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Ultrasound Current Source Density Imaging (UCSDI) potentially improves 3-D mapping of bioelectric sources in the body at high spatial resolution, which is especially important for diagnosing and guiding treatment for cardiac and neurologic disorders, including arrhythmia and epilepsy. In this study, we report 4-D imaging of a time varying electric dipole in saline. A 3-D dipole field was produced in a bath of 0.9% NaCl solution by injected current ranging from 0 to 140 mA. On the electrode chamber made on a 3D printer, each electrode can be placed anywhere on an XY grid (5mm spacing) and individually adjusted in the depth direction for precise geometry of current sources and recording electrodes. A 1 MHz ultrasound beam was pulsed and focused through a plastic film to modulate the current distribution inside the tank filled with saline. Acoustoelectric (AE) signals were simultaneously detected at a sampling frequency of 15MHz on up to 6 recording electrodes simultaneously. One single recording electrode can effectively provide enough information to form volume images of the dipole. The full-width-half-maximum of the reconstructed current dipole is 3.93mm along x-y plane, and 4.93mm along fast time. The ANR for envelope detection of the current waveform was 46 dB at 500 KPa and a 133mA dipole. Real-time 3-D UCSDI of current flow simultaneously co-registered with anatomy (pulse echo ultrasound) and standard electrophysiology (e.g., ECG) potentially facilitates corrective procedures for cardiac and neural abnormalities.