Table 3. False Positive Pulmonary Nodule Detection by Five Observers on ASIR- and FBP-Driven ULDCT Scans and on SCT Images.

	False Positive Nodules			Friedman Test	Wilcoxon Signed Rank Test
	FBP	ASIR	SCT		FBP vs. ASIR	ASIR vs. SCT	SCT vs. FBP
Observer 1	61	70	84	0.648	0.376	0.363	0.215
Observer 2	35	37	64	0.034*	0.510	0.027	0.015
Observer 3	11	9	16	0.142	0.521	0.135	0.159
Observer 4	22	10	27	0.014*	0.030	0.012	0.260
Observer 5	75	82	81	0.659	0.431	0.456	0.867

^*Values are significant by using Friedman test (p < 0.05). ASIR = adaptive statistical iterative reconstruction, FBP = filtered back projection, SCT = standard-dose CT, ULDCT = ultra-low-dose CT