Technical considerations for the use of surface coils in MRI.

The signal-to-noise response characteristics for two surface coils of different construction geometries (a single-turn planar coil and a single-turn saddle-shaped coil) were measured and compared with head and body coils. Measurements were made at different gradient magnifications (0, 20, 30, and 40%, relative to the head coil) and with different numbers of signal averages (3, 8, 12, and 18). The signal-to-noise curves were used to guide the selection of surface coils for use in clinical studies. This technique is useful in determining the optimal technique for specific clinical problems evaluated by surface-coil imaging. For the planar (flat) surface coils, the signal-to-noise per pixel was found to be superior to the conventional head coil at depths equal to or less than 5 cm. For the saddle coil, signal-to-noise per pixel was superior to the head coil for depths below 8.5 cm for magnifications up to 30%. For the 40% magnification, the depth at which the signal-to-noise was equal to the head coil decreased to about 6 cm. Surface coils have demonstrated a marked improvement in signal-to-noise relative to conventional head and body coils for superficial structures.