Objective quantification of the motion of soft tissues in the orbit

Orbital soft-tissue motion analysis aids in the localization and diagnosis of orbital disorders. A technique has been developed to objectively quantif y and visualize motion in the orbit during gaze. T1-weighted MR volume sequ ences are acquired during gaze and soft-tissue motion is quantified using o ptical now techniques. The flow field is visualized using color-coding: ori entation of the flow vector is coded by hue and magnitude by saturation of the pixel. Current clinical circumstances limit MR image acquisition to sho rt sequences and short acquisition times. The effect of these limitations o n the performance of optical flow computation has been studied for four rep resentative optical flow algorithms: on short (nine frames) and long (21 fr ames) simulated sequences of rotation of a magnetic resonance (MR) imaged o bject, on short measured MR sequences of controlled rotation of the same ob ject and an short MR sequences of motion in the orbit. On the short simulat ed and motion-controlled sequences, the Lucas and Kanade algorithm showed t he best performance with respect to both accuracy and robustness. These mot ion estimates were accurate to within 20%. Motion in the orbit ranged betwe en 0.05 and 0.25 mm/degrees gaze. Color-coding was found to be attractive a s a visualization technique, because it shows both magnitude and orientatio n of all flow vectors without cluttering.