Bandwidth

Select a Bandwidth to optimize Signal-to-Noise Ratio (SNR), Time of Echo (TE), number of slices, and chemical shift effect. Bandwidth can be selected for a dual echo Spin Echo acquisition.

Table 1. Bandwidth image legend

Number	Description
1	32 kHz
2	16 kHz
3	Signal
4	Noise

Bandwidth is also the frequency at which the system reads the echo. The faster the sampling rate, the shorter the time the frequency encoding (readout) gradient is applied.

Table 2. Bandwidth as sampling rate image legend

Number	Description
1	32 kHz
2	16 kHz
3	Readout window
4	X-gradient
5	Time

• As the bandwidth decreases, the SNR, chemical shift, minimum TE (and TR values for Fast GRE/SPGR applications), and motion artifact increase. As the minimum TE increases, the number of slices decreases.
• Halving the bandwidth is equivalent in SNR gain to doubling the Number of EXcitations (NEX). Decreasing the bandwidth is often used to increase SNR for T2-weighted scans.
• Increase the bandwidth to decrease the minimum TE, which decreases the echo space for FSE and EPI scans.
• Variable bandwidth narrows the receiver bandwidth to reduce the noise level and therefore increase the SNR.