Magnetic resonance imaging method for at least two separate radio-frequency transmit coils with time-delayed slice-selective excitation pulses

A magnetic resonance system comprising:

• at least one gradient coil operable to generate a gradient field;
• at least two transmit coils, each transmit coil of the at least two transmit coils comprising with an RF transmit channel operable to generate radio-frequency pulses;
• and
• a controller configured to create an image data set of an area under examination using the magnetic resonance system, wherein at least one slice-selective excitation pulse with a prespecified pulse profile is applied to the area under examination during acquisition of image data by an imaging sequence, the controller being further configured to:
• access B1 maps that represent a spatial distribution of the sensitivity of the at least two RF transmit coils over the area under examination;
• access a Gs map that represents a spatial distribution of susceptibility magnetic field gradients in the area under examination;
• for each RF transmit coil of the at least two RF transmit coils, calculate a value for a susceptibility magnetic field gradient to be corrected from the Gs map in combination with the B1 map of the RF transmit coil;
• for each RF transmit coil of the at least two RF transmit coils, calculate a time delay of the excitation pulse based on the susceptibility magnetic field gradient to be corrected, a slice gradient to be applied during the excitation pulse, and an echo time of the imaging sequence;
• calculate a complex weighting factor for scaling a pulse profile for each RF transmit coil of the at least two RF transmit coils to achieve a maximally uniform deflection of the magnetization by the excitation pulse over the area under examination, wherein the calculation takes into account at least the B1 maps;
• and
• pass through the imaging sequence, wherein, during a simultaneous application of a slice gradient, the at least two RF transmit coils each emit an excitation pulse with the calculated time delay and with a pulse profile scaled according to the calculated complex weighting factors.

In a non-transitory computer-readable storage medium that stores instructions executable by a magnetic resonance system to create an image data set of an area under examination, the magnetic resonance system comprising at least two RF transmit coils, wherein at least one slice-selective excitation pulse with a prespecified pulse profile is applied to the area under examination during acquisition of image data by an imaging sequence, the instructions comprising:

• accessing B1 maps that represent a spatial distribution of the sensitivity of the at least two RF transmit coils over the area under examination;
• accessing a Gs map that represents a spatial distribution of susceptibility magnetic field gradients in the area under examination;
• for each RF transmit coil of the at least two RF transmit coils, calculating a value for a susceptibility magnetic field gradient to be corrected from the Gs map in combination with the B1 map of the RF transmit coil;
• for each RF transmit coil of the at least two RF transmit coils, calculating a time delay of the excitation pulse based on the susceptibility magnetic field gradient to be corrected, a slice gradient to be applied during the excitation pulse, and an echo time of the imaging sequence;
• calculating a complex weighting factor for scaling a pulse profile for each RF transmit coil of the at least two RF transmit coils to achieve an as uniform as possible deflection of the magnetization by the excitation pulse over the area under examination, wherein the calculation takes into account at least the B1 maps;
• and
• passing through the imaging sequence, wherein, during a simultaneous application of a slice gradient, the at least two RF transmit coils each emit an excitation pulse with the calculated time delay and with a pulse profile scaled according to the calculated complex weighting factors.