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Radiolabeled agents that bind to specific receptors have shown great promise in diagnosing and characterizing tumor cell biology. In vivo imaging of gene transcription and protein expression represents an other area of interest. The radioisotope I is commercially available as a label for molecular probes and utilized by researchers in small animal studies. We propose an advanced imaging detector based on planar NaI(T1) integral assembly with a Hamamatsu Flat Panel Photomultiplier (MA-PMT) representing one of the best trade-offs between spatial resolution and detection efficiency. We characterized the imaging performances of this planar detector, in comparison with a gamma camera based on a pixellated scintillator. We also tested the in-vivo image capability by acquiring images of mice as a part of a study of inflammatory bowel disease (IBD). In this study, four 25g mice with an IBD-like phenotype (SAMP1/YitFc) were injected with 375, 125, 60 and 30 muCi of I-labelled antibody against mucosal vascular addressin cell adhesion molecule (MAdCAM-1), which is up-regulated in the presence of inflammation. Two mice without bowel inflammation were injected with 150 and 60 muCi of the labeled anti-MAdCAM-1 antibody as controls. To better evaluate the performances of the integral assembly detector, we also acquired mice images with a dual modality (X and Gamma Ray) camera dedicated for small animal imaging. The results coming from this new detector are considerable: images of SAMP1/YitFc injected with 30 muCi activity show inflammation throughout the intestinal tract, with the disease very well defined at two hours post-injection.