Leland Stanford Junior University

General Electric Company

Dwight G Nishimura

John Mark Pauly

Shreyas S Vasanawala

Tolga Cukur

Craig H Meyer

Jin Hyung Lee

Steven M Conolly

David Y Zeng

Albert Macovski

Brian A Hargreaves

Philip James Beatty

Jean Helen Brittain

Joseph Yitan Cheng

Anja C S Brau

Sanjay Mani

Neal K Bangerter

Brain A Hargreaves

Todd S Sachs

Gerard T Luk Pat

Jin Hung Lee

Brad Osgood

Julie Camille DiCarlo

A method for magnetic resonance imaging corrects non-stationary off-resonance image artifacts. A magnetic resonance imaging (MRI) apparatus performs an imaging acquisition using non-Cartesian trajectories and processes the imaging acquisitions to produce a final image. The processing includes reconstructing a complex-valued image and using a convolutional neural network (CNN) to correct for non-stationary off-resonance artifacts in the image. The CNN is preferably a residual network with multiple residual layers.

Deep learning method for nonstationary image artifact correction

A magnetic resonance imaging (MRI) techniques uses a T2-preparation outer volume suppression (OVS) pulse sequence to reduce the longitudinal magnetization outside a region of interest. A region is excited that includes the region of interest, radiofrequency (RF) signals are detected, and MRI images generated from the RF detected signals. The T2-preparation OVS pulse sequence includes, sequentially: a first tip-down excitation pulse, a first refocusing excitation pulse, a first tip-up excitation pulse that is selective spatially and/or spectrally, a second tip-down excitation pulse that is 180&#xb0; out of phase with respect to the first tip-down excitation pulse, a second refocusing excitation pulse, and a second tip-up excitation pulse that is selective spatially and/or spectrally. Alternatively, the first tip-down excitation pulse is selective spatially and/or spectrally instead of the first tip-up excitation pulse, and the second tip-down excitation pulse is selective spatially and/or spectrally instead of the second tip-up excitation pulse.

MRI RF pulse sequence for multidimensional outer volume suppression

A method of providing selective spectral suppression in balanced SSFP magnetic resonance imaging for a first and second species is provided. A plurality of balanced SSFP images are acquired. Each acquisition includes applying RF excitations in a sequence of TR intervals with each being applied in an associated TR interval. The sequence of TR intervals includes at least one data acquisition TR interval and at least two secondary TR intervals each having a duration that is shorter than the data acquisition TR interval. A first secondary TR interval precedes the data acquisition TR interval and a second secondary TR interval follows the data acquisition TR interval. The duration of the second secondary TR interval is substantially equal to the first secondary TR interval such that the sequence of TR intervals is substantially symmetric with respect to duration about a center point of the sequence of TR intervals.

Multiple repetition time steady-state free precession imaging

An RF coil assembly includes a plurality of RF source coils and an RF target coil separate from the plurality of RF source coils. A computer is programmed to acquire MR data of an imaging object from each of the plurality of RF source coils and to acquire MR data of the imaging object from the RF target coil. The computer is further programmed to calculate a set of weights based on a relationship between MR data acquired from each RF source coil and MR data acquired from the RF target coil and to reconstruct an image based on an application of the set of weights to at least a portion of the MR data acquired from each of the plurality of RF source coils.

System and method of parallel imaging with calibration to a separate coil

A method of collecting image data with selective spectral suppression for at least two species is provided. A sequence of RF excitation pulses is repeatedly applied, whereby a repeated sequence of at least two substantially different spectrally selective steady-state magnetizations is established. Magnetic gradients are applied between said RF pulses. A plurality of magnetic resonance image (MRI) signals is acquired. The plurality of MRI signals is combined using a weighted combination where the weights depend on a control parameter that adjusts a trade-off between selective spectral suppression and signal-to-noise ratio (SNR).

Enhanced spectral selectivity for steady-state free precession imaging

A method of reducing artifacts in steady-state free precession (SSFP) signals for use in magnetic resonance imaging is provided. A plurality of SSFP imaging sequences is applied to an object. An imaging data for each of the SSFP imaging sequences is acquired. The imaging data is combined using a weighted combination where weights depend on a control parameter that adjusts a trade-off between banding artifact reduction and signal to noise ratio (SNR).

Artifact reduction in steady-state free precession imaging

An optimal sampling pattern for variable density sampling of a continuous signal uses a statistical knowledge of the signal to determine an autocorrelation matrix from which a basis set is identified. Sampling is performed at locations determined from an eigenvector matrix, and the sampled output provides coefficients for the basis set. The reconstructed signal output is a summation of the multiplication of the coefficients and the basis set.

Variable density signal sampling

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.

Partial k-space reconstruction for radial k-space trajectories in magnetic resonance imaging

Artifact reduction in steady state free precession magnetic resonance imaging uses weighting of acquired image data to emphasize higher signals and then establishing an image signal based on the combined weighted signals. In one embodiment, a SSFP imaging sequence uses phase cycling and acquired image data is squared with the squared data then combined. The final image signal is based on the square root of the squared data.

Artifact reduction in SSFP MRI using weighted sum of combined signals

Imaging time using PILS is reduced by using multiple coils with localized sensitivities with each coil having a separate demodulation channel thereby permitting parallel signal processing and image reconstruction. Images from the multiple coils are then combined to form an image with a larger field of view (FOV).

Multi-coil reconstruction of MRI signals using linear phase multiplied data with separate demodulators for each coil

Real time spatially localized velocity distribution is measured using magnetic resonance techniques by first exciting a column-shaped region using a 2D RF excitation pulse. A cyclical readout gradient is then played along the excited column's axis while the magnetic resonance signal is continuously sampled to create a 2D sample set of velocity frequency vs. spatial frequencies in the same direction. If the cyclical readout gradient, for example a sawtooth-shaped gradient, has lobes of increasing area, the spacing between samples in the velocity-frequency direction is increased to emphasize sampling at low velocity-frequency and to more coarsely sample high velocity-frequencies. The sequence can be repeated to collect a time series of velocity-position images, which can then be sampled to create a velocity-time image at a single location.

Variable density fourier velocity encoding MR imaging

A steady-state condition for tipped nuclear spins is accelerated or catalyzed by first determining magnetization magnitude of the steady state and the scaling magnetization along one axis (Mz) to at least approximate the determined magnetization magnitude. Then the scaled magnetization is rotated to coincide with a real-valued eigenvector extension of the tipped steady-state magnetization. Any error vector will then decay to the steady-state condition without oscillation. In one embodiment, the magnetic resonance imaging utilizes steady-state free precession (SSFP). The scaling and rotating steps are followed by the steps of applying read-out magnetic gradients and detecting magnetic resonance signals from the tipped nuclear spins. The magnetization magnitude is determined by eigenvector analysis, and the eigenvector extension is a real-valued eigenvector determined in the analysis.

Catalyzing the transient response in steady-state MRI sequences

A fast, spectrally-selective steady-state free precession (SSFP) imaging method is presented. Combining k-space data from SSFP sequences with certain phase schedules of radiofrequency excitation pulses permits manipulation of the spectral selectivity of the image. For example, lipid and water can be rapidly resolved. The contrast of each image depends on both T,and T,, and the relative contribution of the two relaxation mechanisms to image contrast can be controlled by adjusting the flip angle. Several applications of the technique are presented, including fast musculoskeletal imaging, brain imaging, and angiography. The technique is referred to herein as linear combination steady-state free precession (LCSSFP) and fluctuating equilibrium magnetic resonance (FEMR).

Linear combination steady-state free precession MRI

A new technique for imaging a material with a high T2/T1 ratio such as articular cartilage uses driven equilibrium Fourier transform (DEFT), a method of enhancing signal strength without waiting for full T1 recovery. Compared to other methods, DEFT imaging provides a good combination of bright cartilage and high contrast between cartilage and surrounding tissue. Both theoretical predictions and images show that DEFT is a valuable method for imaging articular cartilage when compared to spoiled gradient recalled acquisition in the steady-state (SPGR) or fast spin echo (FSE). T2-decay, T1 recovery, echo time, magnetization density, proton density, and equilibrium density per proton are related by a derived equation.

Magnetic resonance imaging using driven equilibrium fourier transform

Flyback imaging is combined with echo planar imaging (EPI) for improved readout flow properties. For increases in imaging time of 50% or less, significant improvements in imaging are realized. The partial flyback improves partial-Fourier EPI and inside-out EPI and can be applied to any EPI trajectory.

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Palo Alto, CA, United States of America

Dwight G Nishimura