Magnetic resonance imaging of hydrostatic pulmonary edema in isolated dog lungs: comparison with computed tomography

Magnetic resonance imaging (MRI) is considered inferior to computed tomography (CT) in the assessment of lung parenchyma, being hampered by low proton density, magnetic susceptibility effects, flow, and cardiac and respiratory motion. In this study the authors assessed the potential usefulness of MRI by comparing it with corresponding CT images of the lung in the absence of motion. They studied eight excised normal canine lung lobes inflated with oxygen before and after induction of pulmonary edema produced by intravascular infusion of saline at 30 cm H2O. T1, T2 and proton density weighted, 5-mm thick, gapped, multislice sequences were performed at 1.5 T. Magnetic resonance images were compared with corresponding 5-mm collimation CT scans at identical levels both before and after the induction of pulmonary edema. The MR and CT scans were assessed independently by two chest radiologists. In normal lung, there was equivalent visualization of vessels down to 1 mm and bronchi to 2 mm in diameter. T1 and proton density scans demonstrated lower spatial resolution but greater contrast than the corresponding CT images. In pulmonary edema both T1 and proton density sequences demonstrated peribronchial edema with greater contrast than CT. Air-space filling was equally well demonstrated by either technique. The authors conclude that, in motionless lung, MRI has lower spatial but greater contrast resolution than CT. It is potentially superior to CT in assessing focal and diffuse lung disease if cardiac and respiratory motion artifacts can be minimized or suppressed.