H. J. C. M. Sterenborg

In vitro double-integrating-sphere optical properties of tissues between 630 and 1064 nm

The optical properties (absorption and scattering coefficients and the scattering anisotropy factor) were measured in vitro for cartilage, liver, lung, muscle, myocardium, skin, and tumour (colon adenocarcinoma CC 531) at 630, 632.8, 790, 850 and 1064 nm. Rabbits, rats, piglets, goats, and dogs were used to obtain the tissues. A double-integrating-sphere setup with an intervening sample was used to determine the reflectance, and the diffuse and collimated transmittances of the sample. The inverse adding-doubling algorithm was used to determine the optical properties from the measurements. The overall results were comparable to those available in the literature, although only limited data are available at 790-850 nm. The results were reproducible for a specific sample at a specific wavelength. However, when comparing the results of different samples of the same tissue or different lasers with approximately the same wavelength (e.g. argon dye laser at 630 nm and HeNe laser at 632.8 nm) variations are large. We believe these variations in optical properties should be explained by biological variations of the tissues. In conclusion, we report on an extensive set of in vitro absorption and scattering properties of tissues measured with the same equipment and software, and by the same group. Although the accuracy of the method requires further improvement, it is highly likely that the other existing data in the literature have a similar level of accuracy.

Haemodynamic Model of Twin-Twin Transfusion Syndrome in Monochorionic Twin Pregnancies

Twin-twin transfusion syndrome in monochorionic twin pregnancies is not understood completely and is controversial which hampers development of acceptable diagnostic and rational treatment strategies. A haemodynamic model was developed that relates fetal growth with (1) fetoplacental blood flow and fetomaternal effects, and (2) net twin-twin transfusion from donor to recipient twin. Fluid balance mechanisms were neglected. Placental vascular anastomoses (arteriovenous, venoarterial, arterioarterial, venovenous) were modelled as straight blood vessels connecting the placental cord insertions that grow during pregnancy. Poiseuilles law predicts significantly decreasing anastomosing resistances, and when placental sharing is unequal it is assumed that smaller placental fractions cause smaller blood volumes and pressures. Two coupled first-order differential equations describing each twins blood volume were determined and analysis showed that placental and anastomotic development cause anastomotic blood flow to increase faster than fetal growth. Hence, it is proposed as the syndromes underlying pathophysiology that fetal discordance increases progressively, beyond fetal compensatory capacity. Fewer anastomoses cause larger discordance, but its onset can vary widely during pregnancy. Arteriovenous plus compensating anastomoses produce dynamic steady-state growth patterns with large, opposite, measurable anastomotic blood flows. Clinical study of fetal growth patterns may identify the syndromes underlying placental anatomy. Predicted trends depend only weakly on implemented fetal physiology and are most likely realistic. This knowledge could improve future management of the syndrome.

Two integrating spheres with an intervening scattering sample

Two integrating spheres placed so that the exit port of one and the entry port of the other are adjacent, with only a sample intervening, will permit the simultaneous determination of the reflectance and the transmittance of the sample. Such a geometry permits measurements to be made as the sample undergoes some external stimulation, such as heat, pressure, or a chemical change. To determine the sample reflectance and the transmittance from the measured values of irradiance within each sphere requires the calculation of the exchange of light through the sample between the spheres. First the power collected by a detector situated in the wall of an integrating sphere is calculated as a function of the area and the reflectance of the wall, the holes, the sample, and the detector for both diffuse and collimated light incident upon the sample and for a sample located at either the exit port (reflectance) or the entry port (transmittance) of the sphere. Next, by using the single-sphere equations, we calculate the effect of the multiple exchange of light between two integrating spheres arranged so that the sample is placed between them. In all the cases of two integrating spheres the power detected is greater than or equal to that for the single sphere and depends on both the reflection and the transmission properties of the sample. Additionally, the effect of a baffle placed between the sample and the detector or of a nonisotropic detector is to reduce the power detected.

Photodynamic destruction of Haemophilus parainfluenzae by endogenously produced porphyrins

Bacterial resistance against antibiotic treatment is becoming an increasing problem in medicine. Therefore methods to destroy microorganisms by other means are being investigated, one of which is photodynamic therapy (PDT). It has already been shown that a variety of Gram-positive and Gram-negative bacteria can be killed in vitro by PDT using exogenous sensitizers. An alternative method of photosensitizing cells is to stimulate the production of endogenous sensitizers. The purpose of this study was to investigate the bactericidal efficacy of PDT for Haemophilus parainfluenzae with endogenously produced porphyrins, synthesized in the presence of delta-aminolaevulinic acid (delta-ALA). H. parainfluenzae incubated with increasing amounts of delta-ALA showed decreased survival after illumination with 630 nm light. No photodynamic effect on the bacterial viability was found when H. parainfluenzae was grown without added delta-ALA. H. influenzae, grown in the presence of delta-ALA, but not capable of synthesizing porphyrins from delta-ALA, was not affected by PDT. Of the range of incident wavelengths, 617 nm appeared to be the most efficient in killing the bacteria. Spectrophotometry of the bacterial porphyrins demonstrated that the maximum fluorescence occurred at approximately 617 nm, with a much lower peak around 680 nm. We conclude that a substantial killing of H. parainfluenzae by PDT in vitro after endogenous sensitization with delta-ALA can be achieved.

Photodynamic therapy with pulsed light sources : a theoretical analysis

The effectiveness of photodynamic therapy using pulsed sources was evaluated using a mathematical model describing the time-dependent excitation and de-excitation of the photosensitizer molecule. Using the various numerical data available in the literature on haematoporphyrin we calculated that the effectiveness of pulsed excitation in PDT is identical to that of CW excitation for peak fluence rates below 4 x 10(8) W m-2. Above this threshold the effectiveness drops significantly. In practice this effect will occur with sources with high pulse energy and low repetition frequency. The commonly used dye lasers pumped by either a Cu vapour laser or a frequency doubled Nd:YAG laser have a PDT effectiveness identical to that of a CW source of the same wavelength and the same average fluence rate.

The spectral dependence of the optical properties of human brain

The in vitro optical properties of slices of human brain tissue were measured. The experiments were performed with an integrating sphere and covered the wavelength range from 400 to 1100 nm. Both normal brain tissue (white and grey matter) and tumour tissue (a malignant glioma and a melanotic melanoma) were investigated. From the experimental data the Kubelka-Munk absorption and scattering coefficients were determined. From these data we calculated the transport absorption and scattering coefficients by using the diffusion approximation. Blood and water appeared to be the dominant chromophores. In the wavelength range mentioned, the absorption coefficients varied over more than two orders of magnitude. The scattering coefficients increased slowly towards the shorter wavelengths.

Fluorescence localization in tumour and normal brain after intratumoral injection of haematoporphyrin derivative into rat brain tumour

In the intracerebral 9L rat gliosarcoma, the spatial distribution of the photosensitizer haematoporphyrin derivative (HpD) was studied after intratumoral injection. The fluorescence volume was measured in histological sections from 10 min up to 5 days after injection. Complete sensitization of the tumours could not be achieved by slow stereotactical injection of 4 mm3 HpD (mean HpD fluorescence volume, 13 +/- 11 mm3). Larger parts of the tumour could be loaded with HpD (39 +/- 23 mm3, p = 0.0001) by increasing the injection velocity and the volume to 50 mm3. Again, complete sensitization of the tumours was not achieved during a time scale of 5 days after intratumoral injection. Although the fluorescence volume did not change significantly with time, it was influenced by the injection site within the tumour. Injection of HpD within 1 mm from the tumour border resulted in significantly smaller fluorescence volumes in the tumour than injection into the tumour centre. Large injection volumes caused an increased leakage of HpD to normal brain, leading to the loss of selectivity of photosensitizer content and the occurrence of dark toxicity of normal brain while the tumours still appeared vital.

The optical properties of lung as a function of respiration

Lung consists of alveoli enclosed by tissue and both structures contribute to volume-dependent scattering of light. It is the purpose of this paper to determine the volume-dependent optical properties of lung. In vivo interstitial fibre measurements of the effective attenuation coefficient mu eff at 632.8 nm differed during inspiration (mu eff = 2.5 +/- 0.5 cm-1) from that during expiration (mu eff = 3.2 +/- 0.6 cm-1). In vitro measurements on a piglet lung insufflated with oxygen from 50 to 150 ml showed the effective attenuation coefficient at 632.8 nm decreases as a function of oxygen volume in the lung (at 50 ml mu eff = 2.97 +/- 0.11 cm-1, at 100 ml mu eff = 1.50 +/- 0.07 cm-1, and at 150 ml mu eff = 1.36 +/- 0.15 cm-1). This was explained by combining scattering of alveoli (Mie theory) with optical properties of collapsed lung tissue using integrating sphere measurements. Theory and measured in vitro values showed good agreement (deviation < or = 15%). Combination of these data yields the absorption coefficient and scattering parameters of lung tissue as a function of lung volume. We conclude that the light fluence rate in lung tissue should be estimated using optical properties that include scattering by the alveoli.

Laserlithotripsy of salivary stones: A comparison between the pulsed dye laser and the Ho-YSGG laser

The feasibility of laser lithotripsy of salivary stones was investigated. Two types of laser systems were evaluated: a 504 nm flashlamp pumped dye laser and a Ho-YSGG laser. With the dye laser, plasma flashes and acoustic phenomena could be observed. The number of laser shots per unit mass necessary to fragment the stone decreased in proportion to the energy per laser pulse to the power −2.7. With the Ho-YSGG laser, a more ablative kind of stone decomposition was observed. Here the number of shots per unit mass necessary for fragmentation was inversely proportional to the energy per laser pulse. For both lasers the total time necessary to fragment the stones is much too long to compete with conventional stone removal.

Influence of Tumour Depth, Blood Absorption and Autofluorescence on Measurements of Exogenous Fluorophores in Tissue

We investigated the influence of tumour depth and differences in blood concentration and autofluorescence between tumour and normal tissue on the fluorescence of a tumour-localising agent. Carotenoporphyrin, CP(Me)3, was injected into rats and nude mice with intradermal tumours. On the tumours an incision was made, uncovering 2 mm2 of the tumour, and fluorescence measurements, including excitation-emission maps and fluorescence ratios, were made on skin, covered and uncovered tumour. The measured fluorescence ratio in the uncovered tumour showed a three- to tenfold increase compared to the covered tumour. We used a one-dimensional layered tissue model to analyse the data. In conclusion, even with a high tumour-selectivity deeper lying tumours cannot always be detected, particularly if the tumour has a high blood concentration or low autofluorescence intensity.