Accurate early prediction of tumour response to PDT using optical coherence angiography

Devices and Methods for Dosimetry of Personalized Photodynamic Therapy of Tumors: A Review on Recent Trends

Significance: Despite the widespread use of photodynamic therapy in clinical practice, there is a lack of personalized methods for assessing the sufficiency of photodynamic exposure on tumors, depending on tissue parameters that change during light irradiation. This can lead to different treatment results. Aim: The objective of this article was to conduct a comprehensive review of devices and methods employed for the implicit dosimetric monitoring of personalized photodynamic therapy for tumors. Methods: The review included 88 peer-reviewed research articles published between January 2010 and April 2024 that employed implicit monitoring methods, such as fluorescence imaging and diffuse reflectance spectroscopy. Additionally, it encompassed computer modeling methods that are most often and successfully used in preclinical and clinical practice to predict treatment outcomes. The Internet search engine Google Scholar and the Scopus database were used to search the literature for relevant articles. Results: The review analyzed and compared the results of 88 peer-reviewed research articles presenting various methods of implicit dosimetry during photodynamic therapy. The most prominent wavelengths for PDT are in the visible and near-infrared spectral range such as 405, 630, 660, and 690 nm. Conclusions: The problem of developing an accurate, reliable, and easily implemented dosimetry method for photodynamic therapy remains a current problem, since determining the effective light dose for a specific tumor is a decisive factor in achieving a positive treatment outcome.

Multimodal OCT Control for Early Histological Signs of Vulvar Lichen Sclerosus Recurrence after Systemic PDT: Pilot Study

Photodynamic therapy (PDT) is a modern treatment for severe or treatment-resistant vulvar lichen sclerosus (VLS). The chronic and recurrent nature of VLS requires control of recurrences at an early stage. In this paper, a non-invasive multimodal optical coherence tomography (OCT) method was used to control for early histological signs of VLS recurrence after systemic PDT using Photodithazine®. To interpret the OCT data, a histological examination was performed before PDT and 3 months after PDT. Two groups of patients were identified: with early histological signs of VLS recurrence (Group I, n = 5) and without histological signs of VLS recurrence (Group II, n = 6). We use structural OCT, OCT angiography, and OCT lymphangiography throughout 6 months after PDT to visually assess the skin components and to quantitatively assess the dermis by calculating the depth-resolved attenuation coefficient and the density of blood and lymphatic vessels. The OCT data assessment showed a statistically significant difference between the patient groups 3 months after PDT. In Group II, all the studied OCT parameters reached maximum values by the 3rd month after PDT, which indicated recovery of the skin structure. At the same time, in Group I, the values of OCT parameters did not approach the values those in Group II even after 6 months. The obtained results of multimodal OCT can be used for non-invasive control of early histological recurrence of VLS after systemic PDT and for adjusting treatment tactics in advance, without waiting for new clinical manifestations of the disease.

PDT-Induced Activation Enhanced by Hormone Response to Treatment

Photodynamic therapy (PDT) is a medical treatment with the use of a photosensitizing agent (PS), which, when activated by light, results in selective tissue damage with a cytotoxic effect on tumor cells. PDT leads to the induction of an acute-phase response, which results in the involvement of adrenal glucocorticoid (GC) hormones. PDT, by activating the hormonal response, affects the treatment of cancer. GC release is observed due to adrenal activity, which is driven by changes in the hypothalamic pituitary-adrenal axis triggered by stress signals emanating from the PDT treated tumor. The hormones released in this process in the context of the PDT-induced acute-phase response perform many important functions during anticancer therapy. They lead, among other things, to the systemic mobilization of neutrophils and the production of acute-phase reagents, and also control the production of immunoregulatory proteins and proteins that modulate inflammation. GCs can radically affect the activity of various inflammatory and immune cells, including the apoptosis of cancer cells. A better understanding of the modulation of GC activity could improve the outcomes of cancer patients treated with PDT.

Pyrrolopyrrole aza-BODIPY-based NIR-II fluorophores for in vivo dynamic vascular dysfunction visualization of vascular-targeted photodynamic therapy

Real-time monitoring vascular responses is crucial for evaluating the therapeutic effects of vascular-targeted photodynamic therapy (V-PDT). Herein, we developed a highly-stable and bright aggregation induced emission (AIE) fluorophore (PTPE3 NP) for dynamic fluorescence (FL) imaging of vascular dysfunction beyond 1300 nm window during V-PDT. The superior brightness (ϵ_maxΦ_{f>1000 nm} ≈ 180.05 M^-1 cm^-1) and high resolution of PTPE3 NP affords not only high-clarity images of whole-body and local vasculature (hindlimbs, mesentery, and tumor) but also high-speed video imaging for tracking blood circulation process. By virtue of the NPs' prolonged blood circulation time (t_1/2 ≈ 86.5 min) and excellent photo/chemical (pH, RONS) stability, mesenteric and tumor vascular dysfunction (thrombosis formation, vessel occlusion, and hemorrhage) can be successfully visualized during V-PDT by FL imaging for the first time. Furthermore, the reduction of blood flow velocity (BFV) can be monitored in real time for precisely evaluating efficacy of V-PDT. These provide a powerful approach for assessing vascular responses during V-PDT and promote the development of advanced fluorophores for biological imaging.

Skin Cancer Pathobiology at a Glance: A Focus on Imaging Techniques and Their Potential for Improved Diagnosis and Surveillance in Clinical Cohorts

Early diagnosis is essential for completely eradicating skin cancer and maximizing patients' clinical benefits. Emerging optical imaging modalities such as reflectance confocal microscopy (RCM), optical coherence tomography (OCT), magnetic resonance imaging (MRI), near-infrared (NIR) bioimaging, positron emission tomography (PET), and their combinations provide non-invasive imaging data that may help in the early detection of cutaneous tumors and surgical planning. Hence, they seem appropriate for observing dynamic processes such as blood flow, immune cell activation, and tumor energy metabolism, which may be relevant for disease evolution. This review discusses the latest technological and methodological advances in imaging techniques that may be applied for skin cancer detection and monitoring. In the first instance, we will describe the principle and prospective clinical applications of the most commonly used imaging techniques, highlighting the challenges and opportunities of their implementation in the clinical setting. We will also highlight how imaging techniques may complement the molecular and histological approaches in sharpening the non-invasive skin characterization, laying the ground for more personalized approaches in skin cancer patients.

Novel Elastography-Inspired Approach to Angiographic Visualization in Optical Coherence Tomography

In this paper, we present a new approach to contrast-agent-free angiographic visualization in optical coherence tomography (OCT). The proposed approach has much in common with imaging of local interframe strains in OCT-based elastography and utilizes the fact that the interframe motion of blood particles leads to discontinuity of strains within the vessel cross section. By this reasoning, we call this approach “elastography-inspired”. Here, we first elucidate the essence and main features of the elastography-inspired approach using numerical simulation of OCT data. The simulations allow one to introduce both moving scatterers imitating blood flow in vessels as well as various masking motions imitating natural motions of living “solid” tissue surrounding the vessels. Second, using real OCT signals, we present comparative results of angiographic processing using the proposed elastography-inspired approach and a realization of OCA based on high-pass filtering of temporal variability of a series of OCT B-scans. The two methods can use the same initial dataset and the high-pass filtering OCA has already been routinely applied in both animal experiments and on patients. The new elastography-inspired method has a similar computational efficiency, and it is intrinsically able to compensate spatially-inhomogeneous masking tissue motions and demonstrates high robustness with respect to motion artefacts. Thus, the new approach looks very promising for enabling wider application of OCA in both laboratory studies on animals and, most importantly, for wider clinical applications on patients.

Nonlinear Elasticity Assessment with Optical Coherence Elastography for High-Selectivity Differentiation of Breast Cancer Tissues

Soft biological tissues, breast cancer tissues in particular, often manifest pronounced nonlinear elasticity, i.e., strong dependence of their Young’s modulus on the applied stress. We showed that compression optical coherence elastography (C-OCE) is a promising tool enabling the evaluation of nonlinear properties in addition to the conventionally discussed Young’s modulus in order to improve diagnostic accuracy of elastographic examination of tumorous tissues. The aim of this study was to reveal and quantify variations in stiffness for various breast tissue components depending on the applied pressure. We discussed nonlinear elastic properties of different breast cancer samples excised from 50 patients during breast-conserving surgery. Significant differences were found among various subtypes of tumorous and nontumorous breast tissues in terms of the initial Young’s modulus (estimated for stress < 1 kPa) and the nonlinearity parameter determining the rate of stiffness increase with increasing stress. However, Young’s modulus alone or the nonlinearity parameter alone may be insufficient to differentiate some malignant breast tissue subtypes from benign. For instance, benign fibrous stroma and fibrous stroma with isolated individual cancer cells or small agglomerates of cancer cells do not yet exhibit significant difference in the Young’s modulus. Nevertheless, they can be clearly singled out by their nonlinearity parameter, which is the main novelty of the proposed OCE-based discrimination of various breast tissue subtypes. This ability of OCE is very important for finding a clean resection boundary. Overall, morphological segmentation of OCE images accounting for both linear and nonlinear elastic parameters strongly enhances the correspondence with the histological slices and radically improves the diagnostic possibilities of C-OCE for a reliable clinical outcome.

A Review of Clinical Applications for Super-resolution Ultrasound Localization Microscopy

Microvascular structure and hemodynamics are important indicators for the diagnosis and assessment of many diseases and pathologies. The structural and functional imaging of tissue microvasculature in vivo is a clinically significant objective for the development of many imaging modalities. Contrast-enhanced ultrasound (CEUS) is a popular clinical tool for characterizing tissue microvasculature, due to the moderate cost, wide accessibility, and absence of ionizing radiation of ultrasound. However, in practice, it remains challenging to demonstrate microvasculature using CEUS, due to the resolution limit of conventional ultrasound imaging. In addition, the quantification of tissue perfusion by CEUS remains hindered by high operator-dependency and poor reproducibility. Inspired by super-resolution optical microscopy, super-resolution ultrasound localization microscopy (ULM) was recently developed. ULM uses the same ultrasound contrast agent (i.e. microbubbles) in CEUS. However, different from CEUS, ULM uses the location of the microbubbles to construct images, instead of using the backscattering intensity of microbubbles. Hence, ULM overcomes the classic compromise between imaging resolution and penetration, allowing for the visualization of capillary-scale microvasculature deep within tissues. To date, many in vivo ULM results have been reported, including both animal (kidney, brain, spinal cord, xenografted tumor, and ear) and human studies (prostate, tibialis anterior muscle, and breast cancer tumors). Furthermore, a variety of useful biomarkers have been derived from using ULM for different preclinical and clinical applications. Due to the high spatial resolution and accurate blood flow speed estimation (approximately 1 mm/s to several cm/s), ULM presents as an enticing alternative to CEUS for characterizing tissue microvasculature in vivo. This review summarizes the principles and present applications of CEUS and ULM, and discusses areas where ULM can potentially provide a better alternative to CEUS in clinical practice and areas where ULM may not be a better alternative. The objective of the study is to provide clinicians with an up-to-date review of ULM technology, and a practical guide for implementing ULM in clinical research and practice.

Combined Fluorescence and Optoacoustic Imaging for Monitoring Treatments against CT26 Tumors with Photoactivatable Liposomes

The newly developed multimodal imaging system combining raster-scan optoacoustic (OA) microscopy and fluorescence (FL) wide-field imaging was used for characterizing the tumor vascular structure with 38/50 μm axial/transverse resolution and assessment of photosensitizer fluorescence kinetics during treatment with novel theranostic agents. A multifunctional photoactivatable multi-inhibitor liposomal (PMILs) nano platform was engineered here, containing a clinically approved photosensitizer, Benzoporphyrin derivative (BPD) in the bilayer, and topoisomerase I inhibitor, Irinotecan (IRI) in its inner core, for a synergetic therapeutic impact. The optimized PMIL was anionic, with the hydrodynamic diameter of 131.6 ± 2.1 nm and polydispersity index (PDI) of 0.05 ± 0.01, and the zeta potential between -14.9 ± 1.04 to -16.9 ± 0.92 mV. In the in vivo studies on BALB/c mice with CT26 tumors were performed to evaluate PMILs' therapeutic efficacy. PMILs demonstrated the best inhibitory effect of 97% on tumor growth compared to the treatment with BPD-PC containing liposomes (PALs), 81%, or IRI containing liposomes (L-[IRI]) alone, 50%. This confirms the release of IRI within the tumor cells upon PMILs triggering by NIR light, which is additionally illustrated by FL monitoring demonstrating enhancement of drug accumulation in tumor initiated by PDT in 24 h after the treatment. OA monitoring revealed the largest alterations of the tumor vascular structure in the PMILs treated mice as compared to BPD-PC or IRI treated mice. The results were further corroborated with histological data that also showed a 5-fold higher percentage of hemorrhages in PMIL treated mice compared to the control groups. Overall, these results suggest that multifunctional PMILs simultaneously delivering PDT and chemotherapy agents along with OA and FL multi-modal imaging offers an efficient and personalized image-guided platform to improve cancer treatment outcomes.

Photodynamic Therapy for the Treatment and Diagnosis of Cancer-A Review of the Current Clinical Status

Photodynamic therapy (PDT) has been used as an anti-tumor treatment method for a long time and photosensitizers (PS) can be used in various types of tumors. Originally, light is an effective tool that has been used in the treatment of diseases for ages. The effects of combination of specific dyes with light illumination was demonstrated at the beginning of 20th century and novel PDT approaches have been developed ever since. Main strategies of current studies are to reduce off-target effects and improve pharmacokinetic properties. Given the high interest and vast literature about the topic, approval of PDT as the first drug/device combination by the FDA should come as no surprise. PDT consists of two stages of treatment, combining light energy with a PS in order to destruct tumor cells after activation by light. In general, PDT has fewer side effects and toxicity than chemotherapy and/or radiotherapy. In addition to the purpose of treatment, several types of PSs can be used for diagnostic purposes for tumors. Such approaches are called photodynamic diagnosis (PDD). In this Review, we provide a general overview of the clinical applications of PDT in cancer, including the diagnostic and therapeutic approaches. Assessment of PDT therapeutic efficacy in the clinic will be discussed, since identifying predictors to determine the response to treatment is crucial. In addition, examples of PDT in various types of tumors will be discussed. Furthermore, combination of PDT with other therapy modalities such as chemotherapy, radiotherapy, surgery and immunotherapy will be emphasized, since such approaches seem to be promising in terms of enhancing effectiveness against tumor. The combination of PDT with other treatments may yield better results than by single treatments. Moreover, the utilization of lower doses in a combination therapy setting may cause less side effects and better results than single therapy. A better understanding of the effectiveness of PDT in a combination setting in the clinic as well as the optimization of such complex multimodal treatments may expand the clinical applications of PDT.

Red and blue light in antitumor photodynamic therapy with chlorin-based photosensitizers: a comparative animal study assisted by optical imaging modalities

The goal of this study is a comparative analysis of the efficiency of the PDT protocols for CT26 tumor model treatment in Balb/c mice employing red and blue light with both topical and intravenous administration of chlorin-based photosensitizers (PSs). The considered protocols include the doses of 250 J/cm² delivered at 660 nm, 200 J/cm² delivered at 405 nm, and 250 J/cm² delivered at both wavelengths with equal energy density contribution. Dual-wavelength fluorescence imaging was employed to estimate both photobleaching efficiency, typical photobleaching rates and the procedure impact depth, while optical coherence tomography with angiography modality (OCT-A) was employed to monitor the tumor vasculature response for up to 7 days after the procedure with subsequent histology inspection. Red light or dual-wavelength PDT regimes with intravenous PS injection were demonstrated to provide the most pronounced tumor response among all the considered cases. On the contrary, blue light regimes were demonstrated to be most efficient among topical application and irradiation only regimes. Tumor size dynamics for different groups is in good agreement with the tumor response predictions based on OCT-A taken in 24h after exposure and the results of histology analysis performed in 7 days after the exposure.

In vivo multimodal optical imaging of dermoscopic equivocal melanocytic skin lesions

There is a wide range of equivocal melanocytic lesions that can be clinically and dermoscopically indistinguishable from early melanoma. In the present work, we assessed the possibilities of combined using of multiphoton microscopy (MPM) and optical coherence angiography (OCA) for differential diagnosis of the equivocal melanocytic lesions. Clinical and dermoscopic examinations of 60 melanocytic lesions revealed 10 benign lesions and 32 melanomas, while 18 lesions remained difficult to diagnose. Histopathological analysis of these lesions revealed 4 intradermal, 3 compound and 3 junctional nevi in the "benign" group, 7 superficial spreading, 14 lentigo maligna and 11 nodular melanomas in the "melanoma" group and 2 lentigo simplex, 4 dysplastic nevi, 6 melanomas in situ, 4 invasive lentigo melanomas and 2 invasive superficial spreading melanomas in the "equivocal" group. On the basis of MPM, a multiphoton microscopy score (MPMS) has been developed for quantitative assessment of melanoma features at the cellular level, that showed lower score for benign lesions compare with malignant ones. OCA revealed that the invasive melanoma has a higher vessel density and thicker blood vessels than melanoma in situ and benign lesions. Discriminant functions analysis of MPM and OCA data allowed to differentiate correctly between all equivocal melanocytic lesions. Therefore, we demonstrate, for the first time, that a combined use of MPM and OCA has the potential to improve early diagnosis of melanoma.

In vivo assessment of vascular-targeted photodynamic therapy effects on tumor microvasculature using ultrahigh-resolution functional optical coherence tomography

Vascular-targeted photodynamic therapy (VTP) is an emerging treatment for tumors. The change of tumor vasculatures, including a newly-formed microvascular, in response to VTP, is a key assessment parameter for optimizing the treatment effect. However, an accurate assessment of vasculature, particularly the microvasculature's changes in vivo, remains challenging due to the limited resolution afforded by existing imaging modalities. In this study, we demonstrated the in vivo imaging of VTP effects on an A431 tumor-bearing window chamber model of a mouse with an 800-nm ultrahigh-resolution functional optical coherence tomography (UHR-FOCT). We further quantitatively demonstrated the effects of VTP on the size and density of tumor microvasculature before, during, and after the treatment. Our results suggest the promising potential of UHR-FOCT for assessing the tumor treatment with VTP in vivo and in real time to achieve an optimal outcome.

Histological validation of in vivo assessment of cancer tissue inhomogeneity and automated morphological segmentation enabled by Optical Coherence Elastography

We present a non-invasive (albeit contact) method based on Optical Coherence Elastography (OCE) enabling the in vivo segmentation of morphological tissue constituents, in particular, monitoring of morphological alterations during both tumor development and its response to therapies. The method uses compressional OCE to reconstruct tissue stiffness map as the first step. Then the OCE-image is divided into regions, for which the Young’s modulus (stiffness) falls in specific ranges corresponding to the morphological constituents to be discriminated. These stiffness ranges (characteristic "stiffness spectra") are initially determined by careful comparison of the "gold-standard" histological data and the OCE-based stiffness map for the corresponding tissue regions. After such pre-calibration, the results of morphological segmentation of OCE-images demonstrate a striking similarity with the histological results in terms of percentage of the segmented zones. To validate the sensitivity of the OCE-method and demonstrate its high correlation with conventional histological segmentation we present results obtained in vivo on a murine model of breast cancer in comparative experimental study of the efficacy of two antitumor chemotherapeutic drugs with different mechanisms of action. The new technique allowed in vivo monitoring and quantitative segmentation of (1) viable, (2) dystrophic, (3) necrotic tumor cells and (4) edema zones very similar to morphological segmentation of histological images. Numerous applications in other experimental/clinical areas requiring rapid, nearly real-time, quantitative assessment of tissue structure can be foreseen.

Automatic protocol for quantifying the vasoconstriction in blood vessel images

Vascular targeted photodynamic therapy (V-PDT) has been successfully utilized for various vascular-related diseases. To optimize the PDT dose and treatment protocols for clinical treatments and to elucidate the biological mechanisms for V-PDT, blood vessels in the dorsal skin-fold window chamber (DSWC) of nude mice are often chosen to perform in vivo studies. In this study, a new automatic protocol to quantify the vasoconstriction of blood vessels in the DSWC model is proposed, which focused on tracking the pixels of blood vessels in pre- V-PDT images that disappear after V-PDT. The disappearing pixels indicate that the blood vessels were constricted, and thus, the vasoconstriction image for pixel distribution can be constructed. For this, the image of the circular region of interest was automatically extracted using the Hough transform. In addition, the U-Net model is employed to segment the image, and the Speeded-Up Robust Features algorithm to automatically register the segmented pre- and post- V-PDT images. The vasoconstriction of blood vessels in the DSWC model after V-PDT is directly quantified, which can avoid by the potential of generating new capillaries. The accuracy, sensitivity and specificity of the U-Net model for image segmentation are 90.64%, 80.12% and 92.83%, respectively. A significant difference in vasoconstriction between a control and a V-PDT group was observed. This new automatic protocol is well suitable for quantifying vasoconstriction in blood vessel image, which holds the potential application in V-PDT studies.

In vivo assessment of functional and morphological alterations in tumors under treatment using OCT-angiography combined with OCT-elastography

Emerging methods of anti-tumor therapies require new approaches to tumor response evaluation, especially enabling label-free diagnostics and in vivo utilization. Here, to assess the tumor early reaction and predict its long-term response, for the first time we apply in combination the recently developed OCT extensions - optical coherence angiography (OCA) and compressional optical coherence elastography (OCE), thus enabling complementary functional/microstructural tumor characterization. We study two vascular-targeted therapies of different types, (1) anti-angiogenic chemotherapy (ChT) and (2) photodynamic therapy (PDT), aimed to indirectly kill tumor cells through blood supply injury. Despite different mechanisms of anti-angiogenic action for ChT and PDT, in both cases OCA demonstrated high sensitivity to blood perfusion cessation. The new method of OCE-based morphological segmentation revealed very similar histological structure alterations. The OCE results showed high correlation with conventional histology in evaluating percentages of necrotic and viable tumor zones. Such possibilities make OCE an attractive tool enabling previously inaccessible in vivo monitoring of individual tumor response to therapies without taking multiple biopsies.

Optical coherence angiography for pre-treatment assessment and treatment monitoring following photodynamic therapy: a basal cell carcinoma patient study

Microvascular networks of human basal cell carcinomas (BCC) and surrounding skin were assessed with optical coherence angiography (OCA) in conjunction with photodynamic therapy (PDT). OCA images were collected and analyzed in 31 lesions pre-treatment, and immediately/24 hours/3-12 months post-treatment. Pre-treatment OCA enabled differentiation between prevalent subtypes of BCC (nodular and superficial) and nodular-with-necrotic-core BCC subtypes with a diagnostic accuracy of 78%; this can facilitate more accurate biopsy reducing sampling error and better therapy regimen selection. Post-treatment OCA images at 24 hours were 98% predictive of eventual outcome. Additional findings highlight the importance of pre-treatment necrotic core, vascular metrics associated with hypertrophic scar formation, and early microvascular changes necessary in both tumorous and peri-tumorous regions to ensure treatment success.

Comparative analysis of single- and dual-wavelength photodynamic therapy regimes with chlorin-based photosensitizers: animal study

Two pronounced absorption peaks in blue and red ranges of the chlorin-based photosensitizer (PS) absorption spectrum provide additional benefits in photodynamic therapy (PDT) performance. Differing optical properties of biological tissues in these ranges allow for both dual-wavelength diagnostics and PDT performance. We provide a comparative analysis of different PDT regimes performed with blue and red lights and their combination, with doses varying from 50 to 150  J  /  cm². The study was performed on the intact skin of a rabbit ear inner surface, with the use of chlorin e6 as a PS. PDT procedure protocol included monitoring of the treated site with fluorescence imaging technique to evaluate PS accumulation and photobleaching, as well as with optical coherence tomography (OCT) to register morphological and functional responses of the tissue. Optical diagnostic observations were compared with the results of histopathology examination. We demonstrated that PDT procedures with the considered regimes induce weaker organism reaction manifested by edema in normal tissue as compared to irradiation-only exposures with the same light doses. The light doses delivered with red light induce weaker tissue reaction as compared to the same doses delivered with blue light only or with a combination of red and blue lights in equal parts. Results of in-vivo OCT monitoring of tissue reaction are in agreement with the results of histopathology study.