# SNR and Phase Encoding Steps

It won't work!

We saw in earlier that *decreasing* N_{y} to increase voxel size would increase SNR. We can understand this by looking at the SNR equation. (Get out a pen and paper and use it to carefully work through the following discussion.) Increasing N_{y} does mean you have an increase in signal, with the associated smaller noise increase as we saw earlier. But you can't increase SNR by just increasing N_{y} on its own, because this also results in a smaller pixel, which has a larger effect on the overall equation. (Try making N_{y} into 2N_{y} in the equation and see what the overall effect is.) Increasing N_{y} only increases SNR if you also maintain the voxel size by changing the FOV.

Further reading on this topic:

Books: MRI The Basics p168

Online: MRItutor 1, 2