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Date of download: 4/4/2017 Copyright © ASME. All rights reserved. From: Magnetic Resonance Imaging Assessment of Mechanical Interactions Between Human Lower Leg Muscles in Vivo J Biomech Eng. 2013;135(9):091003-091003-9. doi:10.1115/1.4024573 Figure Legend: Schematic of the leg and trunk within the MRI instrument. (a) Undeformed state. The body is prone on a table (solid line) that is can be moved in and out of the bore of the MRI machine. MRI compatible ankle-foot orthosis (see inset for a picture) was used to fix the ankle angle at 90°, in such a way to leave a small space between posterior side of the lower leg and the ankle-foot orthosis and also between anterior side of the lower leg and MR patient table to avoid exertion of other external forces. The ankle-foot orthosis was secured onto the patient table using support material. The tips of the toes were not allowed to contact the bore of the MRI machine in order to prevent the foot from being loaded mechanically. (b) The deformed state. The trunk of the subject is now supported and brought as close as possible to the bore wall. This creates movement in hip as well as knee joints, but leaves the lower leg in a similar position. In any case the ankle angle is unchanged. Date of download: 4/4/2017 Copyright © ASME. All rights reserved. From: Magnetic Resonance Imaging Assessment of Mechanical Interactions Between Human Lower Leg Muscles in Vivo J Biomech Eng. 2013;135(9):091003-091003-9. doi:10.1115/1.4024573 Figure Legend: Examples of MR images of the lower leg. (a) Longitudinal image of the lower leg representing a sagittal slice illustrating the locations of the group of cross-sectional slices (white solid rectangle) to be analyzed for strains. For all subjects, the most proximal cross-sectional slice of the slice group was located at the upper third of the imaged portion of the lower leg, a level corresponding to the mid-belly of m. gastrocnemius. The white dashed rectangle encloses the group of cross-sectional slices on which the method was tested by imposing known deformations on m. gastrocnemius. Strains induced as a result of this test were analyzed only for the group of cross-sectional slices enclosed by white solid rectangle for which deformations were maximal. (b) An example of a cross-sectional image of the slice group with anatomical identification of muscles or muscle groups and bones (tibia and fibula). Five anatomical regions of interest were distinguished: m. gastrocnemius, m. soleus, deep flexor muscles, peroneal muscles, and Date of download: 4/4/2017 Copyright © ASME. All rights reserved. From: Magnetic Resonance Imaging Assessment of Mechanical Interactions Between Human Lower Leg Muscles in Vivo J Biomech Eng. 2013;135(9):091003-091003-9. doi:10.1115/1.4024573 Figure Legend: Typical example of a validity test: Comparison of known imposed deformations and those calculated using Demons algorithm. (a) and (b) Known deformations imposed artificially as shown on cross-sectional and sagittal images, respectively. The white horizontal line in (a) denotes the location of sagittal images shown in (b) and (d). (c) and (d) Corresponding deformations detected using Demons algorithm by comparing original (undeformed) and artificially deformed images. Deformations were visualized on a grid at certain pixel intervals (7 × 11 pixels, for better visualization of the combined image and grid). Note that deformations are found exclusively within gastrocnemius muscle (i.e., the only location where they had been imposed). (e) Strain errors higher than actually imposed strains are mapped (scaled according to the color grayscale bar on the right). The errors occur particularly at the boundary of deformed and undeformed volumes. The white curve indicates the peak error (7.88%) occurring at the boundary. For the enlarged Date of download: 4/4/2017 Copyright © ASME. All rights reserved. From: Magnetic Resonance Imaging Assessment of Mechanical Interactions Between Human Lower Leg Muscles in Vivo J Biomech Eng. 2013;135(9):091003-091003-9. doi:10.1115/1.4024573 Figure Legend: A typical example of deformations calculated as caused by changing joint angles. (a) A cross-sectional slice acquired in the undeformed state. A regular grid (made up of lines connecting voxel group centers) is imposed on the image at certain pixel intervals (7 × 11 pixels) for better visualization. (b) The corresponding slice acquired in the deformed state. Using Demons algorithm, displacement fields are calculated. Based on these displacement fields, the regular grid in (a) is deformed. Such deformed grid is imposed on this image. Date of download: 4/4/2017 Copyright © ASME. All rights reserved. From: Magnetic Resonance Imaging Assessment of Mechanical Interactions Between Human Lower Leg Muscles in Vivo J Biomech Eng. 2013;135(9):091003-091003-9. doi:10.1115/1.4024573 Figure Legend: Effect of altered knee angle: Local lengthening and shortening effects (first and third principal strain). Box and whisker plots: The horizontal line inside each box represents the median strain value; the upper and lower edges of each box itself represent upper and lower quartiles respectively (i.e., the 75th and 25th percentiles), and lines extending from each end of the box (whiskers) indicate the peak values of the principal strains plotted. Interquartile ranges (IQR i.e., absolute value of the difference between upper and lower quartiles) were considered as a measure of strain heterogeneity within each anatomical region. Data were represented per anatomical region of interest (muscle or muscle group) and analyzed across all subjects.