Patterns of Signal Intensity in CISS MRI of the Inner Ear and Eye

Abstract

Background: Constructive interference in steady state (CISS) is a gradient echo magnetic resonance imaging (MRI) pulse sequence that provides excellent contrast between cerebrospinal fluid and adjacent structures but is prone to banding artifacts due to magnetic field inhomogeneities. We aimed to characterize artifacts in the inner ear and eye. Methods: In 30 patients (60 ears/eyes) undergoing CISS sequence MRI, nine low-signal intensity regions were identified in the inner ear and compared to temporal bone histopathology. The number and angle of bands across the eye were examined. Results: In the cochlea, all ears had regions of low signal corresponding to anatomy (modiolus (all), spiral lamina (n = 59, 98.3%), and interscalar septa (n = 50, 83.3%)). In the labyrinth, the lateral semicircular canal crista (n = 42, 70%) and utricular macula (n = 47, 78.3%) were seen. Areas of low signal in the vestibule seen in all ears may represent the walls of the membranous utricle. Zero to three banding artifacts were seen in both eyes (right: 96.7%, mean 1.5; left: 93.3%, mean 1.3). Conclusion: Low signal regions in the inner ear on CISS sequences are common and have consistent patterns; most in the inner ear represent anatomy, appearing blurred due to partial volume averaging. Banding artifacts in the eye are more variable.

Clinical High-Resolution Imaging of the Inner Ear by Using Magnetic Resonance Imaging (MRI) and Cone Beam Computed Tomography (CBCT)

“…In comparison to clinical whole-head imaging, our experimental setup and measurement design precluded aliasing (“fold-over” or “wrap-around”) artifacts that in clinical practice can be the source of significant misinterpretations. Likewise, chemical shift artifacts did not occur due to the scarcity of lipid in or near the inner ear and due to the low sensitivity of the measurement sequence chosen with regard to fat, neither did we observe any banding artifacts which can be misleading in T2*-weighted imaging sequences [ 7 ].…”

“…Previous studies have addressed MRI artifacts [ 7 ] and correlated MRI findings with histopathology [ 8 ]. However, imaging was performed on volunteers using clinical whole-head hardware, resulting in a limited spatial resolution.…”

“…On the other hand, MRI of the inner ear has inherent shortcomings due to a bunch of imaging artifacts. Identifying artifacts and distinguishing them from factual anatomy can be difficult and has been addressed in previous work, most of which was conducted on scans of patients or volunteers using clinical hardware and software [ 7 , 8 ]. Therefore, it was the goal of our study to apply our best available imaging protocols on a temporal bone specimen and to perform a one-by-one comparison of slices from imaging scans with histologic sections of the same specimen.…”