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Figure 1a: Graphs show CT noise in the NU2-94 phantom in terms of the standard deviation of the CT numbers for five background regions (ROIs 1–5). (a) Graph shows values as a function of tube current, with tube voltage of 80 kVp. (b) Graph shows values as a function of tube voltage, with tube current of 160 mA. In both cases, the rotation speed was 0.8 second per rotation and the pitch was 1.5:1. ROI 4 is in the center of the phantom, and its values are slightly noisier due to photon attenuation.
