Inflow effects on hemodynamic responses characterized by event-related fMRI using gradient-echo EPI sequences.
Med Phys
; 35(10): 4300-7, 2008 Oct.
Article
en En
| MEDLINE
| ID: mdl-18975675
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.
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Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Corteza Visual
/
Mapeo Encefálico
/
Imagen por Resonancia Magnética
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Circulación Cerebrovascular
/
Potenciales Evocados Visuales
Tipo de estudio:
Diagnostic_studies
Límite:
Adult
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Female
/
Humans
/
Male
Idioma:
En
Revista:
Med Phys
Año:
2008
Tipo del documento:
Article
País de afiliación:
Taiwán
Pais de publicación:
Estados Unidos