# Clinical Brain Monitoring with Time Domain NIRS: A Review and Future Perspectives
## 3 Clinical Brain Monitoring with TD-NIRS
### Stroke Assessment  
The utility of using NIRS technology in the context of stroke has been reviewed by [PERSON] and [PERSON] in 2011 [83]. In that review, they concluded that using TD-NIRS is mandatory for the assessment of pathophysiological state-dependent variables such as perfusion or absolute values of tissue oxygenation. The first works reporting the use of TD-NIRS on stroke patients was by [PERSON] and colleagues [84; 85]. In these studies, the cerebral perfusion was measured by using the method of DCE-TD-NIRS. The bolus transit time through intra- and extra-cerebral tissue was measured in both hemispheres of two stroke patients, using an in-house developed multichannel TD-NIRS system (ID: 11 in Table 2). [PERSON] and colleagues [86] also reported the use of DCE-TD-NIRS to measure the cerebral perfusion in 10 acute stroke patients using an in-house developed multichannel TD-NIRS system (ID: 12 in Table 2). The authors reported to have used the kinetics of the moments to follow the kinetics of the ICG bolus. The kinetic difference between the affect and unaffected hemisphere was compared. The analysis of the variance enabled them to substantially reduce the movement artefacts and to follow the intracerebral compartment, compared to the traditional signals acquired with CW systems, which have been simulated here by time integrating the TPSF (illustrated in Figure 5b). Using the variance, the authors reported a clear difference in perfusion between the affected and non-affected hemisphere.  
Other groups reported the use of an in-house developed system to follow the brain oxygenation of stroke patients. [PERSON] and colleagues [87] compared the neurovascular coupling, induced by a simple motor test, between six patients with subacute ischemic stroke and four healthy volunteers. In this study, the neurovascular coupling was measured using a DC-MEG and a TD-NIRS system (ID: 13 in Table 2) simultaneously. Another in-house developed TD-NIRS system (ID: 14 in Table 2) was used by [PERSON] and colleagues [88] to measure haemoglobin concentrations and \(\text{StO}_{2}\) of the anterior circulation in stroke patients. In this study, 47 stroke patients were monitored in the stroke unit at the bedside. Multiple areas of the brain were probed (i.e., frontal, parietal, occipital) and CT-scans images were used to categorize brain regions below each TD-NIRS probe. Moreover, the results were compared with a group of 35 controls selected from a previous study reported in [82]. Significant differences of haemoglobin concentrations and \(\text{StO}_{2}\) were found between patients and controls, and among patients according to recalanization status.  
Finally, commercial Hamamatsu TD-NIRS systems were also used on stroke patients. [PERSON] and colleges [89; 90] reported the detection of vasospasm in patients with aneurismal subarachnoid haemorrhage (SAH). Another study by [PERSON] and colleagues [91] used a TRS-20 system to measure haemoglobin concentrations, \(\text{StO}_{2}\), and optical path length of five patients suffering from chronic stroke. They compared the results between the unaffected and affected hemisphere. Significant differences between the unaffected and affected hemisphere were found for \(\text{StO}_{2}\) (higher in the affected side), [HHb] (higher in the affected side) and optical path length (longer in the affected side).