Evaluation of response to treatment using DCE-MRI: the relationship between initial area under the gadolinium curve (IAUGC) and quantitative pharmacokinetic analysis.

The initial area under the gadolinium curve (IAUGC) is often used in addition to or as an alternative to parameters derived from pharmacokinetic modelling of T1-weighted dynamic contrast-enhanced (DCE) MRI data in the assessment of response to treatment of cancer. However, the physiological meaning of the IAUGC has not been rigorously defined with respect to model-based parameters. Here, simulations of DCE-MRI data were used to investigate the relationship between IAUGC and the parameters K(trans) (transfer constant), v(e) (fractional extravascular extracellular volume) and v(p) (fractional plasma volume), using two vascular input functions. It is shown that IAUGC is a mixed parameter that can display correlation with K(trans), v(e) and v(p) and ultimately has an intractable relationship with all three. Furthermore, it is demonstrated that the range over which IAUGC is taken and the nature of the vascular input function do not significantly affect this relationship.