Photoacoustic Necrotic Region Mapping for Radiofrequency Ablation Guidance

Abstract

Radiofrequency (RF) ablation is an effective minimally invasive therapy for diseases including cancer and cardiac arrhythmia by heating the problematic lesions using an electric current. RF procedures lack direct, intraoperative, realtime feedback on the size and extent of ablation-induced necrosis, making the assessment of procedure completeness difficult. Previous studies have suggested that photoacoustic (PA) imaging can detect ablated lesions based on their PA spectrum difference from that of non-ablated tissues. In this work, we introduce a PA-based necrotic region mapping, focusing on visualizing the extent of ablation-induced necrosis and its lesion distribution. Real-time visual feedback on the growth of the ablation necrotic region is expected to reduce recurrence and procedural complications by avoiding incomplete and excessive ablation, respectively. The extent of necrosis is quantified based on the contribution from the ablated spectra intensity with respect to the total intensity combining with non-ablated spectra. We visualized it with continuous colormap to present the necrotic lesion size and extent. A PA image-guided ablation system consists of a side-firing linear array transducer, a laser pulse illuminating fiber bundle, and an RF ablation catheter. Three wavelengths (700nm, 740nm, and 760nm) were used for continuous illumination. The necrotic region mapping computation was applied to identify the growth of necrotic lesions over time. We applied continuous PA imaging to an ex-vivo swine liver tissue during the RF ablation. The growth of the necrotic region area was visualized through the ablation. Direct comparison between the acquired image and gross pathology demonstrated the system could monitor necrotic region size. The measured necrotic region was 5.93 mm in width, matching with the actual width of 6.2 mm. The ablated area was measured as 2.81 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> after the ablation. The results suggest that PA image-guided ablation system has the potential to be incorporated into clinical practice to guide ablation procedures.