Objective: Subsecond contrast-enhanced MR angiography, which is not a flow-based technique and does not require cardiac gating or breath-holding, provides multiplanar, rapid, dynamic visualization of the pulmonary arteries. Accordingly, we evaluated the use of this technique in the diagnosis of thrombi in both the proximal and peripheral portions of the pulmonary arteries. Digital subtraction angiography was used as the gold standard for the diagnosis.
Subjects and methods: Twenty-three consecutive patients with suspected pulmonary embolism were included in the study. All patients had intraarterial digital subtraction angiography, which showed emboli in 12 patients (13 proximal and six peripheral emboli). MR angiography was done within 24 hr of digital subtraction angiography. Subsecond contrast-enhanced MR angiograms were obtained in the long axis of each pulmonary artery after a unique injection of contrast medium (0.1 mmol/kg) in an antecubital vein. Fifteen dynamic frames of each pulmonary artery were alternately obtained in less than 1 min. MR angiograms were interpreted by two observers who had no knowledge of the findings on digital subtraction angiography. A diagnosis of pulmonary emboli was made when MR angiograms showed a constant intraluminal filling defect or an abrupt vascular cutoff.
Results: All thrombi in the proximal branches of the pulmonary arteries were visualized on MR angiograms (n = 13), whereas none of the thrombi in the distal part of the pulmonary arteries were seen (n = 6). In the 11 patients in whom no pulmonary emboli were shown by digital subtraction angiography, findings on MR angiograms were normal (sensitivity, 0.7; specificity, 1.0).
Conclusion: Our results suggest that dynamic contrast-enhanced MR angiography is an accurate method for detecting emboli in the proximal portions of the pulmonary arteries but is of no value in detecting peripheral emboli.