TABLE 1

Linear Attenuation Coefficients (μ) and T1-Weighted MRI Intensities Assigned to BrainWeb Tissue Classes

Class	μ (cm⁻¹)	MRI
Background (air)	0.000105	500
Cerebrospinal fluid	0.097000	4,200
Gray matter	0.100000	10,000
White matter	0.100000	11,000
Fat	0.092000	13,000
Muscle or skin	0.100000	8,000
Skin	0.100000	5,000
Skull	^*	1,500
Connective tissue	0.100000	2,000
Paranasal sinuses	0.000105	1,000
Ethmoidal air cells or nasal cavity	0.066000	3,300

↵* The skull was attributed three attenuation coefficient values (0.143 cm⁻, 0.152 cm⁻, and 0.172 cm⁻¹), as described in the text.