What step is performed prior to frequency encoding in MRI?

The correct answer is that a specific step is performed prior to frequency encoding in MRI. Before frequency encoding begins, a key preparation phase occurs, which typically involves the application of radiofrequency (RF) pulses and the selection of slice thickness and positioning. This preparation is crucial because it determines how the MR signal is generated and subsequently encoded.

Frequency encoding involves varying the magnetic field gradient along one axis during signal readout, which allows the MRI system to distinguish between different frequencies emitted by protons in various locations. This differentiation is only possible if the initial conditions, established prior to the encoding, are appropriate. Therefore, the timing of setting parameters like the excitation pulse and slice selection influences the quality and accuracy of the frequency encoding process.

Recognizing the correct sequence of events in MRI acquisition is essential for understanding how imaging modalities work, as it impacts not just the resulting image clarity but also the diagnostic effectiveness of the MRI procedure.