title: The effect of electronically steering a phased array ultrasound transducer on near-field tissue heating.
abstract: OBJECTIVE
  This study presents the results obtained from both simulation and experimental techniques that show the effect of mechanically or electronically steering a phased array transducer on proximal tissue heating.
  
  
  METHODS
  The thermal response of a nine-position raster and a 16-mm diameter circle scanning trajectory executed through both electronic and mechanical scanning was evaluated in computer simulations and experimentally in a homogeneous tissue-mimicking phantom. Simulations were performed using power deposition maps obtained from the hybrid angular spectrum (HAS) method and applying a finite-difference approximation of the Pennes' bioheat transfer equation for the experimentally used transducer and also for a fully sampled transducer to demonstrate the effect of acoustic window, ultrasound beam overlap and grating lobe clutter on near-field heating.
  
  
  RESULTS
  Both simulation and experimental results show that electronically steering the ultrasound beam for the two trajectories using the 256-element phased array significantly increases the thermal dose deposited in the near-field tissues when compared with the same treatment executed through mechanical steering only. In addition, the individual contributions of both beam overlap and grating lobe clutter to the near-field thermal effects were determined through comparing the simulated ultrasound beam patterns and resulting temperature fields from mechanically and electronically steered trajectories using the 256-randomized element phased array transducer to an electronically steered trajectory using a fully sampled transducer with 40 401 phase-adjusted sample points.
  
  
  CONCLUSIONS
  Three distinctly different three distinctly different transducers were simulated to analyze the tradeoffs of selected transducer design parameters on near-field heating. Careful consideration of design tradeoffs and accurate patient treatment planning combined with thorough monitoring of the near-field tissue temperature will help to ensure patient safety during an MRgHIFU treatment.
authors: Utah Center for Advanced Imaging Research, Salt Lake City, UT, USA. apayne@ucair.med.utah.edu
authors: Allison
authors: A
authors: Payne
authors: Urvi
authors: U
authors: Vyas
authors: Nick
authors: N
authors: Todd
authors: Joshua
authors: J
authors: de Bever
authors: Douglas A
authors: DA
authors: Christensen
authors: Dennis L
authors: DL
authors: Parker
mesh_terms: D004867:Equipment Design; D006358:Hot Temperature; D019047:Phantoms, Imaging; D014159:Transducers; D014465:Ultrasonics / Q000295:instrumentation*