X-ray fluoroscopy system for reducing dosage employing iterative power ratio estimation

A method of reduced dose X-ray imaging of a subject comprising the steps of:

• a) selecting a minimum acceptable signal-to-noise ratio, RATIO.sub.min and maximum exposure per image, R.sub.max ;
• b) selecting an X-ray tube voltage range from U.sub.min to U.sub.max ;
• c) selecting a plurality of N X-ray tube voltages U.sub.i where (i=0,1,2,3 . . . N) with increasing subscripts indicating increasing voltage values and each being from U.sub.min to U.sub.max ;
• d) determining a photon count Q.sub.i corresponding to each X-ray tube voltage U.sub.i being less than a maximum allowable photon count Q.sub.max consistent with limiting the subject's exposure to an acceptable level R.sub.max and for creating an image having a signal-to-noise ratio at least as great as RATIO.sub.min ;
• e) transmitting X-ray radiation through said subject by applying the X-ray tube voltage U.sub.i, and a current corresponding to photon count Q.sub.i to an X-ray tube;
• f) sensing the X-ray radiation which was transmitted through said subject;
• g) constructing an X-ray image of said subject from the sensed X-ray radiation:
• h) determining an exposure R.sub.i per image for each voltage U.sub.i and its corresponding photon count Q.sub.i ;
• i) determining the X-ray tube voltage U.sub.l and corresponding photon count Q.sub.l of the selected values which exhibits a minimum exposure to a subject;
• j) setting U.sub.min to U.sub.l -1 unless l-1<0 then setting U.sub.min to U.sub.0 ;
• k) setting U.sub.max to U.sub.l+1 unless l+1>N then setting U.sub.max to U.sub.N ;
• l) if the difference between U.sub.max and U.sub.min is not less than a predetermined increment, then repeating steps "c"-"h" for the new range U.sub.min to U.sub.max ;
• m) setting U.sub.opt to U.sub.l and setting Q.sub.opt to Q.sub.l ;
• and
• n) producing subsequent images with selected X-ray tube voltage U.sub.opt and the corresponding photon count Q.sub.opt.