Article

Dynamic characteristics of oxygenation-sensitive MRI signal in different temporal protocols for imaging human brain activity.

Institute of Neuroradiology, University Hospital of Zurich, Switzerland.
Neuroradiology (impact factor: 2.82). 09/2000; 42(8):591-601. pp.591-601
Source: PubMed

ABSTRACT The temporal characteristics of cerebral blood oxygenation during human brain activation were monitored with dynamic echo-planar imaging (EPI) using the blood oxygenation level dependent (BOLD) fMRI. We investigated oxygenation-sensitive signal changes: 1. during repetitive block stimuli, to determine the latency of the activation-induced signal change in the primary visual cortex; 2. on shortening the rest periods between constant stimulated phases, to investigate the limitations that this latency poses in temporal resolution of the technique; and 3. on sustained steady-state stimulation, to characterise oxygenation changes during prolonged brain activation using different stimuli. Delayed intrinsic haemodynamic response and a finite signal-to-noise ratio limit the temporal resolution achieved with BOLD fMRI. Separate activation periods were resolved when the delay between consecutive stimulations was at least 2 s. In this study oxygenation remained elevated throughout sustained activation, suggesting a constant rate of oxygen consumption by the primary cortical neurones during activation. Characterisation of fMRI signal dynamics in dynamic temporal protocols is significant both in terms of optimising stimulation protocols and the potential to gain insight into the physiological mechanisms underlying neuronal activation which could increase the clinical applicability of the technique.

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Keywords

activation-induced signal change
 
blood oxygenation level dependent
 
brain activation
 
cerebral blood oxygenation
 
characterise oxygenation changes
 
clinical applicability
 
consecutive stimulations
 
Delayed intrinsic haemodynamic response
 
dynamic echo-planar imaging
 
dynamic temporal protocols
 
finite signal-to-noise ratio limit
 
fMRI signal dynamics
 
human brain activation
 
neuronal activation
 
oxygenation-sensitive signal changes
 
primary cortical neurones
 
primary visual cortex
 
repetitive block stimuli
 
Separate activation periods
 
temporal characteristics