Improving bone marrow scintigraphy. A clinical and experimental study

Today bone marrow scintigraphy is performed by imaging either the reticuloendothelial system by means of colloids or the hematopoietic marrow with granulocytes. When visualizing the marrow with radiolabeled colloids most of the administered activity will be taken up by the liver and spleen. To use granulocytes for bone marrow imaging is a comparatively expensive and complicated method. The aim of this study was to investigate the possibilities to shift the uptake of some of the injected activity from the liver-spleen and/or background to the bone marrow. Four small-sized colloids were evaluated in patients routinely referred for single photon emission computed tomography of the liver/spleen. After correction for attenuation and scattering of photons quantitative assessment of the activity in different organs was performed. Of the four colloids Nanocoll turned out to be the most favorable, thus this colloid was decided to be evaluated further. To assess the possibilities to improve the relative bone marrow uptake of Nanocoll, it was separated by gel filtration and different sized subfractions were injected into mice. None of the subfractions exhibited a more favorable bone marrow/liver-spleen ratio than the unseparated colloid. As blood clearance of a colloid is dependent on perfusion different measures were evaluated in mice aiming at either an increase in the blood flow to the bone marrow or a decrease in the liver-spleen perfusion. Nine different pharmaceuticals were tested. None improved the bone marrow uptake in relation to the liver enough to justify administration to humans. Fasting increased, however, the relative bone marrow uptake by approximately 15%. To evaluate the soft tissue background activity for colloids of different size a nanosized colloid (Nanocoll) and a larger colloid (Albu-Res) were investigated in an experimental mouse system and in humans. The latter were examined by quantitative single photon emission computed tomography as described above. The bone marrow activity relative to the soft tissue background activity was higher for the larger colloid in both mice and humans. By quantitative single photon emission computed tomography of the liver, spleen, bone marrow, and background the distribution of in vitro labeled autologous granulocytes and a colloid (Nanocoll) were assessed in patients. The activity of the bone marrow relative to the liver was significantly higher for granulocytes. The influence of scattered radiation is considerable in the vicinity of the liver. A technique for scatter correction with two opposing views was applied in a phantom and a human study. Both showed a considerable improvement of the visibility of the bone marrow close to the liver.(ABSTRACT TRUNCATED AT 400 WORDS)