Interleaved silent steady state (ISSS) imaging: a new sparse imaging method applied to auditory fMRI

Area of Science:

• Neuroimaging
• Auditory Neuroscience
• Magnetic Resonance Imaging

Background:

• Acoustic scanner noise from echo planar imaging (EPI) confounds auditory functional magnetic resonance imaging (fMRI).
• Conventional sparse imaging acquires single brain volumes after silent stimulus periods, but makes assumptions about hemodynamic response timing and reduces statistical power.
• This limits its utility for stimuli with evolving activation or when stimuli cannot be repeated.

Purpose of the Study:

• To introduce and validate the "interleaved silent steady state" (ISSS) sampling scheme for auditory fMRI.
• To overcome limitations of conventional sparse imaging regarding temporal resolution and statistical power.
• To enable fMRI studies of complex auditory stimuli where scanner noise is a significant confound.

Main Methods:

• Developed the ISSS sampling scheme, which rapidly acquires multiple EPI volumes after a silent stimulus period.
• Maintained steady-state longitudinal magnetization using silent slice-selective excitation pulses during the silent interval to ensure constant signal contrast.
• Validated ISSS by comparing its performance to conventional sparse imaging in a study.

Main Results:

• ISSS imaging provides time course information not present in conventional sparse imaging data.
• ISSS achieves event-related (ER) imaging-like temporal resolution within a single trial.
• This contrasts with conventional sparse imaging, which requires compiling data across multiple trials for similar temporal resolution.

Conclusions:

• ISSS is particularly suitable for auditory fMRI experiments where scanner noise interferes with stimulus perception and processing.
• It is advantageous for stimuli lasting several seconds with evolving activation patterns.
• ISSS is also beneficial when stimuli cannot be repeated, such as in studies of repetition priming or familiarity effects.