Baseline blood oxygenation modulates response amplitude: Physiologic basis for intersubject variations in functional MRI signals

Hanzhang Lu, Chenguang Zhao, Yulin Ge, Kelly Lewis-Amezcua

Research output: Contribution to journalArticle

68 Scopus citations


Although BOLD functional MRI (fMRI) provides a useful tool for probing neuronal activities, large intersubject variations in signal amplitude are commonly observed. Understanding the physiologic basis for these variations will have a significant impact on many fMRI studies. First, the physiologic modulator can be used as a regressor to reduce variations across subjects, thereby improving statistical power for detecting group differences. Second, if a pathologic condition or a drug treatment is shown to change fMRI responses, monitoring this modulatory parameter is useful in correctly interpreting the fMRI changes to neuronal deficits/recruitments. Here we present evidence that the task-evoked fMRI signals are modulated by baseline blood oxygenation. To measure global blood oxygenation, we used a recently developed technique, T 2 relaxation under spin-tagging (TRUST) MRI, which yielded baseline oxygenation of 63.7% ± 7.2% in the sagittal sinus with an estimation error of 1.3%. It was found that individuals with higher baseline oxygenation tend to have a smaller fMRI signal, and vice versa. For every 10% difference in baseline oxygenation across subjects, BOLD and cerebral blood flow (CBF) signals differ by -0.4% and -30.0%, respectively, when using visual stimulation. TRUST MRI is a useful measurement for fMRI studies to control for the modulatory effects of baseline oxygenation that are unique to each subject.

Original languageEnglish (US)
Pages (from-to)364-372
Number of pages9
JournalMagnetic resonance in medicine
Issue number2
StatePublished - Aug 1 2008



  • Basal state
  • Blood oxygenation
  • Brain
  • fMRI

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

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