Correlation between resting state fMRI total neuronal activity and PET metabolism in healthy controls and patients with disorders of consciousness

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.

Network Mapping of Connectivity Alterations in Disorder of Consciousness: Towards Targeted Neuromodulation

“…Two separate maps were created: (i) a task-based map including all the coordinates referring to fMRI/PET activations during specific tasks (6 studies; [44][45][46][47][48][49]), and (ii) a resting-state map considering all the coordinates referring to neural deactivation in DoC patients compared to healthy controls (11 studies; [23,25,[50][51][52][53][54][55][56][57][58]). Furthermore, when selecting data for the resting-state ALE map, we divided fMRI/PET activations data for VS (including unresponsive wakefulness syndrome, UWS) and MCS patients, resulting into two distinct maps.…”

“…Patients defined as in 'coma', were considered as in "VS" for the analysis. The final selection included 4 studies for MCS [50,53,55,57] and 7 studies for VS [25,52,[54][55][56][57][58]. Given the limited number of studies focusing on each specific condition, more in-depth analysis was not feasible, therefore results must be considered exploratory in nature.…”

Biomarkers, designs, and interpretations of resting‐state fMRI in translational pharmacological research: A review of state‐of‐the‐Art, challenges, and opportunities for studying brain chemistry

“…Their findings confirm the importance of considering spatial heterogeneity of the relations between metabolism and blood‐flow‐driven measures obtained from fMRI [Aiello et al, ]—a concern that requires more careful modeling and interpretation of pharma‐RSfMRI studies [Khalili‐Mahani et al, ]. Particularly, hybrid PET/fMRI will help better understand the coupling [Riedl et al, ; Soddu et al, ] and the decoupling [Di et al, ] of metabolic and connectivity metrics against the pathological background over which pharmacological interventions may be performed.…”

“…The arguments in favor of MRI versus PET, for mapping neuronal response to pharmacological interventions have already been presented at the very beginning of this article. Although BOLD‐fMRI effects are by and large indirect and nonspecific (confounding neuronal, metabolic, and hemodynamic responses), the convergence between RSfMRI biomarkers and metabolic activity detected by PET [Aiello et al, ; Passow et al, ; Soddu et al, ; Tomasi et al, ; Toussaint et al, ] justifies substitution of some PET experiments with fMRI for localizing brain activity. However, in pharmacological applications, the value of PET rests with its exquisite sensitivity to radioactivity concentration variations, which makes it capable of measuring interactions of PET radioligands with different molecular targets in the physiologic range.…”

Vegetative State: Difficulty in Identifying Consciousness and Predicting Outcome

“…Участниками исследования стали 41 пациент в ВС, 81 -в СМС, 4 -с синдромом запертого человека [41]. Результаты ПЭТ с ФДГ совпали с предполагаемым про-гнозом у 75 пациентов.…”