E.A. Dijkstra

Ultrasonic distance detection for a closed-loop spinal cord stimulation system

When stimulating the spinal cord at a constant strength, the current density in the spinal cord and thus the effects on chronic, intractable pain and vascular insufficiency will change with body position, due to the varying separation of the spinal cord and the stimulating electrode. The current density in the spinal cord has to remain between the perception and discomfort threshold (stimulation window) for a good therapeutic effect, i.e. that the patient does not suffer from pain. The stimulation window is very small. In current SCS systems the stimulus applied to the electrode is set at a constant value. A major improvement could be achieved when the distance between stimulation electrode and spinal cord could be measured and used to control the stimulus amplitude in a closed-loop system. An ultrasonic piezoelectric transducer was chosen to measure the distance between the electrode and the spinal cord.

Amperometric Sensor for Detection of Redox Activity

A method for obtaining the redox activity of a solution is presented. The proposed method does not require the use of a reference electrode, which is a major advantage under many circumstances. A simple setup consisting of two small platinum electrodes and a current source was used to measure the redox activity.

A Low Power Detection Method for Small Ultrasonic Echo Signals

Spinal cord stimulation is used for the management of chronic, intractable pain and vascular insufficiency. However, when stimulating at a constant voltage, the current density in the spinal cord changes due to the varying separation dbetween the spinal cord and the stimulating electrode, thus, preventing a stable clinical effect. In order to control the stimulation of spinal nerve fibers, a closed-loop system using ultrasonic delay time detection is being developed. This system is based on pulse-echo measurements using a piezoelectric transducer. The spinal cord stimulation system is an implanted system. Therefore, low power consumption (μW) is an important requirement. A low power electronic circuit is developed to detect the small echo signals (mV) from the spinal cord. The detection method is based on amplitude demodulation of the echo signal. The method is simulated in MATLAB, and the simulation results are compared to the results of a simulated matched filter method. The amplitude demodulation method shows results similar to the matched filter method.