87 results about "Transverse magnetization" patented technology

The present invention is directed to a method and system of tissue or background suppression for the acquisition of image data from blood flow or tissue perfusion. Background suppression with minimal effects upon inflowing spins is achieved through a series of spin locking low level RF pulses that cause adiabatic demagnetization of tissue with a relaxation time T1-rho that is intermediate between T1 and T2 relaxation times. In this regard, the effective transverse magnetization of static tissue resulting from the application of a series of low level RF pulses is reduced and, with the spin locking, longitudinal magnetization regrowth is minimized. As such, inflowing spins to an imaging volume may be directly imaged with significant background tissue suppression. The present invention is particularly applicable to time-of-flight MRA and MR perfusion imaging.

To prepare magnetization for steady state magnetic resonance imaging, magnetic resonance is primed using a parameterized priming sequence (60). The parameterized priming sequence (60) has a spectral offset parameter value (40) corresponding to a spectral offset of the steady state imaging. Subsequent to the priming, steady state magnetic resonance imaging data at the first spectral offset is acquired using a magnetic resonance imaging scanner (10). A reconstruction processor (44) reconstructs the imaging data to generate an image representation. Preferably, the parameterized priming sequence (60) includes a longitudinal priming sequence (62) that prepares longitudinal magnetization in a state approximating a steady state longitudinal magnetization. A spoiler sequence (64) spoils transverse magnetization while retaining longitudinal magnetization. A transverse priming sequence (66) prepares traverse magnetization in a state approximating a steady state transverse magnetization.

A method for accelerating data acquisition in MRI with N-dimensional spatial encoding has a first method step in which a transverse magnetization within an imaged object volume is prepared having a non-linear phase distribution. Primary spatial encoding is thereby effected through application of switched magnetic fields. Two or more RF receivers are used to simultaneously record MR signals originating from the imaged object volume, wherein, for each RF receiver, an N-dimensional data matrix is recorded which is undersampled by a factor Ri per selected k-space direction. Data points belonging to a k-space matrix which were not recoded by a selected acquisition schema are reconstructed using a parallel imaging method, wherein reference information concerning receiver coil sensitivities is extracted from a phase-scrambled reconstruction of the undersampled data matrix. The method generates a high-resolution image free of artifacts in a time-efficient manner by improving data sampling efficiency and thereby reducing overall data acquisition time.

A method for determining the spatial distribution of magnetic resonance (MR) signals from an imaging region has a preparatory step in which an encoding scheme with I phase encoding steps is defined, for each phase encoding step according to the phase encoding scheme, an excitation pattern of the transverse magnetization is defined and RF pulses to be irradiated to implement this pattern are calculated, wherein the same phase is defined at all spatial locations of the imaging region within an MSEM region and, in the execution step, according to the spatial encoding scheme each encoding step is performed I times according to the phase encoding scheme, wherein selection of the imaging region, amplitude modulation, and phase encoding are performed with the calculated RF pulses during excitation of the nuclear spin. This results in unique determination of the spatial distribution of the magnetic resonance signals with a simple RF receiver configuration using local gradient systems.

In a method and apparatus for magnetic resonance (MR) imaging, a magnetization of nuclear spins in a subject is prepared in multiple preparation modules of an acquisition sequence. MR signals are acquired with at least one imaging module of the sequence. Spoiler gradient fields are generated in the multiple preparation modules in order to affect a transverse magnetization of the spins. The spoiler gradient fields that are applied in at least two different preparation modules are spatially varied along different directions. Spoiler gradient moments of the spoiler gradient fields are selected so that, for at least one of three orthogonal spatial directions, a weighted sum of the spoiler gradient moments that are applied along this spatial direction satisfies a threshold condition.

A method and apparatus for imparting a transverse magnetization to a wellbore tubular is disclosed. In certain exemplary embodiments, tubulars are magnetized to include at least one flux reversal (e.g., at the center of the tubular) at which the direction of the transverse field changes (i.e., from pointing radially inward to pointing radially outward). A plurality of such magnetized wellbore tubulars may be coupled together and lowered into a target well to form a magnetized section of a casing string. Exemplary embodiments of the invention may be utilized to impart a strong, highly uniform magnetic field about a string of wellbore tubulars, thereby providing for improved passive ranging and wellbore twinning.

In a method and system to generate an excitation in an examination subject to acquire magnetic resonance signals from a region of the examination subject, basic magnetic field is generated, an adiabatic half-passage (AHP) pulse is radiated to generate a transverse magnetization in the subject, and at least one first and one second adiabatic full-passage (AFP) pulse is radiated to generate a slice-selective rephasing of the transverse magnetization. The time interval between the first adiabatic half-passage pulse and the first adiabatic full-passage pulse is at least 37 ms, and the time interval between the first adiabatic full-passage pulse and the second adiabatic full-passage pulse is at least 75 ms.

Versatility and the quality of images are to be improved. As preparation pulses, a first RF pulse to flip along the yz plane spins oriented in a magnetostatic field direction in a subject; a velocity encoding gradient pulse which, in spins flipped by that first RF pulse, mutually shifts the phase of spins in a static state and the phase of spins in a moving state; and a second RF pulse to flip along the yz plane spins whose phase has been shifted by the velocity encoding gradient pulse are successively transmitted. After that, a killer pulse is transmitted to extinguish the transverse magnetizations of the spins flipped by the second RF pulse.

In magnetic resonance imaging using a measurement sequence of the “free precession of transverse magnetization in the steady state”-type i.e., an SSFP measurement sequence, during the SSFP measurement sequence, the implementation of a preparation sequence takes place to reduce a signal contribution of the transverse magnetization in an outer region surrounding a measurement region in the MR imaging. The implementation of the preparation sequence includes the radiation of a multidimensional, spatially selective RF pulse that acts in a spatially selective manner on the transverse magnetization in the outer region. Saturation of the transverse magnetization and / or dephasing of the transverse magnetization in the outer region can be achieved by the multidimensional, spatially selective RF pulse.

A method and apparatus for imparting a transverse magnetization to a wellbore tubular is disclosed. In certain exemplary embodiments, tubulars are magnetized to include at least one flux reversal (e.g., at the center of the tubular) at which the direction of the transverse field changes (i.e., from pointing radially inward to pointing radially outward). A plurality of such magnetized wellbore tubulars may be coupled together and lowered into a target well to form a magnetized section of a casing string. Exemplary embodiments of the invention may be utilized to impart a strong, highly uniform magnetic field about a string of wellbore tubulars, thereby providing for improved passive ranging and wellbore twinning.

A magnetic resonance imaging apparatus that carries out a pulse sequence for making a signal of a first substance within an object smaller than a signal of a second substance within the object. The pulse sequence includes an α°-pulse for exciting the object, a refocus pulse for refocusing a phase of spin within a region excited by the α°-pulse, and a readout gradient field for acquiring a magnetic resonance signal from the region. The α°-pulse has a spectral selectivity such that a transverse magnetization of the first substance is made smaller than a transverse magnetization of the second substance. The refocus pulse has a spectral selectivity such that a phase of spin of the second substance is refocused and refocusing of a phase of spin of the first substance is suppressed.

A method for determining amplitude and phase dependencies of radio frequency pulses that are irradiated during traversal of a defined k-space trajectory to produce a spatial pattern of the transverse magnetization in an MR experiment using at least one RF transmission antenna, is characterized in that, in a calibration step, a set of basic pulses is defined, each basic pulse is irradiated individually, the specified k-space trajectory is traversed and at least one set of basic patterns is produced by detection of the MR signals thus excited, which in a range to be examined of the object, are proportional to the complex transverse magnetization produced, wherein the k-space trajectory is traversed fully identically every time at least from the beginning of the irradiation of each basic pulse, and, in a calculation step, a defined target pattern is approximated with a linear combination of the basic patterns of a set or with a mathematical association of linear combinations, with which, within each set, the basic patterns are identically combined, and the amplitude and phase dependencies to be determined are obtained as the corresponding linear combination of the basic pulses. Experimental imperfections can be intrinsically compensated for in this way.

In a sequence of emitting a plurality of refocus RF pulses after one excitation RF pulse, in order to suppress a cusp artifact at a known magnetic field distortion generation position regardless of an imaging condition, such as a slice thickness or an FOV, between an excitation RF pulse and an initial refocus RF pulse, by generating a phase shift to transverse magnetization at the position, and by applying an extremely small dephase gradient magnetic field in the phase encoding direction and / or in the slice encoding direction, a signal value of an NMR signal (echo signal) is suppressed at the position, and the cusp artifact is deteriorated.

A method for obtaining amplitude and phase dependencies of radio frequency pulses, which are irradiated within the scope of a main magnetic resonance experiment for generating a predetermined n-dimensional spatial distribution (n>=1) of transverse magnetization in an object by means of at least one radio frequency transmitting antenna of a magnetic resonance measuring system in combination with spatially and temporally varying additional magnetic fields which are superimposed on the static and homogeneous base field of the magnetic resonance measuring system and change the transverse magnetization phase in the object in dependence on location and time is characterized in that, prior to performance of the main experiment, a preparational measurement is performed in which the change with time of the transverse magnetization phase in the object under the action of the additional magnetic fields is measured in a position-resolved fashion and the amplitude and phase dependencies of the radio frequency pulses for the main experiment are calculated on the basis of this change with time of the transverse magnetization phase, which is measured in a position-resolved fashion. In this fashion, experimental imperfections in the form of unintentional additional magnetic fields can be measured, taken into consideration and compensated for.