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. The most common approach calculates a laterality index (LI) based on 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 epilepsy patients who underwent Wada testing. In addition, clinical results from eletrocortical language mapping and post-operative language findings were used to assess the validity of the fMRI laterality 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.

Localization of Broca's area using verb generation tasks in the MEG: Validation against fMRI

“…The effect of threshold selection is consistent with reports in the literature that choice of thresholds is not straight-forward and needs to be carefully considered [33,38]. We found that at increasingly stringent thresholds, the percent overlap between MEG and fMRI decreased substantially.…”

Role of Semantic Paradigms for Optimization of Language Mapping in Clinical fMRI Studies

“…Furthermore, it has been demonstrated that the combination of multiple tasks, a language-specific region of interest approach and implementation of statistical threshold-independent approaches for determination of hemispheric lateralization, provides more reliable lateralization that correlates better with the criterion standard Wada test. 20,21 One limitation of this study includes the exclusion of the cerebellum from region-of-interest analysis. The cerebellum has demonstrated fMRI activation during silent articulation.…”

Functional MRI language mapping in pre-surgical epilepsy patients: Findings from a series of patients in the Epilepsy Unit at Mediclinic Constantiaberg

“…Therefore, it is recommended that multiple language tasks be administered in fMRI in order to calculate language dominance as a continuous variable. [13] In localising language function, several tasks have been shown to reliably activate expressive and receptive language cortex (Table 1). Generally, verbal fluency paradigms require expressive language and secondarily, language comprehension and therefore activations are noted in Broca's areas and Wernicke's area in the dominant hemisphere, in addition to pre-motor cortex, posterior fusiform gyrus, middle temporal gyrus and dorsolateral prefrontal cortex.…”