λ 2 (4.9%), λ 1 (5.3%), λ 3 (5.7%), and FA (15.2%) 63 . Another study demonstrated the reproducibility of 3D muscle pennation angle and fascicle length measurements using DTI with different leg positions and time points during a training intervention 64 . The latter study also illustrated the importance of successfully registering the diffusion scan to the anatomical reference for strong repeatability results when using DTI.…”