No abstract

No abstract

The dose rate in photodynamic therapy is proportional to the energy fluence rate and the concentration of the photosensitizer. Calculations of the energy fluence rate have been performed in slab, cylindrical and spherical geometries with the discrete ordinates transport method and diffusion theory. The attentuation of the energy fluence rate is least in slab geometry and greatest in spherical geometry. Violet (405 nm) light is attenuated much more rapidly than red (630 nm) light. Small tissue dimensions or narrow beam irradiation further decrease the energy fluence rate with radius and depth. Anisotropic scattering increases the energy fluence rate at large depths, but decreases it near the source. Measurements of the absolute energy fluence rate vs depth in a mouse tumor model exhibit an order of magnitude attenuation through the skin and a 3 mm thick tumor. Calculations of the energy fluence rate of the DHE fluorescence have been carried out to guide measurement of the concentration. Violet light excitation is much more efficient than red light excitation.

Diaphanography, also known as transillumination, is a breast diagnostic technique based on differences in the diffuse transmittance of visible or near-infrared radiation. Previous papers by the authors reported on investigations of the effect of tumor size, depth at which the tumor is located, the thickness of the breast, and the effect of using photons of different wavelengths. The results from the study reported here indicate that absorption of light in hemoglobin is the basis for the luminance contrast, and shift in the infrared to red transmission ratio, in the diaphanographic image. Evidence is based on known extinction coefficients for oxyhemoglobin and deoxyhemoglobin as a function of wavelength, measurements of the transmitted spectrum in specimens, in vivo dual wavelength transillumination imaging of lesions containing different amounts of blood (bloody and clear cysts, hematomas, veins, fibroadenomas, and carcinomas), and comparison of preoperative diaphanographic images to blood vessel volumes measured by microscopic analysis of surgical specimens. Oxygenation affects the relative proportions of infrared and red light transmitted, but does not influence the diagnosis based on luminance contrast.