Analytical modeling of harmonically driven focused acoustic sources with experimental verification. 

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Applied Acoustics, 2024;221,1-19:

T. Zawada, T. Bove. 

https://www.sciencedirect.com/science/article/abs/pii/S0003682X24001403

Abstract: 

Recently, a high intensity focused ultrasound (HIFU) is drawing a lot of attention from medical and non-medical fields due to its potential for extreme high pressure levels as well as ultra high spatial resolution. At the heart of every HIFU system is a focused ultrasound transducer, and its electrical and acoustic properties play a key role. During the transducer design phase, it is important to quickly obtain the electrical and acoustic parameters corresponding to the transducer structure. Currently, researchers mainly use finite element methods for simulation, but by doing so they lose the deeper insight into the key aspects of the complex electro-acoustic interaction between the transducer, the electric matching network and the front and back acoustic load. A theoretical model based on the Krimholtz-Leedom-Matthaei (KLM) approach of a focused acoustic source is presented. The model includes the impact of the dielectric and mechanical losses and allows for evaluation of the performance of the transducer in terms of electro-acoustic efficiency. The theoretical performance and the impact of the included loss mechanisms on it is calculated up to 9th harmonic resonance frequency. The model is verified using test transducers operating at 4 MHz (fundamental), 12 MHz (3rd harmonic) and 20 MHz (5th harmonic) resonance frequencies. Both the predicted input impedance and predicted electro-acoustic efficiency exhibit very good agreement with the experimental data. An effective material and device parameter identification method based on multi-dimensional minimization algorithm is presented, as well. The results can be directly applied to optimization and development of high-frequency focused acoustic sources taking advantage of the high focusing gain and very high spatial resolution. 

High‐intensity focused ultrasound: safety and efficacy of a novel treatment modality for neurofibromatosis type 1 cutaneous neurofibroma.

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JEADV Clin Pract. 2024;1–12: 

Peltonen S, Serup J, Tang M, Gillstedt M, Kantere D, Neittaanmäki N,et al.

https://onlinelibrary.wiley.com/doi/10.1002/jvc2.398

Abstract: 

Background: 

High-intensity focused ultrasound (HIFU) is widely used in the treatment of deep tumours, but clinical trials on skin tumours are not yet available. Neurofibromatosis Type I (NF1) is among the most common single-gene inherited conditions worldwide and predisposes to benign and malignant neoplasms of the nervous system. Multiple cutaneous neurofibromas (cNFs) often cause social and functional limitations, itching and pain. 

Objectives: 

The objective of this study was to investigate the safety, local tolerability and efficacy of a novel method utilizing HIFU for the treatment of cNFs. 

Methods: 

A 20 MHz HIFU-device with an integrated dermoscopic guidance and a handpiece with a focus depth of 2.3 mm below the skin surface was used. Doses of acoustic energy with 0.7 J/dose and pulse duration of 250 ms/dose were manually positioned with 1–2 mm distance between each applied dose. Number of applied doses depended on the size of the cNF. No anaesthetic was applied. 

Results: 

Twenty patients with NF1 were recruited in two centres, and 147 cNFs were treated. There were no serious adverse events. Immediate and transient wheal-and-flare reactions occurred at treatment sites and occasionally there was minor epidermal damage which healed in 1–2 weeks. Dyspigmentation occurred in some tumours after 3–9 months but no scarring was observed at 9-month follow-up. During treatment, the patient-reported pain-score median was 3.5 (range 1–7) on a 0–10-point scale. Clinical rating of cNFs after 9 months showed 48.9% full or major tumour reduction. The median reduction in tumour thickness measured by ultrasound at 9 months was 0.53 mm (range: –100% to +19%). 

Conclusions: 

HIFU treatment is a new noninvasive, rapid and tolerable treatment modality that with high precision targets intradermal lesions. This study demonstrates acceptable safety, local tolerance and efficacy of HIFU for the treatment of cNFs that may further be developed also for other skin tumours.