Inflow effects on hemodynamic responses characterized by event-related fMRI using gradient-echo EPI sequences.
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 degrees to 90 degrees at a repetition time of 1 s. For each FA condition (30 degrees, 60 degrees, and 90 degrees), 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 degrees- and 30 degrees-FA conditions (0.73 +/- 0.15 versus 0.67 +/- 0.12%, p=0.028). BOLD responses with FA=30 degrees exhibited latencies significantly slower than those with FA=90 degrees (3.69 +/- 0.39 s versus 3.37 +/- 0.28 s, p=0.001). The falling time of the 30 degrees-FA responses was earlier but not statistically different from that of the 90 degrees-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 degrees-FA responses were greater at lower CNR but similar at higher CNR levels when comparing to the 30 degrees-FA ones. This study suggests that inflow effects contribute to the BOLD signal, resulting in hemodynamic response with shorter latency.
Liu
Ho-Ling
HL
Graduate Institute of Medical Physics and Imaging Science, Chang Gung University, No. 259, Wenhua 1st Rd., Kweishan, Taoyuan 333, Taiwan. hlaliu@mail.cgu.edu.tw
Wei
Pei-Shan
PS
Wai
Yau-Yau
YY
Kuan
Wan-Chun
WC
Huang
Chih-Mao
CM
Wu
Changwei W
CW
Buckle
Christopher
C
Wan
Yung-Liang
YL
Gao
Jia-Hong
JH
D000328:Adult; D001931:Brain Mapping / Q000379:methods*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014793:Visual Cortex / Q000098:blood supply* / Q000502:physiology*