Table 1. Image noise and CNR in each phantom group.

Item	120 KV+210 mAs/FBP (Group A)	120 KV+125 mAs/L3 (Group B)	120 KV+105 mAs/L4 (Group C)	120 KV+84 mAs/L5 (Group D)	120 KV+63 mAs/L6 (Group E)	F	P
Image noise	15.4±0.8	11.9±1.7	13.2±0.6	15.2±1.1†	14.8±1.4†	16.4	<0.001
	(14.1–16.9)	(10.6–16.2)	(12.2–14.1)	(13.5–16.7)	(13.0–17.8)
CT value of Teflon spheres	965.8±3.7	968.2±2.0	967.8±2.8	966.1±6.4	965.3±3.4	1.1	0.4
	(962.0–973.9)	(965.2–971.7)	(963.9–973.3)	(958.1–975.0)	(957.7–970))
CT value of background	100.9±8.4	98.7±1.3	97.7±1.4	98.0±1.8	98.7±2.0	0.9	0.4
	(97.3–124.6)	(96.0–99.9)	(95.5–100.2)	(95.1–101.6)	(96.4–102.5)
CNR	56.2±2.8	73.9±8.4	66.0±3.0	59.5±2.3†	59.3±5.3†	20.7	<0.001
	(51.3–61.0)	(53.9–82.0)	(53.9–82.0)	(56.9–63.8)	(48.7–66.8)

Note: ^†indicates no significant statistical difference compared to group A; CNR: contrast-to-noise ratio; L: IRT level.