title: Particle-size and radiochemical purity evaluations of filtered 99mTc-sulfur colloid prepared with different heating times.
abstract: Sentinel node lymphoscintigraphy using colloidal particles has become common practice at many institutions. The ideal particle size for colloids such as filtered (99m)Tc-sulfur colloid ((99m)Tc-FSC) in sentinel node studies is 15-100 nm. It is reported that the use of a reduced heating time during the reconstitution process results in an increased number of smaller particles (<30 nm). However, it is unclear whether these smaller particles (>15 nm) would be of benefit in sentinel node studies. This study sought to better define particle size by using electron microscopy, as well as to evaluate the radiochemical purity (RCP) of (99m)Tc-FSC at various time points after filtration.
  
  
  METHODS
  One group of (99m)Tc-sulfur colloid ((99m)Tc-SC) preparations was reconstituted using the standard heating time of 5 min, and another group was prepared using a reduced heating time of 3 min. The (99m)Tc-SC preparations were passed through a 0.2-μm filter, and retained filter activity was measured. RCP values were collected at 0, 1, 3, and 6 h after filtration, and the particle sizes were measured at 0 and 6 h after filtration.
  
  
  RESULTS
  Average RCP values (± SD) for (99m)Tc-FSC with 5-min heating were 98.4% ± 3.0% and 98.3% ± 1.8% for 0 h and 6 h, respectively (n = 6). Average RCP values for (99m)Tc-FSC with 3-min heating were 98.4% ± 4.1% and 96.9% ± 3.1% for 0 h and 6 h, respectively (n = 6). Electron microscopy data showed that median particle sizes for the 3-min heating at 0 and 6 h were 24 and 35 nm, respectively. Median particle sizes for the 5-min heating at 0 and 6 h were 29 and 27 nm, respectively. The proportion of particles within the ideal range for sentinel node lymphoscintigraphy was similar between the heating methods (91.1% for 3-min heating at 0 h and 88.8% for 5-min heating at 0 h, P = 0.1851).
  
  
  CONCLUSIONS
  Our results indicate that although there are slight significant differences in RCP value, particle size, and particle number for (99m)Tc-FSC prepared using either a standard or a reduced heating time, both methods produce particles within the optimum range for sentinel node studies.
authors.affiliation: Division of Nuclear Medicine, Department of Radiology, Mayo Clinic, Rochester, Minnesota; and.
authors.forename: Maggie M
authors.initials: MM
authors.lastname: Michenfelder
authors.affiliation: Division of Nuclear Medicine, Department of Radiology, Mayo Clinic, Rochester, Minnesota; and.
authors.forename: Lucas J
authors.initials: LJ
authors.lastname: Bartlett
authors.affiliation: Division of Biomedical Statistics and Informatics, Mayo Clinic, Rochester, Minnesota.
authors.forename: Douglas W
authors.initials: DW
authors.lastname: Mahoney
authors.affiliation: Division of Nuclear Medicine, Department of Radiology, Mayo Clinic, Rochester, Minnesota; and.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Herold
authors.affiliation: Division of Nuclear Medicine, Department of Radiology, Mayo Clinic, Rochester, Minnesota; and jhung@mayo.edu.
authors.forename: Joseph C
authors.initials: JC
authors.lastname: Hung
mesh_terms: D005374:Filtration / Q000379:methods*; D006358:Hot Temperature; D010316:Particle Size; D011854:Radiochemistry; D013671:Technetium Tc 99m Sulfur Colloid / Q000737:chemistry* / Q000302:isolation & purification*; D013997:Time Factors
chemical_list: D013671:Technetium Tc 99m Sulfur Colloid
keywords: 99mTc-sulfur colloid; lymphoscintigraphy; preparation; radiopharmaceutical; radiopharmacy