A substrate 1 includes a color center excited by excitation light, and at least a pair of reflection members 21a, 21b are arranged with gaps from the substrate 1. The substrate 1 causes the excitation light entering the substrate 1 to exit through its surfaces without reflection, and the reflection members 21a, 21b cause the exited excitation light to reflect at the reflection surface 21-1 or 21-2 and enter the substrate 1, and cause the excitation light to repeatedly enter and exit the substrate 1 and thereby pass through the substrate 1 only a predetermined number of times. Here, the irradiating device 4 emits the excitation light such that the excitation light is incident to the reflection surface 21-1 or 21-2 with an angle perpendicular to one axis among two axes of the reflection surface 21-1 or 21-2 and with a predetermined slant angle from the other axis.

A magnetic field measuring apparatus includes a first cell and a second cell in which alkali metal atoms are respectively enclosed, a light guide that enters laser light into the first cell and the second cell, and a position adjustment mechanism, and a position of a second reference surface with respect to a first reference surface is adjusted and orientations of optical axes of a beam light relating to the first reference surface and a beam light relating to the second reference surface are the same direction.

To enable improved adjustment of at least one shim channel for magnetic resonance imaging of an examination region of an examination object by operation of a magnetic resonance apparatus that has a shim arrangement with a first shim channel volume having at least one first shim channel and a second shim channel volume having at least one second shim channel, the examination region is divided into multiple of sections, multiple first shim parameter sets are determined for the at least one first shim channel, with one first shim parameter set among the multiple first shim parameter sets being ascertained for each of the multiple sections, a second shim parameter set is ascertained for the at least one second shim channel, taking into account the ascertained multiple first shim parameter sets, and magnetic resonance image data of the examination region are acquired, but before this acquisition, the at least one second shim channel is adjusted using the second shim parameter set and the at least one first shim channel is adjusted for acquiring the magnetic resonance image data from a specific section of the multiple sections using a first shim parameter set ascertained for that specific section.

A system and method is provided for producing a map of a static magnetic field (B.sub.0) of a magnetic resonance imaging system. The method includes forming a first dataset by acquiring, with the MRI system, a first plurality of different echo signals occurring at a respective plurality of different echo times. The method also includes forming a second dataset by acquiring, with the MRI system, a second plurality of different echo signals occurring at a respective plurality of different echo times. The second dataset includes signals resulting from a magnetization transfer (MT) between free water and bound molecules. The method further includes generating MT-weighted maps using the first dataset and the second dataset, determining, using the MT-weighted maps, a phase difference between the first plurality of different echo signals, and using the phase differences, generate a corrected map of the static magnetic field (B.sub.0) of the MRI system.

A method includes applying a preparatory radiofrequency (RF) pulse at a first time instant to a Magnetic Resonance (MR) scanner configured to scan an object comprising a plurality of chemical species. The method further includes applying a phase sensitive pulse sequence at a second time instant to the MR scanner, wherein the preparatory RF pulse and a time delay between the first and the second time instants null a first subset of chemical species from the plurality of chemical species. The method further includes receiving an output signal from a second subset of chemical species from the plurality of chemical species in response to the phase sensitive pulse sequence. The method also includes estimating a static magnetic field map based on the output signal from the second subset of chemical species.

Retrospective magnetic resonance imaging (MRI) uses a deep neural network framework [102] to generate from MRI imaging data [100] acquired by an MRI apparatus using a predetermined imaging protocol tissue relaxation parametric maps and magnetic/radiofrequency field maps [104] which are then used to generate using the Bloch equations [106] predicted MRI images [108] corresponding to imaging protocols distinct from the predetermined imaging protocol. This allows obtaining a wide spectrum of tissue contrasts distinct from those of the acquired MRI imaging data.

In a method for correction of a B0 field map measured with a magnetic resonance device, that describes deviations from a nominal field strength in the homogeneity area of the magnetic resonance device by deviations from a nominal frequency for protons bonded to water, the deviations being represented as Larmor frequency values for different picture elements shifted by chemical shifts, the B0 field map is recorded with spins of the fat and water protons not in phase. The B0 field map is segmented by evaluating the differences of the Larmor frequency values of adjacent picture elements of the B0 field map in at least two contiguous clusters. For each cluster, a decision is made on the basis of a smoothness criterion and a compactness criterion as to whether a cluster containing a majority of protons bonded into fat is involved. Clusters identified as containing a majority of protons bonded into fat are corrected by lowering the Larmor frequency values by the difference between the nominal frequency for protons bonded into water and the corresponding nominal frequency for protons bonded to fat.

A method for determining a B.sub.0 map for, for example, performing an imaging magnetic resonance measurement using a magnetic resonance apparatus, includes measuring an original magnetic field distribution in a measurement volume of the magnetic resonance apparatus, and computing a final B.sub.0 map that describes a magnetic field distribution produced in the measurement volume of the magnetic resonance apparatus by setting a shim state. The magnetic field distribution produced in the measurement volume of the magnetic resonance apparatus by setting the shim state differs from the original magnetic field distribution.

A method for acquiring a basic magnetic field inhomogeneity value of a magnetic resonance imaging (MRI) system includes homogenizing an original basic magnetic field of the MRI system into a target magnetic field, providing a magnetic field compensation amount for the MRI system by a dynamic shimming method. The dynamic shimming method includes performing a 3D low-resolution dual-echo gradient echo sequence, and using a general formula to acquire the magnetic field inhomogeneity value, the general formula being: ΔB=ΔB.sub.original+ΔB.sub.compensating, wherein ΔB is the magnetic field inhomogeneity value, ΔB.sub.original is a difference value between the original magnetic field and the target magnetic field, and ΔB.sub.compensating is the magnetic field compensation amount. This method for acquiring a magnetic field inhomogeneity value for an MRI system saves considerable time to map the magnetic field again, thereby shortening the magnetic resonance imaging time, and increasing the efficiency of magnetic resonance imaging.

A method includes: accessing MRI data acquired from a joint area, the MRI data including a series of spatially mapped spectral data points; generating MRI images of the joint area; receiving information encoding a region of interest that encompasses a suspected metal particle deposition area over at least one of the MRI images; constructing magnetic field maps using the MRI data, each representing off-resonance frequency shifts over the joint area; removing a background of off-resonance field inhomogeneity from the magnetic field map such that the region of interest is free from off-resonance field inhomogeneity; identifying clusters from the magnetic field maps with the background of off-resonance field inhomogeneity removed, the clusters defined over a first dimension of offset frequencies and a second dimension of cluster volumes; and computing a quantitative metric by combining information from the identified clusters according to both the first dimension and the second dimension.