In vitro photoacoustic visualization of myocardial ablation lesions.

BACKGROUND: Radiofrequency (RF) ablation to treat atrial arrhythmia is limited by the inability to reliably assess lesion durability and transmurality. OBJECTIVE: The purpose of this study was to determine the feasibility of photoacoustic characterization of myocardial ablation lesions in vitro. In this study, we investigated the feasibility of combined ultrasound (US) and spectroscopic photoacoustic imaging to visualize RF ablation lesions in three dimensions (3D) based on unique differences in the optical absorption spectra between normal and ablated myocardial tissue. METHODS: Tissue samples were excised from the ventricles of fresh porcine hearts. Lesions were generated using an RF catheter ablation system using 20 to 30 W of power applied for 40 to 60 seconds. Ablated samples were imaged in the near-infrared regime (740-780 nm) using a combined PA/US imaging system. Measured PA spectra were correlated to the absorption spectra of deoxyhemoglobin and ablated tissue to produce a tissue characterization map (TCM) identifying 3D lesion location and extent. Tissue samples were stained and photographed for gross pathology. TCM and gross pathology images were coregistered to assess TCM accuracy. RESULTS: TCM reliably characterized ablated and non-ablated tissue up to depths of 3 mm. TCM also assessed lesion position and extent with submillimeter accuracy in multiple dimensions. Segmented TCMs achieved >69% agreement with gross pathology. CONCLUSION: The study results suggest that spectroscopic photoacoustic imaging has the potential to accurately assess RF ablation lesion size and position with submillimeter precision and may be well suited to guide transcatheter RF atrial ablation in clinical practice.