Diverse Patterns of Perilymphatic Space Enhancement in the Rat Inner Ear after Intratympanic Injection of Two Different Types of Gadolinium: A 9.4-Tesla Magnetic Resonance Study

Abstract

Objective: To compare the quality of perilymphatic enhancement in the rat inner ear after intratympanic injection of two types of gadolinium with a 9.4-tesla micro-MRI. Materials and Methods: Gadolinium was injected into the middle ear in 6 Sprague-Dawley rats via the transtympanic route. The left ear was injected with Gd-DO3A-butrol first, and then the right ear was injected with Gd-DOTA. MR images of the inner ear were acquired 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, and 4 h after intratympanic (IT) injection using an Agilent MRI system 9.4T/160/AS. The normalized signal intensity was quantitatively analyzed at the scala vestibuli (SV), scala media, and scala tympani (ST) using a Marosis M-view system. Then the normalized signal intensities (SIs) were compared between the two contrast agents. Results: For Gd-DO3A-butrol, the SI was as low as 1.0-1.5 throughout 1-4 h at the SV and ST of the basal turn. The maximum SI was 1.5 ± 0.5 at the SV (2 h) and 1.3 ± 0.5 at the ST (2 h). For Gd-DOTA, the 1-hour postinjection SI at the basal turn was 2.5 ± 0.5 at the SV, 1.6 ± 0.3 at the ST, and 1.2 ± 0.3 at the scala media. In the apical turn, the maximum SI was reached after 2.5 h. The maximum SI in the apical turn was 1.8 ± 0.4 at the SV (3.5 h), 1.8 ± 0.4 at the ST (4 h), and 1.4 ± 0.3 at the scala media (4 h). Conclusions: We were able to clearly visualize and separate the ST and SV using IT Gd and 9.4-tesla micro-MRI. We recommend using Gd-DO3A-butrol over Gd-DOTA and to perform the MRI 2.5 h after using IT Gd in the rat inner ear.

High-Molecular-Weight Hyaluronic Acid Vehicle Can Deliver Gadolinium Into the Cochlea at a Higher Concentration for a Longer Duration: A 9.4-T Magnetic Resonance Imaging Study

“…Gd-DTPA was selected for the first study (short-term comparison between two HA vehicles) because it has been reported to be superior in enhancing the whole cochlea (from apex to base) in the short term ( 4 ). Gd-DO3A-butrol was selected for the second study (long-term comparison between HA and standard-of-care vehicle) because it was reported to exhibit the strongest enhancement (in the basal turn) over a longer duration ( 3 ). The Gd preparations were diluted to a final concentration of 0.5 mol/L in the first and second studies.…”

“…IT injection was performed as previously described ( 3 , 4 ). The animals were anesthetized with 33 mg/kg zoletil (Virbac, Westlake, TX, USA) and 8 mg/kg xylazine (Bayer AG, Leverkusen, Germany).…”

“…A 9.4-T animal MRI scanner (9.4T/160AS, Agilent Technologies, Santa Clara, CA, USA) was used with an imaging protocol identical to that in our previous studies ( 3 , 4 ). Initially, scout images were acquired using a 2D gradient echo sequence in all three directions.…”

In Vivo Imaging of Click-Crosslinked Hydrogel Depots Following Intratympanic Injection

“…However, the steroid solution injected into the tympanic cavity could be discharged within tens of minutes through the auditory canal. As a consequence, the therapeutic effect of the steroid on the inner ear may not be sufficient [ 10 ]. To treat hearing loss, formulations that maintain a high steroid concentration in the tympanic cavity for a sufficient amount of time must be developed.…”