39 - Optimizing Microbubble Reduction to Facilitate IVUS Guidance during Endovascular Radiofrequency Wire Procedures

Radiofrequency (RF) energy is used for tissue ablation across a range of conditions. Adjusting RF generator parameters allows RF energy to be directed through a wire to puncture tissue with minimal adjacent damage. RF puncture is useful to penetrate dense or fibrous tissue. When RF energy is applied to tissue, however, microbubbles are rapidly produced, obstructing ultrasound (US) visualization. RF wire puncture is frequently paired with intravascular ultrasound (IVUS) guidance. Mitigation of RF-generated microbubbles has been studied for ablation, but not RF wire puncture. This study recreates microbubbles that would be seen on IVUS from RF wire puncture and evaluates methods to improve visualization.

Materials and Methods:

This was IRB exempt. A model with bovine liver submerged in a saline bath was created.  An IVUS catheter (Soundstar ultrasound catheter, Biosense Webster) was placed into the bath parallel to the liver surface. In parallel, the liver was punctured with a RF guidewire (Powerwire, Baylis Med Tech). Three seconds of RF energy was applied at 25W to recreate microbubbles on IVUS. Regions of interest (ROIs) were selected around punctures to calculate average ROI brightness as a proxy for microbubbles on IVUS. MATLAB scripts were written to calculate average ROI pixel brightness from IVUS images. This process was performed without the application of US as a control. This process was repeated with altering the mechanical index of the IVUS for 10 seconds, using external US with a VF10-5 Linear probe (Siemens), and external US with a L12-3 Linear probe (Philips). When external US was used, the probes were secured to the top of the liver prior to any imaging and were applied superficially for 10 seconds. IVUS images before and after US application were compared to evaluate changes. RF energy application with no subsequent US and a 2-minute waiting period was recorded as baseline. Statistical analysis was performed with a one-sample t-test.

Results:

The control increased ROI brightness by 1.5%. Altering the mechanical index of IVUS reduced ROI brightness by 1.2%. VF10-5 probe application increased ROI brightness by 1.2%. L12-3 probe application reduced ROI brightness by 33.0% (P=0.046). Brightness reduction was most pronounced at the site of initial RF wire puncture at sites where microbubbles accumulated. Tip visualization improved, allowing for more precise wire trajectory adjustments.

Conclusion:

External US with an L12-3 probe was able to dissipate microbubbles effectively to improve IVUS guidance following RF wire puncture.