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Modelling of DCE (Dynamic Contrast-Enhanced) image data in MRI has enabled physiological characteristics of tumours and other lesions to be measured, as an aid to monitoring disease progress and treatment response. A contrast agent (CA; e.g. Gd-DTPA) is injected intravenously as a short bolus, and the subsequent enhancement in tissue signal in a T1-weighted imaging sequence is measured. The widely-used one-compartment ‘Tofts model ’ was first used in Multiple Sclerosis[1], was extended to include a vascular compartment[2], taken up by the cancer imaging community[3,4], and analysed in some detail to find its limits of validity[5,6]. The extracted (fitted) tissue parameters (transfer coefficient K trans, extra-vascular extracellular space EES ve, rate constant kep (kep=K trans /ve) and plasma volume vp) are sensitive to some of the fixed parameters (tissue native T1, called T10, and relaxivity r1 (change in 1/T1 per unit volume of CA)[3]. Quantification in medical imaging represents a paradigm shift[7]. Complex equipment can be used as a scientific instrument to make measurements (rather than to visualise in a qualitative way). To be an effectiv