Anatomical and functional MR imaging in the macaque monkey using a vertical large-bore 7 Tesla setup
Josef Pfeuffera, Corresponding Author Contact Information, E-mail The Corresponding Author, Hellmut Merkleb, Michael Beyerleina, Thomas Steudela and Nikos K. Logothetisa
aDepartment Physiology of Cognitive Processes, Max-Planck Institute for Biological Cybernetics, 72012 Tübingen, Germany
bLaboratory of Functional and Molecular Imaging, NINDS/NIH, Bethesda, MD 20892-1065, USA
Received 16 August 2004; accepted 8 October 2004. Available online 8 February 2005.
Abstract
Functional magnetic resonance imaging (MRI) in the nonhuman primate promises to provide a much desired link between brain research in humans and the large body of systems neuroscience work in animals. We present here a novel high field, large-bore, vertical MR system (7 T/60 cm, 300 MHz), which was optimized for neuroscientific research in macaque monkeys. A strong magnetic field was applied to increase sensitivity and spatial resolution for both MRI and spectroscopy. Anatomical imaging with voxel sizes as small as 75×150×300 μm3 and with high contrast-to-noise ratios permitted the visualization of the characteristic lamination of some neocortical areas, e.g., Baillarger lines. Relaxation times were determined for different structures: at 7 T, T1 was 2.01/1.84/1.54 s in GM/GM-V1/WM, T2 was 59.1/54.4 ms in GM/WM and T2* was 29 ms. At 4.7 T, T1 was 25% shorter, T2 and T2* 18% longer compared to 7T. Spatiotemporally resolved blood-oxygen-level-dependent (BOLD) signal changes yielded robust activations and deactivations (negative BOLD), with average amplitudes of 4.1% and −2.4%, respectively. Finally, the first high-resolution (500 μm in-plane) images of cerebral blood flow in the anesthetized monkey are presented. On functional activation we observed flow increases of up to 38% (59 to 81 ml/100 g/min) in the primary visual cortex, V1. Compared to BOLD maps, functional CBF maps were found to be localized entirely within the gray matter, providing unequivocal evidence for high spatial specificity. The exquisite sensitivity of the system and the increased specificity of the hemodynamic signals promise further insights into the relationship of the latter to the underlying physiological activity.
Keywords: Functional imaging; Monkey brain; High-field MR system; Cerebral blood flow