concentration Tc-99m (say I 50 mCi/3 cc), then a newborn dose of 0.5 mCi would contain I 7,000particles. However,preparations containing lessthan 50 mCi would deliver more than 50,000 par tides. The importanceof usinga high concentrationof Tc-99m is obvious, but should beemphasized.Alternatively, if lower Tc ac tivities are consideredin order to avoid waste,a single kit can be split to provide severaldoses,eachdelivering a smaller number of particles. SYDNEYHEYMAN