Children with congenital hyperinsulinism (CHI) have low blood sugar, and some of these children may require surgery to remove part or all of their pancreas. In this study, researchers will test how well a radioactive drug, 18-labeled L-fluorodeoxyphenylalanine (called F-DOPA) can detect a form of hyperinsulinism (focal HI) that may be cured by surgery. Eligible participants in this study will have positron emission tomography/computerized tomography (PET/CT) scans with F-DOPA prior to surgery.