[MRI used in the exploration of occulomotor muscles]

To improve existing MRI (magnetic resonance imaging) methods of assessing ocular motility in horizontal gaze by using a multistatic fast imaging T2W MRI sequence, preventing patient head movement and convergence of the eyes during the study for diagnosis and management of complex paralytic strabismus.

A turbo-RARE image of the orbits was acquired in a set plane each time the patient fixed on a virtual image of 1 of 15 LEDs (light emitting diodes). The head was positioned and immobilized with a security cushion at an 8 degrees tilt of the 25-cm quadrature head coil. After completion of the study (5 mn), the MRI images were transferred to a work station and then onto a magnetic video tape to be replayed in cine mode on a PC using standard software. The qualitative analysis was completed by the study of quantitative parameters: visual axis, minor axis of the lens, the lines and angles of the horizontal rectus muscles with the optic nerve and the visual axis. We used digital image analysis to measure the cross-sectional areas of these muscles and also to determine muscle volume. Twenty normal volunteers and 3 cases of oculomotor palsies were studied.

The experimental setup allowed us to obtain images which:1)

This method will provide useful functional quantitative information in the evaluation of ocular motility disorders. The procedure is readily clinically applicable.