Which of the following describes the coil used in MRI to act as an antenna?

• A. Body coil
• B. Gradient coil
• C. Radiofrequency coil
• D. Surface coil

Answer: (C)

The function of acting as an antenna in MRI is fulfilled by the radiofrequency coil because it is specifically designed to transmit the radiofrequency pulse that flips the protons and then receive the faint MR signal emitted as they relax. This RF energy interaction at the Larmor frequency is what couples energy between the scanner and the tissue, enabling both excitation and signal detection. Gradient coils, by contrast, create spatially varying magnetic fields to encode position and do not serve as antennas for RF energy. RF coils come in various forms—some surround the patient for broad transmission and reception, while others (like surface coils) are placed close to the region of interest to boost sensitivity. So the device that acts as the antenna is the radiofrequency coil.