Design of a low power hybrid HIFU applicator for haemostasis based on acoustic propagation modelling

Abstract

Purpose: The aim of this study was to design an applicator for haemostasis usage needing lower acoustic intensities (<880 W/cm²) than in previous devices intended for it, which is based on ultrasound propagation FEM modelling using a 2-MHz HIFU transducer. Materials and 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.

• Acoustic haemostasis
• acoustic propagation modelling
• finite element method
• HIFU haemostasis
• surgical haemostasis

Acknowledgements

The authors acknowledge the CINVESTAV-IPN for all the facilities given to develop this work and the invaluable assistance of José Hugo Zepeda Peralta and Rubén Pérez Valladares during the experimentation stages.

Declaration of interest

R.M.V. acknowledges CONACYT (Mexico) for fellowship number 219341 and the ‘Ultrasonic Systems and Technologies Laboratories (ITEFI-CSIC)’ for a scientific stay in Madrid related to this work. The authors acknowledge the funding given by the ECOS-ANUIES-CONACYT M10-S02 programme, the CONACYT-F-SALUD 201590 project, CONACYT-F-SALUD 201256 and the Joint Cooperation Fund Mexico–Uruguay (SRE-AUCI) 2012–2013. The authors alone are responsible for the content and writing of the paper.