Abstract #0315

Measuring In Vivo Tumor Phe with a DIACEST MRI Contrast Agent

Liu Qi Chen¹, Vipul R. Sheth², Christine A. Howison³, Phillip H. Kuo⁴, Mark D. Pagel⁵

¹Chemistry & Biochemistry, University of Arizona, Tucson, AZ, USA; ²Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA; ³Arizona Research Laboratories, University of Arizona, Tucson, AZ, USA; ⁴Radiology, Medicine, Biomedical Engineering, University of Arizona, Tucson, AZ, USA; ⁵Biomedical Engineering & Chemistry & Biochemistry, University of Arizona, Tucson, AZ, USA

Ultravist, a contrast agent that is clinically approved for X-ray/CT imaging, can also serve as a DIAmagnetic CEST (DIACEST) MRI contrast agent. A ratio of the two CEST effects from Ultravist can be used to measure pH over a range of 6.2-7.4 pH units with a precision of 0.070 pH units. This ratiometric approach obviates the need to know the agent's concentration or sample's T_1sat relaxation time when measuring pH. We have used this DIACEST agent and a CEST-FISP MRI method to measure the extracellular pH (pHe) within a subcutaneous tumor and muscle of a mouse model of PANC-1 pancreatic cancer.