Abstract
In high field MRI systems, the wavelength of transmitted RF pulse is same order as human body size. So the phase of transmitted RF pulse changes in human body, spatial distribution of RF pulse (B1 map) becomes inhomogeneous. Inhomogeneous B1 map causes some clinical problems like shading, SNR loss, and so on. RF shimming using multi channel RF transmit coil is one of methods to resolve this problem. B1 map for each RF transmit channel is used in RF shimming. To measure B1 maps correctly, the effect of T1 relaxation should be eliminated appropriately, thus long repetition time of pulse sequence is used and the scan time becomes long in previous methods. We developed a new fast B1 mapping method using pre-pulse (multi Td method). In multi Td method, B1 maps are calculated by using images acquired before and after pre-pulse is applied. Acquiring all images sequentially, scan time is 5.5 sec for 2-channel RF transmit coil. Also, using images acquired before pre-pulse is applied, the effect of T1 relaxation is eliminated and accurate B1 maps are calculated.
