title: Gradient-induced voltages on 12-lead ECGs during high duty-cycle MRI sequences and a method for their removal considering linear and concomitant gradient terms.
abstract: OBJECTIVE
  To restore 12-lead electrocardiographic (ECG) signal fidelity inside MRI by removing magnetic field gradient-induced voltages during high gradient duty cycle sequences.
  
  
  METHODS
  A theoretical equation was derived to provide first- and second-order electrical fields induced at individual ECG electrodes as a function of gradient fields. Experiments were performed at 3T on healthy volunteers using a customized acquisition system that captured the full amplitude and frequency response of ECGs, or a commercial recording system. The 19 equation coefficients were derived via linear regression of data from accelerated sequences and were used to compute induced voltages in real-time during full resolution sequences to remove ECG artifacts. Restored traces were evaluated relative to ones acquired without imaging.
  
  
  RESULTS
  Measured induced voltages were 0.7 V peak-to-peak during balanced steady state free precession (bSSFP) with the heart at the isocenter. Applying the equation during gradient echo sequencing, three-dimensional fast spin echo, and multislice bSSFP imaging restored nonsaturated traces and second-order concomitant terms showed larger contributions in electrodes further from the magnet isocenter. Equation coefficients are evaluated with high repeatability (ρ = 0.996) and are dependent on subject, sequence, and slice orientation.
  
  
  CONCLUSIONS
  Close agreement between theoretical and measured gradient-induced voltages allowed for real-time removal. Prospective estimation of sequence periods in which large induced voltages occur may allow hardware removal of these signals.
authors.affiliation: Department of Radiology, Brigham and Women's Hospital, Boston, Massachusetts, USA.
authors.forename: Shelley HuaLei
authors.initials: SH
authors.lastname: Zhang
authors.affiliation: Department of Engineering, University of Georgia, Athens, Georgia, USA.
authors.forename: Zion Tsz Ho
authors.initials: ZT
authors.lastname: Tse
authors.affiliation: Department of Radiology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA.
authors.forename: Charles L
authors.initials: CL
authors.lastname: Dumoulin
authors.affiliation: Department of Cardiology, Brigham and Women's Hospital, Boston, Massachusetts, USA.
authors.forename: Raymond Y
authors.initials: RY
authors.lastname: Kwong
authors.affiliation: Department of Cardiology, Brigham and Women's Hospital, Boston, Massachusetts, USA.
authors.forename: William G
authors.initials: WG
authors.lastname: Stevenson
authors.affiliation: Department of Radiology, Stanford University, Stanford, California, USA.
authors.forename: Ronald
authors.initials: R
authors.lastname: Watkins
authors.affiliation: E-TROLZ Inc, North Andover, Massachusetts, USA.
authors.forename: Jay
authors.initials: J
authors.lastname: Ward
authors.affiliation: Department of Radiology, Brigham and Women's Hospital, Boston, Massachusetts, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.affiliation: Department of Radiology, Brigham and Women's Hospital, Boston, Massachusetts, USA.
authors.forename: Ehud J
authors.initials: EJ
authors.lastname: Schmidt
mesh_terms: D000328:Adult; D000465:Algorithms; D016477:Artifacts; D055424:Cardiac-Gated Imaging Techniques; D004562:Electrocardiography; D004566:Electrodes; D064368:Healthy Volunteers; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D016014:Linear Models; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D015203:Reproducibility of Results
keywords: 12-lead ECG; Maxwell's equations; cardiac magnetic resonance imaging; gradient-induced noise; image-guided intervention