Filtered technetium-99m-sulfur colloid evaluated for lymphoscintigraphy

Several ^99mTc-labeled radiopharmaceuticals have been developed for lymphoscintigraphy of the extremities. In the United States, however, these agents are not widely used clinically. This study evaluates the use of smaller particle sizes (<0.1 μm) of ^99mTc-sulfur colloid (^99mTc-SC) for lymphoscintigraphy. Methods: The ^99mTc-SC was prepared by kit, and the final preparation was filtered through a sterile 0.1-μm filter. The radiochemical purity (RCP) of the filtered ^99mTc-SC was determined before administration. Nineteen patients with suspected lymphedema were injected with 18.5 MBq (500 μCi) filtered ^99mTc-SC intradermally in each foot, and whole-body images were obtained immediately and 1, 3, 6 and 24 hr later. Local views over the inguinal or axillary lymph nodes were also obtained every 5 min for the first hour. Results: The average RCP value was 93.4% ± 4.2% (n = 19), and the RCP difference pre- and postfiltration of the ^99mTc-SC preparation was -1.7% ± 1.4% (n = 40). Evaluation of the particle size with the polycarbonate filter showed that 89.9% ± 4.5% (n = 28) of particles were less than 50 nm, and the particle size was further determined by electron microscopy to be 38.0 ± 3.3 nm (n = 202). The mean particle sizes of two peaks measured by laser light scattering techniques were 7.5 and 53.9 nm (major peak). Clinical studies with filtered ^99mTc- SC demonstrated similar lymphoscintigrams compared with those obtained with ^99mTc antimony sulfide colloid (^99mTc-ATC). Filtered ^99mTc-SC showed a faster transport rate to the inguinal lymph nodes and lower radiation dosimetry for liver, spleen and whole body compared with ^99mTc-ATC. Conclusion: Filtered ^99mTc-SC can be easily prepared and is readily available for routine clinical use in lymphoscintigraphic studies.