Mr imaging with t1 compensated b1 mapping

A magnetic resonance (MR) device comprising at least one main magnet coil for generating a uniform, steady magnetic field within an examination volume, a number of gradient coils for generating switched magnetic field gradients in different spatial directions within the examination volume, at least one RF coil for generating RF pulses within the examination volume and/or for receiving MR signals from an object positioned in the examination volume, a control unit for controlling the temporal succession of RF pulses and switched magnetic field gradients, and a reconstruction unit for reconstructing MR images from the received MR signals, wherein the MR device is arranged to perform a method including:

• subjecting at least portion of the object to a first stimulated echo imaging sequence comprising at least two preparation RF pulses (α) radiated toward the portion of the object during a first preparation period and a sequence of reading RF pulses (β) radiated toward the portion of the object during a first acquisition period temporally subsequent to the first preparation period;
• acquiring a first set of FID signals (IFID) and a first set of stimulated echo signals (ISTE) during the first acquisition period;
• subjecting the portion of the object to a second stimulated echo imaging sequence comprising at least two preparation RF pulses (α) radiated toward the portion of the object during a second preparation period and a sequence of reading RF pulses (β) radiated toward the portion of the object during an second acquisition period temporally subsequent to the second preparation period;
• acquiring a second set of FID signals (IFID) and a second set of stimulated echo signals (ISTE) during the second acquisition period, wherein the first and second sets of FID signals (IFID) have different T1-weightings and/or the first and second sets of stimulated echo signals (ISTE) have different T1-weightings;
• deriving a B1 map indicating the spatial distribution of the RF field of the RF pulses within the portion of the body from the acquired first and second sets of FID (IFID) and stimulated echo (ISTE) signals, wherein the different T1-weightings are made use of to compensate for influences on the B1 map caused by T1 relaxation.

A computer program to be run on a magnetic resonance (MR) device, which computer program comprises instructions stored on a computer readable medium for:

• generating a first stimulated echo imaging sequence comprising at least two preparation RF pulses (α) radiated during a first preparation period and a sequence of reading RF pulses (β) radiated during a first acquisition period temporally subsequent to the first preparation period;
• acquiring a first set of FID signals (IFID) and a first set of stimulated echo signals (ISTE) during the first acquisition period;
• generating a second stimulated echo imaging sequence comprising at least two preparation RF pulses (α) radiated during a second preparation period and a sequence of reading RF pulses (β) radiated during an second acquisition period temporally subsequent to the second preparation period;
• acquiring a second set of FID signals (IFID) and a second set of stimulated echo signals (ISTE) during the second acquisition period, wherein the first and second sets of FID signals (IFID) have different T1-weightings and/or the first and second sets of stimulated echo signals (ISTE) have different T1-weightings;
• deriving a B1 map indicating the spatial distribution of the RF field of the RF pulses from the acquired first and second sets of FID (IFID) and stimulated echo (ISTE) signals, wherein the different T1-weightings are made use of to compensate for influences on the B1 map caused by T1 relaxation.