Koninklijke Philips Corporation N.v.

Toshiba Medical Systems Corporation

Canon Medical Systems Corporation

Picker International, Inc.

Philips Medical Systems (Cleveland), Inc.

Marconi Medical Systems, Inc.

Michael R Thompson

Wayne R Dannels

Christopher K Anand

Andrew James Wheaton

Dee H Wu

Mark J Loncar

Heidi A Schlitt

Ulrich Wolfgang Katscher

Labros S Petropoulos

Paul M Margosian

Deepak V Bhat

Ad L Moerland

An apparatus and method are disclosed for determining a time origin of an input RF pulse of a plurality of input RF pulses. The method includes generating an RF echo based on the plurality of input RF pulses, a time-duration between the input RF pulses being controllable in order to determine a time instance corresponding to an ideal position of the RF echo. The method further includes acquiring a data signal corresponding to a scan of a subject, and computing a time-difference between a measured peak of the acquired data signal and the time instance corresponding to the ideal position of the RF echo, the computed time difference corresponding to a measure of a time-shift of an effective magnetic center of the input RF pulse.

Apparatus and method for calibration of time origin of an RF pulse in MRI data acquisition systems

Magnetic field temporal variations in magnetic resonance imaging (MRI) volume are determined based on the slope of a phase difference &#x394;&#x3c6; between spin responses in plural slices at a given temporal sampling time. Representations of the determined temporal magnetic field variations are stored for subsequent use, e.g., to achieve more accurate re-gridding of acquired k-space date before reconstruction of images in the spatial domain.

MRI gradient trajectory mapping

When performing repetitive scans of a patient using a magnetic resonance imaging machine or the like, patients often tend to move as they relax during a lengthy scanning session, causing movement in the volume or portion of the patient being scanned. A prospective motion correction component accounts for patient movement by calculating transformation data representative of patient movement in multiple planes, as well as rotational movement, and a host evaluates the change in position relative to a most recent scanning geometry of the patient or dynamic volume. In this manner, correction or adjustment to the scanning geometry employed by an associated scanner is made only for the differential between the current geometry and the most recent geometry, to mitigate redundant adjustment that can result in oscillatory over&#x2014;and under&#x2014;compensation during adjustments.

Method of motion correction for dynamic volume alignment without timing restrictions

A magnetic resonance imaging system acquires a final image of a selected field of view with a selected spatial resolution. A magnetic resonance imaging scanner () encodes and receives magnetic resonance samples in phase encode and readout directions using a plurality of receive coils (). The encoding and receiving undersamples in the readout direction. A reconstruction processor () reconstructs magnetic resonance samples acquired by each of the plurality of receive coils () into a corresponding plurality of intermediate reconstructed images. Each intermediate reconstructed image has aliasing and in some aspects degraded high spatial frequency characteristics due to the reduced sampling in the readout direction. A combining processor () combines the plurality of intermediate reconstructed images based on coil sensitivity factors () to produce the final reconstructed image with the selected field of view and the selected spatial resolution in the readout direction.

Mr imaging with sensitivity encoding in the readout direction

A dose of a contrast agent ( ) is administered to the patient ( ). A magnetic resonance is excited by an RF pulse ( ) in a region of interest of the patient ( ). An echo-planar imaging (EPI) readout waveform is implemented a preselected duration after the excitation to generate T or T * weighted data. During the preselected duration, another echo planar readout waveform is implemented to generate T or proton density weighted data. The data is reconstructed ( ) to generate a T or T * weighted image and a T weighted image. The T and T or T * weighted images are combined ( ) to generate a contrast enhanced image.

Multiple contrast echo-planar imaging for contrast-enhanced imaging

To generate a magnetic resonance angiograph, a patient is injected with a contrast-enhancing agent ( ). An ellipsoidal central portion of k-space ( ) and a first surrounding region ( ) are continuously sampled ( ). A portion of each central data set ( ) is reconstructed ( ) into a low-resolution volume and maximum-intensity-projected ( ) onto a line. The maximum intensity projection ( ) is processed ( ) in order to detect the arrival of the contrast enhancing bolus within a volume of interest. Upon detection of the arrival of the bolus, the acquisition of a high-resolution magnetic resonance angiograph is triggered ( ) in which higher phase encode portions ( ) of k-space are sampled. The central data set ( ) along with the higher phase encode views ( ) are reconstructed ( ) into a high-resolution magnetic resonance angiogram. The present technique allows for substantially zero latency between the detection of the contrast-enhancing agent bolus and the acquisition of the magnetic resonance angiogram.

Contrast-enhanced MRA including an effective zero-latency method of bolus detection

A subject is disposed in an imaging region ( ) of a magnetic resonance imaging apparatus. An operator submits a series of user preferences to the apparatus. A gradient optimizer ( ) generates a gradient waveform that is optimal for the imaging procedure based on the user submitted specifications and the apparatus hardware specifications. The optimizer ( ) accesses a memory that stores ideal gradient waveform models. The model that best fits the user specifications is selected and digitized ( ). The digitized waveform is then convolved ( ) with a band-limited kernel ( ) that represents a frequency spectrum ( ) of a gradient amplifier ( ), producing a gradient waveform ( ) that is smooth and does not exceed the capabilities of the amplifier. This optimized waveform is used in an imaging process including a collected data reconstruction portion of the process.

Band-limited gradient waveforms

A subject is disposed in an imaging region ( ) of a magnetic resonance imaging apparatus. An operator designates a steady-state imaging sequence and a sequence controller ( ) coordinates a gradient field controller ( ) and an RF pulse controller ( ) to generate the desired sequence. The gradient controller applies gradients that define a closed trajectory through k-space that starts at an origin point and follows a closed path to an end point. An analyzer ( ) analyzes data sampled at the beginning and end points. A gradient offset processor ( ) signals the sequence controller to apply additional gradients until the analyzer determines that the end point coincides with the origin point. A scaling circuit ( ) scales data sampled between the origin and end points for various anomalies in the steady-state magnetization, reconstructing scaled data into at least one image representation.

Steady-state imaging sequence

A magnetic resonance imaging system includes a gradient hardware subsystem ( ), a radio frequency transmission hardware subsystem ( ), and a data sampling and digitization hardware subsystem ( ) A sequence control processor ( ) applies control signals or pulses to the hardware subsystems to cause the implementation of a selected EPI imaging sequence. Due to inductive loads, analog filters, and other circuit constructions within the hardware subsystems, each of the hardware subsystems has a different inherent delay between receipt of a control signal and actually achieving the controlled function such as applying a gradient or RF pulse or sampling data. Due to these different inherent delays, the imaging sequence occurs with timing variations from the intended sequence. Echo planar imaging sequences are very sensitive to phase errors caused by these relative delays, which phase errors manifest themselves in the form of Nyquist ghosts. A calibration processor ( ) analyzes resultant EPI images for Nyquist ghosts and adjusts a relative delay in the control signals from the signal processor until ghosting is minimized.

Calibration of timing delays using alternating/repeating waveforms and EPI

A magnetic resonance imaging apparatus and method employ a magnet system ( ) creating a temporally constant magnetic field through an examination region ( ) in which at least a portion of an object to be imaged is placed. A radio frequency (RF) excitation system ( ) applies an RF excitation to a volume of interest of the object to be imaged, and a receiver system ( ) detects and demodulates magnetic resonance data from the volume of interest. A magnetic field encoding system ( ) applies encoding magnetic fields to provide spatial discrimination of magnetic resonance data from the volume of interest within a single radio frequency excitation period. The spatial encoding of the magnetic resonance signal data is performed and collected along a preselected k-space trajectory, the k-space trajectory covering a plurality of intersecting. planes or partial planes of k-space data.

MRI method and apparatus for rapid acquisition of multiple views through a volume

A magnetic resonance apparatus includes a main magnet ( ) which generates a main magnetic field through and surrounding an examination region ( ). The main magnetic field contains inhomogeneities which affect image quality. A gradient coil assembly ( ) generates gradient magnetic fields across the examination region, which contain higher order harmonics causing inhomogeneities in the gradient magnetic field. A multi-axis shim set ( ) is selectively excited in order to cancel both the main magnetic and gradient magnetic field inhomogeneities. More particularly, DC currents are applied by a shim coil power supply ( ) to cancel the main magnetic field inhomogeneities. AC current pulses are superimposed on the DC currents by the shim coil power supply ( ) in order to correct the gradient magnetic field inhomogeneities. The existence of correctable higher order gradient magnetic field harmonics provides for fast switching, high duty cycles, and high peak gradients, without adding distortions to the resulting magnetic resonance images.

Real-time multi-axis gradient distortion correction using an interactive shim set

An MRI scanning method and apparatus provide increased efficiency by oversampling in the phase encoding direction. The oversampling is performed during one or more time periods (,) during the scanning sequence that would normally be unused. The addition phase encoding steps (,) can be used to enhance overall image resolution. In preferred embodiments, additional phase encoding steps reduce or eliminate N/2 ghost artifacts with no increase in imaging time. Image throughput is improved by obviating the need for ghost removal post-processing of the image data.

MRI method and apparatus for increasing the efficiency of echo lanar imaging and other late echo techniques

A method of calibrating pre-emphasis gradient pulse conditioning for long term eddy current compensation in an MRI system is provided. It includes positioning an object in the MRI system for imaging therewith. A long term eddy current generating pre-scan gradient pulse is applied, and after a delay, an EPI sequence is run such that a resulting image of the object is acquired. This process of applying the pre-scan gradient pulse followed by the EPI sequence is repeated while varying the delay therebetween. Size variations in the resulting images of the object are observed, and these size variations are fit to an exponential curve to obtain one or more time constants for the long term eddy currents. Next, a reference EPI sequence is run without applying the long term eddy current generating pre-scan gradient pulse such that a reference image of the object is acquired. The long term eddy current generating pre-scan gradient pulse is reintroduced, and after a delay which is shorter than the time constants, a test EPI sequence is run such that a test image of the object is acquired. The process of applying the pre-scan gradient pulse followed by the test EPI sequence is repeated while adjusting the pre-emphasis gradient pulse conditioning which is based upon the time constants obtained. This continues until the test images of the object have a size substantially equivalent to that of the reference image.

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Cleveland Heights, OH, United States of America

Michael R Thompson