Introduction Neuroblastoma is the most common extracranial child- hood cancer, with over 600 cases diagnosed annually in the United States [1]. More than half of neuroblastoma patients have aggressive disease and are at high risk for treatment failure despite intensive chemoradiotherapy. In this population of high-risk patients, the 3-year event- free survival is approximately 35% [1, 2, 3]. It is there- fore important to identify novel and effective therapeutic approaches that do not increase overall toxicity to the patient. As part of a comprehensive strategy for the evalua- tion of new compounds, we are currently developing mouse models that closely mimic human disease and testing candidate drugs in these models to determine effectiveness and appropriateness for integration into ongoing treatment strategies. Metaiodobenzylguanidine (MIBG) has been shown to concentrate in tumors of neuroectodermal origin Roberto Accorsi Michael J. Morowitz Martin Charron John M. Maris Pinhole imaging of 131 I-metaiodobenzyl- guanidine ( 131 I-MIBG) in an animal model of neuroblastoma Received: 10 January 2003 Revised: 23 May 2003 Accepted: 28 May 2003 Published online: 8 August 2003 Ó Springer-Verlag 2003 Abstract Purpose: To evaluate 131 I-MIBG scintigraphic localization of xenotransplanted and spontane- ously arising neuroblastomas in murine models of high-risk neuro- blastoma. Methods: Neuroblas toma xenografts were created by inoculation of human neuroblas- toma cell suspensions into the subcutaneous flanks of athymic nude mice. In addition, spontaneous paraspinal neuroblastomas were de- tected by direct palpation in MYCN transgenic mice. After measured tumor volumes exceeded 200 mm 3 , each mouse received an intraperito- neal injection of 18 lCi/g 131 I-metaiodobenzylguanidine ( 131 I-MIBG). Pinhole scintigraphy was performed to evaluate the MIBG biodistribution and to attempt to visualize the tumors. Each mouse was imaged on a gamma camera equipped with a 3-mm pinhole on one head and an HEGP collimator on the other. Results: Images demonstrated absorption of radiolabeled MIBG and visualization of tumors. Analysis of the images allowed for quantification of relative MIBG uptake and for determination of linear and area measurements of the tumors. Conclusion: High-energy pinhole imaging effectively demonstrates uptake of radiolabeled MIBG by human neuroblastoma tumors in murine laboratory models. This technique allows for in vivo assessment of tumor burden. In the future, we plan to use this method to evaluate sensitivity for detecting metastatic spread as well as investigating the therapeutic efficacy of high-dose 131 I-MIBG in combi- nation with radiosensitizing agents. KeywordsPinhole imaging Æ Small-animal imaging Æ Neuroblastoma Æ Xenografts Æ MYCN transgenic mice Æ Metaiodobenzylguanidine (MIBG) Pediatr Radiol (2003) 33: 688–692 DOI 10.1007/s00247-003-1006-6 ORIGINAL ARTICLE R. Accorsi (&) Division of Nuclear Medicine and Department of Radiology, The Children’s Hospital of Philadelphia, 34th and Civic Center Blvd., Philadelphia, PA 19104, USA E-mail: accorsi@email.chop.edu Tel.: +1-215-5902562 Fax: +1-215-5904318 M.J. Morowitz Æ J.M. Maris Division of Oncology and Department of Pediatrics, The Children’s Hospital of Philadelphia and University of Pennsylvania School of Medicine, 34th and Civic Center Blvd., Philadelphia, PA 19104, USA M. Charron Division of Nuclear Medicine and Department of Radiology, The Children’s Hospital of Philadelphia and University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA