Pim Pullens^{1,2}, Jasper Degryse^{3}, Han Bossier^{3}, Bieke Moerkerke^{3}, Marcel Brass^{4}, Guy Vingerhoets^{4}, and Rik Achten^{2}

Detectability of BOLD signal change is determined by temporal SNR (tSNR, mean divided by standard deviation of the signal over time), and ultimately determines how long needs to be scanned to obtain significant results in a fMRI experiment. With the clinical availability of multiband BOLD-EPI, TR can be shortened significantly, but it is unclear how MB factor influences tSNR. We show in a human subject that tSNR limits up to 192 can be reached and that multiple combinations of MB factor and voxel size can be used to reach similar tSNR values.

[1] C. Triantafyllou, J. R. Polimeni, and L. L. Wald, “Physiological noise and signal-to-noise ratio in fMRI with multi-channel array coils,” Neuroimage, vol. 55, no. 2, pp. 597–606, Mar. 2011.

[2] M. Barth, F. Breuer, P. J. Koopmans, D. G. Norris, and B. A. Poser, “Simultaneous multislice (SMS) imaging techniques,” Magn. Reson. Med., vol. 75, no. 1, pp. 63–81, 2016.

[3] L. Chen et al., “Evaluation of highly accelerated simultaneous multi-slice EPI for fMRI,” Neuroimage, vol. 104, pp. 452–459, Jan. 2015.

[4] K. Murphy, J. Bodurka, and P. A. Bandettini, “How long to scan? The relationship between fMRI temporal signal to noise ratio and necessary scan duration,” Neuroimage, vol. 34, no. 2, pp. 565–574, Jan. 2007.

[5] C. Triantafyllou et al., “Comparison of physiological noise at 1.5 T, 3 T and 7 T and optimization of fMRI acquisition parameters,” Neuroimage, vol. 26, no. 1, pp. 243–250, May 2005.

[6] “BXH/XCEDE tools.” NITRC. https://www.nitrc.org/projects/bxh_xcede_tools/

[7] S. M. S. Smithet al., “Advances in functional and structural MR image analysis and implementation as FSL.,” Neuroimage, vol. 23 Suppl 1, pp. S208-19, Jan. 2004.

SNR vs tSNR in the agar phantom. Color indicates voxel size, while multiband factor is labeled at each point. In the absence of physiological noise, SNR and tSNR are equal.

Whole brain SNR vs tSNR at different voxel sizes, indicated by color, and multiband factor labeled at each point. As voxel size increases, SNR and tSNR increase, while when MB factor is increased at a fixed voxel size, SNR and tSNR drop. Dotted line shows fitted $$$\lambda$$$, indicating tSNR upper limit of 233, for all points, while the continuous line shows fitted $$$\lambda$$$, indicating tSNR limit of 192 when implausible points at MB8, voxel size 2.5 and 3.0, and MB0, size 2.5 are not included in the line fitting. Multiple combinations of MB factor and voxel size can be made to obtain similar tSNR values.

Gray matter SNR vs tSNR formatted as in fig 2. Dotted line shows the fitted $$$\lambda$$$ value, indicating tSNR upper limit of 233, for all points, while the continuous line shows the fitted $$$\lambda$$$ value, indicating a tSNR limit of 172 when the implausible points at MB8, voxel size 2.5 and 3.0, and MB0, size 2.5 are not included in the line fitting. Again, multiple combinations of MB factor and voxel size can be made to obtain similar tSNR values.

Acquisition parameters for the experiments. The phantom was scanned at 1.5, 2.0, 2.5 and 3.0 mm resolution, and the human subject at 1.8, 2.2, 2.5 and 3.0 mm resolution.