Ultralow-field and spin-locking relaxation dispersion in postmortem pig brain.
OBJECTIVE
To investigate tissue-specific differences, a quantitative comparison was made between relaxation dispersion in postmortem pig brain measured at ultralow fields (ULF) and spin locking at 7 tesla (T). The goal was to determine whether ULF-MRI has potential advantages for in vivo human brain imaging.


METHODS
Separate specimens of gray matter and white matter were investigated using an ULF-MRI system with superconducting quantum interference device (SQUID) signal detection to measure T1ULF at fields from 58.7 to 235.0 μT and using a commercial MRI scanner to measure T1ρ7T at spin-locking fields from 5.0 to 235.0 μT.


RESULTS
At matched field strengths, T1ρ7T is 50 to 100% longer than T1ULF. Furthermore, dispersion in T1ULF is close to linear between 58.7 and 235 µT, whereas dispersion in T1ρ7T is highly nonlinear over the same range. A subtle elbow in the T1ULF dispersion at approximately 140 µT is tentatively attributed to the local dipolar field of macromolecules. It is suggested that different relaxation mechanisms dominate each method and that ULF-MRI has a fundamentally different sensitivity to the macromolecular structure of neural tissue.


CONCLUSIONS
Ultralow-field MRI may offer distinct, quantitative advantages for human brain imaging, while simultaneously avoiding the severe heating limitation imposed on high-field spin locking. Magn Reson Med 78:2342-2351, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
Department of Physics, University of California, Berkeley, California, USA.|State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences (CAS), Shanghai, China.|CAS Center for ExcelleNce in Superconducting Electronics (CENSE), Shanghai, China.
Hui
H
Dong
Department of Physics, University of California, Berkeley, California, USA.|Center for Biosignals, Korea Research Institute of Standards and Science, Daejeon, Republic of Korea.
Seong-Min
SM
Hwang
Berkeley Preclinical Imaging Core (BPIC) Facility, University of California, Berkeley, California, USA.
Michael
M
Wendland
Department of Physics, University of California, Berkeley, California, USA.|State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences (CAS), Shanghai, China.|CAS Center for ExcelleNce in Superconducting Electronics (CENSE), Shanghai, China.
Lixing
L
You
Department of Physics, University of California, Berkeley, California, USA.
John
J
Clarke
Henry H. Wheeler, Jr. Brain Imaging Center (BIC), University of California, Berkeley, California, USA.
Ben
B
Inglis
D000818:Animals; D001921:Brain / Q000000981:diagnostic imaging*; D004867:Equipment Design; D066128:Gray Matter / Q000000981:diagnostic imaging; D007091:Image Processing, Computer-Assisted; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging; D011789:Quantum Theory; D013552:Swine; D066127:White Matter / Q000000981:diagnostic imaging
SQUID; T1; T1ρ; dispersion; spin locking; ultralow field