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A comparison of planar versus volumetric numerical observers for detection task performance in whole-body PET imaging

The goal of this project is to determine if there is a difference between planar and volumetric numerical observers. The motivation comes from the use of a volumetric (3D) display of image data (i.e. three orthogonal views through a volume image) to assess whole-body PET images in most, if not all, clinical PET centers. Studies of correlations between numerical observers and human observers (e.g. using receiver operating characteristic (ROC) detection analysis), however, typically use a planar (2D) display and analysis methodology. For images where axial noise correlations exist, Wells et al. [IEEE-TNS, 47:037-1044, 2000] have shown significant differences between single-slice and multi-slice ROC studies, implying that ROC-type studies utilizing a volumetric image display will also yield different results from a single or multi-slice image displays. In particular, planar implementations of the non-prewhitening matched filter (NPWMF) and the channelized Hotelling observer (CHO) have been extensively investigated as surrogates for measuring human detection task performance. To determine if there is a difference between planar and volumetric numerical observers, we analyzed the behavior of 2D and 3D implementations of the NPWMF and CHO numerical observers with multiple realizations of images with noise properties similar to those of whole-body PET oncology imaging. Initial results indicate that there is a significant difference increase in SNR or delectability of volumetric numerical observers relative to planar observers. This implies that volumetric and planar numerical observers may have different strengths of correlation with human observer performance, and that these correlations should be determined prior to using numerical observers to optimize algorithm or protocol performance for whole-body PET imaging.