Phase Relaxed Localized Excitation Pulses for Inner Volume Fast Spin Echo Imaging

摘要

Purpose: To design multidimensional spatially selective radiofrequency(RF) pulses for inner volume imaging (IVI) with threedimensional(3D) fast spin echo (FSE) sequences. Enhancedbackground suppression is achieved by exploiting particularsignal properties of FSE sequences.Theory and Methods: The CPMG condition dictates that echoamplitudes will rapidly decrease if a 90 phase difference betweenexcitation and refocusing pulses is not present, and refocusing flipangles are not precisely 180. This mechanism is proposed as ameans for generating additional background suppression for spatiallyselective excitation, by biasing residual excitation errorstoward violating the CPMG condition. 3D RF pulses were designedusing this method with a 3D spherical spiral trajectory, undersampledby factor 5.6 for an eight-channel PTx system, at 3 Tesla.Results: 3D-FSE IVI with pulse durations of approximately 12ms was demonstrated in phantoms and for T2-weighted brainimaging in vivo. Good image quality was obtained, with meanbackground suppression factors of 103 and 82 6 6 in phantomsand in vivo, respectively.Conclusion: Inner Volume Imaging with 3D-FSE has been demonstratedin vivo with tailored 3D-RF pulses. The proposeddesign methods are also applicable to 2D pulses. M