title: Multi-turn transmit coil to increase b1 efficiency in current source amplification.
abstract: OBJECTIVE
  A multi-turn transmit surface coil design was presented to improve B1 efficiency when used with current source amplification.
  
  
  METHODS
  Three different coil designs driven by an on-coil current-mode class-D amplifier with current envelope feedback were tested on the benchtop and through imaging in a 1.5 T scanner. Case temperature of the power field-effect transistor at the amplifier output stage was measured to evaluate heat dissipation for the different current levels and coil configurations. In addition, a lower power rated device was tested to exploit the potential gain in B1 obtained with the multi-turn coil.
  
  
  RESULTS
  As shown both on the benchtop and in a 1.5 T scanner, B1 was increased by almost 3-fold without increasing heat dissipation on the power device at the amplifier's output using a multi-turn surface coil. Similar gain was obtained when connecting a lower power rated field-effect transistor to the multi-turn coil.
  
  
  CONCLUSIONS
  In addition to reduce heat dissipation per B1 in the device, higher B1 per current efficiency allows the use of field-effect transistors with lower current ratings and lower port capacitances, which could improve the overall performance of the on-coil current source transmit system.
authors: Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio 44106, USA.
authors: N
authors: N
authors: Gudino
authors: M A
authors: MA
authors: Griswold
mesh_terms: D000669:Amplifiers, Electronic; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007089:Image Enhancement / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation; D008280:Magnetics / Q000295:instrumentation*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014159:Transducers
references: Magn Reson Med. 2008 Jun;59(6):1431-9
references: 18506789
references: Magn Reson Med. 2003 Jan;49(1):144-50
references: 12509830
references: J Magn Reson Imaging. 2008 Nov;28(5):1219-25
references: 18972330
references: IEEE Trans Biomed Eng. 2012 Aug;59(8):2152-60
references: 22552545
references: Magn Reson Med. 1990 Nov;16(2):192-225
references: 2266841
references: Magn Reson Med. 2009 Jul;62(1):218-28
references: 19353658
references: Magn Reson Med. 2004 Apr;51(4):775-84
references: 15065251
references: Magn Reson Med. 2013 Jul;70(1):276-89
references: 22890962