This sequence performs a series of excitations with varying durations to determine B1 efficiency. Each repetition includes two RF pulses and two acquisition windows. The first acquisition occurs right after the first RF pulse, following a user-defined dead time, while the second acquisition is centered at the echo time after the second RF pulse.

The sequence plots the amplitude of the spectrum from both acquisitions as a function of the first RF pulse duration. Depending on the calibration point, the first maximum or the first minimum is used to calibrate teh B1 efficiency. The calibrated value is shown in the console and saved for later sequences.

Parameters:

• nPoints: Number of points acquired per repetition.
• Larmor frequency (MHz): Larmor frequency in MHz.
• RF excitation amplitude (a.u.): Amplitude of the first RF pulse (0 to 1).
• RF refocusing amplitude (a.u.): Amplitude of the second RF pulse (0 to 1).
• RF refocusing time (us): Duration of the second RF pulse in microseconds. Use 0 to set it to twice the duration of the first pulse.
• RF pulse time, start (us): Initial duration of the first RF pulse in microseconds.
• RF pulse time, end (us): Final duration of the first RF pulse in microseconds.
• Number of steps: Number of pulse durations.
• Refocusing phase (º): Phase of the first RF pulse in degrees.
• Rephasing method: 0 (1) -> second RF pulse has double the amplitude (duration) of the first RF pulse.
• Number of scans: Number of averages.
• Echo time (ms): Echo time in milliseconds.
• Repetition time (ms): Repetition time in milliseconds.
• Acquisition time (ms): Duration of the acquisition window in milliseconds.
• Dead time (us): Delay between the end of the first RF pulse and the first acquisition window to avoid measuring the ring-down signal from the RF coil.
• Dummy pulses: Number of dummy pulses to reach a steady state.
• Shimming: Offset applied along the three gradient axes in arbitrary units.
• Calibration method: FID -> Uses the acquisition after the first RF pulse to calibrate B1 efficiency. ECHO -> Uses the acquisition after the second RF pulse to calibrate B1 efficiency.
• Calibration point: 'max' to use maximum for 90º or 'min' to use zero-crossing for 180º.