Double pass 595 nm pulsed dye laser at a 6 minute interval for the treatment of port-wine stains is not more effective than single pass.

BACKGROUND: Pulsed dye laser (PDL) is the first choice for treatment of port wine stains (PWS). However, outcome is highly variable and only a few patients achieve complete clearance. The objective of the study was to compare efficacy and safety of single pass PDL with double pass PDL at a 6 minute interval. METHODS: We conducted a randomized within-patient controlled study on PWS resistant to multiple single pass PDL treatments. In each patient two similar PWS areas were randomly allocated to PDL treatment (595 nm, 7 mm spot size, 1.5 mseconds pulse duration) using, as a control treatment, a single pass (12 J/cm(2)) or, as a new treatment, a double pass PDL (11 J/cm(2), second pass 6 minutes after the first pass). Both test areas were treated two times, 8 weeks apart. PWS clearance was assessed by two blinded dermatologists, and by color measurement (L*a*b) using reflectance spectroscopy, at 3 months follow-up. RESULTS: Sixteen out of 17 included patients completed follow-up. The mean number of treatments before inclusion was 15. Overall color assessed by spectrophotometer showed no improvement for either single or double pass PDL. Blinded Physician Global Assessment and Patient Global Assessment showed a high variability in outcome, with mostly only moderate improvement of the PWS for either single pass or double pass PDL. Furthermore, there was no significant difference in any of the outcomes between single pass and double pass PDL. CONCLUSION: At the chosen settings and after two treatment sessions, double pass PDL at a 6 minute interval does not result in improved clearance of PWS as compared to single pass treatment.

Laser-induced (endo)vascular photothermal effects studied by combined brightfield and fluorescence microscopy in hamster dorsal skin fold venules.

The putative features of the (endo)vascular photothermal response, characterized by laser-induced thermal denaturation of blood and vessel wall constituents, have been elucidated individually, but not simultaneously in dynamic, isolated in vivo systems. A hamster dorsal skin fold model in combination with brightfield/fluorescence intravital microscopy was used to examine the effect of laser pulse duration and blood flow velocity on the size of the thermal coagulum, its attachment behavior, and laser-mediated vasomotion. The size of the coagulum and the extent of vasoconstriction and latent vasodilation were proportional to the laser pulse duration, but pulse duration had no effect on coagulum attachment/dislodgement. Blood flow velocity exhibited no significant effect on the studied parameters. The (endo)vascular photothermal response is governed predominantly by laser energy deposition and to a marginal extent by blood flow velocity.

Transmyocardial laser channels.

We present 2-dimensional echocardiographic images of laser-made channels in the myocardium in an experimental model and in a patient treated with transmyocardial laser revascularization.

Light propagation in the brain depends on nerve fiber orientation.

In this study, the penetration of red laser light (632.8 nm) in fresh bovine brain was measured parallel, oblique, and perpendicular to the axis of white matter tracts. The measurements were performed in eight samples with an isotropic light source and detector and were obtained by advancing the detector tip toward the light source in the tissue. A statistically significant difference in the effective attenuation coefficient of the light (mueff) was found between the parallel and perpendicular directions, 0.47 +/- 0.06 mm -1 and 0.63 +/- 0.13 mm-1, respectively (P = 0.005). The measurements taken at an angle of 45 degrees in the same sample resulted in an intermediate mueff of 0.58 +/- 0.09 mm-1. These results suggest a preferential guidance of light along the axis of the white matter tracts of the brain.

Pilot study on light dosimetry for endobronchial photodynamic therapy.

Endobronchial photodynamic therapy (EB-PDT) using photofrin as the photosensitizer is currently being evaluated as a new treatment modality for inoperable endobronchial tumors. One of the current problems with EB-PDT is the lack of adequate light dosimetry, which hampers proper interpretation of treatment results. In this study exploratory light dosimetry experiments were performed in plastic bronchus models using either a microlens-tipped fiber (suitable for illumination of small superficial tumors) or a cylindrical diffuser fiber (suitable for intraluminal illumination or interstitial illumination of partially obstructing tumors). It is shown that the light fluence prescriptions of current clinical protocols yield a different fluence in tissue for each illumination modality. Depending on the actual placement of the cylindrical diffuser within the lumen, the light fluence at 5 mm depth in the homogeneous tissue model may vary by a factor of 3. The results were confirmed by in vivo experiments in the trachea of a pig. There is a possibility of enhanced tissue response by accidental hyperthermia induced during EB-PDT. The temperature rise was therefore estimated in vivo using a rat tumor model to mimic clinical EB-PDT. Temperature rises of at least 5 degrees C and 10 degrees C can be expected for intraluminal and intratumoral illumination, respectively, at 3.5 +/- 1 mm depth in tissue and 400 mW/cm diffuser output. Light fluence and its distribution in the bronchus strongly depend on the geometry and the optical properties of the tissue as well as on the technique of illumination. As a result of inadequate dosimetry, significant variations in treatment response between patients may be expected.

Optical absorption of blood depends on temperature during a 0.5 ms laser pulse at 586 nm.

Optical properties are important parameters in port wine stain laser treatment models. In this study we investigated whether changes in blood optical properties occur during a 0.5 ms laser pulse. Blood from three volunteers was irradiated in vitro with laser pulses (radiant exposure 2-12 J cm-2, wavelength 586 nm, pulse length 0.5 ms). Reflection and transmission coefficients, measured using double integrating spheres, decreased slightly during the first part of the pulse. At 2.9 J cm-2 radiant exposure, the reflectance increased, independent of total radiant exposure of the pulse. This was caused by blood coagulation. A second sudden increase in reflection and a significant increase in transmission occurred near 6.3 J cm-2 and was accompanied by a "popping" sound, indicating rapid expansion of bubbles due to blood vaporization. A multilayered model of blood was used to fit calculated transmission coefficient curves to the measurements and determine temperature-dependent optical blood absorption. Heat diffusion was shown to be of minor importance. A 2.5-fold increase in absorption for temperatures increasing from 20 to 100 degrees C, accurately describes transmission coefficients measured up to 2.9 J cm-2.

Laser, fibrin glue, or suture repair of peripheral nerves: a comparative functional, histological, and morphometric study in the rat sciatic nerve.

OBJECT: This study was undertaken to evaluate CO2 laser-assisted nerve repair and compare it with nerve repair performed with fibrin glue or absorbable sutures. METHODS: In eight rats, the sciatic nerve was sharply transected and approximated using two 10-0 absorbable sutures and then fused by means of CO2 milliwatt laser welding (power 100 mW, exposure time 1 second per pulse, spot size 320 microm), with the addition of a protein solder (bovine albumin) to reinforce the repair site. The control groups consisted of eight rats in which the nerves were approximated with two 10-0 absorbable sutures and subsequently glued using a fibrin sealant (Tissucol), and eight rats in which the nerves were repaired using conventional microsurgical sutures (four to six 10-0 sutures in the perineurium or epineurium). Evaluation was performed 16 weeks postsurgery and included the toe-spreading test and light microscopy and morphometric assessment. The motor function of the nerves in all groups showed gradual improvement with time. At 16 weeks, the motor function was approximately 60% of the normal function, and there were no significant differences among the groups. On histological studies, all nerves revealed various degrees of axonal regeneration, with myelinated fibers in the distal nerve segments. There were slight differences in favor of the group treated with laser repair, in terms of wound healing at the repair site. In all groups, the number of axons distal to the repair site was higher compared with those proximal, but the axon diameter was significantly less than that in control nerves (p < 0.05). There were no significant differences in the number, density, or diameter of the axons in the proximal or distal nerve segments among the three nerve repair groups (p < 0.05), although there was a trend toward more and thicker myelinated axons in the distal segments of the laser-repaired nerves. CONCLUSIONS: It was found that CO2 laser-assisted nerve repair with soldering is at least equal to fibrin glue and suture repair in effectiveness in a rodent model of sciatic nerve repair.

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.

Integrating sphere effect in whole bladder wall photodynamic therapy: I. 532 nm versus 630 nm optical irradiation.

The optical absorption, scattering and anisotropy coefficients of piglet bladder, with and without Photofrin, and of diseased human bladder were determined in vitro with a double integrating sphere set-up in the wavelength range 450-800 nm. Monte Carlo simulations were performed in a spherical geometry, representing the bladder, using the optical properties at 532 nm and 630 nm determined in vitro. The calculated fluence rates support the fluence rates that were measured at the bladder wall of a piglet during an in vivo whole bladder wall (WBW) irradiation at 532 nm and 630 nm. Fluence rates calculated and measured in vivo at 630 nm are in agreement with those measured previously in clinical photodynamic therapy (PDT) at 630 nm. WBW-PDT with red light (630 nm) will be technically more advantageous than with green light (532 nm) because of a stronger integrating sphere effect, which reduces the variations of the fluence rate at the bladder wall when the isotropic light source is moved away from the centre of the bladder. Since the optical properties show considerable variations from bladder to bladder, and since as a result the light fluence rate at the bladder wall can vary by a factor of 3 to 4 for the same non-scattered light fluence rate, we conclude that in situ light dosimetry during clinical WBW-PDT is a necessity.

Integrating sphere effect in whole-bladder-wall photodynamic therapy: II. The influence of urine at 458, 488, 514 and 630 nm optical irradiation.

Whole-bladder-wall (WBW) photodynamic therapy (PDT) performed with 458 nm instead of 630 nm wavelength might be advantageous. On the basis of Monte Carlo (MC) computer simulations using in vitro bladder optical properties, these wavelengths show an equally strong integrating sphere effect, while haematoporphyrin derivatives can be excited equally efficiently and more easily with an Ar+ laser at 458 nm. To test this, fluence rates were measured at the walls of two piglet bladders during in vivo and in vitro WBW optical irradiations at 458, 488, 514 and 630 nm. In the in vitro experiment, a controlled amount of urine with known absorption coefficient at the irradiation wavelengths was introduced in the bladder cavity. The optical absorption and scattering coefficients and anisotropy factor of the tissue of both piglet bladders were determined in vitro with a double integrating sphere set-up. MC simulations, using the in vitro optical properties, agree only partly with the measured bladder wall fluence rates. In the in vitro experiment with saline in the bladder cavity, the fluence rate at the bladder wall is lowest for 514 nm irradiation and highest for 458 and 630 nm irradiation. In the in vivo experiment and the in vitro experiment with light absorbing urine in the bladder cavity, which mimics the clinical situation, irradiation at 458 nm wavelength resulted in the lowest fluence rate for a given optical power emitted. It cannot be completely ruled out that in an in vivo bladder the light absorption by haemoglobin further reduces the integrating sphere effect at wavelengths shorter than 630 nm. Thus, WBW PDT with red light (630 nm) is technically more advantageous than that with green light (514 nm) or blue light (488 and 458 nm) as this gives the strongest integrating sphere effect.

Uniform irradiation of irregularly shaped cavities for photodynamic therapy.

It is difficult to achieve a uniform light distribution in irregularly shaped cavities. We have conducted a study on the use of hollow 'integrating' moulds for more uniform light delivery of photodynamic therapy in irregularly shaped cavities such as the oral cavity. Simple geometries such as a cubical box, a sphere, a cylinder and a 'bottle-neck' geometry have been investigated experimentally and the results have been compared with computed light distributions obtained using the 'radiosity method'. A high reflection coefficient of the mould and the best uniform direct irradiance possible on the inside of the mould were found to be important determinants for achieving a uniform light distribution.

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.

Integrating sphere effect in whole-bladder wall photodynamic therapy: III. Fluence multiplication, optical penetration and light distribution with an eccentric source for human bladder optical properties.

Whole-bladder-wall (WBW) photodynamic therapy (PDT) is performed using approximately 630 nm light emitted by an isotropic light source centered in the bladder cavity. The phenomenon of an increased fluence rate in this spherical geometry, due to light scattering, is denoted as the integrating sphere effect. The fluence rate and the optical penetration depth depend on a single tissue optical parameter, namely the reduced albedo. The optical properties of (diseased) human bladder tissue, i.e. absorption coefficient, scattering coefficient, anisotropy factor and refractive index, were determined in vitro in the wavelength range of 450-880 nm. The integrating sphere effect and optical penetration depth were calculated with diffusion theory and compared to Monte Carlo (MC) computer simulations using approximately 630 nm optical properties. With increasing albedo, the integrating sphere effect calculated with diffusion approximation is increasingly larger than that found with MC simulations. Calculated and simulated optical penetration depths are in reasonable agreement. The smaller the integrating sphere effect for a given tissue absorption, the larger the optical penetration depth into the bladder wall, as the effective attenuation coefficient decreases. Optical penetration depths up to approximately 7.5 mm (definition dependent) can be responsible for unintended tissue damage beyond the bladder tissue. MC simulations were also performed with an eccentric light source and the uniformity of the light distribution at the bladder wall was assessed. The simulations show that even for a small eccentricity, the extremes in deviation from the mean fluence rate are large. All these results indicate that WBW PDT should be performed with some kind of in situ light dosimetry.

Interstitial laser thermotherapy: developments in the treatment of small deep-seated brain tumors.

New technical advances have made feasible the utilization of laser to destroy deep-seated brain tumors under real-time monitoring. Experience with interstitial laser thermotherapy (ILTT) in animal and clinical studies has been obtained. These studies are summarized and the future potential of ILTT in neurosurgery is discussed.

CO2 laser nerve welding: optimal laser parameters and the use of solders in vitro.

To improve the welding strength, an in vitro study was performed to investigate the bonding strength of CO2 laser nerve welding (LNW), with and without the use of human albumin solution, dried albumin solution, egg white, fibrinogen solution, fibrin glue, and red blood cells as a solder. Fifteen different combinations of laser power (50, 100, and 150 mW) and pulse duration (0.1 to 3 s) were used with a spot size of 320 microns. The results have been compared to suture, fibrin glue, and laser-assisted nerve repair (LANR). The strongest welds (associated with whitening and caramelization of tissue) were produced at 100 mW with pulses of 1.0 s and at 50 mW with pulses of 3 s. The use of a dried albumin solution as a solder at 100 mW with pulses of 1 s increased the bonding strength 9-fold as compared to LNW (bonding strength 21.0 +/- 8.6 g and 2.4 +/- 0.9 g, respectively). However, positioning the nerves between cottons soaked in saline for 20 minutes resulted in a decrease of the bonding strength (9.8 +/- 4.5 g). The use of a 20% albumin solution and egg white, both at 50 mW with pulses of 3 s, resulted in a bonding strength of, respectively, 5.7 +/- 2.1 g and 7.7 +/- 2.4 g. Other solders did not increase the bonding strength in comparison to LNW. The substantial increase in bonding strength for some solders suggests that it is worthwhile to investigate the dehiscence rate and nerve regeneration of solder enhanced LNW in an in vivo study.

Alternative surgical exposure of the rat heart in vivo using a simple abdominal approach.

Access to the heart in laboratory rats is usually performed via a median sternotomy or a lateral thoracotomy. An alternative, less traumatic approach to the in vivo rat heart with improved survival is described. The technique uses an upper median laparotomy extending alongside the xyphoid bone. The xyphoid bone is retracted in a rostral direction, and a T-shaped cut is made in the diaphragm thus opening the thoracic cavity. Using a retractor the opening in the diaphragm is spread and the heart is exposed. We performed this abdominal approach in 23 anaesthetised and mechanically ventilated (for 2 h) rats and found physiologic intra-operative haemodynamics, a good postoperative recovery and 0% mortality.