Pulmonary magnetic resonance angiography

Early attempts to image the pulmonary vascualture with spin-echo magnetic r esonance (MR) imaging were hampered by severe image degradation related to respiratory and cardiac pulsation artifact, susceptibility at interfaces be tween lung parenchyma and vessel wall, and poor contrast between flowing bl ood and intravascular filling defects of emboli, With the development of gr adient-echo MR angiographic techniques some of these limitations were overc ome; however, the need for multiple breath-holds and the frequent occurrenc e of flow-related artifacts that could simulate pulmonary emboli diminished their clinical utility. With the development of contrast-enhanced MR angio graphy, many of the limitations of earlier techniques were addressed. Image s of both lungs with high signal-to-noise ratios and high contrast between flowing blood and pulmonary emboli could be acquired in a single breath-hol d, during "first-pass" imaging with extracellular contrast agents in the co ronal plane. However, subsegmental vessels could not be assessed with this approach. The technique has been refined further by imaging each lung separ ately in the sagittal plane: this offers higher resolution and total lung c overage and requires a shorter breath-hold. Finally, several investigators have reported preliminary data on imaging of the pulmonary vasculature with blood pool agents, exploiting respiratory triggering or navigator echoes t o eliminate the need for breath-holding for the detection of pulmonary embo li. (C) 1999 Wiley-Liss, Inc.