An MRI apparatus capable of correcting a static magnetic field inhomogeneity caused by application of a gradient magnetic field by a simple calculation, and a correction method of the MRI apparatus are provided. An image quality deterioration due to the static magnetic field inhomogeneity caused by application of a gradient magnetic field is estimated by a simple calculation using a shape of a pulse sequence for imaging. An amount of distortion to be generated in the image acquired by executing the pulse sequence is estimated based on the estimated static magnetic field inhomogeneity and the shape of the pulse sequence, and a distortion of a reconstructed image is corrected. Alternatively, an output of a compensation magnetic field canceling the estimated static magnetic field inhomogeneity is calculated, and is superimposed on a compensation current with an active shimming so as to be supplied to a shim coil.

Systems and methods for generating a gradient waveform for use by a low-field MRI system to generate a gradient magnetic field are provided herein. The gradient waveform can be determined using first information indicative of the gradient waveform and second information indicative of hardware constraints of the low-field MRI system including a maximum voltage of the gradient power amplifier, a maximum slew rate of the gradient coil, a resistance of the gradient coil, and an inductance of the gradient coil. In some embodiments, the gradient waveform can be a trapezoidal gradient waveform determined to have a non-linear ramp-up portion and/or a non-linear ramp-down portion.

Some implementations provide a system that includes: a housing having a bore in which a subject to be image is placed; a main magnet configured to generate a volume of magnetic field within the bore, the volume of magnetic field having inhomogeneity below a defined threshold; one or more gradient coils configured to linearly vary the volume of magnetic field as a function of spatial location; one or more pulse generating coils configured to generate and apply radio frequency (RF) pulses to the volume of magnetic field in sequence to scan the portion of the subject; one or more shim gradient coils configured to perturb a spatial distribution of the linearly varying volume of magnetic field; and a control unit configured to operate the gradient coils, pulse generating coils, and shim gradient coils such that only the user-defined region within the volume of magnetic field is imaged.

Described here are systems and methods for correcting motion-encoding gradient nonlinearities in magnetic resonance elastography (“MRE”). In general, the systems and methods described in the present disclosure compute gradient nonlinearity corrected displacement data based on information about the motion-encoding gradients used when acquiring magnetic resonance data.

Systems and methods for measuring eddy current fields occurring as a result of gradient pulses in a magnetic resonance sequence at a point in time during the magnetic resonance sequence in relation to at least one direction of pulse effect. At least the parts of the magnetic resonance sequence comprising the gradient pulses relating to the at least one direction of pulse effect are performed as a preparation sequence up until the point in time followed directly by a measurement sequence in which first measurement data is recorded. The preparation sequence is played out again with the same, directly consecutive measurement sequence without the gradient pulses relating to the at least one direction of pulse effect or with gradient pulses having an inverted sign relating to the at least one direction of pulse effect. Second measurement data is recorded. Using a joint evaluation of the first and second measurement data at least one variable characterizing the eddy current field generated by the eddy currents of the gradient pulses in the at least one direction of pulse effect is determined.

The present application describes techniques for determining and eliminating a time delay between a radio frequency pulse and a layer selection gradient in a magnetic resonance device. The techniques for determining and eliminating the time delay direct include measuring the time delay between the layer selection gradient and the radio frequency pulse by using phase information. This technique is more sensitive and accurate than existing methods that use signal or artifact strength.

A correction method for reducing temperature-related deviations in a gradient response of an MR pulse sequence in MR imaging is provided. An MR pulse sequence that includes at least one nominal test gradient is run. A gradient response to the at least one nominal test gradient is repeatedly acquired by a magnetic field measurement in an examination region. A gradient system transfer function is determined based on the gradient response. A corrected MR pulse sequence is determined based on the gradient system transfer function and of the at least one nominal test gradient.

A method for recording a magnetic resonance image data set includes providing a magnetic resonance sequence. The magnetic resonance sequence includes at least one radio-frequency pulse and a slice-selection gradient pulse applied during or before the radio-frequency pulse, which is configured as non-constant. The method includes providing at least one correction term for compensating a magnetic field change of the slice-selection gradient pulse. The magnetic field change is ascertained via a transfer characteristic of the gradient system of the magnetic resonance system. The method also includes recording at least one magnetic resonance image data set with the magnetic resonance sequence using the correction term.

A method for recording a magnetic resonance image dataset includes providing a magnetic resonance sequence with a series of sequence blocks, and providing at least one correction term to compensate for a magnetic field change. The magnetic field change is produced as a change of an actual magnetic field compared to a setpoint magnetic field by gradient pulses. The magnetic field change is established via a transfer characteristic of the gradient system of the magnetic resonance installation. The at least one correction term is used to compensate for the magnetic field change, and at least one magnetic resonance image dataset is recorded with the magnetic resonance sequence using the correction term.

An apparatus for controlling at least one gradient coil of a magnetic resonance imaging (MRI) system. The apparatus may include at least one computer hardware processor; and at least one computer-readable storage medium storing processor executable instructions that, when executed by the at least one computer hardware processor, cause the at least one computer hardware processor to perform a method. The method may include receiving information specifying at least one target pulse sequence; determining a corrected pulse sequence to control the at least one gradient coil based on the at least one target pulse sequence and a hysteresis model of induced magnetization in the MRI system caused by operation of the at least one gradient coil; and controlling, using the corrected gradient pulse sequence, the at least one gradient coil to generate one or more gradient pulses for imaging a patient.