Table 7. Optical Index OI as a function of measurement position and BIRADS category^a.

BIRADS category	1 Outer	2 Chest	3 Inner	4 Nipple	5 Middle	All areas	Full scan
1	1.9 ± 0.5	1.4 ± 0.6	1.4 ± 0.4	2.2 ± 1.1	1.5 ± 0.6	1.6 ± 0.6	1.9 ± 1.0
2	4.1 ± 3.0	4.3 ± 7.7	3.0 ± 3.4	4.0 ± 2.1	2.8 ± 1.6	3.5 ± 3.8	4.8 ± 5.0
3	29 ± 34	17 ± 16	10 ± 10	31 ± 34	20 ± 21	21 ± 25	26 ± 27
4	166 ± 81	149 ± 63	79 ± 45	211 ± 90	164 ± 65	152 ± 76	146 ± 84

^aThe data are averaged over the left and right CC views.