title: Misleading changes of the signal intensity on opposed-phase MRI after injection of contrast medium.
abstract: OBJECTIVE
  The effect of opposed-phase imaging on the interpretation of MR contrast studies is highlighted.
  
  
  METHODS
  A model calculation is performed. It demonstrates the change of signal intensity of an average tumor before and after application of Gd-DTPA on an in-phase and an opposed-phase image, depending on the percentage of fat within the voxels. The effect is then demonstrated, using a small cotton stick soaked with water or a solution of contrast agent representing a tumor before and after i.v. application of Gd-DTPA.
  
  
  RESULTS
  If an average enhancing tumor, which is surrounded by fat, occupies less than 50-60% of the slice thickness, it becomes undetectable on opposed-phase images. The reason is that due to signal cancellation on the opposed image, no signal change or even signal decrease results, while signal increase is visible on the in-phase image.
  
  
  CONCLUSIONS
  In those areas of the body where significant partial volume of a tumor with fat may occur (such as for breast tumors growing along ducts, which are surrounded by fat), severe errors can result. Therefore we explicitly warn from using opposed-image sequences for MR contrast studies.
authors.affiliation: Department of Diagnostic Radiology, Martin Luther University of Halle-Wittenberg, Halle, Germany.
authors.forename: S H
authors.initials: SH
authors.lastname: Heywang-Köbrunner
authors.forename: H D
authors.initials: HD
authors.lastname: Wolf
authors.forename: M
authors.initials: M
authors.lastname: Deimling
authors.forename: S
authors.initials: S
authors.lastname: Kösling
authors.forename: H
authors.initials: H
authors.lastname: Höfer
authors.forename: R P
authors.initials: RP
authors.lastname: Spielmann
mesh_terms: D003287:Contrast Media / Q000008:administration & dosage; D019786:Gadolinium DTPA; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008961:Models, Structural; D008962:Models, Theoretical; D009369:Neoplasms / Q000175:diagnosis*; D009942:Organometallic Compounds / Q000008:administration & dosage; D004369:Pentetic Acid / Q000008:administration & dosage / Q000031:analogs & derivatives*
chemical_list: D003287:Contrast Media; D009942:Organometallic Compounds; D004369:Pentetic Acid; D019786:Gadolinium DTPA