Photodynamic therapy of B16 pigmented melanoma with liposome-delivered Si(IV)-naphthalocyanine.

The possibility of extending photodynamic therapy to the treatment of highly pigmented neoplastic lesions was tested by using Si(IV)-naphthalocyanine (SiNc) as a tumor-localizing agent. Si(IV)-naphthalocyanine displays intense absorbance at 776 nm (epsilon = 5 x 10(5) M-1 cm-1), where melanin absorption becomes weaker. As an experimental model we selected B16 pigmented melanoma subcutaneously transplanted to C57BL mice. Upon injection of 0.5 or 1 mg kg-1 of liposome-incorporated SiNc, maximal accumulation of the photosensitizer in the tumor was observed at 24 h with recoveries of 0.35 and 0.57 microgram g-1, respectively. However, the tumor targeting by SiNc shows essentially no selectivity, since the photosensitizer concentrations in the skin (peritumoral tissue) were very similar to those found in the tumor at all postinjection times examined by us. Irradiation of SiNc-loaded melanoma with 776 nm light from a diode laser at 24 h postinjection induces tumor necrosis and delay of tumor growth. The effect appears to be of purely photochemical nature at dose rates up to 260 mW cm-2; at higher dose rates, thermal effects are likely to become important.

Histopathology of diode and argon laser lesions in rabbit retina. A comparative study.

Argon lasers are the most frequently used laser source for retinal photocoagulation. These are expensive, bulky and low-efficiency devices. In contrast, diode semiconductor lasers have a number of characteristics that make them attractive for medical application: compact size, high electrical-to-optical efficiency, and long operating lifetime. Comparable irradiance lesions (about 120 Wcm2), ophthalmoscopically similar to those obtained therapeutically in humans, were obtained by a diode and an argon laser. Twenty-four hours after the treatment, a study of these lesions was made by light and electron microscopy. Argon irradiations resulted in damage to both the inner and the outer retinal layers, while the diode laser radiation produced damage to the outer retina and choroid. A sufficient diode laser light passed into the choroid to induce small vessel occlusions and/or edema. The histological characteristics of the lesions produced by the two lasers suggest the use of the diode lasers, as well as argon lasers, in the treatment of retinal and subretinal pathologies.

Tunable superradiant emission from a planar dye laser.

A new, simple scheme to tune a double-pass, superradiant dye laser is reported. A planar cell with a thickness below 100 microm filled with a highly concentrated (4-5 x 10(-)-M/liter) solution of Rhodamine 6G in ethanol is used. An unsaturated gain value of 1.7 cm(-) has been measured with flashlamp pumping, and the amplifier has been found to operate at a well saturated regime. Smooth laser linewidths ranging from broadband, gain narrowed values of 10 nm to narrowband values of 8 GHz have been achieved by using appropriate frequency dispersive feedback elements and suitable cell thickness. A 5-GHz output has been observed with a 25-microm gap cell. The absence of a resonant cavity avoids modal structure and ensures improved frequency and intensity stability. The reported configuration should be scalable up as far as output energy is concerned. Simultaneous two-wavelength operation is possible. Pumping with a frequency-doubled Nd-laser should allow a further reduction of the usable cell thickness with narrower output bandwidths.

Tunable lasers in ophthalmology.

The present status of laser application in clinical ophthalmology is breifly reviewed. The potentials of tunable dye lasers as retinal photocoagulators are discussed. Selective irradiation of ocular tissues over the full visible spectrum and the simplicity and reliability of recently developed waveguide lasers are the most attractive features of these lasers. Waveguide dye lasers have permitted to set up very compact and simple retinal photocoagulators, with improved output intensity stability and nearfield distribution uniformity. Preliminary results obtained with pulsed Rhodamine 6G laser show that good retinal photocoagulations are obtained at very low output energies.