Analytic function for predicting light fluence rate of circular fields on a semi-infinite turbid medium: erratum.

Corrections to Eq. (15) and Fig. 6 in our recent publication [Opt. Express24(23), 26261 (2016)] are presented in this erratum.

Analytic function for predicting light fluence rate of circular fields on a semi-infinite turbid medium.

Accurate determination of in-vivo light fluence rate is critical for preclinical and clinical studies involving photodynamic therapy (PDT). The light fluence distribution in tissue depends on both the tissue optical properties and the incident field size. This study compares the longitudinal light fluence distribution inside biological tissue in the central axis of circular uniform light field with different radii for a range of in-vivo tissue optical properties (absorption coefficients (µa) between 0.01 and 1 cm-1 and reduced scattering coefficients (µs') between 2 and 40 cm-1). This was done using Monte-Carlo simulations for a semi-infinite turbid medium in an air-tissue interface. The end goal is to develop simple analytical expressions that would fit the results from the Monte Carlo simulation for circular beams with different radii. A 6-parameter model (ϕ/ϕair=(1-b⋅e-λ1d)(C2e-λ2d+C3e-λ3d)) can be used to fit MC simulation. Each of these parameters (b, C2, C3, λ1, λ2, and λ3) is expressed as a function of tissue optical properties and beam radius. These results can then be compared against the existing expressions in the literature for broad beam for analysis in both accuracy and applicable range. The analytical function can be used as rapid guide in PDT to calculate in vivo light fluence distribution for known tissue optical properties.

Snapshot depth sensitive Raman spectroscopy in layered tissues.

Depth sensitive Raman spectroscopy has been shown effective in the detection of depth dependent Raman spectra in layered tissues. However, the current techniques for depth sensitive Raman measurements based on fiber-optic probes suffer from poor depth resolution and significant variation in probe-sample contact. In contrast, those lens based techniques either require the change in objective-sample distance or suffer from slow spectral acquisition. We report a snapshot depth-sensitive Raman technique based on an axicon lens and a ring-to-line fiber assembly to simultaneously acquire Raman signals emitted from five different depths in the non-contact manner without moving any component. A numerical tool was developed to simulate ray tracing and optimize the snapshot depth sensitive setup to achieve the tradeoff between signal collection efficiency and depth resolution for Raman measurements in the skin. Moreover, the snapshot system was demonstrated to be able to acquire depth sensitive Raman spectra from not only transparent and turbid skin phantoms but also from ex vivo pork tissues and in vivo human thumbnails when the excitation laser power was limited to the maximum permissible exposure for human skin. The results suggest the great potential of snapshot depth sensitive Raman spectroscopy in the characterization of the skin and other layered tissues in the clinical setting or other similar applications such as quality monitoring of tablets and capsules in pharmaceutical industry requiring the rapid measurement of depth dependent Raman spectra.

Fast wide-field Raman spectroscopic imaging based on simultaneous multi-channel image acquisition and Wiener estimation.

Raman spectroscopic imaging is a powerful label-free tool for studying cells and tissues in biology and medicine, but it suffers from extremely slow data acquisition. In this Letter, a novel multi-channel Raman imaging technique is proposed to speed up Raman acquisition. Wide-field Raman images are taken in multiple narrow-band channels, each through a different bandpass filter, simultaneously in one camera frame. Then Wiener estimation is used to quickly reconstruct the full Raman spectrum at each pixel from narrow-band measurements. The proposed system with four channels was evaluated in the mixtures of two and three chemicals exhibiting strong Raman scattering because of convenience in the verification of reconstructed spectra. This new technique is expected to overcome the limitation of traditional Raman spectroscopic imaging in speed, and expand its applications in the label-free analysis of both biological and non-biological samples, where potential species are known and fast imaging is required to investigate temporally varying events.

Fast photoacoustic-guided depth-resolved Raman spectroscopy: a feasibility study.

In this Letter, photoacoustic-guided Raman spectroscopy (PARS) is proposed for a fast depth-resolved Raman measurement with accurate depth localization. The approach was experimentally demonstrated to receive both photoacoustic and Raman signals from a three-layer agar phantom based on a developed synergic photoacoustic-Raman probe, showing strong depth correlation and achieving magnitude of faster operation speed due to photoacoustic time-of-flight measurement and guidance, compared with the conventional depth-resolved Raman spectroscopy method. In addition, further combination with advanced optical-focusing techniques in biological-scattering medium could potentially enable the proposed approach for cancer diagnostics with both tight and fast optical focusing at the desired depth of tumor.

Multifocal noncontact color imaging for depth-sensitive fluorescence measurements of epithelial cancer.

We propose a multifocal noncontact setup to perform depth-sensitive fluorescence imaging on a two-layered epithelial tissue model. The combination of a microlens array and a tunable lens enables the depth of the multifocal plane to be conveniently adjusted without any mechanical movement of the imaging lens or the sample. This advantage is particularly desirable in the clinical setting. Results from the phantom study demonstrate that the setup can achieve depth-sensitive color imaging for fluorescence measurements, which is further confirmed by spectral measurements.

Axicon lens-based cone shell configuration for depth-sensitive fluorescence measurements in turbid media.

We have developed a novel noncontact setup to implement a cone shell illumination and detection configuration using axicon lenses for depth-sensitive fluorescence measurements. The setup was demonstrated experimentally to be capable of detecting fluorescence from a two-layered turbid agar phantom with a larger sensitivity to the deep layer and a larger range of sensitivity to either layer than a conventional cone configuration implemented by a microscope objective lens. Furthermore, the axicon lens-based setup eliminates the need of moving the objective lens up or down to achieve depth-sensitive measurements, which effectively improves the consistency of optical coupling and thus would be preferred in a clinical setting.

Evaluation of Detector Position and Light Fluence Distribution Using an Infrared Navigation System during Pleural Photodynamic Therapy†.

Photodynamic therapy (PDT) has been used to treat malignant pleural mesothelioma. Current practice involves delivering light to a prescribed light fluence with a point source, monitored by eight isotropic detectors inside the pleural cavity. An infrared (IR) navigation system was used to track the location of the point source throughout the treatment. The recorded data were used to reconstruct the pleural cavity and calculate the light fluence to the whole cavity. An automatic algorithm was developed recently to calculate the detector positions based on recorded data within an hour. This algorithm was applied to patient case studies and the calculated results were compared to the measured positions, with an average difference of 2.5 cm. Calculated light fluence at calculated positions were compared to measured values. The differences between the calculated and measured light fluence were within 14% for all cases, with a fixed scattering constant and a dual correction method. Fluence-surface histogram (FSH) was calculated for photofrin-mediated PDT to be able to cover 80% of pleural surface area to 50 J cm-2 (83.3% of 60 J cm-2 ). The study demonstrates that it will be possible to eliminate the manual measurement of the detector positions, reducing the patient's time under anesthesia.

Comparison of principal component analysis and biochemical component analysis in Raman spectroscopy for the discrimination of apoptosis and necrosis in K562 leukemia cells.

Raman spectroscopy has been explored as a promising label-free technique in discriminating apoptosis and necrosis induced cell death in leukemia cells. In addition to Principal component analysis (PCA) as commonly employed in Raman data analysis, another less commonly used but powerful method is Biochemical Component Analysis (BCA). In BCA, a Raman spectrum is decomposed into the contributions from several known basic biochemical components, such as proteins, lipid, nucleic acids and glycogen groups etc. The differences in terms of classification accuracy and interpretability of resulting data between these two methods in Raman spectroscopy have not been systematically investigated to our knowledge. In this study, we utilized both methods to analyze the Raman spectra measured from live cells, apoptotic and necrotic leukemia cells. The comparison indicates that two methods yield comparable accuracy in sample classification when the numbers of basic components are equal. The changes in the contributions of biochemical components in BCA can be interpreted by cell biology principles in apoptosis and necrosis. In contrast, the contributions of most principle components in PCA are difficult to interpret except the first one. The capability of BCA to unveil fine biochemical changes in cell spectra and excellent accuracy in classification can impel the broad application of Raman spectroscopy in biological research.

Reactive oxygen species explicit dosimetry (ROSED) for fractionated photofrin-mediated photodynamic therapy (PDT).

Photodynamic therapy (PDT) is an established modality for cancer treatment and reactive oxygen species explicit dosimetry (ROSED), based on direct measurements of in-vivo light fluence (rate), in-vivo photofrin concentration, and tissue oxygenation concentration, has been proved to be an effective dosimetric quantity which can be used to predict PDT outcome. In this study, ROSED was performed for photofrin-mediated PDT for mice bearing radiation-induced fibrosacorma (RIF) tumor. PDT treatments were performed using single or fractionated illumination to a same total fluence of 135 Jcm-2. The effects of light fractionation on the total reacted [ROS]rx and treatment outcomes were evaluated.

Real-time PDT Dose Dosimetry for Pleural Photodynamic Therapy.

PDT dose is the product of the photosensitizer concentration and the light fluence in the target tissue. For improved dosimetry during plural photodynamic therapy (PDT), an eight-channel PDT dose dosimeter was developed to measure both the light fluence and the photosensitizer concentration simultaneously from eight different sites in the pleural cavity during PDT. An isotropic detector with bifurcated fibers was used for each channel to ensure detected light was split equally to the photodiode and spectrometer. The light fluence rate distribution is monitored using an IR navigation system. The navigation system allows 2D light fluence mapping throughout the whole pleural cavity rather than just the selected points. The fluorescence signal is normalized by the light fluence measured at treatment wavelength. We have shown that the absolute photosensitizer concentration can be obtained by applying optical properties correction and linear spectral fitting to the measured fluorescence data. The detection limit and the optical property correction factor of each channel were determined and validated using tissue-simulating phantoms with known varying concentration of Photofrin. Tissue optical properties are determined using an absorption spectroscopy probe immediately before PDT at the same sites. The combination of 8-channel PDT dosimeter system and IR navigation system, which can calculate light fluence rate in the pleural cavity in real-time, providing a mean to determine the distribution of PDT dose on the entire pleural cavity to investigate the heterogeneity of PDT dose on the pleural cavity.

Algorithms and instrumentation for rapid spatial frequency domain fluorescence diffuse optical imaging.

Significance: Rapid estimation of the depth and margins of fluorescence targets buried below the tissue surface could improve upon current image-guided surgery techniques for tumor resection. Aim: We describe algorithms and instrumentation that permit rapid estimation of the depth and transverse margins of fluorescence target(s) in turbid media; the work aims to introduce, experimentally demonstrate, and characterize the methodology. Approach: Spatial frequency domain fluorescence diffuse optical tomography (SFD-FDOT) technique is adapted for rapid and computationally inexpensive estimation of fluorophore target depth and lateral margins. The algorithm utilizes the variation of diffuse fluorescence intensity with respect to spatial-modulation-frequency to compute target depth. The lateral margins are determined via analytical inversion of the data using depth information obtained from the first step. We characterize method performance using fluorescent contrast targets embedded in tissue-simulating phantoms. Results: Single and multiple targets with significant lateral size were imaged at varying depths as deep as 1 cm. Phantom data analysis showed good depth-sensitivity, and the reconstructed transverse margins were mostly within ∼30 % error from true margins. Conclusions: The study suggests that the rapid SFD-FDOT approach could be useful in resection surgery and, more broadly, as a first step in more rigorous SFD-FDOT reconstructions. The experiments permit evaluation of current limitations.

Real-time tracking of brain oxygen gradients and blood flow during functional activation.

Significance: Cerebral metabolic rate of oxygen ( CMRO 2 ) consumption is a key physiological variable that characterizes brain metabolism in a steady state and during functional activation. Aim: We aim to develop a minimally invasive optical technique for real-time measurement of CMRO 2 concurrently with cerebral blood flow (CBF). Approach: We used a pair of macromolecular phosphorescent probes with nonoverlapping optical spectra, which were localized in the intra- and extravascular compartments of the brain tissue, thus providing a readout of oxygen gradients between these two compartments. In parallel, we measured CBF using laser speckle contrast imaging. Results: The method enables computation and tracking of CMRO 2 during functional activation with high temporal resolution ( ∼ 7 Hz ). In contrast to other approaches, our assessment of CMRO 2 does not require measurements of CBF or hemoglobin oxygen saturation. Conclusions: The independent records of intravascular and extravascular partial pressures of oxygen, CBF, and CMRO 2 provide information about the physiological events that accompany neuronal activation, creating opportunities for dynamic quantification of brain metabolism.

Estimation of fluorescence probing depth dependence on the distance between source and detector using Monte Carlo modeling.

Photosensitizer fluorescence emission during photodynamic therapy (PDT) can be used to estimate for in vivo photosensitizer concentration. We built a surface contact probe with 405nm excitation light source to obtain Photofrin fluorescence signal during clinical PDT. The probe was equipped with multiple detector fibers that were located at distances between 0.14 to 0.87 cm laterally from the excitation source fiber. In this study, we investigated the probing depth of fluorescence in biological tissue with different source-detector separation using our contact probe setup. We used Monte Carlo method to simulate the 405nm excitation light and 630nm fluorescence probing depth at various source and detector (SD) separations. The results provided insight to the most probable depth of origin of detected fluorescence at each SD separation and help to understand the in vivo depth distribution of clinically measured Photofrin concentration.

Monte Carlo (MC) study of dose distribution and Cherenkov imaging in total skin electron therapy (TSET) with TOPAS.

Malignant tissues can be effectively treated by Total Skin Electron Therapy (TSET) over the entire body surface using 6 MeV electron beams. During the radiation treatment, Cherenkov photons are emitted from the patient's skin, and can potentially be used for in-vivo imaging of the radiation dose distribution. A Monte Carlo (MC) simulation toolkit TOPAS is used to study the generation and propagation of Cherenkov photons that are generated from the interaction of electron radiation with human tissues, and to understand the relationship between the dose distributions and the Cherenkov photon distributions. Validation of MC simulations with experiments are performed at 100 SSD and 500 SSD, and simulations of a patient phantom in realistic clinical treatment setups have been done. These simulations with TOPAS show that the emitted Cherenkov distributions at phantom surfaces closely follow their corresponding dose distributions.

Determination of the distribution of drug concentration and tissue optical properties for ALA-mediated anal photodynamic therapy.

PDT efficacy depends on the availability and dynamic interactions of photosensitizer, light, and oxygen. Tissue optical properties influence the delivered light dose and impact PDT outcome. In-vivo measurements of tissue optical properties and photosensitizer concentration enable determination of explicit and implicit dose factors affecting PDT and helps to understand the underlying biophysical mechanism of PDT. In this study, we measure tissue optical properties (absorption µa (λ) and scattering µs' (λ) coefficients) and PpIX concentration in tissue simulating liquid phantoms with a geometry that resembles anal canal. In-vivo light fluence rate and photosensitizer fluorescence of 405nm excitation light source were acquired using a dual-motor continuous wave transmittance spectroscopy system. We characterized the tissue optical properties correction factor of fluorescence signal using a series of tissue simulating phantoms with known PpIX concentrations and with absorption coefficient between 0.1 - 0.9 cm-1 and reduced scattering coefficient between 5 - 40 cm-1. The results demonstrated that our spectroscopy system could determine the distribution of tissue optical properties and PPIX concentration during anal PDT.

A Comparison of Two Probes to Determine Rectum Optical Properties.

Tissue optical properties are crucial for determining the light dose delivered to the tumor. Two probes are compared: the two-catheter probe is based on transmittance measurement between one point source and one isotropic detector inside parallel catheters spaced at 0.5 cm along a 1-inch diameter transparent cylinder; and a 1-inch trans-rectal diffuse optical tomography (DOT) probe designed for prostate measurements, using a multiple fiber-array with source-detector separations of 1.4-10 mm. The two-catheter probe uses an empirical model for primary and scatter light fluence rates in the cylindrical cavity condition for anal PDT to determine optical properties along the source catheter using dual motors to move the source and detector along the catheters. The DOT probe uses finite element method (FEM) to obtain distribution of optical properties in 3D. Validations for the two probes were performed in liquid and solid phantoms. For each method, validation was performed in tissue-mimicking liquid phantoms for a range of known optical properties (µa between 0.05 and 0.9 cm-1 and µs' between 5.5 and 16.5 cm-1). To cross-check the two methods, solid phantoms were created of known optical properties at the University of Pennsylvania and sent for measurement to Princess Margaret Cancer Centre (PMH) to mimic realistic patient simulating conditions. Measurements were taken and optical properties were then recovered without knowing the expected values to cross-validate each probe. The results show modest agreement between the measured µa and µs'values, but high degree of agreement between the measured µeff performed independently using the two methods.

Reactive oxygen species explicit dosimetry to predict tumor growth for benzoporphyrin derivative-mediated vascular photodynamic therapy.

Photodynamic therapy (PDT) is a well-established treatment modality for cancer and other malignant diseases; however, quantities such as light fluence and PDT dose do not fully account for all of the dynamic interactions between the key components involved. In particular, fluence rate (ϕ) effects, which impact the photochemical oxygen consumption rate, are not accounted for. In this preclinical study, reacted reactive oxygen species ([ROS]rx) was investigated as a dosimetric quantity for PDT outcome. The ability of [ROS]rx to predict the cure index (CI) of tumor growth, CI = 1 - k / kctr, where k and kctr are the growth rate of tumor under PDT study and the control tumor without PDT, respectively, for benzoporphyrin derivative (BPD)-mediated PDT, was examined. Mice bearing radiation-induced fibrosarcoma (RIF) tumors were treated with different in-air fluences (Φ = 22.5 to 166.7 J / cm2) and in-air fluence rates (ϕair = 75 to 250 mW / cm2) with a BPD dose of 1 mg / kg and a drug-light interval (DLI) of 15 min. Treatment was delivered with a collimated laser beam of 1-cm-diameter at 690 nm. Explicit measurements of in-air light fluence rate, tissue oxygen concentration, and BPD concentration were used to calculate for [ROS]rx. Light fluence rate at 3-mm depth (ϕ3 mm), determined based on Monte-Carlo simulations, was used in the calculation of [ROS]rx at the base of tumor. CI was used as an endpoint for three dose metrics: light fluence, PDT dose, and [ROS]rx. PDT dose was defined as the product of the time-integral of photosensitizer concentration and ϕ3 mm. Preliminary studies show that [ROS]rx best correlates with CI and is an effective dosimetric quantity that can predict treatment outcome. The threshold dose for [ROS]rx for vascular BPD-mediated PDT using DLI of 15 min is determined to be 0.26 mM and is about 3.8 times smaller than the corresponding value for conventional BPD-mediated PDT using DLI of 3 h.

1O2 determined from the measured PDT dose and 3O2 predicts long-term response to Photofrin-mediated PDT.

Photodynamic therapy (PDT) that employs the photochemical interaction of light, photosensitizer and oxygen is an established modality for the treatment of cancer. However, dosimetry for PDT is becoming increasingly complex due to the heterogeneous photosensitizer uptake by the tumor, and complicated relationship between the tissue oxygenation ([3O2]), interstitial light distribution, photosensitizer photobleaching and PDT effect. As a result, experts argue that the failure to realize PDT's true potential is, at least partly due to the complexity of the dosimetry problem. In this study, we examine the efficacy of singlet oxygen explicit dosimetry (SOED) based on the measurements of the interstitial light fluence rate distribution, changes of [3O2] and photosensitizer concentration during Photofrin-mediated PDT to predict long-term control rates of radiation-induced fibrosarcoma tumors. We further show how variation in tissue [3O2] between animals induces variation in the treatment response for the same PDT protocol. PDT was performed with 5 mg kg-1 Photofrin (a drug-light interval of 24 h), in-air fluence rates (ϕ air) of 50 and 75 mW cm-2 and in-air fluences from 225 to 540 J cm-2. The tumor regrowth was tracked for 90 d after the treatment and Kaplan-Meier analyses for local control rate were performed based on a tumor volume ⩽100 mm3 for the two dosimetry quantities of PDT dose and SOED. Based on the results, SOED allowed for reduced subject variation and improved treatment evaluation as compared to the PDT dose.

Infrared navigation system for light dosimetry during pleural photodynamic therapy.

Pleural photodynamic therapy (PDT) is performed intraoperatively for the treatment of microscopic disease in patients with malignant pleural mesothelioma. Accurate delivery of light dose is critical to PDT efficiency. As a standard of care, light fluence is delivered to the prescribed fluence using eight isotropic detectors in pre-determined discrete locations inside the pleural cavity that is filled with a dilute Intralipid solution. An optical infrared (IR) navigation system was used to monitor reflective passive markers on a modified and improved treatment delivery wand to track the position of the light source within the treatment cavity during light delivery. This information was used to calculate the light dose, incorporating a constant scattered light dose and using a dual correction method. Calculation methods were extensively compared for eight detector locations and seven patient case studies. The light fluence uniformity was also quantified by representing the unraveled three-dimensional geometry on a two-dimensional plane. Calculated light fluence at the end of treatment delivery was compared to measured values from isotropic detectors. Using a constant scattered dose for all detector locations along with a dual correction method, the difference between calculated and measured values for each detector was within 15%. Primary light dose alone does not fully account for the light delivered inside the cavity. This is useful in determining the light dose delivered to areas of the pleural cavity between detector locations, and can serve to improve treatment delivery with implementation in real-time in the surgical setting. We concluded that the standard deviation of light fluence uniformity for this method of pleural PDT is 10%.