The EPIRET3 system can be successfully implanted and explanted in patients with blindness and RP. The surgical steps are feasible, and the postoperative follow-up disclosed an acceptable range of adverse events.
A substitution calibration technique for piezoelectric ultrasonic hydrophones is presented that uses an optical multilayer hydrophone as the reference receiver. Broadband nonlinearly distorted focused pulses are first measured with the reference hydrophone and then with the hydrophone to be calibrated. By Fourier transformation of the time wave forms and division of the frequency spectra, the complex-valued frequency response of the hydrophone under test is obtained in a broad frequency range in a very fast and efficient way and with high frequency resolution. The results obtained for a membrane hydrophone and a needle-type hydrophone are compared with those obtained by independent calibration techniques such as primary calibration using optical interferometry and secondary calibration using time-delay spectrometry, and good agreement is found. The calibration data obtained are apt to improve the results of ultrasound exposure measurements using broadband voltage-to-pressure conversion. This is demonstrated for standard pulse parameter determination from exemplar exposure measurements on a commercial diagnostic ultrasound machine. For the membrane hydrophone, the evaluation method commonly used leads to an overestimation of the positive peak pressure by up to 50%, an underestimation of the rarefactional peak pressure by up to 11%, and an overestimation of the pulse intensity integral by up to 28%.
A technique for the primary calibration of hydrophones based on an optical principle is presented. An interferometer determines the displacement of a pellicle mounted on the surface of the tank fluid perpendicular to the sound propagation axis; the known acoustic field is then measured using the hydrophone. The application range extends from 1 to 50 MHz and, with a lesser accuracy, to 70 MHz. The loaded and the open-circuit sensitivity are obtained pointwise, and the frequency and the number of the measurement points can be arbitrarily chosen. As an example, two membrane hydrophones with a spot diameter of 0.5 mm are calibrated, and the comparison with a theoretical model describing the acoustic and electrical properties of the hydrophone shows good agreement.
Visual sensations in blind patients suffering from retinal degenerations may be restored by electrical stimulation of retinal neurons using implantable microelectrode arrays. The EPI-RET-3 project was initiated to evaluate a wireless intraocular retinal implant system for human use in terms of safety and efficiency. The implant is a remotely controlled fully intraocular prosthesis consisting of a receiver and a stimulator module. The stimulator is placed onto the retina's surface. Data and energy are transmitted via an inductive link from outside the eye to the implant. The EPI-RET-3 device was implanted into six legally blind patients with Retinitis Pigmentosa (RP) for a period of four weeks. The surgery was performed without complications. The implants were activated on days 7, 14 and 27 after implantation. All patients reported visual sensations such as dots, arcs, or lines of different colours and intensities. The required stimulation thresholds were found to be very low. Implantation of the wireless EPI-RET-3 device is safe and the system is suitable to elicit visual sensations in blind RP patients. Major problems in the design and fabrication of a prosthesis for artificial vision could be solved in this approach.
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