title: Threshold-independent functional MRI determination of language dominance: a validation study against clinical gold standards.
abstract: Functional MRI (fMRI) is often used for presurgical language lateralization. In the most common approach, a laterality index (LI) is calculated on the basis of suprathreshold voxels. However, strong dependencies between LI and threshold can diminish the effectiveness of this technique; in this study we investigated an original methodology that is independent of threshold. We compared this threshold-independent method against the common threshold-dependent method in 14 patients with epilepsy who underwent Wada testing. In addition, clinical results from electrocortical language mapping and postoperative language findings were used to assess the validity of the fMRI lateralization method. The threshold-dependent methodology yielded ambiguous or incongruent lateralization outcomes in 4 of 14 patients in the inferior frontal gyrus (IFG) and in 6 of 14 patients in the supramarginal gyrus (SMG). Conversely, the threshold-independent method yielded unambiguous lateralization in all the patients tested, and demonstrated lateralization outcomes incongruent with clinical standards in 2 of 14 patients in IFG and in 1 of 14 patients in SMG. This validation study demonstrates that the threshold-dependent LI calculation is prone to significant within-patient variability that could render results unreliable; the threshold-independent method can generate distinct LIs that are more concordant with gold standard clinical findings.
authors.affiliation: Department of Radiology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Ralph O
authors.initials: RO
authors.lastname: Suarez
authors.forename: Stephen
authors.initials: S
authors.lastname: Whalen
authors.forename: Aaron P
authors.initials: AP
authors.lastname: Nelson
authors.forename: Yanmei
authors.initials: Y
authors.lastname: Tie
authors.forename: Mary-Ellen
authors.initials: ME
authors.lastname: Meadows
authors.forename: Alireza
authors.initials: A
authors.lastname: Radmanesh
authors.forename: Alexandra J
authors.initials: AJ
authors.lastname: Golby
mesh_terms: D000328:Adult; D000368:Aged; D000654:Amobarbital / Q000008:administration & dosage / Q000494:pharmacology; D000704:Analysis of Variance; D001921:Brain / Q000098:blood supply* / Q000473:pathology / Q000503:physiopathology; D001931:Brain Mapping; D004833:Epilepsy, Temporal Lobe / Q000473:pathology* / Q000503:physiopathology; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D007802:Language; D007807:Language Tests; D008279:Magnetic Resonance Imaging / Q000379:methods* / Q000592:standards; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D010100:Oxygen / Q000097:blood; D010775:Photic Stimulation; D011300:Preoperative Care; D015203:Reproducibility of Results; D055815:Young Adult
chemical_list: D000654:Amobarbital; D010100:Oxygen