Imaging of blood flow using hyperpolarized [¹³C]urea in preclinical cancer models

Purpose: To demonstrate dynamic imaging of a diffusible perfusion tracer, hyperpolarized [¹³C]urea, for regional measurement of blood flow in preclinical cancer models. Materials and Methods: A pulse sequence using balanced steady state free precession (bSSFP) was developed, with progressively increasing flip angles for efficient sampling of the hyperpolarized magnetization. This allowed temporal and volumetric imaging of the [ ¹³C]urea signal. Regional signal dynamics were quantified for kidneys and liver, and estimates of relative blood flows were derived from the data. Detailed perfusion simulations were performed to validate the methodology. Results: Significant differences were observed in the signal patterns between normal and cancerous murine hepatic tissues. In particular, a 19% reduction in mean blood flow was observed in tumors, with 26% elevation in the tumor rim. The blood flow maps were also compared with metabolic imaging results with hyperpolarized [1-¹³C]pyruvate. Conclusion: Regional assessment of perfusion is possible by imaging of hyperpolarized [¹³C]urea, which is significant for the imaging of cancer.