Showing papers by "Anders H. Andersen published in 2009"

Aging Influences the Neural Correlates of Lexical Decision but Not Automatic Semantic Priming

Abstract: Human behavioral data indicate that older adults are slower to perform lexical decisions (LDs) than young adults but show similar reaction time gains when these decisions are primed semantically. The present study explored the functional neuroanatomic bases of these frequently observed behavioral findings. Young and older groups completed unprimed and primed LD tasks while functional magnetic resonance imaging (fMRI) was recorded, using a fully randomized trial design paralleling those used in behavioral research. Results from the unprimed task found that age-related slowing of LD was associated with decreased activation in perceptual extrastriate regions and increased activation in regions associated with higher level linguistic processes, including prefrontal cortex. In contrast to these age-related changes in brain activation, the older group showed a preserved pattern of fMRI decreases in inferior temporal cortex when LD was primed semantically. These findings provide evidence that older adults’ LD abilities benefit from contexts that reduce the need for frontally mediated strategic processes and capitalize on the continued sensitivity of inferior temporal cortex to automatic semantic processes in aging.

Calculating T2 in images from a phased array receiver

Abstract: Images reconstructed from multielement, phased array coils and presented as the square root of the sum of the squares of the signals received by the individual elements have a distribution of signal and noise that distorts the relationship between the image intensity and the underlying signal. The distortion is accentuated for long echo times for which the signal-to-noise ratio (SNR) may be low. When measuring T2 or T this signal distortion leads to biased estimates of these parameters. We demonstrate this effect and its dependence on the image SNR and the number of elements in a phased array coil. We evaluated the effects of four techniques for calculating T2 from data acquired in phased array coils (log transform, least squares, lookup table correction, and maximum likelihood [ML] estimation). The ML estimation gave the most accurate T2 in the presence of this bias. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.