Accelerated spin‐echo functional MRI using multisection excitation by simultaneous spin‐echo interleaving (MESSI) with complex‐encoded generalized slice dithered enhanced resolution (cgSlider) simultaneous multislice echo‐planar imaging

Abstract

PurposeSpin‐echo functional MRI (SE‐fMRI) has the potential to improve spatial specificity when compared with gradient‐echo fMRI. However, high spatiotemporal resolution SE‐fMRI with large slice‐coverage is challenging as SE‐fMRI requires a long echo time to generate blood oxygenation level‐dependent (BOLD) contrast, leading to long repetition times. The aim of this work is to develop an acquisition method that enhances the slice‐coverage of SE‐fMRI at high spatiotemporal resolution.Theory and MethodsAn acquisition scheme was developed entitled multisection excitation by simultaneous spin‐echo interleaving (MESSI) with complex‐encoded generalized slice dithered enhanced resolution (cgSlider). MESSI uses the dead‐time during the long echo time by interleaving the excitation and readout of 2 slices to enable 2× slice‐acceleration, while cgSlider uses the stable temporal background phase in SE‐fMRI to encode/decode 2 adjacent slices simultaneously with a “phase‐constrained” reconstruction method. The proposed cgSlider‐MESSI was also combined with simultaneous multislice (SMS) to achieve further slice‐acceleration. This combined approach was used to achieve 1.5‐mm isotropic whole‐brain SE‐fMRI with a temporal resolution of 1.5 s and was evaluated using sensory stimulation and breath‐hold tasks at 3T.ResultsCompared with conventional SE‐SMS, cgSlider‐MESSI‐SMS provides 4‐fold increase in slice‐coverage for the same repetition time, with comparable temporal signal‐to‐noise ratio. Corresponding fMRI activation from cgSlider‐MESSI‐SMS for both fMRI tasks were consistent with those from conventional SE‐SMS. Overall, cgSlider‐MESSI‐SMS achieved a 32× encoding‐acceleration by combining Rinplane × MB × cgSlider × MESSI = 4 × 2 × 2 × 2.ConclusionHigh‐quality, high‐resolution whole‐brain SE‐fMRI was acquired at a short repetition time using cgSlider‐MESSI‐SMS. This method should be beneficial for high spatiotemporal resolution SE‐fMRI studies requiring whole‐brain coverage.