MAGNETIC-SUSCEPTIBILITY ARTIFACTS ON HIGH-RESOLUTION MR OF THE TEMPORAL BONE

PURPOSE: To determine whether signal variations and subtle anatomic de formities observed in high-resolution MR studies of temporal bones wer e caused by the large susceptibility differences at air-fluid interfac es near the round and oval window. METHODS: A systematic study of heal thy subjects and plastic phantoms was conducted. The phantom consisted of a series of cylindrical holes of various small sizes within a soli d block of plastic. These holes were partially filled with water and t hen covered with a reservoir of gelatin to simulate the otic capsule a ir-water interfaces. On a 1.5-T system, T2-weighted fast spin-echo ima ges and three-dimensional Fourier transform gradient acquisition in st eady state images were obtained using dedicated phased-array radio fre quency coils. The directions of the frequency and in-plane phase-encod ing gradients were swapped, and the receiver bandwidth was changed to demonstrate the dependence of the artifacts on these parameters. RESUL TS: The phantom images confirmed and characterized artifacts consisten t with magnetic susceptibility differences at the air-water interfaces . There is a combination of signal loss, misregistration in the freque ncy-encoding direction, and high signal foci related to the air-water interfaces, Furthermore, the artifacts were worse with narrower receiv er bandwidth. Similar consistent artifact patterns were seen near the oval and round windows in studies of healthy subjects. CONCLUSIONS: In high-resolution MR imaging there are significant deformities in the d isplay of the normal anatomy because of magnetic susceptibility.