[88]. Te study found a strong correlation between the mean brightness of UHFUS and the lesion CSAMI score, as well as the percent of the dermis with granulomas on histopathology; ultimately, these results Levy et al. Ultrasound J (2021) 13:24 Page 8 of 12 highlighted the utility of ultrasound in quantifying disease burden in patients with cutaneous sarcoidosis [88]. Another granulomatous disease, idiopathic facial aseptic granuloma (IFAG), is a self-limiting pediatric disease; as such, it does not require aggressive treatment [16]. On ultrasound, IFAG can appear as a poorly defned oval shaped hypoechogenic lesion in the dermis surrounded by areas of hyperechogenicity and hypervascularization due to infammation. Ultrasound can therefore be utilized to diferentiate IFAG from its diferential diagnoses that might require further management. For example, a facial abscess may exhibit a characteristic “squish sign” with ultrasound and would require incision and drainage with antimicrobial therapy [89]. Further diferentiating factors include lack of calcium deposits, diferentiating it from a pilomatricoma, lack of defned borders, as seen in epidermal cysts, and lack of vascularity, as seen in vascular tumors [16]. Te use of ultrasound to properly diagnose, manage and monitor disease progression in IFAG is therefore important and provides a non-invasive alternative to biopsy [16]. Vascular lesions A number of vascular lesions have been studied using ultrasound, including Port-wine stains (PWS), arteriovenous (AV) malformations and spider nevi. Te frst study to successfully examine PWS using ultrasound was conducted in 2018 [90]. Tis retrospective study utilized both 10-MHz and 22-MHz transducers with and without Doppler to assess lesional depth, echogenicity, vessel density and AV fow signals. Te results of this study demonstrated a clear contrast between lesional and normal skin [90]. Furthermore, the study demonstrated ultrasound could help diferentiate a PWS from other vascular anomalies due to their hypoechoic, poorly vascularized appearance with venous fow, while other capillary-arteriovenous malformations appear hyperechoic and well-vascularized with mixed arterial and venous blood fow [90]. Another type of vascular lesion known as a Spider nevus has also been characterized using ultrasound [91]. Spider nevi were historically classifed as low-fow capillary malformations [92]; however, a 2017 study by Alegre-Sanchez et al. found that spider nevi demonstrated pulsatile fow on dermoscopy and ultrasound. Tis fnding was subsequently supported by the presence of high-fow arterial-type waveform as seen on Doppler-ultrasound, suggesting that spider nevi are more similar to arteriovenous malformations, or highfow vascular lesions [91]. Ultrasound can also be used to guide and assess response to treatment [48]. For example, researchers have used its Doppler capabilities to correctly identify venous structures and aid in guiding injectable foam sclerotherapy for the treatment of venous leg ulcers, demonstrating good healing rate and a low refux ratio [93]. Cosmetic applications Several cosmetic applications of ultrasound have been established. For example, botulinum toxin injections demonstrate increase subcutaneous echogenicity leading to a blurring of the normally discrete boundaries between the subcutis and underlying muscle [94]. Similarly, fllers can be visualized using ultrasound to determine locations of prior injections—an important application since a small but signifcant proportion of patients seeking injectable fllers fail to report prior procedures. Te risk of granulomas and fller dermopathies associated with injections of multiple fller materials has been established [95–97]. Te efcacy of topical vitamin C therapy in increasing collagen production, reducing ultraviolet radiation induced oxidative stress and enhancing dermal remodeling has been demonstrated in several studies [98, 99]. One notable study using HFUS evaluated the skin of patients throughout a 60-day period of topical vitamin C therapy, demonstrating increased echogenicity in both the epidermis and dermis after 40 days and to a greater extent after 60 days [98]. Ultrasound at 15-MHz and 20-MHz has