A review of reported tissue optical properties summarizes the wavelength-dependent behavior of scattering and absorption. Formulae are presented for generating the optical properties of a generic tissue with variable amounts of absorbing chromophores (blood, water, melanin, fat, yellow pigments) and a variable balance between small-scale scatterers and large-scale scatterers in the ultrastructures of cells and tissues.

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Optical properties of biological tissues: a review.

The reactive oxygen species (ROS)-mediated mechanism is the major cause underlying the efficacy of photodynamic therapy (PDT). The PDT procedure is based on the cascade of synergistic effects between light, a photosensitizer (PS) and oxygen, which greatly favors the spatiotemporal control of the treatment. This procedure has also evoked several unresolved challenges at different levels including (i) the limited penetration depth of light, which restricts traditional PDT to superficial tumours; (ii) oxygen reliance does not allow PDT treatment of hypoxic tumours; (iii) light can complicate the phototherapeutic outcomes because of the concurrent heat generation; (iv) specific delivery of PSs to sub-cellular organelles for exerting effective toxicity remains an issue; and (v) side effects from undesirable white-light activation and self-catalysation of traditional PSs. Recent advances in nanotechnology and nanomedicine have provided new opportunities to develop ROS-generating systems through photodynamic or non-photodynamic procedures while tackling the challenges of the current PDT approaches. In this review, we summarize the current status and discuss the possible opportunities for ROS generation for cancer therapy. We hope this review will spur pre-clinical research and clinical practice for ROS-mediated tumour treatments.

Reactive oxygen species generating systems meeting challenges of photodynamic cancer therapy

Photodynamic therapy (PDT) is a clinically approved cancer therapy, based on a photochemical reaction between a light activatable molecule or photosensitizer, light, and molecular oxygen. When these three harmless components are present together, reactive oxygen species are formed. These can directly damage cells and/or vasculature, and induce inflammatory and immune responses. PDT is a two-stage procedure, which starts with photosensitizer administration followed by a locally directed light exposure, with the aim of confined tumor destruction. Since its regulatory approval, over 30 years ago, PDT has been the subject of numerous studies and has proven to be an effective form of cancer therapy. This review provides an overview of the clinical trials conducted over the last 10 years, illustrating how PDT is applied in the clinic today. Furthermore, examples from ongoing clinical trials and the most recent preclinical studies are presented, to show the directions, in which PDT is headed, in the near and distant future. Despite the clinical success reported, PDT is still currently underutilized in the clinic. We also discuss the factors that hamper the exploration of this effective therapy and what should be changed to render it a more effective and more widely available option for patients.

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Oncologic photodynamic therapy: Basic principles, current clinical status and future directions

https://iopscience.iop.org/article/10.1088/0031-9155/58/14/5007/pdf

Corrigendum: Optical properties of biological tissues: a review

The near-infrared window between 1000 and 1700 nm, commonly termed the "second near-infrared (NIR-II) window," has quickly emerged as a highly attractive optical region for biological imaging. In contrast to conventional imaging in the visible region between 400 and 700 nm, as well as in the first NIR (NIR-I) window between 700 and 900 nm, NIR-II biological imaging offers numerous merits, including higher spatial resolution, deeper penetration depth, and lower optical absorption and scattering from biological substrates with minimal tissue autofluorescence. Noninvasive imaging techniques, specifically NIR-II fluorescence and photoacoustic (PA) imaging, have embodied the attractiveness of NIR-II optical imaging, with several NIR-II contrast agents demonstrating superior performance to the clinically approved NIR-I agents. Consequently, NIR-II biological imaging has been increasingly explored due to its tremendous potential for preclinical studies and clinical utility. Herein, the progress of optical imaging in the NIR-II window is reported. Starting with highlighting the importance of biological imaging in the NIR-II spectral region, the emergence and latest development of various NIR-II fluorescence and PA imaging probes and their applications are then discussed. Perspectives on the promises and challenges facing this nascent yet exciting field are then given.

Recent Advances of Optical Imaging in the Second Near-Infrared Window

A thorough understanding of optical properties of biological tissues is critical to effective treatment planning for therapies such as photodynamic therapy (PDT). In the last two decades, new technologies, such as broadband diffuse spectroscopy, have been developed to obtain in vivo data in humans that was not possible before. We found that the in vivo optical properties generally vary in the ranges μ(a) = 0.03-1.6 cm⁻¹ and μ'(s) = 1.2-40 cm⁻¹, although the actual range is tissue-type dependent. We have also examined the overall trend of the absorption spectra (for μ(a) and μ'(s)) as a function of wavelength within a 95% confidence interval for various tissues in vivo. The impact of optical properties on light fluence rate is also discussed for various light application geometries including superficial, interstitial, and within a cavity.

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A review of in-vivo optical properties of human tissues and its impact on PDT

Many areas of science are generating large volumes of digital image data. In order to take full advantage of the high-resolution and high-cadence images modern technology is producing, methods to automatically process and analyze large batches of such images are needed. This involves reducing complex images to simple representations such as binary sketches or numerical summaries that capture embedded scientific information. Using techniques derived from mathematical morphology, we demonstrate how to reduce solar images into simple 'sketch' representations and numerical summaries that can be used for statistical learning. We demonstrate our general techniques on two specific examples: classifying sunspot groups and recognizing coronal loop structures. Our methodology reproduces manual classifications at an overall rate of 90% on a set of 119 magnetogram and white light images of sunspot groups. We also show that our methodology is competitive with other automated algorithms at producing coronal loop tracings and demonstrate robustness through noise simulations.  2013 Wiley Periodicals, Inc. Statistical Analysis and Data Mining 6: 329-345, 2013

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Morphological Feature Extraction for Statistical Learning With Applications To Solar Image Data

Uniform light fluence distribution for patients undergoing photodynamic therapy (PDT) is critical to ensure predictable PDT outcome. However, common practice uses a point source to deliver light to the pleural cavity with the light uniformity monitored by 7 detectors placed within the pleural cavity. To improve the uniformity of light fluence rate distribution, we have used a real-time infrared (IR) tracking camera to track the movement of the light point source. The same tracking device is used to determine the surface contour of the treatment area. This study examines the light fluence (rate) delivered between the measurement and calculation in phantom studies. Isotropic detectors were used for in-vivo light dosimetry. Light fluence rate in the pleural cavity is calculated and compared with the in-vivo calculation. Phantom studies show that the surface contour can be determined with an accuracy of 2 mm, with maximum deviation of 5 mm. We can successfully match the calculated light fluence rates with the in-vivo measurements. Preliminary results indicate that the light fluence rate can have up to 50% deviation compared to the prescription in phantom experiments. The IR camera has been used successfully in pleural PDT patient treatment to track the motion of light source in real-time. We concluded that it is feasible to develop an IR camera based system to guide the motion of the light source to improve the uniformity of light distribution.

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An IR navigation system for real-time treatment guidance of Pleural PDT.

Uniform light fluence distribution for patients undergoing photodynamic therapy (PDT) is critical to ensure predictable PDT outcome. However, common practice uses a point source to deliver light to the pleural cavity. To improve the uniformity of light fluence rate distribution, we have developed a treatment planning system using an infrared camera to track the movement of the point source. This study examines the light fluence (rate) delivered to chest phantom to simulate a patient undergoing pleural PDT. Fluence rate (mW/cm2) and cumulative fluence (J/cm2) was monitored at 7 different sites during the entire light treatment delivery. Isotropic detectors were used for in-vivo light dosimetry. Light fluence rate in the pleural cavity is also calculated using the diffusion approximation with a finite-element model. We have established a correlation between the light fluence rate distribution and the light fluence rate measured on the selected points based on a spherical cavity model. Integrating sphere theory is used to aid the calculation of light fluence rate on the surface of the sphere as well as inside tissue assuming uniform optical properties. The resulting treatment planning tool can be valuable as a clinical guideline for future pleural PDT treatment.

A treatment planning system for pleural PDT

We present the results of spectroscopic measurements of diffuse reflectance and fluorescence before and after photodynamic therapy of healthy canine peritoneal cavity. Animals were treated intra-operatively after iv injection of the benzoporphyrin derivative (BPD). The small bowel was treated using a uniform light field projected by a microlenstipped fiber. The cavity was then filled with scattering medium and the remaining organs were treated using a moving diffuser. Diffuse reflectance and fluorescence measurements were made using a multi-fiber optical probe positioned on the surface of various tissues within the cavity before and after illumination. The measured data were analyzed to quantify hemoglobin concentration and oxygenation and sensitizer concentration.

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J Sandell

Papers

A review of in-vivo optical properties of human tissues and its impact on PDT

Morphological Feature Extraction for Statistical Learning With Applications To Solar Image Data

An IR navigation system for real-time treatment guidance of Pleural PDT.

A treatment planning system for pleural PDT

Spectroscopic evaluation of photodynamic therapy of the intraperitoneal cavity.