You can draw a sphere Volume of Interest (VOI) on a CT or PET series of images to view the intensities in that volumetric area. The intensity values of the VOI are added automatically as a bookmark. Open the Bookmark list to see the HU mean value for CT images, and SUV mean and max values for PET images.
NOTE: Depending on configuration, in PET series, the highest intensity value of the sphere can be automatically displayed on the image. See your administrator.
1. From the Viewer, select an image.
2. In the Graphics tab of the toolbar, select Sphere VOI 
from the ROI drop-down in the Measurements ribbon.
3. Click on the image to start drawing a circle.
4. Click again when the area is defined.
The sphere (3D) is automatically created around the diameter of the drawn circle. The contours of the sphere (highlighted voxels) are displayed in each of the slices participating in the sphere.
Using a Pre-Set Size
Pressing the Shift key and clicking on the image while the Sphere VOI tool is selected causes the sphere to be drawn in a pre-set size.
Resizing such a sphere is done in pre-set steps.
To determine the pre-set sphere size -
1. Click on the Vue PACS icon at the top left corner and click Applications Settings.
2. In the left pane of the Application Settings window, expand the Graphics and Measurements node and click Graphic Properties.
3. In the Constant Sized Sphere section, select the radius and step size.
4. Select the measurement units from the drop-down menus.