Fig 1.
Overview of the MR compatible indentation and MRE setup.
Following parts are labeled: Fiberglass tube (A), 3D-printed heating blanket (B), anesthesia mask (C), fixation block (D), indentor (E), MRE actuator (F), shaker base plate (G), electromagnetic shaker (H). Part E and F are shown in more detail in Fig 2.
Fig 2.
Detail of indentation and MRE actuator part of setup.
Indentor and MRE piston are indicated with a label. Indentor can be positioned on the rats TA using the movable indentor holder. The MRE piston is coupled to the tendon at the distal side of the TA muscle. Overview figure indicating all parts is shown in online supplemental S2 Fig.
Fig 3.
Anatomical images and T2 maps.
Axial anatomical images (A-C) and T2 maps (D-F) of the hind limb before, during, and after indentation, respectively.
Fig 4.
Axial 3D ultra-short echo time images of the alginate cast surrounding the rat leg, pre, during and post indentation. FLASH 3D rendering shows anatomical landmarks and location of selected 3D ultra-short echo time images.
Fig 5.
Displacement field of z-direction with line profile.
(A) Shows the displacement in μm along the line profile illustrated as blue line in the (B) displacement field image of the z direction in the TA muscle.
Table 1.
Mean and maximum displacement amplitude Atot before, 30, 60 and 90 min after end of indentation per animal and mean ± sd of the group.
Fig 6.
MRE pre, during post indentation.
SE-MRE magnitude (mag) and wave (θ1—θ8) images before, during and after indentation. Wave images θ1, θ2, θ3, θ4, θ5, θ6, θ7, and θ8 correspond to 00, 450, 900, 1350, 1800, 2250, 2700, 3150 wave phase, respectively.
Fig 7.
Snapshot of a 16 offset 900 Hz SE-EPI-MRE (A) before and (B) after indentation.
Fig 8.
Elastograms and T2 maps before and after indentation.
(A, B) Elastograms representing shear storage modulus Gd and (C, D) T2-maps (A, C) before, and (B, D) after indentation.
Fig 9.
Mean (± sd) T2 and Gd measured in the circular ROI of 4x indentor’s diameter positioned around the center of indentation of 6 animals before and after end of indentation.
(A) Mean (± sd) T2 before and 45 min after end of indentation. T2 45 min after end of indentation was significantly higher (***p < 0.01) than before indentation. (B) Mean (± sd) Gd before, 30, 60 and 90 min after end of indentation. Gd is increased at all time points after indentation. Gd at 30 min after end of indentation was significantly higher than before indentation (**p < 0.05).
Fig 10.
Percentage elevated T2 and Gd pixels of ROI in the TA muscle of 6 animals before and after end of indentation.
Pixels were selected as significantly elevated, if the value was higher as mean value before indentation + 2 x sd. (A) Percentage elevated T2 pixels before and 45 min after end of indentation. Percentage elevated T2 pixels 45 min after end of indentation was significant higher (***p < 0.01) than before indentation. (B) Percentage elevated Gd pixels before, 30, 60 and 90 min after end of indentation. Percentage elevated Gd pixels 30 min after end of indentation was significant higher than before indentation (**p < 0.05).
Table 2.
Measured mean (±sd) shear storage modulus Gd, and percentage elevated pixels of shear storage modulus Gd elev. in ROI of whole TA muscle, and mean shear storage modulus Gd in circular ROI of 4x indentor’s diameter.
Table 3.
Measured mean (±sd) and percentage elevated pixels of T2 map in ROI of whole TA muscle, and mean T2 in circular ROI of 4x indentor’s diameter.