Experimental pulmonary emboli detected using magnetic resonance.

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Abstract
Experimental pulmonary emboli that were labeled with nonmagnetic Ba threads and produced using aminocaproic acid were introduced into the internal jugular veins of 5 dogs. Transverse axial magnetic resonance (MR) images (0.35 T, 15 MHz) and CT [computed tomography] scans (2.0 or 4.8 s, G.E. 9800 or 8800 scanner) were obtained from the lung apex to base in each animal. The MR images were gated to the cardiac cycle, and spin echo techniques were used (TR = gated to the cardiac cycle; TE = 28 and 56 ms). Sites (19) of embolism were determined from the CT scans. Two observers, who had no knowledge of the number or position of the emboli, individually assessed the MR images and marked the sites of emboli on clear acetate overlays. Each observer detected 12 of 19 emboli (63%) and each had 1 false positive result. Of the 19 emboli, 6 were central or parahilar and 13 were in the outer 2/3 of the lungs. Three (1st observer) or 4 (2nd observer) of the 7 false negative results were central. In retrospect, 2 central emboli were mistaken for hilar fat. One peripheral embolus was not visible, even in retrospect. The potential for MR to demonstrate relatively small pulmonary emboli was shown. Clinical trials in patients seem warranted.