Disclosed is a method for generating a time-dependent magnetic field gradient in diffusion weighted magnetic resonance imaging G(t)=[G.sub.x(t)G.sub.y(t)G.sub.z(t)].sup.T, which is asymmetric in time with respect to a refocusing pulse, by meeting one or more of the requirements: A=∫.sub.0.sup.TEh(t)G(t)G(t).sup.Tdt is zero, where TE is an echo time and h(t) is a function of time which is positive during an interval prior to the refocusing pulse and negative during a time interval after the refocusing pulse); minimize A or m=(Tr[AA]).sup.1/2 where A=∫.sub.P1G(t)G(t).sup.Tdt−∫.sub.P2G(t)G(t).sup.Tdt where P1 and P2 represent time intervals prior to and subsequent to the refocusing pulse; m is smaller than a threshold value. an attenuation factor ${\mathrm{AF}}_p=\exp \left(-\frac{t}{T2*}\right)$
due to T2* relaxation is one. Signal attenuation due to concomitant field gradients, regardless of the shape or orientation of the diffusion encoding b-tensor and the location of signal is hereby minimized.

Methods, computing devices, and MRI systems that reduce artifacts produced by Maxwell gradient terms in TSE imaging using non-rectilinear trajectories are disclosed. With this technology, a RF excitation pulse is generated to produce transverse magnetization that generates a NMR signal and a series of RF refocusing pulses to produce a corresponding series of NMR spin-echo signals. An original encoding gradient waveform comprising a non-rectilinear trajectory is modified by adjusting a portion of the original encoding gradient waveform or introducing a zero zeroth-moment waveform segment at end(s) of the original encoding gradient waveform. During an interval adjacent to each of the series of RF refocusing pulses a first gradient pulse is generated. At least one of the first gradient pulses is generated according to the modified gradient waveform. An image is constructed from generated digitized samples of the NMR spin-echo signals obtained.

A system and method are provided for magnetic resonance imaging (MRI) and/or image reconstruction that includes acquiring multi-pass, chemical shift-encoded (CSE)-MRI imaging data of a subject. The method further includes performing a complex, joint estimation of phase terms in the imaging data for each pass of the multi-pass, CSE-MRI imaging data to account for concomitant gradient (CG)-induced phase errors of different passes. The method also includes generating at least one of a proton density fat fraction (PDFF) estimate or an R*2 estimate that is unbiased by CG-induced phase errors using the phase terms and communicating a report that includes at least one of the PDFF estimate or the R*2 estimate.

During operation, a computer system may acquire magnetic resonance (MR) signals associated with a sample from a measurement device or memory. Then, the computer system may access a predetermined set of coil magnetic field basis vectors associated with a surface surrounding the sample, where coil sensitivities of coils in the measurement device are represented by weighted superpositions of the predetermined set of coil magnetic field basis vectors using coefficients, and where the predetermined coil magnetic field basis vectors are solutions to Maxwell's equations. Next, the computer system may solve, on a voxel-by-voxel basis for voxels associated with the sample, a nonlinear optimization problem for MR information associated with the sample and the coefficients using: a forward model that uses the MR information as inputs and simulates response physics of the sample, the MR signals and the predetermined set of coil magnetic field basis vectors.

A method for actuating a magnetic resonance device according to an MR control sequence, wherein the MR control sequence includes a bipolar gradient pulse between an excitation pulse and a first refocusing pulse, and the bipolar gradient pulse induces a defined Maxwell phase and generates a dephasing gradient moment for a readout gradient.

The present disclosure relates to operating an MR system in which MR signals of an object under examination are acquired in an examining region using a multi echo imaging sequence, in which an RF excitation pulse and a plurality of RF refocusing pulses are applied. The techniques include determining a first accumulated phase of a magnetization in the object under examination. Then, a second accumulated phase of the magnetization in the object under examination is determined due to concomitant magnetic fields occurring between a second pair of consecutive RF pulses. Finally, it is determined whether a deviation from the predefined relationship is larger than a threshold and, if this is the case, a measure is applied in view of the fact that the deviation is larger than the threshold.

A method, electromagnet device, and system for reducing a higher order term of a concomitant field in an imaging magnetic field during magnetic resonance imaging is described. The electromagnet system has a first shim coil configured to be driven to generate a first compensation magnetic field during imaging according to a first second-order compensation term, the first compensation magnetic field having a similar amplitude but opposite direction as that of a first second-order concomitant magnetic field.

A system and method are provided for magnetic resonance imaging (MRI) and/or image reconstruction that includes acquiring multi-pass, chemical shift-encoded (CSE)-MRI imaging data of a subject. The method further includes performing a complex, joint estimation of phase terms in the imaging data for each pass of the multi-pass, CSE-MRI imaging data to account for concomitant gradient (CG)-induced phase errors of different passes. The method also includes generating at least one of a proton density fat fraction (PDFF) estimate or an R2* estimate that is unbiased by CG-induced phase errors using the phase terms and communicating a report that includes at least one of the PDFF estimate or the R2* estimate.

A method, electromagnet device, and system for reducing a higher order term of a concomitant field in an imaging magnetic field during magnetic resonance imaging is described. The electromagnet system has a first shim coil configured to be driven to generate a first compensation magnetic field during imaging according to a first second-order compensation term, the first compensation magnetic field having a similar amplitude but opposite direction as that of a first second-order concomitant magnetic field.

An asymmetric electromagnet system, method, and method of producing an asymmetric electromagnet system, wherein the asymmetric electromagnet system is for generating an imaging magnetic field in an imaging region with an imaging isocentre, the imaging region being asymmetrically positioned within a gradient coil bore inside a magnetic resonance imaging (MRI) system during imaging, the electromagnet assembly comprising: an asymmetric gradient coil configured to generate a gradient field in the asymmetrically positioned imaging region, at least one gradient axis having the gradient field with a constant offset component such that the position at which the gradient field passes through zero is offset with respect to the imaging isocentre of the asymmetrically positioned imaging region.