Video loop MRI of ocular motility: a new technique: turbo rare sequence at 2 T for the study of horizontal gaze.

PURPOSE

To improve existing MRI (Magnetic Resonance Imaging) methods of assessing ocular motility in horizontal gaze by using a multi-static fast imaging T2W MRI sequence, preventing patient head motion and convergence of the eyes during the study for the diagnosis and management of complex paralytic strabismus.

SUBJECTS AND METHODS

A turbo-RARE image of the orbits was acquired in a set plane each time the patient fixed on a virtual image of one of 15 LEDs (Light Emitting Diodes). Positioning and securing the head was by a security cushion with an 8 degree tilt of the 25 cm quadrature head coil. After completion of the study (5 minutes) the MRI images were transferred to a work station and on to 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 volumes. Twenty normal volunteers and 3 cases of oculomotor palsies were so studied.

RESULTS

The experimental setup allowed us to obtain: 1) rapid (14 s) and high resolution images (256 x 196 x 3 mm); 2) which were free artifacts; 3) with no detectable eye convergence; 4) in which the lateral and medial rectus muscles and anatomical details of the orbit were clearly depicted; 5) from which additional functional information was obtained from the cine loop analysis; 6) wherein the visual axes did not converge during horizontal versions; 7) which permitted horizontal rectus muscle angles to be followed during contraction and relaxation; and 8) allowed the cross-sectional area of the four rectus muscles to be compared during contraction and relaxation (difference of 0.2 cm2).

CONCLUSIONS

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