High‐frequency (20 MHz) high‐intensity focused ultrasound system for dermal intervention: A 12‐week local tolerance study in minipigs

Abstract

Background High‐intensity focused ultrasound (HIFU) operating at 20 MHz is new and applicable to skin. Details of use and instrumentation are not documented. Materials and Methods A GLP compliant 12‐week study of Göttingen minipigs (n = 3) was undertaken. Effects of HIFU treatment at different focal depths, energy levels and field size (single shot vs 5 × 5 multiple shots) were studied. Clinical scoring and histology of treated sites were made. Results High‐intensity focused ultrasound showed instant and initial effects with wheal and flare responses followed by delayed inflammatory reactions associated with outer skin necrosis, depending on energy dose. HIFU treatment was tunable in the range 0.3‐1.5 J, ablative at higher energy level. Transducers with deeper focal points gave more profound effects, while epidermal effects were comparable. Multiple doses of 5 × 5 shots produced stronger reactions than single dose indicating that nearby applied shots were synergistic. Recovery from single doses was faster than in multidose areas. Clinical scarring at the end point was not seen despite occasional fibrous change of dermis. Findings illustrated intended therapeutic use; no special safety issues of concern were raised. Conclusion The new 20 MHz HIFU was reproducible, tunable and produced targeted effects in the outer skin, for example instant wheal and flare followed by inflammation and possibly necrosis depending on energy setting. Reactions recovered during the study with only minor findings at study end. No special safety concerns were raised. The method can be controlled and modulated, and it is ready for clinical testing of dermatological disease indications including conditions presently treated with lasers.