Comparing diffuse optical tomography and functional magnetic resonance imaging signals during a cognitive task: pilot study

Abstract

, "Comparing diffuse optical tomography and functional magnetic resonance imaging signals during a cognitive task: pilot study," Neurophoton. 4(1), 015003 (2017), doi: 10.1117/1.NPh.4.1.015003. Abstract. Diffuse optical tomography (DOT) measures concentration changes in both oxy-and deoxyhemoglobin providing three-dimensional images of local brain activations. A pilot study, which compares both DOT and functional magnetic resonance imaging (fMRI) volumes through t-maps given by canonical statistical parametric mapping (SPM) processing for both data modalities, is presented. The DOT series were processed using a method that is based on a Bayesian filter application on raw DOT data to remove physiological changes and minimum description length application index to select a number of singular values, which reduce the data dimensionality during image reconstruction and adaptation of DOT volume series to normalized standard space. Therefore, statistical analysis is performed with canonical SPM software in the same way as fMRI analysis is done, accepting DOT volumes as if they were fMRI volumes. The results show the reproducibility and ruggedness of the method to process DOT series on group analysis using cognitive paradigms on the prefrontal cortex. Difficulties such as the fact that scalp-brain distances vary between subjects or cerebral activations are difficult to reproduce due to strategies used by the subjects to solve arithmetic problems are considered. T-images given by fMRI and DOT volume series analyzed in SPM show that at the functional level, both DOT and fMRI measures detect the same areas, although DOT provides complementary information to fMRI signals about cerebral activity.

Is it possible to measure hemodynamic changes in the prefrontal cortex through the frontal sinus using continuous wave DOT systems?

“…The subject wore sensors to measure cardiac cycle and breathing which were recorded continuously at 4 KHz using AD Instrument ML870/P PowerLab16/30 as the measurement system. The physiological data were used to remove physiological noise from raw DOT data using the dynamic retrospective filtering of physiological noise (DRIFTER) algorithm which applies an accurate dynamical tracking of the variations in the cardiac and respiratory frequencies [35].…”

“…The spatial normalization SPM8 tool, which computes an affine and a non-linear transformation between two volumes was used [36]. Therefore, the position of the grid was interpolated between the coordinates marked by the Brainsight neuro-navigational system and assigned to the FE-mesh [35,37].…”

“…The rebuilding of the DOT images requires inverting the weight matrix resulting in an illposed problem formulated as an inverse problem, owing to the fact that NIR light is highly attenuated with an increasing depth. The weight matrix is inverted by the use of a singular value decomposition (SVD) algorithm using minimum description length (MDL) criterion to select the number of singular values which explain the dimensionality of the matrix [35].…”

Diffuse optical tomography in the human brain: A briefly review from the neurophysiology to its applications

“…The spatial coordinates onto the real space must be integrated in the generic head model used to calculate the forward model. Both spaces (real and generic model) are integrated using the fiducial markers on the real space, which will be translocated to the generic model by the use of spatial transformation tools [72, 73].…”

“…One factor which defines the quality of the reconstructed image is the number of σ m , as has been showed in previous studies [77]. The selection of σ m can be ′′ad hoc′′ or using an index such as a minimum description length (MDL) [72] .…”