Fast B1+ mapping using three consecutive RF pulses and balanced gradients for improved bSSFP imaging

Publication date: February 2018
Source:Magnetic Resonance Imaging, Volume 46
Author(s): Min-Oh Kim, Taehwa Hong, Dong-Hyun Kim
PurposeTo develop a B1⁺ mapping during the transient phase of balanced steady state free precession (bSSFP) imaging which can be used for subsequent B1⁺ inhomogeneity compensation.MethodsTwo images with different flip angles (FA) are acquired using single-shot spiral technique during the transient phase of bSSFP with three consecutive RF pulses and balanced gradients. Under the assumptions that the transmit (B1⁺) field varies slowly in spatial domain and T1 and T2 relaxation effects are negligible during 2·TR, B1⁺ was estimated using the two magnitude images and bSSFP data was sequentially acquired. B1⁺ estimation error due to the assumptions and other factors such as FA and off-resonance were assessed using Bloch simulation. Phantom and in vivo experiments were performed with α-2α-3α scheme.ResultsThe simulation results indicated that the proposed method was less sensitive to T1 relaxation and B1⁺ mapping FA (α) of approximately 60° produced minimum estimation error. The B1⁺-induced intensity variation was reduced with the proposed method in the phantom experiment. For both the phantom and in vivo experiments, the estimated B1⁺ map showed comparable to the conventional B1⁺ map using spin-echo DAM.ConclusionB1⁺ map was estimated during the transient phase of bSSFP and subsequently compensated bSSFP images. There was no scan time increment and hence the technique can be used in a prescan manner for B1⁺ mapping or shimming.



http://ift.tt/2iGki0T