Editing Books and References (section)

===Densitometric Measurements===
Densitometry parameters are measured on grayscale data.

====Descriptive Statistics (Mean, Median, SD) of Calibrated Voxel Values====
Bone mineral density (BMD) is defined as the volumetric density of calcium hydroxyapatite (CaHA) in a biological tissue in terms of g.cm-3. It is calibrated by means of phantoms with known density of CaHA. Bone mineral density can refer to two different measurements: 

*'''Bone Mineral Density (BMD)''':  A measure of the density of minerals within the whole bone.  Measured by taking the average grayscale intensity of bone, marrow, and pore voxels, and converting it to hydroxyapatite (HA) mineral density.  The combined density of a well-defined volume which contains a mixture of both bone and soft tissue, such as a selected volume of medullary trabecular bone in a femur or tibia, is measured as “bone mineral density”, or BMD. This parameter BMD relates to the amount of bone within a mixed bone-soft tissue region, but does not give information about the material density of the bone itself.

*'''Tissue Mineral Density (TMD)''':  A measure of the density of minerals within the bone tissue.  Measured by taking the average grayscale intensity of the bone only (usually suppressing 2 voxels at the edges to elimitate partial volume artifacts) and converting it to hydroxyapatite (HA) mineral density.  The density measurement restricted to within the volume of calcified bone tissue, such as cortical bone, excluding surrounding soft tissue, is called “tissue mineral density” or TMD. By contrast to BMD, this gives us information about the material density of the bone itself, and ignores surrounding soft tissue.

*Refer to [[Media:2007-koller-calibration-of-micro-ct-data-for-quantifying-bone-mineral.pdf|'''this article''']] for more details.

Typically trabecular bone is assessed for BMD, averaging bone and marrow within the medullary volume of interest. By contrast, for cortical bone, TMD is measured. Note that in the case of trabecular bone, partial volume effect compromises the measurement of TMD except at very high micro-CT resolutions. As a general rule, resolution should be such that the thickness of a bone structure should equal 10 pixels or more, in order for TMD to be measured.

[[File:BMD_TMD.JPG|500px]]


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