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 scanne rs is the radiofrequency (RF) coil inhomogeneity. It degrades conspicuity c if: lesion(s) in the MR images of the brain and surrounding tissues and red uces accuracy of image postprocessing particularly at the edges of the coil . In this investigation, we have devised and tested a simple method to corr ect 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 identifie d 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 t o this reference value. The resulting set of coefficients "correction matri ces'' 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 diffe rent 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.