Fig. 4.

Temperature estimation method and OA visualization of HIFU lesion progression in a fixed ex vivo liver specimen. (a) Flow diagram of the temperature estimation method using OA signals obtained from the fixed liver specimen. (b) OA images at the beginning (t = 0 s), middle (t = 15 s) and end (t = 30 s) of HIFU exposure for peak-to-peak voltage values of 170 V (first row), 340 V (middle row) and 500 V (third row) in continuous mode. Scalebar – 5 mm. (c) Temperature estimated from the OA signal variations (solid green, solid purple and solid orange curves) versus temperature measured using the thermal camera (dotted solid green, dotted solid purple and dotted solid orange curves) for three driving voltages. The regions of interest considered for the estimated temperatures are marked in green, purple and orange squares in (b).