HIFU Focus Depths 1.5 / 3.0 / 4.5mm Explained

Depth is hardware, not a setting

A focused transducer bends sound to a point. That point sits a fixed focal distance from the cartridge face, set at manufacture, and nothing on the touch screen moves it. Raise the energy and you get a hotter spot in the same place, not a deeper one.

So the cartridge is the depth. Swap the cartridge, change the layer. That one fact explains why a HIFU console arrives with a case of transducers instead of a depth slider, and why a machine shipping only deep cartridges can never sell you a shallow treatment however the brochure reads.

Hold it next to light. Anderson and Parrish described selective photothermolysis in Science in 1983: pulsed light finds its target by absorption, so wavelength and pulse duration decide what heats and what is spared. Our note on selective photothermolysis walks through that logic. Focused ultrasound has no chromophore to chase. It selects by geometry, which is why depth occupies the slot wavelength occupies on a laser spec sheet.

The three layers a facial platform aims at

Skin is thinner than most buyers picture. The skin anatomy training material in our engineering archive puts the epidermis at roughly 0.1 to 0.4mm and the dermis at roughly 0.5 to 4mm, the dermis splitting into a papillary layer above and a reticular layer below. Collagen fibre accounts for about 80 percent of dermal fibre content there. Tightening work lives in the dermis and below it, not at the surface.

Under the dermis sits subcutaneous tissue, loose connective tissue and fat lobules, running down to the fascia. The SMAS, or superficial musculoaponeurotic system, is the fibrous sheet in that region that a surgeon lifts during a facelift.

All of it fits inside about three millimetres. Think about that the next time a supplier answers a depth question with the word "deep".

Focal distance	Layer it lands in	What treating it is meant to achieve	Where it is usually mapped
1.5mm	Superficial dermis and the subdermal layer just beneath it	Surface-level firmness and skin quality; the shallow finish pass rather than the lift	Thin-skinned areas: periorbital margins, upper lip, forehead, decolletage
3.0mm	Deep dermis and fascial tissue	Heating the collagen framework itself, prompting the wound-healing response that remodels it	Cheek, mid-face, jawline, neck
4.5mm	SMAS and the fibrous layers around it	The lift vector, contraction in the sheet a facelift pulls on	Lower face, jawline, submental area, where tissue is thick enough to carry it
6mm and deeper	Fat and deep fascia	Body contouring, not facial lifting	Abdomen, flanks, arms, thighs

Depths and layer assignments follow the published microfocused ultrasound literature cited below. The regions column reflects common practice, not a prescription.

What each focal distance is actually doing

The 1.5mm cartridge

Shallowest of the facial set. A 2021 expert consensus in the Journal of Clinical and Aesthetic Dermatology describes the 1.5mm transducer running at 10MHz into superficial dermal and subdermal layers. Across that platform the lesions it forms are roughly 1mm³ inverted cones. It is the pass that changes how skin looks up close rather than how the face hangs.

It is also the depth with the least margin for error. That same consensus warns that gel-coupling mistakes at shallow delivery can burn. Skin type matters here for a different reason than on a laser: the ultrasound does not seek pigment, but any inflammatory insult in darker phototypes carries a real risk of post-inflammatory hyperpigmentation, so screening and aftercare belong to a trained clinician, not a settings chart. Plenty of single-handle consoles cannot reach 1.5mm at all. Confirm the cartridge exists before you compare prices.

The 3.0mm cartridge

Deep dermal and fascial tissue, at 7MHz on the platform described in that consensus. The workhorse. The dermal collagen framework sits here, which is where the slow remodelling result comes from, and it is the depth most operators lean on across a full face.

The 4.5mm SMAS cartridge

At 4MHz, the 4.5mm transducer reaches the SMAS and the fibrous layers around it. A 2025 narrative review in the Journal of Cosmetic Dermatology puts the therapeutic window for microfocused ultrasound at 60 to 70 degrees Celsius, hot enough to denature collagen at the focus while the tissue above stays intact. The 4.5mm SMAS pass is what people mean when they say a HIFU lift.

One caution worth repeating to your operators. Deeper is not automatically better. The consensus documents cases of tear trough bulging, sunken cheeks and increased laxity after excessive, uncontrolled delivery into the fat layer. A 4.5mm shot into a face that has no 4.5mm target is not a strong treatment. It is the wrong treatment.

Why one treatment map will not fit two faces

Skin thickness is not a constant, and this is the part most cartridge lists quietly skip. A 2023 ultrasonographic study in Skin Research and Technology measured facial sites in detail: total skin thinnest at the lateral forehead, about 1.31mm, and thickest at the mouth corner, about 1.64mm, with dermal thickness ranging from roughly 0.98mm to 1.30mm across those same sites. Full skin and dermal thickness ran thinner in women at several sites.

Read those figures next to the cartridge numbers. At the lateral forehead, a 1.5mm focus can already sit at or past the floor of the dermis on many people. Same cartridge, same face, different region, different tissue.

Fat changes the picture again. Our archive's skin training material notes that a thicker subcutaneous layer buffers heat more effectively, so an identical shot behaves differently on a lean face than on a full one. Age compounds it. The photoaging section of that material describes dermal collagen loss, disordered elastic fibre accumulation and a thinning epidermis with flattened rete ridges. Older skin is not simply laxer. It is thinner, and thinner tissue moves every target closer to the surface.

So there is no universal treatment map. There is a starting map, adjusted per client by someone who understands the anatomy under the handpiece.

Where mapping stops being a purchase decision

Buy on depth set. Treat on judgement. Those are different jobs, and the second one is clinical.

The 2021 consensus recommends imaging to estimate SMAS depth relative to the skin surface before choosing transducers and line density, customising by weight, body mass index, age, sex and target area. Most consoles in this bracket, ours included, carry no imaging. That is a training obligation to fund rather than a detail to bury: an operator without visualisation works from palpation, regional anatomy and caution, so the protocol has to be conservative by design.

A 2025 systematic review in Dermatologic Surgery found transient edema, erythema and post-procedural pain most commonly reported in the peer-reviewed literature, while device-report database entries recorded lipoatrophy, neurologic effects including numbness, dysesthesia and ptosis, and scarring. Those cluster around energy landing in the wrong layer. No machine diagnoses anything, so skin that looks like a lesion goes to a physician before a cartridge comes out of the drawer.

Comparing depth sets across quotations

Two consoles at a similar price can offer wildly different clinical range. Work through this before you compare the numbers at the bottom of the quotation.

Ask this	Weak answer	Answer you can hold a supplier to
Which focal distances ship in the box?	"Multi-depth", or a D-number	A list in millimetres, marked standard or optional, per handle
Can it reach 1.5mm?	"Yes, adjustable"	The specific cartridge and the handle it fits, since depth is not adjustable
Which handle carries which cartridge?	Silence, or one generic handle drawing	A handle-by-handle cartridge table, because cartridges are rarely cross-compatible
What is the operating frequency range?	A single headline figure	The stated range, matched to the depths on offer
How many lines per shot?	Not mentioned	A figure, since it sets how long a full face takes
What does each cartridge cost to replace, and for how many shots?	"Cheap consumables"	Price and rated shot count per cartridge type, in writing, before you price a treatment

For reference, the HF-01 source specification in our device manuals lists a 4D handle taking 3.0 and 4.5mm cartridges as standard with 6, 8, 10, 13 and 16mm optional, and a V-max handle taking 1.5, 3.0 and 4.5mm as standard with 8 and 13mm optional. Output runs 4 to 7MHz at 10 to 200W, twelve lines per shot. Full details sit on the HF-01 4D HIFU machine page. It is a 4D platform, and we would rather write that than inflate the number.

What to settle before you sign

Depth questions are cheap now and expensive later. Put these in the contract, not the chat window.

The complete cartridge list in millimetres, split into standard and optional, per handle.
Rated shot count and replacement price for every cartridge you plan to run weekly.
Confirmation that cartridges stay available separately, from the same factory, for the life of the machine.
Training that covers depth selection, regional mapping and client screening, not just which button fires.
The regulatory class and paperwork the console carries in your market.

Buy the depth set your menu needs. Then train hard on where each one lands. For the physics underneath, our technology notes cover how each modality carries energy into tissue.

Evidence and further reading

Educational material for equipment buyers and operators. It is not medical advice, an operating protocol or a promise of clinical outcome.

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HIFU Focus Depths: What 1.5, 3.0 and 4.5mm Actually Treat