Assessment of hemispheric language lateralization: A comparison between fMRI and fTCD

The cerebral blood flow velocity (CBFV) in the basal arteries during a word -generation task was assessed by functional transcranial Doppler ultrasonog raphy (fTCD) and by functional magnetic resonance imaging (fMRI). The study investigates how event-related CBFV modulations in the middle cerebral art ery (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). Th e maximum differ -ence of relative CBFV changes between the left and right MCA during the word-generation task was used as the language laterality ind ex (LIfTCD). For the fMRI examination during the nearly identical language task, the corresponding index was defined by LIfMRI = 100(N-L- N-R)/(N-L N-R), where N-L and N-R refer to the numbers of voxels activated in the lef t and right hemisphere, respectively. The evoked CBFV changes expressed by LIfTCD and the corresponding laterality index, LIfMRI. estimated by fMRI sh owed a close linear relation (regression analysis: r = 0.95, p < 0.0001). T he results of this study demonstrate that language-related velocity changes in the MCAs relate to rCBF increases in a linear fashion. Since the latera lity indices assessed by fMRI and fTCD are in such close agreement both tec hniques can therefore be used in a complementary way.