Editing Scanco Administration (section)

===Calibration by BMD===
When we know that the x-ray absorption of a material is dominated by one specific material, then we can relate the measured x-ray linear attenuation coefficient (mu_value) to the mass density of that material. The calibration of [[Scanco_User_Instructions#Descriptive_Statistics_.28Mean.2C_Median.2C_SD.29_of_Calibrated_Voxel_Values| '''Bone Mineral Density (BMD)''']] is an example of this. We assume that the x-ray attenuation within mineralized tissues such as bone, dentine and enamel is dominated by, and can be approximated as, the x-ray attenuation of the mineral compound calcium hydroxyapatite (CaHA) which has the formula Ca5(PO4)3(OH). 

Then we obtain “phantoms” with two or more known mass concentrations of CaHA. By linking these mass concentrations of CaHA with measured mu_value in the micro-CT images, we can establish calibration linking the two quantities, allowing us to infer from the micro-CT measured linear attenuation coefficient (mu_value) in a mineralized tissue, to the density of CaHA in mg.cm-3. 

*The assumption of linear correlation between the two quantities is based on a well-applied beam hardening correction and the phantoms' diameter matching with the size of bone within the sample.

*This calibration system could be used to calibrate measurement of other substances apart from CaHA and bone, where x-ray absorption is known to be dominated by a certain substance and phantoms can be prepared with known concentrations of that substance.

{| class="wikitable"
|-
! scope="col"| Symbol
! scope="col"| Name
! scope="col"| Unit
! scope="col"| Value Range
! scope='col'| Meaning or Comments
|-
! scope="row"| BMD 
| Bone Mineral Density 
| mg HA/ccm
| 0～3000 
| Volumetric density of calcium hydroxyapatite (CaHA) in a biological tissue in terms of mg/cm^3
|-
! scope="row"| BMD_value
| Bone Mineral Density in Scanco images
| mg HA/ccm
| -1500～3000 typically
| BMD value in Scanco images
|}
 

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