Journal
MAGNETIC RESONANCE IN MEDICINE
Volume 58, Issue 3, Pages 592-597Publisher
WILEY
DOI: 10.1002/mrm.21342
Keywords
transverse relaxation; BOLD; blood; intravascular; extravascular; oxygenation
Funding
- NCRR NIH HHS [RR15241] Funding Source: Medline
- NIBIB NIH HHS [EB002634, P41 EB015909, EB004130] Funding Source: Medline
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Knowledge of the transverse relaxation rates R2 and R-2(*) of blood is relevant for quantitative assessment of functional MRI (fMRI results, including calibration of blood oxygenation and measurement of tissue oxygen extraction fractions (OEFs). In a temperature controlled circulation system, these rates were measured for blood in vitro at 3T under conditions akin to the physiological state. Single spin echo (SE) and gradient echo [GRE) sequences were used to determine R2 and R;, respectively. Both rates varied quadratically with deoxygenation, and changes in R2* were found to be due predominantly to changes in R2. These data were used to estimate intravascular blood oxygenation level dependent (BOLD) contributions during visual activation. Due to the large R2* in venous blood, intravascular SE BOLD signal changes were larger than GRE effects at echo times above 30 ms. When including extravascular effects to estimate the total BOLD effect, GRE BOLD dominated due to the large tissue volume fraction.
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