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

• Published in: Annals of nuclear medicine Vol. 32; no. 7; pp. 485 - 491
• Main Authors: Aoe, Jo, Watabe, Tadashi, Shimosegawa, Eku, Kato, Hiroki, Kanai, Yasukazu, Naka, Sadahiro, Matsunaga, Keiko, Isohashi, Kayako, Tatsumi, Mitsuaki, Hatazawa, Jun
• Format: Journal Article
• Language: English
• Published: Tokyo Springer Japan 01-08-2018; Springer Nature B.V
• Subjects: Autoradiography; Blood flow; Brain; Brain mapping; Cerebral blood flow; Correlation analysis; Correlation coefficients; Functional magnetic resonance imaging; Gases; Imaging; Magnetic resonance imaging; Mathematical analysis; Medical imaging; Medicine; Medicine & Public Health; Metabolic rate; Networks; Nuclear Medicine; Original; Original Article; Oscillations; Oxygen consumption; Oxygenation; Positron emission; Positron emission tomography; Radiology; Tomography; Cerebral metabolic rate of oxygen; Functional correlation; Default-mode network; Cerebral blood flow; O PET
• ISSN: 0914-7187; 1864-6433
• DOI: 10.1007/s12149-018-1272-x

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 (CMRO
2
). 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
15
O-labeled gases and water PET, and to compare the contribution of the CBF and CMRO
2
to the DMN.
Methods
Nine healthy volunteers (5 men and 4 women; mean age, 47.0 ± 1.2 years) were studied by means of
15
O-O
2
,
15
O-CO gases and
15
O-water PET. Quantitative CBF and CMRO
2
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 CMRO
2
, respectively. We defined
r
 > 0.7 as a significant positive correlation and compared the correlation matrices of CBF and CMRO
2
.
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 CMRO
2
. Among them, 12 overlapping networks were observed between CBF and CMRO
2
. Correlation analysis of CBF led to the detection of more brain networks as compared to that of CMRO
2
, 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
15
O-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 CMRO
2
, indicating that contribution to the functional correlation in the DMN is higher in the blood flow more than the oxygen consumption.