Hi Jacob, thanks for the question. Yes, there is a probability of Compton scatter (inelastic) or even a tiny probably of Thomson scatter (elastic) of the 511 keV photons with the electrons in the attenuating medium (i.e. the brain, skull, etc.). However, a good fraction of these high-energy photons do escape without any interaction at all. (Photoelectric absorption can also occur with relatively low probability).
@ 0:18 Hi Andrew. I was wondering, isn't the photon "going upward" deflected from its path by collisions with atoms in the brain cells?
Hi Jacob, thanks for the question. Yes, there is a probability of Compton scatter (inelastic) or even a tiny probably of Thomson scatter (elastic) of the 511 keV photons with the electrons in the attenuating medium (i.e. the brain, skull, etc.). However, a good fraction of these high-energy photons do escape without any interaction at all. (Photoelectric absorption can also occur with relatively low probability).
@@AndrewJReader Aha, thanks! What is modern physics without probabilities ;-)