Table 1.

Selected reference tissues from the International Commission on Radiation Units and Measurements (ICRU) report 46 [9] with corresponding stopping power ratio (SPR; before optimization) and Hounsfield unit (HU) values. Maximum (Max), minimum (Min), average, and average variation (2σ) of the 6 HU values from the calibration curves for each reference tissue are tabulated.

Tissue	SPR	CT1	CT2	CT3	CT4	CT5	Average	Max	Min	2σ (HU)
Lung inflated	0.257	−701.0	−703.0	−699.9	−701.0	−706.5	−702.3	−699.9	−706.5	4.7
Adipose tissue (ICRU report 49 [10])	0.878	−86.4	−89.1	−85.9	−86.4	−90.8	−87.7	−85.9	−90.8	3.8
Breast, 33-67	0.904	−67.4	−70.2	−67.7	−67.4	−70.5	−68.6	−67.4	−70.5	2.8
Breast, 50-50	0.933	−44.9	−47.9	−46.0	−44.9	−46.5	−46.1	−44.9	−47.9	2.2
Water	1.000	3.3	0.1	−0.2	3.3	6.3	2.6	6.3	−0.2	4.8
GI tract	1.019	26.4	23.2	23.3	26.4	28.7	25.6	28.7	23.2	4.2
Bladder, empty	1.030	39.0	35.8	35.7	39.0	41.8	38.3	41.8	35.7	4.6
Kidney	1.036	45.2	42.0	42.0	45.2	47.7	44.4	47.7	42.0	4.4
Blood	1.047	56.4	53.2	53.1	56.4	59.1	55.6	59.1	53.1	4.5
Skin	1.068	75.8	72.9	74.5	75.8	77.7	75.3	77.7	72.9	3.2
Cartilage	1.087	97.3	94.0	93.0	97.3	101.8	96.7	101.8	93.0	6.2
Humerus	1.186	391.3	388.7	386.1	391.3	397.2	390.9	397.2	386.1	7.4
Femur	1.291	479.9	477.1	474.8	479.9	485.6	479.5	485.6	474.8	7.3
Sacrum (female)	1.355	540.6	537.7	534.4	540.6	548.4	540.4	548.4	534.4	9.3
Rib, second and sixth	1.375	570.8	567.9	564.3	570.8	579.1	570.6	579.1	564.3	9.8
Vertebrae, C4	1.385	584.3	581.3	577.7	584.3	592.8	584.1	592.8	577.7	10.0
Rib, 10th	1.485	730.7	727.7	722.7	730.7	741.6	730.7	741.6	722.7	12.4
Cranium	1.576	863.2	860.3	854.0	863.2	876.4	863.4	876.4	854.0	14.6
Mandible	1.645	961.3	958.4	951.2	961.3	976.2	961.7	976.2	951.2	16.3
Cortical bone (ICRU report 49 [10])	1.825	1219.6	1216.7	1207.2	1219.6	1238.6	1220.3	1238.6	1207.2	20.4
Cortical Bone	1.885	1313.0	1310.1	1299.7	1313.0	1333.8	1313.9	1333.8	1299.7	22.2

Abbreviation: 33-67, 33% fibroglandular tissue–67% fat; 50-50, 50% fibroglandular tissue–50% fat; CT, computed tomography.