双源CT扫描模式对头颈部辐射剂量和影像质量的影响

目的 探讨头颈部CT扫描中，不同扫描模式对辐射剂量和影像质量的影响程度。方法 利用头颈部仿真模体和双源CT，分别使用固定扫描条件120 kV和200 mAs，以及自动管电流调制技术（CARE Dose 4D）、自动管电压调制技术（CARE kV）和部分角度扫描模式（X-CARE）的组合进行成像，分别为120 kV+200 mAs、120 kV+200 mAs+X-CARE、CARE Dose 4D+120 kV、CARE Dose 4D+120 kV+X-CARE、CARE Dose 4D+CARE kV、CARE Dose 4D+CARE kV+X-CARE 6种扫描模式。每次扫描均使用两片热释光剂量片（TLD）分别测量眼晶状体和甲状腺的剂量，两片TLD所测数值取均值。记录以上各种扫描时的容积CT剂量指数（CTDI_vol）和剂量长度乘积（DLP），测量眼晶状体层面和甲状腺层面影像的对比度噪声比（CNR）。结果 120 kV+200 mAs扫描时，眼晶状体和甲状腺的器官剂量分别为19.8和26.0 mGy，使用120 kV+200 mAs+X-CARE可降低剂量至13.3和22.2 mGy；与CARE Dose 4D+120 kV相比，CARE Dose 4D+CARE kV可使CTDI_vol由13.1降至10.1 mGy，眼晶状体剂量和甲状腺剂量由20.8和23.7 mGy分别降至16.6和19.9 mGy，而使用CARE Dose 4D+CARE kV+X-CARE时，器官剂量又进一步分别降至6.3和11.0 mGy，但影像质量显著降低；与CARE Dose 4D+120 kV相比，使用CARE Dose 4D+120 kV+X-CARE，眼晶状体和甲状腺剂量分别由20.8和23.7 mGy降至9.6和15.1 mGy，同时CTDI_vol由13.1 mGy降至9.3 mGy。使用CARE Dose 4D+CARE kV+X-CARE时，CTDI_vol和器官剂量降至最低，但头颅和颈部CNR也降至最低。结论 颅脑扫描时CARE Dose 4D+120 kV+X-CARE模式、颈部扫描时CARE Dose 4D+CARE kV模式在保持影像质量较好的同时可有效降低辐射剂量。当对影像质量要求不高时可选用CARE Dose 4D+CARE kV+X-CARE模式，从而显著降低辐射剂量。

Investigation on effect of dual-source CT scanning patterns on radiation dose and image quality of head and neck

Objective To study the impact on the radiation dose, organ doses of eye lens and thyroid and image quality with different scanning modes in head and neck CT scan. Methods The simulation phantom of head and neck was scanned by using fixed scanning condition (120 kV and 200 mAs), as well as the combinations of automatic tube current modulation (CARE Dose 4D), automatic tube voltage modulation technique (CARE kV) and partial angle scanning mode (X-CARE) respectively. Six kinds of scanning modes were adopted, including 120 kV+200 mAs, 120 kV+200 mAs+X-CARE, CARE Dose 4D+120 kV, CARE Dose 4D+120 kV+X-CARE, CARE Dose 4D+CARE kV, CARE Dose 4D+CARE kV+X-CARE. Two thermoluminescece dosimeters(TLDs) were exposed at the skin surface positions of eye lens and thyroid, and the values measured with two TLDs were averaged. The CT dose index volume(CTDI_vol) and dose length product (DLP) for every scan were recorded, and the contrast to noise ratio (CNR) in eye lens section and thyroid section were measured. Results The organ doses of lens and thyroid were 19.8 and 26 mGy at 120 kV and 200 mAs, as well as 13.3 and 22.2 mGy at X-CARE mode. Compared with the manual selection of 120 kV, the combination of CARE kV and CARE Dose 4D made the values of CTDI_vol drop from 13.1 to 10.1 mGy, the doses of eye lens and thyroid from 16.6 and 20.8 mGy to 23.7 and 19.9 mGy respectively, while the image quality reduced significantly. Compared with CARE Dose 4D+120 kV, the organ doses of eye lens and thyroid were reduced from 20.8 and 23.7 mGy to 9.6 and 15.1 mGy for with additional X-CARE, while CTDI_vol dropped from 13.1 to 9.3 mGy. When the combination of CARE Dose 4D+CARE kV+X-CARE was used, CTDI_vol and organ doses were reduced to a minimum, when the CNRs of head and neck were also minimized. Conclusions The scanning mode CARE Dose 4D+120 kV+X-CARE for head and CARE Dose 4D+CARE kV for neck can effectively reduce the radiation dose while keeping good image quality. When requirements for image quality are not high, CARE Dose 4D+CARE kV+X-CARE mode can be selected to reduce the radiation dose significantly.