Assessing human scalp and brain blood flow sensitivities via superficial temporal artery occlusion using speckle contrast optical spectroscopy.

Cerebral blood flow is a critical metric for cerebrovascular monitoring, with applications in stroke detection, brain injury evaluation, aging, and neurological disorders. Noninvasively measuring cerebral blood dynamics is challenging due to the presence of scalp and skull, which obstruct direct brain access and contain their own blood dynamics that must be isolated. We developed an aggregated seven-channel speckle contrast optical spectroscopy (SCOS) system to measure blood flow and blood volume noninvasively. Each channel, with a distinct source-to-detector distance, targeted different depths to detect scalp and brain blood dynamics separately. By briefly occluding the superficial temporal artery, which supplies blood only to the scalp, we isolated surface blood dynamics from brain signals. Results on 20 subjects show that scalp-sensitive channels experienced significant reductions in blood dynamics during occlusion, while brain-sensitive channels experienced minimal changes. This provides experimental evidence of scalp blood flow sensitivity in diffuse optical measurements such as SCOS, highlighting optimal configuration for preferentially probing brain signals noninvasively.