  Magnetic resonance imaging with hyperpolarized contrast agents can provide
unprecedented \textit{in-vivo} measurements of metabolism, but yields images
that are lower resolution than that achieved with proton anatomical imaging. In
order to spatially localize the metabolic activity, the metabolic image must be
interpolated to the size of the proton image. The most common methods for
choosing the unknown values rely exclusively on values of the original
un-interpolated image. In this work, we present an alternative method that uses
the higher-resolution proton image to provide additional spatial structure. The
interpolated image is the result of a convex optimization algorithm which is
solved with the Fast Iterative Shrinkage Threshold Algorithm (FISTA). Results
are shown with images of hyperpolarized pyruvate, lactate, and bicarbonate
using data of the heart and brain from healthy human volunteers, a healthy
porcine heart, and a human with prostate cancer.
