Selective Imaging of Malignant Ascites in a Mouse Model of Peritoneal Metastasis Using in Vivo Dynamic Nuclear Polarization-Magnetic Resonance Imaging

The presence of malignant ascites in advanced cancer patients is associated with both a poor prognosis and quality of life with a risk of abdominal infection and sepsis. Contemporary noninvasive visualization methods such as ultrasound, computed tomography, and magnetic resonance imaging (MRI) often struggle to differentiate malignant ascites from surrounding tissues. This study aimed to determine the utility of selective H₂O imaging in the abdominal cavity with a free radical probe and deuterium oxide (D₂O) contrast agent using in vivo dynamic nuclear polarization-MRI (DNP-MRI). Phantom imaging experiments established a linear relationship between H₂O volume and image intensity using in vivo DNP-MRI. Similar results were obtained when the radical-D₂O probe was used to determine selective and spatial information on H₂O in vivo, modeled by the injection of saline into the abdominal cavity of mice. To demonstrate the utility of this method for disease, malignant ascites in peritoneal metastasis animal model was selected as one of the typical examples. In vivo DNP-MRI of peritoneal metastasis animal model was performed 7-21 days after intraperitoneal injection of luciferase, stably expressing the human pancreatic carcinoma (SUIT-2). The image intensity with increasing malignant ascites was significantly increased at days 7, 16, and 21. This increase corresponded to in vivo tumor progression, as measured by bioluminescent imaging. These results suggest that H₂O signal enhancement in DNP-MRI using radical-D₂O contrast is positively associated with the progression of dissemination and could be a useful biomarker for malignant ascites with cancer metastasis.