title: Automated tuning of an eight-channel cardiac transceive array at 7 tesla using piezoelectric actuators.
abstract: OBJECTIVE
  Ultra-high field (UHF) MR scanning in the body requires novel coil designs due to B1 field inhomogeneities. In the transverse electromagnetic field (TEM) design, maximum B1 transmit power can only be achieved if each individual transmit element is tuned and matched for different coil loads, which requires a considerable amount of valuable scanner time.
  
  
  METHODS
  An integrated system for autotuning a multichannel parallel transmit (pTx) cardiac TEM array was devised, using piezoelectric actuators, power monitoring equipment and control software. The reproducibility and performance of the system were tested and the power responses of the coil elements were profiled. An automated optimization method was devised and evaluated.
  
  
  RESULTS
  The time required to tune an eight-element pTx cardiac RF array was reduced from a mean of 30 min to less than 10 min with the use of this system.
  
  
  CONCLUSIONS
  Piezoelectric actuators are an attractive means of tuning RF coil arrays to yield more efficient B1 transmission into the subject. An automated mechanism for tuning these elements provides a practical solution for cardiac imaging at UHF, bringing this technology closer to clinical use.
authors.affiliation: Oxford Centre for Clinical Magnetic Resonance Research, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom.
authors.forename: Graeme A
authors.initials: GA
authors.lastname: Keith
authors.affiliation: Oxford Centre for Clinical Magnetic Resonance Research, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom.
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Rodgers
authors.affiliation: Oxford Centre for Clinical Magnetic Resonance Research, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom.
authors.forename: Aaron T
authors.initials: AT
authors.lastname: Hess
authors.affiliation: Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA.
authors.forename: Carl J
authors.initials: CJ
authors.lastname: Snyder
authors.affiliation: Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA.
authors.forename: J Thomas
authors.initials: JT
authors.lastname: Vaughan
authors.affiliation: Oxford Centre for Clinical Magnetic Resonance Research, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Robson
mesh_terms: D000465:Algorithms; D004867:Equipment Design; D064368:Healthy Volunteers; D006321:Heart / Q000033:anatomy & histology*; D006801:Humans; D007089:Image Enhancement / Q000295:instrumentation*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D015203:Reproducibility of Results
keywords: 7 Tesla; RF coil; parallel transmit; piezo-actuator; tuning; ultra-high field