Gadolinium uptake in the rat inner ear perilymph evaluated with 4.7 T MRI: a comparison between transtympanic injection and gelatin sponge-based diffusion through the round window membrane.

OBJECTIVE

To investigate the inner ear uptake of the contrast agent gadolinium administered intratympanically through transtympanic injection or using a gelatin sponge placed on the round window.

METHODS

The T1 contrast agent Gadolinium-tetra-azacyclo-dodecane-tetra-acetic acid (Gd-DOTA) was administrated to the middle ear cavities of 12 male Wistar rats by a transtympanic injection technique (TTI group; 40 microl), gelatin sponge diffusion (GelD40 group; 40 microl), or gelatin sponge diffusion (GelD8 group; 8 microl). Magnetic resonance imaging was performed with a 4.7-T scanner using a T1-weighted 2-dimensional rapid acquisition with relaxation enhancement sequence and a high-resolution T1-weighted 3-dimensional rapid acquisition with relaxation enhancement sequence.

RESULTS

The uptake of Gd-DOTA into the perilymph was more pronounced at 3 than at 1 hour after intratympanic administration for all methods studied. Transtympanic injection and GelD40 induced similar uptake of Gd-DOTA in the lower turns of the rat cochlea. Transtympanic injection induced less efficient Gd-DOTA uptake in the apex than GelD40. GelD8 was less efficient at Gd-DOTA uptake than either TTI or GelD40.

CONCLUSIONS

Both TTI and GelD40 are able to efficiently deliver substances to inner ear destinations. Considering its simplicity, TTI is more practical for use in the clinic for the administration of substances to the inner ear, although it provided less efficient uptake in the apex than GelD40.