title: Alternating steady state free precession for estimation of current-induced magnetic flux density: A feasibility study.
abstract: OBJECTIVE
  To develop a novel, current-controlled alternating steady-state free precession (SSFP)-based conductivity imaging method and corresponding MR signal models to estimate current-induced magnetic flux density (Bz ) and conductivity distribution.
  
  
  METHODS
  In the proposed method, an SSFP pulse sequence, which is in sync with alternating current pulses, produces dual oscillating steady states while yielding nonlinear relation between signal phase and Bz . A ratiometric signal model between the states was analytically derived using the Bloch equation, wherein Bz was estimated by solving a nonlinear inverse problem for conductivity estimation. A theoretical analysis on the signal-to-noise ratio of Bz was given. Numerical and experimental studies were performed using SSFP-FID and SSFP-ECHO with current pulses positioned either before or after signal encoding to investigate the feasibility of the proposed method in conductivity estimation.
  
  
  RESULTS
  Given all SSFP variants herein, SSFP-FID with alternating current pulses applied before signal encoding exhibits the highest Bz signal-to-noise ratio and conductivity contrast. Additionally, compared with conventional conductivity imaging, the proposed method benefits from rapid SSFP acquisition without apparent loss of conductivity contrast.
  
  
  CONCLUSIONS
  We successfully demonstrated the feasibility of the proposed method in estimating current-induced Bz and conductivity distribution. It can be a promising, rapid imaging strategy for quantitative conductivity imaging.
authors.affiliation: Center for Neuroscience Imaging Research, Institute for Basic Science (IBS), Sungkyunkwan University, Suwon, Republic of Korea.
authors.forename: Hyunyeol
authors.initials: H
authors.lastname: Lee
authors.affiliation: Department of Biomedical Engineering, Kyung Hee University, Yongin, Republic of Korea.
authors.forename: Woo Chul
authors.initials: WC
authors.lastname: Jeong
authors.affiliation: Department of Biomedical Engineering, Kyung Hee University, Yongin, Republic of Korea.
authors.forename: Hyung Joong
authors.initials: HJ
authors.lastname: Kim
authors.affiliation: Department of Biomedical Engineering, Kyung Hee University, Yongin, Republic of Korea.
authors.forename: Eung Je
authors.initials: EJ
authors.lastname: Woo
authors.affiliation: Department of Global Biomedical Engineering, Biomedical Imaging and Engineering Lab., Sungkyunkwan University, Suwon, Republic of Korea.
authors.forename: Jaeseok
authors.initials: J
authors.lastname: Park
mesh_terms: D000465:Algorithms; D004553:Electric Conductivity; D005240:Feasibility Studies; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging; D017711:Nonlinear Dynamics; D009991:Oscillometry; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D059629:Signal-To-Noise Ratio
keywords: alternating steady-state free precession; conductivity; magnetic resonance imaging; steady-state free precession