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HSR-EMG

High Spatial Resolution Electromyography

 

Background

 

The motor unit, the smallest functional unit of a muscle, consists of a motor neuron and a specific number of innervated muscle fibers. The activity of these motor units contains detailed information about the structural and functional properties of the muscles. The activation patterns of healthy muscles differ from muscles with neuromuscular pathologies.

Picture 1: Motor Unit

Conventional techniques for measurement of the activity of motor units are invasive, therefore painful and not suitable for long term examinations. On the other hand the resolution of noninvasive techniques is not high enough to visualize the activity of single motor units.

The method of High-Spatial-Resolution EMG (HSR-EMG), developed at the Helmholtz-Institute, allows the non-invasive acquisition of the activity of these units.

 

 

Methods

The High-Spatial-Resolution electromyography consists of a two-dimensional array of electrodes. By the minimum distance between the electrodes the signal of the activity of more distant motor units is filtered. The resulting measured signal contains mainly information about the electrical activity of skin-deep motor units.

Picture 2: electrode array with 16 pins

The usage of a spatial filter increases the effect of filtering the information of the deeper motor units. The Laplace filter is an often used two-dimensional filter.

Picture 3: two-dimensional Laplace-Filter

The result of the filtered signal is the information about the activity of single motor units in the muscle.

Picture 4: activity of a single motor unit

Noninvasive diagnostic

The progression of a disease can be easily measured with the High-Spatial-Resolution EMG system. The technique is noninvasively and can also be used in children.  

A lesion of the brachial plexus, which is a network of nerves that send signals from the spinal cord to shoulder, arm and hand, occurs when the nerves are stretched or torn. Patients who suffer from brachial plexus lesions are impaired in their range of motion because several muscles are paralyzed in the affected arm. In some cases the injury is so serious that surgery becomes necessary. An objective assessment for the need of surgery is available with the HSR-EMG technique. Differences in the activation pattern of the motor units are clearly visible. Also different degrees of impairment can be displayed.

Picture 5: different degrees of paralysis

In addition to the plexus lesion further neuromuscular diseases were examined. An early diagnosis of neuromuscular diseases is very important in order to take appropriate therapies to the patient. The conventional assessment of the activity of motor units is invasive and therefore not suited for children. With the usage of HSR-EMG it is possible to differ between patients with muscular atrophy, patients with muscular dystrophy and healthy people.

Picture 6: differences in the activation pattern of healthy muscles, neuronal disorders and muscular disorders

Conclusion

The method of high-spatial-resolution EMG, developed at the Helmholtz-Institute, enables the noninvasive and therefore pain free assessment of the activity of single motor units. It is possible to gather valuable information for diagnosis and of the effect of therapies of neuromuscular diseases.

Project Manager