PHASED-ARRAY RF COILS FOR HIGH-RESOLUTION MRI OF THE INNER-EAR AND BRAIN-STEM

Objective: The spatial resolution in MRI is predominantly limited by t he 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 brain stem. Materials and Methods: 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 phan toms and compared to commercial 3 in receive and quadrature head coils . Results: At a depth of 4-5 cm, phantom studies yielded S/N improveme nts of a factor of 1.26-1.37 with the large array compared to the 3 in coil and 2.331.74 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 bf 8 cm, phantom studies yielded similar SIN for the quadrature head coil and t wo bilaterally placed large array coils, while a factor of 1.27 was ob tained in brainstem images. Conclusion: The use of phased array coils yields significantly increased S/N and is thus valuable for high resol ution MRI.