Ultrasound-Based Techniques for Visualization of Dermal Microvasculature: A Scoping Review

Abstract

Objectives: To systematically map the existing literature on ultrasound-based techniques for non-invasive visualization of the dermal microvasculature and identify methodological strengths, limitations, and evidence gaps. Methods: This scoping review was conducted according to PRISMA-ScR guidelines and registered on the Open Science Framework (DOI: 10.17605/OSF.IO/7VDUK). MEDLINE, PubMed, Embase, Scopus, and Web of Science were searched (January 2000–October 2025). Studies involving human participants and ultrasound-based techniques explicitly aimed at visualizing dermal microvasculature were included. Data on study design, population characteristics, imaging parameters, and reported outcomes were extracted and synthesized narratively. Results: Thirty-six studies published between 2007 and 2025 were included. Most were small feasibility or experimental studies (n = 24), with a median sample size of three participants and substantial heterogeneity in imaging protocols. Photoacoustic-based techniques were most frequently reported (n = 21) and were the most consistently described as providing high microvascular detail and functional assessment capability. High-frequency ultrasound (n = 10) and advanced Doppler methods (n = 7) also enabled visualization of dermal vessels, but showed variability in sensitivity, reporting, and standardization. Validation against histopathology was reported in only one study. Conclusions: Ultrasound-based techniques can visualize dermal microvasculature in vivo; however, evidence remains fragmented, methodologically heterogeneous, and largely derived from small exploratory studies. Standardized imaging protocols, pathology-based clinical cohorts and robust validation studies are required to establish comparative performance and enable clinical translation in radiology.

1. Introduction

Advances in dermatological imaging over the past decade have contributed to improved diagnostic accuracy and longitudinal assessment of cutaneous disease [1,2,3,4,5]. The ability to visualize the dermal microvasculature has increased with recent imaging developments. Microvascular changes are a key feature of multiple dermatological conditions, including melanoma, psoriasis, systemic sclerosis, chronic wounds, and neovascular remodeling in skin tumors [2,5,6,7,8]. Non-invasive imaging modalities offer advantages related to safety, patient comfort, and the ability to support early diagnosis and intervention [4,7,9].

Ultrasound, as a non-invasive, cost-effective, and readily accessible imaging modality, has emerged as a practical tool for evaluating cutaneous structures. Techniques such as high-frequency ultrasound (HFUS), Doppler ultrasound, and photoacoustic methods have improved the spatial resolution and sensitivity of dermal microvascular visualization; however, their adoption in routine hospital-based clinical practice remains limited [2,4,10,11,12,13]. The reliability, validity, and optimal protocols for ultrasound imaging of the dermal microvasculature have not yet been clearly established. A systematic mapping of existing evidence is therefore necessary to identify current capabilities, limitations, and evidence gaps to guide future research and clinical practice.

The primary aim was to systematically map the existing literature on ultrasound-based non-invasive imaging of the dermal microvasculature, with a focus on identifying methodological strengths, weaknesses, and gaps in current evidence. A secondary aim was to outline priorities for future research to improve diagnostic accuracy and clinical applicability.

2. Materials and Methods

We examined ultrasound-based visualization of the dermal microvasculature, focusing on reported technical parameters, their impact on image quality, and the ability to capture and quantify small dermal vessels. The influence of patient- and lesion-specific characteristics on visualization quality and accuracy was also assessed. Another central aim was to evaluate how effectively different ultrasound parameters capture and quantify the smallest dermal vessels. Finally, the review investigated whether patient demographics or lesion-specific characteristics influence the accuracy or quality of ultrasound-based visualization.

Studies involving human adult participants, both healthy and with dermatological conditions, were included. Only research that used ultrasound-based techniques explicitly aimed at visualizing dermal microvasculature (either visually defined as the smallest vessels within the dermis or measured as structures ≤ 100 µm) was considered. Eligible study types included original research, including clinical trials, cohort studies, and cross-sectional designs, as well as relevant review articles. Publications published between January 2000 and October 2025 in English were included.

Exclusion criteria included studies of non-dermal microvasculature, non-ultrasound modalities without ultrasound comparison, purely laboratory-based studies without clinical relevance, editorials or opinion pieces or letters without visualization of microvasculature, and studies lacking full-text availability.

2.1. Protocol Registration and Search Strategy

This scoping review was registered on the Open Science Framework (OSF) (No. 10.17605/OSF.IO/7VDUK) and conducted in accordance with the preferred reporting items for systematic reviews and meta-analysis extension for scoping reviews (PRISMA-ScR guidelines see Figure S1 in Supplementary Materials) [14].

A systematic search strategy was designed in collaboration with the Medical Library at Rigshospitalet, Copenhagen, employing a combination of relevant keywords and Medical Subject Headings (MeSH) terms. Databases searched included MEDLINE (Ovid), PubMed, Embase (Ovid), Scopus, and Web of Science, covering publications from January 2000 to January 2024. An update search was conducted on 9 October 2025 to include the most recent additions, and totals were updated accordingly. Reference lists from included articles were manually screened for additional studies. For a detailed view of the search strategy, see Appendix A.

2.2. Study Selection and Data Extraction

Identified studies were managed using Covidence software, with a total of 2777 records identified, 1563 duplicates removed, 1214 titles and abstracts screened, and 111 full texts assessed, resulting in 36 studies included in the review.

Titles and abstracts were screened independently by two reviewers, with discrepancies resolved by discussion and when necessary, a third senior reviewer. The study selection process was documented following PRISMA guidelines (Figure 1).

Data extraction utilized a standardized form, refined iteratively, capturing study design, demographics, ultrasound techniques and parameters, clinical context, and findings related to dermal microvascular visualization. Extraction was conducted in duplicate to minimize bias, and discrepancies in extracted items were resolved through discussion or a third senior reviewer. Data were synthesized narratively, highlighting methodological heterogeneity and technological variations. For the full data extraction, see Appendix B. For device-, probe-, transducer-, and software-level technical details reported across the included studies, see Appendix C.

Critical appraisal/risk-of-bias assessment was not performed, as this scoping review aimed to map the extent and characteristics of the evidence base in accordance with PRISMA-ScR/JBI guidance.

2.3. Deviations from Protocol

Several included studies utilized multimodal imaging, requiring careful extraction to isolate ultrasound-specific findings clearly. Inconsistent reporting of demographic and lesion characteristics limited the possibility of detailed subgroup analyses, influencing the comprehensiveness of synthesized results.

3. Results

3.1. Study Characteristics

Out of 2777 records, a total of 36 studies published between 2007 and 2025 were included. The vast majority were non-randomized experimental studies or feasibility studies (n = 24), which were primarily designed as proof-of-concept studies. Only nine studies used a formal clinical design (three case reports, two case series, two case-control studies, and two cohort studies). In addition, three papers were narrative, systematic reviews, or opinion articles. This distribution reflects that the field is still in an early and exploratory stage, with few studies embedded in robust clinical study frameworks. For the complete data extraction, see Appendix B.

3.1.1. Ultrasound Techniques

A wide range of techniques were reported to visualize dermal microvasculature. Photoacoustic-based methods (including photoacoustic imaging, optical-resolution, photoacoustic-ultrasound dermascopy, photoacoustic tomography, and optoacoustic mesoscopy) were the most widely reported (n = 21). These studies primarily focused on technological innovation and demonstration of vascular detail, often at or below the level of the superficial dermal plexus, enabling visualization of the finest microvasculature and superficial vascular loops with penetration depths ranging from 1–5 mm (Figure 2) [8,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34].

High-frequency ultrasound (HFUS) was used in 10 studies, typically in the range 20–70 MHz (Figure 3) [2,4,6,7,9,28,35,36,37,38,39]. In several of these, HFUS served as a structural reference modality without an independent visualization of the microvasculature. However, in five studies, it was used in combination with Doppler, providing visual information of the microvasculature [4,7,9,28,36]. One study by Catalano (2022) investigated three methods—HFUS, color Doppler, and superb microvascular imaging (SMI)—to visualize small dermal vessels in normal skin; however, the visual representation lacks the high resolution that some of the other modalities provide [9]. In 2025, one volumetric HF/ultrafast workflow demonstrated 3D dermal vascular mapping with region-based processing and image-feature extraction [37].

Figure 2. Photoacoustic imaging of inflammation around raised skin papule over 38 days. The lowest image shows a 3D skeleton representation of vascular architecture used to estimate vascular density, Vs, shown as a percentage. This image was published under open access, CC-BY 4.0 rights, and originates from [24].

Figure 2. Photoacoustic imaging of inflammation around raised skin papule over 38 days. The lowest image shows a 3D skeleton representation of vascular architecture used to estimate vascular density, Vs, shown as a percentage. This image was published under open access, CC-BY 4.0 rights, and originates from [24].

Figure 3. Using HFUS, the image shows volumetric visualization of dermal vasculatures on the dorsum of the hand with a new region-based SVD clutter filtering. Rendered in the slice-view and volumetric view to locate the vasculature along the volume in maximum intensity projection images. This image was published under open access, CC-BY 4.0 rights, and originates from Volumetric Visualization of the Dermal Vasculature with Signal and Image-based Feature Extraction on a High-frequency Ultrafast Ultrasound Dataset; [37] Seven studies reported the use of advanced Doppler-based techniques (SMI, MV-Flow, MicroV, and AP), describing enhanced sensitivity to low-flow velocities compared with conventional Doppler ultrasound, while noting limitations in visual representation relative to some other modalities (Figure 4) [9,10,11,35,36,40,41].

Figure 3. Using HFUS, the image shows volumetric visualization of dermal vasculatures on the dorsum of the hand with a new region-based SVD clutter filtering. Rendered in the slice-view and volumetric view to locate the vasculature along the volume in maximum intensity projection images. This image was published under open access, CC-BY 4.0 rights, and originates from Volumetric Visualization of the Dermal Vasculature with Signal and Image-based Feature Extraction on a High-frequency Ultrafast Ultrasound Dataset; [37] Seven studies reported the use of advanced Doppler-based techniques (SMI, MV-Flow, MicroV, and AP), describing enhanced sensitivity to low-flow velocities compared with conventional Doppler ultrasound, while noting limitations in visual representation relative to some other modalities (Figure 4) [9,10,11,35,36,40,41].

Figure 4. Superb Microvascular Imaging (SMI) of the dermal vascularization in the forearm (upper part of the image), with 1933 colored pixels, and with Power Doppler (lower part of the image), with 0 colored pixels. This image was published under open access, CC-BY 4.0 rights, and originates from [10].

Figure 4. Superb Microvascular Imaging (SMI) of the dermal vascularization in the forearm (upper part of the image), with 1933 colored pixels, and with Power Doppler (lower part of the image), with 0 colored pixels. This image was published under open access, CC-BY 4.0 rights, and originates from [10].

Other non-invasive ultrasonic methods include Super Resolution Ultrasound (SURE), a promising field rapidly in progress where tracking of the erythrocytes leads to highly detailed images with a spatial resolution of less than half a wavelength (Figure 5) [12].

Nine studies reported the combined use of two or more ultrasound-based modalities, most commonly HFUS with photoacoustic imaging, Doppler ultrasound, or SMI/MicroV [4,7,9,11,25,28,36,40,41], and furthermore, a 2025 multimodal ultrasound cohort in patients with keloid integrated B-mode, shear-wave elastography, and angiographic parameters for monitoring disease severity and treatment response [36].

3.1.2. Clinical and Pathological Focus Areas

More than half (n = 19) of the studies were performed on the skin of healthy volunteers without a specific disease focus. The purpose of these studies was to establish baseline patterns, test technical concepts, or make direct comparisons between different methods [9,10,30]. Five studies investigated benign pigmented lesions and reported visualization of microvascular patterns in small nevi with high spatial resolution [12,16,17,21,22]. In addition, two studies focused on benign fibrotic lesions (keloid scars) [36,39], and five studies investigated inflammatory or vascular conditions, including plaque psoriasis, chronic venous disease, systemic sclerosis with Raynaud’s phenomenon, and burn depth assessment [11,21,24,38,41]. Four studies examined malignant skin neoplasms, primarily basal cell carcinoma, squamous cell carcinoma, and melanoma [2,21,35,40]. One further study included a subcutaneous tumor within a broader “general dermal imaging” context [15].

For a summarized overview of the articles, see

Table 1. Summarized overview of the preferred methods, focus areas, and reporting variabilities in the included studies. Note that some studies utilized more than one method. Abbreviations: CDFI, Color Doppler Flow Imaging; HFUS, high-frequency ultrasound; MicroV, microvascular imaging; MV-Flow, microvascular flow imaging; n, number; OAM, optoacoustic mesoscopy; PAI, photoacoustic imaging; PAM, photoacoustic microscopy; PAT, photoacoustic tomography; PDI, Power Doppler Imaging; SMI, Superb Microvascular Imaging; VHFUS, very high-frequency ultrasound.

Modality	Number of Studies
Photoacoustic-based (PAI/PAM/PAT/OAM)	21
High-frequency ultrasound (HFUS/VHFUS)	10
Conventional Doppler (CDFI/PDI)	7
Advanced Doppler (SMI/MicroV/MV-Flow)	7
Multimodal combinations (≥2 modalities)	9
Super-Resolution Ultrasound using tracking of the erythrocytes	1
Clinical and pathological focus areas
Healthy volunteers/normal skin	19
Inflammatory/vascular disease	5
Benign fibrotic lesions (keloid)	2
Benign pigmented lesions (nevi/moles)	5
Malignant skin tumours	4
Other pathology	1
Reported variabilities
Median sample size (participants)	3
Studies < 20 participants	21
Studies missing numeric sample size	9
Studies reporting age	13
Studies reporting sex	16
Studies reporting both inclusion and exclusion criteria	7
Studies informing about histopathology	1

.

3.1.3. Key Findings

According to the included studies, ultrasound-based techniques were reported to enable visualization of the dermal microvasculature across all modality groups.

Photoacoustic methods were most consistently reported to provide high spatial detail and the possibility of functional measurements (e.g., oxygen saturation), but, despite being used in 21 studies, these techniques remain primarily experimental, with limited integration into routine clinical workflows [8,15,17,18,21,23,24,25,26,29,30].

HFUS and Doppler ultrasound were reported to provide structural and flow-related information, while demonstrating lower sensitivity to slow flow in the microvasculature compared with other ultrasound-based technique [3,6,38].

Several studies reported improved sensitivity to low-velocity dermal flow using advanced Doppler techniques such as SMI and MicroV compared with conventional Doppler ultrasound [9,10,11,41].

One study using SURE reported detailed microvascular imaging of a benign mole without the use of contrast agents [12]. While technically promising, evidence for dermal application of SURE is currently limited to this single study.

Please refer to Figure 6 and

Table 2. Summary of reported strengths, limitations, and clinical status of the included ultrasound-based modalities for dermal microvascular imaging. Some studies used more than one modality. Abbreviations: AP, AngioPLUS; CDFI, color Doppler flow imaging; HFUS, high-frequency ultrasound; PDI, power Doppler imaging; SMI, superb microvascular imaging; SURE, super-resolution ultrasound using erythrocytes; VHFUS, very high-frequency ultrasound.

Modality	Studies (n)	Main Strengths	Main Limitations	Clinical Status
Photoacoustic-based imaging	21	High microvascular detail; functional imaging possible	Mostly experimental; limited standardization; depth–resolution trade-off; affected by pigmentation/skin type	Mainly experimental
High-frequency ultrasound (HFUS/VHFUS)	10	Widely available; useful structural imaging	Limited capillary-level detail without added processing	Clinically available, but limited for fine microvascular imaging
Conventional Doppler (CDFI/PDI)	7	Flow-related information; widely available	Low sensitivity to slow dermal flow; limited fine-vessel depiction	Clinically established, but limited for dermal microvasculature
Advanced Doppler (SMI/MicroV/MV-Flow/AP)	7	Better sensitivity to low-flow dermal vessels; relatively accessible clinically	Small heterogeneous evidence base; device-dependent; lower detail than highest-resolution techniques	Promising clinical adjunct
Super-resolution ultrasound using erythrocytes (SURE)	1	Very high spatial detail; contrast-free microvascular imaging	Only one included dermal study; no basis yet for clinical readiness	Very early-stage

for an overview of the different modalities, which provides a clear view of their reported accumulated strengths and weaknesses.

3.1.4. Reporting Limitations

Overall, reporting quality and study size were limited. The median sample size was three participants, and, although sample size was clearly reported in most studies (n = 27), the majority enrolled fewer than 20 participants (n = 21). Demographic data were inconsistently reported and often not described. Nine studies did not clearly report their sample size. Demographic descriptors such as age (n = 13) and sex (n = 16) were frequently incomplete, and only seven studies had predefined inclusion and exclusion criteria prior to the study period.

Ultrasound protocols were heterogeneous, even within the same modality, with substantial variation in transducer frequency, imaging depth, frame rate, and reconstruction or postprocessing methods. Validation against reference standards was rarely described, with only a single study validating its findings against histopathology [17]. Technical barriers such as motion artifacts and limited depth penetration were mentioned as limitations in some studies [9,22,24,38]. A detailed overview of systems/platforms, probes/transducers, and reported technical settings is provided in Appendix C.

4. Discussion

Ultrasound-based visualization of the dermal microvasculature has advanced substantially over the past two decades, with recent improvements in spatial and temporal resolution enabling increasingly detailed assessment. Despite these technological gains, the current evidence base is fragmented and at an early stage. Most included studies are small feasibility investigations employing heterogeneous methods and reporting standards, with a median sample size of three participants, and frequent reliance on healthy volunteers rather than pathology-based cohorts. As a result, the clinical utility and comparative performance of these techniques remain uncertain, highlighting the need for standardized evaluation and larger, methodologically robust studies.

Photoacoustic techniques (Figure 2) were the most frequently represented modality group and showed the ability to provide detailed insight into the dermal microvasculature, and some studies have hypothesized the possibility to differentiate benign melanocytic tumors from malignant melanomas by the different vascular pattern parameters, including blood flow, tortuosity, and vessel density [8,15,17,18,21,23,24,25,26,29,30]. Acquisition time and penetration depth, as seen in the early generations of photoacoustic scans, were some of the troubles hindering the use in clinical practice; however, recently there have been successful scans with just a few seconds of acquisition time [24,34]. Schwartz et al. (2015) demonstrated that they can visualize vascular structures as deep as 2 mm with a frequency of 25 MHz [22]; however, with higher frequencies, and therefore details, the depth penetration significantly declines [19]. Clinical availability is still limited, though several studies are making progress in creating and using a hand-held photoacoustic probe. Thus, the research is still largely on experimental basis with larger studies warranted [16,24,27,29,30]. Another limitation discovered by Liu et al. (2016) in a study using photoacoustic tomography was skin type [31,32]. They categorize skin types by the Fitzpatrick scale of I–VI, where the groups are defined by the amount of pigment in the skin and the readiness of it to burn when exposed to direct sunlight [32,42]. The laser is absorbed by the superficial pigment in the skin, thus hindering penetration of the laser, and therefore the depth of the scan will increase with a decreasing amount of pigment in the skin [31,32]. This also applies to moles containing pigment. Schwarz et al. (2015) found that the pigment in a benign mole absorbed the laser and decreased the signal in the area of the mole, however, not hindering visualization of the microvasculature in the skin underneath [22]. More broadly, skin type was not reported consistently across the included studies, representing an important reporting gap, particularly for optical ultrasound techniques in which pigmentation may influence signal penetration and image interpretation.

Photoacoustic tomography is a field continuously researched, and new insights into the methods keep arising. Rodrigues et al. (2022) found that multi-spectral optoacoustic imaging (MSOT) could differentiate physiological parameters in the skin, such as HbO2, Hb, HbT, and mSO2 (MSOT-derived oxygen saturation) [33]. They argue that MSOT can be used as a predictive measure in clinical practice; however, they clearly state that their findings are regarded as exploratory and should be followed by larger clinical studies [33]. Another study by Zheng et al. (2021) argues that they can improve biometric security of fingerprinting by visualization of the underlying microvasculature of the fingertips [26].

HFUS (Figure 3) is widespread and readily available, but generally lacks resolution to visualize the capillary level [2,38]. However, a study by Chen et al. (2017), and more recently by Zhou et al. (2025), showed promising results using a 40 MHz linear probe to visualize the microvasculature in a keloid scar [36,39]. A study by Bhatti et al. (2023) was successful in showing the microvasculature of the dermal layers when HFUS is filtered with region-based SVD and top hat filtering [6]. An automated workflow for processing, using an ultra-high frequency probe (>40 MHz) and super-resolution imaging techniques, was their suggestion for future improvements to visualize microvasculature in the skin [6].

Advanced Doppler methods (SMI, MicroV, MV-Flow, AP), as seen in Figure 4, show improved ability to visualize microvasculature in the skin and could possibly be the first to find their way into dermatological practice due to their widespread availability and high resolution [9,10,11,35,41]. Jasionyte et al. (2023) used a combination of high-resolution ultrasound and SMI to visualize dermal microvascular flow, using a new filtering system that minimizes motion artifacts [35]. They argue that the method can be used in the discrimination of ultrasonic patterns in patients with systemic sclerosis, as the vascular changes appear to be prominent and obvious, but as with many of the studies, it is limited by a small sample size [11,35]. The evidence for identifying malignant melanoma using SMI is sparse and based on very small series. Kho et al. (2024) indicated that vascular patterns can support differentiation of tumors, but the material is still too sparse for clinical conclusions, and the studies are too small in size [40]. A single study using SURE provided highly detailed microvascular images of a benign mole, including flow measurements of 3.2 mm/s and estimated vessel measurements of 65 µm in diameter [12]. Al-though technically promising, dermal application of SURE remains at a very early stage and its clinical relevance cannot yet be inferred from a single included study (Figure 5) [12,43].

Other modalities, such as laser Doppler imaging and laser speckle contrast imaging, have given important insights into the dermal microvasculature by providing high-resolution depictions of vascular flow and morphology at superficial depths [44,45]. Photoacoustic imaging combines pulsed laser excitation with ultrasound detection, thereby serving as a technical bridge between optical contrast and ultrasonic penetration [19,32].

While the current studies remain largely exploratory, several potential clinical uses can be identified based on the included studies. In the context of pigmented lesions, microvascular imaging may serve as a diagnostic tool where differences in vascular architecture and flow patterns could support differentiation and delineation between benign nevi and malignant melanomas [2,12,17,21,35,40]. In inflammatory diseases such as psoriasis and systemic sclerosis, as well as fibrotic skin conditions, these techniques could offer a non-invasive approach to monitoring disease activity and treatment response through changes in microvascular density and perfusion [11,21,24,35,36,39]. Furthermore, preliminary findings suggest a potential role in burn depth assessment, where evaluation of dermal perfusion may support clinical decisions [38]. While interesting and promising, these potential applications remain insufficiently validated.

Across studies, common limitations included non-standardized imaging and analysis protocols, small and homogeneous populations, frequent use of healthy volunteers, and technical challenges such as motion artifacts and restricted imaging depth, all of which may limit the generalizability and reliability of findings. Notably, validation against a clinical reference standard was largely absent, with only one included study reporting histopathological confirmation. This represents a critical evidence gap, as biopsy-correlated studies are essential if these technologies are to move from technical feasibility toward clinically meaningful diagnostic applications.

An additional key challenge, highlighted in the technical overview (Figure 6 and Appendix C), is the substantial heterogeneity not only across imaging modalities, but also within them. Even within commonly used approaches such as high-frequency ultrasound and advanced Doppler techniques, e.g., SMI, there was a notable variation in the used systems, probes, frequencies, and processing methods, which further limits comparability between studies.

Clinical translation will require not only standardized image acquisition, reporting, and quantification, but also greater consistency in the technical implementation across modalities. Future research should prioritize adequately powered pathology-based cohorts and multicenter study designs, including direct comparison of modality, and biopsy-correlated validation studies to establish reliability, generalizability, and clinical relevance.

5. Conclusions

Ultrasound-based techniques can visualize the dermal microvasculature in vivo, but evidence is limited, fragmented, and largely restricted to small exploratory studies with heterogeneous protocols. Among the included studies, photoacoustic-based methods most consistently reported high microvascular detail, whereas advanced Doppler techniques may represent one of the more clinically accessible approaches in the near term. High-frequency ultrasound remains structurally useful but is generally insufficient for capillary-level assessment without specialized processing. Standardized imaging protocols, robust validation, and adequately powered pathology-based studies are needed to determine comparative performance and support clinical translation. With standardized methods and clinically grounded validation, ultrasound-based microvascular imaging may evolve from a technical innovation into a more clinically relevant tool in dermatology.