## 2 Mechanism of Action  
Most High-Intensity Focused Ultrasound (HIFU) machines operate by delivering high energy levels, typically between 100 and 10,000 W/cm\({}^{2}\) (ISA), in the form of mechanical vibrations to heat targeted tissue. This process induces coagulative necrosis, leading to skin rejuvenation and tightening effects [32]. The high-density energy rapidly raises the temperature of the targeted tissue to 95-98 \({}^{\circ}\)C, causing localized necrosis. Large-aperture transducers, nonlinear wave propagation, and phased array applications help achieve these high intensities. In conventional HIFU systems, frequencies range from 0.8 to 5 MHz, producing ultrasound wavelengths in soft tissue of approximately 2-0.3 mm [33]. HIFU machines are designed with specific components to deliver precise, high-energy ultrasound treatments. At the core is a transducer that converts electrical energy into high-frequency ultrasound waves, focusing them at specific points. Methods such as geometric focusing, where the concave surface of a transducer directs waves to converge at a focal point, are often used. An acoustic lens may also be mounted on the transducer to adjust its shape in a process called \"bellying,\" further focusing ultrasound beams. Additionally, electronic focusing with phased array transducers composed of multiple piezoelectric elements allows axial or lateral focusing without moving the transducer. Modern HIFU systems also include essential safety features like temperature sensors, feedback controls, and automatic shut-off mechanisms to protect patients from overheating or unintended damage. Together, these components enable HIFU machines to safely deliver non-invasive treatments for both medical and aesthetic applications. To prevent skin burns and protect nearby tissues, the More Young HIFU device is equipped with cooling systems that regulate surface temperatures, allowing ultrasound energy to penetrate deeper tissue layers safely. Many HIFU devices are also equipped with real-time imaging to guide treatment and visualize tissue targeting before or during sonication--an essential feature for medical applications requiring high precision. The onboard software control unit manages parameters such as ultrasound intensity, frequency, focal depth, and treatment duration, allowing operators to adjust settings in real time based on their observations. The machine's handheld applicator, which houses the transducer, is operated by a clinician to target-specific areas precisely. The power supply generates the electrical energy needed to create ultrasound waves, typically adjusting wattage based on whether the application is aesthetic (lower output) or therapeutic (higher output). Depth and focal size vary according to the targeted tissue layer, with different cartridges used to match the specific treatment type. Enhancing HIFU machine efficacy involves optimizing precision, efficiency, safety, and usability to achieve optimal clinical outcomes. The More Young HIFU device employs high-quality piezoelectric materials and advanced phased array capabilities in its transducers, improving energy efficiency and allowing precise targeting for a wide range of treatment areas. These advancements facilitate dynamic focal point adjustment, offering high-resolution targeting for both shallow and deep tissue, increasing treatment flexibility while minimizing off-target effects. Optimized energy delivery algorithms combined with adjustable pulse modulation enhance power distribution and manage heat buildup to ensure efficient coagulation. Cartridges of varying depths and angles provide a comprehensive range of penetration options, enabling uniform energy delivery even in complex treatment areas. Thermal Control Points (TCPs) are crucial for guiding and tracking the precise application of ultrasound energy in HIFU devices. In the More Young HIFU machine, TCPs define focal point location, energy distribution, and treatment depth, ensuring consistent energy delivery with minimal impact on surrounding tissues.