American Journal of Roentgenology, Vol 162, 1041-1046, Copyright © 1994 by American Roentgen Ray Society
Detection of pulmonary emboli by using MR angiography with MPEG-PL- GdDTPA: an experimental study in rabbits
H Frank, R Weissleder, AA Bogdanov Jr and TJ Brady
Department of Radiology, Massachusetts General Hospital, Charlestown.
OBJECTIVE. A macromolecular MR contrast agent (MPEG-PL-GdDTPA), which
consists of Gd-DTPA covalently attached to a polyamino acid (PL)
derivatized by monomethoxy ether of polyethylene glycol (MPEG), has
recently been developed. This contrast agent exhibits long intravascular
retention, which makes it suitable for MR angiography. The current study
was performed to test whether this agent would improve visualization of the
pulmonary vasculature during MR angiography and whether it aids in the
detection of pulmonary emboli in an animal model. MATERIALS AND METHODS.
All experiments were performed in rabbits (n = 21), six of which were
healthy and 15 of which had induced pulmonary emboli. Contrast-enhanced MR
angiograms (0.02 mmol Gd/kg) were obtained at 1.5 T by using time-of-flight
and phase- contrast sequences. MR images were ultimately compared with
polymer casts of pulmonary arteries and/or pathologic sectioning. RESULTS.
MR angiograms obtained before the administration of a contrast agent were
of low quality primarily because of low vessel/background signal-to- noise
ratio, presumably due to slow and complex flow in the pulmonary
vasculature. After IV administration of the contrast agent, pulmonary
arteries could be visualized up to the third-order branches. Of the 18
pathologically or angiographically proved emboli, 16 could be detected with
contrast-enhanced MR angiography. CONCLUSION. Our results indicate that
macromolecular contrast agents with long blood half-lives, such as
MPEG-PL-GdDTPA, increase signal intensity of pulmonary vessels, improve the
quality of MR angiography, and increase the detectability of pulmonary
emboli.