A passive magnetic field shim arrangement including a plurality of shim pairs. For shimming a number of magnetic field harmonics, each shim pair may include a first shim and a second opposite and substantially equal shim, each shim pair being configured for shimming one of the magnetic field harmonics. Each shim pair may include a first shim of order N and a second opposite and substantially equal shim of order N, the first and second shims together defining a magnetic field shim correction of order N−1. Each shim may include one or more shim elements arranged on a non-magnetic tubular support, the tubular supports being dimensioned such that the tubular supports may be arranged concentrically in relation to each other. A magnetic field may be shimmed by providing a shim pair configured for shimming a magnetic field harmonic, the shim pair including a first shim and a second opposite and substantially equal shim and symmetrically adjusting an axial position of the first shim and an axial position of the second shim to provide a desired shimming magnitude in order to shim the magnetic field harmonic.

In a method and test apparatus for determining a deviation in the homogeneity of a basic magnetic field of a magnetic resonance scanner, test vessels are positioned in a test plane that first and second positions along a direction in the scanner, and measurement data are acquired with the test vessels at said respective positions. The acquired measurement data are provided to a processor, wherein a deviation of the homogeneity of the basic magnetic field is determined based thereon.

In a method and test apparatus for determining a deviation in the homogeneity of a basic magnetic field of a magnetic resonance scanner, test vessels are positioned in a test plane that first and second positions along a direction in the scanner, and measurement data are acquired with the test vessels at said respective positions. The acquired measurement data are provided to a processor, wherein a deviation of the homogeneity of the basic magnetic field is determined based thereon.

In order to eliminate a global phase change caused by static magnetic field inhomogeneity included in a nuclear magnetic resonance signal, focusing on that phase components generated in a nuclear magnetic resonance signal caused by the static magnetic field inhomogeneity is in a predetermined frequency band (low-frequency band), phase components in the frequency band caused by the static magnetic field inhomogeneity is eliminated from an image generated from the nuclear magnetic resonance signal in main imaging. The predetermined frequency band of the phase components caused by the static magnetic field inhomogeneity is calculated from the nuclear magnetic resonance signal obtained in preliminary imaging.

In order to eliminate a global phase change caused by static magnetic field inhomogeneity included in a nuclear magnetic resonance signal, focusing on that phase components generated in a nuclear magnetic resonance signal caused by the static magnetic field inhomogeneity is in a predetermined frequency band (low-frequency band), phase components in the frequency band caused by the static magnetic field inhomogeneity is eliminated from an image generated from the nuclear magnetic resonance signal in main imaging. The predetermined frequency band of the phase components caused by the static magnetic field inhomogeneity is calculated from the nuclear magnetic resonance signal obtained in preliminary imaging.

In a sequence of emitting a plurality of refocus RF pulses after one excitation RF pulse, in order to suppress a cusp artifact at a known magnetic field distortion generation position regardless of an imaging condition, such as a slice thickness or an FOV, between an excitation RF pulse and an initial refocus RF pulse, by generating a phase shift to transverse magnetization at the position, and by applying an extremely small dephase gradient magnetic field in the phase encoding direction and/or in the slice encoding direction, a signal value of an NMR signal (echo signal) is suppressed at the position, and the cusp artifact is deteriorated.

In a sequence of emitting a plurality of refocus RF pulses after one excitation RF pulse, in order to suppress a cusp artifact at a known magnetic field distortion generation position regardless of an imaging condition, such as a slice thickness or an FOV, between an excitation RF pulse and an initial refocus RF pulse, by generating a phase shift to transverse magnetization at the position, and by applying an extremely small dephase gradient magnetic field in the phase encoding direction and/or in the slice encoding direction, a signal value of an NMR signal (echo signal) is suppressed at the position, and the cusp artifact is deteriorated.

Magnetic field sensor, in particular for measuring magnetic noise fields caused by environmental magnetic noise in combination with MRI apparatus, the magnetic field sensor being further provided with field compensation coils assembly and with a compensation circuit driving the field compensation coils assembly to generate a magnetic field compensating the static magnetic field dissipating outside from the static magnetic field generator or from the gantry of the MRI apparatus at the position of the magnetic sensor. A method for operating the magnetic field sensor and a method and a system for compensation magnetic noise caused by environmental noise are also provided. An MRI apparatus is also disclosed comprising such a system and carrying out such a method for compensating magnetic noise fields.

Magnetic field sensor, in particular for measuring magnetic noise fields caused by environmental magnetic noise in combination with MRI apparatus, the magnetic field sensor being further provided with field compensation coils assembly and with a compensation circuit driving the field compensation coils assembly to generate a magnetic field compensating the static magnetic field dissipating outside from the static magnetic field generator or from the gantry of the MRI apparatus at the position of the magnetic sensor. A method for operating the magnetic field sensor and a method and a system for compensation magnetic noise caused by environmental noise are also provided. An MRI apparatus is also disclosed comprising such a system and carrying out such a method for compensating magnetic noise fields.

A method for estimating a magnetic field deviation, a magnetic resonance device, and a computer program product are disclosed. In accordance with the method, at least one gradient value is provided, wherein each gradient value describes a gradient strength of the respective gradient magnetic field, e.g., the setpoint gradient magnetic field. The magnetic resonance device generates a main magnetic field in a main magnetic field direction. The at least one value of a deviation is estimated by applying the at least one gradient value to a magnetic field model. In this case, in accordance with a magnetic field model, a deviation of the gradient magnetic field from a setpoint gradient magnetic field is described by at least one vectorial component in a spatial direction deviating from the main magnetic field direction.