[Preliminary exploration of Gd-DTPA enhanced inner ear image of guinea pig using magnetic resonance scan].

OBJECTIVE

To observe the distribution of Gd-DTPA in the inner ear of guinea pig by MRI at different time points after intratympanic administration, explore the optical time for observing the whole inner ear. To study the pharmacokinetic feature of Gd-DTPA in the inner ear, and find out whether discrimination of endolymph and perilymph can be obtained under current conditions.

METHODS

Sixty-five guinea pigs were randomly divided into 13 groups, after diluted Gd-DTPA intratympanic injection, each group of guinea pigs were scanned through MRI (3D-T1 FSE sequence) at different time points (0 h, 0.5 h, 1 h, 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, 24 h, 48 h, 72 h, 96 h). Pixel intensity values of some locations in the inner ear were analyzed using e-Film software, then pixel intensity was converted into concentration using the results of previous in-vitro study. ABR thresholds of bilateral ears before, 1 d and 7 d after intratympanic injection were compared.

RESULTS

Six hours after transtympanic Gd-DTPA injection was the time point when contrast agent was distributed all over the inner ear, and reached a high concentration: 589.29, 552.54, 570.17, 255.08, 107.09 and 139.18 µmol/L in the vestibule, scala vestibuli and scala tympani of basal turn, the 2(nd), the 3(rd) and the apical turn individually, that was also the optimal time for observing the whole inner ear by MRI. Perilymph appeared to be preferentially enhanced relative to the endolymph, resulting in a distinction between the scales of the inner ear. There was no significant difference between the experimental ear (diluted GD-DTPA injected ear) and contrast ear (physiological saline injected ear) on 1 d and 7 d.

CONCLUSIONS

The best time getting MRI imaging after intratympanic diluted GD-DTPA injection is 6 h. After diluted agent injection perilymph can be enhanced so as to be differentiated with endolymph by MRI, diluted agent have no obvious effect on the ABR threshold. The pharmacokinetic feature of Gd-DTPA in the inner can be studied using MRI.