72 results about "K space trajectory" patented technology

In a first step of image formation by MRI or the like, a gridding convolution is performed for each coil using a Kaiser-Bessel kernel, so that each coil channel now contains data on grid points. In the second step, another 2D convolution is performed on each of the gridded coil data sets in either k-space or image space, and all the convolutions are summed up to produce the composite k-space data set for the target coil. In the third step, the composite data set is then transformed to form an un-aliased image for that coil. In the fourth step, the un-aliased images for all the coils are combined using square-root-of-sum-of-squares to form the final reconstructed image.

First, benchmark data are collected on two thin slices of an object to get measured k-space trajectories. To find delays on different physical gradients, the root mean square error between estimated and measured k-space trajectories is minimized for different delays. To reduce the error further, an eddy current compensation is introduced along each physical gradient axis. A more accurate estimation of the k-space trajectory can be obtained to image the object.

A system and method are provided for designing RF pulses for multi-channel and/or multi-dimensional spatially-selective applications using a linear approximation. Embodiments of the system and method may use a generalized linear-class large tip angle approximation to design RF pulses for multi-channel and parallel transmission. Further, some of these approximations allow for the design of arbitrarily large flip angles, irregularly-shaped flip angle profiles, or arbitrary initial magnetization values. Embodiments of the system and method may also provide for the design of k-space trajectories which aid in maintaining assumptions of the various linear class approximations.

A method for reconstructing a sequence of magnetic resonance (MR) images of an object under investigation, includes the steps of (a) providing a series of sets of image raw data including an image content of the MR images to be reconstructed, the image raw data being collected with the use of at least one radiofrequency receiver coil of a magnetic resonance imaging (MRI) device, wherein each set of image raw data includes a plurality of data samples being generated with a gradient-echo sequence, in particular a FLASH sequence, that spatially encodes an MRI signal received with the at least one radiofrequency receiver coil using a non-Cartesian k-space trajectory, each set of image raw data includes a set of homogeneously distributed lines in k-space with equivalent spatial frequency content, the lines of each set of image raw data cross the center of k-space and cover a continuous range of spatial frequencies, and the positions of the lines of each set of image raw data differ in successive sets of image raw data, and (b) subjecting the sets of image raw data to a regularized nonlinear inverse reconstruction process to provide the sequence of MR images, wherein each of the MR images is created by a simultaneous estimation of a sensitivity of the at least one receiver coil and the image content and in dependency on a difference between a current estimation of the sensitivity of the at least one receiver coil and the image content and a preceding estimation of the sensitivity of the at least one receiver coil and the image content.

In a method and apparatus for calculating the sampling path of the k-matrix under given boundary conditions for the examination of a subject by means of a magnetic resonance tomography apparatus having a gradient amplifier with appertaining gradient coils, an input-display terminal, a sequence controller and a system computer as well as an analog-to-digital converter, boundary conditions are entered into the sequence controller or into the system computer via the input-display terminal, the sampling path of the k-matrix is calculated taking the boundary conditions into consideration by the sequence controller or the system computer, and the gradient current curves are determined by the sequence controller or the system computer that lead to a sampling along the previously calculated sampling path when applied to the corresponding gradient coils with utilization of the ADC.

When generating an MR image using a multi-channel transmit coil arrangement, SAR is reduced by employing a number of different RF pulses in a single scan. Each RF pulse exhibits a different performance and/or accuracy, resulting in different RF pulse-specific SAR values. As a result, the RF pulses differ slightly in actual excitation pattern, B1 waveform and/or k-space trajectory, etc. The average SAR over a single scan is thus reduced compared to a fixed RF pulse, without compromising image quality.

An imaging method comprises acquiring an undersampled magnetic resonance partially parallel imaging (MR-PPI) dataset using a plurality of radio frequency receive coils and reconstructing the under-sampled MR-PPI dataset to generate a reconstructed magnetic resonance (MR) image. The reconstructing includes: (i) using a generalized auto-calibrating partially parallel acquisition (GRAPPA) operator or direct convolution to fill in at least some missing data of the undersampled MR-PPI data-set so as to generate an enhanced dataset; and (ii) using an algorithm other than a GRAPPA operator and other than direct convolution to reconstruct the enhanced dataset or to reconstruct the undersampled MR-PPI dataset using the enhanced dataset as an initialization dataset for an iterative reconstruction algorithm. In some embodiments the MR-PPI dataset is a non-Cartesian dataset and a GRAPPA operator for wider radial bands (GROWL) is used in the operation (i).

In method and a control sequence determination device to determine a magnetic resonance system control sequence that includes at least one radio-frequency pulse train to be emitted by a magnetic resonance system, a target magnetization (m) is initially detected, and an energy distribution function in k-space is determined on the basis of the target magnetization. A k-space trajectory is then determined under consideration of the energy distribution function in k-space, for which the radio-frequency pulse train is then determined in an RF pulse optimization method. The method is suitable for operation of a magnetic resonance system, and a magnetic resonance system includes such a control sequence determination device.

A method for reconstructing a sequence of magnetic resonance (MR) images of an object under investigation, comprises the steps of (a) providing a series of sets of image raw data including an image content of the MR images to be reconstructed, said image raw data being collected with the use of at least one radiofrequency receiver coil of a magnetic resonance imaging (MRI) device, wherein each set of image raw data includes a plurality of data sampies being generated with a gradient-echo sequence, in particular a FLASH sequence, that spatially encodes an MRl signal received with the at least one radiofrequency receiver coil using a non-Cartesian k-space trajectory, each set of image raw data comprises a set of homogeneously distributed lines in k-space with equivalent spatial frequency content,; the lines of each set of image raw data cross the center of k-space and cover a continuous range of spatial frequencies, and the positions of the lines of each set of image raw data differ in successive sets of image raw data, and (b) subjecting the sets of image raw data to a regularized nonlinear inverse reconstruction process to provide the sequence of MR images, wherein each of the MR images is created by a simultaneous estimation of a sensitivity of the at least one receiver coil and the image content and in dependency on a difference between a current estimation of the sensitivity of the at least one receiver coil and the image content and a preceding estimation of the sensitivity of the at least one receiver coil and the image content.

Aspects of the subject disclosure may include, for example, a system that applies magnetic resonance elastography to a sample to obtain uncorrected k-space data where the magnetic resonance elastography utilizes a multi-shot spin-echo sequence with variable density spiral readout gradients, and adjusts the uncorrected k-space data to corrected k-space data by adjusting a k-space trajectory by shifting a center point for each shot to a new center point according to signal intensity and by adjusting a phase for each shot based on a phase offset that is determined according to the signal intensity. Other embodiments are disclosed.

A magnetic resonance control sequence with a pulse arrangement that acts selectively in at least two spatial directions in order to excite a limited rotationally symmetrical excitation profile within an examination subject has an RF excitation pulse formed as a sequence of multiple partial RF pulses, and gradient pulses in the two spatial directions that are coordinated with the partial RF pulses so that the RF energy introduction of different partial RF pulses in transmission k-space occurs on circular k-space transmission trajectories that are concentric to one another. The amplitude of the RF envelope of the partial RF pulses is constant during the duration of a traversal of each circular k-space trajectory. The control sequence can also be used in a calibration of a magnetic resonance system.

A method and a control sequence determination device for the determination of a magnetic resonance system activation sequence including at least one high-frequency pulse sequence to be transmitted by a magnetic resonance system are provided. A current B₀ map and optionally a target magnetization are acquired. In addition, a k-space trajectory type is determined. An error density is calculated in a k-space based on the current B₀ map and optionally based on the target magnetization using an analytic function. This analytic function defines an error density in the k-space as a function of the current B₀ map and optionally the target magnetization. Taking account of the error density in the k-space, a k-space trajectory of the specified k-space trajectory type is determined. The high-frequency pulse sequence is determined for the k-space trajectory in an HF pulse optimization process.

Pulsatile flow is measured using magnetic resonance imaging without cardiac gating using a phase-contrast excitation method to rapidly quantify blood flow and using a spiral k-space trajectory for image data read-out to mitigate deleterious effects of pulsatility. Post-processing of the read-out data provides a cumulative-average velocity plot from which a period of a cardiac cycle is obtained. Time-averaged blood flow rates can be rapidly and robustly measured and is more repeatable than conventional gated techniques.

Measurements of functional, hemographic, and blood flow parameters use a multiple echo or spin echo gradient pulse sequence whereby an early echo is acquired near the beginning of the pulse sequence which avoids saturation effects and a later echo near the end of the pulse sequence which can provide information with more sensitivity to a contrast agent for a susceptibility weighted image.

A method for determining the spatial distribution of magnetic resonance signals from an imaging area, wherein nuclear spins are excited in a spatially encoded fashion through multi-dimensional RF pulses, is characterized in that in a definition step, a resolution grid with resolution grid cells is predetermined, and in accordance with a predetermined phase encoding scheme, an excitation pattern is defined for each phase encoding step, in which the amplitudes within the imaging area are set in accordance with a predetermined distribution identically for each phase encoding step. In a preparatory step, the amplitude and phase behavior of the RF pulses to be irradiated is calculated in accordance with a predetermined k-space trajectory for each defined complex excitation pattern.

In a method and a pulse sequence determination device to determine a pulse sequence for a magnetic resonance system, control protocol parameter values are initially acquired. A determination of k-space trajectory node points within k-space then takes place in a processor on the basis of the control protocol parameter values. The determination of the pulse sequence then takes place on the basis of the k-space trajectory node points. A method for operating a magnetic resonance system uses such a pulse sequence, and a magnetic resonance system embodies such a pulse sequence determination device.

The invention provides an excitation pulse sequence generator for a magnetic resonance system. An excitation pulse sequence generated by the excitation pulse sequence generator is applied to the magnetic resonance system, so that optimized three-dimensional space selective excitation based on a parallel excitation technology can be realized. By using the excitation pulse sequence generator, an appropriate excitation K space track can be determined in an optimized way according to an excitation target and the space sensitivity situation of a plurality of transmitting channels of a radiofrequency coil, so that a gradient pulse waveform and a radiofrequency pulse envelope waveform corresponding to each transmitting channel are determined. A gradient driving unit and a radiofrequency driving unit of the magnetic resonance system are used for generating gradient pulses and radiofrequency pulses accordingly and driving a gradient coil and the radiofrequency coil to apply the gradient pulsesand the radiofrequency pulses to a scanning space, so that the aim of selectively exciting in a desired three-dimensional space is fulfilled.

Magnetic resonance (MR) data are acquired by applying magnetic fields to an examination region concurrent with stimulated echo signals, such that trajectories, which are not straight lines, are generated in k-space. For this purpose, sequence of RF pulses is applied to generate the stimulated echo signals in the examination object, undersampled MR measurement data are detected during reception of the stimulated echo signals in the at least two receiving coils, along the curved k-space trajectories, and fully sampled MR measurement are generated from the undersampled MR measurement data using sensitivity information of the at least two receiving coils. Alternatively, the MR measurement data are fully sampled in a central region of k-space, and a region outside the central region is not fully sampled, and a phase correction with a Partial Fourier technique is executed on the MR measurement data using fully sampled MR measurement data from the central region of k-space.

Systems and method for magnetic resonance imaging are disclosed which utilize sinusoidal gradient waveforms to drive gradient coils in an MRI system. The sinusoidal gradient waveforms may be applied on all two or more (e.g. three) gradient axes to produce a relatively pure acoustic tone. In certain embodiments, gradient directions may be spiraled in three-dimensions to generate a radial pin-cushion k-space trajectory

A modified projection on convex sets (POCS) algorithm and method for partial k-space reconstruction using low resolution phase maps for scaling full sets of reconstructed k-space data. The algorithm can be used with partial k-space trajectories in which the trajectories share a common point such as the origin of k-space, including variable-density spiral trajectories, projection reconstruction trajectories with a semicircle region acquisition, and projection reconstruction trajectories with every other spike acquired.