SEGMENTATION OF THE BODY AND LUNGS FROM COMPTON SCATTER AND PHOTOPEAKWINDOW DATA IN SPECT - A MONTE-CARLO INVESTIGATION

In SPECT imaging of the chest, nonuniform attenuation correction requi res use of a patient specific attenuation (mu) map, Such a map can be obtained by estimating the regions of 1) the lungs and 2) the soft tis sues and bones, and then assigning an appropriate value of attenuation coefficient (mu) to each region. We proposed a method to segment such regions from the Compton scatter and photopeak window SPECT slices of Tc-99m Sestamibi studies, The Compton scatter slices are used to segm ent the body outline and to estimate the regions of the lungs, Locatio ns of the back bone and sternum are estimated from the photopeak windo w slices to assist in the segmentation, To investigate the accuracy of using Compton scatter slices in estimating the regions of the body an d the lungs, a Monte-Carlo SPECT simulation of an anthropomorphic phan tom with an activity distribution and noise characteristics similar to patient data was conducted, Energy windows of various widths were sim ulated for use in locating a suitable Compton scatter window for imagi ng, The effects of attenuation correction using a IL map based on segm entation were also studied, The results demonstrated for the activity and mu maps studied herein that: 1) reasonable contrast could be obtai ned from Compton scatter data for the segmentation of the lung regions , 2) true positive rates of 99% and 89% for determining the body and l ung regions, respectively, with total error rates of 4% and 29%, could be achieved, 3) usage of a mu map based on segmentation for attenuati on correction improved relative quantification over filtered backproje ction, 4) variations in the assigned mu value of 40% smaller or 40% la rger in the lung regions had an insignificant impact on the results of relative quantification, 5) a wide energy window away from the photop eak window for recording scattered events could benefit both the segme ntation of the lung regions and the attenuation correction of the acti vity in the myocardium region, and 6) usage of a smaller than true mu value in the lung regions of an assigned mu map might benefit attenuat ion correction for absolute quantification.