General Pearls

For assessment of the GI tract

Based on very poorly soluble barium sulphate (BaSo ₄ ) ▸ administered PO or PR

Can lead to barium peritonitis if leaks into the peritoneal cavity

For general use in angiography and CT

No marked pharmacological actions – can interfere with clotting times (avoid clotting tests for 6 hours after administration)

Excreted unchanged via the kidneys ▸ >80% excreted after 4 hours with a normal GFR (>60 mL/min/1.73 m ² )

Iodine provides the radio opacity – the other elements of the molecule act as carriers of iodine

Low osmolar non-ionic contrast media

• ▪

  iohexol/iopamidol/iomeron/iopromide/ioversol/ioxilan/iobitridol/ iopentol/iobiditrol

Iso osmolar non-ionic contrast media

• ▪

  isomenol/iotrolan/iodixanol

• ▪

  High viscosity makes injection through thin IV lines difficult – requires preheating

Gadolinium (Gd) has 7 unpaired electrons and therefore demonstrates a very large magnetic dipole moment

Paramagnetic ions (Gd) reduce the T1 and T2 relaxation times

• ▪

  omniscan/optimark/magnevist/gadovist/prohance/dotarem

Gadolinium (Gd) is very toxic – it requires encapsulation with a chelate (linear or cyclic/cyclic or macrocyclic/ionic or non ionic)

• ▪

  Cyclic: Gd caged in a molecular ring

• ▪

  Acyclic : Gd held less tightly

Excreted by passive glomerular filtration (95% by 24 hours)

• ▪

  Can cause spurious hypocalcaemia (interferes with assay method)

• ▪

  Gd chelates do not cross the blood brain barrier

Gd itself does not change the signal intensity – the surroundings change signal when the agent is there

• ▪

  T1 images : increased signal intensity

• ▪

  T2 images: no effect

Supraparamagnetic ions (Fe ²⁺ )

• ▪

  T1 images: increased signal intensity (low concentration) ▸ minimal effect (high concentrations)

• ▪

  T2 images: reduced signal intensity (high concentrations)

Hepatobiliary Agents (Gadolinium disodium – Primovist)

• ▪

  Excreted 50% biliary tree / 50% kidneys

  • 1

    Rapidly distribute into the vascular/interstitial space, allowing acquisition of dynamic images

    • a

      As only of the dose of extracellular agents s required, this may be suboptimal

  • 2

    Then enter functioning hepatocytes via OATP8 receptors – these can be imaged after 20 minutes (hepatobiliary phase T1 images)