RESUMEN
With increasingly strict regulations regarding patient exposure, research on digital radiography technology has recently focused on indirect methods that can produce high-quality images for a low radiation dose. In particular, medical imaging systems based on indirect methods universally use rare-earth metal phosphors, because of their high atomic number and excellent luminescence efficiency. Thus, various studies aiming to improve the luminescence efficiency of phosphors have been conducted. Despite this research, however, the current luminescence efficiencies are insufficient. Here, we report a basic study aiming to develop a phosphor screen containing a three-quarter-wave optical-thickness layer to improve the light transmission efficiency. Specifically, the fabrication and measurement of a Gd2O2S:Tb phosphor screen containing a single three-quarter-wave optical-thickness layer is presented. The screen is fabricated via a screen-printing and spin-coating method. Based on histograms of the degree of luminescence and the pixel values, we demonstrate that the light transmission efficiency is improved by the three-quarter-wave optical-thickness layer. Note that analysis of the full width at half maximum of the pixel value distribution reveals the possibility of resolution loss when obtaining medical images. Overall, the results of this study confirm that the light transmission efficiency can be improved through use of a single-layer anti-reflection coating. However, because the emission spectrum of the Gd2O2S:Tb screen is in the 480-600-nm band, it is necessary to expand the areas exhibiting the lowest reflectance to the wavelengths at the edge of this band. Thus, further study should be conducted to optimize the optical thickness.
RESUMEN
PURPOSE: Pathologic stage is the most accurate prognostic factor of renal cell carcinoma. We evaluated whether perirenal fat infiltration is a significant factor in tumors 7 cm or less in size. MATERIALS AND METHODS: We retrospectively reviewed the record of 164 cases of tumors 7 cm or less in size. We divided the patients into two groups according to the presence of perirenal fat infiltration (group A, pT1; group B, pT3a). We evaluated relationships, recurrence-free survival and disease-specific survival according to clinicopathologic parameters. Statistical differences were calculated by log-rank test. RESULTS: A total 131 patients were included in group A, with a mean age of 55.8 years, average tumor size was 4.2 cm, and a mean follow-up period of 43 months. Group B included 33 patients, with a mean age of 55.9 years, an average tumor size of 4.1 cm, and a mean follow-up period of 38 months. There was no significant difference in disease-specific survival; however, recurrence-free survival showed significantly different between two groups (group A: 95.5%, group B: 84.4%). CONCLUSION: In this study, perirenal fat infiltration proved to be an independent prognostic factor for predicting disease-free survival in patients with tumors of 7 cm or less in size. Therefore, as this study showed, the presence of perirenal fat infiltration requires stricter follow-up planning, even in small renal cell carcinoma.
