Efficacy Assessment of the High-Frequency High-Intensity Focused Ultrasound as a New Treatment for Actinic Keratosis

High Intensity Focused Ultrasound (20 MHz) and Cryotherapy as Therapeutic Options for Granuloma Annulare and Other Inflammatory Skin Conditions

INTRODUCTION

In dermatology, inflammatory skin conditions impose a substantial burden worldwide, with existing therapies showing limited efficacy and side effects. This report aims to compare a novel immunological activation induced by hyperthermic 20 MHz high intensity focused ultrasound (HIFU) with conventional cryotherapy. The bioeffects from the two methods are initially investigated by numerical models, and subsequently compared to clinical observations after treatment of a patient with the inflammatory disease granuloma annulare (GA).

METHODS

Clinical responses to moderate energy HIFU and cryotherapy were analysed using numerical models. HIFU-induced pressure and heat transfer were calculated, and a three-layer finite element model simulated temperature distribution and necrotic volume in the skin. Model output was compared to 22 lesions treated with HIFU and 10 with cryotherapy in a patient with GA.

RESULTS

Cryotherapy produced a necrotic volume of 138.5 mm3 at - 92.7 °C. HIFU at 0.3-0.6 J/exposure and focal depths of 0.8 or 1.3 mm generated necrotic volumes up to only 15.99 mm3 at temperatures of 68.3-81.2 °C. HIFU achieved full or partial resolution in all treated areas, confirming its hyperthermic immunological activation effect, while cryotherapy also resolved lesions but led to scarring and dyspigmentation.

CONCLUSION

Hyperthermic immunological activation of 20 MHz HIFU shows promise for treating inflammatory skin conditions as exemplified by GA. Numerical models demonstrate minimal skin necrosis compared to cryotherapy. Suggested optimal HIFU parameters are 1.3 mm focal depth, 0.4-0.5 J/exposure, 1 mm spacing, and 1 mm margin. Further studies on GA and other inflammatory diseases are recommended.

Focused Ultrasound for Dermal Applications

Focused ultrasound (FUS) is emerging as one of the most promising, non-invasive treatment techniques. The advancement of transducer technology has paved the way for dermatological applications. A comprehensive review is presented for healthcare practitioners and researchers, summarizing the effect of various operational parameters on the injury zone produced by ultrasound beams for various dermatological applications, which include skin tightening, fat reduction, hyperpigmentation and cancer treatment. In this article, we aim to highlight the efficient operational parameters of FUS to enhance pain relief during surgery and its affordability for skin treatment. Finally, a prospective future technique for efficient FUS is discussed.

Head-to-Head Comparison of Acoustic Properties of Lead-Free and PZT-Based HIFU Transducers Operating at 12 MHz

A direct comparison of performance and acoustic properties of high-intensity focused ultrasonic transducers utilizing lead-free (sodium bismuth titanate-NBT) and lead-based (lead zirconate titanate-PZT) piezoceramics is discussed. All transducers operate at 12 MHz at third harmonic frequency, having an outer diameter of 20 mm, a central hole of 5 mm in diameter, and a radius of curvature of 15 mm. The electroacoustic efficiency determined by a radiation force balance is evaluated in a range of input power levels up to 15 W. Schlieren tomography as well as hydrophone measurements are used for evaluation of the acoustic field distribution. It is found that the average electroacoustic efficiency of NBT-based transducers is approximately 40%, while it is around 80% in the PZT-based devices. NBT devices show significantly higher inhomogeneity of the acoustic field under schlieren tomography compared to PZT devices. From pressure measurements in the prefocal plane, it was found that the inhomogeneity could be attributed to depoling of significant areas of the NBT piezo-component during the fabrication process. In conclusion, PZT-based devices performed significantly better than those using lead-free material. However, the NBT devices show promise for this application and their electroacoustic efficiency as well as the uniformity of the acoustic field could be improved by employing a low-temperature fabrication process or repoling after processing.

Treatment of Cutaneous Neurofibromas in Patients with Neurofibromatosis Type 1

Neurofibromatosis type 1 is a genetic disorder impacting approximately 2.5 million people worldwide, often leading to development of numerous benign yet disfiguring cutaneous neurofibromas (cNF). Removal of cNF is limited to excision or laser ablation with common post-operation complications and scarring. The current case explores a new approach to removal or reduction of cNF by a minimally invasive and pain-reduced treatment modality. A 40-year-old female patient with numerous cNF across her body underwent a single treatment using a 20 MHz dermatologically focused ultrasound device on seven selected cNF on the upper back. Each cNF was treated in a single session of 20-60 s without anesthesia due to manageable pain. Only one minimal adverse reaction in the form of dyspigmentation in a single treated tumor was noted from treatment or during the healing of a thin scab that formed on each cNF a few days after treatment. At the 12-month follow-up, four out of seven treated cNF showed full remission, two showed partial or significant reduction in tumor volume, while two did not respond to treatment. The reason for the variability is not fully understood, but speculations include difference in tissue content, e.g., due to tumor age. The method is concluded to be a promising candidate for a new safe and minimally invasive treatment that can potentially be used for single-session removal/reduction of a large number of cNF. Further research should focus on refining treatment parameters and strategies to enhance response predictability.