DCE-MRI
DCE-MRI provides quantitative biomarkers of tissue microvascular function by tracking contrast-agent dynamics and applying pharmacokinetic modelling.
Introduction
Dynamic contrast-enhanced MRI (DCE-MRI) quantifies tissue microvascular function by tracking signal changes induced by intravenous injection of an MRI contrast agent. After converting signal to contrast agent concentration, pharmacokinetic models can be applied to estimate parameters describing perfusion, capillary endothelial permeability, and extracellular volume fraction.
Importantly, no single pharmacokinetic model is appropriate for every tissue type or clinical question. Model selection is therefore a critical part of DCE-MRI analysis, as it influences the interpretation of the data and the physiological meaning of the derived parameters.
Model
The extended Tofts model is a widely used pharmacokinetic model in DCE-MRI. It describes how contrast agent moves between the blood plasma and the extravascular extracellular space.
In practical terms, the model helps translate a changing MRI signal into biologically meaningful parameters. The main parameter, ktrans, reflects the transfer of contrast agent from plasma into tissue, and is influenced by both blood flow and capillary permeability. The parameter ve represents the fractional volume of the extravascular extracellular space, while vp represents the fractional plasma volume. Together, these parameters can provide insight into tissue vascularity, endothelial permeability, and microenvironment.
Although mathematically compact, the extended Tofts model is powerful because it links image data to physiological processes. For this reason, it is widely used in oncology, inflammation and other applications where vascular function matters. Its strength lies in providing quantitative biomarkers that can support tissue characterisation, treatment response assessment, and longitudinal monitoring.
First pass
Perfusion MRI focuses on the first pass of contrast agent through the tissue and is typically based on a short dynamic acquisition, often on the order of 45 seconds. In this setting, the main interest is the early vascular phase, where signal changes are dominated by contrast delivery through the blood vessels rather than by endothelial exchange.
Because the acquisition window is limited, perfusion analysis usually emphasizes parameters related to blood flow, blood volume, and transit behaviour, rather than slower processes such as tissue leakage or delayed uptake. This makes perfusion MRI particularly well suited to tissues or applications where the vascular input and early enhancement pattern are the primary source of physiological information, such as in the heart and lung.
Liver
Unlike most MRI contrast agents, which are excreted via the kidneys, gadoxetate is also actively taken up by functioning hepatocytes in the liver prior to excretion into the biliary system. Liver gadoxetate DCE-MRI therefore requires models that go beyond standard extracellular contrast agent approaches. These models aim to separate perfusion-related effects from hepatocyte transport, providing parameters that reflect not only vascular delivery and extracellular distribution, but also hepatic uptake and excretion.
This makes gadoxetate-enhanced DCE-MRI a powerful tool for probing liver function as well as tissue microvascular properties. It is particularly valuable in diffuse liver disease and drug studies, where changes in transporter activity, hepatocyte function, or regional perfusion may all influence contrast kinetics. Although the underlying physiology is more complex than in standard DCE-MRI, the strength of gadoxetate liver modelling lies in its ability to derive quantitative biomarkers that are directly linked to liver function and tissue status.