One mg of Sr-90 has an activity of ~140 uCi. One mg of Tc-99m has an activity of ~5Ci. You probably understand the differences in the implications of handling a

One mg of Sr-90 has an activity of ~140 uCi. One mg of Tc-99m has an activity of ~5Ci. You probably understand the differences in the implications of handling an amount of material that emits 140uCi compared to one that emits 5Ci. In medical radiology, the amounts of radioactive isotopes are measured in Bq because the samples are so heavily diluted that it's the only thing you can sensibly measure. This easily hides the fact that when you are talking about roughly equal amounts, Tc-99m is roughly 29 years/6 hours ~=40000 times more dangerous than Sr-90. You just never use equal amounts, when you receive a sample of Tc-99m it's about 40000 times smaller than the Sr-90 sample.