What is the role of RF pulses in MRI?

RF (radiofrequency) pulses play a crucial role in the magnetic resonance imaging (MRI) process, specifically in generating images. When a patient is placed in the MRI machine, they are exposed to a strong magnetic field that aligns the protons in their body, particularly in water molecules. The RF pulses are then applied to excite these protons, causing them to absorb energy and move out of their aligned state.

Once the RF pulse is turned off, the protons begin to relax back to their original state, releasing the absorbed energy in the form of radio waves. This emitted signal is detected by the MRI system and is used to construct images of the internal structures of the body. The variation in the relaxation times of different tissues produces contrast in the images, allowing for detailed visualization of anatomy and pathology.

The other options relate to different aspects of MRI technology. Gradients are used for spatial encoding and to localize signals, static fields are necessary for aligning protons before RF excitation, and measuring noise levels is important for image quality but not directly linked to the imaging process itself. Understanding the fundamental role of RF pulses emphasizes their importance in the overall function and capability of MRI as a diagnostic tool.