Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine
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The feasibility of functional MRI of the spinal cord was investigated by carrying out blood oxygen-level dependent (BOLD) imaging of the human cervical spinal cord at a field of 3 T. BOLD imaging of the cervical spinal cord showed an average intensity increase of 7.0% during repeated exercise with the dominant hand with a return to baseline during rest periods. ⋯ The direct correspondence between these areas and those involved with the transmission of motor impulses to the hand, and reception of sensory information from the hand, demonstrates that spinal functional magnetic resonance imaging is feasible. Magn Reson Med 42:571-576, 1999.
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Keyhole acquisition techniques have been used to reduce image acquisition times primarily in contrast agent studies and via simulation in interventional MRI procedures. More recent simulations have suggested that improved definition of an interventional device [e.g., biopsy needles, radio frequency (RF) electrodes] could be achieved by rotating the keyhole pattern in k-space so that the read out direction lies perpendicular to the device orientation in real space. This study seeks to validate the earlier predictions of improved efficacy of a rotated stripes keyhole acquisition in actual in vitro and in vivo interventional MR imaging procedures. ⋯ Apparent needle width was thinner and tip position more accurately determined for placement of phase encoding parallel to the needle in all cases. Rotated keyhole imaging provides the required temporal advantage of conventional keyhole imaging along with a near optimal definition of an interventional device when the phase encoding is oriented parallel to the direction of the needle motion. Magn Reson Med 42:554-560, 1999.
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Electrocardiograph (ECG) triggered or gated magnetic resonance methods are used in many imaging applications. Therefore, a reliable trigger signal derived from to the R-wave of the ECG is essential, especially in cardiac imaging. However, currently available methods often fail mainly due to the artifacts in the ECG generated by the MR scanner itself, such as the magnetohydrodynamic effect and gradient switching noise. ⋯ The "target-distance" R-wave detection algorithm yielded a score of 100% for detection with 0.2% false positives and was superior to all the other selected methods. Thus, the VCG of subjects exposed to a strong magnetic field can be use to separate the magnetohydrodynamic artifact and the actual R-wave, and markedly improves the trigger accuracy in gated magnetic resonance scans. Magn Reson Med 42:361-370, 1999.
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Steady-state arterial spin tagging approaches were used to construct multislice images of relative cerebral blood flow changes during finger-tapping tasks. Statistically significant increases in cerebral blood flow were observed in primary sensorimotor cortex in all seven subjects. ⋯ Magn Reson Med 42:404-407, 1999. Published 1999 Wiley-Liss, Inc.
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Successful radiofrequency (RF) thermal ablation was performed on VX2 tumors implanted in 23 rabbit livers under magnetic resonance (MR) guidance using a C-arm-shaped low-field 0.2 T system. RF application and immediate postprocedure MRI of all animals was performed [T2-weighted, turbo short tau inversion recovery (STIR), T1-weighted before and after gadopentetate dimeglumine administration). Follow-up MRI with a superparamagnetic iron oxide (SPIO) contrast medium was performed in nine rabbits at 2 weeks and in four rabbits at 1 month post RF ablation. ⋯ T2-weighted imaging never overestimated pathologic lesion size by more than 2 mm, and the radiologic-pathologic correlation coefficient was not less than 0.90. In conclusion, MRI-guided RF thermal ablation in implanted liver tumor is feasible using a C-arm-shaped low-field 0.2 T system. The thermal lesion size can be most accurately monitored with T2-weighted and turbo-STIR images.