If your study utilizes radiopharmaceuticals to address basic science questions and meets the other requirements of 21 CFR 361.1, an IND is not necessary.
Instead, your study can be reviewed/approved by the Radioactive Drug Research Committee (RDRC).
If all of the nuclear medicine studies are considered to be standard of care (and thus not research related), approval by the RDRC generally is not necessary. However, if some of the studies would not have been performed except for the subject’s participation in the clinical trial, RDRC review/approval is required.