title: Development and optimization of hardware for delta relaxation enhanced MRI.
abstract: OBJECTIVE
  Delta relaxation enhanced magnetic resonance (dreMR) imaging requires an auxiliary B0 electromagnet capable of shifting the main magnetic field within a clinical 1.5 Tesla (T) MR system. In this work, the main causes of interaction between an actively shielded, insertable resistive B0 electromagnet and a 1.5T superconducting system are systematically identified and mitigated.
  
  
  METHODS
  The effects of nonideal fabrication of the field-shifting magnet are taken into consideration through careful measurement during winding and improved accuracy in the design of the associated active shield. The shielding performance of the resultant electromagnet is compared against a previously built system in which the shield design was based on an ideal primary coil model. Hardware and software approaches implemented to eliminate residual image artifacts are presented in detail.
  
  
  RESULTS
  The eddy currents produced by the newly constructed dreMR system are shown to have a significantly smaller "long-time-constant" component, consistent with the hypothesis that less energy is deposited into the cryostat of the MR system.
  
  
  CONCLUSIONS
  With active compensation, the dreMR imaging system is capable of 0.22T field shifts within a clinical 1.5T MRI with no significant residual eddy-current fields.
authors.affiliation: Physics and Astronomy, Western University, London, Ontario, Canada.
authors.forename: Chad T
authors.initials: CT
authors.lastname: Harris
authors.forename: William B
authors.initials: WB
authors.lastname: Handler
authors.forename: Yonathan
authors.initials: Y
authors.lastname: Araya
authors.forename: Francisco
authors.initials: F
authors.lastname: Martínez-Santiesteban
authors.forename: Jamu K
authors.initials: JK
authors.lastname: Alford
authors.forename: Brian
authors.initials: B
authors.lastname: Dalrymple
authors.forename: Frank
authors.initials: F
authors.lastname: Van Sas
authors.forename: Blaine A
authors.initials: BA
authors.lastname: Chronik
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Scholl
mesh_terms: D016477:Artifacts; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007089:Image Enhancement / Q000295:instrumentation*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D008280:Magnetics / Q000295:instrumentation*; D059346:Magnets; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014159:Transducers
keywords: MRI; coil; molecular imaging; relaxation, eddy-current