M.J.C. van Gemert

Single vs. swarm detection of microparticles and exosomes by flow cytometry.

See also Harrison P, Gardiner C. Invisible vesicles swarm within the iceberg. This issue, pp 916‐8.

Effect of the timing of treatment of port-wine stains with the flash-lamp-pumped pulsed-dye laser

BACKGROUNDnPort-wine stains can be treated with a flash-lamp-pumped pulsed-dye laser, but it is uncertain whether this treatment is more effective if administered early in life, when the skin is thinner and the lesion is smaller.nnnMETHODSnWe prospectively studied 100 patients with a previously untreated port-wine stain of the head or neck. They were treated with the flash-lamp-pumped pulsed-dye laser and divided into four age groups (0 to 5, 6 to 11, 12 to 17, and 18 to 31 years). The outcome measure was lightening of the port-wine stain (reduction in the difference in color between the skin with the stain and contralateral healthy skin) as measured with a colorimeter after an average of five treatments (range, three to seven) of the entire lesion.nnnRESULTSnOf the 100 patients, 11 could not be included in the analysis because they had received fewer than three or more than seven treatments, had an erroneous base-line color measurement, or were lost to follow-up. The sizes, locations, and colors of the port-wine stains were similar among the groups. When all 89 patients were analyzed together, the average reduction in the difference in color between the skin with the port-wine stain and contralateral healthy skin was 40 percent. The differences between age groups in the average reduction in color differences were not significant (P= 0.26). By the end of the study, only 7 of 89 patients had completed laser therapy, and in no case was clearance complete. Treatment was discontinued in all seven because the last three treatments did not lead to further lightening.nnnCONCLUSIONSnWe found no evidence that treatment of port-wine stains with the flash-lamp-pumped pulsed-dye laser in early childhood is more effective than treatment at a later age.

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.

Light dosimetry in optical phantoms and in tissues: I. Multiple flux and transport theory

This is the first of two papers on the quantitative measurement of light energy fluence rates in optical phantoms and in tissues, in vitro and in vivo. The theory discussed in the present paper will be used in a forthcoming experimental paper to quantitatively check measurements of light energy fluence rates. A simple multiple flux model, which is equivalent to the diffusion approximation, is derived from the equation of transfer in a plane as well as in a spherical geometry. The equations obtained are similar to those of the Kubelka-Munk and related heuristic models. This permits conclusions regarding the limitations of these models and the values of their constants. The heuristic models are equivalent to diffusion theory for diffuse incident light, but not for collimated incident light. We also present a simple calculation of the radiance as a function of direction in the diffusion domain. This, together with the effective attenuation coefficient, permits indirect experimental determination of both the albedo and the anisotropy factor (g) of the scattering function. Similarity relations are discussed, as they result from the so called delta-Eddington approximation, leading to the conclusion that far from boundaries and sources light propagation characteristics do not change very much when g and omega s are varied, provided omega s (1-g) is kept constant (omega s = scattering coefficient). Therefore, only two optical constants are required to approximately describe light propagation in homogeneous and isotropic media in the diffusion approximation.

Efficacy of low-level laser therapy in the management of stage III decubitus ulcers: a prospective, observer-blinded multicentre randomised clinical trial

AbstractLow-level laser therapy (LLLT) has been suggested as a promising treatment option for open wounds. In view of the absence of randomised studies with sufficiently large sample sizes, we assessed the efficacy of LLLT in the treatment of stage III decubitus ulcers. We performed a prospective, observer-blinded multicentre randomised clinical trial to assess the effect of LLLT as adjuvant to standard decubitus care. A total of 86 patients were enrolled into the study. Treatment was the prevailing consensus decubitus treatment (n=47); one group (n=39) had LLLT in addition, five times a week over a period of 6 weeks. The primary outcome measure was the absolute (mm2) and relative (%) wound size reduction at 6 weeks compared to baseline. Secondary outcome measures were the number of patients developing a stage IV ulcer during the study period, and the median change in Norton scores at 6 weeks compared to baseline. Based on the intention-to-treat principle, using last-observation-carried-forward analyses, Mann–Whitney U tests showed that the differences between the two groups in terms of absolute improvement (p=0.23) and relative improvement (p=0.42) were not significant. Because the wound size areas were non-normally distributed, we also analysed the data after logarithmic transformation of the wound size measurements. No significant difference in loge improvement scores between groups could be demonstrated (unpaired t-test: p=0.59). During the treatment period 11% of the patients in the control group and 8% of the patients in the LLLT group developed a stage IV decubitus ulcer (Fishers exact test: p=0.72). The patients Norton scores did not change during the treatment period. In this trial we found no evidence that justifies using low-level laser therapy as an adjuvant to the consensus decubitus ulcer treatment.n

Placental Characteristics of Monochorionic Diamniotic Twin Pregnancies in Relation to Perinatal Outcome

To study placental characteristics in relation to perinatal outcome in 150 pairs of monochorionic diamniotic (MCDA) twins. Between January 1998 and January 2007 150 pairs of MCDA twins were delivered in the University Medical Center, Utrecht, The Netherlands. Mortality, neonatal morbidity and birth weight discordancy were studied in relation to type of anastomoses, type and distance between cord insertions and placental sharing. From 14 weeks onwards, there were 45 (15.0%) perinatal deaths. We found no clear relationship between perinatal mortality and type of anastomoses, distance between cord insertions and placental sharing. Perinatal mortality was significantly increased in the presence of velamentous cord insertion (OR 3.65, 95% CI 1.83-7.28). Data concerning neonatal morbidity were similar. TTTS occurred predominantly in the presence of AV-anastomoses without compensating superficial AA-anastomoses (p=0.005) and occurred more frequently in the presence of velamentous cord insertion (OR 1.79, 95% CI 0.94-3.44). Twins with unequal shared placentas had significantly more often severe birth weight discordancy, although only in the presence of AA-anastomoses (OR 4.09, 95% CI 1.74-9.63). If AA-anastomoses were absent in the unequally shared placenta, there was no relation between severe birth weight discordancy and unequal sharing of the placenta (OR 1.06, 95% CI 0.08-13.52). In MCDA twins, placental characteristics determine perinatal outcome, occurrence of TTTS and fetal growth. Prenatal identification of these characteristics by ultrasound may alter counselling and intensity of pregnancy surveillance.

Placental Characteristics of Monoamniotic Twin Pregnancies in Relation to Perinatal Outcome

OBJECTIVEnTo study placental characteristics in relation to perinatal outcome in 55 pairs of monochorionic monoamniotic (MA) twins.nnnMETHODSnBetween January 1998 and May 2008 55 pairs of MA twins were delivered in 4 tertiary care centers and analysed for mortality, birth weight discordancy and twin-to-twin transfusion syndrome (TTTS) in relation to type of anastomoses, type and distance between cord insertions and placental sharing. Five acardiac twins, 2 conjoined twins, 4 higher order multiples and one early termination of pregnancy were excluded, leaving 43 MA placentas for analysis. Of these 43, one placenta could not be analysed for placental vascular anastomoses due to severe maceration after single intra-uterine demise leaving 42 placentas for analysis of anastomoses.nnnRESULTSnArterio-arterial (AA), venovenous (VV) and arteriovenous (AV) anastomoses were detected in 98%, 43% and 91% of MA placentas, respectively. Velamentous cord insertion was found in 4% of cases. Small distance between both umbilical cord insertions (<5 cm) was present in 53% of MA placentas. Overall perinatal loss rate was 22% (19/86). We found no association between mortality and type of anastomoses, type and distance between cord insertions and placental sharing. The incidence of TTTS was low (2%) and occurred in the only pregnancy with absent AA-anastomoses.nnnCONCLUSIONnPerinatal mortality in MA twins was not related to placental vascular anatomy. The almost ubiquitous presence of compensating AA-anastomoses in MA placentas appears to prevent occurrence of TTTS.

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.

Interstitial laser thermotherapy in neurosurgery : A review

SummaryOne of the most recent laser treatment modalities in neurosurgery is interstitial laser thermotherapy (ILTT). In this review, experimental and clinical studies concerning intracranial ILTT are discussed. Two methods for intra-operative control of the laser induced lesions are described; i.e., computer-controlled power delivery, using a thermocouple that is positioned interstitially at the periphery of the tumour to maintain the desired temperature at that point, and MRI, to visualise the extent of the thermal lesions induced by ILTT. The results show that ILTT using a Nd:YAG laser is easy and relatively effective in the treatment of small deepseated brain tumours with minimal risk and complications. This review is concluded with suggestions for further improvement of this treatment modality.

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.