# Optics Based Label-Free Techniques and Applications in Brain Monitoring
## 3 DCS Technology Used Currently in Human Brain Imaging
### Current Clinical Applications of DCS  
In cancer diagnosis and therapies DCS shows high potential, because tumors, due to their extraordinary metabolic demand, have high concentration of HDR accompanied by the low oxygen saturation [108]. Thus, monitoring of tumor hemodynamics in the cancer therapy procedure is highly noteworthy since cancer therapy can modify tumor's region metabolic status, and generally, the combination of DCS and fNIRS can be beneficial to assess tumor hemodynamics e.g., before, during and after the therapy [109; 110]. Usability of DCS-NIRS has been studied for this purpose to some extent, for instance, in the detection and comparison of breast tumor blood flow between healthy and patient subjects [111; 112]. Another application of DCS-NIRS is the therapy procedure monitoring in photodynamic therapy (PDT) [113]. Furthermore, for neural health straightforward assessment, cerebral oxygen metabolism (CMRO\({}_{2}\)) is a clue parameter. DCS-NIRS can provide vital information regional CBF and regional oxygen delivery, resulting regional CMRO\({}_{2}\)[114].  
DCS has been also applied to evaluate special parameters like intracranial pressure (ICP) and rate of CMRO\({}_{2}\). ICP measurement is preferable for diagnosis of disorders like hydrocephalus and meningitis. ICP variation can affect CBF. In the methods presented in the patent [113], DCS measures specifically pulsatile CBF (PCBF). PCBF and some other biological parameters contribute in ICP calculation [113]. In 2010, [PERSON] et al. [17] conducted a study on 11 premature neonates using FD-NIRS and DCS. They quantified cerebral blood volume (CBV), cerebral tissue oxygenation (StO2), CBF index (CBFi) by FD-NIRS and rate of CMRO\({}_{2}\) by DCS. This setup of data is certainly valuable to care neonatal brains who suffer from perinatal brain injuries. Another therapeutic application, cerebral hemodynamics monitoring during mechanical thrombectomy treatment, was performed using DCS-NIRS to identify CBF changes and hemodynamics [115].  
[PERSON] at el. [116] employed functional DCS (fDCS) and time-resolved fNIRS (TR-fNIRS) together with EEG during stimulation. By using this setup, they have observed the increment of CBF and HbO concentration but decrement of HDR during and after active stimulation in the region. To expand the use of DCS, [PERSON] et al. [117] utilized DCS to quantify blood flow and fNIRS for Hb concentrations and reported that low-frequency (1 Hz) repetitive transcranial magnetic stimulation (rTMS) affects CBF and tissue oxygenation.  
In addition, it can be beneficial to imply the DCS usages for neurocritical patients. Head-of-bed manipulation is done for continuous monitoring CBF in neurocritical patients [118]. [PERSON] et al. [119] conducted a study in seven patients during induced blood pressure changes and carbon dioxide arterial partial pressure variation. Their hypothesis was CBF/oxygenation measurement using DCS, comparing with xenon-enhanced computed tomography (XeCT) concurrently, in frontal lobes. The study showed that DCS and NIRS measurements can be successfully done in critically injured brain patients.  
Figure 2: A typical diffuse correlations spectroscopy (DCS) setup uses a long coherent laser, single photon detectors and correlator.