The growing importance of ultrasonography in cosmetic dermatology: An update after the 23rd IMCAS Annual World Congress (2022)

Ultrasound (US) has been used for many years in the field of medicine. Many specialties have embraced US as a quick, painless, and relatively inexpensive tool to assist the clinician in determining anatomy, pathology, and aid in diagnostic or therapeutic procedures. US allows for precise mapping of cutaneous and subcutaneous structures in the face, in particular vascular structures. The use of US leads to reduced chances of complications and clinical failures, rendering more safety and high quality.


| INTRODUC TI ON
The field of medicine has benefited vastly from ultrasound (US) technology. Many medical specialties have embraced US because it is a quick, painless, and relatively inexpensive tool to assist the clinician in determining anatomy, pathology, and aid in diagnostic or therapeutic procedures. US was first introduced in clinical dermatology in 1979. 1 The field of cosmetic dermatology, however, started much later on using US as an important tool. 2,3 US allows for precise mapping of cutaneous and subcutaneous structures in the face, in particular vascular structures. 2 In turn, this knowledge enables the professional to carry out their task in a safe manner. Plus, the use of US leads to reduced chances of complications and clinical failures, rendering more safety and high quality. 4 US has not been routinely used in cosmetic dermatology due to several reasons, such as large equipment, low-definition images, costs, and availability. 5 The miniaturization reduced costs and especially higher megahertz frequencies providing improved quality of superficial tissue layer imaging have eradicated the previously mentioned problems. 6 Simply put, modern era US devices are small, portable, practical, with high frequency and increasingly affordable. Portable wireless probes connectable to smartphones or tablets including software are offered at a fair price and are now easily available. 7

| Ultrasound in cosmetic dermatology: how?
The US transducer (also named probe) emits a sound wave which is reflected by the examined tissue while the echo is detected by the transducer. Practically, the transducer is both transmitter and receiver of US. There are various probes including linear, convex, and phased array used in US. The convex array probe is used for example, abdominal examinations since it has a wide imaging area and focusses deeply. For cosmetic dermatology, the linear array probe is recommended because of its superficial focus. Frequency is another characteristic probe. The higher frequency (HF) probes provide more detailed images. However, their penetration depth is limited. So, HF probes ranging from 10-22 MHz are optimally suited for facial examinations. Recently, literature has shown that US can be deployed for vascular mapping, safe placement of fillers and directed low-dose hyaluronidase reversal of vascular adverse events. 8

| IS US E A SY TO IN CORP OR ATE INTO OUR AE S THE TIC PR AC TI CE?
Yes, US is a noninvasive method that is completed in a few minutes.
The use of US requires training and knowledge of anatomy because it is not easy to identify and find the anatomical structures at the beginning. However, several worldwide US academies as Thinkin Academy, Cutaneous, and Sonosthetics teach practitioners how to utilize US for different aesthetic procedures.

| ULTR A SOUND IN COS ME TIC DERMATOLOGY: WHY ?
Currently, US is considered the first-imaging technique for dealing with fillers and managing their potential complications. In general, physicians tend to use it for prevention. So, prior to injecting a certain area, they inspect with duplex to detect any arteries are in the way or the presence of anatomical variations are present ( Figure 1).
In the case of HA filler-related complications, hyaluronidase can be placed with ultrasound-guided injections exactly into the filler deposit. 9,10 In a study by Schelke et al., 9 35-50 units of hyaluronidase were injected into the HA deposits responsible for the occlusion, resulting in immediate restoration of blood circulation, in comparison with high hyaluronidase dose (>500 UI) with high dose protocol not guided by US. 9 The incidence of vascular adverse effects after filler injections seems to be 1/6600 (0.015%). US can assist in the  11 Although this risk does not seem very high, many injectors even recognized as excellent practitioners, may encounter this event during their career. 12 The use of US is being promoted as a noninvasive imaging modality that provides a good definition for studying the skin and deeper layers ( Figure 2) in real time, including blood flow, taking us from a static anatomy to a dynamic one. There are many anatomical variations as there are humans. 13 For instance, to underscore the variability of lip vasculature, the study by Cotofona et al. 14 shows that the most frequent location of both the Superior and Inferior Labial Artery is the submucosal plane (58.5%) followed by intramuscular (36.2%) and subcutaneous (5.3%) planes. 14 Dermal fillers are used widely; some have a permanent effect, whereas others are temporary. Moreover, US has additional advantages such as recognizing remains of previously injected fillers (presence and type). [15][16][17][18] Another important application is checking filler treatment execution immediately after injection. Physicians will be able to detect exactly the location of the filler placed. [19][20][21][22] Based on the US findings in many studies, doctors can be more precise in their guided facial injectable treatments to provide safety for their patients. Based on Cotofona's findings, it seems that the superficial plane of the lower forehead should be avoided due to the unpredictable and inconsistent presence of the central and paracentral arteries. 23 Another practical fact is that a deep supraperiosteal approach should be favored when augmenting the deep midfacial fat compartments. 24 Lastly, it has been shown that in contrast to current concepts, the angular artery is not located strictly subdermal to the nasolabial sulcus but at a variable depth and in 100% of the investigated cases lateral to the nasolabial sulcus. As people age, the depth and lateral distance between arteries and sulci have been shown to reduce. All these variations can easily be seen with US before injection. 25 In addition, US can guide other minimal invasive procedures. To illustrate, US facilitates defining the muscular planes guiding the application of botulinum toxin in patients with bruxism. 26 US may contribute to a more personalized procedure, better cosmetic results, and minimal complications. 27 Last of all, for research purposes, US examination provides valuable information on the behavior, longevity, and interaction of the filler within the tissues.
In conclusion, this new approach for US-guided treatments is a very practical and an effective method in cosmetic dermatology.
Keeping the patients out of the harm's way is a doctor's main responsibility, primum non nocere. As physicians, we feel that in the near future, US will be an essential diagnostic tool in any dermatology or cosmetic doctor's office to legally protect the professionals and also to keep the patients safe.

| Some testimonials from IMCAS 2022
Dr. Leonie Schelke: "I thought I knew anatomy. I did cadaver courses, I had my books, did injections. But US really made me understand anatomy, visualized the different layers of the skin, I could see the tissue moving, I could relate to different tissue layers, to the mobility, how the filler was looking inside. It's much more than I thought that it would do for safety". Video S2.
Dr. Peter Velthuis: "With US imaging we have made the first steps in researching our injectable techniques, but there is so much more to examine. In the next five years, US will fundamentally change the way we conduct our treatments, making them safer but also more effective".
Dr. Steven Weiner: "I think that US is the ultimate way to examine your patients, even if you're a great anatomist. I use US for safety, for F I G U R E 2 See attachment of picture. The temple is a potential high risk area for injections. In this picture, layers of the temple are visualized by US 18 MHz. treating complications, for objective measurements for treatments that I do. So US should be included in everyone's practice in the future and will likely become the golden standard for facial injections". Video S1.

AUTH O R CO NTR I B UTI O N S
DH had the concept for the review article and performed the majority of the literature search, with assistance from MH. DH, HC, MH, MB, and GD contributed to the planning of the work that led to this manuscript. All authors read and approved the final manuscript.

ACK N OWLED G M ENTS
The authors wish to thank Dr. Leonie Schelke for providing the US picture, Dr. Hugues Cartier and Dr. Peter Velthuis for reviewing the manuscript.

CO N FLI C T O F I NTE R E S T
None declared.

DATA AVA I L A B I L I T Y S TAT E M E N T
The data that support the findings of this study are available from the corresponding author upon reasonable request.

E TH I C A L A PPROVA L
Authors declare human ethical approval was not needed for this study.