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