Significance: Intracranial pressure (ICP), variability in perfusion, and resulting ischemia are leading causes of secondary brain injury in patients treated in the neurointensive care unit. Continuous, accurate monitoring of cerebral blood flow (CBF) and ICP guide intervention and ultimately reduce morbidity and mortality. Currently, only invasive tools are used to monitor patients at high risk for intracranial hypertension.

Aim: Diffuse correlation spectroscopy (DCS), a noninvasive near-infrared optical technique, is emerging as a possible method for continuous monitoring of CBF and critical closing pressure (CrCP or zero-flow pressure), a parameter directly related to ICP.

Approach: We optimized DCS hardware and algorithms for the quantification of CrCP. Toward its clinical translation, we validated the DCS estimates of cerebral blood flow index (CBF_i) and CrCP in ischemic stroke patients with respect to simultaneously acquired transcranial Doppler ultrasound (TCD) cerebral blood flow velocity (CBFV) and CrCP.

Results: We found CrCP derived from DCS and TCD were highly linearly correlated (ipsilateral R²  =  0.77, p  =  9  ×  ^{10  −  7}; contralateral R²  =  0.83, p  =  7  ×  ^{10  −  8}). We found weaker correlations between CBF_i and CBFV (ipsilateral R²  =  0.25, p  =  0.03; contralateral R²  =  0.48, p  =  1  ×  10^−  3) probably due to the different vasculature measured.

Conclusion: Our results suggest DCS is a valid alternative to TCD for continuous monitoring of CrCP.