Data for phantom experiments
Fow phantom imaging sequence
Ultrasound images were acquired using an 18 MHz linear array (L22-14vX LF with 128 piezoelectric elements, 100 μm pitch, 22 mm elevation focus, Verasonics, USA) connected to a programmable ultrasound scanner (Vantage 256 High frequency configuration, Verasonics, USA). We transmitted a sequence of 12 angled plane waves (-10° to 10°), resulting in a 1 kHz frame rate after compounding. Ensembles of 200 compounded frames were acquired every 2 s for a total period of 360 s, resulting
in an effective power Doppler rate of 0.5 Hz. During acquisition, RF data were real-time delay-and-sum beamformed to complex In-phase and Quadrature (IQ) frames, which were saved for later offline Doppler processing. In the phantom study, an ultrasound imaging plane was selected to capture the transverse cross-section of the BMF channel. The imaging probe was positioned at three different distances to the channel, and data were recorded in separate sessions for each distance. During each session, the probe was mounted on a motorized XYZ-stage and positioned over the phantom, which was immersed in a water tank. For each session, recordings were made both without and with the Neural Electrode Phantom (NEP) placed between the probe and the phantom. The NEP consisted of a 2.5 μm ParC substrate, 300 nm Au with a 50 nm Ti adhesion layer, and 1.5 μm ParC insulation. To prevent floating, the NEP was weighted down during placement.