invasive you have to insert into the carotid artery and jugular vein some sensors to detect the oxygen content so can we do this now you massively we can use photo cosec tomography to quantify the oxygen saturation we use so2 to represent the oxygen saturation level at both the caudate artery in the jugular vein and you'll see that they have different values the difference in so2 tells you how much oxygen has been extracted by the brain so this is an indicator that tells you how well our brain is consuming the oxygen if this