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.

An analyte monitor includes a sensor, a sensor control unit, and a display unit. The sensor has, for example, a substrate, a recessed channel formed in the substrate, and conductive material disposed in the recessed channel to form a working electrode. The sensor control unit typically has a housing adapted for placement on skin and is adapted to receive a portion of an electrochemical sensor. The sensor control unit also includes two or more conductive contacts disposed on the housing and configured for coupling to two or more contact pads on the sensor. A transmitter is disposed in the housing and coupled to the plurality of conductive contacts for transmitting data obtained using the sensor. The display unit has a receiver for receiving data transmitted by the transmitter of the sensor control unit and a display coupled to the receiver for displaying an indication of a level of an analyte. The analyte monitor may also be part of a drug delivery system to alter the level of the analyte based on the data obtained using the sensor.

Analyte Monitoring Device And Methods Of Use

The optical properties of human skin, subcutaneous adipose tissue and human mucosa were measured in the wavelength range 400–2000 nm. The measurements were carried out using a commercially available spectrophotometer with an integrating sphere. The inverse adding–doubling method was used to determine the absorption and reduced scattering coefficients from the measurements.

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Optical properties of human skin, subcutaneous and mucous tissues in the wavelength range from 400 to 2000 nm

Advanced drug delivery devices via self-assembly of amphiphilic block copolymers

Light-activated, photosensitizer-based therapies have been established as safe modalities of tumour ablation for numerous cancer indications. Two main approaches are available: photodynamic therapy, which results in localized chemical damage in the target lesions, and photothermal therapy, which results in localized thermal damage. Whereas the administration of photosensitizers is a key component of photodynamic therapy, exogenous photothermal contrast agents are not required for photothermal therapy but can enhance the efficiency and efficacy of treatment. Over the past decades, great strides have been made in the development of phototherapeutic drugs and devices as cancer treatments, but key challenges have restricted their widespread clinical use outside of certain dermatological indications. Improvements in the tumour specificity of photosensitizers, achieved through targeting or localized activation, could provide better outcomes with fewer adverse effects, as could combinations with chemotherapies or immunotherapies. In this Review, we provide an overview of the current clinical progress of phototherapies for cancer and discuss the emerging preclinical bioengineering approaches that have the potential to overcome challenges in this area and thus improve the efficiency and utility of such treatments.

Clinical development and potential of photothermal and photodynamic therapies for cancer

The absorption and transport scattering coefficients of caucasian and negroid dermis, subdermal fat and muscle have been measured for all wavelengths between 620 and 1000 nm. Samples of tissue 2 mm thick were measured ex vivo to determine their reflectance and transmittance. A Monte Carlo model of the measurement system and light transport in tissue was then used to recover the optical coefficients. The sample reflectance and transmittance were measured using a single integrating sphere 'comparison' method. This has the advantage over conventional double-sphere techniques in that no corrections are required for sphere properties, and so measurements sufficiently accurate to recover the absorption coefficient reliably could be made. The optical properties of caucasian dermis were found to be approximately twice those of the underlying fat layer. At 633 nm, the mean optical properties over 12 samples were 0.033 mm(-1) and 0.013 mm(-1) for absorption coefficient and 2.73 mm(-1) and 1.26 mm(-1) for transport scattering coefficient for caucasian dermis and the underlying fat layer respectively. The transport scattering coefficient for all biological samples showed a monotonic decrease with increasing wavelength. The method was calibrated using solid tissue phantoms and by comparison with a temporally resolved technique.

https://iopscience.iop.org/article/10.1088/0031-9155/43/9/003/pdf

Near-infrared optical properties of ex vivo human skin and subcutaneous tissues measured using the Monte Carlo inversion technique

The presence of glucose dissolved in an aqueous solution increases the refractive index of the solution and therefore has an influence on the scattering properties of any particles suspended within it. We present experimental data on the effect of glucose concentration on the scattering coefficient of a suspension of spherical polystyrene particles. The experimental results are in good agreement with Mie theory. The effect of glucose on light transport in highly scattering, tissue-simulating phantoms is demonstrated both experimentally and theoretically by application of diffusion theory. The possible application of this effect for noninvasive glucose monitoring of diabetic patients is discussed.

Influence of glucose concentration on light scattering in tissue-simulating phantoms.

Diabetics would benefit greatly from a device capable of providing continuous noninvasive monitoring of their blood glucose levels. The optical scattering coefficient of tissue depends on the concentration of glucose in the extracellular fluid. A feasibility study was performed to evaluate the sensitivity of the tissue reduced scattering coefficient in response to step changes in the blood glucose levels of diabetic volunteers. Estimates of the scattering coefficient were based on measurements of the diffuse reflectance on the skin at distances of 1-10 mm from a point source. A correlation was observed between step changes in blood glucose concentration and tissue reduced scattering coefficient in 30 out of 41 subjects measured.

Correlation between blood glucose concentration in diabetics and noninvasively measured tissue optical scattering coefficient

The effect of temperature on the optical properties of human dermis and subdermis as a function of near-infrared wavelength has been studied between 25 degrees C and 40 degrees C. Measurements were performed ex vivo on a total of nine skin samples taken from the abdomen of three individuals. The results show a reproducible effect of temperature on the transport scattering coefficient of dermis and subdermis. The relative change of the transport scattering coefficient showed an increase for dermis ((4.7+/-0.5) x 10(-3) degrees C(-1)) and a decrease for subdermis ((-1.4+/-0.28) x 10(-3) degrees C(-1)). Note that the magnitude of the temperature coefficient of scattering was greater for dermis than subdermis. A reproducible effect of temperature on the absorption coefficient could not be found within experimental errors. System reproducibility in transport scattering coefficient with repeated removal and repositioning of the same tissue sample at the same temperature was excellent at +/-0.35% for all measurements. This reproducibility enabled such small changes in scattering coefficient to be detected.

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Effect of temperature on the optical properties of ex vivo human dermis and subdermis

Most instruments used to measure tissue optical properties
noninvasively employ data-analysis algorithms that rely on the
simplifying assumption that the tissue is semi-infinite and
homogeneous. The influence of a layered tissue architecture on the
determination of the scattering and absorption coefficients has been
investigated in this study. Reflectance as a function of distance
from a point source for a two-layered tissue architecture that
simulates skin overlying fat was calculated by using a Monte Carlo
code. These data were analyzed by using a diffusion theory model
for a homogeneous semi-infinite medium to calculate the scatter and
absorption coefficients. Depending on the algorithm and the radial
distance, the estimated tissue optical properties were different from
those of either layer, and under some circumstances, physically
impossible. In addition, the sensitivity and cross talk of the
estimated optical properties to changes in input optical properties
were calculated for different layered geometries. For typical
optical properties of skin, the sensitivity to changes in optical
properties is highly dependent on the layered architecture, the
measurement distance, and the fitting algorithm. Furthermore, a
change in the input absorption coefficient may result in an apparent
change in the measured scatter coefficient, and a change in the input
scatter coefficient may result in an apparent change in the measured
absorption coefficient.

Matthias Essenpreis

Papers

Near-infrared optical properties of ex vivo human skin and subcutaneous tissues measured using the Monte Carlo inversion technique

Influence of glucose concentration on light scattering in tissue-simulating phantoms.

Correlation between blood glucose concentration in diabetics and noninvasively measured tissue optical scattering coefficient

Effect of temperature on the optical properties of ex vivo human dermis and subdermis

Influence of layered tissue architecture on estimates of tissue optical properties obtained from spatially resolved diffuse reflectometry.