| 摘要 |
A focusing voltage and a defocusing voltage are selectively applied to a focus adjusting electrode of an image intensifier included in a fluoroscopic device. An image in focus is picked up when the focusing voltage is applied to the focus adjusting electrode, and this image is used as a live image. On the other hand, an image out of focus is picked up when the defocusing voltage is applied to the focus adjusting electrode. With a degree of being out of focus set appropriately, the image obtained may be an image of a site, e.g. a blood vessel, from which high frequency components are removed. This image is used as a mask image. After the patient is injected with contrast material, the voltages are switched for application to the focus adjusting electrode to pick up successively the mask image with application of the defocusing voltage, and the live image with application of the focusing voltage. Consequently, the interval of time between the two image pickup steps is shortened, and contrast material is not injected during the interval, to reduce the possibility of movement of the patient during the interval. A slip or deviation between the mask image and live image is diminished to suppress artifacts appearing in a subtraction image thereby acquired.
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