Is positron emission tomography (pet) using fluorine-18 fluorodeoxyglucose (18f-fdg) injection used for whole body scan only or can it it be used just for imaging parts of the body separately (just an image of heart or breast)?

Pet scans using FDG are pretty much used to look at a lesion that is or may be a malignant tumor or to determine spread. Since they may miss small breast tumors, they are not used as a screening test to look for breast cancer. Pet scans with FDG can also light up with inflammation, infection,injuries or recent surgery. A radiologist can answer your question best.