TABLE 3

Percentage Contrast, Background Variability, and Average Lung Residual for n = 4

Sphere size (mm)	Contrast (%)					Background variability (%)
Sphere size (mm)		2i × 8s*	4i × 16s^†	FBP	2i × 8s*	4i × 16s^†	FBP
10	12	22	22	3.5	6.2	8.1
13	17	29	29	3.2	5.3	6.4
17	29	38	38	2.9	4.4	4.7
22	41	48	48	2.8	3.8	3.6
28	45	60	67	2.7	3.4	3.0
37	51	62	66	2.6	3.1	2.7
Lung (average relative error)	31	13	0

↵* Two iterations and 8 subsets.
↵^† Four iterations and 16 subsets.