Blood pool contrast extends MRA's ability

The diagnostic capability of MR angiography is directly related to the application of gadolinium-enhanced imaging, said Dr. Thomas Grist, chief of MRI at the University of Wisconsin Medical School in Madison.

Gd-enhanced MRA has some complexities, however, associated with image acquisition and limited spatial resolution/coverage. A different approach will soon be available, as several investigational blood pool contrast agents are under investigation.

Blood pool agents fit into two categories. One is macromolecular contrast agents, which are large molecules that clear from the blood stream relatively slowly. These include gadomer-17 and P792. The other alternative is protein-binding agents such as MS-325 and B22956.

Because the spatial resolution that may be achieved with MRA is directly proportional to the length of the acquisition, high-resolution images can be acquired with blood pool agents in regions of the body with no respiratory motion, Grist said. The long blood half-life also allows for reexamination of vascular territories that may be inadequately imaged on the initial first-pass MRA exam, although these extended acquisition methods require image processing techniques that suppress signal from the venous structures enhanced by blood pool agents.