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FIGURE 2. CT images of heart: (A) Unenhanced CT scan, coronal view, soft-tissue window (center, 50 HU; width, 350 HU). (B) Contrast-enhanced CT scan, coronal view, soft-tissue window. Influence of contrast agent is clearly visible (attenuation value in left ventricle, 370 HU; reference value, 30–45 HU). (C) Cylinder-based CT segmentation of contrast agent in heart area, with transversal view on left and coronal view on right. Every CT pixel value above normal tissue value inside cylinder is considered to represent contrast agent and reduced to 35 HU (cylinder-threshold correction). (D) Size and location of ROI used to determine mean attenuation and uptake values in CT and PET images, respectively (Tables 1 and 2). Also shown is position of heart–lung borderline along craniocaudal axis. Difference in craniocaudal position in the 2 CT images (unenhanced and enhanced) serves as measure of respiratory motion shift of heart.
