Purpose

To assess the negative predictive value (NPV) of magnetic resonance imaging (MRI) to exclude pulmonary embolism (PE) in patients presenting to the emergency department (ED) with suspected PE in the following categories: a) <40 years and/or b) contraindication to iodinated contrast.

Methods

Retrospective study IRB-approved. A cross-departmental protocol was instituted to obtain MRI as the primary diagnostic modality for patients with clinical concern for PE that fit the following categories: a) ≤ 40 years old and/or b) contraindication to iodinated contrast. Patients were enrolled from January 2013 – December 2015. Exams performed on 1.5T system (Magnetom Aera). Chest imaging included 1) breath-hold (BH) contrast-enhanced 3D MR angiography, 2) BH 3D gradient echo (GRE) with 12° flip angle and 3) BH steady state free precession sequence, all in axial and coronal planes. Gadobenate dimeglumine administered at 0.1 mmol/kg mixed with an equal amount of saline and injected at 2 cc/s. Studies were interpreted by radiologist assigned to the clinical service and results were classified as a) positive, b) negative or c) indeterminate for PE. Patients with negative MRI were confirmed with a) phone interview at 3 months after MRI and b) review of medical records for subsequent PE or deep venous thrombosis (DVT). Patients with negative MRI were categorized as false negatives if the patient had documentation of PE or DVT within 3 months after MRI.

Results

447 patients presented to ED with suspected PE and had MRI. 411/447 (92%) had negative MRI, and 36/447 (8%) had positive MRI for PE. Out of 411 patients with negative MRI, follow-up phone interview and records review at 3 months after presentation identified 3 patients developed subsequent PE or DVT. Subgroup analysis demonstrated 157/447 patients had eGFR < 45 at the time of imaging. Negative predictive value of MRI was 99% in our patient population.

Discussion

Our study demonstrated safety and efficacy for using MRI to exclude pulmonary embolism in patients < 40 yo and also in patients with contraindication to iodinated contrast.

Conclusion

MRI holds potential to improve patient safety by reducing exposure to ionizing radiation and iodinated contrast when imaging is required to exclude PE.

Acknowledgements

No acknowledgement found.

References

Schiebler ML, Nagle SK, Francois CJ, et al. Effectiveness of MR angiography for the primary diagnosis of acute pulmonary embolism: clinical outcomes at 3 months and 1 year. J Magn Reson Imaging 2013; 38(4):914-925.