The present invention relates to hyperpolarized [3-13C]acetoacetate. Provided are [3-13C]acetoacetate and compositions comprising said [3-13C]acetoacetate. Further provided are methods of preparing and using hyperpolarized [3-13C]acetoacetate in the determination of the spatial and temporal distribution and metabolism of [3-13C]acetoacetate and/or its metabolites in a cell or subject, preferably by magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS), and/or magnetic resonance spectroscopic imaging (MRSI), whereby conditions, diseases, or disorders associated with the metabolism of acetoacetate and/or other ketone bodies can be diagnosed. The conditions, diseases, or disorders to be diagnosed preferably are cancer, diabetes, cardiovascular diseases, or neurodegenerative diseases.