6.12. Histograms
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Functionality is available in the Pro edition
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The sections with color tables described in Section 2.21.3 are available for segmented structures. The difference is that in the Flat images view mode a histogram is built for the entire density range, and for the structure it is built only for the range of the density that corresponds to the structure mask.
6.12.1 Rendering a Histogram for a Structure
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Functionality is available in the Pro edition
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The DICOM Viewer provides for rendering histograms for the base volume and selected segmented structures.
To view a histogram for a selected segmented structure in the MPR Reconstruction window,
click the 
Rendering transfer function button on the toolbar.
At the bottom of the tab, you will see the panel of the rendering transfer function with the histogram for the selected segmented structure. The color of the histogram for the selected segmented structure will be the same as the user color of the segmented structure. The name of the segmented structure is provided in the histogram legend.
If you have chosen the base volume on the segmentation panel, then only the base volume histogram will be displayed on the panel of the rendering transfer function. The changes in the visibility and transparency of the selected segmented structure or the base volume do not affect the histogram rendering.
When you hover over a point of the base volume or the selected segmented structure histogram, a tip pops up.
The pop-up tip provides the following parameters:
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Chart — the name of the histogram;
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Density (HU) — the Hounsfield density value;
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Value — the number of points characterized by the density value provided;
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Normalized value — is calculated by the following formula:
| (6.1) |
where: y — the present histogram value; ymin — the minimum histogram value; ymax — the maximum histogram value.
The base volume and the name of the segmented structure is stated in the histogram legend.
If the 3D view window is active in the MPR Reconstruction tab, then the histogram for the base volume and the transfer function for the current color table will be displayed on the panel of the rendering transfer function.
When you hover over a point of the rendering transfer function graph, a tip pops up.
The pop-up tip provides the following parameters:
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Density (%) — the density measured as percentage of the window width/level (W/L). The parameter is calculated by the following formula:
(6.2) where: D — the density value; MinW∕L — the minimum window dimensions; MaxW∕L — the maximum window dimensions;
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Opacity — the opacity value from 0.0 to 1.0.
The opacity value shown in the pop-up tip is rounded off to 0.001.
6.12.2 Histogram for a ROI
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Functionality is available in the Pro edition
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A histogram for a ROI is a graph for the density range of the points within the ROI. The DICOM Viewer displays histograms for ROI in the Image Viewer tab, MPR Reconstruction tab, and PET Analysis tab.
To view a histogram for a ROI in the selected window, click the Rendering transfer
function button on the toolbar. At the bottom of the study tab, you will see the rendering transfer
function panel with the histogram for the ROI and the rendering transfer function over
it.
In the Flat Image Viewer tab, the histogram is built for all the ROI displayed in the selected tab window. When you add a new ROI, scroll or switch windows, the histogram for the ROI is changed accordingly.
If you have chosen a mode where several images of the same series are displayed simultaneously, e.g. 2x2, 2x3 etc., then the histogram for the ROI is built in the top left-hand corner.
In the MPR Reconstruction tab, histograms for ROI are shown in the Axial plane, Sagittal plane, Coronal plane, and Involute windows. If the MPR Reconstruction tab is open for merged series, then, when you switch layers, the ROI histogram is changed in accordance with the density values for the current section of the layer selected.
In the PET Analysis tab, the histogram is built for all the ROI of the current image in the selected window: PT, CT, or Fusion (PET+CT). In the Fusion (PET+CT) window, the histogram is built for the PET layer.