Table 2.

Mean contrast recovery and background variability for hot spheres with diameter 10mm, 13, 17, 22 and cold spheres 28, 37, as defined by NEMA with background activity concentration ratio a) 6:1 b) 10:1 c) 14:1

	Contrast Recovery						Background variability
Sphere size (mm)	10	13	17	22	28	37	10	13	17	22	28	37
OSEM	39.3	58.8	62.9	68.1	75.4	83.6	7.9	7.3	6.6	5.9	5.3	4.7
B 400	37.2	57.5	64.9	71.5	75	84	4.7	4.6	4.4	4.2	4.1	4.1
B 600	29.4	49.7	62.5	73.7	73.3	81.7	4	3.9	3.9	3.9	3.9	4
B 800	14.8	32.1	49.5	65.9	58.7	64.1	3.8	3.7	3.6	3.6	3.5	3.5
B 1000	12.5	28.2	45.7	63.3	55.8	61.6	3.8	3.7	3.6	3.5	3.5	3.5
	Contrast Recovery						Background variability
Sphere size (mm)	10	13	17	22	28	37	10	13	17	22	28	37
OSEM	61.2	72	73.6	76.4	78.6	83.8	7	6	4.9	4	3.6	3.4
B 400	63	77.6	84.8	88.4	78.5	86.4	3.2	2.7	2.4	2.5	2.7	2.8
B 600	54.6	72.4	81.9	86.8	75	83.8	2.7	2.4	2.2	2.4	2.6	2.8
B 800	47.8	67.8	79.2	85.3	72.1	81.6	2.4	2.2	2.2	2.3	2.6	2.7
B 1000	42.3	63.8	76.7	83.9	69.6	79.6	2.3	2.1	2.1	2.3	2.6	2.7
	Contrast Recovery						Background variability
Sphere size (mm)	10	13	17	22	28	37	10	13	17	22	28	37
OSEM	62.4	67.5	70.3	77.5	78.7	83.5	6.6	6	5.2	4.6	4	3.3
B 400	64.1	66	72.8	78.9	69	73	3.9	3.6	3.4	3.1	2.9	2.7
B 600	55.8	71.3	78.7	85	74.9	82.8	3	2.8	2.6	2.4	2.2	2.1
B 800	49.4	67.2	76.4	83.7	71.8	80.5	2.8	2.7	2.5	2.3	2.1	2.1
B 1000	44.1	63.5	74.3	82.4	69.3	78.5	2.6	2.5	2.4	2.2	2.1	2.1