Obtaining minimum duration parallel transmit pulses for simultaneous multislice imaging that includes minimizing specific absorption rate hotspots, using an IMPULSE pTx optimization method to determine multiple spoke locations and multiple channel weights for multiple slices while enforcing a specified flip angle inhomogeneity tolerance over the multiple slices when excited, applying a control algorithm to conform a simultaneous multislice (SMS) pulse to the excited multiple slices to minimize a cost function having terms corresponding to an excitation accuracy and a pulse power, where a regularization term in the cost function is configured by the control algorithm for excitation accuracy while limiting a peak pulse power, and applying a time-optimal variable rate selective excitation (VERSE) to enforce a peak power constraint with a minimum pulse duration by reshaping a RF waveform and a gradient waveform without altering an excitation profile if the peak power limit on a channel is exceeded.

Apparatus, methods, and other embodiments associated with NMR fingerprinting with parallel transmission are described. One example apparatus includes individually controllable radio frequency (RF) transmission (TX) coils configured to apply varying NMR fingerprinting RF excitations to a sample. The NMR apparatus may apply excitations in parallel. An individual excitation causes different resonant species to produce different signal evolutions. The apparatus includes a parallel transmission logic that causes one of the coils to apply a first excitation to the sample and that causes a different coil to apply a second, different excitation to the sample. The excitations are configured to produce a spatial inhomogeneity between a first region in the sample and a second region in the sample that allows a resonant species to produce a first signal evolution in the first region and to produce a second signal evolution in the second region to facilitate de-correlating the signal evolutions.

The invention relates to a method of MR imaging of an object (10). The problem of the invention is to provide an improved MR imaging technique that enables fast and robust determination of spatial sensitivity profiles of RF receiving antennas (11, 12, 13) used in parallel imaging as well as B1 and/or B0 mapping. The method of the invention comprises subjecting the object (10) to a stimulated echo sequence. Two or more stimulated echo signals (STE, STE*) are acquired, namely a direct stimulated echo signal (STE) and a conjugated stimulated echo signal (STE*), wherein at least one of the stimulated echo signals (STE, STE*) is received in parallel via an array of two or more RF receiving antennas (11, 12, 13) having different spatial sensitivity profiles, and wherein at least another one of the stimulated echo signals (STE, STE*) is received via a body RF coil (9) having an essentially homogeneous spatial sensitivity profile. Sensitivity maps indicating the spatial sensitivity profiles of the individual RF receiving antennas (11, 12, 13) of the array are derived by comparing the stimulated echo signals (STE, STE*) received via the array of RF receiving antennas (11, 12, 13) with the stimulated echo signals (STE, STE*) received via the body RF coil (9). Moreover, the invention relates to a MR device (1) and to a computer program for a MR device (1).

A computer-implemented method of visualizing blood flow through a patient using magnetic resonance imaging (MRI) includes receiving an image of the portal venous system of the patient's liver at a full field of view. A reduced field of view is defined which encompasses the portal venous system of the patient's liver and excludes extraneous anatomy in the full field of view. A navigator area is defined in the full field of view and outside of the reduced field of view. Transmit channels are used to selectively excite the reduced field of view and the navigator area throughout a cardiac cycle of the patient. Measurement data is acquired in response to the selective excitation. The acquired data is used to generate time-resolved 3D datasets. Additionally, a 3D visualization of blood flow though the portal venous system is generated based on the time-resolved 3D datasets.

A method and system for reducing Nyquist ghost artifact is provide. The method may include: obtaining a plurality of measured data sets; determining, based on the plurality of measured data sets, in a data space, a plurality of convolution kernels, each convolution kernel relating to all of the plurality of measured data sets; generating, based on the plurality of convolution kernels and the plurality of measured data sets, in the data space, a plurality of synthetic data sets; generating, based on the plurality of synthetic data sets and the plurality of measured data sets, in the data space, a plurality of combined data sets, each combined data set relating to one of the plurality of synthetic data sets and a corresponding measured data set of the plurality of measured data sets; and reconstructing, based on the plurality of combined data sets, an image.

Systems and methods for designing RF pulses using a technique that directly controls temperature rise via a compression model that is based on virtual observation points (VOPs) are provided. Thermal pre-simulations are first carried out for a given RF exposure time, coil, and subject model in order to obtain complex temperature matrices, after which the compression scheme follows. As one example, the thermal model employed can be Pennes' bio-heat equation. Focusing design constraints on the temperature rise instead of the absolute temperature allows for uncertain parameters to be dropped from the thermal model, making it more robust and less prone to errors. In some embodiments, the algorithm used for RF pulse design is the active-set (A-S) method.

A multi-channel transmit/receive radio frequency (RF) system for a magnetic resonance examination system with an RF antenna array includes multiple antenna elements and an RF power supply to supply electrical RF power to the antenna elements. Directional couplers are circuited between respective antenna elements and a power distributor. A monitoring module is configured to measure forward electrical wave amplitude(s) and reflected electrical wave amplitude(s) at individual directional couplers. An arithmetic module is configured to compute individual coil element currents on the basis of the measured forward and reflected electrical wave amplitudes.

A computer-implemented method of building a database of pulse sequences for parallel-transmission magnetic resonance imaging, includes a) for each of a plurality of subjects, determining an optimal sequence for the subject; b) for each subject, computing the values of the or of a different cost or merit function obtained by playing the optimal sequences for all the subjects; c) aggregating the subjects into a plurality of clusters using a clustering algorithm taking the values, or functions thereof, as metrics; d) for each cluster, determining an averaged optimal sequence for the cluster; e) receiving, as input, a set of features characterizing an imaging subject, comprising at least a morphological feature of the subject; f) associating the subject to one pulse sequence of the database based on the set of features using the computer-implemented classifier algorithm; and g) performing magnetic resonance imaging using the pulse sequence. A magnetic resonance imaging apparatus for carrying out steps e)-g) of such a method is also provided.

An MRI apparatus performs multi-channel calibration acquisitions using a multi-channel receiver array and uses a convolutional neural network (CNN) to compute an estimated profile map that characterizes properties of the multi-channel receiver array. The profile map is composed of orthogonal vectors and transforms single-channel image space data to multi-channel image space data. The MRI apparatus performs a prospectively subsampled imaging acquisition and processes the resulting k-space data using the estimated profile map to reconstruct a final image. The CNN may be pretrained in an unsupervised manner using subsampled simulated multi-channel calibration acquisitions and using a regularization function included in a training loss function.

A method for optimization of an RF pulse that is multi-band. The RF pulse is a spokes RF pulse including a train of sub-pulses. The method includes using a starting k-space position as a current k-space position, and for each of slices to be excited by the RF pulse, performing: calculating a sub-pulse based on the current k-space position and calculating an expected magnetization after that sub-pulse; calculating an inverse Fourier transform of a difference between an expected magnetization and a target magnetization; and determining an optimal k-space position for a next spoke for this slice to be at a position where an absolute value of the inverse Fourier transform has a maximum. A next k-space position is determined for all slices together based on the optimal k-space positions determined for each slice individually. A multi-band RF pulse is determined based on the determined k-space positions.