Methods and apparatuses for determining spatial distribution of an absolute phase of RF transmit field B.sub.1.sup.+ and/or RF receive field B.sub.1.sup. in an MRI system are described herein. An example method can include selecting a transmit coil for which to measure the absolute phase of the RF transmit field B.sub.1.sup.+, exciting nuclear spins in MR nuclei using at least two transmit configurations of the transmit coil, and detecting first and MR signals arising from exciting nuclear spins in MR nuclei using first and second transmit configurations, respectively. The method can also include acquiring first and second sets of complex k-space data from the first and second MR signals, respectively, and estimating an absolute phase B.sub.1.sup.+ map of the transmit coil using the first set of complex k-space data and the second set of complex k-space data.

The invention relates to a magnetic resonance imaging system (100). The magnetic resonance imaging system (100) is configured to be selectively operated in a default mode and an emulation mode. Execution of machine executable instructions (290) by a processor (203) of the magnetic resonance imaging system (100) causes the magnetic resonance imaging system (100) to receive a selection signal selecting the emulation mode. The magnetic resonance imaging system (100) switches from the default mode to the emulation mode. The magnetic resonance imaging system (100) is operated in the emulation mode using the set of emulation control parameters (292). The emulated magnetic resonance imaging data (270) is acquired from the imaging zone (108) of the magnetic resonance imaging system (100).

A new method is developed for ultrafast, high-resolution magnetic resonance spectroscopic imaging (MRSI) using learned spectral features. The method uses Free Induction Decay (FID) based ultrashort-TE and short-TR acquisition without any solvent suppression pulses to generate the desired spatiospectral encodings. The spectral features for the desired molecules are learned from specifically designed training data by taking into account the resonance structure of each compound generated by quantum mechanical simulations. A union-of-subspaces model that incorporates the learned spectral features is used to effectively separate the unsuppressed water/lipid signals, the metabolite signals, and the macromolecule signals. The unsuppressed water spectroscopic signals in the data can be used for various purposes, e.g., removing the need of additional auxiliary scans for calibration, and for generating high quality quantitative tissue susceptiability mapping etc. Simultaneous spatiospectral reconstructions of water, lipids, metabolite and macromolecule can be obtained using a single .sup.1H-MRSI scan.

A method and apparatus for determining spatial distribution of a complex radio frequency (RF) of both transmit field and receive sensitivity a magnetic resonance imaging (MRI) system. The method includes estimation of the absolute phase of transmit field using a reference transmit coil or array coils with minimal absolute phase. The method and apparatus include estimation of complex receive sensitivity of a transceiver coil using the complex transmit field of the transceiver coil or array coils.

Methods, devices and apparatus for reconstructing a magnetic resonance image are provided. In one aspect, a method includes: determining array coil images according to first data collected by array coils of an MRI device during a prescan, where each coil of the array coils corresponds to a respective one of channels; determining a quadrature body coil image according to at least one of second data collected by a quadrature body coil of the MRI device during the prescan and the first data collected by the array coils; obtaining a corrected quadrature body coil image by correcting an uniformity of the quadrature body coil image; determining coil sensitivity maps according to the array coil images and the corrected quadrature body coil image; and reconstructing a magnetic resonance image with third data collected by the array coils during a normal scan according to the coil sensitivity maps.

An MRI system is provided. The system may obtain a first set of MRI data relating to a subject acquired by an MR scanner in a first acquisition when the subject reaches a first T1 weighting level, and obtain a second set of MRI data relating to the subject acquired by the MR scanner in a second acquisition when the subject reaches a second T1 weighting level different from the first T1 weighting level. The system may also determine a target value of a reference coefficient associated with a first B1 inhomogeneity in the first acquisition and a second B1 inhomogeneity in the second acquisition based on the first and second sets of MRI data.

The invention provides for a magnetic resonance imaging (MRI) (100) system comprising a main magnet (102) with an with an adjustable main magnetic field. The MRI system further comprises a current source (124) for supplying RF current between multiple electrodes (122, 122) divided between a first portion (122) and a second portion (122). The current source is configured for supplying the RF current between the first portion and the second portion. Execution of the machine executable instructions cause a processor controlling the MRI system to: set (200) the average magnetic field strength within the imaging zone to a first value; set (202) the average magnetic field strength within the imaging zone to a second value, the second value is lower than the first value; control (204) the current source to have a known RF current (144) travel between the first portion of the electrodes and the second portion of the electrodes; acquire (206) the magnetic resonance data from the subject by controlling the magnetic resonance imaging system with readout gradient commands according to a three-dimensional imaging protocol; reconstruct (208) three-dimensional image data (148) from the magnetic resonance data; and calculate (210) a resistive model (150) of the subject using the three-dimensional image data and the known RF current through the electrodes.

A method and a magnetic resonance tomography (MRT) system are provided. The MRT system includes a controller configured to store a transmit vector that is established on a local-coil-specific basis. The transmit vector, for a specific local coil, indicates with which amplitudes and phases, transmit elements of the local coil may be controlled by a transmit device. The controller is configured to initiate a patient-specific calibration measurement on a patient to generate patient-specific calibration data representing a field distribution. The controller is also configured to determine deviations in the patient-specific calibration data from the stored transmit vector established on a local-coil-specific basis. The patient-specific calibration data is generated in the patient-specific calibration measurement on the patient and represents a field distribution. An imaging MRT measurement is not allowed if deviations exceed a threshold value, but is otherwise performed and is monitored by a monitoring device.

In a method, computer and magnetic resonance (MR) apparatus for normalizing MR contrast images of an examination object that has two chemically different substances (SW, SF), wherein the first substance produces a first image signal and the second substance produces a second image signal, a processor is provided with a complex-valued contrast having pixels with signal contributions from the first and second substances. A phase correction of this contrast image is performed by calculating a real-valued contrast from the amount of the image signals of each pixel of the complex-valued contrast image. A mathematically smooth correction map is determined based on a number of the pixels that have a defined real-valued contrast. The intensity of pixels of the complex-valued contrast image are homogenized with other scans based on the correction map.

According to one embodiment, a magnetic resonance imaging apparatus includes processing circuitry. The processing circuitry acquires a B.sub.1 sensitivity map of an imaging region that includes a subject. The processing circuitry sets a reference value in the B.sub.1 sensitivity map. The processing circuitry estimates an error generated when calculating a B.sub.1 map setting value based on the B.sub.1 sensitivity map, by using the reference value and the B.sub.1 sensitivity map. The processing circuitry calculates an amplitude and a phase of an RF pulse based on the error.