Disclosed embodiments for assessing brown adipose tissue use imaging of metabolic contrast agents. For example, activated brown adipose tissue may be assessed by evaluating a difference in production of the hyperpolarized 13C metabolic contrast agent from a pre-polarized 13C metabolic contrast agent precursor before and after exposure of the subject to an activating event or agent. In one embodiment, the subject is given a dose of norepinephrine, and the production of the hyperpolarized 13C metabolic contrast agent before and after the dose is assessed.