Bone mineral density in cone beam computed tomography: Only a few shades of gray

Table 1 Factors that might lead to inconsistencies and arbitrariness of grey values on cone beam computed tomography images

Ref.	Factors
Nackaerts et al[4]	Variation in the devices
	Image-acquisition settings
	Relationship between the object evaluated and FOV
	The position held by the region of interest
Mah et al[13]	Variation in the devices
Reeves et al[15]	Abrupt changes of density in the object
Katsumata et al[16]	Projection data discontinuity-related effect
	Variation in the CBCT devices
	Image-acquisition settings
	Relationship between the object evaluated and FOV
Bryant et al[17]	Projection data discontinuity-related effect
	Relationship between the object evaluated and FOV
	The amount of exomass
Katsumata et al[18]	The dimensions of the FOV
	The amount of exomass
Pauwels et al[39]	X-ray beam hardening effect
	Projection data discontinuity-related effect
	Variation in the devices
Schulze et al[41]	Abrupt changes of density in the object
	X-ray beam hardening effect
	Scattered radiation
Pauwels et al[42]	Abrupt changes of density in the object
Goodsitt et al[43]	X-ray beam hardening effect
	Scattered radiation
Liu et al[50]	The position held by the region of interest

CBCT: Cone beam computed tomography; FOV: Field of view.