An implanted 8-channel array coil for high-resolution macaque MRI at 3 T
A.A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA 02129, USA.NeuroImage (Impact Factor: 6.36). 05/2012; 62(3):1529-36. DOI: 10.1016/j.neuroimage.2012.05.028
An 8-channel receive coil array was constructed and implanted adjacent to the skull in a male rhesus monkey in order to improve the sensitivity of (functional) brain imaging. The permanent implant was part of an acrylic headpost assembly and only the coil element loop wires were implanted. The tuning, matching, and preamplifier circuitry was connected via a removable external assembly. Signal-to-noise ratio (SNR) and noise amplification for parallel imaging were compared to single-, 4-, and 8-channel external receive-only coils routinely used for macaque fMRI. In vivo measurements showed significantly improved SNR within the brain for the implanted versus the external coils. Within a region-of-interest covering the cerebral cortex, we observed a 5.4-, 3.6-fold, and 3.4-fold increase in SNR compared to the external single-, 4-, and 8-channel coils, respectively. In the center of the brain, the implanted array maintained a 2.4×, 2.5×, and 2.1× higher SNR, respectively compared to the external coils. The array performance was evaluated for anatomical, diffusion tensor and functional brain imaging. This study suggests that a stable implanted phased-array coil can be used in macaque MRI to substantially increase the spatial resolution for anatomical, diffusion tensor, and functional imaging.
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- "We predict that imaging capabilities will continue to improve using, for example, advanced implanted phased array coils (Janssens et al., 2012) or by moving to superhigh-field scanners (>7 T) and different imaging contrasts. Such methodological advances may vastly increase the spatial and temporal resolution of fMRI up to columnar and laminar levels. "
ABSTRACT: We review recent phase-encoded retinotopic mapping data and discuss the spatial relationship between the retinotopically organized monkey cortex and feature- and category-selective clusters. Four areas sharing a foveal representation, V4t, FST, MT, and MSTv, constitute the MT field map cluster. Rostral to V4, areas V4A, OTd, PITv, and PITd also share a foveal representation, again forming a cluster. Concerning the retinotopic organization of face patches, we observed a gradual shift from posterior patches that are retinotopically organized to anterior, nonretinotopic patches. Feature- and category-selective regions in the nonretinotopic IT cortex form repetitive supermodules, each containing face, body, and color patches.12/2015: pages 293-298; Elsevier., ISBN: 9780123973160
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ABSTRACT: Diffusion tensor MRI is sensitive to the coherent structure of brain tissue and is commonly used to study large-scale white matter structure. Diffusion in grey matter is more isotropic, however, several groups have observed coherent patterns of diffusion anisotropy within the cerebral cortical grey matter. We extend the study of cortical diffusion anisotropy by relating it to the local coordinate system of the folded cerebral cortex. We use 1mm and sub-millimeter isotropic resolution diffusion imaging to perform a laminar analysis of the principal diffusion orientation, fractional anisotropy, mean diffusivity and partial volume effects. Data from 6 in vivo human subjects, a fixed human brain specimen and an anesthetized macaque were examined. Large regions of cortex show a radial diffusion orientation. In vivo human and macaque data displayed a sharp transition from radial to tangential diffusion orientation at the border between primary motor and somatosensory cortex, and some evidence of tangential diffusion in secondary somatosensory cortex and primary auditory cortex. Ex vivo diffusion imaging in a human tissue sample showed some tangential diffusion orientation in S1 but mostly radial diffusion orientations in both M1 and S1.NeuroImage 12/2012; 81. DOI:10.1016/j.neuroimage.2012.11.065 · 6.36 Impact Factor
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ABSTRACT: Advancement of the magnetic resonance radio frequency (RF) phased array coil technology further can improve the MRI quality. However, the commercial RF phased arrays are not organ-oriented, not able to highlight the located ROI. In this paper, an inverse method is presented for designing RF phased array transmit coil in MRI. First, the ROI was set according to the clinical need, and a target field function was created based on the inverse technology. Next, the current density of the phased array coil was calculated accordingly. The highly ill-posed problem was solved using regularization strategy. Last, the contour charts of the RF phased array coil were obtained by using the stream function technology. In this paper, we designed three kinds of phased array transmit coil with different ROI based on different clinical needs. The magnetic field intensity within the ROI reached higher than 0.957 4 A/m, the magnetic field homogeneity of 10 cm ROI was under 5 x 10-8. The experimental results showed that the RF phased array coil designed using the inverse method met theory demands and was capable of used in MRI.
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