Improvement of temporal resolution in fMRI using slice phase encode reordered 3D EPI

Abstract

A magnetic resonance imaging (MRI) pulse sequence was developed for acquiring high temporal resolution 3D functional magnetic resonance images (fMRI). The technique uses a 3D-acquisition scheme that increases the SNR per unit time. Compared to the previously developed methods, the proposed one does not sacrifice the spatial resolution or require a reduction in the number of acquired slices. The method was tested on six control subjects using a well-known visual activation task. Statistical analysis of the acquired data showed significant activation in the primary visual cortex of each subject. The proposed acquisition method makes use of the periodicity of the applied stimulus. A given kz plane is scanned sequentially using a modified 3D EPI pulse sequence while the stimulus cycle (SC) is applied. The same SC is repeated for each acquisition of a new kz plane sequence. After data acquisition, temporal reordering is done on the data to obtain the proper 3D image sequence. Since the familiarization of the subject with the activation task is an important aspect that might affect the performance of the method, habituation of the primary visual cortex was tested by applying a similar visual stimulus and acquiring data using standard 2D Echo Planar Imaging (EPI). No habituation was observed within a duration of 7 min 12 sec. (C) 2000 Wiley-Liss, Inc.