title: Simulation study of the effects of near- and far-field heating during focused ultrasound uterine fibroid ablation using an electronically focused phased array: A theoretical analysis of patient safety.
abstract: OBJECTIVE
  Assess the feasibility of using large-aperture, flat ultrasonic transducer arrays with 6500 small elements operating at 500 kHz without the use of any mechanical components for the thermal coagulation of uterine fibroids. This study examines the benefits and detriments of using a frequency that is significantly lower than that used in clinical systems (1-1.5 MHz).
  
  
  METHODS
  Ultrasound simulations were performed using the anatomies of five fibroid patients derived from 3D MRI. Using electronic steering solely, the ultrasound focus from a flat, 6500-element phased array was translated around the volume of the fibroids in various patterns to assess the feasibility of completing full treatments from fixed physical locations. Successive temperature maps were generated by numerically solving the bioheat equation. Using a thermal dose model, the bioeffects of these simulations were quantified and analyzed.
  
  
  RESULTS
  The simulations indicate that such an array could be used to perform fibroid treatments to 18 EM(43) at an average rate of 90 ± 20 cm(3)/h without physically moving the transducer array. On average, the maximum near-field thermal dose for each patient was below 4 EM(43). Fibroid tissue could be treated as close as 40 mm to the spine without reaching temperatures expected to cause pain or damage.
  
  
  CONCLUSIONS
  Fibroids were successfully targeted and treated from a single transducer position to acceptable extents and without causing damage in the near- or far-field. Compared to clinical systems, treatment rates were good. The proposed treatment paradigm is a promising alternative to existing systems and warrants further investigation.
authors.affiliation: Sunnybrook Research Institute, Toronto, Ontario M4N 3M5, Canada and Department of Medical Biophysics, University of Toronto, Toronto, Ontario M5G 1L7, Canada.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Ellens
authors.affiliation: Sunnybrook Research Institute, Toronto, Ontario M4N 3M5, Canada and Department of Medical Biophysics, University of Toronto, Toronto, Ontario M5G 1L7, Canada.
authors.forename: Kullervo
authors.initials: K
authors.lastname: Hynynen
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D004581:Electronics; D004867:Equipment Design; D005240:Feasibility Studies; D005260:Female; D057086:High-Intensity Focused Ultrasound Ablation / Q000009:adverse effects / Q000295:instrumentation* / Q000379:methods; D006358:Hot Temperature / Q000009:adverse effects; D006801:Humans; D021621:Imaging, Three-Dimensional; D007889:Leiomyoma / Q000473:pathology / Q000628:therapy*; D008279:Magnetic Resonance Imaging; D008954:Models, Biological; D061214:Patient Safety; D014465:Ultrasonics