Pulmonary embolism MRI

Associate Editors-in-Chief: Ujjwal Rastogi, MBBS [mailto:urastogi@perfuse.org]

Overview
Magnetic resonance imaging (MRI) is a medical imaging procedure that uses strong magnetic fields and radio waves to produce cross-sectional images of organs and internal structures in the body. Because the signal detected by an MRI machine varies depending on the water content and local magnetic properties of a particular area of the body, different tissues or substances can be distinguished from one another in the study image. MRI can give different information about structures in the body than can be obtained using a standard x-ray, ultrasound, or computed tomography (CT) exam. Magnetic resonance pulmonary angiography should be considered 1) Only at centers that routinely perform it well and 2) Only for patients for whom standard tests are contraindicated.

Magnetic Resonance Imaging

 * Gadolinium-enhanced MRI is a non-invasive diagnostic modality that has the advantage of no contrast exposure.
 * A study examined 30 patients with suspected PE via angiography and Magnetic Resonance Angigraphy (MRA).
 * 8 patients had + PA grams, and MRA identified all 5 lobar emboli, in addition to 16 of 17 segmental emboli.
 * Another potential benefit of MR, is that is incredibly sensitive, perhaps even better than contrast venography, in imaging clot in the inferior vena cava (IVC) and pelvic veins, and these images can be obtained at the same time as the lung scan.
 * Additionally, although MR is more expensive than V/Q   scanning, when one takes into account the high number of indeterminate findings on V/Q, the effective cost per diagnosis may be cheaper with MR.
 * It needs to be pointed out, that although the criticism of using CT and MR angio lacks sensitivity when examining the subsegmental arteries, inter-reader agreement was only 66% with pulmonary angiography in PIOPED Study. However, the clinical significance of undetected subsegmental PE is uncertain because they rarely cause severe symptoms.


 * Magnetic resonance pulmonary angiography and magnetic resonance venography combined have a higher sensitivity than magnetic resonance pulmonary angiography alone in patients with technically adequate images, but it is more difficult to obtain technically adequate images with the 2 procedures.


 * Technically adequate MRA has a sensitivity and specificity of 78% and 99% respectively.