Global Measurements

Dragonfly's Bone Analysis Wizard can compute common bone morphometric measurements from segmented regions of interest, as described by Bouxsein et al*, as well as additional parameters, such as anisotropy, bone mineral density, and structure model indices (see Computing Global Measurements for information about computing measurements and selecting the inputs and parameters in the Global Measurements dialog).

* Bouxsein et al, Guidelines for assessment of bone microstructure in rodents using micro-computed tomography, Journal of Bone and Mineral Research, 25, 7, (1468-1486), (2010)

In addition to the available global measurements, per slice measurements in any oblique are also available (see Computing Slice-by-Slice Measurements).
Bone mineral density and tissue mineral density measurements are only available in Dragonfly 3D World ZEISS edition. Contact Comet Technologies Canada Inc. for information about the availability of this version of Dragonfly.

The following global measurements are available in the Global Measurements dialog

Global measurements
Abbr. Measurement Description Unit
Ani.MIL* Anisotropy (MIL) A measurement of the orientation of trabecular architecture computed with the Mean Intercept Length (MIL) method and is computed from the input 'Trabecular bone' ROI. This method uses the mean distance between material intersections (bone–marrow interfaces) along linear traverses over a range of orientations. Because MIL traverses cross both materials, the result is a combined measure that incorporates features of both materials.

Refer to W.J. Whitehouse, The quantitative morphology of anisotropic trabecular bone, Journal of Microscopy, 101, 2, (153–168), (1974) for more information about the MIL method.

 none
Ani.SVD* Anisotropy (SVD) A measurement of the orientation of trabecular architecture that uses the Star Volume Distribution (SVD) method and is computed from the input 'Trabecular bone' ROI. In this method, the distribution is determined by placing a series of points within the material of interest, and then measuring the lengths of the lines emanating from them in various directions until they encounter a boundary. These lines are considered infinitesimal cones, with their vertex at the origin and subtending a solid angle as they approach the material interface.

Refer to L.M. Cruz-Orive, L.M. Karlsson, S.E. Larsen, F. Wainschtein, Characterizing anisotropy: A new concept, Micron and Microscopica Acta, 23, (75-76), (1992) for more information about the SVD method.

 none
BMD.Me** Bone mineral density (trabecular bone + medullary cavity) Is the mean intensity of bone mineral density (BMD) computed for calibrated bone data that corresponds to trabecular bone and the medullary cavity.

Note This parameter relates to a mixed bone-soft tissue region. Refer to TMD.BV and TMD.Co for measurements of the mineral density of bone itself.

 mg.cm-3
BS Bone surface Is the surface of the input 'Trabecular bone' ROI and can be computed with the marching cube method or weighted voxel approximation. These computation methods are available as shown below.

(default unit)2
BS/BV Specific bone surface Is the ratio of bone surface (BS) to bone volume (BV).

Note Surface to volume ratio or "specific bone surface" can be a useful parameter for characterizing the complexity of structures.

 (default unit)-1
BS/TV Bone surface density Is the ratio of bone surface (BS) to total volume (TV). (default unit)-1
BV Bone volume Is the volume of the selected 'Cortical bone' and 'Trabecular bone' ROIs and is computed as follows:

BV = (voxel volume) x (voxel count),
where voxel volume = (X spacing) x (Y spacing) x (Z spacing)

 (default unit)3
BV/TV Bone volume fraction Is the ratio of bone volume (BV) to total volume (TV).

Note Several studies show that the degree of anisotropy, a description of how the structural elements are oriented, together with bone volume fraction may explain a significant part of the mechanical properties of a 3D structure.

 none
Conn.D*** Connectivity density Is a measure of the degree of connectivity of the input 'Trabecular bone' ROI normalized by its volume. This measurement is computed as:

Conn.D = (1 - Euler number) / trabecular bone volume

 (default unit)-3
Ct.Ar Average cortical area Is the average cortical bone area within the selected bone length, in which 'bone length' is the length in Z of the labeled voxel in the 'Filled bone' ROI when 'Full volume' is selected as the computation area or in the selected computation box. Required inputs are the 'Filled bone' ROI, 'Cortical bone' ROI, 'Trabecular bone' ROI, and trabecular thickness. (default unit)2
Ct.Ar/Tt.Ar Average cortical area fraction Is the ratio of the average cortical area (Ct.Ar) to the average total area (Tt.Ar). none
Ct.Po Cortical porosity Is the ratio of pore volume to the total volume in the input 'Cortical bone' ROI and is computed as:

Ct.Po = [total pore volume (Po.V)]/[total volume of cortical bone (Ct.V)].

none
Ct.Th**** Average cortical thickness Is the average thickness of the input 'Cortical bone' ROI, in which thickness at a point is the diameter of the greatest sphere that fits within the structure and which contains the point. The average is calculated directly from values in the resulting thickness map.

Note Processing times are dependent on the size of the area of computation and you could consider reducing the area if processing times are excessively long.

(default unit)
Ec.Pm Average endocortical perimeter Is the average perimeter of the endocortex within the selected bone length, in which 'bone length' is the length in Z of the labeled voxel in the 'Filled bone' ROI when 'Full volume' is selected as the computation area or in the selected computation box. Required inputs are the 'Filled bone' ROI, 'Cortical bone' ROI, 'Trabecular bone' ROI, and trabecular thickness. (default unit)
Ec.S3D Endocortical surface (3D) Is the total surface area of the endocortex and is computed with a weighted voxel approximation using the trabecular bone area. Required inputs are the 'Filled bone' ROI, 'Cortical bone' ROI, and 'Trabecular bone' ROI. (default unit)2
Ma.Ar Average marrow area Is the average marrow (or medullary) area within the selected bone length, in which 'bone length' is the length in Z of the labeled voxel in the 'Filled bone' ROI when 'Full volume' is selected as the computation area or in the selected computation box. Required inputs are the 'Filled bone' ROI, 'Cortical bone' ROI, 'Trabecular bone' ROI, and trabecular thickness.

Note Treatments that tend to increase total cross-sectional area Tt.Ar and cortical area Ct.Ar can lead to a decrease in Ma.Ar, as an increase in bone area also increases the ratio of cortical to medullary bone.

 (default unit)2
Ps.Pm Average periosteal perimeter Is the average perimeter of the periosteum within the selected bone length, in which 'bone length' is the length in Z of the labeled voxel in the 'Filled bone' ROI when 'Full volume' is selected as the computation area or in the selected computation box. Required inputs are the 'Filled bone' ROI, 'Cortical bone' ROI, 'Trabecular bone' ROI, and trabecular thickness. (default unit)
Ps.S3D Periosteal surface (3D) Is the total surface area of the periosteum and is computed with a weighted voxel approximation using the cortical bone area. Required inputs are the 'Filled bone' ROI, 'Cortical bone' ROI, and 'Trabecular bone' ROI. (default unit)2
SMI***** Structure model index Is an indicator of the relative structure of the trabeculae and involves measurements of surface convex curvature. Required inputs are the 'Cortical bone' ROI and 'Trabecular bone' ROI. In addition, you can choose to use mesh or ROI dilation, as shown below. For ROI dilatation, the bone surface will be dilated by one voxel, while mesh dilation is computed as 0.1 x spacing in the direction of the vertex normal.

SMI = 6 x [(S' x V) / S], where
S' is the difference between the dilated bone surface and the initial surface, V is the bone volume, and S is the bone surface

Note This parameter is of importance in osteoporotic degradation of trabecular bone, which is characterized by a transition from a plate-like to rod-like architecture.

 none
TMD.BV** Tissue mineral density
(Bone volume)		 Is the mean intensity of tissue mineral density (TMD) computed for calibrated bone data that corresponds to the input cortical and trabecular bone regions. In contrast to BMD, tissue mineral density (TMD) provides information about the material density of the bone itself and ignores surrounding soft tissue. mg.cm-3
TMD.Co** Tissue mineral density
(Cortical bone)		 Is the mean intensity of tissue mineral density (TMD) computed for calibrated bone data that corresponds to the cortical bone ROI. In contrast to BMD, tissue mineral density (TMD) provides information about the material density of the bone itself and ignores surrounding soft tissue. mg.cm-3
TV Total volume Is the volume of the selected 'Filled bone' ROI and is computed as follows:

TV = (voxel volume)x(voxel count),
where voxel volume = (X spacing)x(Y spacing)x(Z spacing)

(default unit)3
Tb.N Trabecular number Is a measure of the average number of trabeculae per unit length and is computed as follows:

Tb.N = 1 / Tb.Th + Tb.Sp

 (default unit)-1
Tb.Sp Average trabecular separation Is the average distance between trabeculae, and is sometimes called trabecular spacing.

Note Higher Tb.Sp is associated with vertebral fracture and generally increases with age, exhibiting a linear dependence on age in the lumbar spine.

 (default unit)
Tb.Th**** Average trabecular thickness Is the average thickness of the input 'Trabecular bone' ROI, in which thickness at a point is the diameter of the greatest sphere that fits within the structure and which contains the point. The average is calculated directly from values in the resulting thickness map.

Note Processing times are dependent on the size of the area of computation and you could consider reducing the area if processing times are excessively long.

 (default unit)
Tt.Ar Average total area
(cortical bone + marrow) 		Is the area of the selected 'Filled bone' ROI and is computed as follows:

Tt.Ar = total volume / bone length,
where 'total volume' is TV and 'bone length' is the length in Z of the labeled voxels in the ROI when 'Full volume' is selected as the area of computation or in the selected computation box

Note Tt.Ar has been found to increase with age with continued periosteal apposition in both men and women at the distal radius and distal tibia. Cross-sectional area measurements characterize resistance to axial compression and tension.

 (default unit)2
* The degree of anisotropy, computed using with the MIL or SVD method, is a measure of how highly oriented substructures are within a volume. Trabecular bone varies its orientation depending on mechanical load and can become anisotropic. For an isotropic (perfectly oriented) system, the degree of anisotropy (DA) is equal to 0. As the system becomes more anisotropic (less well-oriented), the DA increases to some value less than or equal to 1.
** Bone mineral density (BMD) and tissue mineral density (TMD) are defined as the volumetric density of calcium hydroxyapatite (CaHA) in a biological tissue in terms of mg.cm-3. These measurements are calibrated by means of phantoms with known density values of CaHA (see Intensity Calibration for BMD and TMD Computations).
*** Refer to A. Odgaard and H. J. Gundersen, Quantification of connectivity in cancellous bone, with special emphasis on 3-D reconstructions, Bone vol. 14,2 (1993): 173-82 (doi:10.1016/8756-3282(93)90245-6) for information about computing Conn.D.
**** Refer to R. Dougherty and K.-H. Kunzelmann, Computing Local Thickness of 3D Structures with ImageJ, Microscopy and Microanalysis, vol. 13, no. S02, pp. 1678–1679, 2007 (doi:10.1017/S1431927607074430) for additional information about the implementation of local thickness measurements.
***** Refer to T. Hildebrand and P. Ruegsegge, Quantification of Bone Microarchitecture with the Structure Model Index, Comput Methods Biomech Biomed Engin. 1997; 1: 15–23 for more information about SMI.