In vitro photoacoustic visualization of myocardial ablation lesions

Abstract

Background Radiofrequency (RF) ablation to treat atrial arrhythmia is limited by an inability to reliably assess lesion durability and transmurality. Objective Determine feasibility of photoacoustic characterization of myocardial ablation lesions in vitro. In this study, we investigate the feasibility of combined ultrasound (US) and spectroscopic photoacoustic (sPA) imaging to visualize RF ablation lesions in 3-D 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 - 30 W of power applied for 40 - 60 s. Ablated samples were imaged in the NIR regime (740-780 nm) using a combined PA/US imaging system. Measured PA spectra were correlated to the absorption spectra of deoxy-hemoglobin and ablated tissue to produce a tissue characterization map (TCM) identifying 3-D lesion location and extent. Tissue samples were stained and photographed for gross pathology. TCM and gross pathology images were co-registered to assess TCM accuracy. Results The TCM reliably characterized ablated and non-ablated tissue up to depths of 3 mm. The TCM also assessed lesion position and extent with sub-millimeter accuracy in multiple dimensions. Segmented TCMs achieved greater than 69% agreement with gross pathology. Conclusion These results suggest that sPA imaging has the potential to accurately assess RF ablation lesion size and position with sub-millimeter precision and may be well suited to guide trans-catheter RF atrial ablation in clinical practice.

Spectroscopic photoacoustic imaging of radiofrequency ablation in the left atrium

“…The PA response at wavelengths around 500 and 600 nm is higher than that of fresh tissue. In the near infrared range, as in [20], we find that the lesion is characterized by an attenuation of the 760 nm peak associated with the optical absorption of hemoglobin and myoglobin.…”

“…Two groups have previously performed PA imaging of RF ablation lesions on porcine cardiac tissue ex-vivo [19,20]. Pang et al [19] have identified a maximum lesion to nonablated tissue contrast at 780 nm using a 3 MHz transducer.…”

“…Pang et al [19] have identified a maximum lesion to nonablated tissue contrast at 780 nm using a 3 MHz transducer. Dana et al [20] revealed a spectral signature providing contrast at wavelengths near 760 nm (which was attributed to the hemoglobin spectral signature disappearing) using a 21 MHz transducer. Both studies evaluated lesion formation in ventricular tissue, which is not directly generalizable to atrial ablation.…”

“…We introduce a dual wavelength (790/930 nm) imaging method which forms an image based on two consecutive frames acquired at two optical wavelengths. Advantages over single wavelength imaging approaches presented before [19,20] are insensitivity to fluence and temperature variations, resulting in more robust lesion detection, contrast and outlining (mainly transmurality). Quantitatively, we find that the best-performing single wavelength is 640 nm, in contrast to 780 nm that was suggested previously, based on qualitative assessment in single lesions [19].…”

Synthetic-aperture based photoacoustic re-beamforming (SPARE) approach using beamformed ultrasound data

“…However, the option to use an FDAapproved clinical ultrasound system eases the transition of photoacoustic technology into the clinic. Potential applications include real-time in vivo photoacoustic visualization for brachytherapy monitoring [15,16], image-guided surgery [17,18], interventional photoacoustic tracking [19], multispectral interventional imaging [20], and cardiac radiofrequency ablation monitoring [21].…”