For limb imaging, which coil is recommended?

• A. Head coil
• B. Body coil
• C. Surface or circumferential whole-volume coil
• D. Gamma camera

Answer: (C)

Maximizing signal from the limb in MRI comes down to coil proximity and coverage. A surface coil placed directly on the limb has very high sensitivity just under the coil, boosting the signal from the tissues of interest. A circumferential whole-volume coil wraps around the limb, giving strong and relatively uniform sensitivity around its circumference while still staying close to the tissue, which yields excellent signal-to-noise and good spatial resolution along the length of the limb. In contrast, a head coil is tailored for cranial anatomy and sits farther from limb tissue, reducing signal for the area of interest. A body coil provides broad coverage but is larger and farther from small structures in the limb, resulting in lower SNR for fine details. The gamma camera, used in nuclear medicine, is not an MRI coil and doesn’t provide the MRI signal information needed for limb imaging. Therefore, a surface or circumferential whole-volume coil is the best choice for limb imaging due to its high SNR and appropriate coverage.