Patent Number: 
Section: claims

1. A CT system comprising: rotatable gantry having an opening defining a scanning bay;  a movable table configured to translate a subject to be scanned along a first axis within the scanning bay;  an x-ray projection source configured to project x-rays projected toward the subject;  a pre-subject filter to filter x-rays projected toward the subject, the filter having a variable attenuation profile; and  a computer programmed to:  determine an attenuation pattern of the subject;  translate the filter along the first axis as a function of the attenuation pattern of the subject; and  acquire imaging data of the subject. 2. The CT system of  claim 1  wherein the computer is further programmed to translate the filter in a transverse direction as a function of the attenuation pattern of the subject. claim 1 3. The CT system at  claim 2  wherein the computer is further programmed to position the filter as a function of the attenuation pattern of the subject to reduce radiation exposure to dose reduction regions of the subject. claim 2 4. The CT system of  claim 3  wherein the dose reduction regions include anatomical regions sensitive to radiation. claim 3 5. The CT system of  claim 1  wherein the computer is further programmed to determine the attenuation pattern of the subject from a set of patient projections. claim 1 6. The CT system of  claim 1  wherein the computer is further programmed to move the filter as a function of gantry rotation. claim 1 7. A radiographic imaging system comprising: a scanning bay;  a movable table configured to move a subject to be scanned fore and aft along a first direction within the scanning bay;  an x-ray projection source configured to project x-rays in an x-ray beam toward the subject;  a pair of cam filters formed of attenuating matter, wherein each cam filter has a length and an attenuation profile that varies as a function of filter length and wherein the attenuation profile of each filter is a function of filter thickness; and  a computer programmed to:  determine a region-of-interest of the subject;  position the pair of cam filters to limit x-ray exposure outside the region-of-interest; and  translate at least one of the filters in the first direction to either increase or decrease x-ray exposure to the region of interest. 8. The radiographic imaging system of  claim 7  wherein the pair of cam filters is oriented in an x-axis. claim 7 9. The radiographic imaging system of  claim 7  wherein each cam filter has an elliptical shape. claim 7 10. The radiographic imaging system of  claim 7  wherein the computer is further programmed to decrease a space between the pair of filters to narrow the x-ray beam and increase the space between the pair of filters to widen the x-ray beam. claim 7