Evolving role of magnetic resonance techniques in primary sclerosing cholangitis

Table 1 Summary of magnetic resonance techniques used in primary sclerosing cholangitis

MR technique	Description of technique	Role in PSC
T2-weighted MRCP	Non-contrast sequences that depict fluid-filled structures such as bile ducts as high-intensity (white) compared to low-intensity (grey/black) of adjacent structures.	Visualisation of biliary anatomy.
Three-dimensional MRCP	Respiratory-triggered, single volume thin slab acquisitions producing isotropic images.	Preferred sequences for optimal multi angle visualisation of the biliary anatomy.
Two-dimensional MRCP	Specific sequences combining coronal thin-slab and rotating oblique-coronal thick-slab image acquisition.	Single shot T2w MRCP sequences are used when three-dimensional MRCP has artefacts or not feasible.
T2-weighted liver axial	Measure of T2 relaxation time in liver parenchyma. Both fat and water appear bright.	Sequence for optimal visualisation of the liver parenchyma.
T1-weighted liver axial	Measure of T1 relaxation time in liver parenchyma. Fat appears bright, water appears dark.	Sequence for optimal visualisation of the liver parenchyma.
MR elastrography	Generates an elastogram map. Specific regions can be selected to obtain mean liver stiffness (kilopascals; kPa).	Quantification and distribution of liver fibrosis.
Diffusion-weighted MRI	Captures changes in the diffusion properties of water protons in tissue represented as the apparent diffusion coefficient.	Can be used to assess liver parenchymal morphological changes (e.g., tumours) and as surrogate for liver fibrosis.
Dynamic contrast-enhanced MRI	Measures T1 changes in liver parenchyma following bolus administration of gadolinium in different phases of uptake and elimination.	Delineates flow in vessels, permeability and enhancement of parenchyma. Can be used to quantify liver function using flow and permeability parameters as surrogate for liver fibrosis.

MR: Magnetic resonance; PSC: Primary sclerosing cholangitis; MRI: Magnetic resonance imaging; MRCP: Magnetic resonance cholangiopancreatography.