After how many half-lives is the earliest disposal reading taken in PET?

In positron emission tomography (PET), disposal readings are crucial for assessing the safety and radiation levels after the use of radioisotopes. The concept of "half-life" refers to the time required for half of a radioactive substance to decay. In the context of PET, the earliest disposal reading is typically taken after two half-lives have passed.

This is because, after two half-lives, the activity of the radioactive material is significantly reduced, typically to about 25% of its original amount. This decline in radioactivity minimizes radiation exposure risk during disposal. Moreover, taking readings at this point allows for a more accurate assessment of the remaining radionuclide levels, ensuring that any remaining radioactivity is at a safer level for handling and disposal.

Understanding the half-life concept is essential in ensuring the safety protocols are adhered to, which is why taking the disposal reading after two half-lives is a standard procedure in the field.