Three-dimensional tracking of lesion profile during laser surgery based on shock wave detection

Lack of sensory feedback during laser surgery prevents surgeons from keeping track of the exact lesion profile and cutting depth. As a result, duration and complexity of the treatments are significantly increased. In this study we propose a new method for enabling three-dimensional tracking of the exact lesion profile, based on detection of shock waves emanating from the ablated tissue and subsequent reconstruction of the incision location using time-of-flight data obtained from multiple acoustic detectors. Ablation was performed in fresh bovine tissue samples using a Q-switched Nd-YAG laser, delivering 8 ns duration 150mJ pulses at a wavelength of 1064nm and repetition rate of 5Hz. The beam was focused by a 50mm lens on the tissue surface, which resulted in a deep cut of up to 9mm depth. The generated shock waves were detected using a spherical matrix ultrasonic array. The exact cutting profile was subsequently rendered by reconstructing the origin of shockwaves detected during the entire procedure. Different combinations of the detector positions were considered with respect to the resulting reconstruction quality. It was observed that, by utilizing at least 12 detection elements, the lesion profile could be characterized with high accuracy in all three dimensions, which was confirmed by histological evaluations. The proposed method holds promise for delivering highly precise and accurate real-time feedback during laser surgeries.