@article{noske90,
  author = {D. P. Noske and S. A. Prahl and H. J. C. M. Sterenborg and J. G. Wolbers and W. Kamphorst},
  title = {Digital Imaging of {H}p{D} Distribution in Normal Rat Brain after Intracerebral {H}p{D} Administration},
  journal = {Lasers Med. Sci.},
  volume = {5},
  pages = {},
  year = {1990 abstract only},
  abstract = {\textbf{Introduction.} For PDT intratumoral injection of photosensitizer may have advantages over intravenous administration. Earlier studies with cerebral tumour models have shown a high HpD concentration in the infiltrating part of the tumor after intratumoral injection, HpD, however, was also present in normal brain. In case of intratumoral administration of HpD spreading of HpD through the interstitial space of the healthy part of the brain may occur. Nothing is know about preferential pathways of clearance or the distribution of HpD in normal brain tissue when HpD is administered in this way. In the present study the distribution of HpD in normal rat brain after intracerebral administration was investigated, using a digital imaging technique. \vskip2mm \textbf{Materials and Methods.} HpD was introduced stereotactically in the caudate nucleus of Wistar rats by slow infusion. Animals were sacrificed at different intervals up to 5 days by vascular perfusion. Tissue sections of 100\,$\mu$m thickness of the brain where the HpD was localized, were cut on a vibratome and left unstained. HpD in the tissue sections was visualized using a microscope with a stabilized white light source and a bandpass filter between 425 and 445\,nm. video images of the tissue sections were digitized. This resulted in digitized gray images of 512 by 512 pixels which were analyzed on an Apple Macintosh II computer. The gray images were calibrated for a neutral density filter step tablet, which allowed determination of the local optical density of an image. This made it possbile to measure the local HpD concentration in arbitrary units. \vskip2mm \textbf{Results.} There was a clear preference of HpD for gray matter. The ratio of HpD located in gray matter and HpD located in white matter was approximately 2:1. HpD in the gray matter was especially located in the cell bodies. The ratio of HpD in cell bodies and gray matter minus cell bodies was 3:2. This ratio was the same for intervals of 5 minutes and 5 hours between infusion and perfusion. The HpD distribution around the site of infusion showed a more or less spherical pattern and a sharp decrease of HpD concentration as a function of distance to the peripherey of the HpD spot. There was hardly any transport of HpD noticeable, HpD remained located at the site of administration as was seen earlier with fluorescence microscopy. \vskip2mm \textbf{Conclusions.} HpD shows a preference for gray matter rather than for white matter. It accumulates rapidly in cell bodies of neurons in case of interstitial administration, preventing it from being transported any further. The distribtuion pattern as demonstrated here does not suggest transport by bulkflow as has been reported before for extrcellular tracers in the brain.},
}