Table 2.

Mean absolute error in the CT numbers of each site: lung, soft tissue, bone, and air regions. These values were calculated with respect to the CT numbers in the original images and are shown in terms of mean ± standard deviation for evaluation images.

	Interval of projection data acquisition angle
	1°	2°	5°	10°
Lung
With artifacts	0.08 ± 0.05	0.12 ± 0.09	0.49 ± 0.44	3.88 ± 3.44
AE	53.11 ± 0.84	48.89 ± 0.72	47.67 ± 1.74	75.72 ± 7.01
U-Net	54.22 ± 0.31	55.17 ± 0.45	55.11 ± 0.79	59.97 ± 2.24
CGAN	1.48 ± 0.20	0.85 ± 0.26	1.61 ± 1.05	5.40 ± 2.86
Soft tissue
With artifacts	0.10 ± 0.07	0.12 ± 0.08	0.66 ± 0.46	2.51 ± 1.38
AE	17.35 ± 0.34	9.93 ± 0.62	5.83 ± 1.44	3.64 ± 2.13
U-Net	19.75 ± 0.28	25.65 ± 0.20	14.66 ± 1.08	21.18 ± 1.79
CGAN	2.99 ± 0.11	0.83 ± 0.14	1.38 ± 1.03	1.28 ± 1.39
Bone
With artifacts	0.21 ± 0.10	0.48 ± 0.34	2.64 ± 1.39	11.89 ± 7.33
AE	10.61 ± 2.66	3.96 ± 1.94	8.78 ± 4.27	9.56 ± 7.83
U-Net	14.41 ± 1.27	20.71 ± 1.40	8.86 ± 2.56	9.35 ± 4.52
CGAN	3.27 ± 0.46	0.59 ± 0.43	4.17 ± 4.27	9.42 ± 6.36
Air
With artifacts	1.30 ± 0.08	0.66 ± 0.25	12.25 ± 2.50	36.09 ± 1.56
AE	62.51 ± 0.24	62.71 ± 0.14	61.43 ± 0.46	58.98 ± 0.97
U-Net	62.20 ± 0.19	61.21 ± 0.21	60.71 ± 0.46	62.19 ± 0.48
CGAN	0.45 ± 0.09	1.13 ± 0.18	0.86 ± 0.50	1.23 ± 0.45