Table 1. Semi-quantitative metrics of DCE-MRI.

Parameter	Definition	Unit
Initial area under the curve (iAUC)	Calculates the area under tissue concentration time curve until a stipulated time point that includes a major portion of the tissues’ response*
Maximum (relative) enhancement	Defined as maximum signal difference (MSD)/signal baseline (SB), where MSD is the difference between the signal intensity at its maximum (SImax) and SB	In %
Time to maximum signal intensity	Time elapsed between the arterial peak enhancement and	In sec
Time to peak enhancement	Time elapsed between the arterial peak enhancement and the end of the steepest portion of enhancement (Figure 4)	In sec
Rate of peak enhancement	[(SIend – SIprior/(SIbase × T)] ×100	In %/min
Rate of enhancement	[(SImax–Slbase)/(SIbsae × Tmax)] ×100**	In %/min
T90	Measurement of the time taken for the tissue to attain 90% of its subsequent maximal enhancement***	In sec
Maximum rate of change of enhancement (MITR)	Maximal intensity change per time interval ratio***	in %/min

*, iAUC can be normalized by the corresponding area under the AIF time concentration curve. It can then be used as an approximate index of the CA distribution volume in the tissue. In oncological studies, iAUC_norm is demonstrative of the combined volumes of v_ρ and v_e (see Table 2) and several studies have shown its usefulness as a potential biomarker in antiangiogenic drug trials (34); **, The slope of the TCC can be normalized as well by dividing it with the arterial TIC slope. This parameter is termed perfusion index (PI) and has been used both in studies of skeletal muscle and the myocardium (1,3,11); ***, Parameters 9 and 10 are designed to minimize physiological patient variables, variations in contrast dose and injection technique as well as scanning protocols and different scanner types (35). DCE-MRI, dynamic contrast-enhanced magnetic resonance imaging; CA, contrast agent; MITR, maximum intensity time ratio.