title: Optically controlled switch-mode current-source amplifiers for on-coil implementation in high-field parallel transmission.
abstract: We tested the feasibility of implementing parallel transmission (pTX) for high-field MRI using a radiofrequency (RF) amplifier design to be located on or in the immediate vicinity of an RF transmit coil.
  
  
  
  We designed a current-source switch-mode amplifier based on miniaturized, nonmagnetic electronics. Optical RF carrier and envelope signals to control the amplifier were derived, through a custom-built interface, from the RF source accessible in the scanner control. Amplifier performance was tested by benchtop measurements as well as with imaging at 7T (300 MHz) and 11.7 T (500 MHz). The ability to perform pTX was evaluated by measuring interchannel coupling and phase adjustment in a two-channel setup.
  
  
  
  The amplifier delivered in excess of 44 W RF power and caused minimal interference with MRI. The interface derived accurate optical control signals with carrier frequencies ranging from 64 to 750 MHz. Decoupling better than 14 dB was obtained between two coil loops separated by only 1 cm. Application to MRI was demonstrated by acquiring artifact-free images at 7 T and 11.7 T.
  
  
  
  We propose an optically controlled miniaturized RF amplifier for on-coil implementation at high fields that should facilitate implementation of high-density pTX arrays. Magn Reson Med 76:340-349, 2016. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.
authors.affiliation: Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Natalia
authors.initials: N
authors.lastname: Gudino
authors.affiliation: Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Qi
authors.initials: Q
authors.lastname: Duan
authors.affiliation: Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Jacco A
authors.initials: JA
authors.lastname: de Zwart
authors.affiliation: Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Joe
authors.initials: J
authors.lastname: Murphy-Boesch
authors.affiliation: Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Dodd
authors.affiliation: Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Hellmut
authors.initials: H
authors.lastname: Merkle
authors.affiliation: Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: van Gelderen
authors.affiliation: Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Jeff H
authors.initials: JH
authors.lastname: Duyn
mesh_terms: D000669:Amplifiers, Electronic; D004582:Electronics, Medical / Q000295:instrumentation; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005240:Feasibility Studies; D007089:Image Enhancement / Q000295:instrumentation*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D008280:Magnetics / Q000295:instrumentation*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*; D014159:Transducers
keywords: RF amplifiers; high-field MRI; parallel transmission