A technique for manual definition of an irregular volume of interest in single photon emission computed tomography

A technique is described for manually outlining a volume of interest (VOI) in a three-dimensional SPECT dataset. Regions of interest (ROIs) are drawn on three orthogonal maximum intensity projections. Image masks based on these ROIs are backprojected through the image volume and the resultant 3D dataset is segmented to produce the VOI. The technique has been successfully applied in the exclusion of unwanted areas of activity adjacent to the brain when segmenting the organ in SPECT imaging using Tc-99m HMPAO. An example of its use for segmentation in tumour imaging is also presented. The technique is of value for applications involving semi-automatic VOI definition in SPECT.