Segmentation of fat in MRI using a preparatory pair of rectangular RF pulses of opposite direction

Abstract

A radiofrequency (RF) pulse-based MRI method is introduced as a novel fat (or water) segmentation method that, unlike the mostly used Dixon’s method, does not depend on the echo times. A pair of rectangular RF pulses of opposite direction, when the duration of its rectangular pulse and the off-resonance of its carrier frequency are set to specific values, is proposed as a preparatory RF pulse to be used for the quantitative fat segmentation. The optimal duration of its rectangular pulse and its specific off-resonance were first determined theoretically. Then, such pair of rectangular pulses of opposite direction (PROD pulse) was applied in imaging a few phantoms and volunteers. During the imaging experiments, MRI images were dynamically acquired with the PROD pulse while its carrier frequency was varied in a predefined off-resonance range. By analyzing the dynamically acquired signal changes, the theoretical properties of the PROD pulse were confirmed and the utility of the PROD pulse for the fat segmentation was verified. All MRI scans were performed in a clinical 3T system. The PROD pulse, if the duration of each rectangular pulse was set to 1.66ms and its carrier frequency was set to a specific off-resonance (e.g. ±223.5Hz, or −670.5Hz) in 3T, was effective in optimally modulating MRI signals to be used for the fat–water segmentation. Therefore, the PROD pulse can successfully be used as a preparatory RF pulse in MRI to achieve effective fat (or water) segmentation in MRI.