Nonlinear ΔR2* Effects in Perfusion Quantification Using Bolus-Tracking MRI

Dynamic susceptibility contrast MRI involves injection of a contrast agent, whose concentration is estimated from Delta R-2* changes. However, measurement of contrast-agent concentration is prone to various sources of error; in particular, the commonly assumed linear relationship between contrast agent concentration and Delta R-2* in arterial blood is known to be invalid. In this study, we characterized the associated perfusion errors. Large errors were found when the linear assumption is used; these errors were highly dependent on the choice of tissue relaxivity. The errors were greatly reduced when using the quadratic model, and were further reduced when quantifying perfusion as a relative measure. This study suggests the linear assumption should be abandoned in favor of the quadratic model. Thus, the errors are minimized leading to improved quantification that will enable perfusion MRI to continue to play an important role in quantifying perfusion in brain diseases (e.g., acute stroke). Magn Reson Med 61:486-492, 2009. (C) 2009 Wiley-Liss, Inc.