A radiopharmaceutical agent comprised of a peptide targeting the gastrin releasing peptide receptor (GRPR) chelated with 1,4,7-triazacyclononane,1-glutaric acid-4,7 acetic acid (NODAGA) and radiolabeled with gallium Ga 68, with potential tumor imaging activity upon positron emission tomography (PET). After administration of gallium Ga 68-labeled-NODAGA-MJ9, the MJ9 moiety binds to GRPR located on tumor cells. Upon PET imaging, GRPR-expressing tumor cells can be visualized and expression levels can be quantified. GRPR is overexpressed on certain tumor cells and plays a key role in tumor proliferation and survival.