A novel sequence to improve auditory functional MRI with variable silent delays

Purpose: Auditory functional MRI (fMRI) often uses silent inter-volume delays for stimulus presentation. However, maintaining the steady-state of the magnetization usually requires constant delays. Here, a novel acquisition scheme dubbed "pre-Saturated EPI using Multiple delays in Steady-state" (SEPIMS) is proposed, using spin saturation at a fixed delay before each volume to maintain steady-state conditions, independent of previous spin history. This concept allows for variable inter-volume delays and thus for flexible stimulus design in auditory fMRI. The purpose was to compare the signal stability of SEPIMS and conventional sparse EPI (CS-EPI).

Methods: The saturation module comprises two non-selective adiabatic saturation pulses. The efficiency of the saturation and its effect on the SEPIMS signal stability is tested in vitro and in vivo.

Results: Data show that SEPIMS yields the same signal stability as CS-EPI, even for extreme variations between inter-volume delay durations. However, dual saturation pulses are required to achieve sufficiently high saturation efficiency in compartments with long T₁ values. Importantly, spoiler gradient pulses after the EPI readout have to be optimized to avoid eddy-current-induced image distortions.

Conclusion: The proposed SEPIMS sequence maintains high signal stability in the presence of variable inter-volume durations, thus allowing for flexible stimulus design.