J.G. Aarnoudse

Condensed Monte Carlo simulations for the description of light transport

A novel method, condensed Monte Carlo simulation, is presented that applies the results of a single Monte Carlo simulation for a given albedo micro(s)/(micro(alpha) & micro(s)) to obtaining results for other albedos; micro(s) and micro(alpha), are the scattering and absorption coefficients, respectively. The method requires only the storage of the number of interactions of each photon with the medium. The reflectance and transmittance of turbid slabs can thus be found from a limited number of condensed Monte Carlo simulations. We can use an inversion procedure to obtain the absorption and scattering coefficients from the total reflectance and total transmittance of slabs. Remitted photon densities from a semi-infinite medium as a function of the distance between the light source and the detector for all albedos can be found even from the results of a single condensed Monte Carlo simulation. The application of similarity rules may reduce further the number of Monte Carlo simulations that are needed to describe the influence of the distribution of scattering angles on the results.

Optical properties of human dermis in vitro and in vivo

Condensed Monte Carlo simulation results have been used for calculating absorption and reduced scattering coefficients from the literature data on the measured total transmittance and total reflectance of samples of the human skin in vitro. The results of several measuring methods have been compared. We have also estimated the range for absorption coefficients and reduced scattering coefficients at 660 and 940 nm from measured intensities at the skin surface as a function of the distance from the location where the light enters the skin by using condensed Monte Carlo simulations for a homogeneous semi-infinite medium. The in vivo values for the absorption coefficients and the reduced scattering coefficients appear to be much smaller than the values from the in vitro measurements, that have been assumed until now. The discrepancies have been discussed in detail. Our in vivo results are in agreement with other in vivo measurements that are available in the literature.

A syndrome of liver damage and intravascular coagulation in the last trimester of normotensive pregnancy. A clinical and histopathological study

Candida was also associated with chemical damage of vagina and vulva1 epithelium and we feel that it is possible that recurrences in diaphragm-users are as likely to be associated with the spermicide or other infections in this highly sexually active group rather than re-infection from the diaphragm. The seed must, of course, be present but the soil is all important in clinical candidal infection. It would be interesting to note if disinfection of the diaphragm leads to improvement in the relapse rate of patients. E. A. F. Davidson Consultant Physician in Genitourinary Medicine J. K. Oates Consultant in Genitourinary Medicine St Helier Hospital Wrythe Lane Carshalton Surrey SM5 IAA treatment for fungal infections. It is now our practice to advise women using occlusive pesaries who develop fungal infection, to wash the cap in hypochlorite solution and rinse it thoroughly before starting to use it again after completing a course of therapy. Nancy B. Loudon Medical Co-ordinator, Family Planning & Well Woman Services Lothian Health Board Brian Watt Consultant Bacteriologist, City Hospital Edinburgh Michael Goldacre Lecturer The Department of Community Medicine and General Practice Oxford

Laser Doppler velocimetry and Monte Carlo simulations on models for blood perfusion in tissue

Laser Doppler flow measurements and Monte Carlo simulations on small blood perfusion flow models at 780 nm are presented and compared. The dimensions of the optical sample volume are investigated as functions of the distance of the laser to the detector and as functions of the angle of penetration of the laser into the sample. The effects of homodyne and heterodyne scattering are investigated.

Laser Doppler velocimeter based on the self-mixing effect in a fiber-coupled semiconductor laser : theory

A laser Doppler velocimeter that consists of a semiconductor laser coupled to a fiber and that uses the self-mixing effect is presented. The velocimeter can be used for solids and fluids. A theoretical model is developed to describe the self-mixing signals as a function of the amount of feedback into the laser and the distance from the laser to the moving object. Good agreement is found between this theory and measurements.

Small laser Doppler velocimeter based on the self-mixing effect in a diode laser

A very small and simple velocimeter is presented consisting of a diode laser with a gradient-index lens in front of it. The basis of the velocity measurement is the mixing that occurs when light, scattered back by the moving object into the laser cavity, interferes with light inside the laser. This mixing induces large fluctuations of the laser intensity with the Doppler frequency. These fluctuations can be detected either with a photodiode or by measuring the voltage across the diode laser. As an illustration of the performance of the velocimeter, velocity measurements of a rotating disk covered with white paper are described. The differences arising because of using a single-mode or a multilongitudinal mode laser were calculated and verified in experiments. The advantage of the use of a multimode laser is that differential measurements of the distance between laser and moving object are also possible.

Mini laser-Doppler (blood) flow monitor with diode laser source and detection integrated in the probe

A mini laser-Doppler instrument for monitoring capillary flow or flow in tubes, in which a small solid state laser and two photodiodes are integrated in the probe, is described. The instrument is meant for use with skin or arterial blood flow. The mean Doppler frequency derived from the normalized first moment of the frequency distribution, measured with this instrument, appears to be linearly dependent on the flow velocity in the 0–2-mm sec−1 region.

SELF-MIXING LASER-DOPPLER VELOCIMETRY OF LIQUID FLOW AND OF BLOOD PERFUSION IN TISSUE

The velocimetry method of self-mixing, i.e., the feedback of Doppler-scattered light into the laser cavity, is used for the measurement of liquid flow and of blood perfusion in human tissue. The method is elucidated by the registration of the blood perfusion of a finger under repeated occlusion of the veins in the upper arm and with the velocity measurement of a liquid flow containing scattering particles.

Reflectance Pulse Oximetry in Fetal Lambs

ABSTRACT: Transmission pulse oximetry is used for monitoring in many clinical settings. However, for fetal monitoring during labor and in situations with poor peripheral perfusion, transmission pulse oximetry cannot be used. Therefore, we developed a reflectance pulse oximeter, which uses the relative intensity changes of the reflected red and infrared light (red/infrared ratio) to measure the arterial oxygen saturation. The performance of the reflectance pulse oximeter was studied in acute experiments in fetal lambs. By stepwise reduction of the inspired oxygen concentration of the ewe, measurements were done at the fetal scalp at various arterial oxygen saturation levels (17− 82%). Reflectance pulse oximeter readings were averaged over periods of 15 s and compared with simultaneously taken fetal arterial blood samples. A calibration curve for the relationship between red/infrared ratio and arterial oxygen saturation was obtained from 53 measurements in four fetal lambs, by linear regression analysis [red/infrared = 4.088 - (0.038 Sao2), r = 0.96]. In these experiments, the pulse oximeter showed a precision of 4.7% oxygen saturation around the calibration curve, with a 95% confidence interval of ± 9.4%.

Laser Doppler blood flowmetry using two wavelengths: Monte Carlo simulations and measurements.

A new laser Doppler blood flowmeter for measuring skin perfusion is presented. The flowmeter consists of a probe that uses two different wavelengths and is able to measure at different depths. It may be used to distinguish the superficial microcirculation of the skin providing nutritional flow and the flow in deeper situated blood vessels (thermoregulatory flow). Measurements and Monte Carlo simulations of the Doppler signals for human skin are shown.