A Two-Criterion Model for Microvascular Bio-Effects Induced In Vivo by Contrast Microbubbles Exposed to Medical...

Area of Science:

• Ultrasound physics
• Biomedical engineering
• Medical imaging safety

Background:

• The mechanical index (MI) is a theoretical parameter for diagnostic ultrasound bio-effects.
• MI assumes a wide range of bubble sizes, approximated by microbubble contrast agents.
• Current MI predictions often conflict with experimental bio-effects thresholds, especially frequency dependence.

Purpose of the Study:

• To investigate discrepancies between MI predictions and experimental bio-effects thresholds.
• To develop a more accurate safety metric for contrast-enhanced diagnostic ultrasound.
• To compute cavitation thresholds using a novel two-criterion model.

Main Methods:

• Calculated cavitation thresholds for acoustic pulses with varying bubble compositions (air, C3F8, mixture) and surrounding tissues (blood, kidney).
• Employed linear acoustic pulse versions and specific bubble dynamics models.
• Combined criteria for capillary wall stress and inertial collapse to predict thresholds.

Main Results:

• No single criterion accurately predicted experimental thresholds.
• A combined model incorporating circumferential stress and inertial collapse showed consistency with experimental data.
• Thresholds calculated using the combined model aligned with the linear frequency dependence observed experimentally.

Conclusions:

• The mechanical index (MI) requires refinement for accurate safety guidance in contrast-enhanced ultrasound.
• A novel two-criterion model shows potential for predicting bio-effects thresholds.
• Further validation of this contrast-specific model is needed to establish reliable safety metrics.