Partial pressure of Oxygen, that is, amount of oxygen in the blood (normally referred to as Dissolved Oxygen).

Monitoring the partial pressure of oxygen in brain tissue (PbtO2) is an important tool for traumatic brain injury (TBI) but is invasive and inconvenient for real-time monitoring.

Near-infrared spectroscopy (NIRS), which can monitor hemoglobin parameters in the brain tissue, has been used widely as a noninvasive tool for assessing cerebral ischemia and hypoxia. Therefore, it may have the potential as a noninvasive tool for estimating the change of PbtO2.