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Comparative Study
. 2018 Aug;32(7):485-491.
doi: 10.1007/s12149-018-1272-x. Epub 2018 Jun 22.

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

Jo Aoe  1 , Tadashi Watabe  2 , Eku Shimosegawa  1   3 , Hiroki Kato  1 , Yasukazu Kanai  3 , Sadahiro Naka  4 , Keiko Matsunaga  3 , Kayako Isohashi  1 , Mitsuaki Tatsumi  5 , Jun Hatazawa  1
Affiliations
Comparative Study

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

Jo Aoe et al. Ann Nucl Med. 2018 Aug.

Abstract

Objective: Resting-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.

Methods: Nine 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.

Results: Significant 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.

Conclusions: We 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.

Keywords: 15O PET; Cerebral blood flow; Cerebral metabolic rate of oxygen; Default-mode network; Functional correlation.

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Figures

Fig. 1
Fig. 1
Setting of ROIs using a 12-mm sphere (note that the center of the sphere is located in the specific MNI coordinate point)
Fig. 2
Fig. 2
Correlation analysis between pairs of brain regions and correlation matrices. Above example calculated the intersubject Pearson’s correlation coefficient between a pair of brain regions showing a significant positive correlation. Each plot in the left graph represents the data for one subject
Fig. 3
Fig. 3
Correlation matrices of the DMN (a) based on the CBF (b) based on the CMRO2. Color represents the value of the correlation coefficients
Fig. 4
Fig. 4
Correlation matrices of the DMN showing significant positive correlations. Red color represents r > 0.7 (a) based on the CBF (b) based on the CMRO2 (c) overlap between CBF and CMRO2
Fig. 5
Fig. 5
Visualization of the correlation matrices of the DMN showing significant positive correlations. a Based on the CBF; b CMRO2; c overlap between CBF and CMRO2
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