General Electric Company

Ge Medical Systems Global Technology Company, LLC

Yiping Du

Matthew A Bernstein

Joseph K Maier

Xiaohong Zhou

Jason Andrew Polzin

Hammond G Reynolds

Kevin Franklin King

Thomas K F Foo

Elliot R McVeigh

Navigator signals are acquired during a cardiac gated MRI scan to measure the position and velocity components of respiratory motion. Acquired cardiac image views are discarded and/or corrected based on the measurement of the positional and velocity components of respiratory motion to reduce motion artifacts. In one embodiment the navigator pulse sequence includes velocity encoding gradient, and in a second embodiment, velocity is determined by measuring the change in diaphragm position between successive navigator pulse sequences.

Respiratory displacement and velocity measurement using navigator MRI echo signals

A method is disclosed for providing a time efficient and accurate measure of the absolute positional displacements of a reference structure in navigator echo MR imaging. The method comprises the steps of operating an MR system to acquire a reference navigator echo associated with the object at a specified reference position, and applying an MR sequence to the object to acquire a set of MR image data when the object is selectively displaced from the reference position. The data set includes an acquired navigator echo having a specified field of view. The method further comprises truncating the acquired navigator echo by means of a selectively positioned truncation window, calculating the difference between linear phase shifts respectively associated with acquired and reference navigator echoes, and displacing the truncation window by an amount representing or corresponding to the phase shift difference in spatial units. Thereupon, the truncating, difference calculation, and truncation window displacement steps are iteratively repeated a specified number of times or when the calculated displacements converge to zero, to provide a final phase shift difference value and an absolute spatial displacement of a reference structure. The final value is used to determine the displacement of the object from the specified reference position when the MR data set is acquired.

Iterative method for reducing errors in navigator echo MR imaging

An MRI system acquired NMR data from which a three-dimensional image of a patient's heart is reconstructed. The NMR data is acquired as a plurality of three-dimensional slabs that are concatenated to reconstruct the image. A plurality of respiratory gating windows are established and NMR data for each slab is acquired during a different one of the respiratory gating windows.

Multi-slab multi-window cardiac MR imaging

In an MR imaging system, a method is provided for operating an MR gradient coil to provide a pulse sequence which comprises first and second sub-sequences. During the first sub-sequence, the coil is operated to produce a pair of diffusion-weighted imaging pulses, each having a gradient amplitude and a slew-rate. During the second sub-sequence the coil is operated to produce a train of echo-planar imaging pulses, each having a gradient amplitude which is selectively less than the amplitude of the diffusion-weighted pulses, and a slew-rate which is selectively greater than the slew-rate of the diffusion-weighted pulses. Thus, the invention is directed to a gradient system which can provide optimal performance for both diffusion-weighted imaging and echo-planar imaging, while using only a single coil for a given gradient axis. At the same time, the system enables gradient performance parameters to be selected so as to ensure that constraints imposed by the Reilly curve will not be exceeded, and to thereby avoid peripheral nerve stimulation.

System for operating MR gradient coil to produce pulses of different amplitudes and slew-rates

NMR data required to reconstruct an image is divided into central k-space views and peripheral k-space views. NMR navigator signals are acquired during a scan to indicate patient respiration and a first gating signal is produced when respiration is within a narrow acquisition window and a second gating signal is produced when respiration is within a wider acquisition window. Central k-space views are acquired when the first gating signal is produced and peripheral k-space views are acquired when the second gating signal is produced.

Respiratory gating method for MR imaging

Two methods are disclosed to remove the image artifacts produced by Maxwell terms arising from the imaging gradients in an echo planar imaging pulse sequence. In the first method, the frequency and phase errors caused by the Maxwell terms are calculated on an individual slice basis and subsequently compensated during data acquisition by dynamically adjusting the receiver frequency and phase. In the second method, two linear phase errors, one in the readout direction and the other in the phase-encoding direction, both of which arise from the Maxwell terms, are calculated on an individual-slice basis. These errors are compensated for in the k-space data after data acquisition.

Correction of artifacts caused by maxwell terms in slice offset echo

A method is disclosed to remove the image artifacts produced by Maxwell terms arising from the imaging gradients in an echo planar imaging pulse sequence. The frequency and phase errors caused by the Maxwell terms are calculated on an individual slice basis. During the subsequent data acquisition these errors are compensated by dynamically adjusting the receiver frequency and phase.

Correction of artifacts caused by Maxwell terms in slice offset echo

A method for correcting Maxwell field induced distortion, ghosting, and blurring artifacts in non-axially oriented EPI images is disclosed. In one embodiment phase corrections are calculated and used to offset Maxwell term errors during the image reconstruction process, and in another embodiment corrections are made after the image is reconstructed.

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Towson, MD, United States of America

Yiping Du