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4703272 Apparatus and method for decoupling MRI RF coil from selected body portions using passive components
New Patents
IV
applied between the excitation and first refocusing pulses; a second read gradient (92) is applied between the first refocusing pulse and the first spin echo; a third read gradient (94) is applied between the first spin echo and the second refocusing pulse; and a fourth read gradient (96) is applied between the second refocusing pulse and the second spin echo. Because the 90 degrees and 180 degrees pulses are imperfect, parasitic echoes occur at durations 3A + B, 3A + 2B, and 4A + 2B after the 90 degrees excitation pulse. To avoid contamination of the spin echo data by the parasitic echoes, the durations A and B are selected such that the parasitic echoes are each displaced from the spin echoes. To shift the parasitic echoes into times which are non-coincident with the spin echoes, the amplitudes of the read gradients are similarly varied between the spin echoes to shift the parasitic echoes relative to the spin echoes.
4703269 NUCLEAR MAGNETIC RESONANCE IMAGING METHODS AND APPARATUS Ian Young, Sunbury on Thames, United Kingdom assigned to Picker International Ltd A nuclear magnetic resonance imaging method and apparatus using the Hahn spin echo technique wherein dephasing of spins due to selection field gradients (Glx, G2x, G3x) applied during the radio frequency excitation pulses (Bl (90 degrees), B2 (90 degrees), B3 (90 degrees) of the Hahn technique is corrected solely by magnetic field gradients (-G’x, -G2’x) applied before the last radio frequency excitation pulse.
4703270 ZERO QUANTUM NMR IMAGING AND SPECTROSCOPY IN A LOW HOMOGENEITY MAGNETIC FIELD Laurance Hall, Timothy J Norwood, Cambridge, United Kingdom assigned to The University of British Columbia Zero-quantum nuclear magnetic resonance imaging and spectroscopy in an inhomogeneous or low homogeneity magnetic field are disclosed. Specific pulse sequences have been developed which produce zero-quantum coherence resolved images and spectra. Unlike conventional
NMR resolved images and spectra the zeroquantum coherence resolved images and spectra are unaffected by magnetic field inhomogeneity, thereby allowing the images and spectra of substances to be obtained where magnetic field inhomogeneity would previously have made it impossible.
4703271 NMR TOMOGRAPHIC APPARATUS Wilfried Loeffler, Arnulf Oppelt, Herzogenaurach, Federal Republic Of Germany assigned to Siemens Aktiengesellschaft The disclosure relates to an NMR tomographic apparatus wherein an improved local resolution is obtained in a selected segment of the examination region. To this end, in a spin-echo-sequence in conjunction with a 90 degrees-Hf-pulse, a first field gradient is generated in one direction for a spatial selection of a first dimension of the segment which is energized to precession and hence signal emission. In an excitation interval with a 180 degrees-Hf-pulse, a second field gradient is generated in a second direction perpendicular to the first cited direction, for achieving a spatial selection of a second dimension of the segment contributing to the echo signal. The echo signal is read out in the presence of a third field gradient which, in turn, is perpendicular to the first and second field gradients. A three dimensional Fourier-Zeugmatography data set for the representation of a series of layers can be pickedup. In addition, it is possible to represent a noncentral region. Finally, a zoom imaging is provided such that any selected plural layer volume of the initially selected segment of the examination region can be imaged with increased resolution.
4703272 APPARATUS AND METHOD FOR DECOUPLING MRI RF COIL FROM SELECTED BODY PORTIONS USING PASSIVE COMPONENTS Mitsuaki Arakawa assigned to The Regents of the University of California In an MRI system, a passive conductive RF decoupling structure is disposed about a portion of the volume to be imaged but at a location
New Patents
which is proximate a sub-volume from which MRI RF responses are to suppressed. The passive decoupling structure may be a sheet of conductive material or a shorted loop of conductive material (preferably having a gap in conductivity bridged by RF bypass capacitance so as to suppress lower frequency eddy currents otherwise caused by changing magnetic gradient fields in the MRI system).
4703274 ARRANGEMENT OF RF COILS AND RELATED METHOD FOR MAGNETIC RESONANCE IMAGING OF A SELECTED INNER-VOLUME Leon Kaufman, Joseph W Carlson, Mitsuaki Arakawa, Barry M McCarten, John H Fehn assigned to The Regents of the University of California Shaped RF field distributions from separate surface coils overlap to define a limited innervolume deep within a human body or other object under examination. A spin echo MRI signal is effectively elicited only from such limited inner-volume so as to permit conventional MRI signal processing (e.g., utilizing Fourier Transformations) to derive and display magnetic resonance images of desired crosssections of the limited inner-volume thus avoiding possible motion artifact and/or other potential noise sources located elsewhere in the object. A special receiver coil decoupling circuit is used to automatically increase its resonant frequency during RF transmit times.
4703275 METHOD AND APPARATUS TO COMPENSATE FOR EDDY CURRENTS IN MAGNETIC RESONANCE IMAGING
V
ding to the magnetic field the unmodified energization profile would have produced but for the presence of induced eddy currents.
4703276 PERMANENT MAGNET RING ASSEMBLY FOR NMR IMAGING SYSTEM AND METHOD FOR USING SUCH ASSEMBLY Steve Beer assigned to Elscint Ltd An NMR imaging system includes apparatus for producing a uniform magnetic field in a predetermined volume. Such apparatus includes a ring assembly having an axial extent L defined by a plurality of nonmagnetic rings, each having an axis and positioned side-by-side so that the axes of the rings are colinear and define the axis of the ring assembly. A plurality of discrete permanent magnet segments are angularly mounted within each ring for defining a central coaxial aperture. Each segment in a ring has a easy axis of magnetization whose orientation is functionally related to the angular position of the segment in the ring. Each segment has inner and outer edges that are nominally located at distances r 1 and r2, respectively, from the axis of the ring from which it is mounted. The inner free ends of the segments of all of the rings define a central aperture of length L within the ring assembly. Finally, an adjustment is provided for moving the segments in each ring such that the distance rl and r2 of each segment are nonuniformly, but functionally related to the axial extent L of the assembly.
4706023 METHOD OF REDUCING ARTEFACTS IN IMAGES FORMED BY MEANS OF FOURIER ZEUGMATOGRAPHY
G Nei Holland assigned to Picker International Inc
Boef Johannes H Den, Eindhoven, Netherlands assigned to U S Philips Corporation
An electronic module for generating gradient energization signals in magnetic resonance imaging to correct for eddy current effects. An energization profile is modified by an amount related to the magnitude of eddy current fields generated in the vicinity of a gradient coil. This modification produces an energization profile resulting in a gradient magnetic field correspon-
NMR images formed by means of Fourier zeugmatography contain disturbing artefacts which are caused by coherent interference signals (for example, off-set signals, non-ideal 180 degrees reversing pulses). In accordance with the invention, an additional phase difference ( Delta phi = pi in the case of even rows, and Delta phi= pi. (m-1)/m rad/sec in the case of m odd rows) is
IV
applied between the excitation and first refocusing pulses; a second read gradient (92) is applied between the first refocusing pulse and the first spin echo; a third read gradient (94) is applied between the first spin echo and the second refocusing pulse; and a fourth read gradient (96) is applied between the second refocusing pulse and the second spin echo. Because the 90 degrees and 180 degrees pulses are imperfect, parasitic echoes occur at durations 3A + B, 3A + 2B, and 4A + 2B after the 90 degrees excitation pulse. To avoid contamination of the spin echo data by the parasitic echoes, the durations A and B are selected such that the parasitic echoes are each displaced from the spin echoes. To shift the parasitic echoes into times which are non-coincident with the spin echoes, the amplitudes of the read gradients are similarly varied between the spin echoes to shift the parasitic echoes relative to the spin echoes.
4703269 NUCLEAR MAGNETIC RESONANCE IMAGING METHODS AND APPARATUS Ian Young, Sunbury on Thames, United Kingdom assigned to Picker International Ltd A nuclear magnetic resonance imaging method and apparatus using the Hahn spin echo technique wherein dephasing of spins due to selection field gradients (Glx, G2x, G3x) applied during the radio frequency excitation pulses (Bl (90 degrees), B2 (90 degrees), B3 (90 degrees) of the Hahn technique is corrected solely by magnetic field gradients (-G’x, -G2’x) applied before the last radio frequency excitation pulse.
4703270 ZERO QUANTUM NMR IMAGING AND SPECTROSCOPY IN A LOW HOMOGENEITY MAGNETIC FIELD Laurance Hall, Timothy J Norwood, Cambridge, United Kingdom assigned to The University of British Columbia Zero-quantum nuclear magnetic resonance imaging and spectroscopy in an inhomogeneous or low homogeneity magnetic field are disclosed. Specific pulse sequences have been developed which produce zero-quantum coherence resolved images and spectra. Unlike conventional
NMR resolved images and spectra the zeroquantum coherence resolved images and spectra are unaffected by magnetic field inhomogeneity, thereby allowing the images and spectra of substances to be obtained where magnetic field inhomogeneity would previously have made it impossible.
4703271 NMR TOMOGRAPHIC APPARATUS Wilfried Loeffler, Arnulf Oppelt, Herzogenaurach, Federal Republic Of Germany assigned to Siemens Aktiengesellschaft The disclosure relates to an NMR tomographic apparatus wherein an improved local resolution is obtained in a selected segment of the examination region. To this end, in a spin-echo-sequence in conjunction with a 90 degrees-Hf-pulse, a first field gradient is generated in one direction for a spatial selection of a first dimension of the segment which is energized to precession and hence signal emission. In an excitation interval with a 180 degrees-Hf-pulse, a second field gradient is generated in a second direction perpendicular to the first cited direction, for achieving a spatial selection of a second dimension of the segment contributing to the echo signal. The echo signal is read out in the presence of a third field gradient which, in turn, is perpendicular to the first and second field gradients. A three dimensional Fourier-Zeugmatography data set for the representation of a series of layers can be pickedup. In addition, it is possible to represent a noncentral region. Finally, a zoom imaging is provided such that any selected plural layer volume of the initially selected segment of the examination region can be imaged with increased resolution.
4703272 APPARATUS AND METHOD FOR DECOUPLING MRI RF COIL FROM SELECTED BODY PORTIONS USING PASSIVE COMPONENTS Mitsuaki Arakawa assigned to The Regents of the University of California In an MRI system, a passive conductive RF decoupling structure is disposed about a portion of the volume to be imaged but at a location
New Patents
which is proximate a sub-volume from which MRI RF responses are to suppressed. The passive decoupling structure may be a sheet of conductive material or a shorted loop of conductive material (preferably having a gap in conductivity bridged by RF bypass capacitance so as to suppress lower frequency eddy currents otherwise caused by changing magnetic gradient fields in the MRI system).
4703274 ARRANGEMENT OF RF COILS AND RELATED METHOD FOR MAGNETIC RESONANCE IMAGING OF A SELECTED INNER-VOLUME Leon Kaufman, Joseph W Carlson, Mitsuaki Arakawa, Barry M McCarten, John H Fehn assigned to The Regents of the University of California Shaped RF field distributions from separate surface coils overlap to define a limited innervolume deep within a human body or other object under examination. A spin echo MRI signal is effectively elicited only from such limited inner-volume so as to permit conventional MRI signal processing (e.g., utilizing Fourier Transformations) to derive and display magnetic resonance images of desired crosssections of the limited inner-volume thus avoiding possible motion artifact and/or other potential noise sources located elsewhere in the object. A special receiver coil decoupling circuit is used to automatically increase its resonant frequency during RF transmit times.
4703275 METHOD AND APPARATUS TO COMPENSATE FOR EDDY CURRENTS IN MAGNETIC RESONANCE IMAGING
V
ding to the magnetic field the unmodified energization profile would have produced but for the presence of induced eddy currents.
4703276 PERMANENT MAGNET RING ASSEMBLY FOR NMR IMAGING SYSTEM AND METHOD FOR USING SUCH ASSEMBLY Steve Beer assigned to Elscint Ltd An NMR imaging system includes apparatus for producing a uniform magnetic field in a predetermined volume. Such apparatus includes a ring assembly having an axial extent L defined by a plurality of nonmagnetic rings, each having an axis and positioned side-by-side so that the axes of the rings are colinear and define the axis of the ring assembly. A plurality of discrete permanent magnet segments are angularly mounted within each ring for defining a central coaxial aperture. Each segment in a ring has a easy axis of magnetization whose orientation is functionally related to the angular position of the segment in the ring. Each segment has inner and outer edges that are nominally located at distances r 1 and r2, respectively, from the axis of the ring from which it is mounted. The inner free ends of the segments of all of the rings define a central aperture of length L within the ring assembly. Finally, an adjustment is provided for moving the segments in each ring such that the distance rl and r2 of each segment are nonuniformly, but functionally related to the axial extent L of the assembly.
4706023 METHOD OF REDUCING ARTEFACTS IN IMAGES FORMED BY MEANS OF FOURIER ZEUGMATOGRAPHY
G Nei Holland assigned to Picker International Inc
Boef Johannes H Den, Eindhoven, Netherlands assigned to U S Philips Corporation
An electronic module for generating gradient energization signals in magnetic resonance imaging to correct for eddy current effects. An energization profile is modified by an amount related to the magnitude of eddy current fields generated in the vicinity of a gradient coil. This modification produces an energization profile resulting in a gradient magnetic field correspon-
NMR images formed by means of Fourier zeugmatography contain disturbing artefacts which are caused by coherent interference signals (for example, off-set signals, non-ideal 180 degrees reversing pulses). In accordance with the invention, an additional phase difference ( Delta phi = pi in the case of even rows, and Delta phi= pi. (m-1)/m rad/sec in the case of m odd rows) is