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Accumulation of thermal energies by highly repeated irradiation of femtosecond laser pulses inside a glass induces the heat-modification whose volume is much larger than that of the photoexcited region. It has been proposed that the heat-modification occurs in the region in which the temperature had overcome a threshold temperature during exposure of laser pulses. In order to understand the mechanism of the heat-modification, we investigated the temperature distribution during laser exposure and the threshold temperature by analyzing the volume of the modification based on a thermal diffusion model. We found that the threshold temperature becomes lower with increasing laser exposure time. The dependence of the threshold temperature on the laser exposure time was explained by the deformation mechanism based on the temperature-dependent viscosity and viscoelastic behavior of a glass under a stress loading by thermal expansion. The deformation mechanism also could simulate a tear-drop shape of a heat-modification by simultaneous double-beams' irradiation and the distribution of birefringence in a heat-modification. The mechanism proposed in this study means that the temperature-dependence of the viscosity of a glass should be essential for predicting and controlling the heat-modification.

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Transcatheter arterial embolization (TAE) is an effective means of treating primary hepatocellular carcinoma (HCC). However, in many cases of HCC the tumor recurs after treatment. In an attempt to obtain complete tumor necrosis, the authors studied the clinical and histologic effect of simultaneous embolization of both the hepatic artery and portal vein in ten patients with HCC. In those cases in which combined embolization caused infarction, tumor cells in the main tumor, tumor cells that had invaded the tumor capsule, and small intrahepatic metastases had become totally necrotic following treatment. No viable tumor cells were detected in four patients who subsequently underwent operations; nor were viable tumor cells present in one other patient who later died as a result of a perforated duodenal ulcer. Five patients who did not subsequently undergo operations were still free of the disease 2-17 months after combined arterial and portal embolization. The impact of combined embolization on liver function was nearly the same as that produced when TAE was performed alone. Combined embolization may be a viable alternative to hepatectomy for the treatment of HCC.