# Clinical Brain Monitoring with Time Domain NIRS: A Review and Future Perspectives
## 3 Clinical Brain Monitoring with TD-NIRS
### Peroperative Care  
It has been demonstrated that the use of NIRS to monitor the level of anaesthesia could lead to better postoperative cognitive performance of the patient [108]. In a peroperative context, [PERSON] and colleagues [109] evaluated the application of TD-NIRS to monitor cerebral oxygenation during carotid surgery. The authors used an in-house developed multichannel TD-NIRS system (ID: 15 in Table 2) on a group of 16 patients with atherosclerotic disease and monitored them during routine carotid endarterectomy surgery. The authors reported that the changes in the haemoglobin signals, as estimated from intracerebral tissue, are very sensitive to clamping of the internal carotid artery, whereas its sensitivity to clamping of the external carotid artery is limited. This is a good indicator that the TD-NIRS method used in this paper can achieve in-depth selectivity. Furthermore, seven studies using Hamamatsu systems were reported in a peroperative context. [PERSON] and colleagues [110] reported the monitoring of cerebral circulation during cardiopulmonary bypass surgery using a TRS-10 system. In this study, 23 patients who underwent coronary-artery bypass surgery were evaluated reporting that TD-NIRS can be used to follow brain oxygenation during cardiac bypass surgery. Moreover, the authors reported a large fluctuation of the mean optical path length among patients. The authors also reported that the inter-patient variability of saturation was low compared to that of the haemoglobin concentrations. This finding was also recently reported in healthy volunteers [82]. In another study, [PERSON] and colleagues [111] also monitored the cerebral tissue saturation of patients undergoing a cardiac surgery requiring a cardiopulmonary bypass using a TRS-10 system. The jugular venous oxygen saturation (SjvO\({}_{2}\)) was also monitored. Moreover, postoperative cognitive dysfunction (POCD) was evaluated using the MMSE before and seven days after the operation. It was found that there was no significant difference between the SjvO\({}_{2}\) and StO\({}_{2}\) in patients without POCD, but that those two values were significantly different in patients with POCD. Therefore, the combination of SjvO\({}_{2}\) and cerebral StO\({}_{2}\) might help predict the occurrence of POCD. Lastly, [PERSON] and colleagues [112] also used a TRS-10 system to investigate the depth-dependence of haemoglobin concentration changes during carotid endarterectomy (CEA) in eight male patients with symptomatic carotid stenosis during CEA surgery reporting brain specificity of the TD-NIRS. Additionally, two studies using TRS-20 systems investigated the cerebral oxygenation of pregnant women during child delivery. [PERSON] and colleagues [113] reported cerebral oxygenation, on the PFC, of eighteen pregnant women during caesarean section, reporting that in a case of placenta previa, massive bleeding immediately decreased cerebral StO\({}_{2}\). [PERSON] and colleagues [114] reported the cerebral [HbT] in pregnant women in delivery. They showed difference between normotensive and hypertensive women with or without epidural anaesthesia. Moreover, a decrease in cerebral [HbT] in the hemi-prefrontal lobe in a woman 2 h after the onset of haemorrhagic stroke in labour could also be detected. This reinforces the possibilities of using TD-NIRS in the context of child delivery. Finally, [PERSON] and colleagues [115] using the latest TD-NIRS device developed by [PERSON] (a two-channel tNIRS-1) reported in one patient a decrease in brain [HbT] and StO\({}_{2}\) during circulatory arrest in cardiac surgery.