FIGURE 3. Example of the performed analysis. (A) CT image with thresholds [-160 HU, 240 HU] showing regions that define oral CT contrast, tumor, and reference tissue. (B) CT image after replacement of contrast-enhanced pixels by normal values. (C) PET emission image attenuation corrected with CT image A. (D) PET emission image attenuation corrected with CT image B, resulting in approximation of true ¹⁸F-FDG uptake. (E) Difference image C - D normalized to D, showing percentage error due to attenuation correction with CT contrast-enhanced pixels. Maximal difference is 9.6%.