09-Segmentation.pdf

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S
.
EGMENTATION
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9
.....
he egmentation tools of
VGStudio
MAX 2.1
are truly three-dimensional.
The segments are treated as masks that can be stored and retrieved.
A CT dataset can have multiple ROIs each with their own separate
analysis and render settings.
T
Selections and ROIs
A ROI is a 3-dimensional mask defining a region of interest within a
dataset. The ROI can be used for registration purposes or as a region within
which to perform a certain analysis such as a defect detection. By adding
Volume Rendering settings
to a ROI the rendering properties of the ROI can
be set independently of those of the main dataset.
A ROI can be created from a selection made within the CT dataset. This
selection can either be transformed into a ROI directly or alternatively be
added to or subtracted from an already existing ROI. In
VGStudio
MAX 2.1
selections are made independently of slice orientation and are propagated
by dragging the selection tool across the volume.
Shor tcuts
The shortcut icons for the
Region of Interest
and
Segmentation
tools are
located in the toolbar as indicated in the image below:
Release 2.1
Introduction to VGStudio MAX 2.1
9-1
9
SEGMENTATION
Create ROI from Calibration.
Enable ROI render settings.
Add ROI to ROI.
Subtract ROI from ROI.
Split ROIs.
Merge ROIs.
Intersect ROIs.
Invert ROI.
Extract ROI.
Import ROI mask.
Export ROI mask.
Create new selection (pull down menu to select type).
Region growing tools (pull down menu to select type).
Create a ROI in the 3D view.
Launch selection/ROI erode/dilate tool.
Example
As an example of the usage of selections and ROIs consider the following
dataset:
In this case we would like to perform a wall thickness analysis on the cylin-
drical part of the object. To do so we first have to create a ROI covering the
cylindrical part as illustrated below.
9-2
Introduction to VGStudio MAX 2.1
Release 2.1
SEGMENTATION
To start please load the project called
09-Align+wall.vgl.
From the slice views you will notice that the part is not properly aligned
along the axis of the CT slices:
To be able to define a selection covering the cylindrical section we first
have to align the slices accordingly to simplify the selection process. This
can be done by fitting a cylinder reference object to the part using the coor-
dinate measurement tools. Select
Measurements > Cylinder
and using <Ctrl>
and left mouse button set a number of fit points on either the inside or out-
side cylindrical section of the part. Finish by selecting
Fit
in the
Fit reference
object
tool. To align the slices highlight the
Cylinder
object in the
Scene
Tree
and select
Align Slices to object
from the right mouse button menu.
Release 2.1
Introduction to VGStudio MAX 2.1
.....
9-3
9
SEGMENTATION
One of the slice views will now be oriented so that it looks along the axis of
the fitted cylinder:
From the menu choose
Selection > Selection modes > Ellipse
and by pressing
and holding the left mouse button drag a selection across the slice covering
the outside diameter of the region:
The extent of the ellipse selection can be adjusted by pressing and holding
the left mouse over any of the red handles and readjusting their position.
The full selection can be repositioned by pressing and holding the left
mouse button anywhere inside the selection and dragging it into the new
position. To propagate the selection along the axis of the cylinder press and
hold the left mouse button over the red outline in any of the two other slice
views. First drag the selection downwards until the lower end of the object
is reached then release the mouse button.
Repeat the process using the upper red outline but this time dragging
upwards until the top of the object is covered:
9-4
Introduction to VGStudio MAX 2.1
Release 2.1
SEGMENTATION
Create a ROI from the current selection by choosing the
New region of inter-
est
icon from the
Ellipse selection
tool. The ROI thus defined still contains
some material which is not of interest for the analysis we are planning to
perform. To exclude this material create a new selection inside the part just
slightly smaller than the inside diameter:
In one of the other two slice views extend the new selection so that it cov-
ers the material which is not of interest:
With the previously defined ROI selected in the
Scene Tree
choose the
Sub-
tract from region of interest
icon in the
Ellipse selection
tool. The ROI now only
contains the material of the cylindrical section of the part.
Release 2.1
Introduction to VGStudio MAX 2.1
.....
9-5

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