ArticlesComparison of contrast-enhanced magnetic resonance angiography and conventional pulmonary angiography for the diagnosis of pulmonary embolism: a prospective study
Introduction
Pulmonary embolism has an incidence of three suspected cases per 1000 inhabitants in the western world per year1, 2, 3 30–40% of these patients need anticoagulant drugs and have to be distinguished from those in whom anticoagulation can be safely withheld to avoid unnecessary risks3, 4, 5. The reference method, conventional pulmonary angiography, is invasive and carries an, albeit small, risk of complications6, 7. Hence, diagnostic strategies are often complex, consisting of non-invasive diagnostic tests, such as plasma D-dimer measurement, lung scintigraphy, and ultrasonography of the leg veins, to try to avoid conventional pulmonary angiography in as many patients as possible8, 9, 10.
Helical computed tomography (CT) has shown great promise for the diagnosis of pulmonary embolism11, 12 Improved techniques, decreased slice thickness, improved reconstruction, and faster CT scanners will enhance the diagnostic power of CT. However, use of CT for the safe exclusion of pulmonary embolism is currently restricted by its insensitivity to small, subsegmental emboli13, 14.
Magnetic resonance angiography (MRA) is another possible approach for diagnosis of suspected pulmonary embolism15. This diagnostic technique has safer contrast agents than CT and does not involve ionising radiation. MRA is rapidly improving, and with use of contrast-enhanced breath-hold techniques a detailed MRA of most body areas can be done. Furthermore, magnetic resonance imaging can be used to assess soft tissues, lung perfusion, and pulmonary angiography in a single investigation. Development of new and faster scanning sequences has enabled MRA to be done in shorter time spans than previously, allowing people who have difficulty in holding their breath for long periods to undergo MRA of the pulmonary vasculature. Finally, improved methods are being introduced that allow almost simultaneous imaging of ventilation and perfusion of the lung. Thus, magnetic resonance imaging is increasingly applied for diagnosis of a rising number of chest disorders.
We aimed to assess the diagnostic accuracy of MRA for diagnosis of pulmonary embolism, using conventional pulmonary angiography as the reference method, in non-selected patients with suspected pulmonary embolism.
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Patients
We recruited consecutive patients from ongoing trials of diagnostic strategy in pulmonary embolism10 and the value of rapid plasma D-Dimer test in diagnosis of the disease.16 141 patients with clinically suspected pulmonary embolism and an abnormal perfusion lung scintigram were referred for conventional pulmonary angiography. In these patients, MRA was done before conventional pulmonary angiography. All patients were managed on the basis of the conventional pulmonary angiography results. All
Results
The initial cohort was 141 patients, 61 men and 80 women, with a median age of 53 years (range 16–87). In 13 patients (9%), MRA could not be done for medical reasons, such as extreme dyspnoea, metal in orbits, or claustrophobia. In eight patients (6%), MRA was not interpretable because of insufficient contrast enhancement (four patients) or technical failure (four). In these 21 patients, DSA showed pulmonary emboli in three, and was normal in the remaining 18. Finally, MRA was done in two
Discussion
Our results show that the findings of MRA are similar to helical CT: there is good performance in larger (segmental or greater) emboli, whereas the diagnosis of (isolated) subsegmental pulmonary embolism is more difficult11, 12, 13, 19, 20. Few data exist that show the value and feasibility of MRA in patients with suspected pulmonary embolism15. These data are mainly based on selected patients with previously documented pulmonary embolism. MRA has many more advantages than helical CT. First, it
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