Quantitative lymphoscintigraphy. I. Basic concepts for optimal uptake of radiocolloids in the parasternal lymph nodes of rabbits

The activity-size distribution of radiocolloids has been studied using gel-chromatography scanning (GCS) of columns filled with Sepharose 4B gel. Rabbits were injected subcutaneously with the colloid of interest, laid supine beneath a gamma camera, and imaged every 15 sec for 2 to 4 hr. From the stored data, the uptakes in the parasternal lymph nodes were analyzed in terms of a two-compartment model, and the rate constants measured. The substances tested were Au-198 colloid, Tc-99m antimony sulfide colloid, Tc-99m tin colloid, Tc-99m phytate, and Tc99m sulfur colloid. It was shown that the optimal particle size for the colloid is in the range 1-10 nm. The largest and most rapid uptake was found for Au-198 colloid, with a particle size of 5 nm, which appeared as a single peak in the GCS spectrum. The percentage uptake after 2 hr for Au-198 colloid was 8%, while it was 5% for antimony sulfide colloid, which was the best of the Tc-99m-labeled colloids. The GCS spectrum for the antimony product showed a single-peaked size distribution with a somewhat broader range: 5-15 nm. The particles of the other colloids were either too large to pass into the lymphatic system, or too small to be trapped.