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Oxygen-induced frequency shifts in hyperoxia: a significant component of BOLD signal.
MedLine Citation:
PMID:  24828299     Owner:  NLM     Status:  Publisher    
In comparison to the well-documented significance of intravascular deoxyhemoglobin (deoxyHgb), the effects of dissolved oxygen on the blood-oxygen-level-dependent (BOLD) signal have not been widely reported. Based on the fact that the prolonged inspiration of high oxygen fraction gas can result in up to a sixfold increase of the baseline tissue oxygenation, the current study focused on the influence of dissolved oxygen on the BOLD signal during hyperoxia. As results, our in vitro study revealed that the r1 and r2 (relaxivities) of the oxygen-treated serum were 0.22 mM(-1)  · s(-1) and 0.19 mM(-1)  · s(-1) , respectively. In an in vivo experiment, hyperoxic respiration induced negative BOLD contrast (i.e. signal decrease) in 18-42% of measured brain regions, voxels with accompanying significant decreases in both the T2 (*) (-12.1% to -19.4%) and T1 (-5.8% to -3.3%) relaxation times. In contrast, the T2 (*) relaxation time significantly increased (11.2% to 14.0%) for the voxels displaying positive BOLD contrast (in 41-50% of the measured brain), which reflected a hyperoxygenation-induced reduction in tissue deoxyHgb concentration. These data imply that hyperoxia-driven BOLD signal changes are primarily determined by the counteracting effects of extravascular oxygen and intravascular deoxyHgb. Oxygen-induced magnetic susceptibility was further demonstrated by the study of 1 min hypoxia, which induced BOLD signal changes opposite to those under hyperoxia. Vasoconstriction was more common in voxels with negative BOLD contrast than in voxels with positive contrast (% change of blood volume, -9.8% to -12.8% versus 2.0% to 2.2%), which further suggests that negative BOLD contrast is mainly evoked by an increase in extravascular oxygen concentration. Conclusively, frequency shifts, which are induced by the accumulation of oxygen molecules and associated magnetic field inhomogeneity, are a significant source of the negative BOLD contrast during hyperoxia. Copyright © 2014 John Wiley & Sons, Ltd.
Youngkyu Song; Gyunggoo Cho; Song-I Chun; Jin Hee Baek; HyungJoon Cho; Young Ro Kim; Sung Bin Park; Jeong Kon Kim
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2014-5-15
Journal Detail:
Title:  NMR in biomedicine     Volume:  -     ISSN:  1099-1492     ISO Abbreviation:  NMR Biomed     Publication Date:  2014 May 
Date Detail:
Created Date:  2014-5-15     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  8915233     Medline TA:  NMR Biomed     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Copyright Information:
Copyright © 2014 John Wiley & Sons, Ltd.
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