Partial-k-space acquisition method for improved SNR efficiency and temporal resolution in 3D fMRI.

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 can be the dominant component at the center of k-space. In this study we demonstrate that the signal-to-noise ratio (SNR) efficiency and temporal resolution for 3D functional MRI (fMRI) are increased by the use of a partial-k-space acquisition method. In partial-k-space methods, the high-spatial-frequency components are doubled in amplitude during reconstruction, 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, the effect on the final MR images is almost negligible due to the square summation rule. Thus, the partial-k-space 3D method sacrifices much less SNR than is expected from the thermal noise model, and the SNR efficiency is increased compared to a full-k-space acquisition since more time frames can be collected for the same scan time. Accordingly, the temporal resolution can be increased in 3D acquisitions because only partial coverage of k-space is necessary. Experimental results confirm that more activation with a higher average t-score is detected by this method.