An image-reconstruction technique called ASIR (adaptive statistical iterative reconstruction) allows CT scanners to deliver high-quality chest CT images at radiation levels up to 75 percent lower than standard exams, according to a paper by several Mass General radiologists published in the May issue of Radiology. The researchers obtained raw CT data at four different radiation levels, and then processed those images using both ASIR and an alternative technique called FBP (filtered back projection). They then asked radiologists to rate the various images. The radiologists, who didn't know what type of image they were seeing at any time, reported confidence in the ASIR images down to much lower radiation levels than they did with the FBP images. In other words, ASIR enabled the use of less radiation in chest CT exams than did FBP.