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Figure 5b: Effect of CT noise on adequacy of CT-based attenuation correction. (a) Graph shows relationship of CT noise (graph at bottom), CT number, and µ511 transformation. The graph at left shows the transformed distribution of CT numbers. The wide range in CT numbers leads to an underestimation in µ511. (b) Plot of CT noise (standard deviation) versus µ511. CT scans of all eight of the tissue-equivalent CT phantoms were acquired, and these were processed into attenuation correction files and reconstructed to yield estimates of µ511. Both calculated (based on a Gaussian model) and measured data were plotted, and there was very good agreement between the calculated and measured data. The slight bias is most likely a result of the inadequacy of the Gaussian noise assumption.
