Keisuke Konishi

An evaluation of protracted low dose rate irradiation from an acute dose survival curve

A method of transformation from an acute survival curve to a protracted low dose rate survival curve based on the concept of the dose equivalent sublethal damage advanced by Oliver is introduced. The transformation was done by solving a differential equation which was formulated between the slope of both survival curves and which was able to be applied to the situation where the dose rate might change with time, e.g., in using short‐life radioisotope or the complexity of the recovery of sub‐lethal damage. The effects of the short‐life radioisotopes (radon seeds and radiogold grains) in radiotherapy were estimated by using this method and applying it to Lajtha‐Olivers model; our data are compared with the data obtained by Orton. Cancer 42:2211–2215, 1978.

Fluoroscopic computed tomography: An attempt at 3-D imaging of teeth and jaw bones

A microcomputer-based low exposure X-ray computed tomography system has been developed for scanning of dentomaxillo-facial region, which utilizes an image intensifier as a two dimensional photon detector. A dry human mandible on a rotating table was projected onto the two dimensional imaging system by a cone beam of X-rays from the source. A total of 120 projection images covering 180° were acquired and stored on a hard disk. The transverse cross sectional images were reconstructed by the usual CT reconstruction algorithm, while longitudinal section images such as panoramic images were obtained by directly backprojecting the filtered 3-D projection data onto the curved surfaces. The radiation exposure was measured with an ionization chamber, and the dose of the present fluoroscopic CT was estimated to be about 10 to 20 times less than that of conventional X-ray CT. It is suggested that this type of CT can be an effective imaging system in a variety of dental diagnostic applications.A microcomputer-based low exposure X-ray computed tomography system has been developed for scanning of dentomaxillo-facial region, which utilizes an image intensifier as a two dimensional photon detector. A dry human mandible on a rotating table was projected onto the two dimensional imaging system by a cone beam of X-rays from the source. A total of 120 projection images covering 180° were acquired and stored on a hard disk. The transverse cross sectional images were reconstructed by the usual CT reconstruction algorithm, while longitudinal section images such as panoramic images were obtained by directly backprojecting the filtered 3-D projection data onto the curved surfaces. The radiation exposure was measured with an ionization chamber, and the dose of the present fluoroscopic CT was estimated to be about 10 to 20 times less than that of conventional X-ray CT. It is suggested that this type of CT can be an effective imaging system in a variety of dental diagnostic applications.

X-Ray K-Edge Subtraction Television System

An X-ray K-edge subtraction television system utilizing synchrotron radiation is investigated. The phantom is irradiated by two monochromatized X-ray beams closely bracketing the K-absorption edge of iodine (33.17 keV) alternately, by means of a vibrating single crystal monochromator combined with a white synchrotron X-ray beam. The subtraction of the successive two images produced by these beams results in images that enhance signals arising from attenuation by iodine and suppresses signals by other materials. The prototype system is fully implemented using two kinds of real time image processing subsystems. The results are compared with those obtained by the conventional (nonreal time) processing system.