A simple method to improve image nonuniformity of brain MR images at the edges of a head coil.

One of the major sources of image nonuniformity in the high field MR scanners is the radiofrequency (RF) coil inhomogeneity. It degrades conspicuity of lesion(s) in the MR images of the brain and surrounding tissues and reduces accuracy of image postprocessing particularly at the edges of the coil. In this investigation, we have devised and tested a simple method to correct for nonuniformity of MR images of the brain at the edges of the RF head coil. Initially, a cylindrical oil phantom, which fit exactly in the head coil, was scanned on a 1.5 T imager. Then, a correction algorithm identified a reference pixel value in the phantom at the most homogeneous region of the RF coil. Next, every pixel inside the phantom was normalized relative to this reference value. The resulting set of coefficients or "correction matrices" was obtained for different types of MR contrast agent. Finally, brain MR images of normal subjects and multiple sclerosis patients were acquired and processed by the corresponding correction matrices obtained with different pulse sequences. Application of correction matrices to brain MR images showed a gain in pixel intensity particularly in the slices at the edge of the coil.

MR imaging of neuronal transport in the guinea pig facial nerve: initial findings.

Certain dextran coated iron oxides such as MION (monocrystalline iron oxide nanocompound) coupled to wheat germ agglutinin (MION-WGA) have been shown to exhibit i) neuronal uptake ii) axonal transport and iii) strong magnetic effects on tissues (superparamagnetism) in which they are localized. In the current study, we utilized such an agent to visualize axonal transport in the facial nerve in vivo by magnetic resonance (MR) imaging. Following injection of the compound into the facial nerves of guinea pigs, MR images were obtained at multiple time points (1, 3 and 5 days) and the imaged tissues were processed for subsequent histological examination. In nerves that had been injected with MION-WGA, the entire nerve appeared as a uniformly hypointense structure with a calculated transport rate of 5 mm/day. By 3 days, the agent within the facial nerve was traceable by MRI from a site of injection in the buccal branch to the stylomastoid foramen. Fluorescence and autoradiography studies confirmed axonal transport. These results show that MION-based magnetopharmaceuticals can be used to demonstrate slow axonal transport, and thereby visualize functional peripheral nerves in vivo by MR imaging. The method holds promise for developmental neuroscience research as well as a method to detect neural abnormalities by MR imaging.

Prospective evaluation of the course of disc herniations in patients with proven radiculopathy.

Although surgery is often recommended as the definitive treatment for radiculopathy when definite disc herniation is demonstrated with imaging techniques, complete improvement can occur with nonoperative treatment. However, what happens to the disc in the latter circumstance is not well defined. We report the first prospective study in subjects with proven radiculopathy and definite disc herniation who improve with nonoperative management to determine what occurs to the herniated disc material. Eighteen subjects with lower extremity pain or paresthesia, positive straight leg raising, weakness in a myotomal distribution, reflex asymmetry, or electromyogram evidence of radiculopathy were studied. Subjects were admitted to the study if computed tomography (CT) scanning demonstrated definite disc herniation corresponding to the side and level of the radiculopathy. After complete clinical improvement, repeat CT scan was performed at six to 18 months after the initial study. The CT scans were interpreted separately by two neuroradiologists. Disc herniations were characterized by size (large, moderate, or minimal); the presence of absence of free fragments; and location. Follow-up scans were compared with the original study and characterized as resolved, improved, or unchanged. Fourteen subjects completed the study, an additional three had operative treatment, and one refused repeat scanning. Subjects were followed an average of 30.4 months with no recurrence of radicular symptoms during this follow-up period in 13 patients. One had recurrence of symptoms at 21 months and surgery at 26 months. Six follow-up scans (43%) were interpreted as completely resolved, five (36%) as improved, and three (21%) as unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)