Polarity detection in ultrasound current source density imaging

Abstract

Modulating the electric dipole field with ultrasound pulse, ultrasound current source density imaging (UCSDI) can detect current direction and form spatial 3D imaging of dipole changing in one period of treatment. As ultrasound pulse passes through the conductive media, it convolves/correlates with the inner product of the electric field of a dipole and lead field of a pair of detectors, making the shifting frequency of polarity lower than the center frequency of the ultrasound pulse. After acoustoelectric (AE) signal is shifted to base band, the AE voltage is positive at anode and negative at cathode. In the simulation, the lead fields of detectors and electric field of dipole were calculated by the finite element (FE) method; the convolution and correlation in the computation of AE signal were accelerated using 3-D fast Fourier transforms. The current direction and amplitude are encoded in the phase and amplitude of the AE signal. Based on the analysis of polarity algorithms on the simulated and in-vitro ultrasound current source density images, it is concluded that the cross-correlation method is significantly better than the autocorrelation method to extract the frequency shift for high pulse bandwidth.

Selective Mapping of Deep Brain Stimulation Lead Currents Using Acoustoelectric Imaging

“…As an US beam is pulsed and swept in a conductive medium, a recording electrode detects the high frequency AE interaction signal, which is proportional to the local pressure and current. Feasibility of AEI for mapping current densities has been demonstrated in a variety of preparations, including time-varying dipoles (Olafsson et al, 2008, Wang et al, 2011, Wang et al, 2016, Berthon et al, 2017) and imaging of the cardiac depolarization wave in the live rabbit heart (Olafsson et al, 2009, Qin et al, 2015). The primary goals for this study are to 1) assess the performance (spatial resolution, sensitivity, and accuracy) of AEI for detecting and resolving current densities near a DBS device using stimulation parameters resembling those used clinically, and 2) demonstrate feasibility and benchmark performance of AEI through a human skullcap.…”

Biological current source imaging method based on acoustoelectric effect: A systematic review

“…In other words, conventional methods of cardiac potential conduction mapping suffer from low spatial resolution, low SNR, and long imaging times (He and Wu, 2001 ). The ultrasound current source density imaging (UCSDI) is a very effective method for mapping cardiac potential conduction (Li et al, 2012 ), and it has been demonstrated by various techniques (e.g., time-varying dipoles) (Nguyen et al, 2008 ; Wang et al, 2016b ).…”