Fig. 5. ( A ) Optoacoustic signal (with a distinct peak from the SSS) measured in vivo from the sheep head at an Fio2of 1.0 ( dashed line ) and an Fio2of 0.07 ( solid line ). ( B ). First derivatives (in arbitrary units; au) of the optoacoustic signals from the sheep head at an Fio2of 1.0 ( dashed line ) and an Fio2of 0.07 ( solid line ). First derivatives were obtained from the signals presented in ( A ). Dashed areas represent the signals from the SSS calculated by using the second algorithm.