Adaptive, segmented attenuation correction for whole-body PET imaging

A technique is presented for segmented attenuation correction in positron emission tomography (PET) based on the local thresholding technique (LTS) described previously. To accommodate the substantially different body sections encountered in whole-body PET, an adaptive thresholding has been added to yield more uniform results throughout the body. By evaluating the intensity distribution of a set of transverse transmission images, the algorithm determines an optimal threshold for separating two or three different groups or classes of similar pixels. Interclass variance is maximized and intra-class errors are minimized. The algorithm also switches automatically between a three-class mode (background, lungs/air pockets, soft tissue) and a two-class mode (background, soft tissue), thereby achieving more uniform segmentation where lung spaces and bowel air pockets are alternately present then absent from the volume of interest. The addition of adaptive thresholding virtually eliminates the need for operator intervention. The clinical implementation requires short-duration, count-limited, transmission images that would otherwise be too noisy for direct attenuation correction. Emission images corrected with adaptive LTS were shown to be equivalent, both quantitatively and qualitatively, to those corrected using conventional measured attenuation correction.