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.

抄録全体を表示

Comparison of the cerebral blood flow (CBF) values obtained with continuous arterial spin labeling (CASL) and maximum ΔR₂^* with dynamic susceptibility contrast (DSC) was made in ischemic rat brain. The CBF values estimated with the CASL and DSC methods were first normalized by the average of the noninfarcted hemisphere in four male Sprague-Dawley rats. The size of the ischemic area was then estimated from the number of voxels under a given threshold. The ischemic area estimated from the DSC technique was statistically smaller than that obtained with the CASL technique (p<0.05) when CBF values were lower than 50% of the normal level. This result suggests that the CBF estimated with DSC may be overestimated in ischemic brain areas.

抄録全体を表示

We studied a method for preparing a thin optical window in the human fingernail to enable the optical monitoring of biosubstances in the nail bed. To prepare a thin optical window without injuring the nail bed, an ArF excimer laser was used to ablate the nail plate. The fluorescence induced during laser processing was measured to control ablation. The etching depth of the nail plate per pulse during ArF excimer laser ablation at a practical pulse energy density of 630 mJ/cm² was about 0.3 μm. The result indicates that the nail plate can be accurately processed to a thickness of less than 1 μm during ArF excimer laser ablation. The ArF excimer laser-induced fluorescence spectrum of the nail bed was different from that of the nail plate. This result suggests that it may be possible to discriminate between the tissues in the nail plate and nail bed by measuring the fluorescence induced by the ablation laser. We used an ArF excimer laser to ablate the nail plate of the fluorescence model of a nail bed, and controlled ablation by measuring the laser-induced fluorescence. A thin optical window having a minimum thickness of 4 μm was made in the nail without ablation of the fluorescence model in the nail bed. This proves that it is possible to use ArF laser ablation to prepare a thin optical window in the fingernail without injuring the nail bed, the process of which is controlled by measuring the laser-induced fluorescence.

抄録全体を表示