Iodine 125 imaging in mice using NaI(Tl)/Flat panel PMT integral assembly

Radiolabeled agents that bind to specific receptors have shown great promise in diagnosing and characterizing tumor cell biology. A second area of interest is in vivo imaging of gene transcription and protein expression. The radioisotope I¹²⁵ 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(TI) integral assembly with a Hamamatsu Flat Panel PMT, representing one of the best trade-off between spatial resolution and detection efficiency. We tested the in-vivo performance of the detector by acquiring images of mice as a part of a study of inflammatory bowel disease (IBD). In this study, four 25 g mice with an IBD-like phenotype (SAMPl/YitFc) were injected with 375, 125, 60 and 30 μCi of ¹²⁵I-labelled antibody against MAdCAM-1, a gut-specific endothelial cell adhesion molecule that is up-regulated in the presence of inflammation. Two mice without bowel inflammation were injected with 150 and 60 μCi of the labelled 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 of this new detector are impressive: images of SAMP1/YitFc injected with 30 μCi activity show inflammation throughout the intestinal tract, with the disease very well defined at two hours post-injection.