When is the frequency encoding gradient activated during an MRI procedure?

The frequency encoding gradient is activated during echo collection. In MRI, this process involves capturing the signal emitted by protons after they have been excited by the radiofrequency (RF) pulse. While the RF pulse is being transmitted, the slice selection gradient is utilized to define the specific slice of tissue being imaged. Phase encoding and frequency encoding are involved in spatially encoding the signal, but frequency encoding specifically occurs after the phase encoding is implemented.

During the echo collection phase, the frequency encoding gradient separates the signals based on their frequency variations. This allows for the spatial localization of the signals, ultimately contributing to constructing the final image. Therefore, recognizing that the frequency encoding gradient is crucial during the echo collection phase highlights the intricate process of how MR images are generated based on the signals collected.