MRI dynamic color mapping: a new quantitative technique for imaging soft tissue motion in the orbit

To investigate both feasibility and clinical potential of magnetic resonance imaging-dynamic color mapping (MRI-DCM) in measuring the motion of soft tissues in the orbit and in the diagnosis of orbital disorders by detecting changes in motion.

Sequences of MRI scans were acquired (acquisition time, 5 seconds) in a shoot-stop manner, while the patient fixated at a sequence of 13 gaze positions (8 degrees intervals). Motion was quantified off-line (in millimeters per degree of gaze change) using an optical flow algorithm. The motion was displayed in a color-coded image in which color saturation of a pixel shows the displacement and the hue the displacement's orientation. Six healthy volunteers and four patients (two with an orbital mass and two with acrylic ball implant after enucleation) were studied.

The technique was found to be clinically feasible. For a gaze change of 1 degrees, orbital tissues moved between 0.0 and 0.25 mm/deg, depending on the type of tissue and location in the orbit. In the patients with an orbital mass, motion of the mass was similar to that of the medial rectus muscle, suggesting disease of muscular origin. In the enucleated orbits, soft tissue motion was decreased. One eye showed attachment of the optic nerve to the implant, which could be verified by biopsy.

MRI-DCM allows noninvasive and quantitative measurement of soft tissue motion and the changes in motion due to pathologic conditions. In cases in which the diagnosis of a tumor in the apex is in doubt, it may reduce the need for biopsy. In contrast to static computed tomographic (CT) scans and MRIs, it can differentiate between juxtaposition and continuity and may be a new and promising tool in the differential diagnosis of intraorbital lesions.