Abstract 122, Date 1:00 pm, Tuesday, February 19, 2008 (48 hours)
Session O5: Poster
MR Microscopy in Studying the Development of the Embryonic Chick Inner Ear
*Jerod Rasmussen, Vinod Kaimal, Jaye Ward, Ronald Pratt, Scott Holland, Daniel Choo
Advancing our understanding of inner ear morphogenesis is essential to our comprehension of and strategies for managing congenital hearing loss. This study investigates the feasibility of visualizing development through embryological time points using MR microscopy as a non-invasive and non-terminal imaging modality.&[nl]&[nl]In ovo proton images were acquired on a Bruker 7T BioSpec 30/70 scanner using an in-house designed single loop coil, 44 mm in diameter. 3D spin echo (RARE) and steady state (FISP) imaging sequences were utilized in order to investigate the spatial and temporal resolution limits respectively. T2-weighted RARE imaging consisted of TR/TE=1500/100 ms and a nearly isotropic resolution of 100 microns. T2/T1-weighted FISP protocols consisted of TR/TE=4/2 ms and an isotropic resolution of 200 microns. The high spatial resolution images were obtained using deceased in ovo embryos at varying embryonic stages (E4,7,10,14-18,20,21) to simulate a longitudinal study. A single embryo (E18) was imaged to examine range of motion at high temporal resolution in vivo. &[nl]&[nl]Microstructures become resolvable as early as E7 using RARE imaging. As maturation progresses, many identifiable inner ear structures are clearly visible, including the ampulla, sacculus, lagena, cochlear duct, and the lateral, posterior and superior semicircular canals. In vivo FISP imaging, though more susceptible to motion artifact and reduced spatial resolution, was able to resolve the inner ear structures faster than the rate of gross motion. The feasibility of performing a longitudinal study of inner ear development in the chick embryo has been demonstrated. RARE imaging is not optimal for in vivo imaging due to motion sensitivity during the long TRs necessary. FISP imaging is adequate for in vivo studies, but will likely benefit from motion reduction via sedation or other means.&[nl]