Abstract:Conventional functional magnetic resonance imaging (FMRI) allows the measurement of functional cerebral blood flow changes occurring with specific tasks using standard clinical MR systems. However, the spatial relationship between neuronal activity and functional cerebral blood flow changes is not yet known. This article reviews studies which compared the center of neuronal activation (measured by magnetoencephalography) with that of the hemodynamic response (measured by FMRI) using motor and visual stimulatio… Show more
“…In addition, the results indicate overadditive effects with multimethod approaches. In recent papers concerning combined MEG-FMRI approaches, several authors (Belliveau et al, 1993;NBattSinen et al, 1994Beisteiner et al, 1995b have pointed out that FMRI may help MEG to constrain the inverse problem. As we show, with certain paradigms MEG may also help FMRI to improve data analysis strategies and thus brain mapping validity.…”
The validity of functional magnetic resonance imaging (FMRI) brain maps with respect to the sites of neuronal activation is still unknown. One source of localization error may be pixels with large signal amplitudes, since such pixels may be expected to overlie large vessels, running remote from the centre of neuronal activation. In this study, magnetoencephalography was used to determine the centre of neuronal activation in a simple finger tapping task. The localization accuracy of conventional FMRI depending on FMRI signal enhancement was investigated relative to the magnetoencephalography reference. The results show a deterioration of FMRI localization with increasing signal amplitude related to increased contributions from large vessels. We conclude that FMRI data analysis should exclude large signal amplitudes and that magnetoencephalography may help to improve FMRI brain mapping results in a multimethod approach.
“…In addition, the results indicate overadditive effects with multimethod approaches. In recent papers concerning combined MEG-FMRI approaches, several authors (Belliveau et al, 1993;NBattSinen et al, 1994Beisteiner et al, 1995b have pointed out that FMRI may help MEG to constrain the inverse problem. As we show, with certain paradigms MEG may also help FMRI to improve data analysis strategies and thus brain mapping validity.…”
The validity of functional magnetic resonance imaging (FMRI) brain maps with respect to the sites of neuronal activation is still unknown. One source of localization error may be pixels with large signal amplitudes, since such pixels may be expected to overlie large vessels, running remote from the centre of neuronal activation. In this study, magnetoencephalography was used to determine the centre of neuronal activation in a simple finger tapping task. The localization accuracy of conventional FMRI depending on FMRI signal enhancement was investigated relative to the magnetoencephalography reference. The results show a deterioration of FMRI localization with increasing signal amplitude related to increased contributions from large vessels. We conclude that FMRI data analysis should exclude large signal amplitudes and that magnetoencephalography may help to improve FMRI brain mapping results in a multimethod approach.
The potential of statistical analyses of functional magnetic resonance images using various threshold strategies in combination with correlation analysis was studied by simulating brain activation. Differences in statistical Type I (alpha) and II (beta) errors are substantial for the various thresholds. Absolute thresholds and individualized thresholds based on the assumption of a gaussian noise distribution are producing constant alpha-errors and thus do not sufficiently improve discrimination of "truly" activated pixels even for very high contrast-to-noise ratios (CNR). Only relative threshold strategies related to the maximum correlation coefficient and thus the individual data quality and activation level, i.e., a data-driven approach, can perfectly discriminate true positives, at least for CNR > 2.5. To further improve discrimination of activated and non-activated pixel in studies with lower CNR, additional prior knowledge would be necessary. From the data presented, one would also expect that the best performing threshold strategy in this simulation study would perform best under in vivo conditions.
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