Purpose: The purpose of this experimental study was to evaluate the influence of contrast material concentration and flow velocity on pulsatile flow in Gd-DTPA-enhanced 3D gradient echo MR angiographic sequence.
Method: In vivo flow experiments were performed in Plexiglas phantoms with artificial stenosis (50% stenotic ratio and 20 mm stenotic length) attached to a cardiac pump that generated physiological pulsatile flow similar to that of the bloodstream in a closed circuit. We used a steady-state gradient echo sequence with different TEs (6, 3, and 1.4 ms). A TR of 15 ms was used for all parameters. The concentration of Gd-DTPA varied from 0 to 2.0 mmol/L and flow velocities from 25 to 80 cm/s. We measured the degree of stenosis and length of stenosis in comparison with the actual values.
Results: The degree and length of stenosis on 3D gradient echo MR angiographic images were markedly influenced by the velocity of the flow and concentration of Gd-DTPA. The degree of stenosis was overestimated when the flow was fast or when the concentration of Gd-DTPA was low. When the concentration of Gd-DTPA was low, stenosis was elongated. These effects were less prominent on short TE (1.4 ms) sequence.
Conclusion: The stenotic lesions were markedly overestimated on MR angiographic images obtained with Gd-DTPA-enhanced fast 3D gradient echo sequence. Spin dephasing can be compensated for almost entirely by a high concentration of Gd-DTPA and/or a short TE sequence.