You can draw a Region of Interest (ROI) to measure the area, average pixel value, and standard deviation of pixel values in an image. The graphic is added automatically as a bookmark. Open the Bookmark list to see its details.
1. From the Viewer, select an image.
2. In the Graphics tab of the toolbar, select Freehand ROI 
from the ROI drop-down in the Measurements ribbon.
3. Click on the image where you want the ROI to start.
4. Draw the area you want as the ROI by moving the mouse.
5. Click where you want the ROI to end.
The area of the ROI, and the average digital value and standard deviation of the digital values in the ROI are automatically measured. The start and end points will always be connected.
To replace a section of the boundary of the ROI:
1. Place the mouse cursor on the line where you want to start the change.
The cursor changes to a four-way arrow.
2. Hold down the Shift key and draw the new line, joining to a point on the original freehand shape.
3. Release the mouse button.
The new line replaces the original line between those points.
To remove a segment while drawing the ROI:
To remove a small segment of the boundary while you are still drawing, press the Backspace key.