. Author manuscript; available in PMC: 2012 Sep 1.

Published in final edited form as: Magn Reson Imaging. 2012 May 11;30(7):907–915. doi: 10.1016/j.mri.2012.03.006

Table 2.

SNR/CNR optimized WHAT sequence parameters at different resolutions for a 10-min scan

Voxel size (mm³)	Matrix N_x×N_y	N_z	FOV_z (mm)	TS_min (ms)	TR_min (ms)	TE_min (ms)	BW (Hz)	Calculated TI_WM=0 (ms)	Expected TI_WM=0 (ms)^a	Calculated GM	Expected SNR_GM^b	Estimated CNR_GM-CL
0.33×0.33×0.66	666×544	81	53	5820	5.4	1.6	560	595	–	0.034	–	3.4
0.35×0.35×0.7	628×514	90	64	5230	4.5	1.5	580	595	–	0.034	–	3.9
0.4×0.4×0.8	550×450	104	83	4550	3.5	1.4	665	595	600	0.034	11.4	4.7
0.5×0.5×1.0	440×360	117	117	4010	3.0	1.2	830	595	550	0.033	18.1	6.5
0.6×0.6×1.2	366×300	129	155	3660	2.7	1.1	990	590	–	0.032	–	8.5
0.7×0.7×1.4	314×254	135	188	3500	2.5	1.0	1155	590	–	0.031	–	10.3
1.0×1.0×2.0	220×180	135	270	3500	2.1	0.9	1660	595	600	0.033	79	18.2

FOV=220×180 cm; TFE factor=N_y; minimal TR, TE and water/fat shift; partial echo; FA=8°; orientation orthogonal to gradient axes; and NSA=1. The number of slices, N_z, was adjusted to give a total scan time of 10 min; this includes the scanner’s default oversampling by a factor of N_shots/N_z=1.28.

The experimental null was determined from scans of healthy subjects by changing TI=50–100 ms near the computed value and recording the TI value with minimal WM signal.

The experimental SNR for GM was determined from a set of RF on/RF off scans under the listed conditions, except the number of slices which was reduced to shorten scan time for the SNR measurement. The listed experimental SNR was corrected by $\sqrt{N_{z} / N_{z, \exp}}$ to account for using fewer slices in the acquisition.