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Coil Used (coil + used)

Distribution by Scientific Domains

Medical Sciences	75%

Selected Abstracts

SAR and power implications of different RF shimming strategies in the pelvis for 7T MRI

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2009
Bob van den Bergen MSc
Abstract Purpose To determine the best radiofrequency (RF) shimming method for 7 T body imaging that provides sufficient B1+ excitation inside the target region while energy deposition (SAR) and power demands are as low as possible and that does not incorporate anatomy specific electric field information inside the patient models, as this information is not available in practice. Materials and Methods Finite difference time domain (FDTD) simulations were used to evaluate five RF shimming strategies for the pelvis inside a body coil. The results were compared to the theoretical best solution that could be achieved if the electric field inside the patient was known. Results Most of the RF shimming strategies were successful. However, between the different strategies a factor of two difference in average SAR reduction, a factor of three difference in local maximum SAR reduction, and a factor of 20 difference in power efficiency was observed. Phase matching was found to be the most promising RF shimming method for the body coil used and patient models. Conclusion RF shimming can reduce the SAR and improve power efficiency in an accurate patient model without knowing the electric field. However, choosing the right method is critical to prevent unexpected behavior in local SAR deposition. J. Magn. Reson. Imaging 2009;30:194,202. © 2009 Wiley-Liss, Inc. [source]

Metabolic changes detected by proton magnetic resonance spectroscopy in vivo and in vitro in a murin model of Parkinson's disease, the MPTP-intoxicated mouse

JOURNAL OF NEUROCHEMISTRY, Issue 3 2008
Carine Chassain
Abstract Parkinson's disease is a neurodegenerative disorder characterized by the progressive loss of the dopaminergic neurons in the substantia nigra pars compacta, which project to the striatum. The aim of this study was to analyze in vivo and in vitro consequences of dopamine depletion on amount of metabolites in a mouse model of Parkinson's disease using proton 1H magnetic resonance spectroscopy (MRS). The study was performed on control mice (n = 7) and MPTP-intoxicated mice (n = 7). All the experiments were performed at 9.4 T. For in vivo MRS acquisitions, mice were anesthetized and carefully placed on an animal handling system with the head centered in birdcage coil used for both excitation and signal reception. Spectra were acquired in a voxel (8 ,L) centered in the striatum, applying a point-resolved spectroscopy sequence (TR = 4000 ms, TE = 8.8 ms). After in vivo MRS acquisitions, mice were killed; successful lesion verified by tyrosine hydroxylase immunolabeling on the substantia nigra pars compacta and in vitro MRS acquisitions performed on perchloric extracts of anterior part of mice brains. In vitro spectra were acquired using a standard one-pulse experiment. The absolute concentrations of metabolites were determined using jmrui (Lyon, France) from 1H spectra obtained in vivo on striatum and in vitro on perchloric extracts. Glutamate (Glu), glutamine (Gln), and GABA concentrations obtained in vivo were significantly increased in striatum of MPTP-lesioned mice (Glu: 15.5 ± 2.5 vs. 12.9 ± 1.0 mmol/L, p < 0.05; Gln: 2.3 ± 0.9 vs. 1.8 ± 0.6 mmol/L, p < 0.05; GABA: 2.3 ± 0.9 vs. 1.3 ± 0.6 mmol/L, p < 0.05). The in vitro results confirmed these results, Glu (10.9 ± 2.5 vs. 7.9 ± 1.7 ,mol/g, p < 0.05), Gln (6.8 ± 2.9 vs. 4.3 ± 1.0 ,mol/g, p < 0.05), and GABA (2.9 ± 0.9 vs. 1.5 ± 0.4 ,mol/g, p < 0.01). The present study strongly supports a hyperactivity of the glutamatergic cortico-striatal pathway hypothesis after dopaminergic denervation in association with an increase of striatal GABA levels. It further shows an increased of striatal Gln concentrations, perhaps as a strategy to protect neurons from Glu excitotoxic injury after striatal dopamine depletion. [source]

Effects of coil characteristics for femoral nerve magnetic stimulation

MUSCLE AND NERVE, Issue 3 2010
Katja Tomazin PhD
Abstract The aim of this study was to compare the efficiency of two coils used for femoral nerve magnetic stimulation and to compare them with electrical stimulation in inducing maximal response of the quadriceps. The mechanical and electromyographic (EMG) responses were dependent on the coil used. The 45-mm double coil showed greater efficiency to elicit a maximal quadriceps response, which was similar to electrical stimulation. Muscle Nerve, 2010 [source]