Optimizing frequency and pulse shape for ultrasound current source density imaging

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.