87 results about "Transverse magnetization" patented technology

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 R_i 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 to compensate for the magnetic field heterogeneity inside an object of investigation in a MR device obtains an uncorrected magnetic field distribution of the object and executes an MR sequence with a desired k-space coverage by applying RF pulses to generate a transverse magnetization within the object. MR signal data is recorded, magnetic field shimming parameters are dynamically updated and MR signal data are reconstructed to produce images or localized spectroscopic data. Artifacts in a reconstructed image resulting from an uncorrected magnetic field distribution are suppressed by temporally separating MR signals originating from at least two different sub-volumes within a volume of transverse magnetization by generating a nonlinear phase distribution within the object and by dynamically updating shimming parameters to compensate for the field inhomogeneity distributions within the different sub-volumes in the volume of transverse magnetization.

A method that exploits the intrinsic selectivity of steady-state free precession (SSFP) to perform spectral suppression is disclosed. Such a method avoids the need to incorporate additional spectrally selective pulse sequence elements. The scheme is based on breaking the FISP imaging sequence into short trains having, for example, 8–64 RF pulses. At the moment of echo formation (i.e., TE=TR/2) after the last full RF pulse of the train, water signal is z-stored. Residual transverse magnetization, which include isochromats phase-opposed to the on-resonance water, is gradient crushed and RF spoiled. The stored magnetization is subsequently re-excited with little disturbance to the on-resonance steady-state water signal. The additional time required to perform the steady-state interruption is typically as little as a single TR, minimally affecting the efficiency of the imaging process. The sequence can be employed repetitively, greatly reducing the amplitude of fat signals throughout a real-time or cine imaging process.

A system and method of free-breathing MR imaging saturates an entire navigator profile at the end of an imaging segment of physiological motion cycle, e.g., heart cycle, thereby providing a uniform recovery of longitudinal magnetization for the next imaging cycle. Through use of at least one dephaser gradient following the image acquisition segment and a navigator RF saturation pulse, residual transverse magnetization is dephased and spins within a navigator tracker are saturated to ensure a uniform recovery of longitudinal magnetization for the next imaging period.

An MRI apparatus obtains an ASL (Arterial Spin Labeling) image of a region to be imaged in a subject by performing a scan to the region to be imaged independently in a control mode and in a tag mode according to a pulse sequence based on an ASL technique. The pulse sequence includes a velocity-selective pulse, BVS (Band-limited Velocity-Selective)-pulse, that selectively excites magnetization spins in a blood flow passing through the region to be imaged and having a constant velocity range for the spins to undergo transition to transverse magnetization, and then performs excitation to cause the transverse magnetization to flip back to longitudinal magnetization. The velocity-selective pulse is formed in such a manner that the transverse magnetization excited in each of the control mode and the tag mode gives rise to a phase shift in an opposite polarity upon velocity-selective excitation.

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.

In a magnetic resonance imaging apparatus and a method for generating magnetic resonance image data of a field of view of an examination object, magnetic resonance raw data are acquired by preferably different transverse magnetizations being excited in at least one sub-volume of a navigator volume and at least one sub-volume of an image volume, and are used for position determination and for imaging. These preferably different transverse magnetizations are simultaneously present in at least one period of the scan.

A method of magnetic resonance, in which a sample introduced in a measurement volume in an external magnetic field is excited by an excitation pulse and the signal formed by the transverse magnetization thus produced is read out by a receiving coil. The method is characterized in that a prewinding pulse is used as the excitation pulse, which prewinding pulse is characterized in that the formed transverse magnetization M_⊥(ω) of spins of different Larmor frequency ω after the pulse has a phase φ₀(ω), wherein φ₀(ω) as a function of ω within a predefined frequency range Δω has an approximately linear course having negative slope, such that the spins refocus after an echo time defined by the pulse without an additional refocusing pulse being necessary.

In a method for designing a selective RF pulse for a magnetic resonance apparatus, based on a determination of a first polynomial (A_n(z)) and a second polynomial (B_n(z)) that are Shinnar-LeRoux transforms of the RF pulse, a flip angle distribution (α(x)) to be achieved with the RF pulse is prescribed, the first polynomial (A_n(z)) is determined proceeding from the flip angle distribution (α(x)), the phase distribution of the transverse magnetization to be achieved with the RF pulse is prescribed, and the second polynomial (B_n(z)) is determined such that the magnitude is determined by the flip angle distribution (α(x)) and the phase thereof corresponds to a sum of the prescribed phase distribution and the phase of the, first polynomial (A_n(z)).

A magnetic resonance imaging system or method is provided including a balanced steady-state free-precession transient imaging (transient bSSFP) device capable of increasing the overall signal during transient bSSFP acquisition by fully or better utilization of the magnetization through variable RF flip angles. The transient bSSFP device is capable of generating a series of echoes with a desired transverse magnetization profile M_T. It is further capable of generating RF pulses each having a distinct RF flip angle for each of the echoes in the series of echoes. The transient bSSFP device is coupled to a computer capable of calculating the distinct RF flip angle for the nth echo in the series of echoes. The computer calculation utilizes a program encoding an analytical inversion of the Bloch equation. Once the RF flip angle is calculated, it is used by the transient bSSFP device in the generation of the nth echo.

A method and magnetic resonance system for imaging a particle that is located in an examination subject with an imaging magnetic resonance measurement execute a gradient echo sequence in which at least two gradient echoes are acquired following a single excitation pulse, wherein the particle in an applied basic magnetic field causes a magnetic interference field. An RF pulse is radiated to generate a transverse magnetization from a magnetization appearing in the basic magnetic field. A first dephasing gradient is shifted to adjust a first dephasing of the transverse magnetization, and the first gradient echo is acquired. A second dephasing gradient is shifted to adjust a second dephasing of the transverse magnetization that is different than the first dephasing, and the second gradient echo is acquired. The two dephasing gradients are shifted such that a dephasing of the transverse magnetization caused by the interference field of the particle is at least partially compensated in a region around the particle or within the particle given the acquisition of at least one of the echoes.

A magnetic resonance imaging apparatus includes a gradient coil for applying a gradient pulse, a transmitting coil for transmitting an RF pulse, and a coil control device for controlling the gradient coil and the transmitting coil in such a manner that a pulse sequence for (A) making an absolute value of longitudinal magnetization of a first background tissue and an absolute value of longitudinal magnetization of a second background tissue longer in T1 value than the first background tissue smaller than an absolute value of longitudinal magnetization of body fluid of a subject, (B) acquiring magnetic resonance signals from the subject, and (C) flipping transverse magnetization of the second background tissue to longitudinal magnetization is repeatedly executed.

A method for determining the spatial distribution of magnetic resonance signals from at least one of N subvolumes predefines a reception encoding scheme and determines unique spatial encoding for at least one of the subvolumes but not for the entire volume under examination (UV). A transmission encoding scheme is also defined, wherein encoding is effected via the amplitude and/or phase of the transverse magnetization. The temporal amplitude and phase profile of the RF pulses is then calculated and each reception encoding step is carried out I times with variations according to the I transmission encoding steps in the transmission encoding scheme. The method makes it possible to largely restrict the spatially resolving MR signal encoding and image reconstruction to subvolumes of the object under examination without the achievable image quality sensitively depending on imperfections in the MR apparatus.

In a magnetic resonance method and apparatus for imaging a particle that is located in an examination subject, a pulse sequence is emitted that includes an excitation pulse that generates a transverse magnetization of the examination subject from a magnetization appearing in a basic magnetic field, so the particle causes a magnetic interference field in the applied basic magnetic field in a magnetic resonance measurement. After the excitation pulse, at least one spectrally selective refocusing pulse is generated in a non-resonant frequency range at the generation of a spin echo.

A method of obtaining an arbitrary, admissible transverse magnetization profile as the summed response of two, self refocused selective “half pulse” excitations for use in, e.g., magnetic resonance imaging pulse generation. The problem of finding the pair of half pulses is rephrased in the inverse scattering formalism and a simple closed form algorithm for the solution is given, provided the target transverse profile has constant phase (modulo 180°). The problem has a unique low energy solution for sufficiently small, complex valued data, and an algorithm for finding the solution is provided. This solution is used to generate pairs of half pulses for given target transverse profiles.

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.