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Fig. 3 —Graph illustrates how we created tube current modulation table. For example, to reach target SD of 12 H in patient with SD of 10 H on unenhanced images, we placed transverse line (line A) to pass through point of intersection between 300-mA exponential curve and SD value equal to 12 H (red circle), desired target noise level; second, we placed a vertical line (line B) at point where 300-mA exponential curve crosses SD value of 10 H (blue circle), which is SD value obtained from unenhanced images of patient; third, we read crossing point of vertical and transverse lines (green circle) that lies between exponential lines of 200 and 250 mA, closer to 200 mA. Positive slope of line A shows increasing difference of SD values between unenhanced and contrast-enhanced images as phantom size increases from 180 to 300 cm, and it reflects difference in radiation dose between two parameters on reconstructed images.