# SNR and Receiver Bandwidth

A *wider* bandwidth includes more noise. Remember that bandwidth (BW) = N_{x } / T_{line} where N_{x } is the number of frequency encoding steps and T_{line} is the total sampling time for a whole line of k-space. Decreasing the bandwidth by a factor of 2 results in an increase in the SNR by a factor of √2. Again, just use the SNR equation.

The confusing subject of receiver bandwidth is addressed in the receiver bandwidth tutorial.

Tradeoffs:

- increases chemical shift artefact (see the chemical shift tutorial)
- longer TE (sampling time is inversely proportional to BW. A longer TE means more time for T2 dephasing, reducing SNR. However, the reduction noise contamination as a result of a smaller receiver bandwidth outweighs the decrease in SNR from the extra T2 dephasing, and overall the SNR goes up.)
- decreases number of slices (longer TE means fewer slices can be fitted into the TR period).

Further reading on this topic:

Books: MRI From Picture to Proton p75, Q&A in MRI p99, MRI The Basics p168

Online: e-MRI