抄録
We propose a new method for removing blood using a Ho: YAG laser (λ=2.1 μm)-induced water-vapor bubble for intra-vascular optical measurement including angioscopic imaging. We have successfully proven this blood removal method using a blood-filled porcine coronary artery ex vivo. The laser irradiation conditions were a pulse energy of 200 mJ and a 2 Hz repetition rate. The Ho: YAG laser, for blood removal, and flash lamp, for endoscopic illumination, were irradiated into the porcine coronary artery through individual optical fibers using a specified delay time. The delay time between the Ho: YAG laser irradiation and flash lamp 2 μs illumination duration was arranged to last until the maximum blood removal space was established. We successfully obtained an intra-lumen view via a angioscope using the laser blood removal method without saline injection. The obtained angioscopic view was clear and had a wide viewing angle because of low optical scattering and the low refractive index of the water-vapor bubble. We studied how to form the optimum laser-induced bubble, which is indicative of minimum invasion against the blood vessel. Time-resolved photography in vitro, transient pressure measurement in vitro, and acute histological study of the irradiated vessel wall in vivo were employed to determine the optimum bubble formation.: a large oblong bubble generated by a high-energy laser pulse of around 500 mJ/pulse enabled the removal of a large volume of blood with a low-acoustic-pressure/injury-free bubble. No dissection was seen in the vessel after 400 mJ/pulse laser irradiation with 10 shots, so we concluded that this bubble blood removal method might be safe for actual applications. This laser blood removal method might be effective for not only angioscope, but also for optical coherence tomography or other optical diagnoses.
