Inflow effects on hemodynamic responses characterized by event-related fMRI using gradient-echo EPI sequences

Ho Ling Liu, Pei Shan Wei, Yau Yau Wai, Wan Chun Kuan, Chih Mao Huang, Changwei W. Wu, Christopher Buckle, Yung Liang Wan, Jia Hong Gao

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)


The purpose of this study is to determine whether blood inflow impacts the temporal behavior of BOLD-contrast fMRI signal changes in a typical event-related paradigm. The inflow contributions in the hemodynamic response to repeated single trials of short visual stimulation were assessed with a gradient-echo EPI sequence by altering the flip angle (FA) from 30°to 90°at a repetition time of 1 s. For each FA condition (30°, 60°, and 90°), 30 trials were performed on 15 healthy volunteers on a 3T MRI scanner. Comparing the percent BOLD contrast, prominent inflow effects were found with statistical significance between the 90°- and 30°-FA conditions (0.73±0.15 versus 0.67±0.12%, p=0.028). BOLD responses with FA=30°exhibited latencies significantly slower than those with FA=90°(3.69±0.39 s versus 3.37±0.28 s, p=0.001). The falling time of the 30°-FA responses was earlier but not statistically different from that of the 90°-FA (8.17±1.04 s versus 8.03±1.15 s, p=0.3). Using a voxelwise analysis, the latency variations of the activated visual areas were determined at several contrast-to-noise ratio (CNR) levels (controlled by averaging different numbers of randomly selected trials). The latency variations from the 90°-FA responses were greater at lower CNR but similar at higher CNR levels when comparing to the 30°-FA ones. This study suggests that inflow effects contribute to the BOLD signal, resulting in hemodynamic response with shorter latency.

Original languageEnglish
Pages (from-to)4300-4307
Number of pages8
JournalMedical Physics
Issue number10
Publication statusPublished - Jan 1 2008
Externally publishedYes


  • Flip angle
  • fMRI
  • Gradient-echo EPI
  • Hemodynamic response
  • Inflow effect

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging


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