Study on optimum scheme of thyroid CT plain scan / 实用放射学杂志

ABSTRACT

Objective To preliminarily investigate the optimum scheme of thyroid CT flat scanning plan,to reduce the artifacts and the radiation dosage.Methods Patients who were involved in this research with thyroid CT flat scanning were divided into three groupsgroup A (conventional scan group),group B (dosage- reduced group)and group C (a combination of body posture change and dosage reduction).In group A (50 patients),the patients’bilateral arms were naturally drooped on both sides of the body during scanning (scan parameters120 kV,250 mA).In group B (50 patients),the patients were scanned under the same circumstance with group A,but difference in scanning condition (scan parameters100 kV,280 mA).In group C (50 patients),the patients kept one arm rise upward,another arm reach firmly toward the contralateral iliac bone during CT scan(scan parameters100 kV,250 mA).CT attenuations,noise and SNR values around the soft tissue of thyroid gland,which was in the most severe thyroid artifacts (seventh cervical vertebrae to the first thoracic vertebrae level),were measured among the three groups.Meanwhile,the patient’s dose length product (DLP)and effective dosage (ED)were calculated.The images of the three groups were measured by double-blind method,i.e. severe artifacts,moderate artifacts,mild artifacts,and no artifacts.Results The image quality in group C was significantly higher than that of group A and group B (P＜0.05).There was no difference in subj ective quality between group A and group B (P＞0.05).The CT and noise values of group C were better than those of group A and group B (P＜0.05),while the radiation dosage was lower than that of group A and group B (P＜0.05).Conclusion When the thyroid CT scan is performed with the unilateral limb lifting and the other arm extending to the contralateral iliac bone,the thyroid band artifacts can be effectively reduced and decreasing the kV can reduce the radiation dosage.