Interstitial Doppler Optical Coherence Tomography as a Local Tumor Necrosis Predictor in Photodynamic Therapy of Prostatic Carcinoma: An In vivo Study

In vivo burn scar assessment with speckle decorrelation and joint spectral and time domain optical coherence tomography

Significance

Post-burn scars and scar contractures present significant challenges in burn injury management, necessitating accurate evaluation of the wound healing process to prevent or minimize complications. Non-invasive and accurate assessment of burn scar vascularity can offer valuable insights for evaluations of wound healing. Optical coherence tomography (OCT) and OCT angiography (OCTA) are promising imaging techniques that may enhance patient-centered care and satisfaction by providing detailed analyses of the healing process.

Aim

Our study investigates the capabilities of OCT and OCTA for acquiring information on blood vessels in burn scars and evaluates the feasibility of utilizing this information to assess burn scars.

Approach

Healthy skin and neighboring scar data from nine burn patients were obtained using OCT and processed with speckle decorrelation, Doppler OCT, and an enhanced technique based on joint spectral and time domain OCT. These methods facilitated the assessment of vascular structure and blood flow velocity in both healthy skin and scar tissues. Analyzing these parameters allowed for objective comparisons between normal skin and burn scars.

Results

Our study found that blood vessel distribution in burn scars significantly differs from that in healthy skin. Burn scars exhibit increased vascularization, featuring less uniformity and lacking the intricate branching network found in healthy tissue. Specifically, the density of the vessels in burn scars is 67% higher than in healthy tissue, while axial flow velocity in burn scar vessels is 25% faster than in healthy tissue.

Conclusions

Our research demonstrates the feasibility of OCT and OCTA as burn scar assessment tools. By implementing these technologies, we can distinguish between scar and healthy tissue based on its vascular structure, providing evidence of their practicality in evaluating burn scar severity and progression.

Novel Imaging-Based Biomarkers for Identifying Carotid Plaque Vulnerability

Carotid artery disease has traditionally been assessed based on the degree of luminal narrowing. However, this approach, which solely relies on carotid stenosis, is currently being questioned with regard to modern risk stratification approaches. Recent guidelines have introduced the concept of the "vulnerable plaque," emphasizing specific features such as thin fibrous caps, large lipid cores, intraplaque hemorrhage, plaque rupture, macrophage infiltration, and neovascularization. In this context, imaging-based biomarkers have emerged as valuable tools for identifying higher-risk patients. Non-invasive imaging modalities and intravascular techniques, including ultrasound, computed tomography, magnetic resonance imaging, intravascular ultrasound, optical coherence tomography, and near-infrared spectroscopy, have played pivotal roles in characterizing and detecting unstable carotid plaques. The aim of this review is to provide an overview of the evolving understanding of carotid artery disease and highlight the significance of imaging techniques in assessing plaque vulnerability and informing clinical decision-making.

Saturation transfer properties of tumour xenografts derived from prostate cancer cell lines 22Rv1 and DU145

Histopathology is currently the most reliable tool in assessing the aggressiveness and prognosis of solid tumours. However, developing non-invasive modalities for tumour evaluation remains crucial due to the side effects and complications caused by biopsy procedures. In this study, saturation transfer MRI was used to investigate the microstructural and metabolic properties of tumour xenografts in mice derived from the prostate cancer cell lines 22Rv1 and DU145, which express different aggressiveness. The magnetization transfer (MT) and chemical exchange saturation transfer (CEST) effects, which are associated with the microstructural and metabolic properties in biological tissue, respectively, were analyzed quantitatively and compared amongst different tumour types and regions. Histopathological staining was performed as a reference. Higher cellular density and metabolism expressed in more aggressive tumours (22Rv1) were associated with larger MT and CEST effects. High collagen content in the necrotic regions might explain their higher MT effects compared to tumour regions.

A deep-learning-based approach for noise reduction in high-speed optical coherence Doppler tomography

Optical coherence Doppler tomography (ODT) increasingly attracts attention because of its unprecedented advantages with respect to high contrast, capillary-level resolution and flow speed quantification. However, the trade-off between the signal-to-noise ratio of ODT images and A-scan sampling density significantly slows down the imaging speed, constraining its clinical applications. To accelerate ODT imaging, a deep-learning-based approach is proposed to suppress the overwhelming phase noise from low-sampling density. To handle the issue of limited paired training datasets, a generative adversarial network is performed to implicitly learn the distribution underlying Doppler phase noise and to generate the synthetic data. Then a 3D based convolutional neural network is trained and applied for the image denoising. We demonstrate this approach outperforms traditional denoise methods in noise reduction and image details preservation, enabling high speed ODT imaging with low A-scan sampling density.

Light Fluence Rate and Tissue Oxygenation (St O2 ) Distributions Within the Thoracic Cavity of Patients Receiving Intraoperative Photodynamic Therapy for Malignant Pleural Mesothelioma

The distributions of light and tissue oxygenation (S_t O₂ ) within the chest cavity were determined for 15 subjects undergoing macroscopic complete resection followed by intraoperative photodynamic therapy (PDT) as part of a clinical trial for the treatment of malignant pleural mesothelioma (MPM). Over the course of light delivery, detectors at each of eight different sites recorded exposure to variable fluence rate. Nevertheless, the treatment-averaged fluence rate was similar among sites, ranging from a median of 40-61 mW cm^-2 during periods of light exposure to a detector. S_t O₂ at each tissue site varied by subject, but posterior mediastinum and posterior sulcus were the most consistently well oxygenated (median S_t O₂ >90%; interquartile ranges ~85-95%). PDT effect on S_t O₂ was characterized as the S_t O₂ ratio (post-PDT S_t O₂ /pre-PDT S_t O₂ ). High S_t O₂ pre-PDT was significantly associated with oxygen depletion (S_t O₂ ratio < 1), although the extent of oxygen depletion was mild (median S_t O₂ ratio of 0.8). Overall, PDT of the thoracic cavity resulted in moderate treatment-averaged fluence rate that was consistent among treated tissue sites, despite instantaneous exposure to high fluence rate. Mild oxygen depletion after PDT was experienced at tissue sites with high pre-PDT S_t O₂ , which may suggest the presence of a treatment effect.

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.

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

Prediction of tumour treatment response may play a crucial role in therapy selection and optimization of its delivery parameters. Here we use optical coherence angiography (OCA) as a minimally-invasive, label-free, real-time bioimaging method to visualize normal and pathological perfused vessels and monitor treatment response following vascular-targeted photodynamic therapy (PDT). Preclinical results are reported in a convenient experimental model (CT-26 colon tumour inoculated in murine ear), enabling controlled PDT and post-treatment OCA monitoring. To accurately predict long-term treatment outcome, a robust and simple microvascular metric is proposed. It is based on perfused vessels density (PVD) at t = 24 hours post PDT, calculated for both tumour and peri-tumour regions. Histological validation in the examined experimental cohort (n = 31 animals) enabled further insight into the excellent predictive power of the derived early-response OCA microvascular metric. The results underscore the key role of peri-tumour microvasculature in determining the long-term PDT response.

In-vivo longitudinal imaging of microvascular changes in irradiated oral mucosa of radiotherapy cancer patients using optical coherence tomography

Mucositis is the limiting toxicity of radio(chemo)therapy of head and neck cancer. Diagnostics, prophylaxis and correction of this condition demand new accurate and objective approaches. Here we report on an in vivo longitudinal monitoring of the oral mucosa dynamics in 25 patients during the course of radiotherapy of oropharyngeal and nasopharyngeal cancer using multifunctional optical coherence tomography (OCT). A spectral domain OCT system with a specially-designed oral imaging probe was used. Microvasculature visualization was based on temporal speckle variations of the full complex signal evaluated by high-pass filtering of 3D data along the slow scan axis. Angiographic image quantification demonstrated an increase of the vascular density and total length of capillary-like-vessels before visual signs or clinical symptoms of mucositis occur. Especially significant microvascular changes compared to their initial levels occurred when grade two and three mucositis developed. Further, microvascular reaction was seen to be dose-level dependent. OCT monitoring in radiotherapy offers a non-invasive, convenient, label-free quantifiable structural and functional volumetric imaging method suitable for longitudinal human patient studies, furnishing fundamental radiobiological insights and potentially providing useful feedback data to enable adaptive radiotherapy (ART).

Lesion oxygenation associates with clinical outcomes in premalignant and early stage head and neck tumors treated on a phase 1 trial of photodynamic therapy

BACKGROUND

We report on a Phase 1 trial of photodynamic therapy (PDT) for superficial head and neck (H&N) lesions. Due to known oxygen dependencies of PDT, translational measurements of lesion hemoglobin oxygen saturation (S_tO₂) and blood volume (tHb) were studied for associations with patient outcomes.

METHODS

PDT with aminolevulinc acid (ALA) and escalating light doses was evaluated for high-grade dysplasia, carcinoma-in-situ, and microinvasive carcinomas of the H&N. Among 29 evaluable patients, most (18) had lesions of the tongue or floor of mouth (FOM). Disease was intact in 18 patients and present at surgical margins in 11 patients. In 26 patients, lesion S_tO₂ and tHb was measured.

RESULTS

Local control (LC) at 24 months was 57.5% among all patients. In patients with tongue/FOM lesions LC was 42.7%, and it was 50.1% for those with intact lesions. Lesion tHb was not associated with 3-month complete response (CR), but S_tO₂ was higher in patients with CR. In tongue/FOM lesions, baseline S_tO₂ [mean(SE)] was 54(4)% in patients (n=12) with CR versus 23(8)% in patients (n=6) with local recurrence/persistence (p=0.01). Similarly, for intact disease, baseline S_tO₂ was 54(3)% in patients (n=10) with CR versus 28(8)% in patients (n=5) without CR (p=0.03). In patients with intact disease, higher baseline S_tO₂ associated with 24-month local control (p=0.02).

CONCLUSIONS

Measurement of the physiologic properties of target lesions may allow for identification of patients with the highest probability of benefiting from PDT. This provides opportunity for optimizing light delivery based on lesion characteristics and/or informing ongoing clinical decision-making in patients who would most benefit from PDT.

Photodynamic therapy monitoring with optical coherence angiography

Photodynamic therapy (PDT) is a promising modern approach for cancer therapy with low normal tissue toxicity. This study was focused on a vascular-targeting Chlorine E6 mediated PDT. A new angiographic imaging approach known as M-mode-like optical coherence angiography (MML-OCA) was able to sensitively detect PDT-induced microvascular alterations in the mouse ear tumour model CT26. Histological analysis showed that the main mechanisms of vascular PDT was thrombosis of blood vessels and hemorrhage, which agrees with angiographic imaging by MML-OCA. Relationship between MML-OCA-detected early microvascular damage post PDT (within 24 hours) and tumour regression/regrowth was confirmed by histology. The advantages of MML-OCA such as direct image acquisition, fast processing, robust and affordable system opto-electronics, and label-free high contrast 3D visualization of the microvasculature suggest attractive possibilities of this method in practical clinical monitoring of cancer therapies with microvascular involvement.

Customized Tool for the Validation of Optical Coherence Tomography in Differentiation of Prostate Cancer

OBJECTIVE

To design and demonstrate a customized tool to generate histologic sections of the prostate that directly correlate with needle-based optical coherence tomography pullback measurements.

MATERIALS AND METHODS

A customized tool was created to hold the prostatectomy specimens during optical coherence tomography measurements and formalin fixation. Using the tool, the prostate could be sliced into slices of 4 mm thickness through the optical coherence tomography measurement trajectory. In this way, whole-mount pathology slides were produced in exactly the same location as the optical coherence tomography measurements were performed. Full 3-dimensional optical coherence tomography pullbacks were fused with the histopathology slides using the 3-dimensional imaging software AMIRA, and images were compared.

RESULTS

A radical prostatectomy was performed in a patient (age: 68 years, prostate-specific antigen: 6.0 ng/mL) with Gleason score 3 + 4 = 7 in 2/5 biopsy cores on the left side (15%) and Gleason score 3 + 4 = 7 in 1/5 biopsy cores on the right side (5%). Histopathology after radical prostatectomy showed an anterior located pT2cNx adenocarcinoma (Gleason score 3 + 4 = 7). Histopathological prostate slides were produced using the customized tool for optical coherence tomography measurements, fixation, and slicing of the prostate specimens. These slides correlated exactly with the optical coherence tomography images. Various structures, for example, Gleason 3 + 4 prostate cancer, stroma, healthy glands, and cystic atrophy with septae, could be identified both on optical coherence tomography and on the histopathological prostate slides.

CONCLUSION

We successfully designed and applied a customized tool to process radical prostatectomy specimens to improve the coregistration of whole mount histology sections to fresh tissue optical coherence tomography pullback measurements. This technique will be crucial in validating the results of optical coherence tomography imaging studies with histology and can easily be applied in other solid tissues as well, for example, lung, kidney, breast, and liver. This will help improve the efficacy of optical coherence tomography in cancer detection and staging in solid organs.

Staging Early Esophageal Cancer

Staging esophageal cancer provides a standardized measure of the extent of disease that can be used to inform decisions about therapy and guide prognosis. For esophageal cancer, the treatment pathways vary greatly depending on stage of disease, and accurate staging is therefore crucial in ensuring the optimal therapy for each patient. For early esophageal cancer (T1 lesions), endoscopic resection can be curative and simultaneously gives accurate staging of depth of invasion. For tumors invading the submucosa or more advanced disease, comprehensive investigation is required to accurately stage the tumor and assess suitability for curative resection. A combined imaging approach of computed tomography (CT), positron emission tomography (PET), and endoscopic ultrasound (EUS) offers complementary diagnostic information and gives the greatest chance of accurate staging. Staging laparoscopy can identify peritoneal disease and small superficial liver lesions that could be missed on CT or PET, and alters management in up to 20 % of patients. Optical diagnostic techniques offer the prospect of further extending the possibilities of endoscopic staging in real time. Optical coherence tomography can image superficial lesions and could provide information on depth of invasion for these lesions. Real-time lymph node analysis using optical diagnostics such as Raman spectroscopy could be used to support immediate endoscopic therapy without waiting for results of cytology or further investigations.

Optical clearing of melanoma in vivo: characterization by diffuse reflectance spectroscopy and optical coherence tomography

Melanoma is the most aggressive type of skin cancer, with significant risk of fatality. Due to its pigmentation, light-based imaging and treatment techniques are limited to near the tumor surface, which is inadequate, for example, to evaluate the microvascular density that is associated with prognosis. White-light diffuse reflectance spectroscopy (DRS) and near-infrared optical coherence tomography (OCT) were used to evaluate the effect of a topically applied optical clearing agent (OCA) in melanoma in vivo and to image the microvascular network. DRS was performed using a contact fiber optic probe in the range from 450 to 650 nm. OCT imaging was performed using a swept-source system at 1310 nm. The OCT image data were processed using speckle variance and depth-encoded algorithms. Diffuse reflectance signals decreased with clearing, dropping by ∼ 90% after 45 min. OCT was able to image the microvasculature in the pigmented melanoma tissue with good spatial resolution up to a depth of ∼ 300 μm without the use of OCA; improved contrast resolution was achieved with optical clearing to a depth of ∼ 750 μm in tumor. These findings are relevant to potential clinical applications in melanoma, such as assessing prognosis and treatment responses. Optical clearing may also facilitate the use of light-based treatments such as photodynamic therapy.

Optical coherence tomography in respiratory science and medicine: from airways to alveoli

Optical coherence tomography is a rapidly maturing optical imaging technology, enabling study of the in vivo structure of lung tissue at a scale of tens of micrometers. It has been used to assess the layered structure of airway walls, quantify both airway lumen caliber and compliance, and image individual alveoli. This article provides an overview of the technology and reviews its capability to provide new insights into respiratory disease.

Real-time monitoring of hemodynamic changes in tumor vessels during photoimmunotherapy using optical coherence tomography

Photoimmunotherapy (PIT) is a cell-specific cancer therapy based on an armed antibody conjugate that induces rapid and highly selective cancer cell necrosis after exposure to near-infrared (NIR) light. The PIT treatment also induces the superenhanced permeability and retention effect, which allows high concentrations of nanoparticles to accumulate in the tumor bed. In our pilot studies, optical coherence tomography (OCT) reveals dramatic hemodynamic changes during PIT. We developed and applied speckle variance analysis, Doppler flow measurement, bulk motion removal, and automatic region of interest selection to quantify vessel diameter and blood velocity within tumors in vivo. OCT imaging reveals that blood velocity in peripheral tumor vessels quickly drops below the detection limit while the vessel lumen remains open (4 vessels from 3 animals). On the other hand, control tumor vessels (receive NIR illumination but no PIT drug) do not show the sustained blood velocity drop (5 vessels from 3 animals). Ultraslow blood velocity could result in a long drug circulation time in tumor. Increase of the blood pool volume within the central tumor (shown in histology) may be the leading cause of the periphery blood velocity drop and could also increase the drug pool volume in tumor vessels.

The effect of photoimmunotherapy followed by liposomal daunorubicin in a mixed tumor model: a demonstration of the super-enhanced permeability and retention effect after photoimmunotherapy

In general, de novo solid tumors are composed of phenotypically and functionally heterogeneous malignant cells. This heterogeneity interferes with the effectiveness of targeted molecular cancer therapies. Even if most of the tumor is killed by a targeted treatment, recurrences are common and can be lethal. In this study, a mixed tumor model, which is predominantly a population of epidermal growth factor receptor (EGFR)-positive A431 cells combined with a smaller population of EGFR-negative Balb3T3/DsRed cells, was established. This mixed tumor was then treated with photoimmunotherapy, a newly developed target-cell-selective cancer therapy using a monoclonal antibody (mAb)-photosensitizer (IR700 fluorescence dye) conjugate and exposure of near-infrared light. Although photoimmunotherapy successfully treated EGFR-positive A431 cells in the mixed tumor, EGFR-negative Balb/DsRed cells were not responsive. However, photoimmunotherapy also induced a large increase in tumor permeability, known as the super-enhanced permeability and retention (SUPR) effect, which allowed a 5-fold increase in the accumulation of a liposomal chemotherapy (DaunoXome) and resulted in more effective therapy than either photoimmunotherapy or liposomal daunorubicin alone. The liposomal daunorubicin, administered 1 hour after EGFR-targeted photoimmunotherapy, was homogeneously distributed, allowing delivery to tiny surviving nests of EGFR-negative Balb3T3/DsRed cells, resulting in prolonged survival of mice.

Imaging deep skeletal muscle structure using a high-sensitivity ultrathin side-viewing optical coherence tomography needle probe

We have developed an extremely miniaturized optical coherence tomography (OCT) needle probe (outer diameter 310 µm) with high sensitivity (108 dB) to enable minimally invasive imaging of cellular structure deep within skeletal muscle. Three-dimensional volumetric images were acquired from ex vivo mouse tissue, examining both healthy and pathological dystrophic muscle. Individual myofibers were visualized as striations in the images. Degradation of cellular structure in necrotic regions was seen as a loss of these striations. Tendon and connective tissue were also visualized. The observed structures were validated against co-registered hematoxylin and eosin (H&E) histology sections. These images of internal cellular structure of skeletal muscle acquired with an OCT needle probe demonstrate the potential of this technique to visualize structure at the microscopic level deep in biological tissue in situ.

Real-time speckle variance swept-source optical coherence tomography using a graphics processing unit

Advances in swept source laser technology continues to increase the imaging speed of swept-source optical coherence tomography (SS-OCT) systems. These fast imaging speeds are ideal for microvascular detection schemes, such as speckle variance (SV), where interframe motion can cause severe imaging artifacts and loss of vascular contrast. However, full utilization of the laser scan speed has been hindered by the computationally intensive signal processing required by SS-OCT and SV calculations. Using a commercial graphics processing unit that has been optimized for parallel data processing, we report a complete high-speed SS-OCT platform capable of real-time data acquisition, processing, display, and saving at 108,000 lines per second. Subpixel image registration of structural images was performed in real-time prior to SV calculations in order to reduce decorrelation from stationary structures induced by the bulk tissue motion. The viability of the system was successfully demonstrated in a high bulk tissue motion scenario of human fingernail root imaging where SV images (512 × 512 pixels, n = 4) were displayed at 54 frames per second.

Intraoperative handheld optical coherence tomography forward-viewing probe: physical performance and preliminary animal imaging

A prototype intraoperative hand-held optical coherence tomography (OCT) imaging probe was developed to provide micron resolution cross-sectional images of subsurface tissue during open surgery. This new ergonomic probe was designed based on electrostatically driven optical fibers, and packaged into a catheter probe in the form factor of clinically accepted Bayonet shaped neurosurgical probes. Optical properties of the probe were measured to have a ~20 μm spot size, 5 mm working distance and 4 mm field of view. Feasibility of this probe for structural and Doppler shift imaging was tested on porcine femoral blood vessel imaging.

Cancer imaging by optical coherence tomography: preclinical progress and clinical potential

The past decade has seen dramatic technological advances in the field of optical coherence tomography (OCT) imaging. These advances have driven commercialization and clinical adoption in ophthalmology, cardiology and gastrointestinal cancer screening. Recently, an array of OCT-based imaging tools that have been developed for preclinical intravital cancer imaging applications has yielded exciting new capabilities to probe and to monitor cancer progression and response in vivo. Here, we review these results, forecast the future of OCT for preclinical cancer imaging and discuss its exciting potential to translate to the clinic as a tool for monitoring cancer therapy.

Vascular wall imaging of vulnerable atherosclerotic carotid plaques: current state of the art and potential future of endovascular optical coherence tomography

As stroke is one of the leading causes of death and long-term morbidity worldwide, the research community has studied cardiac embolic sources, as well as vessel wall pathologies. For the latter, attention has been focused on defining morphologic tissue features associated with catastrophic events stemming from the carotid artery. Multiple noninvasive imaging modalities are currently being used to image and classify carotid atherosclerotic plaques, such as MR imaging, CT, and sonography, in an effort to provide clinically relevant predictive metrics for use in patient risk stratification and to define appropriate treatment options. This article compares and contrasts these existing clinical imaging modalities along with discussion of a new endovascular technique originally developed for cardiology, OCT, with which 3D comprehensive high-resolution images of the arterial wall can be acquired.

Motion-insensitive optical coherence tomography based micro-angiography

An improved image processing procedure for suppressing the phase noise due to a motion artifact acquired during optical coherence tomography scanning and effectively illustrating the blood vessel distribution in a living tissue is demonstrated. This new processing procedure and the widely used procedure for micro-angiography application are based on the selection of high-frequency components in the spatial-frequency spectrum of B-mode scanning (x-space), which are contributed from the image portions of moving objects. However, by switching the processing order between the x-space and k-space, the new processing procedure shows the superior function of effectively suppressing the phase noise due to a motion artifact. After the blood vessel positions are precisely acquired based on the new processing procedure, the projected blood flow speed can be more accurately calibrated based on a previously reported method. The demonstrated new procedure is useful for clinical micro-angiography application, in which a stepping motor of generating motion artifacts is usually used in the scanning probe.

Increasing damage to tumor blood vessels during motexafin lutetium-PDT through use of low fluence rate

Photodynamic therapy (PDT) with low light fluence rate has rarely been studied in protocols that use short drug-light intervals and thus deliver illumination while plasma concentrations of photosensitizer are high, creating a prominent vascular response. In this study, the effects of light fluence rate on PDT response were investigated using motexafin lutetium (10 mg/kg) in combination with 730 nm light and a 180-min drug-light interval. At 180 min, the plasma level of photosensitizer was 5.7 ng/microl compared to 3.1 ng/mg in RIF tumor, and PDT-mediated vascular effects were confirmed by a spasmodic decrease in blood flow during illumination. Light delivery at 25 mW/cm(2) significantly improved long-term tumor responses over that at 75 mW/cm(2). This effect could not be attributed to oxygen conservation at low fluence rate, because 25 mW/cm(2) PDT provided little benefit to tumor hemoglobin oxygen saturation. However, 25 mW/cm(2) PDT did prolong the duration of ischemic insult during illumination and was correspondingly associated with greater decreases in perfusion immediately after PDT, followed by smaller increases in total hemoglobin concentration in the hours after PDT. Increases in blood volume suggest blood pooling from suboptimal vascular damage; thus the smaller increases after 25 mW/cm(2) PDT provide evidence of more widespread vascular damage, which was accompanied by greater decreases in clonogenic survival. Further study of low fluence rate as a means to improve responses to PDT under conditions designed to predominantly damage vasculature is warranted.

Application of intravital microscopy in studies of tumor microcirculation

To grow and progress, solid tumors develop a vascular network through co-option and angiogenesis that is characterized by multiple structural and functional abnormalities, which negatively influence therapeutic outcome through direct and indirect mechanisms. As such, the morphology and function of tumor blood vessels, plus their response to different treatments, are a vital and active area of biological research. Intravital microscopy (IVM) has played a key role in studies of tumor angiogenesis, and ongoing developments in molecular probes, imaging techniques, and postimage analysis methods have ensured its continued and widespread use. In this review we discuss some of the primary advantages and disadvantages of IVM approaches and describe recent technological advances in optical microscopy (e.g., confocal microscopy, multiphoton microscopy, hyperspectral imaging, and optical coherence tomography) with examples of their application to studies of tumor angiogenesis.

The potential of biophotonic techniques in stem cell tracking and monitoring of tissue regeneration applied to cardiac stem cell therapy

The use of injected stem cells, leading to regeneration of ischemic heart tissue, for example, following coronary artery occlusion, has emerged as a major new option for managing 'heart attack' patients. While some clinical trials have been encouraging, there have also been failures and there is little understanding of the multiplicity of factors that lead to the outcome. In this overview paper, the opportunities and challenges in applying biophotonic techniques to regenerative medicine, exemplified by the challenge of stem cell therapy of ischemic heart disease, are considered. The focus is on optical imaging to track stem cell distribution and fate, and optical spectroscopies and/or imaging to monitor the structural remodeling of the tissue and the resulting functional changes. The scientific, technological, and logistics issues involved in moving some of these techniques from pre-clinical research mode ultimately into the clinic are also highlighted.