Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Patent
1998-04-09
2000-11-21
Oda, Christine K.
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
324307, G01V 300
Patent
active
061508152
ABSTRACT:
A method of correcting for magnetic field inhomogeneity caused by various factors, such as implanted metal and air/tissue interfaces, in magnetic resonance imaging (MRI) is provided. Geometric distortion due to inhomogeneity in a static magnetic field B.sub.0 is corrected for by addition of a compensation gradient. The compensation gradient is applied in the slice selection direction Z, has a timing substantially identical to the standard frequency encoding gradient G.sub.x, and has an amplitude identical to the slice selection gradient G.sub.z that is applied during the initial RF excitation. Inhomogeneity in an RF field B.sub.1 is compensated for by utilizing an RF coil that is large enough in size as compared with a metal implant to make the volumetric percentage of the metal in the coil insignificant. Inhomogeneity in a gradient field G=(G.sub.x, G.sub.y, G.sub.z) is corrected for by a treatment of the most significant error factor G.sub.z that causes slice thickness error. Specifically, the method acquires two images with complementary slice thickness error by using two pulse sequences with flipped slice selection gradients G.sub.z ; combination of the two images successfully cancels the effect of the slice thickness error. Local dephasive MRI signal loss due to magnetic field inhomogeneity is corrected for by acquisition of two images with positive and negative offset G.sub.z gradient lobes, respectively. The pair of images are combined to cancel the effect of local signal loss error.
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Connell Douglas George
Janzen Dennis Lyle
MacKay Alexander Lloyd
Xiang Qing-San
Fetzner Tiffany A.
Oda Christine K.
The University of British Columbia
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