Sophia Z. Liu1, Ying Ann Chiao2, Peter S. Rabinovitch3 and David J. Marcinek1 1Department of Radiology, University of Washington, Seattle, Washington 98195, USA 2Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104, USA 3Department of Laboratory Medicine and Pathology, University of Washington, Seattle, Washington 98195, USA Correspondence: dmarc{at}uw.edu