Distance detection improves effect of spinal cord stimulation

The effect of spinal cord stimulation, in chronic pain treatment, can be drastically improved using continuous distance detection. The strength of the stimulation pulses then depends on the distance measured between the electrodes and the spinal cord. In this way, negative side-effects belong to the past. These side-effects arise with a varying distance, causing diminished pain treatment in case of a distance that is too large, or unwanted sensations when the distance is too small. Emiel Dijkstra of the University of Twente developed a distance detection system. He finishes his PhD-research with the MESA+ research institute on February 27.

Spinal cord stimulation is effective in treatment of chronic pain. An electrode-array is implanted, sending short pulses to the spinal cord. This artificial nerve stimulation blocks certain pain signals. The electrodes have a fixed position, however, this means that the distance varies with movements of the patient. By measuring this distance along with the stimulation, the pulses can be adjusted continuously.

From MRI-scans, Dijkstra concludes that the distance can vary up to several millimeters. This has a direct effect on the signal reaching the spinal cord. With maximum distance, the signal can be too weak to have an effect. With minimum distance, the effect can be that the patient feels the pulses themselves, this is unpleasant as well. Using ultrasound, Dijkstra is now able to detect the distance. He therefore places a piezo-electric transducer on the electro-array.

This transducer has to face strict demands. It has to be able to distinguish between the spinal cord and the surrounding fluid, while the acoustic difference between them is small. Secondly, it has to be integrated along with the implantable electrodes. Its size therefore may not exceed 25 square millimetres, with a thickness of not more than two millimetres. And it has to be highly biocompatible: the human body has to accept this ‘intruder’.

In addition to these demands, the energy consumption must be close to zero. The electrode array is fed from outside the body, using radio signals, or a complete stimulation system is implanted in the abdomen region. In both cases, the distance detector may not consume substantial electric power.

Electric eals
The combination of electrodes, distance detection and control electronics provides a more comfortable and precise way of pain treatment. While in ancient Rome, already electric eals were used to treat pain, Dijkstra’s method is more friendly for the patient.

Emiel Dijkstra MscEE has performed his research under supervision of prof. Piet Bergveld within the MESA+ Institute of the University of Twente, and he was financially supported by Medtronic Inc., manufacturer of spinal cord stimulation electrodes.