Cerebrospinal fluid-iophendylate contrast on gradient-echo MR images

The effect on the signal intensities of cerebrospinal fluid (CSF) and iophendylate (Pantopaque) and on CSF-iophendylate contrast was studied in vitro with a small-nutation-angle (alpha) gradient refocused magnetic resonance (MR) imaging technique (GRASS) as alpha, repetition time (TR), and echo time (TE) were varied. CSF signal intensity was consistently greater than that of iophendylate. Therefore, retained intraspinal iophendylate may be considered in the differential diagnosis of focal areas of low signal intensity at the periphery of the spinal canal on GRASS images. At constant TE and TR, an increase in alpha from 6 degrees to 45 degrees increased the signal intensities of CSF and iophendylate but decreased CSF-iophendylate contrast. At constant alpha and TR, an increase in TE from 13 to 28 msec decreased the signal intensities of CSF and iophendylate but increased contrast. At constant alpha and TE, an increase in TR from 50 to 400 msec increased the signal intensities of CSF and iophendylate, as well as contrast. Clinical examples of the contrast behavior of retained intraspinal iophendylate on both spin-echo and GRASS images corroborate the experimental findings. Retained intraspinal iophendylate may mimic the appearance of intra-or extra-dural lesions, magnetic susceptibility artifact, and flow on gradient-echo MR images of the spine.