CORRECTION OF NONUNIFORMITY IN IMAGES OF THE SPINE AND OPTIC-NERVE FROM FIXED RECEIVE-ONLY SURFACE COILS AT 1.5-T

Objective: Our goal was to analyze the sources of nonuniform image intensity of two surface coil configurations used on a General Electric 1.5 T Signa scanner and to correct the major source. Materials and Methods: Correction of receive coil nonuniform sensitivity is achieved using division by images of a uniform phantom. Patient images are transferred to a network of Sun workstations for routine correction by technologists. Spinal cord images, originally 512 x 512, are truncated to 128 x 512 to allow four slices to be copied onto one X-ray film. Results: Images of the spinal cord, collected using a four coil multiarray, show marked coil-to-coil nonuniformity and a high signal level from subcutaneous tissue near the coils. After correction the cord has uniform intensity, with improved visualization in the posterior fossa and upper thoracic region, enabling more reliable detection of small intrinsic lesions as occur in multiple sclerosis. Images of the optic nerves, collected using a two coil array, show bright signal in the brain and subcutaneous tissue. After correction the images are more uniform. Conclusion: Nonuniformity in images of the spine can be corrected using division by a phantom image. Water phantoms must be restricted in size to avoid standing wave effects; for the optic nerves a cylindrical oil phantom 20 cm in diameter was used.