Successful PET Imaging of Pancreatic Tumors in Mice, Achieved by Reverse Contrast CT

Objectives Experimental therapy of pancreatic cancer is ideally carried out on tumors growing in the pancreas (orthotopic or GEMM). However, such models are difficult for PET imaging. We sought to overcome this by combining PET with a technique we describe as reverse contrast CT.

Methods Mice bearing orthotopic pancreatic xenografts were injected with ¹⁸F tracers (FDG, FMISO, and the gemcitabine analog, FAC) and imaged on an Inveon PET/CT scanner. Immediately prior to imaging, mice were injected ip with 3 ml of the CT contrast agent, iohexol, diluted to 25% in saline; animals were sacrificed, and images were collected and quantified in terms of ID/g. Tumors were removed weighed and counted ex vivo.

Results The internal structures of the mouse abdomen were well delineated with the CT imaging technique. They appear as uniformly dark objects bathed in a large volume of contrast; tumors growing in pancreas can be recognized as anomalous masses compared to tumor-free mice. Tumors identification was confirmed by MR imaging. When combined with PET, it was possible to delineate tumors on the CT scans, though PET images alone failed to identify the tumors. When CT ROIs were used for tracer quantification, a good correlation was found between %ID/G on the PET images and the ex vivo data.

Conclusions IP contrast is a simple addition to PET/CT scanning that enhances our ability to conduct nuclear medicine experiments in murine models of pancreatic cancer.

Research Support VL (MSKCC Small Animal Imaging Core Facility): The SAICF is supported in part by US National Institutes of Health (NIH) P30 CA008748-48, S10 RR020892-01, S10 RR028889-01 and the Geoffrey Beene Cancer Research Center. DLJT was supported by the R25T Molecular Imaging Fellowship: Molecular Imaging Training in Oncology (5R25CA096945-07; Principal Investigator H. Hricak) and the Steve Wynn Prostate Cancer Foundation Young Investigator Award.