Assessment of Hemispheric Language Lateralization: A Comparison between fMRI and fTCD

Abstract

The cerebral blood flow velocity (CBFV) in the basal arteries during a word-generation task was assessed by functional transcranial Doppler ultrasonography (fTCD) and by functional magnetic resonance imaging (fMRI). The study investigates how event-related CBFV modulations in the middle cerebral artery (MCA) relate to regional cerebral blood flow (rCBF) changes. Both fMRI and fTCD were used in 13 subjects (7 men, 6 women, aged 21 to 44 years). The maximum difference of relative CBFV changes between the left and right MCA during the word-generation task was used as the language laterality index ( LI_fTCD). For the fMRI examination during the nearly identical language task, the corresponding index was defined by LI_fMRI = 100(N_L − N_R)/(N_L + N_R), where N_L and N_R refer to the numbers of voxels activated in the left and right hemisphere, respectively. The evoked CBFV changes expressed by LI_fTCD and the corresponding laterality index, LI_fMRI, estimated by fMRI showed a close linear relation (regression analysis: r = 0.95, p < 0.0001). The results of this study demonstrate that language-related velocity changes in the MCAs relate to rCBF increases in a linear fashion. Since the laterality indices assessed by fMRI and fTCD are in such close agreement both techniques can therefore be used in a complementary way.