RF transmission in MRI

[aelster]

In an MR scanner, a range of frequencies is transmitted by each RF-pulse, not just the single center (Larmor) frequency. This is known as the RF-bandwidth (different from the receiver bandwidth). The RF-bandwidth depends on the type of pulse used. Spatially selective pulses (such as sinc-like ones) typically excite a relatively narrow range of frequencies (RF bandwidth ≈ 2 kHz). Nonselective pulses (so-called hard or rectangular pulses) excite a much larger range (RF bandwidth ≈ 250 kHz).

So, depending on how far away the body section to be imaged is from magnet isocenter and the type of RF excitation desired, the table (patient) may or may not need to be moved.