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Making Measurements

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Adding Measurements

Measurement tools, such as the Ruler and Protractor, as well as the Elliptical, Rectangular and Polygonal ROIs, can be drawn on an image in the following way:

1.On the toolbar, click on the measurement tool you wish to use.
2.Click on the image where you want the measurement to begin. This lays down the measurement's first anchor point. Note that you can just click and release; you do not need to hold.
3.Move the mouse to where you want the next anchor point to be located.  Click and release again.
4.If the measurement tool you're using only requires two anchor points (as in the case of the Ruler, as well as Elliptical and Rectangular ROIs), you're done. However, if the tool requires more anchor points (as in the case of the Protractor and Polygonal ROI), you need to repeat step 3 until the measurement is complete.
5.A Polygonal ROI can be closed in one of two ways: by bringing the mouse back to the first point (a circular "snap-to" region will appear to assist), or by simply double-clicking provided you have already placed at least  two points.

Modifying Measurements

1.You can add and remove vertices (anchor points) on a Polygonal ROI after the fact by using the right-click menu.  To add a new vertex, right-click on the body of the ROI approximately where you would like the new vertex to be added and select Insert Vertex.  To remove a vertex, simply right-click the individual vertex and choose Delete Vertex.
2.To resize a measurement, hover the mouse over one of its square control points then click and drag as necessary.
3.To move a measurement, hover the mouse over its body, then click and drag to the new location. Note that the callout can also be moved out of the way by dragging.
4.To delete a measurement, right-click on the measurement, and select Delete.
5.To delete all annotations, including measurements and text, right-click on the item itself or on the image and select Delete All Annotations.
6.To assign a name to a particular measurement, simply right-click and choose Rename; a text edit box will appear.  Enter an appropriate name (notice in the screen capture below, there are two measurements with names: Polygon1 and Ellipse1) and press Enter on the keyboard, or simply click away from the measurement with the mouse.  The text will appear in the measurement's callout along with its statistics/analysis.
7.To hide the statistics, leaving only the name if one has been entered, simply right-click on the measurement and uncheck Show Analysis.

Saving Measurements

If you would like to save all the measurements on the image, you can use the Create Key Image tool which will save the presentation state of the image along with any measurements and text annotations you have made on the image.  For a more detailed discussion on this feature, please see the section on Key Images.

Important Note

For cross-sectional modalities (e.g. CT, MR, PT, etc.), measured values correspond to actual anatomical size.

For projection modalities (e.g. CR, DX, MG, etc.), measured values may or may not have been corrected for geometric magnification by the modality.  The text overlay will indicate one of the following values describing the method of calibration.

Detector - Indicates that measured values are known to be in the plane of the detector, and therefore do not account for any geometric magnification.
Geometry - Indicates that measured values are adjusted by the modality for geometric magnification at some assumed depth in the patient.  Additional details, if provided by the modality, are displayed in parentheses.
Fiducial - Indicates that measured values are calibrated by the modality according to an object of known size (fiducial).  Additional details, if provided by the modality, are displayed in parentheses.
Unknown - Indicates that no calibration details have been provided by the modality.  Please exercise discretion if this is the case, as the meaning of measured values cannot be determined, and should be clarified with the vendor of the modality.
User - Indicates that the user has manually recalibrated the image using the Calibration Tool.

If the modality has not provided any calibrated pixel spacing, measurements will be returned in units of image pixels.

Technical Notes

For cross-sectional modalities (e.g. CT, MR, PT, etc.), the Pixel Spacing (0028,0030) tag is used which corresponds to the actual anatomical size.

For projection modalities (e.g. CR, DX, MG, etc.),  the Vetstation supports the use of either Imager Pixel Spacing (0018,1164) or Pixel Spacing (0028,0030) as per DICOM CP-586.

Where Imager Pixel Spacing (0018,1164) is provided alone or with the same value as that of Pixel Spacing (0028,0030), measurements will be given at the detector plane.
Where Pixel Spacing (0028,0030) is provided alone or with a different value as that of Imager Pixel Spacing (0018,1164), measurements will be given using the calibrated Pixel Spacing (0028,0030) value, and the method of calibration will be displayed in the text overlay.

 

ClearCanvas Vetstation - User's Guide
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