Optimizing frequency and pulse shape for ultrasound current source density imaging

Abstract

Electric field mapping is commonly used to identify irregular conduction pathways in the heart (e.g., arrhythmia) and brain (e.g., epilepsy). A new technique, ultrasound current source density imaging (UCSDI) based on the acoustoelectric (AE) effect, provides an alternative method for current activity mapping in four-dimension with high resolution. The ultrasound transducer frequency and pulse shape significantly affect the sensitivity and spatial resolution of UCSDI. In this paper, we analyze the tradeoff between spatial resolution and sensitivity in UCSDI from two aspects: (1) ultrasound transducer frequency and (2) coded excitation pulses. For frequency dependence, we imaged an electric dipole using ultrasound transducers with different center frequencies (1 MHz and 2.25 MHz) and compared the sensitivity and resolution. For coded excitation, we measured AE signals with chirp excitation at 1 MHz and demonstrated improved sensitivity for chirps (3.5 µV/mA at 1 MHz) compared with square pulse excitation (1.6 µV/mA). Pulse compression was also applied to preserve spatial resolution, demonstrating enhanced detection while preserving spatial resolution.

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

“…A non-linear chirp with optimized inverse filtering can improve SNR by >6 dB under certain conditions compared to a short linear frequency modulated pulse (chirp) (Tseng et al, 2017). They also demonstrated that chirp excitation can improve the SNR (Qin et al, 2012a) and sensitivity (Qin et al, 2012b)) of AE signals compared to broadband square wave pulse excitation. In addition to this, they designed a test chamber (Figure 6) and found that the AE interaction constant K was strongly concentration dependent for the divalent salt CuSO4, but not for the monovalent salt NaCl (Li et al, 2012).…”

“…Despite the importance of current source imaging for brain and heart treatment, current imaging methods are difficult to have both non-invasive and high spatiotemporal resolution. In recent years, hybrid current source imaging techniques, represented by AE effect-based current source imaging, have been widely pursued (Witte et al, 2007 ; Olafsson et al, 2008b , 2009 ; Wang et al, 2011 ; Li et al, 2012 ; Qin et al, 2012b , 2015 ; Renhuan et al, 2013 ; Wang and Witte, 2014 ). These techniques not only allow imaging of currents injected from outside and have the promise of imaging real currents in tissue (see Table 1 for details).…”

Mapping the ECG in the live rabbit heart using Ultrasound current source density imaging with coded excitation

“…A pulse compression algorithm was also employed to preserve the spatial resolution for chirp excitations. The details of the pulse compression algorithm for UCSDI were discussed in another study [18]. …”

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

“…7 Influential in the research of acousto-electric interaction signal in the recent years, has been a group of American researchers at the University of Michigan, that have performed several investigations on the AEI signal and the possibility of using the signal to map biological current. 2,[8][9][10][11][12][13][14][15][16][17] Several more studies have been performed for further investigations and improvements of measurements and setup. 18 Also our group has made some investigations and come up with a potentially useful application for denervated muscles.…”