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Inflow effects on hemodynamic responses characterized by event‐related f MRI using gradient‐echo EPI sequences
Author(s) -
Liu HoLing,
Wei PeiShan,
Wai YauYau,
Kuan WanChun,
Huang ChihMao,
Wu Changwei W.,
Buckle Christopher,
Wan YungLiang,
Gao JiaHong
Publication year - 2008
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2975141
Subject(s) - hemodynamics , flip angle , inflow , latency (audio) , haemodynamic response , contrast (vision) , nuclear medicine , magnetic resonance imaging , medicine , cardiology , psychology , physics , blood pressure , heart rate , radiology , computer science , optics , telecommunications , mechanics
The purpose of this study is to determine whether blood inflow impacts the temporal behavior of BOLD‐contrast f MRI 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.