Diffusion tensor MRI for the in vivo determination of skeletal muscle architecture in two ankle angles

Introduction: Mechanisms of force loss that occur during progressive muscular diseases are more and more studied using mouse models. Such diseases generally cause both a decrease in maximal tension and progressive muscle wasting, which may result in profound changes in muscle architecture. Muscle architecture is a main determinant of the mechanical behavior of skeletal muscle [1], and is characterized by various parameters, including muscle length, fiber length, pennation angle, and physiological cross-sectional area (PCSA). The pennation angle is the angle between the muscle fibers and the tendon plate, while the PCSA is the sum of the cross-sectional areas of all fibers. Recently it has been established that Diffusion Tensor Imaging (DTI) with MRI offers the opportunity to quantitatively determine the muscle architecture of rodents [2,3]. Until then this architecture was determined by ultrasonography or anatomical reconstruction methods [1], which both have severe limitations. DTI is a noninvasive technique and enables the reconstruction of whole muscles in longitudinal studies. The aim of this study was to detect changes in skeletal muscle architecture using DTI-based fiber tracking. Therefore, the architecture of the tibialis anterior (TA) was determined in two ankle angles. It was hypothesized that an increased ankle angle would result in increased fiber length and a decreased PCSA and pennation angle.