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Radiological fluoroscopy, using x-ray image intensifiers (XRII) and TV systems, is limited in visual noise or mottle by the requirement of minimizing radiation dose to the patient. Various methods have been used for making this noise more acceptable, such as using laggy vidicons (rather than plumbicons) or digital stores to integrate and thus reduce noise. Integration implies some motional blurring and this problem has to be balanced against noise reduction. In obtaining static images from such XRII-TV system, further choices come into play, (a) optical exposure time in the multiformat camera and (b) whether or not the radiation is pulsed. We have performed mottle and motion blurring evaluations on radiographic images produced during continuous fluoroscopy via TV systems (i.e. videofluorographs) or directly from x-ray image intensifiers for various exposure times. These results are compared with each other and direct measurements of the TV system's temporal frequency response. It was found for the particular clinical system evaluated (Siemens 1023 line TV and Matrix Instruments FV1-1 multiformat camera) that (a) TV generated noise was sufficiently high to require several TV frames to be integrated onto the film image to reduce it to acceptable proportion. (b) That the vidicon had a consider-able lag--effectively integrating for ~ 0.2 s with consequent motional blurring problems. (c) Finally that clinically useful images were obtained using (allowing for system integration) 10μR to the imaging system. This is a factor of 10 smaller than 100mm photofluorographs and 100 times smaller than PAR speed film-screen combinations. The compromises to image quality which are intrinsic and those which are particular to the system used are distinguished. Based on these results an ideal, yet feasible imaging system is outlined for digital radiography which is optimized for low dose-low information content general radiography.
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