Infographics / Ultrasound Physics

Microbubble and nanoparticle contrast agents

A gas-filled microbubble of roughly two to five micrometres with a stabilising shell sits within the blood pool. When insonated it oscillates non-linearly and returns a strong echo rich in harmonics, shown in teal, compared with the weak echo returned by soft tissue from an equal ultrasound pulse. A lower panel shows that at low mechanical index the bubble oscillates stably and is preserved, whereas at high mechanical index it undergoes inertial cavitation and is destroyed.

Microbubble ultrasound contrast agent: strong non-linear echo versus weak tissue echo A gas-filled microbubble of roughly two to five micrometres with a stabilising shell sits within the blood pool. When insonated it oscillates non-linearly and returns a strong echo rich in harmonics, shown in teal, compared with the weak echo returned by soft tissue from an equal ultrasound pulse. A lower panel shows that at low mechanical index the bubble oscillates stably and is preserved, whereas at high mechanical index it undergoes inertial cavitation and is destroyed. Microbubble ultrasound contrast agent Microbubble in blood ultrasound in gas shell strong non-linear echo (+ harmonics) ≈ 2–5 µm intravascular blood-pool agent (~RBC-sized) Soft tissue ultrasound in (equal) weak (linear) echo weak scatterer small impedance mismatch → low echo amplitude Higher mechanical index destroys the bubble low MI stable oscillation, preserved high MI inertial cavitation, destroyed increasing mechanical index →
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