# 📖 **Chapter 4.1 Principles of HIFU (High-Intensity Focused Ultrasound)** --- ## 1. Introduction High-Intensity Focused Ultrasound (HIFU) is a **non-invasive lifting technology** that delivers focused acoustic energy into **dermis, subcutaneous tissue, and SMAS (Superficial Musculoaponeurotic System)**. Unlike RF (which heats tissue broadly), HIFU creates **precise focal thermal injury points** (thermal coagulation points, TCPs) without damaging the epidermis. --- ## 2. Physics of HIFU - **Frequency range**: 4–10 MHz (for aesthetic use). - **Focal depth**: controlled by cartridge (1.5 mm, 3.0 mm, 4.5 mm, and deeper for body). - **Energy delivery**: - Ultrasound waves converge at a focal point. - Tissue temperature rises rapidly (60–70°C). - Duration: microseconds. - **Effect**: - Instantaneous coagulative necrosis in ~1 mm³ focal zone. - Surrounding tissue preserved. --- ## 3. Biological Mechanism 1. **Immediate Phase** - Collagen fibril contraction from heat-induced denaturation. - Subtle tightening effect. 2. **Delayed Phase (3–6 months)** - Fibroblast stimulation → new collagen (types I & III). - Elastogenesis, angiogenesis. - Thickening of dermis, improved elasticity. 3. **Long-Term Remodeling** - Reorganization of SMAS and connective tissue. - Visible lifting of brows, jawline, neck. --- ## 4. Depth-Specific Targets - **1.5 mm cartridge** → Superficial dermis (fine wrinkles, periorbital). - **3.0 mm cartridge** → Deep dermis (skin tightening, midface). - **4.5 mm cartridge** → SMAS (true lifting, jawline, submental). - **6–9 mm (body cartridges)** → Subcutaneous fat (abdominal, thigh, arm contouring). --- ## 5. Treatment Advantages - Non-invasive, no downtime. - Precise energy deposition (layer-specific). - Safe for all skin types (not chromophore-dependent). - Long-lasting effect (9–18 months). --- ## 6. Limitations - Pain during procedure (requires analgesia, sometimes nerve blocks). - Results less dramatic than surgery. - Less effective for severe laxity or very heavy subcutaneous fat. - Operator-dependent (proper cartridge depth and pattern crucial). --- ## 7. Comparison with RF |Feature|RF|HIFU| |---|---|---| |**Energy source**|Electrical current|Ultrasound| |**Depth**|Dermis (2–4 mm)|Dermis + SMAS (1.5–4.5 mm)| |**Heat distribution**|Diffuse, volumetric|Focal TCPs| |**Target**|Collagen remodeling|Collagen + SMAS tightening| |**Skin type safety**|All|All| |**Discomfort**|Mild–moderate|Moderate–severe| --- ## 8. Clinical Pearls - HIFU is the **only non-invasive modality** that reaches the **SMAS** (similar target layer as surgical facelift). - Optimal for **patients in their 30s–50s** with mild-to-moderate laxity. - Combination therapy (HIFU + RF + fillers/threads) provides layered rejuvenation. - Counseling is critical: results are **gradual, not immediate**, with peak at 3–6 months. --- ## 📌 정리 - **울쎄라 (Ultherapy)** - 미국 장비 (Ulthera사, Merz 소속) - 최초 FDA 승인 HIFU 리프팅 장비 - 강점: 가장 많은 임상 연구, 글로벌 스탠다드, 안전성 검증 - 단점: 시술 통증이 비교적 강하고, 비용이 높음 - **슈링크 (Shurink, Shurink Universe)** - 한국 장비 (Classys社) - 울쎄라와 동일한 HIFU 원리 사용 - 강점: 통증 완화, 빠른 시술 속도, 비용 효율적, 다양한 카트리지 보유 (얼굴 + 바디) - 단점: 울쎄라만큼 대규모 해외 임상 데이터는 부족