AIM: MR pulmonary angio should be sparsely performed in proven centers

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MR angiography of upper extremity vascular sisease
Image source: Radiographics

Magnetic resonance (MR) pulmonary angiography should be considered only at centers that routinely perform the procedure well and only for patients for whom standard tests are contraindicated, according to the prospective PIOPED III study, published April 6 in the Annals of Internal Medicine.

Prior to this study, the accuracy of gadolinium-enhanced MR pulmonary angiography (MRA) and MR venography for diagnosing pulmonary embolism has not been determined conclusively, said lead author Paul D. Stein, MD, from Michigan State University in East Lansing, and his colleagues.

The PIOPED III (Prospective Investigation of Pulmonary Embolism Diagnosis III) investigators conducted the multi-center, prospective study from April 10, 2006, to Sept. 30, 2008, to assess performance characteristics of MRA, with or without MR venography, for diagnosing pulmonary embolism (PE). They evaluated 371 adult patients with diagnosed or excluded PE at seven hospitals and their emergency services.

Independent readers measured the sensitivity, specificity and likelihood ratios with comparison MRIs to the reference standard for diagnosing pulmonary embolism. Reference standard diagnosis or exclusion was made by using various tests, including CT angiography and venography, ventilation-perfusion lung scan, venous ultrasonography, d-dimer assay and clinical assessment.

MRA, averaged across centers, was technically inadequate in 25 percent of patients, Stein and colleagues wrote. The proportion of technically inadequate images ranged from 11 percent to 52 percent at various centers.

Including patients with technically inadequate images, MRA identified 57 percent with PE, the researchers reported. Technically adequate MRA had a sensitivity of 78 percent and a specificity of 99 percent. Technically adequate MRA and venography had a sensitivity of 92 percent and a specificity of 96 percent, but 52 percent of patients had technically inadequate results.

Among the study’s limitations, the authors acknowledged a high proportion of patients with suspected embolism were not eligible or declined to participate.

Based on their findings, Stein and colleagues concluded that MR pulmonary angiography and MR venography combined have a higher sensitivity than MR pulmonary angiography alone in patients with technically adequate images, but it is more difficult to obtain technically adequate images with the two procedures.

The National Heart, Lung and Blood Institute provided the primary source of funding.