Technetium(99mTc) sulfur colloid (99mTc-SC) is a dispersion of particleslarger than those found in solution, but small enough to remainsuspended in the delivery matrix for a very long time.It is indicated for use by injection to assess functional capacityof reticuloendothelial cells of the liver, spleen, and bonemarrow, to evaluate peritoneovenous (LeVeen) shunt patency.It is indicated orally to assess gastric emptying.
Another use involves the intralymphatic or peritumoral administrationfor radioguided sentinel lymph node biopsy.
Kits for the preparation of 99mTc-SC include the followingthree vials: (a) a reaction vial containing sodium thiosulfate,edentate disodium, and gelatin; (b) “vial A,” which is anaqueous solution of dilute hydrochloric acid; and (c) “vialB,” which is an aqueous solution of sodium biphosphate andsodium hydroxide. Sodium pertechnetate (99mTc) solution isadded to the shielded reaction vial followed by the additionof the dilute hydrochloric acid. Upon heating in a water bath,the acid reacts with the thiosulfate and 99mTcO4- to form thecolloidal metal sulfide, 99mTc2S7. Short heating periods providea higher population of smaller colloid particles in thefinal preparation,whereas extended heating periods producelarger particles with increasing amounts of colloidalsulfur.After the heating period has ended, the reaction vialis cooled for a brief period, and then the chemical reaction isquenched by the addition of the aqueous solution of sodiumbiphosphate and sodium hydroxide to the reaction vial. Theinclusion of gelatin as an ingredient prevents colloid particlesfrom clumping together. Particle sizes range from 0.1 to1μm, with a mean size of 0.3μm.
