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A 200 MHz flexible receive phased array for (f)MRI of macaques in a vertical scanner

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Logothetis,  NK
Max Planck Institute for Biological Cybernetics, Max Planck Society;
Department Physiology of Cognitive Processes, Max Planck Institute for Biological Cybernetics, Max Planck Society;

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Goense,  JBM
Max Planck Institute for Biological Cybernetics, Max Planck Society;
Department Physiology of Cognitive Processes, Max Planck Institute for Biological Cybernetics, Max Planck Society;

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Citation

Merkle, H., Logothetis, N., & Goense, J. (2008). A 200 MHz flexible receive phased array for (f)MRI of macaques in a vertical scanner. Poster presented at ESMRMB 2008 Congress: 25th Annual Meeting, Valencia, Spain.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0013-C6CF-9
Abstract
Introduction: Since high SNR is necessary for high-resolution FMRI it is advantageous to place the coils close against the monkey’s head whenever possible. To this end, we designed a flexible 4-channel receive-only phased array that can be used on monkeys of different sizes as well as for different cortical areas. In addition, the preamplifiers including control electronics are detachable and can serve a variety of prefabricated and phase-matched fourelement arrays of different configurations. Methods: A linear array of 4 circular coils of ~23 mm diameter with gaps of ~11 mm was sutured onto a soft plastic strip (Figure 1). The assembly having in-line connectors was attached to phase-matched coaxial cables to modified commercial high reflection coefficient preamplifiers (Stark Contrast Inc., Erlangen, Germany) via cable traps. Detuning of the individual coils during RF transmission was achieved using DC currents within the coaxial cables and pin diode controlled notch filters within the array elements. Experiments were done on anesthetized monkeys on a vertical 4.7T Bruker Biospec running ParaVision 5. The array was positioned over the occipital pole. RF transmission was done with a de-tunable ‘type D’ partial volume coil. We obtained high-resolution FLASH (Figure 2) and FMRI data using EPI with and without acceleration (GRAPPA). The stimulus was a full-field rotating checkerboard. FLASH: resolution 100x100x1000 μm, TE 23 ms, TR 2000 ms, 1 average; FMRI: GE-EPI, resolution 500x500x2000 μm, TE 21 ms, TR 750 ms, 8 segments with R = 1, or 4 segments with R = 2. Results: The high-resolution FLASH anatomical images show intracortical veins and the Gennari line in entire V1, including peripheral V1, which is located deep in the brain. Using a dual-coil setup, it is only possible to observe these features in parts of V1 that are close to the surface. The functional map proofs that the increased coverage allows us to obtain activation in V1-V5 in both hemispheres at high resolution (Figure 3). SNR was sufficient to also allow accelerated FMRI at the same resolution. Discussion: Compared to a dual-coil setup the phased array provides improved SNR and coverage, which allows for high resolution anatomical imaging and FMRI of the entire early visual cortex, including better performance in deep brain areas.