Phased array RF coils for high-resolution MRI of the inner ear and brain stem

The spatial resolution in MRI is predominantly limited by the available signal-to-noise ratio (S/N). To increase the S/N, a four coil phased array consisting of bilateral pairs of semioval coils was constructed for high resolution imaging of the temporal bone and brainstem.

Coil sizes of 10 x 6 and 6 x 4.5 cm were tested. The S/N values were measured in vivo and with homogeneous phantoms and compared to commercial 3 in receive and quadrature head coils.

At a depth of 4-5 cm, phantom studies yielded S/N improvements of a factor of 1.26-1.37 with the large array compared to the 3 in coil and 2.33-1.74 compared to the head coil. Similar improvements (1.16 and 2.37) were obtained in inner ear images. No further improvement was achieved at this depth with the small array. At a depth of 8 cm, phantom studies yielded similar S/N for the quadrature head coil and two bilaterally placed large array coils, while a factor of 1.27 was obtained in brainstem images.

The use of phased array coils yields significantly increased S/N and is thus valuable for high resolution MRI.