## 1 Introduction
The control panel on the handpiece includes buttons labeled \(\mathbf{A}\) (amplitude control) and \(\mathbf{T}\) (treatment mode selection) that allow the clinician to adjust energy intensity and mode during treatment. This controlled micro-damage stimulates a healing response, which gradually thickens and shortens collagen fibers, increasing tissue tension due to collagen's elastic properties, ultimately leading to skin tightening [24]. The High-Intensity Focused Ultrasound (HIFU) machine incorporates several core features designed to deliver targeted ultrasound waves effectively. The transducer, considered the heart of any ultrasound machine, converts electrical energy into high-frequency sound waves and focuses them with precision. An acoustic lens may be used to further concentrate the waves, while a cooling system, typically water or gel, protects the skin from burns and shields surrounding tissues [25]. Many HIFU machines also offer real-time imaging, enabling clinicians to visualize the sonication area, which is particularly valuable for tasks such as tumor ablation. Key parameters, including ultrasound intensity, frequency, focal depth, and treatment duration, can be adjusted in real time through the control unit and graphical user interface (GUI) [26; 27; 28]. The handheld applicator, equipped with a transducer, allows clinicians to direct ultrasound energy to specific treatment areas. Powered by a 208-volt supply, the applicator can support multiple cartridges to adjust penetration depth as required. Built-in safety features, such as temperature sensors and automatic shut-offs, enhance patient comfort and ensure safe, non-ablative treatments across various applications [29]. In our previous research and clinical observations, we identified specific limitations in existing HIFU platforms, including insufficient focal control, lack of real-time feedback, and inconsistent energy delivery. Motivated by these findings, we aimed to develop a modified HIFU platform--\"More Young\"--with integrated improvements in safety and performance. This study builds upon our ongoing work in energy-based dermatologic devices and introduces technical enhancements such as additional safety checkpoints, adaptive energy modulation, and machine-learning-guided precision targeting. Another significant challenge with HIFU equipment is maintaining accuracy when targeting deep, hard-to-access, or moving tissues. Challenges include difficulty in sustaining a stable focal point, limitations in real-time tracking of tissue movement, and risk of skin burns [30]. Inconsistent energy delivery can lead to uneven treatment, and limited penetration depth may restrict HIFU's effective range [31]. Additionally, patient discomfort due to prolonged treatment times, noise, and vibration can make anesthesia necessary, particularly for aesthetic procedures. In this study, we considered the challenges with HIFU technology in skin rejuvenation and aimed to enhance its performance. The objective of this study is to assess the clinical efficacy and safety of the More Young HIFU device--an advanced ultrasound-based therapeutic platform currently under investigation at the Department of Life and Biomedical Sciences, Beijing University of Engineering--in comparison to the widely used 7D HIFU system through a randomized clinical trial. The main aim is to determine whether these enhancements translate into a superior aesthetic outcomes and patient satisfaction. Key modifications include the integration of additional stabilization checkpoints--referred to as \"stuck points\"--designed to ensure safer and more controlled energy delivery, reducing the risk of overheating or damage to surrounding tissues. In addition to this safety enhancement, the device has been optimized for improved focal depth control, adaptive energy modulation based on tissue feedback, and real-time thermal monitoring. These refinements aim to increase treatment accuracy, minimize patient discomfort, and improve clinical outcomes in non-invasive facial rejuvenation.