Diffuse correlation spectroscopy for measurement of cerebral blood flow: future prospects

Abstract

Diffuse correlation spectroscopy (DCS) is an emerging optical modality used to measure cortical cerebral blood flow. This outlook presents a brief overview of the technology, summarizing the advantages and limitations of the method, and describing its recent applications to animal, adult, and infant cohorts. At last, the paper highlights future applications where DCS may play a pivotal role individualizing patient management and enhancing our understanding of neurovascular coupling, activation, and brain development.

Keywords: biomedical optics; cerebral blood flow; medical imaging; spectroscopy.

Fig. 1

(a) Schematic of typical DCS instrumentation that consists of a long-coherence length source coupled to a multimode fiber for light delivery to the tissue, photon-counting detector(s), and an autocorrelator board that computes the intensity of the autocorrelation function, ${\mathrm{g}}_2(\tau )$, based on photon arrival times (b), (c) Sample ${\mathrm{g}}_2(\tau )$ curves obtained over the frontal cortex in a subject under baseline conditions (black) and under hypercapnia (3% inspired carbon dioxide, gray). The increased decay rate of ${\mathrm{g}}_2(\tau )$ during hypercapnia reflects the increase in CBF by vasodilation.

Fig. 2

Selected validation of DCS measured ${\mathrm{CBF}}_{\mathrm{i}}$ against other CBF modalities. (a) Relative changes in CBF measured by DCS (${\mathrm{rCBF}}_{\mathrm{DCS}}$) is highly correlated with relative CBF measured with fluorescent microspheres (${\mathrm{rCBF}}_{\mathrm{FM}}$); (b) Absolute ${\mathrm{CBF}}_{\mathrm{i}}$ correlates well with absolute CBF measured with phase encoded velocity mapping MRI in neonates.

Fig. 3

Relative changes in cerebral blood flow measured with DCS during postural manipulation of head-of-bed (HOB) position from 30 to $-5°$ (inset) for (a) a typical healthy subject, (b) a stroke patient who demonstrated the typical response of impaired autoregulation in the injured hemisphere when HOB is lowered, and (c) a stroke patient who demonstrated a paradoxical response in the injured hemisphere during the lowering of HOB, seen in approximately 20% of stroke patients. (a) Left hemisphere in dark gray, right in light gray, (b,c) contralesional in dark gray, ipsalesional in light gray. Figure courtesy of Mesquita et al.

Fig. 4

Fractional changes of oxy- and deoxy-hemoglobin concentrations (rHbO and rHbR, respectively), as well as cerebral blood flow (rCBF) and cerebral oxygen metabolism (${\text{rCMRO}}_{2\text{i}}$) measured with NIRS and DCS overthe left somatosensory cortex in preterm infants during 5 seconds of gentle stimulation of the hand, indicated by the gray shaded region.