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

PURPOSE. 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 d etecting changes in motion. METHODs. 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 millim eters per degree of gaze change) using an optical flow algorithm. The motio n 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 hea lthy volunteers and four patients (two with an orbital mass and two with ac rylic ball implant after enucleation) were studied. RESULTS. The technique was found to be clinically feasible. For a gaze chan ge of 1 degrees, orbital tissues moved between 0.0 and 0.25 mm/deg, dependi ng 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, so ft tissue motion was decreased. One eye showed attachment of the optic nerv e to the implant, which could be verified by biopsy. CONCLUSIONS. MRI-DCM allows noninvasive and quantitative measurement of sof t tissue motion and the changes in motion due to pathologic conditions. Tn cases in which the diagnosis of a tumor in the apex is in doubt, it may red uce the need for biopsy. In contrast to static computed tomographic (CT) sc ans and MRIs, it can differentiate between juxtaposition and continuity and may be a new and promising tool in the differential diagnosis of intraorbi tal lesions.