Quantifying Tumor Vascular Heterogeneity with Dynamic Contrast-Enhanced Magnetic Resonance Imaging: A Review

Table 2

Model-free parameters often used for DCE-MRI dynamic curve description^†.

Parameter	Definition	Units	Alternative names	Literature
Area-under-the-curve (AUC)	Area under the signal intensity or gadolinium dynamic curve	a.u·min or mmol·min/L	IAUC, AUGC, IAUGC	[29]
Relative signal intensity (RSI)	RSI=𝑆(𝑡)/𝑆0	N/A		[30]
Initial slope	Maximum or average slope in the initial enhancement	a.u./min	Enhancement slope, upslope, enhancement rate	[31]
Washout slope	Maximum or average slope in the washout phase	a.u./min	Downslope, washout rate	[32]
Peak enhancement ratio (PER)	PER=(𝑆max−𝑆0)/𝑆0	N/A	Maximum signal enhancement ratio (SERmax)	[33]
𝑇max	Time from contrast agent arrive to peak enhancement	s	Time-to-peak (TTP)
Maximum intensity-time ratio (MITR)	MITR=PER/𝑇max	s^−1		[34]

^†Unlike the pharmacokinetic parameters, the nomenclature for model-free parameters has not been standardized.
Notation and abbreviations: 𝑆(𝑡): MR signal intensity at time 𝑡; 𝑆₀: precontrast signal intensity; 𝑆_max: maximum signal intensity; a.u.: arbitrary unit.