We propose to develop high resolution (250-500 mum) magnetic resonance imaging techniques to study small anatomic details of the inner ear. Radiographic detection of inner ear pathology in patients with sensorineural hearing loss has significant therapeutic implications, yet until recently high resolution computed tomography (HR-CT) was the primary means for such examinations. The major disadvantage of HR-CT is that it can only delineate the osseous margins of the otic capsule, but fails to visualize the internal soft tissue features of the membranous labyrinth and neural structures. MRI has the tremendous advantage of displaying soft tissue structures. Since many of the inner ear structures are very small in size (tenth of a millimeter to several millimeters) ultra high resolution imaging with sufficient contrast is required. To achieve this goal two novel three dimensional (3D) image acquisition methods, specialized hardware and image reconstruction techniques will be developed. The proposed acquisition pulse sequences are 1) 3D gradient echo imaging with very short TR<20ms and TE<4ms and 2) fast 3D Driven Equilibrium Fourier Transformation (DEFT) obtaining three signals per TR interval. Very short TE are obtained by using reduced phase encode times. Short TR will be achieved by using a head sized z-gradient coil providing higher gradient field strength. To obtain highest S/N at 4-5cm depth for inner imaging, different multi-coil arrays will be developed. Image reconstruction algorithms will be optimized. This includes evaluation of different phase correction methods producing improved image quality for partial echo data. Phase correction also permits noise-reduced real, rather than magnitude, representation of images. The new modalities will be carefully evaluated in phantom studies and studies of normal volunteers and subsequently applied to study patients with sensorineural hearing loss.
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