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

• Published in: Journal of computer assisted tomography Vol. 23; no. 6; pp. 1008 - 1012
• Main Authors: MOHAMED, F. B, VINITSKI, S, FARO, S. H, ORTEGA, H. V, ENOCHS, S
• Format: Journal Article
• Language: English
• Published: Hagerstown, MD Lippincott 01-11-1999
• Subjects: Algorithms; Biological and medical sciences; Brain - anatomy & histology; Brain - pathology; Contrast Media; Humans; Image Enhancement - methods; Investigative techniques, diagnostic techniques (general aspects); Magnetic Resonance Imaging - instrumentation; Magnetic Resonance Imaging - methods; Medical sciences; Multiple Sclerosis - pathology; Nervous system; Oils; Phantoms, Imaging; Radio Waves; Radiodiagnosis. Nmr imagery. Nmr spectrometry; Reference Values; Image quality; Improvement; Instruments; Central nervous system; High field; Medical imagery; Nuclear magnetic resonance imaging; Non uniform distribution; Brain (vertebrata); Test object
• ISSN: 0363-8715; 1532-3145
• DOI: 10.1097/00004728-199911000-00035

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.