title: Design of a low power hybrid HIFU applicator for haemostasis based on acoustic propagation modelling.
abstract: OBJECTIVE
  The aim of this study was to design an applicator for haemostasis usage needing lower acoustic intensities (<880 W/cm(2)) than in previous devices intended for it, which is based on ultrasound propagation FEM modelling using a 2-MHz HIFU transducer.
  
  
  METHODS
  Acoustic field characterisation and numerical simulations in water were performed with and without the proposed applicator. Parameters such as form factor, ellipsoidal shape ratio, and Euclidean distance were used (among others) to compare simulated data with transducer measurements without applicator. A low density polyethylene cone was manufactured from geometries validated from acoustic field modelling. The hollow cone was filled with 10% polyacrylamide gel as a coupling medium with liver phantom or chicken liver. Focal temperature was measured with a thermocouple embedded in the phantom for 1-20 W driving powers for 120 s. Standing wave ratios (SWR) were used as coupling indexes. Ex vivo experimentation in chicken liver was made at 10-20 W.
  
  
  RESULTS
  Simulated acoustic patterns showed good concordance with measurements. Experimental focal distance was 20.72 ± 0.24 mm, while the simulated was 19.79 mm (≈4% error). SWR at low power were: 2.01 with transducer emitting in air, 1.53 at applicator tip, and 1.35 after phantom placement. Average SWR at high power was 1.31. Similarity of percentages for data comparison in focal plane was over 60%. Maximum temperature measured at focus was 88.7 °C with 20 W after 85 s.
  
  
  CONCLUSIONS
  Temperatures reached at focus suggest that this applicator has good efficiency, which notably reduces the power typically needed for haemostasis effect.
authors.affiliation: a Department of Electrical Engineering , Bioelectronics Section, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional , Cinvestav , Mexico City , Mexico , and.
authors.forename: Raquel
authors.initials: R
authors.lastname: Martínez-Valdez
authors.affiliation: b R&D Group 'Sistemas y Tecnologías Ultrasónicas', Instituto de Tecnologías Físicas y de la Información , CSIC , Madrid , Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Ramos Fernández
authors.affiliation: a Department of Electrical Engineering , Bioelectronics Section, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional , Cinvestav , Mexico City , Mexico , and.
authors.forename: Arturo
authors.initials: A
authors.lastname: Vera Hernandez
authors.affiliation: a Department of Electrical Engineering , Bioelectronics Section, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional , Cinvestav , Mexico City , Mexico , and.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Leija Salas
mesh_terms: D000162:Acoustics; D000818:Animals; D002645:Chickens; D004867:Equipment Design; D020342:Finite Element Analysis; D006487:Hemostasis; D057086:High-Intensity Focused Ultrasound Ablation / Q000295:instrumentation*; D008099:Liver; D008962:Models, Theoretical; D020959:Polyethylene; D014159:Transducers
chemical_list: D020959:Polyethylene
keywords: Acoustic haemostasis; HIFU haemostasis; acoustic propagation modelling; finite element method; surgical haemostasis