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Excerpt
Lymphoscintigraphy with colloids requires particular attention to particle size. Previously, Technetium (Tc)-99m antimony sulfide colloid provided good results with a particle size of 3-30 μm, but this agent is no longer available for clinical use in this country. Currently, Tc-99m-Human Serum Albumin (HSA) and reduced particle size Tc-99m-Sulfur Colloid (SC) are among the agents being used for lymphoscintigraphic studies. Tc-99m-HSA, while not a colloid, does possess a wide range of molecular weights which result in a complex clearance pattern.
Particle size reduction of Tc-99m-SC can be accomplished by simple filtration or by a reduction in the reaction vial boiling time. This presentation compares both methods. Results were obtained by radiopharmaceutical testing, electron microscopy, and patient studies. Comparison patient lymphoscintigrams are presented to demonstrate the effectiveness of reduced particle size Tc-99m-SC in lymphoscintigraphy as compared with Tc-99m-HSA. Particle size distribution can be derived from the electron micrographs. Electron microscopy shows a spectrum of particle sizes from 0.22 μm down to less than 0.1 μm. Filtration with a 0.22 μm Millipore filter provides a 10% yield. Altering the boiling time from the recommended 5 minutes down to 3 minutes increases the yield by a meager 3.4%. The yield remains relatively constant at 10% and does not appear to be affected by kit volume and Tc-99m concentration.
The patient's lymphoscintigrams indicate the filtered product is superior to Tc-99m-HSA and delineates more features in the lymphatic system. Sulfur colloid kits are readily available and cheap! With modification of the standard sulfur colloid kit, which is readily available, an ideal small particle size colloid can now be made available for lymphoscintigraphy.
