Dynamic capillaroscopy: a minimally invasive technique for assessing photodynamic effects in vivo

A noninvasive method for visualizing the microvasculature in the mouse tail is described, consisting of a custom-built microscope with through-lens illumination. The microscope is fitted with a television camera and images can be recorded on videotape and displayed on a television monitor. Blood vessels are imaged as columns of red blood cells, in which flow is clearly observed. Administration of photosensitizers and illumination with the standard light source produces no observable photodynamic effect on blood flow. The combination of photosensitizer and a more intense light source (either broadband light from a filtered mercury arc or red light from a laser) causes photodynamic cessation of flow within a few minutes. The magnitude of the effect is dependent on the dose and nature of the photosensitizer, the delay after photosensitization and the match between the laser light and the absorption spectra of the photosensitizers in the red region. We conclude that the technique yields results consistent with the known photodynamic effects of the photosensitizers in tumors and propose its use as an initial screening method in vivo, as a means of conducting pharmacokinetic experiments and as an assay of prolonged cutaneous photosensitivity.