Somatosensory activation of two fingers can be discriminated with ultrahigh-density diffuse optical tomography

Abstract

Topographic non-invasive near infrared spectroscopy (NIRS) has become a well-established tool for functional brain imaging. Applying up to 100 optodes over the head of a subject, allows achieving a spatial resolution in the centimeter range. This resolution is poor compared to other functional imaging tools. However, recently it was shown that diffuse optical tomography (DOT) as an extension of NIRS based on high-density (HD) probe arrays and supplemented by an advanced image reconstruction procedure allows describing activation patterns with a spatial resolution in the millimeter range. Building on these findings, we hypothesize that HD-DOT may render very focal activations accessible which would be missed by the traditionally used sparse arrays. We examined activation patterns in the primary somato-sensory cortex, since its somatotopic organization is very fine-grained. We performed a vibrotactile stimulation study of the first and fifth finger in eight human subjects, using a 900-channel continuous-wave DOT imaging system for achieving a higher resolution than conventional topographic NIRS. To compare the results to a well established high-resolution imaging technique, the same paradigm was investigated in the same subjects by means of functional magnetic resonance imaging (fMRI). In this work, we tested the advantage of ultrahigh-density probe arrays and show that highly focal activations would be missed by classical next-nearest neighbor NIRS-approach, but also by DOT, when using a sparse probe array. Distinct activation patterns for both fingers correlated well with the expected neuro-anatomy in five of eight subjects. Additionally we show that activation for different fingers are projected to different tissue depths in the DOT image. Comparison to the fMRI data yielded similar activation foci in seven out of ten finger representations in these five subjects when comparing the lateral localization of DOT and fMRI results.

A review on continuous wave functional near-infrared spectroscopy and imaging instrumentation and methodology

“…• Some devices offer interfaces to allow for multi-modal imaging and have successfully been used for example in simultaneous measurements of fNIRI and MEG (Seki et al, 2012), EEG (Hebden et al, 2012;Leamy and Ward, 2010), fMRI (Habermehl et al, 2012a;Toronov et al, 2001;X. Zhang et al, 2005) and other modalities.…”

Extended hierarchical Bayesian diffuse optical tomography for removing scalp artifact

“…Continuous-wave DOT reconstructs the distribution of the changes in optical properties inside the tissue from the changes in measured light intensity using knowledge of the spatial information of the optical paths of measurement channels [6,[19][20][21][22]. In our previous study, we proposed a three-dimensional reconstruction method with high spatial resolution in both the depth and horizontal directions [23], where we introduced sparse regularization to improve the depth accuracy and the spatial resolution.…”

Quantitative evaluation of atlas-based high-density diffuse optical tomography for imaging of the human visual cortex

“…The most striking result is that although it has been shown that geometric surface error (and hence) sensitivity error (light propagation error) can be substantial depending on different types of registration algorithms, no single algorithm is providing errors greater than 4.5 mm in location error. This is perhaps expected as in most functional DOT imaging experiments, we are concerned with dynamic (often referred to temporal or difference) imaging, whereby rather than recovering an absolute image of optical properties, we are only concerned with recovery of changes with respect to a baseline and this type of image recovery has shown to be less prone to geometric and model errors as compared to static (absolute) imaging [14,47,48]. The relative overlay depends (as expected) on the threshold value and is closer to the expected 100% using the 70% threshold.…”

“…While most hemodynamic-based neuroimaging research studies in adult subjects are typically performed using functional magnetic resonance imaging (fMRI), its relative high cost, fixed scanner locations and physical constraints during imaging, limit fMRI's translation as a bedside clinical tool [10]. DOT has shown a strong potential in clinical application specifically for neonate and long-term bedridden patients [11] and NIR studies of the human brain have demonstrated its ability to recover abnormalities as haemorrhage detection from stroke patients [12] with accurate recovery of stimulated activations [13][14][15] and functional networks [5,16,17].…”