Xeni Deligianni1,2, Francesco Santini1,2, Anna Hirschmann3, Ning Jin4, Nicolas Place5, Oliver Bieri1,2, and Claudia Weidensteiner1,2
1Radiology/Division of Radiological Physics, University Hospital of Basel, Basel, Switzerland, 2Biomedical Engineering, University of Basel, Basel, Switzerland, 3Radiology, University Hospital of Basel, Basel, Switzerland, 4Siemens Medical Solutions, Cleveland, Cleveland, OH, United States, 5Institute of Sport Sciences, University of Lausanne, Lausanne, Switzerland
Synopsis
MRI of the upper extremities is important for the follow-up of
muscle dystrophies. The goal of this study was to investigate the
feasibility of 4D-velocity imaging during neuromuscular electrical
stimulation(NMES) of the arm, standardized with the force output. Two
healthy volunteers were scanned at 3T during isometric contraction of
the biceps brachii for different elbow angles. While the force output
was different in intensity, the waveforms of force and strain were
similar. In conclusion, it was shown that it is possible to acquire
3D-dynamic velocity data synchronized with NMES of the arm
and simultaneously record
the evoked force.
INTRODUCTION
The upper extremities can be severely affected by various muscle
dystrophies1,2, with a serious impact on the patients’ life
quality. Although MRI techniques for voluntary contraction of the arm
have been presented for the understanding of contraction mechanisms3,4, the literature is limited regarding 3D dynamic visualization
of the arm function. The goal of this study was to investigate the
feasibility of three-directional 3D velocity imaging of neuromuscular electrical muscle stimulation (NMES) of the upper extremities, that
can be beneficial both for diagnosis and for treatment follow-up.METHODS
Two healthy volunteers (1 male (age: 31 y) /1 female (age: 47 y))
were scanned twice with different settings at a 3T MRI scanner
(MAGNETOM Prisma, Siemens Healthcare, Erlangen, Germany) during
neuromuscular electrical stimulation of the biceps brachii muscle.
Superficial gel-based electrodes of different sizes (5x8 cm2 and
5x5 cm2) were placed on the biceps brachii (see Fig. 1)
and the arm was positioned at 0° and 60° flexion angle.
During the experiment, the participant was holding
a 3D-printed handle (see Fig. 1), adapted to measure volar flexion
force5. The muscle belly stimulation intensity was increased until
a clearly periodic force curve was registered by the force sensor.
This level was defined in a test session before placing the subject
in the bore.
A commercial 2-channel NMES device (EM49, Beurer
GmbH, Ulm, Germany), was used to induce periodic muscle contraction.
Biphasic stimulation with rectangular pulses was applied (pulse
width: 400μs, pulse frequency: 80Hz, contraction duration: 750ms,
release duration: 750ms release, current amplitude 10-20 mA). The
second channel of the NMES device generated a signal, which was
converted by a custom electronic device and used as trigger for the
MRI acquisition6.
A prototype prospectively-gated highly accelerated
Cartesian 4D flow imaging sequence was applied for the dynamic
acquisition7,8. The sequence uses L1-regularized wavelet-based
compressed sensing. The volume-of-interest was placed in a sagittal
orientation, parallel to the bone to cover the part of the upper arm
between the two electrodes. The force output of volar flexion was
continuously recorded. The imaging protocol had the following
parameters: TE/ Time resolution/ TR= 3.5/ 49.6/ 6.2 ms, flip angle
10°, bandwidth 455 Hz/px, matrix size 144x72x48, resolution
2.1x2.1x2.1mm3, Venc 25 cm/s, 2 k-space lines per segments,
acceleration factor 7.1. The acquisition time was 5 minutes per each
dataset.
The 3D-velocity datasets were subsequently
post-processed offline to calculate the strain (i.e., the two
principal eigenvalues and eigenvectors of the strain tensor) at each
spatial location throughout the stimulation cycle 9. Time-resolved
color-coded maps of the tensile strain (positive eigenvalue) and
compressive strain (negative eigenvalue) were produced.RESULTS
The 3D-velocity imaging and strain calculation was successful in all
cases, but the force could only be successfully registered when the
elbow was flexed to 60° angle. On the strain maps, the different
activation of various regions could be clearly visualized. The two
different positions of the arm at 0° (i.e. parallel to the bore) and
at 60° resulted in different 3D strain maps (Figs.2 and 3).
At
0°, the biceps brachii
and triceps brachii
muscle could be easily
differentiated (see Fig. 2) and corresponded to different
eigenvalues. At
60°, the
force-measurement setup and the arm positioning allowed to
acquire
dynamic images during NMES of
the upper arm and
simultaneously register the evoked force (see
Figure 4). The velocity
images were artifact-free and the Venc
of 25 cm/s was
sufficient for image acquisition.
While the force output of the two volunteers was
very different in intensity at 60° position (see Fig. 4), the shape
of the waveform of the evoked force was very similar. The same effect
was observed for the strain waveforms (see Fig. 5).DISCUSSION
It is well known that the upper extremities are affected by various
muscle dystrophies2, with an important impact on the patients’
life quality. Therefore, non-invasive methods and biomarkers to study
their physical condition and response to treatments are valuable.
Here, it was shown that it is possible to acquire 3D-dynamic velocity
data synchronized with NMES of the upper arm. The evoked force could
be simultaneously registered when the elbow was flexed to 60°.
Strain maps were successfully calculated and the first and second
primary strain eigenvalues were
extracted. In future
studies,
the current can also be chosen to reach a certain target force for a
more quantitative analysis of the results.CONCLUSION
3D-velocity imaging of the upper arm can be performed during NMES
with simultaneous evoked force recording. Moreover, important
differences were observed in the evoked force and strain for
different positions of the arm. The proposed method is easily
implementable, allows dynamic 3D-velocity imaging and can potentially
give insight into the physical condition of the upper extremities.Acknowledgements
This
work was supported by the Swiss National Science Foundation (grant
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