Optical property changes as a result of protein denature in albumen and yolk

Non-invasive classification of single and double-yolk eggs using Vis-NIR spectroscopy and multivariate analysis

1. This study was conducted to develop an efficient technique for separating double-yolked (DY) from single-yolked (SY) light brown broiler eggs with comparable shape and size, that were hard to distinguish merely by their external characteristics, using Vis-NIR transmission spectroscopy combined with multivariate analysis.2. Spectroscopic transmission (200-900 nm) was measured after collecting the eggs, and the yolk number was verified by breaking the eggs after boiling. The absorbance of important spectral wavelengths sensitive to yolk amount were identified using feature selection techniques (Principal Component Analysis and Genetic Algorithm).3. Discriminant analysis (DA) and support vector machine (SVM) classifiers were used to develop classification models for DY and SY eggs using the selected important spectral wavelengths.4. When compared to alternative nonlinear techniques, the developed model applying linear discriminant analysis produced greater accuracies in the first (96%) and second (100%) experiments, implying lower inter-egg variability from spectral data and a linear relationship between classes. However, the position and orientation of yolks in DY eggs may limit the classification accuracy of the eggs.

Thermochromic Tissue-Mimicking Phantoms for Thermal Ablation Based on Polyacrylamide Gel

In recent years, thermal ablation has played an increasingly important role in treating various tumors in the clinic. A practical thermochromic phantom model can provide a favorable platform for clinical thermotherapy training of young physicians or calibration and optimization of thermal devices without risk to animals or human participants. To date, many tissue-mimicking thermal phantoms have been developed and are well liked, especially the polyacrylamide gel (PAG)-based phantoms. This review summarizes the PAG-based phantoms in the field of thermotherapy, details their advantages and disadvantages and provides a direction for further optimization. The relevant physical parameters (such as electrical, acoustic, and thermal properties) of these phantoms are also presented in this review, which can assist operators in a deeper understanding of these phantoms and selection of the proper recipes for phantom fabrication.

Cryopreservation and Laser Nanowarming of Zebrafish Embryos Followed by Hatching and Spawning

This study shows for the first time the ability to rewarm cryopreserved zebrafish embryos that grow into adult fish capable of breeding normally. The protocol employs a single injection of cryoprotective agents (CPAs) and gold nanorods (GNRs) into the yolk and immersion in a precooling bath to dehydrate the perivitelline space. Then embryos are encapsulated within CPA and GNR droplets, plunged into liquid nitrogen, cryogenically stabilized, and rewarmed by a laser pulse. Postlaser nanowarming, embryos (n = 282) exhibit intact structure by 1 h (40%), continued development after 3 h (22%), movement after 24 h (11%), hatching after 48 h (9%), and swimming after Day 5 (3%). Finally, from fish that survives till Day 5, two larvae are grown to adulthood and spawned, yielding survival comparable to an unfrozen control. Future efforts will focus on improving the survival to adulthood and developing methods to cryopreserve large numbers of embryos for research, aquaculture, and biodiversity preservation.

Multimodality characterization of microstructure by the combination of diffusion NMR and time-domain diffuse optical data

Combining datasets with a model of the underlying physics prior to mapping of tissue provides a novel approach improving the estimation of parameters. We demonstrate this approach by merging near infrared diffuse optical signal data with diffusion NMR data to inform a model describing the microstructure of a sample. The study is conducted on a homogeneous emulsion of oil in a dispersion medium of water and proteins. The use of a protein based background, rich in collagen, introduces a similarity to real tissues compared to other models such as intralipids. The sample is investigated with the two modalities separately. Then, the two datasets are used to inform a combined model, and to estimate the size of the microstructural elements and the volume fraction. The combined model fits the microstructural properties by minimizing the difference between experimental and modelled data. The experimental results are validated with confocal laser scanning microscopy. The final results demonstrate that the combined model provides improved estimates of microstructural parameters compared to either individual model alone.

Real-time optical monitoring of radio-frequency tissue fusion by continuous wave transmission spectroscopy

Radio-frequency (RF) tissue fusion is a novel method of tissue approximation that can seal tissue without the need for sutures or staples, based on the combined effects of heat and pressure on the apposed tissue surfaces. RF delivery must be controlled and optimized to obtain a reproducible, reliable seal. We use real-time optical measurements to improve understanding of the tissue modifications induced by RF fusion. The main macroscopic transformations are thermal denaturation and dehydration. Light propagation in tissue is a function of both and therefore should provide interesting insight into the dynamic of occurring phenomena. Quantification by continuous wave technique has proven challenging. We proposed an algorithm based on the measurement of the absolute transmittance of the tissue, making use of the modified Beer-Lambert law. The experimental method and the data algorithm are demonstrated by RF fusion of porcine small bowel. The proposed optical measurement modality is well adapted to modern surgical instrumentation used for minimally invasive procedures.

Changes in relative light fluence measured during laser heating: implications for optical monitoring and modelling of interstitial laser photocoagulation

Dynamic changes in internal light fluence were measured during interstitial laser heating of tissue phantoms and ex vivo bovine liver. In albumen phantoms, the results demonstrate an unexpected rise in optical power transmitted approximately I cm away from the source during laser exposure at low power (0.5-1 W), and a decrease at higher powers (1.5-2.5 W) due to coagulation and possibly charring. Similar trends were observed in liver tissue, with a rise in interstitial fluence observed during 0.5 W exposure and a drop in interstitial fluence seen at higher powers (1-1.5 W) due to tissue coagulation. At 1.5 W irradiation an additional, later decrease was also seen which was most likely due to tissue charring. Independent spectrophotometric studies in Naphthol Green dye indicate the rise in fluence observed in the heated albumen phantoms may have been primarily due to light exposure causing photobleaching of the absorbing chromophore. and not due to heat effects. Experiments in liver tissue demonstrated that the observed rise in fluence is dependent on the starting temperature of the tissue. Correlating changes in light fluence with key clinical endpoints/events such as the onset of tissue coagulation or charring may be useful for on-line monitoring and control of laser thermal therapy via interstitial fluence sensors.

Thermal-feedback-controlled coagulation of egg white by the CO2 laser

Temperature feedback control during laser-assisted tissue coagulation was investigated and demonstrated with the egg-white model. We observed the dynamics of photothermal denaturation during CO2 laser irradiation by simultaneously controlling surface temperature and monitoring He-Ne laser transmission of egg-white samples. Once a quasi-constant surface temperature was established, transmission of egg white tended to decrease linearly with time. Analysis of experimental data strongly suggested a first-order rate process. Since transmission was primarily affected by heat-induced increase in the scattering coefficient and depth of coagulation, we speculated that changes in transmission were reliable indicators of accumulating photothermal damage. Our experiments demonstrated that thermal feedback can effectively control or limit photothermal damage.

The effects of dynamic optical properties during interstitial laser photocoagulation

A nonlinear mathematical model was developed and experimentally validated to investigate the effects of changes in optical properties during interstitial laser photocoagulation (ILP). The effects of dynamic optical properties were calculated using the Arrhenius damage model, resulting in a nonlinear optothermal response. This response was experimentally validated by measuring the temperature rise in albumen and polyacrylamide phantoms. A theoretical study of ILP in liver was conducted constraining the peak temperatures below the vaporization threshold. The temperature predictions varied considerably between the static and dynamic scenarios, and were confirmed experimentally in phantoms. This suggests that the Arrhenius model can be used to predict dynamic changes in optical and thermal fields. An increase in temperature rise due to a decrease in light penetration within the coagulated region during ILP of the liver was also demonstrated. The kinetics of ILP are complex and nonlinear due to coagulation, which changes the tissue properties during treatment. These complex effects can be adequately modelled using an Arrhenius damage formulation.

Optical phantom materials for near infrared laser photocoagulation studies

BACKGROUND AND OBJECTIVE

Phantoms were developed that simulate tissue with dynamic and static optical properties with which to study the effects of laser irradiation.

STUDY DESIGN/MATERIALS AND METHODS

Albumen, agar, and an absorbing dye (Naphthol Green) were combined to form a phantom with heat sensitive optical properties to mimic tissue response. The optical properties of this phantom were measured by using the added absorber technique. A polyacrylamide phantom with static optical properties was designed with the equivalent values of micro(a) and micro'(s) by combining appropriate concentrations of Naphthol Green and Intralipid-10%.

RESULTS

The absorption and reduced scattering coefficient of the phantoms were 0. 50 +/- 0.04 cm(-1) and 2.67 +/- 0.07 cm(-1) respectively, in the native state at 805 nm. In the coagulated state, the absorption and scattering coefficient were 0.7 +/- 0.1 cm(-1) and 13.1 +/- 0.5 cm(-1) respectively.

CONCLUSION

Two phantoms with dynamic or static optical properties were developed with properties similar to tissue. They may be used in future studies of opto-thermal effects in tissues.

High-frequency ultrasound properties of multicellular spheroids during heating

High-frequency ultrasound monitoring is a possible method for real-time imaging of thermal therapy in tissues at microscopic resolution. The objective of this work was to measure changes in the ultrasound properties of V79 spheroids (grown from Chinese Hamster lung fibroblasts) exposed to heating. Spheroids are clonal aggregates of cells that provide a useful model for investigating the ultrasound properties of cells in the absence of connective tissue. Relative echo signal power and attenuation coefficients were measured over the frequency range 30 MHz to 70 MHz, from spheroids heated from 37 degrees C to 50 degrees C or 60 degrees C. Echo signal power from the viable rim decreased during the first 5 min by a factor of 1.08 before the spheroid reached 50 degrees C. For the next 25 min, echo signal power rose to a factor of 1.27 above the initial level, after which it remained relatively constant over the remainder of the 50 degrees C heating period. At 60 degrees C, echo signal from the viable rim remained relatively constant, although it appeared to have possibly decreased slightly over the duration of the heating period. Echo signal power from the necrotic core fell to a factor of 1.4 and 1.54 below the initial level at 50 degrees C and 60 degrees C, respectively. First-order chemical rate analysis applied to the echo signal power results in the viable rim at 50 degrees C revealed a rate constant for the 5-15-min heating interval. Interpretation of the echo signal power results in terms of histological stains indicates that the rise in echo signal power at 50 degrees C was due to a loss of cell cohesion, and the possible drop in echo signal power at 60 degrees C was due to spheroid coagulation. Attenuation coefficients decreased by up to 1.54 dB mm-1 over a 30-min period at 60 degrees C. The appearance of a real-time ultrasound image of lesion formation in cells is discussed.

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.

Nonlinear optical behavior of ocular tissue during laser irradiation

A pump (cw Ho-YAG laser) and probe (He-Ne laser) system was used to study the dynamics of the optical behavior of ocular tissue during laser heating. The nonlinear optical behavior of porcine corneal and vitreous-humor tissue was characterized in vitro by means of measurements of the radial profile of a He-Ne laser beam transmitted through the tissue. Temperature gradients in the tissue created by the absorption of pump radiation caused the probe beam to diverge. For constant laser power, the rate of divergence was made dependent on the spot size of the pump beam. The profile of the transmitted probe beam returned to its original magnitude and shape after the tissue was permitted to cool. This reversible change in optical behavior was attributed to the formation of a negative lens owing to thermally induced local gradients in the refractive index of the tissue.

Ultrastructural alterations in heated canine myocardium

BACKGROUND AND OBJECTIVE

The anisotropy factor of light scattering (g) (wavelength 632.8 nm) in heated myocardium decreases as a function of temperature, suggesting, on the basis of Mie theory of light scattering, formation of an increasing number of particles with diameters smaller than the incident wavelength.

STUDY DESIGN/MATERIALS AND METHODS

To test this hypothesis, fresh myocardium was heated at constant temperatures between 37 degrees C and 75 degrees C for 1,000 s. Changes in size and number of granules generated by disintegrating organelles and sarcomeres were studied as a function of temperature by transmission electron microscopy, planimetry and particle counting.

RESULTS

The mitochondria started to disintegrate at 45 degrees C and myofibrils between 45 degrees C and 50 degrees C into increasing numbers of small electron dense granules (diameter 50-200 nm), which correlated with the observed decrease of g from 0.93 +/- 0.02 (at room temperature to 45 degrees C) to 0.77 +/- 0.05 at 75 degrees C.

CONCLUSION

The scattering coefficient microseconds of 161 +/- 33 cm-1 did not change significantly.