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(a) Axial CT scan of skull in a nasopharyngeal carcinoma patient before radiotherapy. The image density of the parotid gland (P) is about the same as the adjacent masseter muscle (M). (b) Axial CT scan of a skull in the same patient after radiotherapy. There is an increased image density of the parotid gland (P) when compared with the pre-radiotherapy scan. The image density of the parotid gland is greater than that of the adjacent masseter muscle (M).
