The peak uptake of a lesion is defined as the average uptake in a 1ml sphere, which is positioned such that the average is maximal (see also Sphere with Max Average (Peak VOI)). So the peak sphere VOI requires the definition of an enclosing boundary. The hot-key peak variant uses a simplified boundary defined as a sphere with diameter defined in the configuration illustrated below.
The procedure for placing a peak VOI in a lesion is as follows:
1.Activate the VOI functionality.
2.Triangulate the lesion center in the orthogonal layout, potentially using the MIP for fast localization.
3.Hit the Ctrl+Q keyboard keys. This places the enclosing sphere (VOI in dashed line) at the triangulation point and determines the location of the 1ml peak VOI with maximal average (VOI with solid line) as illustrated below.
The search diameter may need to be modified depending on the actual situation in the image for excluding neighboring structures.
Note: The average calculation in the Peak VOI uses area-weighted statistics, corresponding to the Fraction classification mode. For the peak VOI only spheres are considered with center inside the bounding sphere.