Mapping cutaneous field carcinogenesis of nonmelanoma skin cancer using mesoscopic imaging of pro‐inflammation cues

Nonmelanoma skin cancers remain the most widely diagnosed types of cancers globally. Thus, for optimal patient management, it has become imperative that we focus our efforts on the detection and monitoring of cutaneous field carcinogenesis. The concept of field cancerization (or field carcinogenesis), introduced by Slaughter in 1953 in the context of oral cancer, suggests that invasive cancer may emerge from a molecularly and genetically altered field affecting a substantial area of underlying tissue including the skin. A carcinogenic field alteration, present in precancerous tissue over a relatively large area, is not easily detected by routine visualization. Conventional dermoscopy and microscopy imaging are often limited in assessing the entire carcinogenic landscape. Recent efforts have suggested the use of noninvasive mesoscopic (between microscopic and macroscopic) optical imaging methods that can detect chronic inflammatory features to identify pre‐cancerous and cancerous angiogenic changes in tissue microenvironments. This concise review covers major types of mesoscopic optical imaging modalities capable of assessing pro‐inflammatory cues by quantifying blood haemoglobin parameters and hemodynamics. Importantly, these imaging modalities demonstrate the ability to detect angiogenesis and inflammation associated with actinically damaged skin. Representative experimental preclinical and human clinical studies using these imaging methods provide biological and clinical relevance to cutaneous field carcinogenesis in altered tissue microenvironments in the apparently normal epidermis and dermis. Overall, mesoscopic optical imaging modalities assessing chronic inflammatory hyperemia can enhance the understanding of cutaneous field carcinogenesis, offer a window of intervention and monitoring for actinic keratoses and nonmelanoma skin cancers and maximise currently available treatment options.


| INTRODUC TI ON/BACKG ROUND
Field cancerization (or field carcinogenesis) is the proposition that an invasive tumour may arise from a molecularly and genetically altered field affecting a large tissue area.3][4][5] Field cancerization can be defined as an expanse of cells that are susceptible to dysplastic and neoplastic growth due to a common chronic carcinogenic exposure. 4eld cancerization can be related to the growing appreciation for the role of tissue microenvironments, which are even considered to drive early carcinogenesis.Because chronic ultraviolet (UV) exposure is the primary cause of skin cancer, cutaneous field carcinogenesis can be defined as "a photoexposed, chronically damaged skin area with multiple actinic keratosis lesions besides other damages caused by UV radiation exposure." 6e detection of field cancerization and its altered tissue microenvironments have tremendous impacts on almost all dermatological applications.][9][10] Once a lesion of malignant potential is determined, the provider would likely take a biopsy of the lesion and send it to a pathology lab to be histologically examined to confirm or deny the diagnosis of skin cancer.This method has proved to be effective for more than a century. 11However, as strongly indicated in the name 'field cancerization', it is critical for its effective utilisation to determine the lesion's exact spatial extent by examining large suspected areas.The carcinogenesis field alteration present in precancerous tissue is not easily detected by routine visualization techniques.Given that the carcinogenesis field can be present in large areas, even advanced microscopy technologies have the major limitation of examining the entire carcinogenesis field with high sensitivity/resolution.Consequently, there is a need for identifying appropriate imaging approaches that would allow biologically meaningful noninvasive mapping of the cutaneous carcinogenesis field.Fortunately, recent advancements in optical imaging technologies have allowed the possibility of a noninvasive way to visualise and detect field carcinogenesis in the apparently normal epidermis and dermis.In particular, mesoscopic (between microscopic and macroscopic) optical imaging could be a new gateway to diagnosing skin lesions without having to break the skin.While visible change is the most common way to attempt to identify cancerization, it is imperative that more sophisticated noninvasive imaging methodologies are employed to not only identify active pre-or cancerous lesions but also risk stratify. 6,12ch imaging methods can assist in triaging which patients will most benefit from field therapies such as topical 5-fluorouracil. 13,14reover, these technologies could also be employed to assess the effectiveness of field therapies.
In this minireview paper, we focus on mesoscopic optical imaging modalities that can be used for detecting chronic inflammatory hyperemia in the tissue microenvironments to assess cutaneous cancerization.We hypothesize that mesoscopic imaging of chronic inflammation can detect cutaneous field carcinogenesis, opening a window of intervention for treating actinic keratosis (AKs) and nonmelanoma skin cancers (NMSCs).There is a plethora of literature on optical imaging of AKs and NMSCs.The fusion of optical imaging with NMSC research has a rich history, significantly contributing to the development of biomedical optics or biophotonics. 15The skin's easy accessibility has allowed numerous noninvasive imaging technologies to be both developed and tested extensively.Indeed, optical imaging of the skin has significantly contributed to the field of biomedical optics and biophotonics.In this respect, we narrow the scope of this review to the key biological events associated with cutaneous field carcinogenesis, mesoscopic imaging (excluding microscopic imaging) of blood haemoglobin parameters and hemodynamics in the tissue microenvironments and relevant experimental animal and human clinical studies related to AKs and NMSCs.

| AC TINI C K ER ATOS E S AND NONMEL ANOMA S KIN C AN CER
In 2020, cancer was the second-leading cause of death around the world and in the US. 167][18] While the two most frequent NMSCs uncommonly cause death or metastasize to other parts of the body, they account for tremendous morbidity, including a large financial burden on the healthcare system. 19It is estimated that the financial burden of diagnosis and treatment of NMSCs in the US is $650 million yearly. 20The two most prevalent types of NMSC are cutaneous squamous cell carcinoma (SCC) and basal cell carcinoma (BCC). 17,21AKs are precancerous lesions that are thought to be precursor lesions of SCC and are also markers of severe photodamage that put individuals at increased risk of developing BCC.Malignant transformation of AKs to SCCs is estimated to be less than one percent per single lesion per year, but around 60% of SCCs are thought to originate from AKs. 22,23 UV exposure is the single most prominent factor in predetermining AK and NMSC growth, which typically occurs on the most sun-exposed places on the body including the head and neck. 19sible photodamage occurs and correlates to areas of increased inflammation.Discoloration, ulceration, wrinkling, or actual rash may be present on the skin in an area of cancerization. 6A systematic review completed in 2006 reported that the clinical features most commonly associated with malignant transformation of AKs were inflammation and induration, diameter greater than 1 cm, rapid enlargement, bleeding, ulceration and erythema. 24However, not all skin cancerization is able to be assessed with these clinical criteria; many AKs and premalignant lesions do not show these visible changes and instead appear clinically as undamaged skin. 6stologic changes that may occur in premalignant AKs include parakeratosis and hyperkeratosis, increased cellularity in the basal layer of the skin, nuclear pleomorphism and increased mitoses. 25ost of these features are also present in the histology of SCC, but they can also include inflammatory cells within the dermis if the lesion is ulcerated. 25BCC has many different histological presentations, but is most commonly present with clusters of basaloid cells with peripheral palisading. 25

| PRO -INFL AMMATORY CUE S IN TISSUE MICROENVIRONMENTS
It is well known that UV light radiation (specifically UV-B radiation) damages the DNA in skin cells by inducing mutations in many genes, including TP53, SERPINB2, MC1R, ENTPD1, CYIP2 and HOXB5. 26,27-B radiation also exerts pro-inflammatory effects on both the epidermis and dermis, resulting in pathologic effects on inflammatory hyperemia and angiogenesis within the dermis.In particular, inflammatory hyperemia is the term used to describe the vasodilation and increased blood flow and content in an area of inflammation.This produces the appearance of the colloquial term, "sunburn."Chronic injury to the skin by UV radiation causes inflammatory and oxidative injury to cells.Prolonged inflammatory hyperemia can predict sites of angiogenesis, which is thought to contribute to skin cancer development. 289][30][31][32] While the exact mechanism has yet to be determined, it has been shown that inflammatory and angiogenic markers such as cyclo-oxygenase-2 (COX-2) play a role in early angiogenesis in pre-malignant conditions yielding carcinogenesis. 28,33A recent trial by our team showed that visualised subclinical hyperemic foci on a mouse model predicted the formation of cancerization following chronic irradiation; 28 UV-B radiation contributed to angiogenesis by inducing inflammatory hyperemia within the mice, and the hyperemic foci continued to expand in the absence of UV-B exposure.
5][36] The influence of dermal senescence and genetic mutations plays an important role in the setting of continued tumorigenesis after the cessation of exogenous stimuli. 37It was shown that p53 + clones were focused within the dermal hyperemic foci, suggesting that tumour growth following initial genetic mutations can continually expand after cessation of extrinsic carcinogenic treatment in areas of increased vascularity. 28In addition, dermal senescent cells produce senescence-associated secretory phenotype, which triggers angiogenesis and inflammation surrounding the cells, leading to the production of more dermal senescent cells and an environment suitable for continued carcinogenesis. 37This could potentially explain the hyperemic expansion noted in the previous study. 28Importantly, this also identifies a need for noninvasive imaging of subclinical lesions, as it has now been shown that tumorigenic expansion can continue in individuals no longer exposed to UV-B radiation.

| ME SOSCOPI C (B E T WEEN MI CROSCOPI C AND MACROSCOPI C) IMAG ING
Biomedical optical imaging can be categorized in terms of the field of view (or imaging area).Simple microscopy and dermoscopy (also known as dermatoscopy) have traditionally been useful for the evaluation of suspicious skin lesions. 11Advanced microscopic imaging modalities enable relatively high resolutions at the cellular levels, but their field of view is significantly limited.9][40][41] However, it remains a challenge to overcome the key limitation of these technologies for the investigation of field cancerization in a large tissue area.Because such microscopic approaches allow sampling of a small fraction of tissue under investigation, it is practically challenging to examine the entire suspicious area of interest.For example, considering a relatively small field of view (e.g., ~0.2-0.3 mm in diameter) of high-resolution microscopy, 10 000 microscopic images would have to be stitched together to reconstruct an area of only 25 mm × 25 mm.A mosaic of highresolution microscopy images for such a large area would require significant time and extremely high computational power.
In this minireview, we focus on key representative biomedical optical imaging modalities that enable mesoscopic (between microscopic and macroscopic) imaging of chronic inflammatory hyperemia in the skin, quantifying haemoglobin parameters and hemodynamics in relation to NMSC in both preclinical and clinical settings.Figure 1 illustrates that mesoscopic imaging is beneficial for efficiently imaging the entire carcinogenesis field and its associated alterations in the tissue microenvironment.Among other diverse components of the tissue microenvironments, chronic inflammatory hyperemia plays an important role as a contributor to carcinogenesis.Emerging evidence suggests that early inflammatory angiogenesis in premalignant stages serves a tumour-promoting function.However, only limited information on inflammatory angiogenesis in early carcinogenesis is available in part because of technical limitations of current invasive immunohistochemistry methods.It is also virtually impossible to map inflammatory angiogenesis alterations in a relatively large area because several conventional microscopic technologies for the assessment of microcirculation and microvasculature have only a small field of view.
Figure 2 illustrates how mesoscopic hyperspectral imaging can detect pro-inflammatory changes in the dermis.Hyperspectral imaging allows to map out alterations in blood haemoglobin content and oxygen saturations, which are indicative of hyperemia in a mesoscopic manner.5][46][47][48][49] Oxygenated and deoxygenated haemoglobin have the unique spectral profiles in the visible range and near-infrared range.Other various derivatives of blood haemoglobin (e.g., carboxyhemoglobin and methemoglobin) also have distinct spectral profiles.Hyperspectral imaging allows the quantification of local blood content, and oxygen saturation can be quantified by analysing the spectrum in each pixel.Thus, hyperspectral imaging can provide remarkable insight in understanding chronic inflammatory hyperemia in the skin.It should be noted that pro-inflammatory alterations are not directly used to diagnose AK or NMSC; instead, inflammatory infiltrate and increased angiogenesis serve as strong predictors for future AK or NMSC.In addition, pro-inflammatory alterations cannot be used to differentiate BCC and AK or SCC.
1][52][53] In this case, a full spectrum in the visible range is computationally reconstructed from an RGB image.Owing to its hardware simplicity, hyperspectral learning can be performed by using a smartphone camera.In practice, dispersive optical components, such as spectrometers and bulky optical filters, are usually attached to mobile dermatology applications, potentially weakening user acceptance and hampering the practical translation from research to clinical practice.Importantly, hyperspectral learning requires only an onboard smartphone camera, potentially offering hardware-independent tools using unmodified smartphones.Spatial frequency domain imaging (SFDI) can be used to map out alterations in blood haemoglobin content and oxygen saturations. 54 In particular, SFDI offers high spatial resolution, enabling detailed imaging of biological tissues at the microscale.This allows for the detection of subtle changes and abnormalities in chronic inflammatory hyperemic lesions of the skin.
6][57][58][59][60] DRS is characterised by the use of near-infrared light to examine the properties of tissue, including haemoglobin saturation concentration, 55,61 while LIFS is used to identify and quantify biochemical products such as nicotinamide adenine dinucleotide (NAD) and collagen. 563][64][65] One study actually compared the two imaging modalities, reporting a correlation of both DRS and LIFS with haemoglobin concentrations in NMSC conditions. 667][58][59][60] One pilot clinical study determined that 42% of biopsies could have been avoided by using this imaging technique prior to intervention. 56If these findings are representative of the population, using these methodologies has the potential to save millions of dollars by avoiding unnecessary skin biopsies.
8][69] Short laser pulses are delivered to tissues, leading to the generation of acoustic waves through the photoacoustic effect-the absorption of light energy by tissues results in thermoelastic expansion and the subsequent emission of ultrasound waves.These ultrasound signals are then detected and used to construct high-resolution images that reveal the distribution of light-absorbing molecules, such as haemoglobin, within biological tissue.Photoacoustic imaging provides deep tissue penetration, enabling imaging of structures several centimetres beneath the skin, and offers excellent contrast, making it particularly advantageous for visualising blood vessels.

| E XPERIMENTAL PHOTOC ARCINOG ENIC S TUDIE S
Our team successfully applied hyperspectral imaging to determine spatiotemporal and carcinogenic changes following UV radiation in a mouse model. 28,37This study focused on finding a correlation between UV-B exposure and cutaneous tumour production.Mice were exposed to UV-B light three times weekly for 10 weeks to induce experimental carcinogenesis.After stopping the UV treatments, spectral analyses of haemoglobin were used to pinpoint spots of increased haemoglobin content.It was found that tumours developed in areas with persistently increased haemoglobin content.Both histologic slides as well as microvessel density measures showed a significant increase in vasculature in areas with high observed haemoglobin content after UV-B exposure as compared to areas with low haemoglobin content with and without UV-B exposure.Areas of high haemoglobin content have epidermal hyperplasia and exhibit inflammatory infiltrate and dermal expansion (Figure 4A).These results further showed that inflammatory hyperemia and angiogenesis may be a key step contributing to cutaneous carcinogenesis due to F I G U R E 3 Representative imaging setups for hyperspectral imaging, RGB imaging, and spatial frequency domain imaging (SFDI).(A) Schematics of an imaging setup that simultaneously acquires hyperspectral and RGB image data.For hyperspectral imaging, a liquid crystal tunable filter (LCTF) is placed in front of the xenon lamp, and a mono CCD camera is used.For RGB imaging, LCTF is removed, and a conventional 3-colour CCD camera (trichromatic camera) is employed.(B) Schematics and photo of an SFDI system.LEDs are focused into a liquid light guide and directed onto a digital micromirror device (DMD).DMD generates sine wave patterns acquired by an sCMOS camera.Crossed polarised light is implemented to reject specular reflection.Adapted with permission from Kim et al. 42 and Travers et al. 43 UV-B light. 28The spatial and temporal extent of focal hyperemia shows that hyperemic foci not only persist but also expand in size, leading up tumour formation (Figure 4B).Compared with hyperspectral imaging (with a high spectral resolution), multispectral imaging (with several spectral bands) was successfully used to study a twostep chemical induction of carcinogenesis in mice.Increased haemoglobin "hot spots" were found to predict where skin lesions develop, indicating increased dermal vascularity for precancerous lesions. 70other study by our team demonstrated that inflammatory hyperemia can be spatiotemporally quantified using the hyperspectral learning algorithm, which converts an RGB image acquired from a conventional camera to a hypercube. 42A similar experimental protocol to the previous study was used to create UV-B-induced carcinogenesis in mice. 28,42It was shown to be just as accurate as the hyperspectral imaging system used at predicting carcinogenesis from the photographed areas of hyperemia.This significant study proposed the notion that conventional photos (RGB images), capture by a smartphone camera, can be used to evaluate and predict inflammatory hyperemia leading to tumorigenesis.This could have a monumental impact on the future of teledermatology practices.All of these previously mentioned preclinical studies display the utility of mesoscopic imaging methods in the detection of skin at risk for NMSC development by way of measuring dermal angiogenesis and elevated haemoglobin concentration.
These provide clear justification to pursue human clinical models to show its versatility in human medicine.

| CLINI C AL S TUD IE S OF AK s AND NMSC s
While several of these methodologies may be combined, DRS specifically has a rich history in imaging NMSC using dermal vasculature changes that should be highlighted.One of the first papers that utilised reflectance imaging in the classification of NMSCs using F I G U R E 4 Representative preclinical histology and haemoglobin (Hgb) content images from experimental carcinogenesis studies.(A) H&E stain (200×) images showing hyperemic foci at 20 weeks after the cessation of UVB irradiation.(B) Haemoglobin content images from the same UVB-treated mouse at biweekly intervals following the cessation of UVB irradiation.These haemoglobin-content images can be generated using hyperspectral imaging or a hyperspectral learning algorithm.Adapted with permission from Kim et al. 42 vascular properties dates back to 2004. 55A pilot clinical study has been tested in a small scale to measure total haemoglobin, absolute oxygenated haemoglobin, and oxygen saturation in cutaneous lesions. 63One clinical trial focused on using visible and near-infrared spectroscopy in a large population to classify lesions based on optical properties of the dermis and differentiating between malignant versus non-malignant areas of the skin using associated with absorption bands from haemoglobin species. 64Other studies have focused on validating lookup tables that were constructed on the basis of using DRS to detect NMSCs by identifying different parameters such as blood vessel radius and oxygen saturation. 65[73] A specific type of SFDI was successfully used to capture images of superficial blood vessels in the human forearm. 75This was one of the first studies of its kind to validate spatial frequency domain quantification to display absorption and scattering imaging technology to quantify turbid intravenous properties.This study laid the groundwork for upcoming trials to display tomographic and chromatographic changes in the skin. 76The use of SFDI to survey characteristics of NMSCs has been tested for its validity in a variety of studies.Researches have used it to help determine NMSC's response to 5-aminolaevulinic acid photodynamic therapy (ALA-PDT), a common dermatologic therapy to rid the skin of cancerous cells, by measuring protoporphyrin IX levels in NMSCs after ALA-PDT therapy. 77A human study of using SFDI and highfrequency ultrasound imaging determined the depth and blood oxygen saturation in NMSCs. 74Specifically, tissue oxygenation and blood haemoglobin content were informative parameters that helped a clinician to monitor PDT therapy responses (Figure 5).This proved to be helpful not only in terms of PDT treatment management but also by showing this modality's efficacy in visualising NMSC tumour margins. 74,77,78pilot study using SFDI conducted by our team quantitatively mapped cutaneous field carcinogenesis using the optical and vascular patterns of NMSC lesions and AKs.43 For patients with increasing degrees of actinic damage, with skin tones of Fitzpatrick scale I or II, absorption and scattering maps were created to depict changes in vasculature with parameters including total haemoglobin concentration, blood oxygen saturation, and deoxyhemoglobin (Figure 6).
The map of the patient who had the most actinic change (visible AKs present) compared to the map of the patient with the least visible actinic change showed a significant change in the percent variation across the images.This study has shown that SFDI has the potential to be a useful, noninvasive mesoscopic imaging method in the future to monitor actinic change in "fair" skin-toned individuals if used in serial sessions.
Our team further conducted a larger-scale follow-up study to statistically validate SFDI-generated maps for measuring quantitative actinic change. 43,79The same protocol was utilised; however, in this study, a statistically valid number of subjects (55, total of 110 forearm photographs) were used, analysed, spatially mapped, and compared among each other.Importantly, 15 board-certified dermatologists trained on assessing photodamage independently rated each subject's actinic damage using a photodamage score of 0-9 (also known as McKenzie scale 80 ).The maps and results were also fed into an artificial neural network, dividing actinic damage quantitatively into "low, medium and high" categories.Once outliers of the data were removed, it was determined that SFDI-measured parameters could be correlated with clinician grading of lesions in the values of low, medium and high amounts of actinic damage.While this method will not soon replace trained clinicians on analysing skin lesions, it provides a supplemental resource to categorically monitor actinic change in patients.
Photoacoustic imaging is an advanced imaging method used to detect chromophore (i.e., haemoglobin) density in the blood by emitting high-frequency waves that can be detected and mapped using an ultrasound probe. 81This method has been used in several settings to detect NMSC, including a study that was used to measure biopsy-confirmed BCC prior to photodynamic therapy intervention. 82Another pilot study using high-frequency ultrasound was able to accurately reconstruct the thickness of various NMSC using haemoglobin absorption as its vehicle, allowing for pre-surgical mapping of the lesion. 83It should be noted that mesoscopic imaging of haemoglobin using photoacoustic imaging could be useful in detecting NMSC. 84In addition, multispectral optoacoustic tomography is another modality that can be used to visualise in-vivo changes of the dermal layer during the formation of NMSC. 85Using this imaging method, visualisations of the tumours' morphology and vasculature using 3-D real-time imaging were achieved.This is a showcase study that exemplifies exactly how this modality could be used in the future: to guide NMSC removal surgery, monitor the growth of lesions and screen for which patients would be good candidates for intervention.

| MA JOR OPEN QUE S TI ON S
The major focus of this review is to highlight the mesoscopic imaging modalities used for mapping out skin cancerization based on chronic inflammatory hyperemia.7][88] These studies have obtained promising findings using ex-vivo tissue and a human xenograft to a murine model.These pilot studies are just the beginning; mesoscopic imaging techniques could be used to screen for field carcinogenesis during colonoscopies and endoscopic procedures routinely.The current studies support the idea that mesoscopic imaging of blood haemoglobin parameters and hemodynamics in the tissue microenvironments can be beneficial as research and clinical diagnostic tools for cutaneous field cancerization associated with AKs and NMSCs.However, additional clinical studies will need to be carried out in the future to address the following critical applications.
Can mesoscopic imaging modalities be used to detect and differentiate benign NMSC mimickers, such as sebaceous hyperplasia?Although benign tumours, such as sebaceous gland-derived tumours, are often associated with microvascular changes, 89,90 no mesoscopic imaging studies have been conducted to compare these changes in NMSC/AK precursor lesions to the best of our knowledge.Furthermore, there are currently no studies on other premalignant field cancerization conditions, such as disseminated superficial actinic porokeratosis or chronic burn scars, which also pose a risk of malignant degeneration to SCC, including the Marjolin ulcer phenotype observed in chronic burn scars.
Can mesoscopic imaging modalities be used to screen for chronic inflammatory conditions, such as rosacea and acne?2][93] Differentiating inflammatory conditions from actinic Can mesoscopic imaging modalities be used for individuals with darker Fitzpatrick skin types?Melanin and haemoglobin are the most prevalent chromophores in the skin for optical imaging. 94cause almost all of the previous studies rely on lighter Fitzpatrick skin types, there is limited literature about melanin-rich Asian and African American patients.6][97] Overall, to address such gaps, extensive validation studies of mesoscopic imaging technologies are required before widespread clinical use.
Mesoscopic imaging also has the potential to be integrated into spatial omics technologies for mapping the spatial heterogeneity in gene expression within the carcinogenesis field.][100][101] This integrated approach will enhance our understanding of cancer and facilitate the development of new cancer prevention approaches.Mesoscopic imaging of chronic hyperemia and proinflammatory cues in tissue microenvironments can offer spatial coordinate information for spatial omics analyses across a relatively large area.Such larger-scale patterns or organisations of profiling at a single-cell level can contribute to a better understanding of organspecific tumour microenvironments, benefiting both research and clinical applications.
Current research is being conducted in our laboratories on the utility of photographs taken by smartphones in analysing skin lesions.As previously mentioned, hyperspectral learning algorithms can be highly useful to minimise hardware complexity, allowing us to take advantage of smartphone cameras using machine learning. 85perspectral learning needs only an onboard camera, potentially offering digital health and mobile health tools with unmodified smartphones in at-home settings.The results of this study could change the future of dermatology practice by providing patients a way to have their skin lesions noninvasively analysed by sending a simple photograph from the comfort of their homes via a telemedicine platform.Not only will patients no longer need to have their lesions biopsied, but this could expand access to care for those who do not have a dermatologist in their vicinity.Obviously, this mesoscopic imaging modality will not replace the eyes of a trained boardcertified dermatologist; however, it is an avenue to explore in the future.
Unlike traditional imaging methods, SFDI operates in the spatial frequency domain, utilising patterns of light and measuring F I G U R E 2 Progression of NMSC cancerization and how mesoscopic imaging modalities can detect cutaneous field carcinogenesis.(A) Example of a focal area of normal vascularization and quantities of epidermal and dermal cells prior to radiation or damage.(B) Once prolonged irritation to the area occurs due to radiation or other types of damage (chemical irritation and ageing), inflammation causes increased haemoglobin extravasation and angiogenesis.(C) Prolonged irritation and inflammation resulting in inflammatory hyperemia and angiogenesis associated with field carcinogenesis.Mesoscopic imaging technology can efficiently detect such pro-inflammatory changes within the dermis.F I G U R E 1 Comparison of microscopic versus mesoscopic imaging views of true cutaneous field cancerization.Microscopic imaging only captures a fraction of the field cancerization, while mesoscopic imaging offers a broader view.how they interact with tissue at different frequencies, as illustrated in Figure 3B.In this method, patterns of light with varying spatial frequencies are projected onto the tissue, and the resulting diffuse light is measured.By examining how these patterns interact with the tissue at different frequencies, SFDI can extract valuable information about the tissue's absorption properties, including tissue parameters such as haemoglobin content and oxygen saturation.

F I G U R E 5 74 F I G U R E 6
Representative clinical images of tissue oxygen saturation (StO 2 ) and haemoglobin (Hb) content from lesions.(A) Tissue oxygen saturation and haemoglobin content images generated using SFDI from a patient with BCC.(B) Tissue oxygen saturation and haemoglobin content images generated using SFDI for a patient with SCC.The scale bar corresponds to 2 mm.Adapted with permission from Rohrbach et al.Representative clinical images of photodamage using SFDI.(A) Photos of patients' arms, labelled P1, P2 and P3, showing increasing visible photodamage.(B) Corresponding images of total haemoglobin, oxygenated haemoglobin, and tissue oxygen saturation.Adapted with permission from Travers et al. 43 neoplasia is important for known inflammatory conditions that carry an associated risk of malignant degeneration to SCC.Lichen planus, lichen sclerosis et atrophicans and leukoplakia are considered classic examples of inflammatory conditions that can be complicated by NMSC.Even though experienced dermatologists can differentiate inflammatory conditions such as dermatitis from actinic damage, mesoscopic imaging could presumably help detect malignant degeneration at an earlier stage, for example, at the in-situ stage of squamous cell carcinoma.Current mesoscopic imaging methods are presently constrained in their ability to directly distinguish between inflammatory and neoplastic disorders, necessitating further technological research and development.

8 |
CON CLUS I ON S AND PER S PEC TIVE S The NMSC is the most prevalent form of cancer in the world and in the US.Mesoscopic imaging of inflammatory hyperemia in tissue microenvironments can allow for noninvasive approaches to determine the spatial extent of cutaneous field cancerization associated with NMSCs in both the preclinical and clinical settings.Mesoscopic biomedical imaging modalities for dermatological applications can allow researchers and clinicians a chance to look at and biopsy highrisk "hot spots" and low-risk areas to understand the mechanism of cutaneous carcinogenesis.While UV-B exposure or another chemical carcinogens may be the initial reason for inflammatory hyperemia and angiogenesis to occur, tumours can still expand following cessation of the irritant.Recognising and identifying premalignant lesions noninvasively may allow researchers and clinicians to continue to study how cancerization occurs in the absence of carcinogens such as UV-B.An improved understanding of cutaneous field cancerization will identify patients who will most benefit from personalised therapies for NMSCs and open new possibilities of intervention for treating AKs and NMSCs.