Selective Imaging of Malignant Ascites in a Mouse Model of Peritoneal Metastasis Using <i>in Vivo</i> 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 H<sub>2</sub>O imaging in the abdominal cavity with a free radical probe and deuterium oxide (D<sub>2</sub>O) contrast agent using <i>in vivo</i> dynamic nuclear polarization-MRI (DNP-MRI). Phantom imaging experiments established a linear relationship between H<sub>2</sub>O volume and image intensity using <i>in vivo</i> DNP-MRI. Similar results were obtained when the radical-D<sub>2</sub>O probe was used to determine selective and spatial information on H<sub>2</sub>O <i>in vivo</i>, 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. <i>In vivo</i> 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 <i>in vivo</i> tumor progression, as measured by bioluminescent imaging. These results suggest that H<sub>2</sub>O signal enhancement in DNP-MRI using radical-D<sub>2</sub>O contrast is positively associated with the progression of dissemination and could be a useful biomarker for malignant ascites with cancer metastasis.