A Dual Radiologic Contrast Agent Protocol for ¹⁸F-FDG and ¹⁸F-FLT PET/CT Imaging of Mice Bearing Abdominal Tumors

Purpose: The aim of the study was to improve abdominal tumor detection by use of a dual radiologic contrast protocol. Procedures: eXia160® (Benitio international) was mixed with 2-deoxy-2-[¹⁸F]fluoro-D-glucose or 3′-[¹⁸F]fluoro-3′-deoxythymidine for intravenous (IV) injections. Omnipaque® 300 (GE healthcare) was used for intraperitoneal (IP) injections. Positron emission tomography/computed tomography (PET/CT) scans were acquired on a Siemens Biograph® equipped with point spread function reconstruction. The optimal concentration and injection schedule of IP contrast agent was studied in 12 mice. The impact of IP contrast media on PET quantitative accuracy was investigated by phantom studies and by imaging six mice before and after IP injection of Omnipaque®. The impact of a dual contrast media protocol on tumor delineation and quantitation was evaluated in 15 tumor-bearing mice using ex vivo counting as the reference. Results: The optimal sequence was a mixture of tracer plus IV contrast agent followed by 1 mL of IP contrast agent (20 mg iodine/mL) administered 10 min before PET/CT acquisition. Phantom studies showed that the use of a 20-mg iodine/mL concentration of Omnipaque® led to a 4.8% overestimation of radioactivity concentration, as compared to saline. This was confirmed by animal studies that demonstrated a 4.3% overestimation. Tumor detection was excellent and correlation between PET/CT quantitative data and ex vivo counting was good (r²=0.91, slope=0.7). Conclusions: A dual radiologic contrast protocol is useful in PET/CT scanning of mice bearing abdominal tumors. Contrast agents used in this manner lead to a small but acceptable overestimation of quantitative PET data.