Abstract
IntroductionThe mildly invasive 18F‐fluorodeoxyglucose positron emission tomography (FDG‐PET) is a well‐established imaging technique to measure ‘resting state’ cerebral metabolism. This technique made it possible to assess changes in metabolic activity in clinical applications, such as the study of severe brain injury and disorders of consciousness.ObjectiveWe assessed the possibility of creating functional MRI activity maps, which could estimate the relative levels of activity in FDG‐PET cerebral metabolic maps. If no metabolic absolute measures can be extracted, our approach may still be of clinical use in centers without access to FDG‐PET. It also overcomes the problem of recognizing individual networks of independent component selection in functional magnetic resonance imaging (fMRI) resting state analysis.MethodsWe extracted resting state fMRI functional connectivity maps using independent component analysis and combined only components of neuronal origin. To assess neuronality of components a classification based on support vector machine (SVM) was used. We compared the generated maps with the FDG‐PET maps in 16 healthy controls, 11 vegetative state/unresponsive wakefulness syndrome patients and four locked‐in patients.ResultsThe results show a significant similarity with ρ = 0.75 ± 0.05 for healthy controls and ρ = 0.58 ± 0.09 for vegetative state/unresponsive wakefulness syndrome patients between the FDG‐PET and the fMRI based maps. FDG‐PET, fMRI neuronal maps, and the conjunction analysis show decreases in frontoparietal and medial regions in vegetative patients with respect to controls. Subsequent analysis in locked‐in syndrome patients produced also consistent maps with healthy controls.ConclusionsThe constructed resting state fMRI functional connectivity map points toward the possibility for fMRI resting state to estimate relative levels of activity in a metabolic map.
Highlights
The mildly invasive 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) is a well-established imaging technique to measure ‘resting state’ cerebral metabolism
We considered the following contrasts: (1) FDG-PET metabolic activity higher in healthy controls with respect to VS/UWS patients; (2) FDG-PET metabolic activity preserved in VS/UWS patients; (3) functional magnetic resonance imaging (fMRI) total neuronal activity higher in healthy controls with respect to VS/UWS patients; (4) fMRI total neuronal activity preserved in VS/UWS patients; (5) cona 2015 The Authors
We found for controls a significant (P < 0.001) correlation for all voxels of q = 0.75 Æ 0.05, within the range 0.63–0.83, for VS/UWS patients a significant (P < 0.001) correlation of q = 0.58 Æ 0.09, within the range 0.45–0.76, and for LIS patients a significant (P = 0.001) correlation of q = 0.67 Æ 0.03 ranging from 0.63 to 0.70
Summary
The mildly invasive 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) is a well-established imaging technique to measure ‘resting state’ cerebral metabolism. If no metabolic absolute measures can be extracted, our approach may still be of clinical use in centers without access to FDG-PET It overcomes the problem of recognizing individual networks of independent component selection in functional magnetic resonance imaging (fMRI) resting state analysis. It intends to measure the patients’ spontaneous activity while lying inside the scanner without performing any specific task or being exposed to any stimulation During such resting state conditions, human cortex manifests ultra-slow modulations of neuronal activity reflected both in firing rate modulations of individually isolated cortical neurons, as well as in modulation of high frequency gamma power of local field potentials (He et al 2008; Nir et al 2008).
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