SignificanceAlthough multilayer analytical models have been proposed to enhance brain sensitivity of diffuse correlation spectroscopy (DCS) measurements of cerebral blood flow, the traditional homogeneous model remains dominant in clinical applications. Rigorous in vivo comparison of these analytical models is lacking.AimWe compare the performance of different analytical models to estimate a cerebral blood flow index (CBFi) with DCS in adults.ApproachResting-state data were obtained on a cohort of 20 adult patients with subarachnoid hemorrhage. Data at 1 and 2.5 cm source-detector separations were analyzed with the homogenous, two-layer, and three-layer models to estimate scalp blood flow index and CBFi. The performance of each model was quantified via fitting convergence, fit stability, brain-to-scalp flow ratio (BSR), and correlation with transcranial Doppler ultrasound (TCD) measurements of cerebral blood flow velocity in the middle cerebral artery (MCA).ResultsThe homogeneous model has the highest pass rate (100%), lowest coefficient of variation (CV) at rest (median [IQR] at 1 Hz of 0.18 [0.13, 0.22]), and most significant correlation with MCA blood flow velocities (Rs = 0.59, p = 0.010) compared with both the two- and three-layer models. The multilayer model pass rate was significantly correlated with extracerebral layer thicknesses. Discarding datasets with non-physiological BSRs increased the correlation between DCS measured CBFi and TCD measured MCA velocities for all models.ConclusionsWe found that the homogeneous model has the highest pass rate, lowest CV at rest, and most significant correlation with MCA blood flow velocities. Results from the multilayer models should be taken with caution because they suffer from lower pass rates and higher coefficients of variation at rest and can converge to non-physiological values for CBFi. Future work is needed to validate these models in vivo, and novel approaches are merited to improve the performance of the multimodel models.
We use diffuse correlation spectroscopy (DCS) to measure changes in microvascular blood flow in subarachnoid hemorrhage patients treated with intrathecal nicardipine. Our results suggest that IT nicardipine achieves the desired effect of microvascular vasodilation in the majority of patients. The CBF response plateaus by day 3, indicative of steady state of drug concentration in the brain. Interestingly, those patients whose microvascular cerebral blood flow did not respond were the ones who went on to develop worse outcome in the form of a secondary stroke.
Subarachnoid hemorrhage (SAH) is a neurosurgical emergency that results from the rupture of an aneurysm in the subarachnoid space. One common complication of SAH is cerebral vasospasm, which can lead to a secondary stroke. Intrathecal (IT) Nicardipine holds promise in treating cerebral vasospasm through its direct vasodilatory effect on the cerebral vasculature. Here, we used diffuse correlation spectroscopy to continuously monitor microvascular cerebral blood flow changes in medium-high grade subarachnoid hemorrhage patients in response to the first dose of IT Nicardipine. To date, we have recruited 9 patients, 3 of whom developed a secondary stroke.
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