Inobitec DICOM Viewer

4.4. Image registration

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Functionality is available in the Pro edition
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This tools allows you to deform the images so that their coincidence is maximal. If the inconsistencies of the series are too large (for example, the patient has turned), you must first merge the layers manually or automatically (see Section 4.3), and then register the images.

If the study contains images with a changing density over time (for example, due to the introduction of contrast), then registration may not be performed correctly. To do this, exclude tussue with varying density.

  • Set the maximum value of the density for which registration is performed. In this case tissue with a density higher than the specified value do not participate in the registration and their deformation is performed according to another algorithm.
  • Check the Use image gradient in the Series registration settings dialog. This mode requires a large amount of video card memory. If the registration failed due to the lack of memory of the video card, turn off this mode or select a CPU(software) render device (see Section 15.4.3).

If the images contain air outside the patient’s body then the density of such areas for CT examinations is usually less than or equal to -1024. It makes no sense to register these sections of images. So for CT studies the default minimum density value is -1023.

If the registration failed due to a lack of video card memory, select the CPU(Software) render device (see Section 15.4.3). In this case registration takes more time, but it is performed regardless of the amount of GPU memory.

4.4.1 Series registration

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Functionality is available in the Pro edition
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To register two series:

  1. Create a fused series of at least two series.
  2. Open the fused series in the Multiplanar Reconstruction window.
  3. If the inconsistencies of the series are too large (for example, the patient has turned), you must first merge the layers manually or automatically (see Section 4.3). More accurate merging of layers allows faster registration.
  4. Open the segmentation panel by clicking the Segmented structure panel PIC button.
  5. Select a base layer on the layers panel (fixed layer). Its images will not be changed.
  6. Click the Volumes registration PIC button. The dialog shown in Fig. 4.9 appears. If more than two series are fused, then a list from which you must to select one series is displayed in the dialog (fig. 4.10).
  7. The Output series description field will be automatically filled in based on the name of the series being registered and will contain the mark (registered). If necessary change the description.
  8. Select desired registration options checking the Affine registration, Non rigid registration and Use image gradient boxes.
  9. Set the minimum size of parts that will affect registration. The default size is 20 voxels. The smaller the value the more minor details are registered, but the risk of incorrect registration increases.
  10. Set the percentage of voxels that are used during registration. The larger the value, the higher the accuracy, but the lower the registration rate.
  11. If it is necessary to perform registration for a specific range of densities then set the minimum and/or maximum values. To do this, set the appropriate flag and enter a numeric value. If the flag is set but the value is not set then the OK button is unavailable. For CT series the minimum default value is -1023.
  12. Click OK to export the series or Cancel to cancel. Registration can take a long time depending on the amount of RAM and speed of the computer.





4.4.2 Phases registration

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Functionality is available in the Pro edition
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To register the phases of one series:

  1. Open the multiphase series in the Multiplanar or Volume Reconstruction window.
  2. Open the segmentation panel by clicking the Segmented structure panel PIC button.
  3. Click the Volumes registration PIC button. The dialog shown in Fig. 4.11 appears.
  4. The Output series description field will be automatically filled in based on the name of the series being registered and will contain the mark (registered). If necessary change the description.
  5. Select the base phase that should not be changed (fixed phase).
  6. Select desired registration options checking the Affine registration, Non rigid registration and Use image gradient boxes.
  7. Set the minimum size of parts that will affect registration. The default size is 20 voxels. The smaller the value the more minor details are registered, but the risk of incorrect registration increases.
  8. Set the percentage of voxels that are used during registration. The larger the value, the higher the accuracy, but the lower the registration rate.
  9. If it is necessary to perform registration for a specific range of densities then set the minimum and/or maximum values. To do this, set the appropriate flag and enter a numeric value. If the flag is set but the value is not set then the OK button is unavailable. For CT series the minimum default value is -1023.
  10. Click OK to export the series or Cancel to cancel. Registration can take a long time depending on the amount of RAM and speed of the computer.