Improved methods for perfusion imaging with hyperpolarized carbon-13

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Abstract Disorders of perfusion underlie the majority of the causes of mortality and disability in the developed world. Ischemic disorders, including myocardial infarction, stroke, and pulmonary embolism are obvious manifestations of pathologic perfusion. Perfusion also plays a major role in many cancers. Clearly, methods for high quality perfusion imaging are an important priority for radiologic evaluation of patients. Unfortunately, the resolution, quality, and accuracy of perfusion imaging is still far inferior to the clinical and research needs. Techniques based on arterial spin labeling (ASL) are limited by signal strength and by the short relaxation times of labeled protons. Methods that make use of gadolinium contrast agents face challenges arising from the complex relationship between the underlying perfusion and the resulting image dynamics, in addition to growing safety concerns. Here we propose to develop robust new methods for perfusion imaging by making use of a hyperpolarized carbon-13 labeled perfusion tracer that is freely diffusible in tissue. The tracer has long T1 and T2 relaxation times and long residence times in tissue, and can be imaged with essentially no endogenous background. Consequently, the temporal dynamics of this agent can be monitored using robust imaging techniques with high signal strength. We will develop methods for measuring local blood flow using dynamic imaging techniques. Hyperpolarized perfusion imaging will be compared against ASL techniques, and both methods will be validated against microsphere perfusion quantitation as a gold standard to assess the accuracy and reproducibility of perfusion imaging with diffusible polarized tracers.