However, there are some notable drawbacks to hyperpolarized H MRI: 1. Rapid relaxation -Relaxation of hyperpolarized proton signals typically occurs with a characteristic temporal scale on the order of seconds, which is not enough time to perform an imaging experiment; 2. Proton background -There is a large proton background signal in the body because the natural abundance is ≈100%, and water and fat molecules are prevalent in the body; 3. Chemical shift dispersion -The relatively small chemical shift dispersion can make distinguishing different chemical species a challenge, especially in vivo where broad NMR lines are common.