Transients may occur in functional magnetic resonance imaging without physiological basis

Area of Science:

• Neuroimaging
• Biophysics

Background:

• Functional magnetic resonance imaging (fMRI) measures brain activity via the blood oxygen level dependent (BOLD) signal.
• BOLD signal changes, including transient overshoots and undershoots, are of significant interest for understanding neural responses.
• Previous interpretations of these transients often linked them to cerebral blood flow and volume dynamics.

Purpose of the Study:

• To investigate the origin of transient deflections observed in fMRI BOLD signals.
• To determine if these transients represent genuine physiological changes or measurement artifacts.

Main Methods:

• Simulated BOLD responses in fMRI phantoms with controlled magnetic field variations.
• Detailed analysis and computational modeling of signal transients.
• Investigation of the influence of measurement parameters, such as the time between excitations.

Main Results:

• Prominent transient deflections were observed in phantom BOLD signals, even with square-wave magnetic field changes.
• These transients were found to originate from partial misalignment between imaging slices and neuronal activation.
• The magnitude of transients was significantly dependent on measurement parameters like repetition time.

Conclusions:

• Transient overshoots and undershoots in fMRI BOLD signals may not always reflect physiological changes.
• Activation-related partial slice misalignment is a potential source of spurious transients.
• Careful consideration of measurement parameters is crucial for accurate physiological interpretation of BOLD signal dynamics.