Generating Motion- and Distortion-Free Local Field Map Using 3D Ultrashort TE MRI: Comparison with T₂* Mapping
10.13104/imri.2019.23.4.328
- Author:
Kyle JEONG
1
;
Bijaya THAPA
;
Bong Soo HAN
;
Daehong KIM
;
Eun Kee JEONG
Author Information
1. Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, UT, USA. ek.jeong@utah.edu
- Publication Type:Original Article
- Keywords:
Ultrashort TE;
UTE;
Fieldmap;
Phasemap;
Quantitative susceptibility mapping;
Susceptibility imaging
- MeSH:
Abdomen;
Artifacts;
Boidae;
Brain;
Humans;
Image Processing, Computer-Assisted;
Magnetic Resonance Imaging;
Methods
- From:Investigative Magnetic Resonance Imaging
2019;23(4):328-340
- CountryRepublic of Korea
- Language:English
-
Abstract:
PURPOSE: To generate phase images with free of motion-induced artifact and susceptibility-induced distortion using 3D radial ultrashort TE (UTE) MRI.MATERIALS AND METHODS: The field map was theoretically derived by solving Laplace's equation with appropriate boundary conditions, and used to simulate the image distortion in conventional spin-warp MRI. Manufacturer's 3D radial imaging sequence was modified to acquire maximum number of radial spokes in a given time, by removing the spoiler gradient and sampling during both rampup and rampdown gradient. Spoke direction randomly jumps so that a readout gradient acts as a spoiling gradient for the previous spoke. The custom raw data was reconstructed using a homemade image reconstruction software, which is programmed using Python language. The method was applied to a phantom and in-vivo human brain and abdomen. The performance of UTE was compared with 3D GRE for phase mapping. Local phase mapping was compared with T₂* mapping using UTE.RESULTS: The phase map using UTE mimics true field-map, which was theoretically calculated, while that using 3D GRE revealed both motion-induced artifact and geometric distortion. Motion-free imaging is particularly crucial for application of phase mapping for abdomen MRI, which typically requires multiple breathold acquisitions. The air pockets, which are caught within the digestive pathway, induce spatially varying and large background field. T₂* map, that was calculated using UTE data, suffers from non-uniform T₂* value due to this background field, while does not appear in the local phase map of UTE data.CONCLUSION: Phase map generated using UTE mimicked the true field map even when non-zero susceptibility objects were present. Phase map generated by 3D GRE did not accurately mimic the true field map when non-zero susceptibility objects were present due to the significant field distortion as theoretically calculated. Nonetheless, UTE allows for phase maps to be free of susceptibility-induced distortion without the use of any post-processing protocols.
