Determining parameter values in image points of an examination object in an MR system by an MRF technique. Comparison signal waveforms, established using predetermined recording parameters, and each assigned to predetermined values of the parameters to be determined, are loaded. An image point time series of the examination object is acquired with an MRF recording method such that the acquired image point time series are comparable with the loaded comparison signal waveforms. A signal comparison of a section of the respective signal waveform of the acquired one image point time series is carried out with a corresponding section of loaded comparison signal waveforms to establish similarity values. The values of the parameters to be determined on the basis of the most similar comparison signal waveforms determined are determined, and then stored or output.

In a method for generating an image data set and a reference image data set: a first raw data set is provided that is acquired with a MR system and that includes measurement signals at read-out points in k-space that lie on a first k-space trajectory; a second raw data set is provided that is acquired with the same MR system and at the same examination object at read-out points that lie on a second, different k-space trajectory that is different from the first k-space trajectory; image data sets are reconstructed from the first raw data set; a reference image data set is reconstructed from the second raw data set; the reference image data set is compared with each image dataset to generate respective similarity values; and an image data set is selected having a greatest similarity value.

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.

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.

Techniques are disclosed for acquiring MR signals of an object under examination in an MR system using a multi echo imaging sequence. The method comprises the steps of applying an RF excitation pulse to the object to generate a transverse magnetization, applying at least two RF refocusing pulses for refocusing the transverse magnetization to generate at least two MR spin echoes for the RF excitation pulse, applying a first magnetic field gradient in a read out direction between the RF excitation pulse and the first of the at least two RF refocusing pulses, applying a second magnetic field gradient in the read out direction after each of the at least two RF refocusing pulses such that the zeroth and first gradient moment is substantially zero for the second magnetic field gradient, and acquiring the at least two MR spin echoes during the at least two second magnetic field gradients.

Magnetic resonance (MR) data are acquired from a volume segment of an examination object and an MR image composed of multiple image pixels is reconstructed therefrom. For a magnetic field assumed to have been generated by the scanner, a summed field deviation is calculated, from which a respective displacement vector is calculated for each image pixel. A signal portion is assigned to each image pixel that has been displaced with the respective displacement vector from the respective image pixel. The summed field deviation is the sum of deviations caused by at least two of: non-linearities in gradient coils, Maxwell fields, field inhomogeneities independent of the gradients, and dynamic field disturbances.

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.

A MRI device including a main field unit for establishing a main magnetic field (MF) in an imaging region, a gradient coil assembly for generating a gradient field in the imaging region, a RF arrangement for sending excitation signals to and receiving MR signals from the imaging region, a field camera for determining MF information in the imaging region, the field camera comprising multiple MF sensors arranged at measurement positions enclosing the imaging region, and a controller. The controller is configured to receive sensor data for each measurement positions, from the sensor data, calculate the MF information for the imaging region, and implement a calibration and/or correction measure depending on the MF information. The field camera may be a vector-field camera acquiring vector-valued sensor data describing the MF at each measurement positions three-dimensionally. The controller may determine the MF information to three dimensionally describe the MF in the imaging region.

A MRI device including a main field unit for establishing a main magnetic field (MF) in an imaging region, a gradient coil assembly for generating a gradient field in the imaging region, a RF arrangement for sending excitation signals to and receiving MR signals from the imaging region, a field camera for determining MF information in the imaging region, the field camera comprising multiple MF sensors arranged at measurement positions enclosing the imaging region, and a controller. The controller is configured to receive sensor data for each measurement positions, from the sensor data, calculate the MF information for the imaging region, and implement a calibration and/or correction measure depending on the MF information. The field camera may be a vector-field camera acquiring vector-valued sensor data describing the MF at each measurement positions three-dimensionally. The controller may determine the MF information to three dimensionally describe the MF in the imaging region.

An MRI apparatus capable of correcting a static magnetic field inhomogeneity caused by application of a gradient magnetic field by a simple calculation, and a correction method of the MRI apparatus are provided. An image quality deterioration due to the static magnetic field inhomogeneity caused by application of a gradient magnetic field is estimated by a simple calculation using a shape of a pulse sequence for imaging. An amount of distortion to be generated in the image acquired by executing the pulse sequence is estimated based on the estimated static magnetic field inhomogeneity and the shape of the pulse sequence, and a distortion of a reconstructed image is corrected. Alternatively, an output of a compensation magnetic field canceling the estimated static magnetic field inhomogeneity is calculated, and is superimposed on a compensation current with an active shimming so as to be supplied to a shim coil.