Evaluation of the default-mode network by quantitative 15O-PET: comparative study between cerebral blood flow and oxygen consumption

Abstract

ObjectiveResting-state functional MRI (rs-fMRI) has revealed the existence of a default-mode network (DMN) based on spontaneous oscillations of the blood oxygenation level-dependent (BOLD) signal. The BOLD signal reflects the deoxyhemoglobin concentration, which depends on the relationship between the regional cerebral blood flow (CBF) and the cerebral metabolic rate of oxygen (CMRO2). However, these two factors cannot be separated in BOLD rs-fMRI. In this study, we attempted to estimate the functional correlations in the DMN by means of quantitative 15O-labeled gases and water PET, and to compare the contribution of the CBF and CMRO2 to the DMN.MethodsNine healthy volunteers (5 men and 4 women; mean age, 47.0 ± 1.2 years) were studied by means of 15O-O2, 15O-CO gases and 15O-water PET. Quantitative CBF and CMRO2 images were generated by an autoradiographic method and transformed into MNI standardized brain template. Regions of interest were placed on normalized PET images according to the previous rs-fMRI study. For the functional correlation analysis, the intersubject Pearson’s correlation coefficients (r) were calculated for all pairs in the brain regions and correlation matrices were obtained for CBF and CMRO2, respectively. We defined r > 0.7 as a significant positive correlation and compared the correlation matrices of CBF and CMRO2.ResultsSignificant positive correlations (r > 0.7) were observed in 24 pairs of brain regions for the CBF and 22 pairs of brain regions for the CMRO2. Among them, 12 overlapping networks were observed between CBF and CMRO2. Correlation analysis of CBF led to the detection of more brain networks as compared to that of CMRO2, indicating that the CBF can capture the state of the spontaneous activity with a higher sensitivity.ConclusionsWe estimated the functional correlations in the DMN by means of quantitative PET using 15O-labeled gases and water. The correlation matrix derived from the CBF revealed a larger number of brain networks as compared to that derived from the CMRO2, indicating that contribution to the functional correlation in the DMN is higher in the blood flow more than the oxygen consumption.

Two distinct modes of hemodynamic responses across the human cortex

“…To the best of our knowledge, we here used mul parametric, quan ta ve fMRI for the first me to examine the widespread metabolic effects in the human brain during different cogni ve states. All quan ta ve parameter values obtained in this study fell within the range of previously reported data for the healthy human brain, with average values for CBF of 44.5 ± 7.2 ml/100g/min, CBV of 4.8 ± 0.2 %, OEF of 0.39 ± 0.04 [frac on], and CMRO2 of 127.8 ± 18.4 μmol/100g/min in the gray ma er (Aoe et al, 2018;Cho et al, 2018;Ito et al, 2021;Lee & Wehrli, 2022;Leon ev & Buxton, 2007;Liang et al, 2013;Raichle et al, 2001;Stone & Blockley, 2017;Wise et al, 2013;J. Zhang et al, 2015J.…”

Non-invasive measurement of oxygen metabolism. Part 1: Historical review and state of the art

“…В медицинской школе Осаки [50] велись работы по сравнению данных CBF и CRMO 2 , измеренных с помощью ингаляции радиоактивных газов, для изучения default-mode network (DMN). Было показано, что количество связанных отделов мозга по данным CBF превышает таковое по данным CRMO 2 , и, таким образом, измерение перфузии является более чувствительным методом.…”

Evaluation of Functional Connectivity in the Brain Using Positron Emission Tomography: A Mini-Review

“…Regional CBF and CMRO 2 can be quantitatively evaluated via 15 O-labeled gas and water PET (Hatazawa et al, 1996; Watabe et al, 2014). Our group recently reported that functional correlations in the DMN can be estimated using quantitative 15 O-PET (Aoe et al, 2018). Our findings indicated that evaluation based on changes in CBF revealed a larger number of brain networks than evaluation based on changes in CMRO 2 , suggesting that the contribution of blood flow to functional correlations in the DMN is greater than that of oxygen consumption (Figure 1).…”

“…Significant positive functional correlations involving the DMN. (A) Correlations based on CBF; (B) CMRO 2 ; (C) the overlap between CBF and CMRO 2 (reprint from Aoe et al, 2018; permission obtained from the Annals of Nuclear Medicine in accordance with their open access policy).…”