Design of a transmissive optical system of a laser metal deposition three-dimensional printer with metal powder.

A transmissive optical system of a three-dimensional (3D) printer using the laser metal deposition (LMD) technique with a metal powder is proposed here, together with its design method. An f-number of the focused laser beam emitted from the optical system should be large enough for the laser beam not to be absorbed or reflected by the metal powder injection nozzle. On the other hand, owing to the Lagrange-Helmholtz relation, the f-number should be small enough to form a minute laser spot diameter for high-resolution building. A temperature rise induced by the high-power laser may cause damage or a thermal lens effect on the optical system, which can be reduced by using lenses having plano-surfaces contacting thermally with holders. A formula of the relationship of the thermal lens effect with an f-number of each lens is derived to determine the lens specifications. A formula of longitudinal spherical aberration (LSA) of these lenses is also derived, and the total LSA is shown to be able to be zero with an acceptable f-number of the focused laser beam. The prototype LMD 3D printer with 6 kW laser is fabricated and shows favorable properties, such as a minimum building width of 0.3 mm and a building speed of over 500 cc/h.

[CR-mammography with pixel size of 50 microm and dual-sided reading system: effect of the oblique incident of the X-ray beam on imaging properties and detection].

In mammography units, the X-ray tube focal spot is located directly above the chest wall edge of the detector. Therefore, the X-ray beam is incident at a different angle along the cathode-anode axis. When the X-ray beam is incident on the imaging plate (IP) at a relatively large angle, the resolution property of a new imaging plate with dual-sided reading system would be degraded compared with the conventional imaging plate because of the parallax effect, which produces a shift in the image on two sides of the imaging plate. To evaluate the oblique incidence effect of the X-ray beam on the degradation of resolution properties and detection of simulated microcalcifications of a new CR system with a pixel size of 50 microm, its basic imaging properties and observer performance tests were compared with those of a conventional CR system. The resolution properties were evaluated by measuring modulation transfer functions (MTFs). Observer performance tests were conducted to compare the detectability of simulated microcalcifications of CR systems. Degradation of presampling MTFs for the new system is greater than that of the conventional CR system when the X-ray beam was incident at the same angle on the imaging plate. We found that the degradation of the area under the ROC curve (Az) for the new CR system was greater than that of the conventional CR system when the X-ray beam was incident at the same angle on the imaging plate.

New CR system with pixel size of 50 microm for digital mammography: physical imaging properties and detection of subtle microcalcifications.

PURPOSE: To investigate the physical imaging properties and detection of simulated microcalcifications of a new computed radiography (CR) system with a pixel size of 50 microm for digital mammography. MATERIALS AND METHODS: New and conventional CR were employed in this study. The new CR system included a high-resolution imaging plate coupled with the FCR5000MA (50 microm pixel pitch) including transparent support and a dual-sided reader. The conventional CR system was coupled with the FCR9000 (100 microm pixel pitch). Modulation transfer functions (MTFs) and Wiener spectra (WS) of the new and conventional CR systems were measured. Observer performance tests were conducted to compare the effects of pixel size (50 microm vs. 100 microm) on the diagnostic accuracy of CR systems in the detection of simulated microcalcifications. RESULTS: The presampling MTF of the new CR system was higher at high frequencies than the conventional CR system. The WS of the new CR system was comparable to that of the conventional CR system at all frequencies. The area under the receiver operating characteristic (ROC) curve (Az) obtained with the new CR and the conventional CR systems were 0.84 and 0.79, respectively. Results showed that the detection of simulated clustered microcalcifications was significantly improved by use of the new CR system compared with the conventional CR system (p<0.05). CONCLUSION: The new CR mammography system improved physical imaging properties and detection of simulated microcalcifications over conventional CR mammography.

Melatonin alleviates jet lag symptoms caused by an 11-hour eastward flight.

The effect of 3 mg of melatonin on the rate of re-entrainment of plasma melatonin rhythm after an 11-h eastward flight was assessed. Eight subjects participated in the study, and underwent 24-h blood samplings once before the flight and twice after the flight. Subjects were exposed to natural zeitgeber outdoors and took 3 mg of malatonin at 20:00 h local time on the days when no blood sampling was done. Antidromic re-entrainment was dominant whereby melatonin administration in the evening promoted re-entrainment. Melatonin accelerated the rate of re-entrainment by 15 min per day and alleviated the jet lag symptoms.