Computing Global Measurements

Segmented bone areas drive the computation of measurements for the common bone morphometric indices that provide quantitative descriptions of bone micro-architecture (see Global Measurements for descriptions of the available measurements).

Inputs and global measurements are available in the Global Measurements dialog, shown below.

Global Measurements dialog

Global Measurements dialog

You can filter the available measurements by input. For example, only measurements related to trabecular bone will appear if you only input a trabecular bone region of interest. If you add the filled bone ROI, then measurements related to those inputs will also appear in the dialog,
How to Compute Global Measurements
  1. In the Global Measurements dialog, select the region of interest(s) that represent the Filled bone, Cortical bone, and Trabecular bone in the drop-down menus, as required.

    Note You can select the regions of interest you created previously, imported regions of interest, or any other region of interest that satisfies the required criteria.

  2. Do one of the following for Trabecular thickness:
    • If you selected the regions of interest you created previously in the Bone Analysis Wizard, the value you entered previously will appear in the edit box. You can keep this value or adjust it, if required.
    • If you selected other regions of interest as your inputs, enter the expected maximal thickness of the trabeculae in the edit box.
  3. Select the measurement(s) that you want to compute.

    • If you are computing anisotropy with the MIL or SVD method, you will need to select the required settings. These settings are available at the bottom of the dialog whenever you select Ani(MIL) or Ani(SVD) (see ).

    • If you are computing bone mineral density (BMD) or tissue mineral density (TMD), you will need to select the required bone dataset. This setting, as well options to calibrate the selected dataset and include distributions of BMD and TMD in reports, are available at the bottom of the dialog whenever you select BMD.Me, TMD.BV, or TMD.Co (see Computing Bone and Tissue Mineral Densities).

  4. Double-click inside Area of computation for each measurement that you want to compute and then choose an area of computation, as shown below.

    • Choose Default computation box if you want to limit computations to the default computation box. If required, you can resize the default computation box to include only a sub-sample of your data (see Editing Shapes).

      Note You can also add and resize a new computation box, if required (see Adding and Editing Computation Boxes).

    • Choose Full volume if you want to compute measurements for the full region(s) of interest.
  5. Click the Compute Measurements button at the bottom of the dialog.

    The selected measurements are computed and appear in the Bone Analysis dialog.

  6. Click the Export to CSV button to export your results in a comma-separated values file (*.csv extension), optional.

    Note The delimiter for exporting in the CSV file format — comma, semicolon, or tab — can be selected in the Preferences dialog (see Miscellaneous Preferences).

  7. Click Next to advance to the next page in the wizard (see Computing Scalar and Vector Fields).

If you are computing anisotropy with the MIL or SVD method, you will need to select the required settings, which are available at the bottom of the Global Measurements dialog.

Settings for computing anisotropy

Refer to the table below for the settings applicable to anisotropy computations.

Settings for computing anisotropy
  Description
Radius (default unit) The radius of the sampling sphere, which determines the length of each sampling vector (lengthToAnalyze).
Sampling (default unit) The resolution, or distance between subsequent samples along each vector (samplingDistance).

Recommendations You can accept the default value or enter a value can be equal to the voxel size of the input region of interest.
Orientations The number of lines to analyze per sampling sphere(countOrientations).
Min iterations The minimum number of random points in the sample that will be analyzed.
Max iterations Is the maximum number of random points in the sample that will be analyzed. Fitting will stop automatically after this number is completed or if the coefficient of variation (tolerance) is reached.
Tolerance The coefficient of variation. Sampling new random points will continue until either a coefficient of variation equal to the tolerance is reached or the set maximum number of iterations is completed.

Refer to the following publications for additional information:

A. Odgaard, Three-dimensional methods for quantification of cancellous bone architecture, Bone, 20, 4, (315-328), (1997).

T.P. Harrigan, R.W. Mann, Characterization of microstructural anisotropy in orthotropic materials using a second rank tensor, Journal of Materials Science, 19, (761-767), (1984).

Measurements of bone mineral density (BMD) and tissue mineral density (TMD) require calibrated bone data, which is calibrated by means of phantoms with a known density of calcium hydroxyapatite (CaHA). Calibration can be done beforehand and is also made available on demand in the Bone Analysis Wizard by clicking the Calibrate Intensity Now button in the Global Measurements dialog.

How to Compute Bone and Tissue Mineral Densities

  1. Select a measurement of bone mineral density or tissue mineral density.

  2. Choose the required calibrated or uncalibrated bone dataset in the Bone dataset drop-down menu, as shown below.

    Note If you selected an uncalibrated bone dataset, click the Calibrate Intensity Now button and then calibrate the selected dataset (see Intensity Calibration for BMD and TMD Computations).

  3. Check the BMD distribution and/or TMD distribution options if you want to include histograms of bone mineral density (BMD.Me) and/or tissue mineral density (TMD.BV and TMD.Co) distributions in your bone analysis report (see Adding Distributions of BMD and TMD).

If required, you can add and edit custom computation boxes for computing global measurements. Box shapes can be resized and/or reoriented as required. You can also add multiple boxes to compute anisotropy in different orientations.

How to Add and Edit a Computation Box
  1. Make sure that the required region of interest is selected in the Data Properties and Settings panel.
  2. Click the Box button in the Shapes panel.

    A new Box shape appears in the Data Properties and Settings panel. Click the Eye icon to show the box in the workspace views.

  3. Adjust the box in the 2D and/or 3D views of the region of interest, as required.

    You can resize and rotate the box, as well as change its position with the available control points (see Editing Shapes).

  4. You can choose your new computation box in the drop-down menus for selected measurements as shown below.