title: Assessment of the language laterality index in patients with brain tumor using functional MR imaging: effects of thresholding, task selection, and prior surgery.
abstract: OBJECTIVE
  Functional MR imaging (fMRI) is used to determine preoperatively the laterality of cortical language representation along with the relationship of language areas to adjacent brain tumors. The purpose of this study was to determine whether changing the statistical threshold for different language tasks influences the language laterality index (LI) for a group of controls, patients with tumor without prior surgery, and patients with tumor and prior surgery.
  
  
  METHODS
  Seven controls, 9 patients with tumor without prior surgery, and 4 patients with tumor and prior surgery performed verb-generation, phonemic fluency, and semantic fluency language tasks during fMRI. Interhemispheric activation differences between the left and right Broca regions of interest were determined by calculating language LIs. LIs were compared within each group, between groups, and between language tasks. Intraoperative electrocortical mapping or the presence of aphasia during postoperative neurology examinations or both were used as ground truth.
  
  
  RESULTS
  The language LI varied as a result of statistical thresholding, presence of tumor, prior surgery, and language task. Although patients and controls followed a similar shape in the LI curve, there was no optimal P value for determining the LI. Three patients demonstrated a shift in the LI between hemispheres as a function of statistical threshold. Verb generation was the least variable task both between tasks and across groups.
  
  
  CONCLUSIONS
  For preoperative patients with tumor, the LI should be examined across a spectrum of P values and a range of tasks to ensure reliability. Our data suggest that the LI may be threshold- and task-dependent, particularly in the presence of adjacent tumor.
authors.affiliation: Northwestern University Feinberg School of Medicine, Chicago, Ill., USA.
authors.forename: I M
authors.initials: IM
authors.lastname: Ruff
authors.forename: N M
authors.initials: NM
authors.lastname: Petrovich Brennan
authors.forename: K K
authors.initials: KK
authors.lastname: Peck
authors.forename: B L
authors.initials: BL
authors.lastname: Hou
authors.forename: V
authors.initials: V
authors.lastname: Tabar
authors.forename: C W
authors.initials: CW
authors.lastname: Brennan
authors.forename: A I
authors.initials: AI
authors.lastname: Holodny
mesh_terms: D000328:Adult; D001931:Brain Mapping / Q000379:methods; D001932:Brain Neoplasms / Q000175:diagnosis* / Q000601:surgery*; D002540:Cerebral Cortex / Q000473:pathology*; D004056:Differential Threshold; D005260:Female; D007839:Functional Laterality; D006801:Humans; D007802:Language; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011300:Preoperative Care / Q000379:methods*; D011379:Prognosis; D018570:Risk Assessment / Q000379:methods