# SNR Parameters

As usual, apply the SNR equation:

SNR | D_{x}(cm) | D_{y}(cm) | N_{x} | N_{y} | thk(cm) |
---|---|---|---|---|---|

1 | 20 | 20 | 128 | 128 | 1 |

1/4 | 10 | 10 | 128 | 128 | 1 |

1/√2 | 20 | 20 | 256 | 128 | 1 |

1/2 | 20 | 20 | 256 | 256 | 1 |

1/4 | 20 | 20 | 256 | 256 | 0.5 |

Thus we see that increasing the image size by a factor of two (same matrix size but half the FOV dimensions), decreases the SNR by a factor of four. Doubling the resolution (doubling the matrix size N_{x}.N_{y}) yields a decrease of SNR by a factor of 2, as well as causing an increase in scan time.

Regarding scan time: consider reducing the FOV by a factor of two in both directions, and the slice thickness by a factor of 2. How much longer would we have to scan to maintain SNR (how many times must we multiply NEX (NSA))? Answer: sixty-four!