This proposal is based on findings from our previous work involving ferumoxytol-enhanced cardiac magnetic resonance angiography. The resolution of the pulmonary vasculature based on our previous imaging protocol was exceptional (PMID: 26786296). In the Partners Healthcare System between January 1, 2014 and January 1, 2015 there were 541 patients evaluated in Partners Healthcare-affiliated hospitals with a diagnosis of pulmonary embolism and acute or chronic kidney disease at the same visit between 01/01/2014 and 01/01/2015. Ventilation perfusion scanning was performed in 201 patients during this same time interval. Up to 63% of these patients in one year did not receive the diagnostic test of choice.