This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Introduction: Previous studies have shown the relative importance of physiological noise and thermal noise in 2D MR images. Since physiological noise is proportional to the signal, it is the dominant component at the center of k-space. In partial k-space methods, the high spatial frequency components are doubled, resulting in twice as much noise from those components. However in sum these contributions are relatively small compared to those at the low spatial frequencies where physiological noise is dominant. Therefore, an improved SNR efficiency and temporal resolution can be achieved since the SNR benefit from increased time frames overcomes the SNR decrease from the partial k-space method itself. Methods and Discussion: Experiments were performed on a 1.5T scanner equipped with the manufacturer s head coil. A 3D stack-of-spirals trajectory was used to cover k-space. In the slab-select direction, the excited slab thickness was 93mm with a FOV of 96mm and slice thickness of 1.5mm. Two end slices were discarded to reduce aliasing artifacts. The in-plane trajectory is a single shot, uniform density spiral with FA/TE/FOV/MAT = 27?/40ms/22cm/64*64. To make the effective scan time the same, only 5/8 of time frames with full-k coverage and all time frames but with only 5/8 of the k-space coverage were used for full-k and partial-k methods respectively for functional studies. Rest state studies among 6 volunteers showed that the average SNR increase is 8.8%. Paired 2-tails Student T tests were calculated using functional data from all 7 volunteers, showing significant differences in the number of activations (p = 0.004, 0.0005 and 0.014 for motor, auditory and visual activations respectively) between full-k and partial-k methods. Experiments have shown advantages of the partial-k method over the full-k method in detecting neuronal activation. Although the technique was tested using a 3D stack-of-spirals trajectory, it is also applicable to fMRI studies using EPI trajectories as long as reduced number of k-space lines collected can result in a reduced number of RF excitations (scan time).
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