Spacing-Compensated Measurement of the Acoustoelectric Interaction Constant for Quantitative Current-Density Imaging in Saline and Brain Tissue.

Abstract

Transcranial acoustoelectric brain imaging (tABI) combines focused ultrasound with electrical sensing for high-resolution current-density imaging. Its sensitivity and comparability depend on accurate measurement of the acoustoelectric (AE) interaction constant K, an intrinsic material property. Previous studies estimated K using equivalent current-source approximations under voltage-source stimulation, overlooking transient current variations. This study derives the AE amplitude-spacing relation and proposes a spacing-compensation method to eliminate spacing-induced bias, enabling quantitative estimation of current density. Guided by finite-element modeling (FEM), a chamber with adjustable electrode spacing was constructed to ensure a uniform current density distribution. Under voltage-source conditions, AE data were acquired across multiple spacings, and a spacing-compensation curve was derived. With spacing compensation, K in saline stabilized at -0.024 ± 0.001%/MPa, and its coefficient of variation decreased from 44.69% to 4.41%. Application to ex vivo porcine brain tissue yielded the first reported K for biological brain: -0.022 ± 0.005%/MPa. FEM comparison showed strong agreement, with RMSEs of 9.57% for saline and 6.86% for brain tissue in the uniform current-density region. Spacing compensation corrects spacing-dependent bias in K under voltage-source stimulation, preserving its physical meaning and enabling accurate conversion of AEamplitude into local current density. Accurate quantification of K enables reproducible and interpretable AE measurements, providing a quantitative foundation for current-density imaging and future applications in neural mapping and epilepsy localization.