Impedance Modulation by Pulsed Ultrasound

Abstract

The propagation of an acoustic wave in an electrolyte solution produces local and periodic conductivity changes. This acousto‐electrical interaction is due to the variations of the parameters controlling ionic conductivity against pressure and temperature. The overall effect is about 10−7% Pa−1 for solutions of physiological ions and is practically independent of the ionic species involved. The bulk compressibility of the medium is responsible for about 47% of the effect, the change in viscosity due to pressure changes is responsible for about 18%, and the changes of ionic mobility against temperature are responsible for about 35%. Detectable impedance changes were produced in the focal zone of a 500‐kHz focused transducer using moderate intensity ultrasound (peak pressure < 1 MPa). This technique potentially enables the association of the spatial resolution of pulsed ultrasound and impedance measurement, although technical improvements and feasibility studies are still needed prior to practical applications.

Application of acoustic-electric interaction for neuro-muscular activity mapping: A review

“…4 It was only several microvolts. A very small change in conductivity is caused by change in pressure, about 0.1% per MPa for NaCl solution, 1,5 which contributes to small AEI signal.…”

Expression for noninvasive measurement of internal map of local Joule heat consumption using acousto-electric effect

“…where K I is an interaction constant [15,16]. Thus, the temporal impedance change ÁZðtÞ due to a pressure pulse wave [15] can be written as …”

“…For an electric and echoic medium, using the AE effect [14][15][16][17], the temporal change Á'ðx; y; z; tÞ in conductivity 'ðx; y; zÞ due to a pressure wave pðx; y; z; tÞ can be written as Á'ðx; y; z; tÞ ¼ 'ðx; y; zÞK I pðx; y; z; tÞ;…”

“…That is, the relation between the AE voltage signal detected using paired electrodes and the ultrasound (US) pulsed echo signal is used (for instance, the amplitude of the AE signal is proportional to that of the US signal [15], in which the proportional coefficient is about 0.1% MPa À1 in a 0.9% NaCl solution used [16]) for monitoring cardiac [18,20] and nerve [19] activity. However, for the reconstructions, a major assumption is required, i.e., the homogeneity of conductivity.…”

“…Recently, the combination of a sensitivity theorem [8,12,13] and the acousto-electric (AE) effect [14][15][16] first described in [17] has been used to map internal currents [18,19] and dipoles [20]. That is, the relation between the AE voltage signal detected using paired electrodes and the ultrasound (US) pulsed echo signal is used (for instance, the amplitude of the AE signal is proportional to that of the US signal [15], in which the proportional coefficient is about 0.1% MPa À1 in a 0.9% NaCl solution used [16]) for monitoring cardiac [18,20] and nerve [19] activity.…”