The main purpose of a skin rejuvenation procedure for people is to make aged skin look younger. Signs of aged facial skin are sagging and wrinkling as well as fine lines and surface irregularities. Skin aging occurs when collagen, elastic fiber, and connective tissue in the dermis are decreased [1]. There are various methods for improving skin aging, including botulinum toxin, surgical face lifting, radiofrequency, laser therapy, and ultrasound therapy. Recently, patients prefer a non-invasive procedure with a good effect and want to return to their daily life more quickly. In this regard, high-intensity focused ultrasound (HIFU) is a widely used procedure for skin rejuvenation because it minimizes damage to the epidermis and shows an effect by targeting only the superficial musculoaponeurotic system (SMAS) layer with coagulated thermal energy [2-5]. However, due to its long procedure time, some patients feel discomfort such as pain. In addition, the risk of epidermal burns has always existed. The 10thera^® (Tentech Inc.) is a device with characteristics of 2-lines cartridge. It has the advantage of reducing treatment time by half compared to existing devices. The objective of this study was to confirm the effect of 10thera^® on aged skin.

A retrospective study was conducted on 21 patients with sagging and laxity of the facial skin who were treated with HIFU using 4-MHz, 4.5 mm and 7-MHz, 3.0 mm depth transducers (10thera^®) from August 2021 to September 2022. Through chart review, demographic data (sex, age, and race) and clinical information (HIFU parameters, procedure time, and photographs) of patients were collected. Treatment was performed following the manufacturer’s recommended protocol. Before treatment, patients with active systemic infection, local infection or local skin diseases that might alter wound healing, those with a history of psychiatric illness, and those with soft tissue augmentation material were excluded.

Pretreatment preparation

Topical anesthetic ointment (EMLA; Recipharm), was applied to the face for 30 minutes before the procedure. The ointment was washed off with a mild soap and water immediately before the procedure.

Ultrasound exposure protocol

All procedures including setting HIFU parameters were performed by a single, skilled plastic surgeon. First, the ultrasound gel was applied to the skin. The transducer was placed firmly on the targeted skin surface and pressed uniformly for coupling to the skin. Treatment exposure was initiated (4-MHz, 4.5 mm depth transducers; 0.8 J/mm², 60 to 110 shots on each side; and 7-MHz, 3.0 mm depth transducers; 0.4 J/mm², 20 to 91 shots on each side) with a line of individual ultrasound pulses delivered within approximately 2 seconds. The transducer was then slid to the next location and repositioned 3 to 5 mm laterally such that it was adjacent and parallel to the previous treatment line.

Posttreatment care

The ultrasound gel was washed off. Patients experienced mild redness and swelling that could persist for several days. Patients were instructed to visit our hospital promptly if they encountered any other adverse effects.

Outcome evaluation

Patients were evaluated using an automatic skin diagnosis system (Mark-Vu^®; PSI Plus Corp.) at pretreatment and at 1-4 months after treatment. The automatic skin diagnosis system evaluated skin laxity using a scanner. The sagging and laxity of the skin were graded in a numeric scale using the system. A high skin grade means that the sagging and laxity of the skin are severe. The clinician evaluated the presence of complications such as edema, erythema, hypopigmentation, and hyperpigmentation and the procedure time through a chart review.

Statistical analysis

All statistical analyses were performed using IBM SPSS version 24.0 (IBM Corp.). The Wilcoxon signed-rank test was used to compare grades of patients at pretreatment and posttreatment (1-4 months after treatment). Statistical significance was considered when p-value was less than 0.05.

All patients were treated with 10thera^®. Five patients were lost to follow-up for non-study related reasons. In our study, 16 patients (3 males and 13 females) aged 39 to 80 years were evaluated, including one patient from Central Asia (Table 1).

Table 1 . Demographic characteristics of the patients

Characteristics	Value (n = 16)
Mean age	55 (39-80)
Sex (female, male)	13, 3

Values are presented as number (range) or only number.

Fourteen patients immediately presented with slight erythema and edema after treatment. Two patients immediately presented with moderate erythema and edema after treatment. In all patients, both erythema and edema completely resolved within two days after treatment. There were no other complications such as hypopigmentation, hyperpigmentation, or ulceration in any patient. There was no adverse event such as nerve or muscle dysfunction, severe pain, bruising, fat necrosis, or bleeding.

The median procedure time was 14 minutes (IQR: 13-14; Fig. 1). The average post-treatment photo evaluation time was 3 months (IQR: 1-4 months). The mean skin grade was 17 (IQR: 16-19) at pretreatment and 14 (IQR: 14.00-15.25) at posttreatment (Figs. 2-4; Table 2). There was a statistically significant (p < 0.01) difference in skin grade between pretreatment and posttreatment.

Table 2 . The skin grade score

	Pretreatment	Posttreatment	p-valuea)
Skin grade score	17a) (16-19)	14.5a) (14.00-15.25)	<0.01

Values are presented as median (IQR).

^a)p-value by Wilcoxon signed-rank test.

Figure 1. Procedure time. The median procedure time was 14 minutes (IQR: 13-14 minutes).

Figure 2. Comparisons of skin grades at pretreatment and posttreatment. Mean value of skin grades was 17 (IQR: 16-19) at pretreatment and 14 (IQR: 14.00-15.25) at posttreatment. There was a statistically significant (p < 0.01) difference in skin grade between pretreatment and posttreatment.

Figure 3. A 40-year-old female patient with moderate skin sagging and wrinkling. At pretreatment, she was examined with an automatic skin diagnosis system, showing a skin grade of 16 (A). At one month posttreatment, her skin grade was 13 (B).

Figure 4. A 46-year-old female patient with mild skin sagging and wrinkling. At pretreatment, she was examined by an automatic skin diagnosis system, showing skin grade of 15 (A). At 2 months posttreatment, her skin grade score was 13 (B).

HIFU has been used to treat tumor of internal organs in various areas since the 1960s as a principle of concentrating energy to a certain depth without damaging the skin [6-8]. In 2007, White et al. [5] first reported the aesthetic use of HIFU. The author studied the effect of HIFU by targeting the SMAS layer on the skin of cadaveric specimen and confirmed that a selective thermal injury zone could be created non-invasively, suggesting that this principle could be used for skin rejuvenation. Since then, Ulthera^® (Merz) was developed for aesthetic purpose. The U.S. Food and Drug Administration approved HIFU treatment for eyebrow lifting in 2009, neck skin lifting and tightening in 2012, and for décolleté rejuvenation in 2014. In addition, various HIFU devices have been developed for the purpose of skin rejuvenation, showing effectiveness in several studies. Choi et al. [9] demonstrated that ULTRAFORMER III, SHURINK^® (CLASSYS INC.) was effective for body tightening in 2016. Lee et al. [10] reported that ULTRAFORMER III, SHURINK^® was effective in improving aging face such as wrinkling and sagging while minimizing injury to the epidermis and dermis in 2015.

Similar to Ulthera^®, SHURINK^® recommends 200-300 shots in a single session. However, after its safety was confirmed, the number of shots was increased to 500-600 shots to show the maximum effect. It was found that higher number of shots was associated with better effect. However, procedure time, pain, edema, and erythema of patients also increase when the number of shots is increased. Cases of fat atrophy have also been reported [11]. In a previous study, the author performed 300 shots, which usually took 15-20 minutes [10]. It takes about 30-40 minutes to perform about 500-600 shots, although it varies from operator to operator. A long procedure time not only causes stress for the patient, but also increases the burden of the operator.

The 10thera^® uses two lines irradiating transducers, theoretically halving the time to perform the same number of shots. Since the total number of shots is the same, the effect felt by the patient is the same. However, the treatment time is short. Thus, it can increase satisfaction of both the patient and the operator.

According to results of our study, the skin was more tightened at three months after the procedure compared to that at pretreatment. This was not significantly different from skin tightening results of previous studies using other HIFU equipment including our previous study [10]. On the other hand, the treatment time was shortened to an average of 11 minutes. This not only could reduce the operator’s fatigue, but also could increase patient satisfaction.

This study has several limitations. First, as it was a retrospective study, treatment protocols and follow-up periods were not constant. Second, it was difficult to determine the duration of the effect because there was only one follow-up period. Third, our study did not include patients who had severe skin sagging or wrinkling. We recommended a surgical face-lift procedure for these patients. Fourth, posttreatment results were evaluated with an automatic skin diagnosis system whose liability was not established. Therefore, discrepancies might occur between the automatic skin diagnosis system and realistic skin conditions. In addition, detailed data such as histologic findings were not obtained and comparison with existing HIFU devices was not performed. These should be investigated in further studies.

In conclusion, this study suggests that 2-line HIFU can improve an aging face with wrinkling and sagging. It is thought that 2-line HIFU can increase the satisfaction of both the operator and the patient due to a shortened treatment time.

None.

Conceptualization: HGC, ESP. Data curation: SHK, SKL. Formal analysis: SHK, SKL, ESP. Funding acquisition: ESP. Investigation: SHK, SKL. Methodology: SHK, HGC, ESP. Project administration: SHK, ESP. Software: SKL, HGC, ESP. Validation: SHK, SKL, ESP. Visualization: SHK, SKL. Writing–original draft: all authors. Writing–review & editing: all authors.

Eun Soo Park is an editorial board member of the journal but was not involved in the review process of this manuscript. Otherwise, there is no conflict of interest to declare.

This work was supported by the Soonchunhyang University Research Fund.

Contact the corresponding author for data availability.

None.