| 摘要 |
VARIABLE X-RAY BEAM MODULATOR FOR WIDE-FIELD ANGIOGRAPHY A computer-controlled, motor-driven shutter assembly to be used with the X-ray tube of a large field angiographic system. The shutter assembly installed onto the angiography system enables to compensate for different patient anatomy by reducing the relative X-ray exposure time from the feet to the abdomen of the patient, so as to achieve uniform radiographic exposure, without affecting the X-ray beam hardness. The X-ray exposure time reduction is obtained by gradually masking the X-ray beam during each exposure from the feet to the abdomen, through use of a motor-driven lead shutter. A radiation sensor detects the beginning of every X-ray beam exposure at the upper (leading) port of the large field, X-ray beam tube and in turn, triggers a shutter controlling circuitry. The X-ray exposure time of the patient from feet to abdomen is reduced according to computergenerated attenuation curves and gradients of patient contour. In consequence, body contrast remains high and constant from feet to abdomen and from patient to patient.
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