Double Integrating Sphere System Research Articles

Application of single integrating sphere system to obtain the optical properties of turbid media

In this study, a simple method to determine the reflectance and transmittance of turbid media is proposed. The method is based on a single integrating sphere system. The integrating sphere theory is used to calculate the reflectance and transmittance under diffuse and directional illumination, and an experimental setup is proposed to measure these quantities. This method was used to determine the reflectance and transmittance of poly(vinyl alcohol) (PVA) hydrogels. Monte Carlo calculations were also implemented to validate our results. The comparison shows that the optical properties obtained through this method propagate low values of uncertainty, and a setup simpler than that of the double integrating sphere system can be realized. However, our system is limited to the diffuse–diffuse transmittance. The results suggest that the single sphere system and Monte Carlo method can be a strong combination to calculate the inherent optical properties of PVA samples.

Theoretical algorithm and application of a double-integrating sphere system for measuring leaf transmittance and reflectance spectra.

We present the theoretical background and analytical equations for calculating spectral reflectance and transmittance factors for plant leaves from data collected by a field spectroradiometer attached to a double-integrating sphere. The sphere constants required for the calculations are derived from measurements of an empty sample port and a diffuse reflectance panel. The new method is applied in measuring the spectra of leaves belonging to 13 tree species. The greatest advantages of a double-sphere system compared with the conventional single-sphere substitution method is the speed of measurements, ease of operation, and increased portability and field-ruggedness.

Application of double-layered skin phantoms for optical flow imaging during laser tattoo treatments

The feasible application of double-layered skin phantoms was evaluated to identify artificial blood flow with a Doppler optical coherence tomography (DOCT) system for laser tattoo treatments. Polydimethylsiloxane (PDMS) was used to fabricate the artificial phantoms with flow channels embedded. A double-integrating sphere system with an inverse adding-doubling method quantified both the absorption and the reduced scattering coefficients for epidermis and dermis phantoms. Both OCT and caliper measurements confirmed the double-layered phantom structure (epidermis = 136 ± 17 µm vs. dermis = 3.0 ± 0.1 mm). The DOCT method demonstrated that high flow rates were associated with high image contrast, visualizing the position and the shape of the flow channel. Application of the channel-embedded skin phantoms in conjunction with DOCT can be a reliable technique to assess dynamic variations in the blood flow during and after laser tattoo treatments.

Effects of varying local temperature on the optical properties of cells in-vitro

Increase in local temperature during light exposure of biological tissues plays an important role in determining the fate of most therapeutic modalities. Variations in the optical properties (absorption coefficient, scattering coefficient, anisotropy factor, optical depth etc.) of two cancer cell lines "Rhobdomyosarcoma and Cervical carcinoma" due to gradual increase in temperature were determine quantitatively with a double integrating sphere system. It was observed that all three coefficients showed decreasing tendency as the temperature increases for both the cell lines except for scattering coefficient of HeLa which remain constant within error limit. Anisotropy factor for both cell lines increased indicating temperature dependent subcellular density variations. Temperature dependent optical properties information may lead to precise dosimetry and could help clinicians for predicting the therapeutic modality outcome.

Optical efficiency characterization of LED phosphors using a double integrating sphere system

Abstract We report on the methodology and implementation of a robust and accurate double integrating sphere system for measuring the absolute photoluminescence quantum yield and its temperature dependence of commercially available phosphors (garnets, silicates and nitrides). The potential of our instrument for the examination of light interaction with samples of different absorption and diffusion coefficients is also presented, as optical properties of luminescent materials have a major impact on the efficiency of LED’s packaging. Our work gives special attention to the control and the optimization of light losses in the optical system in order to ensure reliable measurements. The YAG:Ce phosphor shows the highest luminescence quantum yield at 97% efficiency, the green silicate the lowest with 79% efficiency. Silicate phosphors show up to 15% loss of luminescence intensity when temperature is raised to 140°C.

Optical properties of pig skin epidermis and dermis estimated with double integrating spheres measurements

Non-invasive and non-destructive Near Infrared Reflectance Spectroscopy (NIRS) analysis of pork quality parameters is challenging due to the presence of a structured skin layer. The optical characterization (absorption coefficient, scattering coefficient and anisotropy factor) of porcine skin tissue can help in a better understanding of the light-tissue interaction, more efficient instrumental sensor designs and data modeling. For this purpose, double integrating spheres combined with an unscattered transmittance measurement system working in the range 1150–2250 nm (interval step of 10 nm) were used for optical characterization of pig epidermis and dermis. The estimated pig skin absorption coefficient spectra were dominated by water, while scattering coefficient spectra showed a steady decreasing tendency with increasing wavelength, except at strong absorption bands. The anisotropy factor spectra showed a stable value for each layer, although also some signatures were observed at strong absorption bands. A novel double integrating sphere system combined with an unscattered transmittance detector based both on a supercontinuum laser is used for optical characterization (absorption, scattering and angular scattering distribution) of pig skin tissues (epidermis and dermis) in the 1150–2250 nm wavelength range. The estimated data reported are relevant to understand individual effects of absorption, scattering and angular scattering distribution of NIR light through the tissue. Moreover, it can be used for simulating non-destructive NIRS measurement what can have an impact in the advance of NIRS technology toward in vivo/intact analysis. • A novel DIS and unscattered transmittance measuring system is used. • Absorption, scattering and anisotropy factor of pig skin tissues are estimated. • Sample thickness is a critical point in the measurement and estimation procedure. • The results would promote efficient NIRS sensor designs for non-destructive analysis.

Poster — Thur Eve — 19: Polyvinyl Alcohol Cryogels: A Promising Material for Tissue‐Mimicking Optical Phantoms

Tissue‐mimicking phantoms with specific radiological, elastic, or optical properties are desirable for calibration and quality assurance purposes. Polyvinyl alcohol (PVA) is a non‐toxic, water‐soluble polymer with many existing uses in medicine, ranging from artificial tissues for use in humans to anatomical phantoms for magnetic resonance imaging and ultrasound. It has not been well characterized optically. The process by which the polymer is crosslinked, repeated freeze‐thaw cycles, imparts optical properties that lie in the range of tissue and can be selectively tuned using different production conditions. A double integrating sphere system has been constructed to measure diffuse reflectance and transmittance from an illuminated sample. Monte Carlo modeling of the measurement geometry allows for optical property estimation using the Marquardt‐Levenberg algorithm. The scattering by PVA cryogels increases with additional freeze‐thaw cycles. PVA scattering is also affected by the ambient conditions at the time of production. Most tissue scattering properties can be mimicked using 6 freeze‐thaw cycles at most.

Laser-induced effects in different biological samples

Experiments were carried out on cancerous HeLa cells and blood serum using a double integrating sphere and a He-Ne laser to investigate the optical properties and cellular effects due to photodynamic therapy (PDT). In the first experiment, HeLa cells were exposed to Photofrin at concentrations of 0, 10, 20, 30, 50 and 112.4 microg/ml at an irradiance of 0.2 W/cm(2) using diode laser light. Using a confocal microscope, cell debris and morphological changes in HeLa cells were recorded at different Photofrin concentrations. The results showed cell debris in HeLa cells at the highest concentration of Photofrin. In a second experiment, photobleaching was observed in HeLa cells in the presence of various concentrations of 5-aminolaevulinic acid ranging from 0-50 microg/ml. There was progressive degradation of the 635 nm peak during continuous laser irradiation at an irradiance of 0.2 W/cm(2). We conclude that cells demonstrating high initial fluorescence undergo bleaching at a faster rate than those with lower fluorescence. Finally in a third experiment, cancerous and noncancerous blood serum was irradiated at an irradiance of 0.1 W/cm(2) using a He-Ne laser in conjunction with a double integrating sphere system. Forward and back scattering of normal and malignant serum showed an exponential decrease in fluorescence amplitude. The results indicate that there is notable amplitude difference between malignant and normal blood serum with malignant blood serum showing decreased scattering. These results have important implications for photodiagnosis and photodynamic therapy.

Spectrophotometer Calibration by a Double Integrating Sphere Reference Light Source and Display Panel Measurement Using Dark Sphere

We succeeded to develop a reference light source in the range of very low luminance using a double integrating sphere system, and calibrated a commercial spectrophotometer below 1 × 10-5cd/m2 levels, which is 1/100 lower than the specified limit for measurement. And we improved measurements in the ultra low luminance range of displays using the calibrated commercial spectrophotometer and a dark sphere to suppress the influence of the surround.

Development of a quantitative optical biochip based on a double integrating sphere system that determines absolute photon number in bioluminescent solution: application to quantum yield scale realization

We report a new design of an optical biochip based on a double integrating sphere system to quantify the absolute number of the emitted photons or the total photon flux by a whole cell bioluminescent biosensor, for water toxicity detection, based on genetically engineered Escherichia coli bacteria carrying a recA::luxCDABE promoter-reporter fusion. The new design of the double integrating sphere system does not require any external standard light source for calibration of the tested bioluminescent solution and allows a direct determination of the total photon flux of the bioluminescent solution. In our design, we required that the two spheres are symmetric (have the same radius and reflectance) with a surface area larger than the cut cap area between the spheres.

Effects of dehydration on the optical properties of in vitro porcine liver.

It is of crucial importance to determine the effects of dehydration on the optical properties of tissue so that optimization of therapy and device for laser applications in medicine can be made. After being incubated directly or indirectly in an oven of 37 degrees C for different periods of time, the porcine liver samples were weighed with an electronic scale and their optical properties were measured by a double integrating sphere system. When samples were incubated directly for 20 hours, the average weight loss was 68.5% +/- 1.2%, and the absorption coefficient and scattering coefficient increased 146.1% +/- 26.9% and 10.8% +/- 1.1%, respectively. In comparison, there was only 21.5% +/- 1.0% of water loss for the control samples, and the absorption coefficient increased 30.7% +/- 7.6%, while the reduced scattering coefficient increased 386.5% +/- 29.7%. The effective attenuation coefficients increased 111% and 103% for dehydration group and control group, respectively. The absorption coefficient and effective attenuation coefficient increase with dehydration level of tissue. However, there is no direct correlation between dehydration and reduced scattering coefficient.

Optical properties of native and coagulated porcine liver tissue between 400 and 2400 nm.

Laser induced thermotherapy (LITT) is a promising treatment for irresectable liver tumors. For predicting the effects of laser applications and optimizing irradiation planning in LITT, knowledge about light distribution in tissue, optical tissue properties (absorption, scattering, anisotropy, penetration depth) and their changes due to thermal denaturation is indispensable. The optical parameters in healthy porcine liver were determined in the native state and after thermal coagulation using a double integrating sphere system in the wavelength range of 400-2400 nm. Optical parameters showed significant fluctuations in the examined wavelength range mainly due to the water and hemoglobin content in the tissue. The greatest optical penetration depth of 7.46 mm was achieved at 1070 nm. After thermal coagulation, a clear increase in scattering and a slight decrease in absorption was found, which results in a decreased optical penetration depth. In order to ensure a safe and effective procedure, an adjustment of the laser power to the decreasing penetration depth is recommended during therapy. These results provide a better understanding of laser-tissue interaction and may be helpful to investigators in the field of light dosimetry in liver tissue.

Continuous changes in the optical properties of liver tissue during laser-induced interstitial thermotherapy.

Laser-induced thermotherapy (LITT) is a promising treatment for irresectable liver tumors. To predict the effects of laser applications and to optimize treatment planning in LITT, it is essential to gain knowledge about light distribution in tissue, tissue optical properties (absorption, scattering, anisotropy, penetration depth), and their continuous changes during therapy. Measurements of optical properties were performed with a double integrating-sphere system and a laser diode (830 nm). Porcine liver tissue samples were examined in a native state (35 degrees C) and after exposure to different temperatures (45 degrees C to 80 degrees C). Rising temperature was accompanied by a decrease in the absorption coefficient and anisotropy factor and an increase in the scattering coefficient. These changes were only significant in the temperature range of 50 degrees to 65 degrees C (P < 0.01). The optical penetration depth decreased from 3.1mm in the native state to 1.7mm at 65 degrees C (P < 0.01). Above 65 degrees, there was no significant change in the tissue optical properties. The optical properties of liver tissue change significantly under the influence of tissue heating, resulting in a decreased optical penetration depth. These changes occur mainly in the temperature range of 50 degrees C to 65 degrees C, corresponding to protein denaturation. To ensure a safe and effective procedure, an adjustment of the laser power to the actual penetration depth is recommended during therapy.

Changes in optical properties of ex vivo rat prostate due toheating

This study examines the effectiveness of a single, first-order Arrheniusprocess in accurately modelling the thermally induced changes in the opticalproperties, particularly the reduced scattering coefficient, µ's, and theabsorption coefficient, µa, of ex vivo rat prostate. Recent workhas shown that µ's can increase as much as five-fold due to thermalcoagulation, and the observed change in µ's has been modelled wellaccording to a first-order rate process in albumen. Conversely, opticalproperty measurements conducted using pig liver suggest that this change inµ's cannot suitably be described using a single rate parameter. In canineprostate, measurements have indicated that while the absorption coefficientvaries with temperature, it does not do so according to first-order kinetics.A double integrating sphere system was used to measure the reflectance andtransmittance of light at 810 nm through a thin sample of prostate. Usingprostate samples collected from Sprague-Dawley rats, optical properties weremeasured at a constant elevated temperature. Tissue samples were measured overthe range 54-83 °C. The optical properties of the sample weredetermined through comparison with reflectance and transmittance valuespredicted by a Monte Carlo simulation of light propagation in turbid media. Afirst-order Arrhenius model was applied to the observed change in µ's andµa to determine the rate process parameters for thermal coagulation. Themeasured rate coefficients were Ea = (7.18±1.74)×104 J mol-1 and Afreq = 3.14×108 s-1 for µ's. Itwas determined that the change in µ's is well described by a singlefirst-order rate process. Similar analysis performed on the changes in µadue to increased temperatures yielded Ea = (1.01±0.35)×105 J mol-1 and Afreq = 8.92×1012 s-1. The resultsfor µa suggest that the Arrhenius model may be applicable to the changesin absorption.

Dynamics of tissue optics during laser heating of turbid media

The dynamics of the optical behavior of tissue during the photothermal interaction of laser radiation with tissue could significantly affect the optimization of light doses for effective and safe applications of lasers in medicine. Characterization of the dynamics of tissue optics during laser heating was performed by means of simultaneous measurements of the total transmittance, diffuse reflectance, and surface temperature of fresh and thermally coagulated human skin and canine aorta during long-pulsed Nd:YAG laser heating with a double integrating-sphere system and an infrared camera. Thermally induced changes in the optical properties of tissue caused a decrease in the total transmittance and an increase in the diffuse reflectance of both fresh and precoagulated skin and aorta samples. For fresh tissue, these changes were primarily reversible until photocoagulation occurred, then both the reversible, as well as the irreversible, changes were observed. However, for precoagulated tissue the reversible changes in the optical properties were dominant, whereas the irreversible changes were insignificant. Results from this study indicate the existence of the nonlinear behavior in the optics of turbid biological media during pulsed laser heating. Possible mechanisms responsible for this nonlinear optical behavior are discussed.