Figure 4 : Simulation geometry (a) and simultaneously reconstructed absorbed optical energy (b) / acoustic heterogeneity (c) by finite element based photoacoustic reconstruction algorithm considering acoustic heterogeneity. The optical contrast for target A, B, C is 2:1, 1:1 and 2:1, respectively. The acoustic contrast (speed of sound) for target A, B, C is 1485:1485, 1560:1485 and 1560:1485, respectively.