Improving the temporal resolution of functional MR imaging using keyhole techniques.

Using a keyhole technique, it is shown that the data acquisition rate of gradient-echo imaging for functional MRI (fMRI) studies can be increased substantially. The resulting enhancement of the temporal resolution of fMRIs was accomplished without modifying the hardware of a conventional MRI system. High spatial resolution fMRI images were first collected with conventional full k-space acquisition and image reconstruction. Using the same data set, simulation reconstruction using the keyhole principle and zero-padding were performed for comparison with the full k-space reconstruction. No significant changes were found for fMRI images generated from the keyhole technique with a data sharing profile of 50% of the k-space. As k-space data sharing profiles increased to 75 and 87.5%, the keyhole fMRI images began to show only modest changes in activation intensity and area compared with the standard images. In contrast, zero-padding fMRI images produced a significant disparity both in activation intensity and area relative to the truly high-resolution fMRI images. The keyhole technique's ability to retain the intensity and area of fMRI information, while substantially reducing acquisition time, makes it a promising method for fMRI studies.