Figure 7. The local ultrasound amplitude measurement for mid-plane detection.

a, b) the amplitude of the signal received by the active echo element verses the position of the probe. The depth of the US transmission beam focus is close to the catheter to probe distance, so the two plots are showing the signal distribution near the focus. a) The results with catheter perpendicular to the image plane (off-plane) b) catheter parallel to the image plane (in-plane). The error bar represents the standard deviation over 10 measurements, each time the translation stage moves from −9 mm to 9 mm, stops at the same sample positions and takes the signal amplitude reading.