Fig 3.

Test-retest fitted curves in the normal head and neck tissues (4b, 4b gating and 17b) in a 50-year-old male volunteer and a neurogenic tumor (4b gating and 17b) in the left level II. The blue dots and line indicate the data points and fitted curves of the 1st exam (test), and the red dots and line indicate the data points and fitted curves of the 2nd exam (retest). In the brain, muscle and submandibular gland, more similar curves being fitted in the test-retest series of 4b gating are noted than those of 4b or 17b. In the parotid gland and tonsil, test-retest fitted curves were not improved using 4b gating compared to 4b. However, in the parotid gland, 4b gating curves show definite hockey – stick appearance which reflects a tendency of higher perfusion fraction of the salivary glands. In 4b series of the parotid gland, the curves are flat. Regarding the tonsils, the shortest sequence, 4b series seem to be the most reliable method because tonsil is susceptible to swallowing motion.