Ultrasound Contrast Agents Overview

Contrast Media Overview

• Contrast media is a chemical substance that increases or decreases the density of the organ under examination.
• Contrast depends on the absorption coefficients of different tissues.

History of Contrast Media

• 1896: Walter Bradford discovered contrast media.
• 1897: First reported GI contrast study performed using Bismuth, which was toxic.
• 1910: Barium Sulphate was used as a safer alternative.
• 1920s: Sodium Iodide was used to treat syphilis, and iodine was found to be radio-opaque to x-rays.
• 1927: First reported IVU with iodised organic salts (Uroselectan).

Ultrasound Contrast Agents (Echo Enhancers)

• Increase the echogenicity of blood, which heightens tissue contrast and allows better delineation of body cavities.
• Consist of microscopic gas-filled bubbles.
• High reflectivity arises from the fact that microbubbles easily change their size, contracting in compression and expanding in the rarefaction part of the ultrasonic cycle.

Generations of Echo Enhancers

• First generation: Unstabilized bubbles in indocyanine green, used only for cardiac and large vein studies.
• Second generation: Longer-lasting bubbles coated with shells of protein, lipids, or synthetic polymers.
• Third generation: Encapsulated emulsions or bubbles, offering high reflectivity.

Types of Ultrasound Agents

• Non-encapsulated microbubbles
• Encapsulated microbubbles:
  • Encapsulated air microbubbles (e.g., Albunex, Echovist)
  • Encapsulated perfluorcarbon microbubbles (e.g., Optison)

Ideal Ultrasound Contrast Agent

• Should be injectable by a peripheral vein
• Should be non-toxic
• Should be small enough to pass through pulmonary, cardiac, and capillary systems
• Should be stable enough to undergo shear forces, hydrostatic pressure changes, and diameter changes
• Should have a sufficient half-life to allow complete examination
• Should require little preparation