Definition
HIFU utilizes three interchangeable cartridges, each focused at a different anatomical depth (1.5mm, 3mm, 4.5mm), enabling precise multi-layer targeting of skin layers. Each depth creates thermal coagulation points (TCP) at a specific level, stimulating targeted collagen and producing distinct clinical effects. The ideal complete protocol uses all three depths in succession (1.5mm then 3mm then 4.5mm), creating a continuum of TCP from surface to depth, optimizing global facial lift results.
The Three HIFU Depths: Characteristics and Applications
Detailed depth cartridge comparison
| depth | target_tissue | cartridge_name | tcp_formation | collagen_stimulation | clinical_goal | expected_improvement | pain_profile | anesthesia_required | downtime | sessions_number | patient_selection |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1.5mm | Deep epidermis, epidermal-dermal junction | 1.5mm Cartridge | Superficial TCP in granular/basal epidermal layer | Fine fibrillar epidermal collagen, basal fibers | Skin texture, fine wrinkle smoothing, clarity, luminosity, superficial resurfacing | 30-50% reduction in fine wrinkles, pore size improvement | Very high (high epidermal innervation). Intense burning sensation, stinging. Generally intolerable without anesthesia. | Yes, anesthetic cream for 30 minutes or lidocaine injection recommended | Minimal (erythema 24-48 hours) | Generally 1-2 sessions, sufficient standalone or combined with 3mm | Perfectionist patients regarding texture; young patients (<40 years) with fine superficial wrinkles; oily skin prone to acne (pore refinement) |
| 3mm | Mid to deep reticular dermis (primary collagen zone) | 3mm Cartridge (STANDARD BASELINE) | TCP in reticular dermis, prime collagen zone | Type I/III collagen in main dermis, elastin fibers | General tightening, wrinkle volume improvement, dermal density, skin thickness | 50-70% reduction in moderate wrinkles, tightness improvement 40-60% | Moderate-high (sensation of deep heat, dull pain). Tolerable without anesthesia for most patients | Not mandatory (topical anesthesia may suffice), but can be used for comfort | Minimal (erythema, possible edema 4-24 hours) | Generally 1-2 sessions (sometimes 3 for major laxity) | Majority of patients ("workhorse" cartridge). Moderate laxity, moderate wrinkles, general texture improvement desired |
| 4.5mm | SMAS (Superficial Musculoaponeurotic System), deep dermis, superficial fat pad | 4.5mm Cartridge (STRUCTURAL LIFTING) | Deep TCP at SMAS level, just above muscular layer | SMAS collagen (robust type I), direct muscle contraction, adipocyte in SMAS region | Structural facial lifting, jawline redefinition, jowl elimination, neck tightening, direct SMAS contraction | 60-80% structural lifting, jowl elimination 70-85%, mandibular angle improvement, facial oval redefinition | Moderate (sensation of deep vibration, mild discomfort). Tolerable, less intense than 1.5mm | Not mandatory for most (lidocaine may diminish desirable sensory sensation during lifting) | Minimal (slight erythema possible, generally very minimal) | Generally 1 session sufficient (sometimes 2 for severe SMAS laxity) | Patients with jowls/mandibular ptosis/neck laxity, seeking structural lifting, moderate-severe facial laxity |
Clinical Protocols: Depth Sequencing
STANDARD COMPLETE PROTOCOL (Recommended for majority of patients):
3MM CARTRIDGE FIRST ("BASE"):
- Reason: primary dermal collagen zone, baseline effect for global tightening
- Baseline establishes fundamental texture/tone improvement
- Duration: ~20-30 minutes per zone (full face)
- TCP density: 100-150 TCP per facial side (cheek/jawline)
- 1-2 passes (2 passes optimal for complete coverage)
THEN 1.5MM CARTRIDGE ("TEXTURE"):
- Reason: adds texture smoothing, pore refinement, clarity
- Applied AFTER 3mm because of very high pain; if first, patient cumulative pain becomes intolerable
- Duration: ~10-15 minutes per zone
- TCP density: 50-100 TCP full face (selective: focus cheekbones, forehead)
- 1 pass generally sufficient
THEN 4.5MM CARTRIDGE ("STRUCTURAL LIFT"):
- Reason: final SMAS structural lifting, contour redefinition
- Applied last because of moderate pain but final lifting importance
- Focus zones: mandibular, neck (SMAS critical areas)
- Duration: ~15-20 minutes per jawline/neck
- TCP density: 80-120 TCP mandibular/neck (less forehead/temple where SMAS less prominent)
- 1-2 passes per zone
TOTAL PROTOCOL TIME: ~60-90 minutes per treatment
ALTERNATIVE SELECTIVE PROTOCOL (according to indication):
For Fine Wrinkles Only (no major laxity): 1.5mm + 3mm (skip 4.5mm)
For Jowls Only: 4.5mm + 3mm (skip 1.5mm)
For Complete Lifting (Normative approach): 3mm + 4.5mm + 1.5mm (as standard)
SESSION FREQUENCY:
- 1.5mm + 3mm: 1-2 sessions spaced 4-8 weeks
- 4.5mm: 1-2 sessions spaced 4-8 weeks (or combined with 3mm in same session)
- Complete protocol: 1-3 complete sessions over 2-6 month period
TOUCH-UPS/MAINTENANCE:
- After initial protocol, annual touch-up 1 session (generally 3mm+4.5mm) recommended
- Or "touch-up" 1.5mm+3mm at 6-9 months for texture maintenance
Frequently Asked Questions
Ideally, the complete three-depth protocol offers best results (70-80% combined improvement). But you can adapt: if fine wrinkles only, 1.5mm+3mm suffice. If jowls only, 4.5mm+3mm are priority. With budget/pain constraints, 3mm alone is acceptable baseline (50-60% improvement). Consult your practitioner for personalized selection.
Because the epidermis is highly innervated (extreme tactile sensation). The 1.5mm depth creates TCP very close to dense cutaneous nerves. Intense burning pain results. Cartridges at 3-4.5mm are deeper with less local innervation, making pain more tolerable. This is why the 3mm→1.5mm sequence is recommended (cumulative pain remains tolerable).
Yes, 4.5mm targeting of SMAS creates significant structural lifting. Efficacy of 70-85% jowl reduction is observable. But it depends on baseline severity: light jowls → near-complete elimination possible. Very severe jowls → significant improvement but may have slight residual jowling. Realistic expectations are important; 4.5mm is powerful but not magical for extreme laxity.
The 4.5mm cartridge is focused at SMAS level. The 4.5mm depth corresponds anatomically to the SMAS plane just above the muscular layer. The 3mm cartridge reaches the deep dermis-superficial SMAS interface (slight SMAS effect). The 1.5mm cartridge does not reach SMAS (epidermis only). Therefore: 4.5mm = direct SMAS target, 3mm = indirect SMAS, 1.5mm = no SMAS effect.
Generally not simultaneously. HIFU creates thermal trauma; adding laser/RF at the same depths risks cumulative burn. But spaced 1-2 weeks apart: HIFU week 1, laser week 3 is acceptable (sufficient recovery). Consult your practitioner for safe combined protocol.
1 pass = 50-60% zone coverage with moderate TCP density. 2 passes = 90-95% coverage with optimal TCP density for maximal collagenesis. 2 passes recommended for weak zones (cheek ptosis, mandible), 1 pass for zones with good support (forehead). With budget/time constraints, 1 pass is acceptable for moderate results.
Sources scientifiques
- Park H et al.. HIFU for Treatment of Wrinkles in Seven Facial Areas. Ann Dermatol (2015) ;27 (6) :688-693 . PMID: 26719637
- MacGregor JL, Tanzi EL. Microfocused ultrasound for noninvasive skin tightening. Semin Cutan Med Surg (2013) ;32 (1) :18-24 . PMID: 24049918
- Fabi SG. Noninvasive skin tightening: focus on new ultrasound techniques. Clin Cosmet Investig Dermatol (2015) ;8 :47-52 . PMID: 25653545
- Haykal D et al.. Systematic Review of HIFU in Skin Tightening. Aesthet Surg J (2025) ;45 (7) :690 . PMID: 40184185
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