1. From the Department of Medical Imaging (D.M.M., J.P., A.P.C., J.A.S., D.J.M.), Toronto Western Hospital, Toronto, Ontario, Canada; the Departments of Medical Imaging (D.M.M., D.J.M.) and Physiology (J.S.H., J.A.F.), University of Toronto, Toronto, Ontario, Canada; GE Healthcare (J.A.S.), Milwaukee, Wisc, USA; and the Department of Anesthesia (J.S.H.), Toronto General Hospital, Toronto, Ontario, Canada.