title: Evaluation of a signal intensity mask in the interpretation of functional MR imaging activation maps.
abstract: OBJECTIVE
  The purpose of this study was to determine the incidence of susceptibility artifacts on functional MR imaging (fMRI) studies and their effect on fMRI readings. We hypothesized that the availability of the signal intensity maps (SIMs) changes the interpretation of fMRI studies in which susceptibility artifacts affected eloquent brain regions.
  
  
  METHODS
  We reviewed 152 consecutive clinical fMRI studies performed with a SIM. The SIM consisted of the initial echo-planar images (EPI) in each section thresholded to eliminate signal intensity from outside the brain and then overlaid on anatomic images. The cause of the artifact was then determined by examining the images. Cases with a susceptibility artifact in eloquent brain were included in a blinded study read by four readers, first without and then with the SIM. For each reader, the number of times the interpretation changed on viewing the SIM was counted.
  
  
  RESULTS
  Of 152 patients, 44% had signal intensity loss involving cerebral cortex and 18% involving an eloquent brain region. Causes of the artifacts were: surgical site artifact, blood products, dental devices, calcium, basal ganglia calcifications, ICP monitors, embolization materials, and air. When provided with the SIM, readers changed interpretations in 8-38% of patient cases, depending on reader experience and size and location of susceptibility artifact.
  
  
  CONCLUSIONS
  Patients referred for clinical fMRI have a high incidence of susceptibility artifacts, whose presence and size can be determined by inspection of the SIM but not anatomic images. The availability of the SIM may affect interpretation of the fMRI.
authors.affiliation: Department of Radiology, University of Wisconsin, Madison, 53792-3252, USA.
authors.forename: Roberta M
authors.initials: RM
authors.lastname: Strigel
authors.forename: Chad H
authors.initials: CH
authors.lastname: Moritz
authors.forename: Victor M
authors.initials: VM
authors.lastname: Haughton
authors.forename: Behnam
authors.initials: B
authors.lastname: Badie
authors.forename: Aaron
authors.initials: A
authors.lastname: Field
authors.forename: David
authors.initials: D
authors.lastname: Wood
authors.forename: Michael
authors.initials: M
authors.lastname: Hartman
authors.forename: Howard A
authors.initials: HA
authors.lastname: Rowley
mesh_terms: D016477:Artifacts; D001927:Brain Diseases / Q000175:diagnosis; D001931:Brain Mapping; D017352:Echo-Planar Imaging / Q000379:methods*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008280:Magnetics; D012189:Retrospective Studies; D016037:Single-Blind Method