Effect of multiple-sweeping on ablation performance during ex vivo laser nephrectomy

Fiber-assisted laser surgery has been employed as a minimally invasive method in various medical fields. In spite of multiple sweeping on tissue during laser treatments, the rate of tissue removal gradually decreases and eventually leads to longer irradiation times as well as deeper thermal injury. The objective of the current study was to quantitatively investigate the effect of multiple fiber sweeps on ablation performance during ex vivo 532-nm laser nephrectomy.

Porcine kidney tissue was used to evaluate variations in tissue ablation and coagulative necrosis after pre- and multiple-sweeping with a 532 nm wavelength at various fiber speeds (2, 4, and 6 mm/second). The distance between a fiber tip and tissue surface was initially set at 1.5 mm, and no further distance change was performed. Double-integrating spheres in conjunction with an adding-doubling method were employed to measure variations in optical properties of the tested tissue. The extent of ablation and coagulation was quantified to identify the role of multiple-sweeping at various fiber conditions.

Optical property measurements showed a 30% decrease in light absorption but a more than threefold increase in light scattering after irreversible thermal denaturation. Pre-sweeping yielded insignificant effects on tissue coagulation due to almost consistent coagulation depths with numbers of pre-sweeps. Ablation depths increased with more numbers of fiber sweeps and slower fiber speeds whereas coagulation depths thickened primarily with the slower speeds. Multiple-sweeping induced saturation in ablation volume with the increasing numbers of multiple-sweeps irrespective of the fiber speed.

A combination of coagulation barriers, spatial distribution of power, and temporal interplay of optical energy could attribute to continuously lessen the amount of the ablated tissue with the multiple sweeps. Optical power modulation with varying fiber conditions (speed and distance) will be examined to optimize surgical parameters and to sustain the equivalent ablation performance of the first sweep with the multiple sweeping for laser nephrectomy. Lasers Surg. Med. 48:616-623, 2016. © 2016 Wiley Periodicals, Inc.