The development of a kilohertz-range pulsed x-ray generator and its applications in dental medicine are described. The pulsed x-ray generator consists of the following major components: a constant high-voltage power supply, a high-voltage main condenser, a hotcathode triode, a DC power supply for the filament (hot cathode), and a grid controller. The main condenser of 0.5μF-100 kV is charged up to 100 kV by the power supply, and the electric charges in the condenser are discharged repetitively to the triode by the grid controller. To be exact, the tube voltage slightly decreased during the discharging for generating pulsed x rays, yet the maximum value was almost equivalent to the initial charging voltage of the main condenser. The maximum tube current had a value of about 0.5 A. The x-ray exposure and the repetition rate with a charging voltage of 60 kV and a total resistance R of 5.1M Ω were 0.55μC/kg at 1.0 m per pulse and about 800 Hz, respectively. The focal spot dimension was reduced by the electron focusing, and stable repetitive x-ray pulses were obtained when the rectangular pulses were input by the oscillator. In the case where the x-ray television system utilizing an image-memory device was employed, the x-ray exposure decreased with corresponding decreases in the repetition rate of pulsed x-rays.

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It is difficult to obtain accurate characteristic curves for screen-film combinations because of technological factors. The purpose of this study is to present a new method for accurate and simple sensitometry.
To evaluate the method, we used inverse- square and the Bednarek's technique for bootstrap. Characteristic curves obtained by the new sensitometry were compared with these obtained by the inverse-square sensitometry.
As a result, maximum percentage errors of gradient were found to be within 6.62%. It was confirmed that the new sensitometry had the same accuracy as the inverse-square sensitometry.

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The development of an x-ray generator utilizing a cold-cathode triode with a molybdenum target (anode tip) and its application to high -speed dental radiography are described. This generator employs the following essential components: a high-voltage power supply, a highvoltage condenser of 0.2μF, a turbo-molecular pump, a trigger device, and a cold-cathode x -ray tube. The main condenser is charged from 40 to 60 kV by the power supply, and the electric charges in the condenser are discharged to the tube after closing a high-voltage switch. In this generator, the trigger electrode is connected to the anode electrode through a resistor in order to induce the main discharging for producing x-rays. Because this tube employs a long target, the x-ray source which consists of molybdenum ions and electrons is easily produced by the target evaporating. The peak tube voltage was nearly equivalent to the initial charging voltage of the main condenser, and the maximum current had a value of 22 kA with a charging voltage of 60 kV. The average width of flash x-rays was less than 1μs, and the maximum exposed dose was about 4.8μSv. The characteristic x-ray intensities of molybdenum K-series lines substantially increased with corresponding increases in the charging voltage. Using this generator having a molybdenum-target x-ray tube, we have performed wide-range radiography in oral surgery in order to image soft to hard tissues simultaneously by means of high-current discharge in the x-ray tube.

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In this study, we investigated quantitative evaluation of aortic calcification employing thoracic images scanned by helical CT.
To measure a volume of aortic calcification in a series of thoracic images, we developed a software on Apple Macintosh personal computer that extract calcification semiautomatically. The measurement process of calcification in this program consists of the following steps: (1)manual designation of an approximate center point in the aorta area on the first image, (2)semiautomatical extraction of aortic ROI by successive radial edge detection, (3) measurement of the sum of calcification pixels in the ROI and of the sum of scored calcification values that was weighted by the factors alloted to the CT numbers of the calcification pixels, and (4)calculation of the total sum of the number of the calcification pixels and the total sum of scored calcification values by applying(1)-(3) repeatedly to whole slice images of a patient.
We proccessed 10 series of thoracic helical CT images containing aortic calcification at an interval of 2 years.
In consequence, our evaluation method could quantitate the temporal change of amounts of aortic calcification.

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