Despite recent progress with MRI, imaging of membranous structures of the inner ear is still an obstacle to diagnosing inner ear diseases that originate in these structures. One potential technique to address this shortcoming is ultra-high field MRI, which is known for improving the resolution of finer structures. This could help pave the way to revolutionizing diagnostics of inner ear diseases.
The researchers employed a field strength of 11.7 T. They analyzed cylindrical extracts of the inner ear originating from adult head cadavers with a vertical bore scanner. Samples were incubated with a physiological medium for 48 hours before imaging. Images with and without a perfluoropolyether contrast agent were obtained. Images of both T1- and T2-weighting were acquired, by employing a RARE imaging sequence. An ITK-SNAP software was used to help guide the three-dimensionality of their images. In order to compare the efficacy of the imaging at 11.7 T, histology samples of the inner ear were imaged with a microscope.
By employing an 11.7 T field, the researchers were successful in imaging membranous structures of the inner ear. A qualitative analysis of their images in comparison to the histology samples revealed an improved resolution and signal to noise ratio (although these were never quantified) in inner ear structures such as the Reissner’s membrane (pictured in Figuer 1), nerves, the vestibular canals, the crista ampullaris, the maculae of the utricle and saccule, and ducts. However, the basilar membrane (Figure 1) inside the cochlea were not detected at a high enough resolution, as well as smaller divisions of the duct network draining the inner ear.
Figure 1. Comparison of ITK-SNAP software with their acquired images. The Reissner’s membrane is indicated with the arrow, and the basilar membrane with the asterisk.
Despite the research advancements in imaging capabilities of the inner ear, they were unable to acquire the depth and resolution necessary to image thinner membrane structures, such as the basilar membrane. Additionally, they were unable to discern bony- and air-filled structures due to the higher production of artefacts in their images (seen in Figure 1), which is one of the problems associated with higher-field strengths in MRI. Finally, it is apparent from this study that follow-up quantitative data is needed in order to show the efficacy of high-field MRI in comparison to both histology and lower-field MRI.
1 Thylur, D.S., Jacobs, R.E., Go, J.L., Toga, A.W., and Niparko, J.K.: ‘Ultra-High-Field Magnetic Resonance Imaging of the Human Inner Ear at 11.7 Tesla’, Otol Neurotol, 2017, 38, (1), pp. 133-138