fNIRS Optodes' Location Decider (fOLD): a toolbox for probe arrangement guided by brain regions-of-interest

Abstract

The employment of functional near-infrared spectroscopy (fNIRS) as a method of brain imaging has increased over the last few years due to its portability, low-cost and robustness to subject movement. Experiments with fNIRS are designed in the face of a limited number of sources and detectors (optodes) to be positioned on selected portion(s) of the scalp. The optodes locations represent an expectation of assessing cortical regions relevant to the experiment's hypothesis. However, this translation process remains a challenge for fNIRS experimental design. In the present study, we propose an approach that automatically decides the location of fNIRS optodes from a set of predefined positions with the aim of maximizing the anatomical specificity to brain regions-of-interest. The implemented method is based on photon transport simulations on two head atlases. The results are compiled into the publicly available "fNIRS Optodes' Location Decider" (fOLD). This toolbox is a first-order approach to bring the achieved advancements of parcellation methods and meta-analyses from functional magnetic resonance imaging to more precisely guide the selection of optode positions for fNIRS experiments.

Conflict of interest statement

G.A.Z.M. was a full-time employee at NIRx Medizintechnik GmbH during the manuscript preparation and toolbox development. J.B.B. and J.R.S. declare no competing financial interests.

Figures

Figure 1

Challenge commonly faced when designing an fNIRS experiment to assess a set of regions of interest expected to be activated according to a study hypothesis: the translation to an fNIRS optode layout by choosing appropriate sources and detectors positions to maximize anatomical specificity to regions of interest. Illustrated are Brodmann areas 4, 9 and 19 and 21 and the fNIRS cap layout with corresponding color-coded channels.

Figure 2

Axial view of the tissue segmentation of (A) Colin27 template and (B) SPM12 tissue probability maps (TPM.nii). This resulted on five layers: scalp (blue), skull (cyan), cerebrospinal fluid (CSF, yellow), gray matter (red) and white matter (black).

Figure 3

(A) MNI space localization (in mm) of fiducial points on mesh of Colin27. (B) Left view of sources (red) and detectors (green) positions on the 10–10 international system that have been initially considered for photon transport simulation (Methods section).

Figure 4

(A) Illustration of a single-channel photon transport simulation after sensitivity normalization. (B) Normalized sensitivity results for all channels considered based on sources and detectors positions depicted in Fig. 3B. In both cases, the color scale has been set from 10−6 (black) to 3*10−3 (white) and the head atlas was Colin27.

Figure 5

Illustration of brain parcellation atlases’ results incorporated in the toolbox: (A) Automated Anatomical Labeling (AAL2),, (B) Atlas of Intrinsic Connectivity of Homotopic Areas (AICHA), (C) Brodmann, (D) Jülich (SPM Anatomy Toolbox)–, (E) LONI Probabilistic Brain Atlas (LPBA40). (A,C,D) were overlaid on Colin27. And (B,E) overlaid on head atlas generated from tissue probability maps of SPM12.

Figure 6

(A) Expansion of the method described for 10–10 international system to (B) the 10–5 system to allow for multi-modal measurements with EEG, either 32 or 64 electrodes. EEG and fNIRS positions are based on a layout accommodating 130 positions in total. EEG 1–32 electrodes positions are depicted in green, while the complimentary 33–64 are in yellow; fNIRS sources positions are in red and the detectors are in blue.

Figure 7

Graphical user interface of the fNIRS Optodes’ Location Decider (fOLD). Depicted is the blank 10–10 layout as displayed upon toolbox initialization.

Figure 8

Illustration of further tabs available under “Summary”. ‘Landmarks’ (top), ‘Channels’ (center) and ‘Sources and Detectors’ (bottom), each of them presenting tables with summarized information about the fNIRS optode layout designed.

Figure 9

Representative NIfTI file for posterior temporal-parietal junction (pTPJ) as obtained from Archive of Neuroimaging Meta-Analyses (ANIMA) and published by Bzdok et al.. was loaded in the fOLD toolbox in the ‘Image Mask’ Mode, (A) resulting on channel formed by positions CP6 and P6. (B) Overlay of pTPJ (in violet) on Colin27 segmented atlas with an additional overlay of sensitivity for channel CP6-P6.