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  Spatial resolution of BOLD versus MION in a macaque fMRI paradigm at 4.7 T

Schmid, M., Tolias, A., Augath, M., Logothetis, N., & Smirnakis, S. (2004). Spatial resolution of BOLD versus MION in a macaque fMRI paradigm at 4.7 T. Poster presented at 10th Annual Meeting of the Organization for Human Brain Mapping (HBM 2004), Budapest, Hungary.

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Item Permalink: http://hdl.handle.net/11858/00-001M-0000-0013-D921-1 Version Permalink: http://hdl.handle.net/11858/00-001M-0000-0013-D922-0
Genre: Poster

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Schmid, MC1, Author              
Tolias, AS1, Author              
Augath, MA1, Author              
Logothetis, NK1, Author              
Smirnakis, SM, Author
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1Department Physiology of Cognitive Processes, Max Planck Institute for Biological Cybernetics, Max Planck Society, ou_1497798              

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 Abstract: Most macaque functional magnetic resonance imaging (fMRI) studies are based on monitoring the intrinsic blood oxygen level dependent signal (BOLD) or, alternatively, on measuring changes in cerebral blood volume (CBV) after injection of a contrast agent. The intravascular contrast agent MION (monocrystalline iron oxide nanoparticles) has been recently applied in a number of studies (Dubowitz et al., 2001; Leite et al., 2002; Mandeville et al., 1997; Mandeville et al., 1998; Mandeville and Marota, 1999; Tsao et al., 2003a; Tsao et al., 2003b; Vanduffel et al., 2001). In comparison to BOLD, imaging with MION results in higher contrast to noise ratios (CNR) (Leite et al., 2002;Vanduffel et al., 2001) which may provide improved fMRI sensitivity, making MION especially appealing at low to moderate magnetic field strengths. Moreover, it has been suggested that MION may result in improved spatial specificity, since it appears to arise primarily from small parenchymal vessels (Mandeville et al., 1998; Mandeville and Marota, 1999) as opposed to BOLD which, at low magnetic fields, is known to be influenced by larger vessels that run along the cortical surface (Gati, Menon, et al., 1997). In order to directly compare the spatial resolution of BOLD versus MION, we conducted a series of experiments in the anaesthetized macaque monkey preparation (macaca mulatta) at a magnetic field strength of 4.7 T. We acquired data using 8-segment multishot EPI with flip angle = 40 deg, TE = 20 ms, TR = 805 ms, for both BOLD and MION experiments. We typically injected 8mg/kg MION which is known to give near optimal CNR (Mandeville, Marota, et al., 1998; Vanduffel, Fize, et al., 2001). In a first set of experiments we measured the distribution of BOLD/MION as a function of gray matter depth in macaque primary visual cortex (V1). Stimulation was done by alternating a rotating polar checkerboard with a field of uniform light intensity. Voxel size was 0.2 x 0.2 x 1mm 3 . Correlation coefficients were computed voxel by voxel and then averaged for voxels lying at the same cortical depth. Figure 1 plots the average correlation coefficients for BOLD (blue) versus MION (red) as a function of depth in the primary visual cortex (V1) of one macaque. Note that the correlation coefficients for MION appear to peak deeper in gray matter as compared to BOLD. To compare the spatial extent of functional activation seen with BOLD versus MION along the cortical surface, we used a similar stimulation paradigm as before, except that now the rotating polar checkerboard pattern contained a 6 deg diameter occluder (artificial scotoma) centered at 6 deg from the fovea. This assured that the corresponding cortical area in V1 received no direct visual stimulation. Figure 2 shows the correlation maps obtained with BOLD and MION under these stimulation conditions in a slice through the left V1 of one macaque (voxel resolution: 1 x 1 x 2 mm 3 ). Note that the spread of functional activity into the cortical area corresponding to the artificial scotoma (i.e. where there is no visual stimulation) appears to be markedly greater for MION than for BOLD.

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 Dates: 2004-06
 Publication Status: Published in print
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Title: 10th Annual Meeting of the Organization for Human Brain Mapping (HBM 2004)
Place of Event: Budapest, Hungary
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