Evaluation of the value of neck extension in chest CT scanning

Objective To explore the possibility that the neck extension in chest CT scanning would make thyroid move upward and reduce thyroid radiation exposure. Methods The images of 1 994 patients who underwent chest CT examination in Beijing Chaoyang Hospital from March to June in 2017 were compared and analyzed retrospectively. According to different cervical positions, patients were divided into extension group and routine group with 997 cases in each group. In the extension group, the head and neck bended back to the maxillary top position while in the regular group with normal position. The length of thyroid glands exposed to the scanning range and the number of cases of all glands moved out of the scanning range were observed with the first rib head as the baseline counting mark. The differences in exposed length of thyroid gland in primary radiation area between the two groups were compared. Results The length of exposed thyroid gland by primary radiation in the extension group (4.69±5.68) mm was significantly shorter (U=91 073.5, P<0.05) than that in the routine group (17.16±6.68) mm. In addition, the number of thyroid glands out of scanning range completely in the extension group (n=519, with ratio of 52.1%) was significantly more (U=594.8, P<0.05) than those in the routine group (n=32, with ratio of 3.2%). Conclusions During chest CT scan, the length of thyroid gland in the scanning field can be shortened with neck backbend position and the radioation protection for thyroid gland can be effectively improved. Key words: Computed tomography(CT); Neck position; Thyroid; Radiation dose