Charles McGrath1, Mohammed M Albannay1, Alexander Jaffray1, Christian Guenthner1, and Sebastian Kozerke1
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland
We developed a synthetic MR image generator based on first principles to compare SNR at various fields. Findings show that SNR can deviate significantly from commonly used SNR scaling laws, specifically when acquisition times are short relative to RF pulse durations.
Figure 3: (A-F) show images generated at three field strengths when no restriction is put on the repetition time. (A,D): TR=7ms,FA=60,SNR≈6 (B,E):TR=6ms,FA=50,SNR≈10 (C,F):TR=5ms,FA=30,SNR≈14 (G-L) are generated with repetition time restricted such that the intra-TR phase wrap is no more than π/3 with an inhomogeneity of 0.5ppm. (G,J): same as A (H,K):same as B (I,L):TR=4ms,FA=23,SNR≈5 (G-L) A significant decrease can be seen in the SNR at 3T due to this restriction.
Figure 5: Optimized SNR plots for both the unrestricted case (left) and case where TR is restricted such that banding is limited to π/3 (right). Both plots also show the expected scaling according to coil dominated and noise dominated SNR scaling laws. Note that bandwidth (BW) changes with the optimization. In both cases SNR scales better than the linear case at low fields. These results also approximately match the images generated in Figure 3, with a drop in SNR seen in the restricted case at 3T.
