Magnetic Resonance Imaging (MRI) Practice Test

During which process is the readout gradient usually activated in MRI?

1. While acquiring images

2. During frequency encoding

3. During slice selection

4. While initializing sequences

The correct answer is: During frequency encoding

The readout gradient is activated during frequency encoding, which occurs after the slice selection phase in MRI. This gradient is responsible for distinguishing the signals coming from different locations within the selected slice based on their frequency. When a radiofrequency pulse is applied, it excites the protons within the selected slice, and as these protons relax, they emit signals. The readout gradient manipulates the magnetic field strength within the slice, causing variations in resonance frequency. This allows the system to spatially encode the positional information of the emitted signals across the slice, translating them into image data. Activating the readout gradient is crucial for effectively capturing the signals' spatial information, which is what ultimately forms the MRI image. Without this gradient, the frequency information from the protons would be mixed together, making it impossible to reconstruct an accurate image of the anatomical structures within the body.