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Review
. 2017 Jul;4(3):031208.
doi: 10.1117/1.NPh.4.3.031208. Epub 2017 Apr 7.

From brain to blood vessels and back: a noninvasive optical imaging approach

Gabriele Gratton  1   2 , Antonio M Chiarelli  2 , Monica Fabiani  1   2
Affiliations
Review

From brain to blood vessels and back: a noninvasive optical imaging approach

Gabriele Gratton et al. Neurophotonics. 2017 Jul.

Abstract

The seminal work of Grinvald et al. has paved the way for the use of intrinsic optical signals measured with reflection methods for the analysis of brain function. Although this work has focused on the absorption signal associated with deoxygenation, due to its detailed mapping ability and good signal-to-noise ratio, Grinvald's group has also described other intrinsic signals related to increased blood flow, scattering effects directly related to neural activation, and pulsation effects related to arterial function. These intrinsic optical signals can also be measured using noninvasive diffuse optical topographic and tomographic imaging (DOT) methods that can be applied to humans. Here we compare the reflection and DOT methods and the evidence for each type of intrinsic signal in these two domains, with particular attention to work that has been conducted in our laboratory. This work reveals the refined two-way relationship that exists between vascular and neural phenomena in the brain: arterial health is related to normal brain structure and function, both across individuals and across brain regions within an individual, and neural function influences blood flow to specific cortical regions. DOT methods can provide quantitative tools for investigating these relationships in normal human subjects.

Keywords: deoxygenation signal; diffuse optical tomography; fast optical signals; intrinsic optical signal; neurovascular coupling; optical measures of cerebrovascular pulse (pulse-DOT); oxygenation signal; reflection optical imaging.

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Figures

Fig. 1
Fig. 1
Schematic representation comparing (a) exposed-cortex reflection optical imaging methods with (b) noninvasive diffuse optical imaging methods. The MR image of the monkey head presented in (a) is obtained from Ref. .
Fig. 2
Fig. 2
(a) Maps and (b) time course of the fNIRS hemodynamic response (measured as a change in the concentration of oxy- and deoxy-hemoglobin in occipital regions) during repeated visual stimulation in 19 young adults. (c) Maps and (d) time course of the fast optical signal (EROS—measured as a change in the delay of near-infrared photons migrating through occipital regions) during repeated visual stimulation measured concurrently with the fNIRS response in the same subjects. For the EROS activity, the two maps refer to two different latencies (80 and 192 ms) from the individual stimulus onset (grid reversals).
Fig. 3
Fig. 3
(a) Typical pulse wave as measured at the carotid by ultrasound Doppler. (b) Pulse wave measured optically as a change in the intensity of the AC light moving between a source and a detector located on the surface of the head. The peak of the systole corresponds to a minimum (and the peak of the diastole to a maximum) in the amount of light detected after traveling through the tissue. (c) Schematic depiction of changes in arterial diameter and oxy-hemoglobin content during a pulse cycle, causing the changes in light intensity shown in (b), as more light is absorbed during the systole. (d) Spatially filtered images of the pulse in the brain overtime averaged across participants, emphasizing the largest arteries. Images are based on changes from the diastolic peak value (on average 153 ms after onset of the EKG R-wave). The systolic peak (on average 409 ms after R-wave onset) shows the maximum change with respect to the diastolic peak value. At this point, the large arteries are most visible. (e) Distribution of the sources (in yellow) and detectors (in red) used for data collection over the MR-rendered scalp of a representative participants. Other digitized locations used for coregistration with the structural MRI recordings are shown in green. FL = front left. Figure reprinted from Ref.  with permission from the publisher (Wiley).
Fig. 4
Fig. 4
Maps of the arterial pulse relaxation function obtained with diffuse optical imaging methods in four healthy adults varying in age and CRF. Figure reprinted from Ref.  with permission from the publisher (Wiley).
See this image and copyright information in PMC

References

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