A comparison of T2*-weighted magnitude and phase imaging for measuring the arterial input function in the rat aorta following intravenous injection of gadolinium contrast agent

The arterial input function (AIF) is important for quantitative MR imaging perfusion experiments employing Gd contrast agents. This study compared the accuracy of T2*-weighted magnitude and phase imaging for noninvasive measurement of the AIF in the rat aorta. Twenty-eight in vivo experiments were performed involving simultaneous arterial blood sampling and MR imaging following Gd injection. In vitro experiments were also performed to confirm the in vivo results. At 1.89 T and TE=3 ms, the relationship between changes in 1/T2* in blood (estimated from MR signal magnitude) and Gd concentration ([Gd]) was measured to be ∼19 s−1 mM−1, while that between phase and [Gd] was ∼0.19 rad mM−1. Both of these values are consistent with previously published results. The in vivo phase data had approximately half as much scatter with respect to [Gd] than the in vivo magnitude data (r2=.34 vs. r2=.17, respectively). This is likely due to the fact that the estimated change in 1/T2* is more sensitive than the phase to a variety of factors such as partial volume effects and T1 weighting. Therefore, this study indicates that phase imaging may be a preferred method for measuring the AIF in the rat aorta compared to T2*-weighted magnitude imaging.