A radioimmunoconjugate consisting of 3F8, a murine anti-GD2 ganglioside monoclonal antibody labeled with iodine I 124 (I-124), with radioimaging activity using positron emission tomography (PET). Upon intravenous administration of iodine I 124 monoclonal antibody 3F8, the 3F8 moiety binds to GD2 expressed on tumor cells. This binding enables both PET imaging via iodine I 124 and the visualization of GD2-expressing tumor cells. GD2 is a ganglioside overexpressed in a variety of cancer cells, including neuroblastoma cells.