Laura Secondulfo1, Joep J M Suskens2, Ozgur Kilic2, Valentina Mazzoli3, Mario Maas4, Hans J.L Tol2, Aart Nederveen4, Melissa Hooijmans1, and Gustav J Strijkers1
1Biomedical Engineering and Physics, UMC Amsterdam, Location AMC, Amsterdam, Netherlands, 2Orthopedic Surgery, UMC Amsterdam, Location AMC, Amsterdam, Netherlands, 3Radiology, Lucas Center for Imaging, Stanford University, Stanford, CA, United States, 4Radiology and Nuclear Medicine, UMC, Amsterdam, Location AMC, Amsterdam, Netherlands
Synopsis
Hamstring injuries have high recurrence rates in elite athletes,
which motivates the investigations in novel diagnostic methods for muscle
injury and follow-up. Diffusion tensor imaging facilitates direct and indirect
monitoring of the muscle condition and architecture. Fiber orientations and changes
therein due to injury or training are considered a key parameter; however, the
assessment over the full volume of an individual muscle is still difficult.
Therefore, we developed a method to generate reproducible quantitative
fiber-angle color maps of the whole volume of leg muscles, which proved
sensitive to changes due to muscle stretch and a training intervention.
Introduction
In elite athletes, hamstring re-injuries have a high recurrence
rate, which motivates the development of novel diagnostic methods for muscle
injury and follow-up [1]. Diffusion tensor imaging provides parameters to
assess both muscle condition and architecture such as muscle volume, fiber
length and orientation which are important determinants of muscle function [2].
Fiber orientation has shown to change due to training, muscle injury [3] and in
muscle diseases [4,5]. We developed a method to generate reproducible
quantitative fascicle-angle color maps (FACM) of the whole leg muscles from DTI
acquisitions, which proved sensitive to changes due to muscle stretch
and a training intervention.Methods
The repeatability of our approach was assessed in both the upper
legs (exp.1) and in one lower leg in three foot positions (exp.2). The
sensitivity to changes detection with this method was gauged in the lower leg
at 3 different passive ankle angles (15˚ dorsiflexion, 0˚ neutral position, and
30˚ plantarflexion) using a costume device (exp.2) and in a clinical case in
the upper leg before and after training intervention in basketball players (exp.3).
The intervention consisted of Nordics exercises for a period of 12 weeks, 54
times per leg per week; the training regime was reached after 4 weeks.
All three datasets consisted of 5 subjects and were acquired
twice with a 3T Philips MRI, using a 16-channel anterior coil and the 10 table
posterior coils. Subjects were positioned in feet-first supine position.
The MRI protocols included a 3-point mDixon scan for anatomical reference and a
DT-MRI protocol (Figure 1). The scanning parameters for the upper legs were: FFE: TR=8.0ms,
TE/ΔTE=133/1.1ms, voxel size=1.5x1.5x3mm3; SE-EPI: TR=4630ms, TE=53ms
voxel-size=3x3x6mm3 , diffusion b-value=450s/mm2; for the
lower leg FFE: TR=7.7ms, TE/ΔTE=2.1/1.7ms, voxel-size=1x1x2.5mm3; SE-EPI:
TR=11191ms, TE=51.63ms, voxel-size=3x3x5mm3, diffusion b-value =
400s/mm2 with SPAIR fat suppression.
The DT-MRI data were analyzed with QMRITools for Mathematica 12 [6]
which included noise suppression, registration to anatomical images, tensor fitting (iWLLS), eigenvalue and
eigenvector calculations.
FACM were calculated between the principal eigenvector in each
voxel and the vector parallel to a chosen reference line. Reference lines were
defined in ITK-SNAP based on anatomical data of tendons, muscle insertions, and
bone orientations.
In the repeatability experiment of the upper legs (exp.1), ROIs
were manually defined on the anatomical image in the biceps femoris long head (BFlh) of the right and the left
leg, while in the intervention experiment (exp.3), only the FACM of the left
leg BFlh was measured. In both datasets of the upper legs (exp.1&3) the
reference line was defined between the insertion points of the BFlh (Figure 2).
In the lower leg (exp2), ROIs were the soleus (SOL) and the
tibialis anterior (TA) and the reference line was described by a point on the
tibia plate and the most distal and posterior point in the FOV of the
diaphysis.
The repeatability and the precision of the measurements were
assessed using Bland-Altman analysis and the coefficient of variation (CV).
Additionally, the distributions of the measurements and the FACM in proximal
and medial small ROIs close to the intramuscular tendon were measured and
compared.Results and Discussion
FACM were obtained in the whole muscle body for 4 muscles of the
upper and lower legs (exp.1-3) and changes therein were measured with passive foot
stretch in the lower leg muscles (exp.2) and with training intervention in the
upper legs in both the whole BFLh volume as well as in smaller ROIs (exp.3).
The Bland-Altman analysis of
average FACM showed good agreement for
both exp.1&2 (Figures 2&3).
In exp.1 the CV was 6.4, with
limits of agreements (LoA) between -2.0° and 0.4°. For
exp.2 the LoA ranges were between -2.5°
and 6.9° for the TA and between -2.4° and 3.0° for
the SOL. These larger LoA ranges can be explained by the 3 degrees of freedom
of the ankle.
The changes in the mean value of FACM with passive foot stretch (Figure 3) agreed with literature [7] and, as expected, the overall
change was minor in the SOL [8].
The repeatability results should
be considered in light of the quality of the diffusion scan, the muscle anatomy
and location, and fat composition. The most important factor seems a successful
registration of the diffusion scan to the anatomical reference, which is highly
dependent on scan quality and which affects the selection of the correct ROIs
where the FACM are measured.
The results of exp.3 show that our
method can successfully be applied to measure changes in fibers orientation due
to a training intervention. In fact, in individual subjects changes in mean fascicles
orientation between baseline and after training were above the LoA of exp.1 (range
1.0-6.0°). Fiber distributions of the
BFlh for 2 cases out of 5 are shown in Figure 4. Moreover, larger changes in the mean values were detectable in
smaller ROIs defined close to the intramuscular tendon
(Figure 5).Conclusions
Our approach facilitates the generation of reproducible
fiber-angle color maps of the muscles in the leg, for monitoring changes in
training and recovery. Small
changes with passive foot stretch and due to training intervention in the whole
muscle volume and in smaller ROIs can be quantified. References
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