Synchronous Magnetic Resonance Imaging of Muscle Contraction induced by Electrical Stimulation
Xeni Deligianni1,2, Michele Pansini3, Meritxell Garcia4, Anna Hirschmann4, Arno Schmidt-Trucksäss5, Oliver Bieri1, and Francesco Santini1,2

1Department of Radiology, Division of Radiological Physics, University of Basel Hospital, Basel, Switzerland, 2Department of Biomedical Engineering, University of Basel, Basel, Switzerland, 3Radiology, Kantonsspital Basel-Landschaft, Brudeholz, Switzerland, 4Department of Radiology, University of Basel Hospital, Basel, Switzerland, 5Department of Sports Medicine, University of Basel, Basel, Switzerland

Synopsis

Magnetic Resonance Imaging can be used to provide structural and functional muscle information either from oxygenation or contraction imaging. Contraction imaging can be based on real-time imaging or on voluntary movements. However, synchronization of the acquisition is challenging. Here, we present a new method for accurate, quantitative measurement of muscle contraction using a commercially available electrical muscle stimulator. This allows the direct assessment of the reaction time of muscle fibers, contraction speed, displacement, and strain providing complementary information to electromyography. MR images of the vastus lateralis muscle of five healthy volunteers were acquired at 3 Tesla field strength during electro-stimulation.

PURPOSE

Assessing the functionality of muscle fibers is essential to monitor both pathological and physiological processes, such as in athletes, or in patients with muscular diseases. Structural and functional muscle information can be obtained with MRI using oxygenation1 or contraction imaging2. Phase contrast (PC)2,3 or spin tag (ST) techniques4 are commonly used to image muscle motion. Contraction can be assessed using real-time methods5, possibly in combination with a mechanical restriction to the movement to improve repeatability6, but synchronization and standardization are very challenging. Here, we propose a dedicated setup to accurately measure muscle contraction with high temporal resolution using MRI in combination with a commercial electrical muscle stimulator (EMS), hence allowing a direct assessment of muscle kinematics.

METHODS

A commercially-available EMS device was used to induce involuntary periodic muscle contraction of the vastus lateralis muscle (VL) synchronized with high-temporal-resolution cine phase contrast (PC) MRI acquisition at 3T. The EMS device produced a monopolar square wave with adjustable frequency and pulse duration (set to 150 pulses per second and 300 μs, respectively, see Figure 1). A three-directional gradient echo PC velocity encoding sequence was applied for three different stimulation settings. MR acquisitions were performed on a parasagittal slice with a spatial resolution of 2.3 x 2.3 x 5 mm3 and a temporal resolution of 42 ms. The velocity encoding had a VENC of 25 cm/ s (TR/ TE = 10.6/ 7.21 ms, bandwidth/ pixel = 400 Hz / Px, flip angle = 10°, matrix = 96 x 128, FOV= 225 x 300 mm2,1 k-space line per segment, acquisition time 5 min) and 94 temporal phases were acquired. The proposed method was evaluated in five male volunteers at varying levels of stimulation (10, 14, 18-20 mA). Maximum contraction speed was calculated offline, and the strain tensors were extracted from the velocity fields.

RESULTS

The proposed MRI acquisition produced artifact-free velocity and strain maps and the data were consistent across all volunteers. We observed two different phases with different velocity vectors close to the beginning and end of the contraction, respectively, (see Figure 2). For maximum stimulation, at the time point of release, the velocity was in general much higher and approximately double as compared to the one at the beginning of the contraction period (see Figure 3). There were also apparent differences in the velocity directions for the proximal and the distal part of the VL, being reflected in the derived strain maps as well (see Figure 4). Moreover, the distal part of the muscle appeared to be activated earlier in time.

At different stimulation levels, all derived quantitative parameters varied substantially and appeared to follow an approximate power-law. At 18 mA, the maximum contraction speed was 3.77±0.78 cm/s with a maximum principal strain of 0.37±0.14, whereas at 10 mA, no contraction was induced.

DISCUSSION

The purpose of this study was to introduce a method for assessing functional and dynamic muscle properties with MRI in a controlled way by inducing involuntary muscle contraction with an EMS device. We chose to use a widely available commercial EMS device and open hardware and software in order to make our setup easily reproducible. Furthermore, the generation of the trigger from the stimulation signal itself allows the usage of a wide range of triggered MRI sequences, including conventional cardiovascular sequences, usually available on commercial scanners with little or no modification.

The proposed method was successful in producing accurate velocity and strain maps of the vastus lateralis muscle. All considered quantitative parameters resulting from the proposed method showed a prominent dependency on the stimulation current, which was consistently observed across all subjects.

CONCLUSION

MRI of EMS-controlled involuntary muscle contraction is feasible and allows offline calculation of velocity and strain maps that significantly depend on the stimulation current used. The main advantages of this method is that it is non invasive, utilizes a commercially available electrical muscle stimulator and simple open-source hardware and offers simultaneous acquisition of synchronized MRI images with controlled muscle contraction.

Acknowledgements

This work was supported by the Swiss Foundation for Research on Muscle Diseases.

References

1. Noseworthy MD, Davis AD, Elzibak AH. Advanced MR imaging techniques for skeletal muscle evaluation. Semin Musculoskelet Radiol 2010;14:257–268.

2. Sinha S, Hodgson JA, Finni T, et al. Muscle kinematics during isometric contraction: development of phase contrast and spin tag techniques to study healthy and atrophied muscles. J Magn Reson Imaging 2004;20:1008–1019.

3. Drace JE, Pelc NJ. Measurement of skeletal muscle motion in vivo with phase-contrast MR imaging. J Magn Reson Imaging 1994;4:157–163.

4. Axel L, Dougherty L. MR imaging of motion with spatial modulation of magnetization. Radiology 1989;171:841–845.

5. Mazzoli V, Sprengers A, Nederveen AJ, et al. Real Time fat suppressed MRI of the knee joint during flexion/extension allows the study of PCL motion. In: Proc. Intl. Soc. Mag. Med. 23. Toronto; 2015. p. 1211.

6. Sinha S, Shin DD, Hodgson JA, et al. Computer-controlled, MR-compatible foot-pedal device to study dynamics of the muscle tendon complex under isometric, concentric, and eccentric contractions. J Magn Reson Imaging 2012;36:498–504.

Figures

Figure 1: Experimental setup: stimulation waveform as recorded using an oscilloscope. The trigger signal is also depicted on the oscilloscope trace. The EMS device, was programmed to deliver a stimulus of 1-s rise time, 1-s plateau and 2-s pause.

Figure 2. Color-coded velocity images from an 18 mA stimulation, at the beginning (top) and at the end of the contraction (bottom). Velocity vectors for each voxel are represented as lines, color-coded according to the direction (red: phase, blue: readout, green: through-plane), and their length is proportional to their magnitude.

Figure 3. Exemplary diagrams of peak velocity for three different stimulation settings for a region-of-interest covering the vastus lateralis muscle.

Figure 4. Quantitative strain maps for different amplitude currents and different time frames. Three stimulation levels of the same volunteer are presented. At the maximum current the principal strain of the vastus lateralis muscle is homogeneous, while for a medium current pronounced local differences can be observed.



Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)
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