Novel MRI Contrast Agent for Monitoring Thermal Ablation R21-CA111988
The hypothesis behind this collaboration led by the Focused Ultrasound Core of the NCIGT is that a novel MRI contrast agent that is activated at a threshold temperature level can be used to reliably and successfully monitor thermal ablation of liver tumors. Through better monitoring, we can theoretically improve surgical resection that, while an effective treatment for secondary liver tumors, has five-year survival rates between 20-30%.
The agent consists of paramagnetic material encapsulated in a liposome shell. When encapsulated, the material has a minimal effect on MR signal intensity. The liposome shell undergoes a phase transition at a temperature (Tc) that can be precisely chosen. MR signal enhancement occurs that can be easily detected with standard imaging methods. With a Tc of 57°C, which is the approximate threshold for thermal coagulation for heating of at least a few seconds, the signal intensity enhancement indicates regions that are thermally ablated. Since perfusion is halted after thermal coagulation, any released paramagnetic agent will remain in the tissue for an extended period of time, clearly marking the ablation progression. Preliminary tests of this agent in vivo demonstrated its functionally.
In experiments, characterization of the agent will have to be performed for different exposure conditions in the liver. Since the liver moves during respiration, focused ultrasound exposures will need to be performed by using short sonications during a breath hold period, by actively tracking the liver position, by steering the focal beam along with the motion or by using gated, very short (less than a second), sonications.
To date, NCIGT researchers have
- developed a one-dimensional imaging method that maps temperature rise during extremely short heating periods
- demonstrated an ultrafast method for monitoring frequency or phase changes along selected columns, allowing for rapid temperature change estimates
- performed additional preliminary experiments on determining the optimal way to sonicate a liver in an animal model