Reference tissue quantification of DCE-MRI data without a contrast agent calibration

The quantification of dynamic contrast- enhanced ( DCE) MRI data conventionally requires a conversion from signal intensity to contrast agent concentration by measuring a change in the tissue longitudinal relaxation rate, R-1. In this paper, it is shown that the use of a spoiled gradient- echo acquisition sequence ( optimized so that signal intensity scales linearly with contrast agent concentration) in conjunction with a reference tissue- derived vascular input function ( VIF), avoids the need for the conversion to Gd- DTPA concentration. This study evaluates how to optimize such sequences and which dynamic time-series parameters are most suitable for this type of analysis. It is shown that signal difference and relative enhancement provide useful alternatives when full contrast agent quantification cannot be achieved, but that pharmacokinetic parameters derived from both contain sources of error ( such as those caused by differences between reference tissue and region of interest proton density and native T-1 values). It is shown in a rectal cancer study that these sources of uncertainty are smaller when using signal difference, compared with relative enhancement ( 15 +/- 4% compared with 33 +/- 4%). Both of these uncertainties are of the order of those associated with the conversion to Gd- DTPA concentration, according to literature estimates.