Pulmonary MR angiography is a suitable alternative to computed tomography angiography when ruling out pulmonary embolus, according to new data comparing the two modalities. 

When CTA exams are used to confirm or rule out PE, iodinated contrast is required to visualize the entirety of the thorax. MRA exams can do the same either with or without contrast and utilize gadolinium-based contrast agents when necessary, rather than iodinated agents. This became an especially important detail during the iodinated contrast shortage of 2022 when clinics were forced to deploy mitigation tactics as a means of preserving their supply. 

During the height of the shortage, the radiology department at the University of Wisconsin in Madison adjusted its PE protocols as part of a contrast preservation strategy. Between early May and mid-July of 2022, the department sent patients with suspected PE for MRA exams instead of CTA. 

Thanks to advances in technology that have addressed prior limitations of MRA with respect to PE protocols, the modality switch did not come at the expense of poor image quality. In fact, when researchers from the university compared CTA and MRA exams before, during and after the contrast shortage (and COVID), they found that MRA exams were less frequently reported as having poor image quality (10.3% of MRA exams versus 13.9% of CTAs). 

The switch also saved an estimated 27 liters of iohexol (Omnipaque) 350mg/ml from April 1 to July 31 of 2022. 

The group concluded that not only is the modality switch suitable for uncommon situations such as the contrast shortage, but it can also suffice in emergency settings in general. 

“This single-center experience demonstrates use of pulmonary MRA as a practical substitute for pulmonary CTA in emergency settings,” concluded lead investigator Jitka Starekova, MD, from the radiology department at the University of Wisconsin in Madison. 

The study abstract is available in the American Journal of Roentgenology.